THE EFFECT IN MAN OF CHANGES IN INTRATHORACIC PRESSURE ON CARDIAC OUTPUT

Abstract

Left ventricular output [Formula: see text] was measured in 18 patients by the dye dilution technique during breath holding for 20 seconds at the mid-tidal level and at a mean intraoesophageal pressure (lop) of −2.97 mm Hg. [Formula: see text] was 4.86 l./minute, cardiac index (CI) 3.47 l./minute m2, and stroke volume 75 ml. Increments of lop during phase 2 of Valsalva's manoeuver in the range of 12 to 35 mm Hg led to a significant stepwise decrease in [Formula: see text], CI, and stroke volume. Extrapolation back to zero lop indicated that [Formula: see text] decreases by 0.1 l./minute with each rise of 1 mm Hg. During phase 4, or the "overshoot" phase, a significant increase in [Formula: see text], CI, and stroke volume was found which could not be related to temporary hyperventilation or decrease in lop characteristic of that phase. Reduction in lop during Mueller's manoeuver in 10 observations reached the range of −3 to −25 mm Hg. After an initial decrease in [Formula: see text] by 13.0% in the range of −3 to −7 mm Hg of lop, mean [Formula: see text] increased by approximately 40% with progressive decreases of 6 mm Hg Iop. Statistical significance could, however, not be established for the [Formula: see text] changes during acute decreases in Iop.