3. Physiology
        3.2. Cardiovascular
            3.2.4. Regulatory mechanisms
                3.2.4.3. Control of cardiac output
3.2.4.3.2. Vascular function curve

Vascular function curve (of Guyton)

[Ref: KB2:p103-104, PK1:p135-141;BL8:p200-215]

Shows the effect of increases in cardiac output (independent variable) on right atrial pressure (dependent variable)

Mean systemic pressure [KB2]

aka static pressure [BL8]

aka mean circulatory pressure [BL8]

aka mean systolic filling pressure [PK1]

[KB2:p103] ... a theoretical pressure that is said to represent the force promoting venous return.

[PK1:p136] MSFP is (proposed by Guyton)... the average of all the pressures in the different vessels weighted according to their relative compliances.

--> MSFP approximates to mean venous pressure

Normal value ~ 7mmHg

Basically, my understanding is:

Mean systemic pressure is the mean pressure exerted by the volume of blood alone, at a given vascular system (and vessel compliances) without any contribution from the heart, or any activation of compensatory reflexes.

Changes in mean systemic pressure

Mean systemic pressure increases with:

Not significantly affected by total peripheral resistance
* Because arterioles which contribute the most to resistance only contain very little blood (1-2% of total blood volume)

 

NB:

Slope of vascular function curve

Compliance of arteries to veins
~ 1:19

When cardiac output increase, blood is moved from venous circulation to arterial circulation

Increase in arterial blood volume
= Decrease in venous blood volume

However, because of the differences in compliance

--> Increase in arterial BP is 19 times the decrease in venous BP

Mathematical expression

[BL8:p203-205]

[##20050614(01)]

dPa = -19 x dPv

R = (Pa-Pv)/Qr

--> Pv = - [R.Ca/(Ca+Cv)]Qr + Pmc

Thus, slope of the curve is only dependent on:

 

Shifts in vascular function curve

Increase in blood volume

--> MSP increased, gradient unchanged

--> Vascular function curve moves up

 

Vasoconstriction

--> MSP unchanged, gradient decreases

--> Vascular function curve rotate downwards

 

Sympathetic stimulation

--> MSP increased (due to venoconstriction), gradient decreased (due to vasoconstriction)

--> Vascular function curve shifts upwards and slope flatter

 

Heart failure

--> MSP increased (due to fluid retention), gradient unchanged

--> Vascular function curve shifts upwards

About
Reviewed20050816


Table of contents  | Bibliography  | Index