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Thoracic Blood Volume Changes during the Valsalva Maneuver
1 Department of Physiology, New York Medical College, Valhalla, NY, USA
2 LDM Associates, San Jose, Ca, USA
* To whom correspondence should be addressed. E-mail: stewart{at}nymc.edu.
The Valsalva maneuver (VM) is frequently used to test autonomic function. Prior work demonstrated that the blood pressure decrease during the Valsalva maneuver relates to thoracic hypovolemia which may preclude pressure recovery during phase II even with normal resting peripheral vasoconstriction. We hypothesized that variations in regional circulations, specifically splanchnic hypervolemia accounts for variations in thoracic hypovolemia during the Valsalva maneuver. We studied 17 healthy volunteers aged 15-22 years. All had normal blood volumes by dye dilution. Subjects also had normal vascular resistance while supine as well as normal vasoconstrictor responses during 35° upright tilt. We assessed changes in estimated splanchnic, pelvic-thigh, lower leg blood volume along with thoracic blood volume shifts by impedance plethysmography before and during the VM performed supine. Early increases of splanchnic blood volume dominated the regional vascular changes during VM. The increase in splanchnic blood volume correlated well (r2=0.65, p<.00001) with decrease in thoracic blood volume, pelvic less well (r2=0.21, p<.03), and leg not at all (r2=0.001, p=.9). There was no relation of thoracic hypovolemia with blood volume, or peripheral resistance in supine or upright positions. Thoracic hypovolemia during the Valsalva maneuver is closely related to splanchnic hyperemia and weakly related to regional changes in blood volume elsewhere. Changes in baseline splanchnic vascular properties may account for variability in thoracic blood volume changes during the Valsalva maneuver.
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