pressure will only be about 40/0 mm Hg in the feet, with diastolic blood pressure dropping to zero, and with the systolic blood pressure of 40 mm Hg barely sufficing to perfuse the capillaries. Even then it's marginal, which is why your feet may "go to sleep" and get pins-and-needlcs sensations if you remain in the headstand for a long time.
We can calculate that blood pressure at the top of the head increases from 100/60 mm Hg in a standing position to 150/110 mm Hg in the head-stand (fig. 8.2b), or even higher if you are not confident of the posture. The headstand is therefore contraindicated for anyone who has abnormally high blood pressure for the simplest of reasons: the posture can increase blood pressure in the brain to dangerous levels—perhaps well above 150/110 mm Hg. Conservative medical opinion also recommends that you avoid the headstand even if high blood pressure is brought to a normal level with medication.
As important as blood pressure is, we can't understand the cardiovascular responses to inverted postures without also considering the flow of blood through the system both bulk flow through the major segments of the system and the rate of flow though specific vessels. Since it's a oneway circuit, the same volume of blood per unit of time (about 5 liters per minute at rest) has to flow through each segment of the cardiovascular system. And there is also the question of rate of flow through individual arteries, capillaries, and veins. Just as a river carries water sluggishly where the river is wide, and briskly where it is constrained by tubes and by turbines that generate electricity, so does the rate of flow vary in the vascular system. The flow is speediest through arterioles, where it is choked off the most as well. It is slowest in the capillaries, and it flows at an intermediate rate through the veins, which carry blood back to the heart.
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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...