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Friday, November 09, 2018

Endurance exercise,aortic stiffness,Windkessel effect

The beneficial effect of prolonged endurance aerobic exercise on the aortic and great vessels may be as  important or more important that its effects on diastolic function and favorable remodeling. 

First the aorta is not  a stiff pipe. One  model used to explain aortic function and the shape of  the aortic pressure waves is the Windkessel effect model which considers the aortic and large elastic arteries as if it were an elastic buffering chamber which provides a cushioning or reservoir effect providing blood flow during diastole and damping the pulsatile flow. This reservoir effect flow is said to be as much as 40% of the stroke volume. The large elastic arteries act as capacitors , storing energy during systolic while bulging  a bit and then pushing back  or recoiling during diastole maintaining  a more or less steady flow of blood and offering protection to the vulnerable arterial vessels of the brain and kidney to which excessive pulsatile flow may be harmful. The capacitance effect does not eliminate pulsatilty,of course ,the textbook normal diastolic blood pressure is 80 and  not zero which is what it would be if  the aorta were a lead pipe. 

With aging,and arguably more so with sedentary aging,the elastic vessels become less elastic, stiffer and provide less of the Windkessel effect reflected in higher systolic blood pressure, lower diastolic blood pressure (increased pulse pressure) and more rapid blood flow. This   can measured  by noninvasive measurement of pulse wave velocity with an higher velocity indicating stiffer arteries.Loss of the reservoir  function. i.e.. a stiffer aorta and other great vessels  increase the left ventricular afterload predisposing to left ventricular wall thickening. 

It is easy to find data supporting the claim that exercise will improve aortic compliance.As early as 1973 a report from the Baltimore  Longitudinal Study on Aging (BLSA) (ref 1) indicated improved pulse wave velocity ,augmentation index and systolic blood pressure in older endurance athletes as compared with sedentary controls.

Other more recent detailed physiologic studies have confirmed that finding. Gates et al(2) studied men with varying exercise histories in three different age groups and reported that the regular endurance trained subjects has lower large artery stiffness as measured by a reduced aortic pulse wave velocity.

An excellent, detailed exposition of the physiology of the adaptation of the aorta to endurance exercise can be found in full free text in reference 3.

1)Vaitkevicius, PV et al Effect of age and aerobic capacity or arterial stiffness in healthy adults.Exp Physiology 2005:90.645-651

2)Gates PE,Left ventricular structure and diastolic function in human aging. Europen Heart Journal 2003,24, 2213-2220

3) Montero, FJC Adaptation of the aorta to training.Physiological perspective.
Apunts,Medicena de L'esport. 2017:52 (193): 3-9

"All models are wrong, some are useful" George Box  1976

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