Effects of the Valsalva maneuver on blood flow in the thoracic aorta in man.

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Abstract
Moment-to-moment changes in blood flow down the thoracic aorta, a flow representing a major fraction of the cardiac output, were measured by the constant-rate-injection indicator-dilution technic before, during, and after 15-sec. periods of voluntary increases in airway pressure to 40 mm Hg (Valsalva maneuver). In 12 experiments in 8 healthy men, thoracic aortic flow decreased to a mean value of 35% of the control flow during the period of forced expiration (stage II) and then increased to a value 19% above the control level during the overshoot (stage IV). A postulated increase in flow during the initial phase of the maneuver (stage I) was not demonstrated. The time course of changes in thoracic aortic flow during the Valsalva maneuver calculated from the dilution curves was similar in contour to the changes in total cardiac output estimated from simultaneously recorded central arterial pressure pulses. The changes in systemic and pulmonary artery pressures resembled those reported previously during this maneuver.