Acute manipulations of plasma volume alter arterial pressure responses during Valsalva maneuvers

The effects of changes in blood volume on arterial pressure patterns during the Valsalva maneuver are incompletely understood. In the present study we measured beat-to-beat arterial pressure and heart rate responses to supine Valsalva maneuvers during normovolemia, hypovolemia induced with intraveno us furosemide, and hypervolemia induced with ingestion of isotonic saline. Valsalva responses were analyzed according to the four phases as previously described (W. F. Hamilton, R. A. Woodbury, and H. T. Harper, Jr. JAMA 107: 853-856, 1936; W F. Hamilton, R. A. Woodbury, and H. T. Harper, Jr. Am. J. Physiol. 141: 42-50, 1944). Phase I is the initial onset of straining, whi ch elicits a rise in arterial pressure; phase II is the period of straining , during which venous return is impeded and pressure falls (early) and then partially recovers (late); phase III is the initial release of straining; and phase IV consists of a rapid "overshoot" of arterial pressure after the release. During hypervolemia, early phase II arterial pressure decreases w ere significantly less than those during hypovolemia, thus making the respo nse more "square." Systolic pressure hypervolemic vs. hypovolemic falls wer e -7.4 +/- 2.1 vs. -30.7 +/- 7 mmHg (P = 0.005). Diastolic pressure hypervo lemic vs, hypovolemic falls were -2.4 +/- 1.6 vs. -15.2 +/- 2.6 mmHg (P = 0 .05). A significant direct correlation was found between plasma volume and phase II systolic pressure falls, and a significant inverse correlation was found between plasma volume and phase III-TV systolic pressure overshoots. Heart rate responses to systolic pressure falls during phase II were signi ficantly less during hypovolemia than during hypervolemia (0.7 +/- 0.2 vs. 2.82 +/- 0.2 beats.min(-1).mmHg(-1); P = 0.05) but were not different durin g phase III-TV overshoots. We conclude that acute changes in intravascular volume from hypovolemia to hypervolemia affect cardiovascular responses, pa rticularly arterial pressure changes, to the Valsalva maneuver and should b e considered in both clinical and research applications of this maneuver.