3. Physiology
        3.2. Cardiovascular
            3.2.6. Special circumstances
3.2.6.4. Exercise

Exercise

Summary of CVS changes during exercise

 

Muscle blood flow

At rest, blood flow is low (2-4mL/100g/min)

When muscle tension is >10% maximum
--> Compression of the vessels

When muscle tension is >70% of maximum
--> Blood flow stops

At the start of exercise

Blood flow sometimes increase at or before the start of exercise

Initial rise may be due to neural factors
--> sympathetic vasodilator system involved

Systemic vs local

Neural and local mechanism oppose each other.
[BL8:p247]

In inactive muscles, increased sympathetic activity causes vasoconstriction

In exercising muscles, local mechanism (vasodilatory) dominates

Local mechanism of vasodilation

 

10-100 fold increase in the number of open capillaries
--> Recruitment

Systemic CVS changes

Systemic response to exercise depends on whether muscle contractions are primarily isometric or isotonic

Isometric exercises

Heart rate increases at the start

Total peripheral resistance increased

--> Both SBP and DBP increase sharply

However,

Stroke volume remain relatively unchanged

Isotonic exercises

HR also increases

Marked increase in stroke volume

Net decrease in total peripheral resistance

Thus,

--> SBP increases moderately

--> DBP remains steady or even falls

Changes in cardiac output

[BL8:p218;WG21:p637]

Increased in venous return and cardiac output during exercise is mainly due to:

NB:

Fluid shift and lymph flow

Fluid transudation into interstitial spaces because

Thus,

Changes in oxygen dissociation

Decreased pH and increased temperature

--> Shift oxygen dissociation curve to RIGHT
(i.e. Oxygen affinity decreased)

2,3-DPG also increases

--> Further decreases oxygen affinity

Overall, right shift in ODC

--> Increased offloading of oxygen at tissue

--> Increased A-V O2 difference

Thermoregulation

Hypothalamic temperature rises

--> Stimulate anterior hypothalamus

Thus,

 

About
Reviewed20050816


Table of contents  | Bibliography  | Index