lecture.6 bp

Cardiovascular Cardiovascular SystemSystem

Blood PressureBlood Pressure

SMS 1053SMS 1053

Dr. Mohanad R. AlwanDr. Mohanad R. Alwan

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Blood FlowBlood Flow

Actual volume of blood flowing through a vessel, Actual volume of blood flowing through a vessel, an organ, or the entire circulation in a given an organ, or the entire circulation in a given period:period: Is measured in Is measured in ml per min.ml per min. Is equivalent to cardiac output (CO), considering the Is equivalent to cardiac output (CO), considering the

entire vascular systementire vascular system Is relatively constant when at restIs relatively constant when at rest Varies widely through individual organs, according to Varies widely through individual organs, according to

immediate needsimmediate needs


Blood Pressure (BP)Blood Pressure (BP)

Force per unit area exerted on the wall of a Force per unit area exerted on the wall of a blood vessel by its contained bloodblood vessel by its contained blood Expressed in Expressed in millimeters of mercury (mm Hg)millimeters of mercury (mm Hg) Measured in reference to systemic arterial BP in large Measured in reference to systemic arterial BP in large

arteries near the heartarteries near the heart

The differences in BP within the vascular system The differences in BP within the vascular system provide the driving force that keeps blood provide the driving force that keeps blood moving from higher to lower pressure areasmoving from higher to lower pressure areas


ResistanceResistance

Resistance – opposition to flow Resistance – opposition to flow Measure of the amount of friction blood encounters as Measure of the amount of friction blood encounters as

it passes through vesselsit passes through vessels Generally encountered in the systemic circulationGenerally encountered in the systemic circulation Referred to as peripheral resistance (PR)Referred to as peripheral resistance (PR)

The three important sources of resistance are The three important sources of resistance are blood viscosity, total blood vessel length, and blood viscosity, total blood vessel length, and blood vessel diameterblood vessel diameter


Resistance factors that remain relatively Resistance factors that remain relatively constant are:constant are: Blood viscosity – thickness or “stickiness” of the blood Blood viscosity – thickness or “stickiness” of the blood Blood vessel length – the longer the vessel, the Blood vessel length – the longer the vessel, the

greater the resistance encounteredgreater the resistance encountered

Resistance Factors: Viscosity and Vessel Resistance Factors: Viscosity and Vessel LengthLength


Resistance Factors: Blood Vessel DiameterResistance Factors: Blood Vessel Diameter

Changes in vessel diameter are frequent and Changes in vessel diameter are frequent and significantly alter peripheral resistance.significantly alter peripheral resistance.

Resistance varies inversely with the fourth Resistance varies inversely with the fourth power of vessel radius (diameter) (one-half the power of vessel radius (diameter) (one-half the diameter)diameter) For example, if the radius is doubled, the resistance is For example, if the radius is doubled, the resistance is

1/16 as much1/16 as much


Resistance = tendency of the vascular system to oppose flow; Flow =

• Influenced by: length of the tube (L), radius of the tube (r), and viscosity of the blood ()

Poiseuille’s Law R = Lr4

• In a normal human, length of the system is fixed, so blood viscosity and radius of the blood vessels have the largest effects on resistance

1

R


Resistance Factors: Blood Vessel DiameterResistance Factors: Blood Vessel Diameter

Small-diameter arterioles are the major Small-diameter arterioles are the major determinants of peripheral resistancedeterminants of peripheral resistance

Fatty plaques from atherosclerosis:Fatty plaques from atherosclerosis: Cause turbulent blood flowCause turbulent blood flow Dramatically increase resistance due to turbulenceDramatically increase resistance due to turbulence


Blood Flow, Blood Pressure, and ResistanceBlood Flow, Blood Pressure, and Resistance

Blood flow (F) is directly proportional to the Blood flow (F) is directly proportional to the difference in blood pressure (difference in blood pressure (PP) between two ) between two points in the circulationpoints in the circulation If If PP increases, blood flow speeds up; if increases, blood flow speeds up; if PP

decreases, blood flow declinesdecreases, blood flow declines Blood flow is Blood flow is inverselyinversely proportional to resistance proportional to resistance

(R)(R) If R increases, blood flow decreases If R increases, blood flow decreases

R is more important than R is more important than PP in influencing local in influencing local blood pressureblood pressure


Systemic Blood PressureSystemic Blood Pressure

The pumping action of the heart generates blood The pumping action of the heart generates blood flow through the vessels along a pressure flow through the vessels along a pressure gradient, always moving from higher- to lower-gradient, always moving from higher- to lower-pressure areaspressure areas

Pressure results when flow is opposed by Pressure results when flow is opposed by resistanceresistance

Systemic pressure:Systemic pressure: Is highest in the aortaIs highest in the aorta Declines throughout the length of the pathwayDeclines throughout the length of the pathway Is 0 mm Hg in the right atriumIs 0 mm Hg in the right atrium

The steepest change in blood pressure occurs in The steepest change in blood pressure occurs in the arteriolesthe arterioles


Systemic Blood PressureSystemic Blood Pressure

Figure 19.5


Arterial Blood PressureArterial Blood Pressure

Arterial BP reflects two factors of the arteries close Arterial BP reflects two factors of the arteries close to the heartto the heart Their elasticity (compliance or distensibility)Their elasticity (compliance or distensibility) The amount of blood forced into them at any given timeThe amount of blood forced into them at any given time

Blood pressure in elastic arteries near the heart is pulsatile Blood pressure in elastic arteries near the heart is pulsatile (BP rises and falls). (BP rises and falls).


Arterial Blood PressureArterial Blood Pressure

Systolic pressure – pressure exerted on arterial Systolic pressure – pressure exerted on arterial walls during ventricular contraction walls during ventricular contraction

Diastolic pressure – lowest level of arterial Diastolic pressure – lowest level of arterial pressure during a ventricular cyclepressure during a ventricular cycle

Pulse pressure – the difference between systolic Pulse pressure – the difference between systolic and diastolic pressureand diastolic pressure

Mean arterial pressure (MAP) – pressure that Mean arterial pressure (MAP) – pressure that propels the blood to the tissuespropels the blood to the tissues

MAP = diastolic pressure + 1/3 pulse pressure MAP = diastolic pressure + 1/3 pulse pressure


Capillary Blood PressureCapillary Blood Pressure

Low capillary pressure is desirable because high Low capillary pressure is desirable because high BP would rupture fragile, thin-walled capillariesBP would rupture fragile, thin-walled capillaries

Capillary BP ranges from Capillary BP ranges from 20 to 40 mm Hg20 to 40 mm Hg Low BP is sufficient to force filtrate out into Low BP is sufficient to force filtrate out into

interstitial space and distribute nutrients, gases, interstitial space and distribute nutrients, gases, and hormones between blood and tissuesand hormones between blood and tissues


Venous Blood PressureVenous Blood Pressure

Venous BP is steady and changes little during Venous BP is steady and changes little during the cardiac cyclethe cardiac cycle

The pressure gradient in the venous system is The pressure gradient in the venous system is only about 20 mm Hg only about 20 mm Hg

A cut vein has even blood flow; a lacerated A cut vein has even blood flow; a lacerated artery flows in spurtsartery flows in spurts


Maintaining Blood PressureMaintaining Blood Pressure

The main factors influencing blood pressure are:The main factors influencing blood pressure are: Cardiac output (CO)Cardiac output (CO) Peripheral resistance (PR)Peripheral resistance (PR) Blood volumeBlood volume

Blood pressure = CO x PRBlood pressure = CO x PR Blood pressure varies directly with CO, PR, and Blood pressure varies directly with CO, PR, and

blood volumeblood volume

Maintaining blood pressure requires:Maintaining blood pressure requires: Cooperation of the heart, blood vessels, and Cooperation of the heart, blood vessels, and

kidneyskidneys Supervision of the brainSupervision of the brain


Cardiac Output (CO)Cardiac Output (CO)


Controls of Blood PressureControls of Blood Pressure

Short-term controls: Short-term controls: Are mediated by the nervous system and blood borne Are mediated by the nervous system and blood borne

chemicalschemicals Counteract moment-to-moment fluctuations in blood Counteract moment-to-moment fluctuations in blood

pressure by altering peripheral resistancepressure by altering peripheral resistance Long-term controls regulate blood volumeLong-term controls regulate blood volume


Regulation of Blood Pressure

• Main coordinating center is in the medulla oblongata of the brain; medullary cardiovascular control center


Regulation of Cardiovascular SystemRegulation of Cardiovascular SystemOverview-Overview-


Short-Term Mechanisms: Neural ControlsShort-Term Mechanisms: Neural Controls Neural controls of peripheral resistance:Neural controls of peripheral resistance:

Alter blood distribution to respond to specific demandsAlter blood distribution to respond to specific demands Maintain MAP by altering blood vessel diameterMaintain MAP by altering blood vessel diameter

Neural controls operate via reflex arcs involving:Neural controls operate via reflex arcs involving:BaroreceptorsBaroreceptors The system relies on specialized neurons, known as The system relies on specialized neurons, known as

baroreceptors, baroreceptors, in the aortic arch, carotid sinuses, and in the aortic arch, carotid sinuses, and elsewhere to monitor changes in blood pressure and relay elsewhere to monitor changes in blood pressure and relay them to the brainstem. them to the brainstem.

Subsequent changes in blood pressure are mediated by Subsequent changes in blood pressure are mediated by the autonomic nervous systemthe autonomic nervous system

Vasomotor centers of the medulla and vasomotor fibersVasomotor centers of the medulla and vasomotor fibers Vascular smooth muscleVascular smooth muscle


Short-Term Mechanisms: Vasomotor CenterShort-Term Mechanisms: Vasomotor Center

Vasomotor center Vasomotor center – a cluster of sympathetic – a cluster of sympathetic neurons in the medulla that oversees changes in neurons in the medulla that oversees changes in blood vessel diameterblood vessel diameter Maintains blood vessel tone by innervating smooth Maintains blood vessel tone by innervating smooth

muscles of blood vessels, muscles of blood vessels, especially arteriolesespecially arterioles

Cardiovascular center Cardiovascular center – vasomotor center plus – vasomotor center plus the cardiac centers that integrate blood pressure the cardiac centers that integrate blood pressure control by altering cardiac output and blood vessel control by altering cardiac output and blood vessel diameterdiameter


Short-Term Mechanisms: Vasomotor ActivityShort-Term Mechanisms: Vasomotor Activity

Sympathetic activity causes:Sympathetic activity causes: Vasoconstriction and a rise in blood pressure if Vasoconstriction and a rise in blood pressure if

increasedincreased Blood pressure to decline to basal levels if decreasedBlood pressure to decline to basal levels if decreased

Vasomotor activity is modified by:Vasomotor activity is modified by: Baroreceptors (pressure-sensitive), chemoreceptors Baroreceptors (pressure-sensitive), chemoreceptors

(O(O22, CO, CO22, and H, and H++ sensitive), higher brain centers, sensitive), higher brain centers,

blood borne chemicals, and hormonesblood borne chemicals, and hormones


Increased blood pressure stimulates the Increased blood pressure stimulates the Cardioinhibitory Center Cardioinhibitory Center to:to: Increase vessel diameterIncrease vessel diameter Decrease heart rate, cardiac output, peripheral Decrease heart rate, cardiac output, peripheral

resistance, and blood pressure resistance, and blood pressure

Short-Term Mechanisms: Baroreceptor-Initiated Short-Term Mechanisms: Baroreceptor-Initiated ReflexesReflexes


Declining blood pressure stimulates the Declining blood pressure stimulates the cardio cardio acceleratory center acceleratory center to:to: Increase cardiac output and peripheral resistanceIncrease cardiac output and peripheral resistance

Low blood pressure also stimulates the Low blood pressure also stimulates the vasomotor center to constrict blood vesselsvasomotor center to constrict blood vessels

Short-Term Mechanisms: Baroreceptor-Short-Term Mechanisms: Baroreceptor-Initiated ReflexesInitiated Reflexes


Baroreceptor ReflexesBaroreceptor Reflexes


Short-Term Mechanisms: Chemical ControlsShort-Term Mechanisms: Chemical Controls

Blood pressure is regulated by Blood pressure is regulated by ChemoreceptoChemoreceptor r reflexes sensitive to oxygen and carbon dioxidereflexes sensitive to oxygen and carbon dioxide Prominent chemoreceptors are the carotid and aortic Prominent chemoreceptors are the carotid and aortic

bodiesbodies Reflexes that regulate blood pressure are integrated in Reflexes that regulate blood pressure are integrated in

the medullathe medulla Higher brain centers (cortex and hypothalamus) can Higher brain centers (cortex and hypothalamus) can

modify BP via relays to medullary centersmodify BP via relays to medullary centers


Chemicals that Increase Blood PressureChemicals that Increase Blood Pressure

Adrenal medulla hormones Adrenal medulla hormones – norepinephrine – norepinephrine and epinephrine increase blood pressureand epinephrine increase blood pressure

Antidiuretic hormone (ADH) Antidiuretic hormone (ADH) – causes intense – causes intense vasoconstriction in cases of extremely low BPvasoconstriction in cases of extremely low BP

Angiotensin II Angiotensin II – kidney release of renin – kidney release of renin generates angiotensin II, which causes intense generates angiotensin II, which causes intense vasoconstrictionvasoconstriction

Endothelium-derived factors Endothelium-derived factors – endothelin and – endothelin and prostaglandin-derived growth factor (PDGF) are prostaglandin-derived growth factor (PDGF) are both vasoconstrictorsboth vasoconstrictors


Chemicals that Decrease Blood PressureChemicals that Decrease Blood Pressure

Atrial natriuretic peptide (ANP) – causes blood Atrial natriuretic peptide (ANP) – causes blood volume and pressure to declinevolume and pressure to decline

Nitric oxide (NO) – has brief but potent Nitric oxide (NO) – has brief but potent vasodilator effectsvasodilator effects

Inflammatory chemicals – histamine, Inflammatory chemicals – histamine, prostacyclin, and kinins are potent vasodilatorsprostacyclin, and kinins are potent vasodilators

Alcohol – causes BP to drop by inhibiting ADHAlcohol – causes BP to drop by inhibiting ADH


Control of Cardiovascular Function – HormonesControl of Cardiovascular Function – HormonesDecreased Blood PressureDecreased Blood Pressure


Control of Cardiovascular Function – Control of Cardiovascular Function – HormonesHormones

Increased Blood PressureIncreased Blood Pressure


Long-Term Mechanisms: Renal RegulationLong-Term Mechanisms: Renal Regulation

Long-term mechanisms control BP by altering Long-term mechanisms control BP by altering blood volumeblood volume

Baroreceptors adapt to chronic high or low blood Baroreceptors adapt to chronic high or low blood pressurepressure Increased BP stimulates the kidneys to eliminate Increased BP stimulates the kidneys to eliminate

water, thus reducing BPwater, thus reducing BP Decreased BP stimulates the kidneys to increase Decreased BP stimulates the kidneys to increase

blood volume and BPblood volume and BP


Kidney Action and Blood PressureKidney Action and Blood Pressure

Kidneys act directly and indirectly to maintain Kidneys act directly and indirectly to maintain long-term blood pressure:long-term blood pressure: Direct renal mechanism alters blood volumeDirect renal mechanism alters blood volume Indirect renal mechanism involves the renin-Indirect renal mechanism involves the renin-

angiotensin mechanismangiotensin mechanism



• Declining BP causes the release of renin, which Declining BP causes the release of renin, which triggers the release of angiotensin IItriggers the release of angiotensin II

• Angiotensin II is a potent vasoconstrictor that Angiotensin II is a potent vasoconstrictor that stimulates aldosterone secretionstimulates aldosterone secretion

• Aldosterone enhances renal reabsorption and Aldosterone enhances renal reabsorption and stimulates ADH releasestimulates ADH release


Autoregulation: Local Regulation of Blood FlowAutoregulation: Local Regulation of Blood Flow

Autoregulation – automatic adjustment of blood Autoregulation – automatic adjustment of blood flow to each tissue in proportion to its flow to each tissue in proportion to its requirements at any given point in timerequirements at any given point in time

Blood flow through an individual organ is Blood flow through an individual organ is intrinsically controlled by modifying the diameter intrinsically controlled by modifying the diameter of local arterioles feeding its capillariesof local arterioles feeding its capillaries

MAP remains constant, while local demands MAP remains constant, while local demands regulate the amount of blood delivered to regulate the amount of blood delivered to various areas according to needvarious areas according to need


Metabolic ControlsMetabolic Controls

Declining tissue nutrient and oxygen levels are Declining tissue nutrient and oxygen levels are stimuli for autoregulationstimuli for autoregulation

Hemoglobin delivers nitric oxide (NO) as well as Hemoglobin delivers nitric oxide (NO) as well as oxygen to tissuesoxygen to tissues

Nitric oxide induces vasodilation at the capillaries to Nitric oxide induces vasodilation at the capillaries to help get oxygen to tissue cellshelp get oxygen to tissue cells

Other autoregulatory substances include: Other autoregulatory substances include: potassium and hydrogen ions, adenosine, lactic potassium and hydrogen ions, adenosine, lactic acid, histamines, kinins, and prostaglandins acid, histamines, kinins, and prostaglandins


Myogenic ControlsMyogenic Controls

Inadequate blood perfusion or excessively high Inadequate blood perfusion or excessively high arterial pressure:arterial pressure: Are autoregulatory Are autoregulatory Provoke myogenic responses – stimulation of Provoke myogenic responses – stimulation of

vascular smooth musclevascular smooth muscle Vascular muscle responds directly to:Vascular muscle responds directly to:

Increased vascular pressure with increased tone, Increased vascular pressure with increased tone, which causes vasoconstrictionwhich causes vasoconstriction

Reduced stretch with vasodilation, which promotes Reduced stretch with vasodilation, which promotes increased blood flow to the tissueincreased blood flow to the tissue


Monitoring Circulatory EfficiencyMonitoring Circulatory Efficiency

Efficiency of the circulation can be assessed by Efficiency of the circulation can be assessed by taking pulse and blood pressure measurementstaking pulse and blood pressure measurements

Vital signs – pulse and blood pressure, along Vital signs – pulse and blood pressure, along with respiratory rate and body temperaturewith respiratory rate and body temperature

Pulse – pressure wave caused by the expansion Pulse – pressure wave caused by the expansion and recoil of elastic arteriesand recoil of elastic arteries Radial pulse (taken on the radial artery at the wrist) is Radial pulse (taken on the radial artery at the wrist) is

routinely usedroutinely used Varies with health, body position, and activityVaries with health, body position, and activity


Variations in Blood PressureVariations in Blood Pressure

Blood pressure cycles over a 24-hour periodBlood pressure cycles over a 24-hour period BP peaks in the morning due to waxing and BP peaks in the morning due to waxing and

waning levels of retinoic acidwaning levels of retinoic acid Extrinsic factors such as age, sex, weight, race, Extrinsic factors such as age, sex, weight, race,

mood, posture, socioeconomic status, and physical mood, posture, socioeconomic status, and physical activity may also cause BP to varyactivity may also cause BP to vary


Alterations in Blood PressureAlterations in Blood Pressure

Hypotension – low BP in which systolic pressure is Hypotension – low BP in which systolic pressure is below 100 mm Hgbelow 100 mm Hg

Hypertension – condition of sustained elevated Hypertension – condition of sustained elevated arterial pressure of 140/90 or higherarterial pressure of 140/90 or higher Transient elevations are normal and can be caused by Transient elevations are normal and can be caused by

fever, physical exertion, and emotional upsetfever, physical exertion, and emotional upset Chronic elevation is a major cause of heart failure, Chronic elevation is a major cause of heart failure,

vascular disease, renal failure, and strokevascular disease, renal failure, and stroke


HypotensionHypotension

Orthostatic hypotension – temporary low BP and Orthostatic hypotension – temporary low BP and dizziness when suddenly rising from a sitting or dizziness when suddenly rising from a sitting or reclining position reclining position

Chronic hypotension – hint of poor nutrition and Chronic hypotension – hint of poor nutrition and warning sign for Addison’s diseasewarning sign for Addison’s disease

Acute hypotension – important sign of circulatory Acute hypotension – important sign of circulatory shockshock Threat to patients undergoing surgery and those in Threat to patients undergoing surgery and those in

intensive care unitsintensive care units


HypertensionHypertension

Hypertension maybe transient or persistentHypertension maybe transient or persistent Primary or essential hypertension – risk factors in Primary or essential hypertension – risk factors in

primary hypertension include diet, obesity, age, primary hypertension include diet, obesity, age, race, heredity, stress, and smokingrace, heredity, stress, and smoking

Secondary hypertension – due to identifiable Secondary hypertension – due to identifiable disorders, including excessive renin secretion, disorders, including excessive renin secretion, arteriosclerosis, and endocrine disordersarteriosclerosis, and endocrine disorders


Blood Flow Through TissuesBlood Flow Through Tissues

Blood flow, or tissue perfusion, is involved in:Blood flow, or tissue perfusion, is involved in: Delivery of oxygen and nutrients to, and removal of Delivery of oxygen and nutrients to, and removal of

wastes from, tissue cells wastes from, tissue cells Gas exchange in the lungsGas exchange in the lungs Absorption of nutrients from the digestive tractAbsorption of nutrients from the digestive tract Urine formation by the kidneysUrine formation by the kidneys

Blood flow is precisely the right amount to Blood flow is precisely the right amount to provide proper tissue functionprovide proper tissue function


Velocity of Blood FlowVelocity of Blood Flow

Blood velocity: Blood velocity: Changes as it travels through the systemic circulationChanges as it travels through the systemic circulation Is inversely proportional to the cross-sectional areaIs inversely proportional to the cross-sectional area

Slow capillary flow allows adequate time for Slow capillary flow allows adequate time for exchange between blood and tissuesexchange between blood and tissues


Velocity of Blood FlowVelocity of Blood Flow

Figure 19.13

lecture.6 bp

Technology

blood blood vessel length

blood pressure p

local blood pressure

blood vessels

contained blood

blood pressure bp force

systemic blood pressure

x pr blood pressure