Valsalva

The normal physiological response consists of 4 phases, which are marked on the figure:

1.Initial pressure rise: On application of expiratory force, pressure rises inside the chest forcing blood out. This causes a transient rise in blood pressure. 2.Reduced venous return and compensation: Return of blood to the heart is impeded by the pressure inside the chest. The output of the heart is reduced, the blood pressure falls. This occurs from 5 to about 14 seconds in the illustration. The fall in blood pressure reflexly causes blood vessels to constrict with some rise in pressure(15 to 20 seconds. This compensation can be quite marked with pressure returning to near or even above normal, but the cardiac output and blood flow to the body remains low. During this time the pulse rate increases. 3. Pressure release: The pressure on the chest is released, allowing the aorta to expand again, causing a further initial slight fall in pressure. (20 to 23 seconds). Venous blood can once more enter the chest and the heart, cardiac output begins to increase. 4. Return of cardiac output: Blood return to the heart is enhanced by the effect of entry of blood which had been dammed back, causing a rapid increase in cardiac output and of blood pressure (24 seconds on). The pressure usually rises above normal before returning to a normal level. With return of blood pressure, the pulse rate returns towards normal. Deviation from this response pattern signifies either abnormal heart function or abnormal autonomic nervous control of the heart.