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Gravity: The effects of gravity on venous return seem paradoxical because when a person stands up, hydrostatic forces cause the right atrial pressure to decrease and the venous pressure in the dependent limbs to increase. This increases the pressure gradient for venous return from the dependent limbs to the right atrium; however, venous return ...
Gravity affects blood pressure via hydrostatic forces (e.g., during standing), and valves in veins, breathing, and pumping from contraction of skeletal muscles also influence blood pressure in veins. [32] The relationship between pressure, flow, and resistance is expressed in the following equation: [12]
Between muscle relaxations, intramuscular pressure transiently returns to a level below the venous blood pressure. This allows blood from the capillary system to refill the veins until the next contraction. It is postulated that this change in pressure may be great enough to draw blood from the arterial side to the venous side. It is ...
The Bainbridge reflex (or Bainbridge effect or atrial reflex) is a cardiovascular reflex causing an increase in heart rate in response to increased stretching of the wall of the right atrium and/or the inferior vena cava as a result of increased venous filling (i.e., increased preload).
On the other hand, gravity causes a gradient in blood pressure between the top and bottom of the lung of 20 mmHg in the erect position (roughly half of that in the supine position). Overall, mean pulmonary venous pressure is ~5 mmHg. Local venous pressure falls to -5 at the apexes and rises to +15 mmHg at the bases, again for the erect lung.
In cardiovascular physiology, stroke volume (SV) is the volume of blood pumped from the ventricle per beat. Stroke volume is calculated using measurements of ventricle volumes from an echocardiogram and subtracting the volume of the blood in the ventricle at the end of a beat (called end-systolic volume [note 1]) from the volume of blood just prior to the beat (called end-diastolic volume).
The venous valves serve to prevent regurgitation (backflow) due to the low pressure of veins, and the pull of gravity. [1] They also serve to prevent the over-widening of the vein. [20] [21] A venous valve is bicuspid (having two leaflets) and is formed by an infolding of part of the tunica intima on either side of the lumen of the veins.
Over time these deconditioning effects can impair astronauts' performance, increase their risk of injury, reduce their aerobic capacity, and slow down their cardiovascular system. [58] As the human body consists mostly of fluids, gravity tends to force them into the lower half of the body, and our bodies have many systems to balance this situation.