Pulse Pressure Wave Velocity.

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From the 07/10/13 Human Physiology prac.

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Question Answer
What is the pulse pressure wave? The pulse pressure wave is the wave of pressure/volume changes that occurs down an elastic arterial blood vessel to maintain blood pressure and flow during diastole.
What effect would completely rigid arteries have? Completely rigid arteries would result in an equal volume of blood being returned to the heart as is ejected from it – but this would move blood at too rapid a speed for exchange and would not allow for control.
What does the rate at which the pulse pressure wave travel along the blood vessels depend on? The rigidity/elasticity of the vessel wall.
What happens to the velocity of the pulse pressure wave, the more elastic the vessel wall is? The more ‘relaxed’ they are, the more blood pushes and stretches the wall rather than pushing on the blood further down, so the slower the pressure wave travels.
What happens to the pulse pressure wave the more rigid the blood vessel walls are? The ‘stiffer’ the blood vessels are, the less able blood is to stretch the blood vessel wall and the greater the ‘push’ on blood further downstream, so that the pulse pressure wave travels faster.
What three measurements were used in this practical to establish the velocity of the pulse pressure wave? We used the R wave from an ECG as the start of the pulse pressure wave (ventricular systole) and the peak blood volume at the index finger to indicate the blood arriving at the distal arteries (using a plethysmograph). This calculated the time taken. We then measured the distance from the subject's sternum to the tip of their index finger, and divided distance by time to establish speed.
What is the average pulse pressure wave in quiet/relaxed conditions? 4.67±0.41 m/s
What effect do you think the subject being supine would have on their pulse pressure velocity? It would not have an effect because there would be no more hydrostatic (or any other) force exerted on the blood in the vessel than when standing up.
What effect do you think the subject holding their recording arm above their head would have on their pulse pressure wave velocity? An increase in gravity/hydrostatic forces on the blood involved would mean the pulse pressure wave would be slower as it would take longer for the blood to move from the left ventricle to the fingertip.
What effect do you think the subject putting their non-recording hand in ice would have on their pulse pressure wave velocity? The ice would cause vasoconstriction to occur systemically in order to preserve heat, which would make the vessels more rigid and result in the pulse pressure wave velocity increasing. Alternatively, it may make the subject panic and develop a sympathetic response, in which the vessels to the limbs dilate to increase blood supply for muscle activity, and thus result in a slower pulse pressure wave.
What effect do you think two minutes of moderate exercise would have on a subject's pulse pressure wave velocity? The moderate exercise would cause vasodilation, both for the increased transport of oxygenated blood to the muscle to support its changed metabolic needs, and to increase heat loss to prevent raising the body's temperature too far. This vasodilation would result in more relaxed vessel walls and a slower pulse pressure wave velocity.
What effect do you think occluding the blood vessels in the recording arm would have on a subject's pulse pressure wave velocity (after cuff removed)? The pulse pressure wave velocity would be increased as a result of the pressure that had built up behind the cuff when the blood supply to the arm was occluded. However, it could also be decreased as a result of vasodilation in order to best perfuse the starved tissue.
Using an unpaired T-test, there was evidence for a difference between female and male pulse pressure wave velocities in the quiet/relaxed, arm raised, and ice experimental conditions. Why do you think this is? We established in the blood pressure lab that males have a higher blood pressure than females, likely as a result of usually being taller and composed of more muscle and so needing a greater cardiac output. Given that stroke volume was increased rather than heart rate, it is likely this increased pressure that increases the speed of the pulse pressure wave in males.
What is aortic pulse pressure wave velocity considered the gold standard for assessing? Arterial stiffness.
The aortic pulse pressure wave velocity is calculated between which two arteries? Carotid-to-femoral.
What is arterial stiffness a reliable parameter for predicting? Cardiovascular events.
What are the four major determinants of pulse pressure wave velocity? Age, blood pressure, gender, and heart rate.
How does age affect pulse pressure wave velocity? With increasing age the pulsatile strain breaks the elastic fibres (in elastic arteries such as the aorta, carotid, or iliac), which are replaced by collagen. These changes in the arterial structure lead to increased arterial stiffness, and consequently to increased central PWV.
How does blood pressure affect the pulse pressure wave velocity? The pulse pressure wave is matched by a reflective wave travelling back to the heart. Increased arterial stiffness increases the velocity of the reflective wave so that it interferes with systole rather than arriving at the ascending aorta during diastole. This increases the afterload and thus blood pressure. This would likely produce a faster PPWV initially, between two points reasonably close together, but could produce a slower PPWV over a longer distance, as the reflective wave interfered.
How does gender affect pulse pressure wave velocity? Pre-menopausal women have lower pulse pressure wave velocities than age-matched men, but post-menopausal women have similar values to age-matched men. The former is likely a result of physiological differences in height and muscle composition affecting blood pressure.
How does heart rate affect the pulse pressure wave velocity? If heart rate increases, the time for vessels to distend is reduced, resulting in increased rigidity of the arterial wall. Also, sympathetic activation is associated with increased stiffness of the arteries due to an increase in heart rate, blood pressure and smooth muscle cells tonus.
What is the first stage of atherosclerosis, which can be caused by increased arterial stiffness? Endothelial damage.
How can increased arterial stiffness lead to left ventricular hypertrophy? Increased arterial stiffness leads to an increase in central systolic pressure associated with an increased afterload, which in turn can lead to left ventricular hypertrophy.
Left ventricular hypertrophy is associated with lower diastolic pressure. What might this mean for the left ventricle tissue? Lower diastolic pressure results in less filling of the ventricle, and so the tissue may not receive an adequate blood supply for its hypertrophied size and this could result in ischaemic events.
How does increased arterial stiffness and blood pressure affect arterial beds in the brain and/or kidneys? The arterial beds in the brain and kidneys are relatively weak structures and, unlikely other arterial vessels, lack vasoconstrictive protection. As a result, they receive a high-volume blood flow throughout systole and diastole, which can lead to vascular injuries.
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