Precision-guided munition

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Precision-guided_munition

Afghan Air Force GBU-58 guided bomb strikes a Taliban compound in Farah Province, Afghanistan

A precision-guided munition (PGM, smart weapon, smart munition, smart bomb) is a guided munition intended to precisely hit a specific target, to minimize collateral damage and increase lethality against intended targets. During the First Gulf War guided munitions accounted for only 9% of weapons fired, but accounted for 75% of all successful hits. Despite guided weapons generally being used on more difficult targets, they were still 35 times more likely to destroy their targets per weapon dropped.

Because the damage effects of explosive weapons decrease with distance due to an inverse cube law, even modest improvements in accuracy (hence reduction in miss distance) enable a target to be attacked with fewer or smaller bombs. Thus, even if some guided bombs miss, fewer air crews are put at risk and the harm to civilians and the amount of collateral damage may be reduced.

The advent of precision-guided munitions resulted in the renaming of older, low-technology bombs as "unguided bombs", "dumb bombs", or "iron bombs".

Types

Main article: Missile guidance

A laser-guided GBU-24 (BLU-109 warhead variant) strikes its target

Recognizing the difficulty of hitting moving ships during the Spanish Civil War, the Germans were first to develop steerable munitions, using radio control or wire guidance. The U.S. tested TV-guided (GB-4), semi-active radar-guided (Bat), and infrared-guided (Felix) weapons.

Inertial-guided

The CBU-107 Passive Attack Weapon is an air-dropped guided bomb containing metal penetrator rods of various sizes. It was designed to attack targets where an explosive effect may be undesirable, such as fuel storage tanks or chemical weapon stockpiles in civilian areas.

Radio-controlled

Main article: Command guidance

The Germans were first to introduce PGMs in combat, with KG 100 deploying the 3,100 lb (1,400 kg) MCLOS-guidance Fritz X armored glide bomb, guided by the Kehl-Straßburg radio guidance system, to successfully attack the Italian battleship Roma in 1943, and the similarly Kehl-Straßburg MCLOS-guided Henschel Hs 293 rocket-boosted glide bomb (also in use since 1943, but only against lightly armored or unarmored ship targets).

The closest Allied equivalents, both unpowered designs, were the 1,000 lb (450 kg) VB-1 AZON (from "AZimuth ONly" control), used in both Europe and the CBI theater, and the US Navy's Bat, primarily used in the Pacific Theater of World War II — the Navy's Bat was more advanced than either German PGM ordnance design or the USAAF's VB-1 AZON, in that it had its own on board, autonomous radar seeker system to direct it to a target. In addition, the U.S. tested the rocket-propelled Gargoyle, which never entered service. Japanese PGMs—with the exception of the anti-ship air-launched, rocket-powered, human-piloted Yokosuka MXY-7 Ohka, "Kamikaze" flying bomb did not see combat in World War II.

Prior to the war, the British experimented with radio-controlled remotely guided planes laden with explosives, such as Larynx. The United States Army Air Forces used similar techniques with Operation Aphrodite, but had few successes; the German Mistel (Mistletoe) "parasite aircraft" was no more effective, guided by the human pilot flying the single-engined fighter mounted above the unmanned, explosive-laden twin-engined "flying bomb" below it, released in the Mistel's attack dive from the fighter.

The U.S. programs restarted in the Korean War. In the 1960s, the electro-optical bomb (or camera bomb) was reintroduced. They were equipped with television cameras and flare sights, by which the bomb would be steered until the flare superimposed the target. The camera bombs transmitted a "bomb's eye view" of the target back to a controlling aircraft. An operator in this aircraft then transmitted control signals to steerable fins fitted to the bomb. Such weapons were used increasingly by the USAF in the last few years of the Vietnam War because the political climate was increasingly intolerant of civilian casualties, and because it was possible to strike difficult targets (such as bridges) effectively with a single mission; the Thanh Hoa Bridge, for instance, was attacked repeatedly with iron bombs, to no effect, only to be dropped in one mission with PGMs.

Although not as popular as the newer JDAM and JSOW weapons, or even the older laser-guided bomb systems, weapons like the AGM-62 Walleye TV guided bomb are still being used, in conjunction with the AAW-144 Data Link Pod, on US Navy F/A-18 Hornets.

Infrared-guided/electro-optical

Main article: Infrared homing

In World War II, the U.S. National Defense Research Committee developed the VB-6 Felix, which used infrared to home on ships. While it entered production in 1945, it was never employed operationally. The first successful electro optical guided munition was the AGM-62 Walleye during the Vietnam war. It was a family of large glide bombs which could automatically track targets using contrast differences in the video feed. The original concept was created by engineer Norman Kay while tinkering with televisions as a hobby. It was based on a device which could track objects on a television screen and place a "blip" on them to indicate where it was aiming. The first test of the weapon on 29 January 1963 was a success, with the weapon making a direct hit on the target. It served successfully for three decades until the 1990s.

The Raytheon Maverick is the most common electro optical guided missile. As a heavy anti-tank missile it has among its various marks guidance systems such as electro-optical (AGM-65A), imaging infrared (AGM-65D), and laser homing (AGM-65E). The first two, by guiding themselves based on the visual or IR scene of the target, are fire-and-forget in that the pilot can release the weapon and it will guide itself to the target without further input, which allows the delivery aircraft to manoeuvre to escape return fire. The Pakistani NESCOM H-2 MUPSOW and H-4 MUPSOW is an electro-optical (IR imaging and television guided) is a drop and forget precision-guided glide bomb. The Israeli Elbit Opher is also an IR imaging "drop and forget" guided bomb that has been reported to be considerably cheaper than laser-homing bombs and can be used by any aircraft, not requiring specialized wiring for a laser designator or for another aircraft to illuminate the target. During NATO's air campaign in 1999 in Kosovo the new Italian AF AMX employed the Opher.

Laser-guided

Main article: Laser-guided bomb

BOLT-117, the world's first laser-guided bomb

In 1962, the US Army began research into laser guidance systems and by 1967 the USAF had conducted a competitive evaluation leading to full development of the world's first laser-guided bomb, the BOLT-117, in 1968. All such bombs work in much the same way, relying on the target being illuminated, or "painted," by a laser target designator on the ground or on an aircraft. They have the significant disadvantage of not being usable in poor weather where the target illumination cannot be seen, or where a target designator cannot get near the target. The laser designator sends its beam in a coded series of pulses so the bomb cannot be confused by an ordinary laser, and also so multiple designators can operate in reasonable proximity.

Originally the project began as a surface to air missile seeker developed by Texas Instruments. When TI executive Glenn E. Penisten attempted to sell the new technology to the Air Force they inquired if it could instead be used as a ground attack system to overcome problems they were having with accuracy of bombing in Vietnam. After 6 attempts the weapon improved accuracy from 148 to 10 ft (50 to 3 m) and greatly exceeded the design requirements. The system was sent to Vietnam and performed well. Without the existence of tracking pods they had to be aimed using a hand held laser from the back seat of an F-4 Phantom, but still performed well. Eventually over 28,000 were dropped during the war.

Diagram showing the operation of a laser-guided ammunition round. From a CIA report, 1986.

Laser-guided weapons did not become commonplace until the advent of the microchip. They made their practical debut in Vietnam, where on 13 May 1972 they were used in the second successful attack on the Thanh Hóa Bridge ("Dragon's Jaw"). This structure had previously been the target of 800 American sorties (using unguided weapons) and was partially destroyed in each of two successful attacks, the other being on 27 April 1972 using Walleyes.

They were used, though not on a large scale, by the British forces during the 1982 Falklands War. The first large-scale use of smart weapons came in the early 1990s during Operation Desert Storm when they were used by coalition forces against Iraq. Even so, most of the air-dropped ordnance used in that war was "dumb," although the percentages are biased by the large use of various (unguided) cluster bombs. Laser-guided weapons were used in large numbers during the 1999 Kosovo War, but their effectiveness was often reduced by the poor weather conditions prevalent in the southern Balkans.

There are two basic families of laser-guided bombs in American (and American-sphere) service: the Paveway II and the Paveway III. The Paveway III guidance system is more aerodynamically efficient and so has a longer range; however, it is more expensive. Paveway II 500 lb (230 kg) LGBs (such as GBU-12) are a cheaper lightweight PGM suitable for use against vehicles and other small targets, while a Paveway III 2,000 lb (910 kg) penetrator (such as GBU-24) is a more expensive weapon suitable for use against high-value targets. GBU-12s were used to great effect in the first Gulf War, dropped from F-111F aircraft to destroy Iraqi armored vehicles in a process informally referred to by pilots as "tank plinking."

• AGM-123 Skipper II is a short-range laser-guided missile developed by the United States Navy. The Skipper was intended as an anti-ship weapon, capable of disabling the largest vessels with a 1,000 lb (450 kg) impact-fuzed warhead.

It is composed of a Mark 83 bomb fitted with a Paveway guidance kit and two Mk 78 solid propellant rockets that fire upon launch.

• Sudarshan is an Indian laser-guided bomb kit, developed by Aeronautical Development Establishment (ADE), a DRDO lab with technological support from another DRDO lab Instruments Research and Development Establishment (IRDE), for the Indian Air Force (IAF).
• KAB-1500L and KAB-500L are Russian laser-guided bombs.
• LT PGB is a family of Chinese laser-guided munitions.
• LS PGB is a family of Chinese GPS+INS or laser guided munitions.
• The Advanced Precision Kill Weapon System (APKWS) also known as Laser, infrared Guided Rocket (LiGR) is a design conversion of Hydra 70 unguided rockets with a laser guidance kit to turn them into precision-guided munitions (PGMs).
• Ugroza (Russian: Угроза, meaning "menace") is a precision-guided weapons system made in Russian Federation. It is an upgrade for standard Russian "dumb" rockets, including the S-5, S-8, and S-13 rockets. The system upgrades the "dumb" rockets with laser guidance, very significantly increasing their accuracy. It requires a laser target designator, from either an airborne or land based source, to "paint" a target. Circular error probable (CEP) is about 2.6 to 5.9 ft (0.8 to 1.8 m), while maximum ranges of rockets varies from the rockets used 0.93 to 4.97 mi (1.5 to 8 km). Ugroza allows rockets to be ripple-fired up to 7 at a time.

The notable novelty is that the system does not use aerodynamic flight control (e.g. tail fins), but impulse steering with mini-thrusters. It has been dubbed as the Russian concept of impulse corrections (RCIC).

• The Roketsan Cirit is a Turkish laser guided missile.
• Cirit is a 2.8 in (70 mm) guided missile system fitted with a semi-active laser homing seeker. The seeker and guidance section is attached to a purpose-built warhead with a Class 5 Insensitive Munition (IM). The multipurpose warhead has a combined armour-piercing ammunition with enhanced behind armor anti-personnel and incendiary effects. The engine is of reduced smoke design, with IM properties. It is connected to the rear section by a roll bearing that enables it to rotate in flight. There are four small stabilising surfaces at the very rear of the missile in front of the exhaust nozzle that ensures stable flight. Roketsan has developed a new launch pod and a new canister in which Cirit is delivered as an all-up round. The Cirit has a maximum effective guided range of 5.0 mi (8 km) with a high probability of hit on a 9.8 ft × 9.8 ft (3 m × 3 m) target at this range.

Radar-guided

Main article: radar guidance

The Lockheed-Martin Hellfire II light-weight anti-tank weapon in one mark uses the radar on the Boeing AH-64D Apache Longbow to provide fire-and-forget guidance for that weapon.

Satellite-guided

Main article: Satellite navigation systems

A F-22 releases a JDAM from its center internal bay while flying at supersonic speed

HOPE/HOSBO of the Luftwaffe with a combination of GPS/INS and electro-optical guidance

Lessons learned during the first Gulf War showed the value of precision munitions, yet they also highlighted the difficulties in employing them—specifically when visibility of the ground or target from the air was degraded. The problem of poor visibility does not affect satellite-guided weapons such as Joint Direct Attack Munition (JDAM) and Joint Stand-Off Weapon (JSOW), which make use of the United States' GPS system for guidance. This weapon can be employed in all weather conditions, without any need for ground support. Because it is possible to jam GPS, the guidance package reverts to inertial navigation in the event of GPS signal loss. Inertial navigation is significantly less accurate; the JDAM achieves a published Circular Error Probable (CEP) of 43 ft (13 m) under GPS guidance, but typically only 98 ft (30 m) under inertial guidance (with free fall times of 100 seconds or less).

• The Joint Direct Attack Munition (JDAM) is a guidance kit that converts unguided bombs, or "dumb bombs", into all-weather "smart" munitions. JDAM-equipped bombs are guided by an integrated inertial guidance system coupled to a Global Positioning System (GPS) receiver, giving them a published range of up to 17 mi (28 km). JDAM-equipped bombs range from 500 to 2,000 pounds (230 to 910 kg). When installed on a bomb, the JDAM kit is given a GBU (Guided Bomb Unit) nomenclature, superseding the Mark 80 or BLU (Bomb, Live Unit) nomenclature of the bomb to which it is attached.
• Wind Corrected Munitions Dispenser (WCMD) is a GPS/INS-guided US tail kit for use with the TMD (Tactical Munitions Dispenser) family of cluster bombs to convert them to precision-guided munitions.
• Wan chien – Taiwanese indigenous version of JDAM.
• The Griffin Laser Guided Bomb (Griffin LGB) is a laser-guided bomb system made by Israel Aerospace Industries' MBT missile division. It is an add-on kit which is used to retrofit existing Mark 82, Mark 83, and Mark 84 and other "dumb fire" gravity bombs, making them into laser-guided smart bombs (with the option of GPS guidance). Initial development completed in 1990.

The Griffin conversion kit consists of a front "seeker" section and a set of steerable tailplanes. The resulting guided munition features "trajectory shaping", which allows the bomb to fall along a variety of trajectories – from a shallow angle to a vertical top attack profile. IAI publishes a circular error probable figure for the weapon of 5 metres.

KAB-500S-E. Russian GLONASS-Guided Bomb

• The GBU-57A/B Massive Ordnance Penetrator (MOP) is a U.S. Air Force, precision-guided, 30,000-pound (14,000 kg) "bunker buster" bomb. This is substantially larger than the deepest penetrating bunker busters previously available, the 5,000-pound (2,300 kg) GBU-28 and GBU-37.
• The SMKB (Smart-MK-Bomb) is a Brazilian guidance kit that turns a standard 500-pound (230 kg) Mk 82 or 1,000-pound (450 kg) Mk 83 into a precision-guided weapon, respectively called SMKB-82 and SMKB-83. The kit provides extended range up to 31 mi (50 km) and are guided by an integrated inertial guidance system coupled to three satellites networks (GPS, Galileo and GLONASS), relying on wireless to handle the flow of data between the aircraft and the munition.
• FT PGB is a family of Chinese satellite and Inertial, guided munitions.
• LS PGB is a family of Chinese GPS+INS or laser guided munitions.

The precision of these weapons is dependent both on the precision of the measurement system used for location determination and the precision in setting the coordinates of the target. The latter critically depends on intelligence information, not all of which is accurate. According to a CIA report, the accidental United States bombing of the Chinese embassy in Belgrade during Operation Allied Force by NATO aircraft was attributed to faulty target information. However, if the targeting information is accurate, satellite-guided weapons are significantly more likely to achieve a successful strike in any given weather conditions than any other type of precision-guided munition.

Advanced guidance concepts

Responding to after-action reports from pilots who employed laser or satellite guided weapons, Boeing developed a Laser JDAM (LJDAM) to provide both types of guidance in a single kit. Based on the existing Joint Direct Attack Munition configurations, a laser guidance package is added to a GPS/INS-guided weapon to increase its overall accuracy. Raytheon has developed the Enhanced Paveway family, which adds GPS/INS guidance to their Paveway family of laser-guidance packages. These "hybrid" laser and GPS guided weapons permit the carriage of fewer weapons types, while retaining mission flexibility, because these weapons can be employed equally against moving and fixed targets, or targets of opportunity. For instance, a typical weapons load on an F-16 flying in the Iraq War included a single 2,000-pound (910 kg) JDAM and two 1,000-pound (450 kg) LGBs. With LJDAM, and the new GBU-39 Small Diameter Bomb (SDB), these same aircraft can carry more bombs if necessary, and have the option of satellite or laser guidance for each weapon release.

• Spice (munition) is an Israeli EO/GPS-guided guidance kit for converting air-droppable unguided bombs into precision guided bombs. Spice can be preprogrammed, with up to 100 different targets it may have to engage during a mission. The one target it will actually engage may then be selected, inflight, by an aircrewman.
• The HGK guidance kit (HGK), Turkish: Hassas Güdüm Kiti / Precision Guidance Kit), developed by TÜBİTAK-SAGE, is a GPS/INS guidance kit that converts 2,000-pound (910 kg) Mark 84 bombs into smart weapons. It enables precision strike capability in all weather conditions with long range at a dispersion of 20 ft (6 m).
• Armement Air-Sol Modulaire (AASM) is a French equivalent to JDAM. AASM comprises a frontal guidance kit and a rear-mounted range extension kit matched to a dumb bomb. The weapon is modular because it can integrate different types of guidance units and different types of bombs. It uses hybrid inertial navigation system (INS) / Global Positioning System (GPS) guidance. Other variants add infrared homing or laser guidance to increase accuracy.
• Paveway IV is a dual mode GPS/INS and laser-guided bomb manufactured by Raytheon UK (formerly Raytheon Systems Limited). It is the latest iteration of the Paveway series.
• Denel Dynamics Umbani a precision-guided bomb kit manufactured by Denel Dynamics in South Africa. It consists of a number of modules fitted to NATO standard Mk81, Mk82 or Mk83 low drag free-fall bombs to convert them to glide bombs.
• Smart Anti-Airfield Weapon (SAAW) is an Indian precision-guided Anti-Airfield Weapon developed by Research Centre Imarat of DRDO with a range up to 62 mi (100 km) .
• High Speed Low Drag Bomb (HSLD) is an Indian precision guided munition developed by Armament Research and Development Establishment that is comparable with the US' Mark 80 series. It uses inertial and satellite navigation with laser guidance kit for target accuracy.
• Moving Target Artillery Round (MTAR)

The U.S. Navy leads development for a new 155 mm (6.1 in) artillery round called Moving Target Artillery Round, capable of destroying moving targets in GPS-denied environments". The Office of Naval Research (ONR), the Naval Surface Warfare Center Dahlgren Division (NSWC Dahlgren), and the U.S. Army Research Laboratory (ARL) have been coordinating MTAR, with final development scheduled for 2019.

Key features of the MTAR shell include extended range against moving targets, precision guidance and navigation without GPS, subsystem modularity, subsystem maturity, weapon system compatibility, restricted altitude, all-weather capability, reduced time of flight, and affordability. The new munition is intended for the Army or Marine Corps M777A1 howitzer, the M109A6 Paladin, and M109A7 Paladin Integrated Management (PIM) self-propelled 155 mm (6.1 in) artillery systems. The shell also would be for the Navy's Advanced Gun System (AGS) aboard the Zumwalt-class destroyer, and other future naval gun systems.

• Precision Guidance Kit – Modernization (PGK-M)

The U.S. Army is planning for GPS-denied environments with the new Precision Guidance Kit – Modernization (PGK-M). An enhancement of previous technologies, PGK-M will give U.S. forces the ability to continue launching precision strikes when GPS is compromised by the enemy.

Picatinny Arsenal engineers are leading the development of a GPS alternative using image navigation for precision guidance of munitions, under the Armament Research, Development and Engineering Center (ARDEC). Other research partners include Draper Labs, U.S. Army Research Laboratory, Air Force Research Laboratory and the Aviation and Missile Research, Development, and Engineering Center.

The enhanced munition can navigate to a desired location, through a reference image used by the technology to reach the target. The PGK-M includes a collection of ad hoc software programmable radio networks, various kinds of wave-relay connectivity technologies and navigational technology.

• PBK-500U Drel is a Russian guided jamming-resistant stealth glide bomb.

Cannon and mortar-launched guided projectiles

Main article: Cannon-launched guided projectile

A cannon-launched guided projectile (CLGP), is fired from artillery, ship's cannon, or armored vehicles. Several agencies and organizations sponsored the CLGP programs. The United States Navy sponsored the Deadeye program, a laser-guided shell for its 5 in (127 mm) guns and a program to mate a Paveway guidance system to an 8 in (203 mm) shell for the 8"/55 caliber Mark 71 gun in the 1970s (Photo). Other Navy efforts include the BTERM, ERGM, and LRLAP shells.

• The U.S. Army's MGM-51 Shillelagh missile can be considered a type of CLGP. Intended for use on the M551 Sheridan light tank, the Shillelagh missile was fired out of the Sheridan's cannon to provide robust anti-tank capability. The Army's M712 Copperhead laser guided artillery round was used in Desert Storm. Army CLGPs include the M982 Excalibur 155 mm (6.1 in) artillery shell, the XM395 Precision Guided Mortar Munition, and the XM1156 Precision Guidance Kit to refit existing 155 mm shells with precision guidance, as the Air Force's JDAM program converts dumb bombs into precision munitions.
• M982 Excalibur, GPS-guided munitions (XM982) for 155 mm artillery was developed in a collaborative effort between U.S. Army Research Laboratory (ARL) and the Armaments Research and Development Center (ARDEC). Research included developing GPS and microelectromechanical systems (MEMS) Inertial Sensor Technology. Excalibur was fielded in Operation Iraqi Freedom in the summer of 2007. Technology developed on the Excalibur is also applied in the Army's Precision Guidance Kit (PGK) for use on existing conventional projectiles and the Mortar Guidance Kit (MGK) for use on conventional mortars.
• XM1111 Mid-Range Munition is cancelled 120 mm (4.7 in) tank gun launched missile.
• LAHAT is Israeli semi-active laser homing guided low-weight anti-tank guided missile that can be launched from smoothbore tank guns.
• KSTAM is South Korean guided munition shot from the gun of K2 Black Panther tank.
• 30F39 Krasnopol is a Russian 152 / 155 mm (6.0 / 6.1 in) cannon-launched, fin-stabilized, base bleed-assisted, semi-automatic laser-guided, explosive projectile. It automatically 'homes' on a point illuminated by a laser designator, typically operated by a ground-based artillery observer.
• Kitolov-2M is a Russian laser-guided 120 / 122 mm (4.7 / 4.8 in) artillery shell with Malakhit automated artillery fire control system.
• 9M119 Svir/Refleks are Russian tank gun-launched laser-guided projectiles.
• Pansarsprängvinggranat m/94 STRIX is a Swedish endphase-guided projectile fired from a 120 mm (4.7 in) mortar currently manufactured by Saab Bofors Dynamics.

STRIX is fired like a conventional mortar round. The round contains an infrared imaging sensor that it uses to guide itself onto any tank or armoured fighting vehicle in the vicinity where it lands. The seeker is designed to ignore targets that are already burning.

• Basir is an Iranian artillery fired laser-guided, 155 mm explosive projectile designed to destroy enemy tanks, vehicles and other moving or non-moving targets with high precision. This weapon is similar in function with Russian Kransnopol or American M712 Copperhead.
• SMArt 155 is a German 155 mm artillery round, designed for a long range, indirect fire top attack role against armoured vehicles. The SMArt carrier shell contains two submunitions with infrared sensor and millimeter wave radar, which descend over the battlefield on ballutes and attack hardened targets with explosively formed penetrator warheads. Built with multiple redundant self-destruct mechanisms, these submunitions were specifically designed to fall outside the category of submunition weapons prohibited by the 2008 Convention on Cluster Munitions.
• SAMHO is an Indian gun-launched anti-tank guided missile developed by the Armament Research and Development Establishment (ARDE) for the Arjun MBT of the Indian Army.
• Rheinmetall Denel Munitions 155 mm V-LAP
• GP1: Chinese laser-guided 155 mm artillery projectile based on Krasnopol.
• GP6: Chinese laser-guided 155 mm artillery projectile based on Krasnopol.
• XM395 Precision Guided Mortar Munition
• Strix mortar round
• KM-8 Gran is a Russian guided 120 mm mortar shell with Malakhit fire control system.
• GP120 (GP4) is a Chinese terminal corrected 120 mm mortar shell.
• GP140 is a Chinese semi-active laser (SAL) guided 120 mm mortar shell.

Guided small arms

Main article: Precision-guided firearm

Precision-guided small arms prototypes have been developed which use a laser designator to guide an electronically actuated bullet to a target. Another system in development uses a laser range finder to trigger an explosive small arms shell in proximity to a target. The U.S. Army plans to use such devices in the future.

In 2008 the EXACTO program began under DARPA to develop a "fire and forget" smart sniper rifle system including a guided smart bullet and improved scope. The exact technologies of this smart bullet have not been released. EXACTO was test fired in 2014 and 2015 and results showing the bullet alter course to correct its path to its target were released.

In 2012 Sandia National Laboratories announced a self-guided bullet prototype that could track a target illuminated with a laser designator. The bullet is capable of updating its position 30 times a second and hitting targets over a mile away.

In mid-2016, Russia revealed it was developing a similar "smart bullet" weapon designed to hit targets at a distance of up to 6 mi (10 km).

Pike is a precision-guided mini-missile fired from an underslung grenade launcher.

Air burst grenade launchers are a type of precision-guided weapons. Such grenade launchers can preprogram their grenades using a fire-control system to explode in the air above or beside the enemy.

Blood pressure

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Blood_pressure

 

Blood pressure
A healthcare worker measuring blood pressure using a sphygmomanometer.
MeSH	D001795
MedlinePlus	007490
LOINC	35094-2

Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" refers to the pressure in a brachial artery, where it is most commonly measured. Blood pressure is usually expressed in terms of the systolic pressure (maximum pressure during one heartbeat) over diastolic pressure (minimum pressure between two heartbeats) in the cardiac cycle. It is measured in millimeters of mercury (mmHg) above the surrounding atmospheric pressure, or in kilopascals (kPa).

Blood pressure is one of the vital signs—together with respiratory rate, heart rate, oxygen saturation, and body temperature—that healthcare professionals use in evaluating a patient's health. Normal resting blood pressure, in an adult is approximately 120 millimetres of mercury (16 kPa) systolic over 80 millimetres of mercury (11 kPa) diastolic, denoted as "120/80 mmHg". Globally, the average blood pressure, age standardized, has remained about the same since 1975 to the present, at approx. 127/79 mmHg in men and 122/77 mmHg in women, although these average data mask significantly diverging regional trends.

Traditionally, a health-care worker measured blood pressure non-invasively by auscultation (listening) through a stethoscope for sounds in one arm's artery as the artery is squeezed, closer to the heart, by an aneroid gauge or a mercury-tube sphygmomanometer. Auscultation is still generally considered to be the gold standard of accuracy for non-invasive blood pressure readings in clinic. However, semi-automated methods have become common, largely due to concerns about potential mercury toxicity, although cost, ease of use and applicability to ambulatory blood pressure or home blood pressure measurements have also influenced this trend. Early automated alternatives to mercury-tube sphygmomanometers were often seriously inaccurate, but modern devices validated to international standards achieve an average difference between two standardized reading methods of 5 mm Hg or less, and a standard deviation of less than 8 mm Hg. Most of these semi-automated methods measure blood pressure using oscillometry (measurement by a pressure transducer in the cuff of the device of small oscillations of intra-cuff pressure accompanying heartbeat-induced changes in the volume of each pulse).

Blood pressure is influenced by cardiac output, systemic vascular resistance, blood volume and arterial stiffness, and varies depending on patient's situation, emotional state, activity and relative health or disease state. In the short term, blood pressure is regulated by baroreceptors, which act via the brain to influence the nervous and the endocrine systems.

Blood pressure that is too low is called hypotension, pressure that is consistently too high is called hypertension, and normal pressure is called normotension. Both hypertension and hypotension have many causes and may be of sudden onset or of long duration. Long-term hypertension is a risk factor for many diseases, including stroke, heart disease, and kidney failure. Long-term hypertension is more common than long-term hypotension.

Classification, normal and abnormal values

Systemic arterial pressure

The Task Force for the management of arterial hypertension of the European Society of Cardiology (ESC) and the European Society of Hypertension (ESH) classification of office blood pressure (BP)^a and definitions of hypertension grade^b.

Category	Systolic BP, mmHg	Diastolic BP, mmHg
Optimal	< 120	< 80
Normal	120–129	80–84
High normal	130–139	85–89
Grade 1 hypertension	140–159	90–99
Grade 2 hypertension	160–179	100–109
Grade 3 hypertension	≥ 180	≥ 110
Isolated systolic hypertensionb	≥ 140	< 90
The same classification is used for all ages from 16 years. a BP category is defined according to seated clinic BP and by the highest level of BP, whether systolic or diastolic. b Isolated systolic hypertension is graded 1, 2, or 3 according to systolic BP values in the ranges indicated.

Diastolic vs systolic blood pressure chart comparing European Society of Cardiology and European Society of Hypertension classification with reference ranges in children

The risk of cardiovascular disease increases progressively above 115/75 mmHg, below this level there is limited evidence.

Observational studies demonstrate that people who maintain arterial pressures at the low end of these pressure ranges have much better long-term cardiovascular health. There is an ongoing medical debate over what is the optimal level of blood pressure to target when using drugs to lower blood pressure with hypertension, particularly in older people.

The table shows the 2018 classification of office (or clinic) blood pressure by The Task Force for the management of arterial hypertension of the European Society of Cardiology (ESC) and the European Society of Hypertension (ESH). Similar thresholds had been adopted by the American Heart Association for adults who are 18 years and older, but in November 2017 the American Heart Association announced revised definitions for blood pressure categories that increased the number of people considered to have high blood pressure.

Blood pressure fluctuates from minute to minute and normally shows a circadian rhythm over a 24-hour period, with highest readings in the early morning and evenings and lowest readings at night. Loss of the normal fall in blood pressure at night is associated with a greater future risk of cardiovascular disease and there is evidence that night-time blood pressure is a stronger predictor of cardiovascular events than day-time blood pressure. Blood pressure varies over longer time periods (months to years) and this variability predicts adverse outcomes. Blood pressure also changes in response to temperature, noise, emotional stress, consumption of food or liquid, dietary factors, physical activity, changes in posture (such as standing-up), drugs, and disease. The variability in blood pressure and the better predictive value of ambulatory blood pressure measurements has led some authorities, such as the National Institute for Health and Care Excellence (NICE) in the UK, to advocate for the use of ambulatory blood pressure as the preferred method for diagnosis of hypertension.

A digital sphygmomanometer used for measuring blood pressure

Various other factors, such as age and sex, also influence a person's blood pressure. Differences between left-arm and right-arm blood pressure measurements tend to be small. However, occasionally there is a consistent difference greater than 10 mmHg which may need further investigation, e.g. for peripheral arterial disease, obstructive arterial disease or aortic dissection.

There is no accepted diagnostic standard for hypotension, although pressures less than 90/60 are commonly regarded as hypotensive. In practice blood pressure is considered too low only if symptoms are present.

Systemic arterial pressure and age

Fetal blood pressure

Further information: Fetal circulation § Blood pressure

In pregnancy, it is the fetal heart and not the mother's heart that builds up the fetal blood pressure to drive blood through the fetal circulation. The blood pressure in the fetal aorta is approximately 30 mmHg at 20 weeks of gestation, and increases to approximately 45 mmHg at 40 weeks of gestation.

The average blood pressure for full-term infants:

• Systolic 65–95 mmHg
• Diastolic 30–60 mmHg

Childhood

Reference ranges for blood pressure (BP) in children

Stage	Approximate age	Systolic BP, mmHg	Diastolic BP, mmHg
Infants	0–12 months	75–100	50–70
Toddlers and preschoolers	1–5 years	80–110	50–80
School age	6–12 years	85–120	50–80
Adolescents	13–18 years	95–140	60–90

In children the normal ranges for blood pressure are lower than for adults and depend on height. Reference blood pressure values have been developed for children in different countries, based on the distribution of blood pressure in children of these countries.

Aging adults

In adults in most societies, systolic blood pressure tends to rise from early adulthood onward, up to at least age 70; diastolic pressure tends to begin to rise at the same time but to start to fall earlier in mid-life, approximately age 55. Mean blood pressure rises from early adulthood, plateauing in mid-life, while pulse pressure rises quite markedly after the age of 40. Consequently, in many older people, systolic blood pressure often exceeds the normal adult range, if the diastolic pressure is in the normal range this is termed isolated systolic hypertension. The rise in pulse pressure with age is attributed to increased stiffness of the arteries. An age-related rise in blood pressure is not considered healthy and is not observed in some isolated unacculturated communities.

Systemic venous pressure

Site		Normal pressure range (in mmHg)
Central venous pressure		3–8
Right ventricular pressure	systolic	15–30
	diastolic	3–8
Pulmonary artery pressure	systolic	15–30
	diastolic	4–12
Pulmonary vein/ Pulmonary capillary wedge pressure		2–15
Left ventricular pressure	systolic	100–140
	diastolic	3–12

Blood pressure generally refers to the arterial pressure in the systemic circulation. However, measurement of pressures in the venous system and the pulmonary vessels plays an important role in intensive care medicine but requires invasive measurement of pressure using a catheter.

Venous pressure is the vascular pressure in a vein or in the atria of the heart. It is much lower than arterial pressure, with common values of 5 mmHg in the right atrium and 8 mmHg in the left atrium.

Variants of venous pressure include:

• Central venous pressure, which is a good approximation of right atrial pressure, which is a major determinant of right ventricular end diastolic volume. (However, there can be exceptions in some cases.)
• The jugular venous pressure (JVP) is the indirectly observed pressure over the venous system. It can be useful in the differentiation of different forms of heart and lung disease.
• The portal venous pressure is the blood pressure in the portal vein. It is normally 5–10 mmHg

Pulmonary pressure

Main article: Pulmonary artery pressure

Normally, the pressure in the pulmonary artery is about 15 mmHg at rest.

Increased blood pressure in the capillaries of the lung causes pulmonary hypertension, leading to interstitial edema if the pressure increases to above 20 mmHg, and to pulmonary edema at pressures above 25 mmHg.

Mean systemic pressure

Main article: Mean systemic pressure

If the heart is stopped, blood pressure falls, but it does not fall to zero. The remaining pressure measured after cessation of the heart beat and redistribution of blood throughout the circulation is termed the mean systemic pressure or mean circulatory filling pressure; typically this is proximally ~7mm Hg.

Disorders of blood pressure

Disorders of blood pressure control include high blood pressure, low blood pressure, and blood pressure that shows excessive or maladaptive fluctuation.

High blood pressure

Main article: Hypertension

Overview of main complications of persistent high blood pressure.

Arterial hypertension can be an indicator of other problems and may have long-term adverse effects. Sometimes it can be an acute problem, such as in a hypertensive emergency when blood pressure is more than 180/120 mmHg.

Levels of arterial pressure put mechanical stress on the arterial walls. Higher pressures increase heart workload and progression of unhealthy tissue growth (atheroma) that develops within the walls of arteries. The higher the pressure, the more stress that is present and the more atheroma tend to progress and the heart muscle tends to thicken, enlarge and become weaker over time.

Persistent hypertension is one of the risk factors for strokes, heart attacks, heart failure, and arterial aneurysms, and is the leading cause of chronic kidney failure. Even moderate elevation of arterial pressure leads to shortened life expectancy. At severely high pressures, mean arterial pressures 50% or more above average, a person can expect to live no more than a few years unless appropriately treated.

Both high systolic pressure and high pulse pressure (the numerical difference between systolic and diastolic pressures) are risk factors. In some cases, it appears that a decrease in excessive diastolic pressure can actually increase risk, probably due to the increased difference between systolic and diastolic pressures. If systolic blood pressure is elevated (>140 mmHg) with a normal diastolic blood pressure (<90 mmHg), it is called isolated systolic hypertension and may present a health concern. According to the 2017  American Heart Association blood pressure guidelines state that a systolic blood pressure of 130-139 mmHg with a diastolic pressure of 80-89 mmHg is "stage one hypertension".

For those with heart valve regurgitation, a change in its severity may be associated with a change in diastolic pressure. In a study of people with heart valve regurgitation that compared measurements two weeks apart for each person, there was an increased severity of aortic and mitral regurgitation when diastolic blood pressure increased, whereas when diastolic blood pressure decreased, there was a decreased severity.

Low blood pressure

Main article: Hypotension

Blood pressure that is too low is known as hypotension. This is a medical concern if it causes signs or symptoms, such as dizziness, fainting, or in extreme cases, circulatory shock.

Causes of low arterial pressure include:

• Sepsis
• Hemorrhage – blood loss
• Cardiogenic shock
• Neurally mediated hypotension (or reflex syncope)
• Toxins including toxic doses of blood pressure medicine
• Hormonal abnormalities, such as Addison's disease
• Eating disorders, particularly anorexia nervosa and bulimia

Orthostatic hypotension

Main article: Orthostatic hypotension

A large fall in blood pressure upon standing (persistent systolic/diastolic blood pressure decrease of >20/10 mm Hg) is termed orthostatic hypotension (postural hypotension) and represents a failure of the body to compensate for the effect of gravity on the circulation. Standing results in an increased hydrostatic pressure in the blood vessels of the lower limbs. The consequent distension of the veins below the diaphragm (venous pooling) causes ~500 ml of blood to be relocated from the chest and upper body. This results in a rapid decrease in central blood volume and a reduction of ventricular preload which in turn reduces stroke volume, and mean arterial pressure. Normally this is compensated for by multiple mechanisms, including activation of the autonomic nervous system which increases heart rate, myocardial contractility and systemic arterial vasoconstriction to preserve blood pressure and elicits venous vasoconstriction to decrease venous compliance. Decreased venous compliance also results from an intrinsic myogenic increase in venous smooth muscle tone in response to the elevated pressure in the veins of the lower body.

Other compensatory mechanisms include the veno-arteriolar axon reflex, the 'skeletal muscle pump' and 'respiratory pump'. Together these mechanisms normally stabilize blood pressure within a minute or less. If these compensatory mechanisms fail and arterial pressure and blood flow decrease beyond a certain point, the perfusion of the brain becomes critically compromised (i.e., the blood supply is not sufficient), causing lightheadedness, dizziness, weakness or fainting. Usually this failure of compensation is due to disease, or drugs that affect the sympathetic nervous system. A similar effect is observed following the experience of excessive gravitational forces (G-loading), such as routinely experienced by aerobatic or combat pilots 'pulling Gs' where the extreme hydrostatic pressures exceed the ability of the body's compensatory mechanisms.

Variable or fluctuating blood pressure

Some fluctuation or variation in blood pressure is normal. Variations in pressure that are significantly greater than the norm are associated with increased risk of cardiovascular disease brain small vessel disease, and dementia independent of the average blood pressure level. Recent evidence from clinical trials has also linked variation in blood pressure to mortality, stroke, heart failure, and cardiac changes that may give rise to heart failure. These data have prompted discussion of whether excessive variation in blood pressure should be treated, even among normotensive older adults.

Older individuals and those who had received blood pressure medications are more likely to exhibit larger fluctuations in pressure, and there is some evidence that different antihypertensive agents have different effects on blood pressure variability; whether these differences translate to benefits in outcome is uncertain.

Physiology

Cardiac systole and diastole

Blood flow velocity waveforms in the central retinal artery (red) and vein (blue), measured by laser Doppler imaging in the eye fundus of a healthy volunteer.

During each heartbeat, blood pressure varies between a maximum (systolic) and a minimum (diastolic) pressure. The blood pressure in the circulation is principally due to the pumping action of the heart. However, blood pressure is also regulated by neural regulation from the brain (see Hypertension and the brain), as well as osmotic regulation from the kidney. Differences in mean blood pressure drive the flow of blood around the circulation. The rate of mean blood flow depends on both blood pressure and the resistance to flow presented by the blood vessels. In the absence of hydrostatic effects (e.g. standing), mean blood pressure decreases as the circulating blood moves away from the heart through arteries and capillaries due to viscous losses of energy. Mean blood pressure drops over the whole circulation, although most of the fall occurs along the small arteries and arterioles. Pulsatility also diminishes in the smaller elements of the arterial circulation, although some transmitted pulsatility is observed in capillaries.

Schematic of pressures in the circulation

Gravity affects blood pressure via hydrostatic forces (e.g., during standing), and valves in veins, breathing, and pumping from contraction of skeletal muscles also influence blood pressure, particularly in veins.

Hemodynamics

Main article: Hemodynamics

A simple view of the hemodynamics of systemic arterial pressure is based around mean arterial pressure (MAP) and pulse pressure. Most influences on blood pressure can be understood in terms of their effect on cardiac output, systemic vascular resistance, or arterial stiffness (the inverse of arterial compliance). Cardiac output is the product of stroke volume and heart rate. Stroke volume is influenced by 1) the end diastolic volume or filling pressure of the ventricle acting via the Frank Starling mechanism—this is influenced by blood volume; 2) cardiac contractility; and 3) afterload, the impedance to blood flow presented by the circulation. In the short-term, the greater the blood volume, the higher the cardiac output. This has been proposed as an explanation of the relationship between high dietary salt intake and increased blood pressure; however, responses to increased dietary sodium intake vary between individuals and are highly dependent on autonomic nervous system responses and the renin–angiotensin system, changes in plasma osmolarity may also be important. In the longer-term the relationship between volume and blood pressure is more complex. In simple terms, systemic vascular resistance is mainly determined by the caliber of small arteries and arterioles. The resistance attributable to a blood vessel depends on its radius as described by the Hagen-Poiseuille's equation (resistance∝1/radius⁴). Hence, the smaller the radius, the higher the resistance. Other physical factors that affect resistance include: vessel length (the longer the vessel, the higher the resistance), blood viscosity (the higher the viscosity, the higher the resistance) and the number of vessels, particularly the smaller numerous, arterioles and capillaries. The presence of a severe arterial stenosis increases resistance to flow, however this increase in resistance rarely increases systemic blood pressure because its contribution to total systemic resistance is small, although it may profoundly decrease downstream flow. Substances called vasoconstrictors reduce the caliber of blood vessels, thereby increasing blood pressure. Vasodilators (such as nitroglycerin) increase the caliber of blood vessels, thereby decreasing arterial pressure. In the longer term a process termed remodeling also contributes to changing the caliber of small blood vessels and influencing resistance and reactivity to vasoactive agents. Reductions in capillary density, termed capillary rarefaction, may also contribute to increased resistance in some circumstances.

In practice, each individual's autonomic nervous system and other systems regulating blood pressure, notably the kidney, respond to and regulate all these factors so that, although the above issues are important, they rarely act in isolation and the actual arterial pressure response of a given individual can vary widely in the short and long term.

Mean arterial pressure

Main article: Mean arterial pressure

Mean Arterial Pressure (MAP) is the average of blood pressure over a cardiac cycle and is determined by the cardiac output (CO), systemic vascular resistance (SVR), and central venous pressure (CVP):

${\displaystyle \text{MAP}=(\text{CO}\cdot \text{SVR})+\text{CVP}}$

In practice, the contribution of CVP (which is small) is generally ignored and so

${\displaystyle \text{MAP}=\text{CO}\cdot \text{SVR}}$

MAP is often estimated from measurements of the systolic pressure, ${\displaystyle P_{\text{sys}}}$ and the diastolic pressure, ${\displaystyle P_{\text{dias}}}$  using the equation:

${\displaystyle \text{MAP}\approxeq P_{\text{dias}}+k(P_{\text{sys}}-P_{\text{dias}})}$

where k = 0.333 although other values for k have been advocated.

Pulse pressure

Main article: Pulse pressure

A schematic representation of the arterial pressure waveform over one cardiac cycle. The notch in the curve is associated with closing of the aortic valve.

The pulse pressure is the difference between the measured systolic and diastolic pressures,

${\displaystyle P_{\text{pulse}}=P_{\text{sys}}-P_{\text{dias}}.}$

The pulse pressure is a consequence of the pulsatile nature of the cardiac output, i.e. the heartbeat. The magnitude of the pulse pressure is usually attributed to the interaction of the stroke volume of the heart, the compliance (ability to expand) of the arterial system—largely attributable to the aorta and large elastic arteries—and the resistance to flow in the arterial tree.

Regulation of blood pressure

Main articles: Blood pressure regulation and Renin–angiotensin system

The endogenous, homeostatic regulation of arterial pressure is not completely understood, but the following mechanisms of regulating arterial pressure have been well-characterized:

• Baroreceptor reflex: Baroreceptors in the high pressure receptor zones detect changes in arterial pressure. These baroreceptors send signals ultimately to the medulla of the brain stem, specifically to the rostral ventrolateral medulla (RVLM). The medulla, by way of the autonomic nervous system, adjusts the mean arterial pressure by altering both the force and speed of the heart's contractions, as well as the systemic vascular resistance. The most important arterial baroreceptors are located in the left and right carotid sinuses and in the aortic arch.
• Renin–angiotensin system (RAS): This system is generally known for its long-term adjustment of arterial pressure. This system allows the kidney to compensate for loss in blood volume or drops in arterial pressure by activating an endogenous vasoconstrictor known as angiotensin II.
• Aldosterone release: This steroid hormone is released from the adrenal cortex in response to activation of the renin-angiotensin system, high serum potassium levels, or elevated adrenocorticotropic hormone (ACTH). Renin converts angiotensinogen to angiotensin I, which is converted by angiotensin converting enzyme to angiotensin II. Angiotensin II then signals to the adrenal cortex to release aldosterone. Aldosterone stimulates sodium retention and potassium excretion by the kidneys and the consequent salt and water retention increases plasma volume, and indirectly, arterial pressure. Aldosterone may also exert direct pressor effects on vascular smooth muscle and central effects on sympathetic nervous system activity.
• Baroreceptors in low pressure receptor zones (mainly in the venae cavae and the pulmonary veins, and in the atria) result in feedback by regulating the secretion of antidiuretic hormone (ADH/Vasopressin), renin and aldosterone. The resultant increase in blood volume results in an increased cardiac output by the Frank–Starling law of the heart, in turn increasing arterial blood pressure.

These different mechanisms are not necessarily independent of each other, as indicated by the link between the RAS and aldosterone release. When blood pressure falls many physiological cascades commence in order to return the blood pressure to a more appropriate level.

1. The blood pressure fall is detected by a decrease in blood flow and thus a decrease in glomerular filtration rate (GFR).
2. Decrease in GFR is sensed as a decrease in Na⁺ levels by the macula densa.
3. The macula densa causes an increase in Na⁺ reabsorption, which causes water to follow in via osmosis and leads to an ultimate increase in plasma volume. Further, the macula densa releases adenosine which causes constriction of the afferent arterioles.
4. At the same time, the juxtaglomerular cells sense the decrease in blood pressure and release renin.
5. Renin converts angiotensinogen (inactive form) to angiotensin I (active form).
6. Angiotensin I flows in the bloodstream until it reaches the capillaries of the lungs where angiotensin-converting enzyme (ACE) acts on it to convert it into angiotensin II.
7. Angiotensin II is a vasoconstrictor that will increase blood flow to the heart and subsequently the preload, ultimately increasing the cardiac output.
8. Angiotensin II also causes an increase in the release of aldosterone from the adrenal glands.
9. Aldosterone further increases the Na⁺ and H₂O reabsorption in the distal convoluted tubule of the nephron.

Currently, the RAS is targeted pharmacologically by ACE inhibitors and angiotensin II receptor antagonists, also known as angiotensin receptor blockers (ARBs). The aldosterone system is directly targeted by spironolactone, an aldosterone antagonist. The fluid retention may be targeted by diuretics; the antihypertensive effect of diuretics is due to its effect on blood volume. Generally, the baroreceptor reflex is not targeted in hypertension because if blocked, individuals may experience orthostatic hypotension and fainting.

Taking blood pressure with a sphygmomanometer

Measurement

Main article: Blood pressure measurement

Measuring systolic and diastolic blood pressure using a mercury sphygmomanometer

Arterial pressure is most commonly measured via a sphygmomanometer, which uses the height of a column of mercury, or an aneroid gauge, to reflect the blood pressure by auscultation. The most common automated blood pressure measurement technique is based on the oscillometric method. Fully automated oscillometric measurement has been available since 1981. This principle has recently been used to measure blood pressure with a smartphone. Measuring pressure invasively, by penetrating the arterial wall to take the measurement, is much less common and usually restricted to a hospital setting. Novel methods to measure blood pressure without penetrating the arterial wall, and without applying any pressure on patient's body are currently being explored. So-called cuffless measurements, these methods open the door to more comfortable and acceptable blood pressure monitors. An example is a cuffless blood pressure monitor at the wrist that uses only optical sensors.

One common problem in office blood pressure measurement in the United States is terminal digit preference. According to one study, approximately 40% of recorded measurements ended with the digit zero, whereas "without bias, 10%–20% of measurements are expected to end in zero" Therefore, addressing digit preference is a key issue for improving blood pressure measurement accuracy.

In animals

Blood pressure levels in non-human mammals may vary depending on the species. Heart rate differs markedly, largely depending on the size of the animal (larger animals have slower heart rates). The giraffe has a distinctly high arterial pressure of about 190 mm Hg, enabling blood perfusion through the 2 metres (6 ft 7 in)-long neck to the head. In other species subjected to orthostatic blood pressure, such as arboreal snakes, blood pressure is higher than in non-arboreal snakes. A heart near to the head (short heart-to-head distance) and a long tail with tight integument favor blood perfusion to the head.

As in humans, blood pressure in animals differs by age, sex, time of day, and environmental circumstances: measurements made in laboratories or under anesthesia may not be representative of values under free-living conditions. Rats, mice, dogs and rabbits have been used extensively to study the regulation of blood pressure.

Blood pressure and heart rate of various mammals

Species	Blood pressure mm Hg		Heart rate beats per minute
	Systolic	Diastolic
Calves	140	70	75–146
Cats	155	68	100–259
Dogs	161	51	62–170
Goats	140	90	80–120
Guinea-pigs	140	90	240–300
Mice	120	75	580–680
Pigs	169	55	74–116
Rabbits	118	67	205–306
Rats	153	51	305–500
Rhesus monkeys	160	125	180–210
Sheep	140	80	63–210

Hypertension in cats and dogs

Hypertension in cats and dogs is generally diagnosed if the blood pressure is greater than 150 mm Hg (systolic), although sight hounds have higher blood pressures than most other dog breeds; a systolic pressure greater than 180 mmHg is considered abnormal in these dogs.