2. Blood Pressure :
The lateral pressure exerted by the column of blood on the wall of
arteries .
Systolic Blood Pressure :
The maximum pressure exerted during systole.
Diastolic Blood Pressure :
The minimum pressure exerted during diastole.
3. Systolic and diastolic blood pressures have different determinants .(by the fact that they alter
differentially)
For example
with strenuous whole-body isotonic exercise
○ SBP rises (Determined by cardiac output as increases during strenuous
exercise)
○ DBP may fall (Determined by TPR -• falls during strenuous exercise
• due to vasodilation in skeletal muscles
& skin for thermoregulation. )
4. Determinants
:
○ Any condition that will change either the ‘CO’ or ‘PR’ will cause a change in arterial BP.
● Heart Rate ( HR )
● Stroke Volume ( SV )
● Velocity of Blood
● Viscosity of Blood
● Cardiac Output ( CO )
● Pulse Pressure ( PP )
● Arterial Compliance
● Transmission of PP to peripheral arteries
● Vascular Distensibility
● Elasticity of vessel wall
BP = ‘CO’ × ‘PR’
5. 1. Role of Cardiac Output (CO) :
● Pumping action of Heart is the main factor for controlling ‘CO’ .
● Therefore, alterations of ‘CO’ will alter arterial BP.
● As CO = HR × SV
○ Increase in ‘CO’
(due to increase
HR)
increase in DBP (because with increased HR
- diastole duration decreases
- & tendency of BP to fall during diastole decreases )
causes
causes
○ Increase in ‘CO’ increase in SBP
(due to se in SV)
○ Increase in ‘CO’
(due to both HR & SV)
Increase in SBP as well as
Increase in DBP
causes
6. 2. Arterial Compliance:
• Ability of the arterial wall to distend and increase volume with increasing transmural
pressure.
• Less the Compliance of Arterial System
Greater is the rise in pressure ( for a given stroke volume
of blood pumped into arteries)
Demonstrated
in this fig.
Aortic pressure pulse contours in arteriosclerosis, aortic stenosis,
patent ductus arteriosus,aortic regurgitation.
7. 3. Arterial Pressure Pulsations :
● Compliance of Arterial tree normally reduces pressure Pulsations to almost
no Pulsations by the time of blood reaches capillaries.
● Therefore tissue blood flow is mainly continuous with very little pulsations.
● factors affecting the pulse pressure : (1) the stroke volume output of heart
(2) the compliance arterial tree
● Greater the stroke vol. Output Greater is amount of blood
accommodated in arterial tree (with each
and heart beat)
Therefore,Greater the pressure rise and fall during systole &
diastole
Thus causing A greater pulse pressure
○ Pluse Pressure ~
~ Stroke Vol.
arterial compliance
- Any condition of circulation that can affect either of these two factors
also affects PP
8. 4. Transmission of PP to Peripheral arteries:
● When the heart ejects blood into the aorta during systole, at first only the proximal portion of
the aorta becomes distended because the inertia of the blood prevents sudden blood
movement all the way to the periphery.
● However, the rising pressure in the proximal aorta rapidly overcomes this inertia and the wave
front of distention spreads farther and farther along the aorta.
● This phenomenon is called transmission of the pressure pulse in the arteries.
● Compliance damps the pulsations because the more compliant a vessel, the greater is the
quantity of blood required at pulse wave front to cause an increase in pressure.
● Therefore, Degree of damping is almost directly proportional to Resistance × Compliance
9. 5.Vascular Distensibility
:
Vascular Distensibility = increase in volume
Increase in pressure × original volume
6. Delayed Compliance of vessels:
(Stress Rela ation)
•Means that a vessel e posed to increased volume at first e hibits a large increase in pressure, but progressive
delayed stretching of smooth muscle in the ves sel wall allows the pressure to return toward normal over a
period of minutes to hours.
•Due to immediate elastic distension of vessels.
•It is a valuable mecha. by which the circulation can accommodate e tra blood
when necessary. (Such as after too large transfusion)
