Cerebral Hemodynamics During the Valsalva Maneuver

Abstract

0166 PURPOSE: The aim of this study was to differentiate the mechanical effects of the Valsalva maneuver (VM) from the effects of changes in autonomic neural activity on cerebral hemodynamics in humans. METHODS: Nine healthy subjects performed the VM before and after ganglionic blockade of autonomic neural activity (trimethaphan). Blood pressure (BP) was measured in the radial artery using an indwelling catheter, or at the finger by Finapres. Cerebral blood flow (CBF) velocity was measured in the middle cerebral artery using transcranial Doppler. End-tidal CO2 was monitored by mass spectrometry. RESULTS: Before blockade, during phase II of the VM, BP was reduced by 27%, CBF velocity by 33% (P < 0.05). Cerebrovascular conductance index (CVCI) increased by 21% associated with a reduction in cerebral perfusion pressure. During phase IV, overshoot of CBF velocity was proportionately greater than that of BP (46% vs. 30%). After blockade, during phase II, BP fell to a much greater degree by 50%, while CBF velocity decreased even more by 60% associated with an increase in CVCI by 33%. During phase IV, despite the elimination of BP overshoot by ganglionic blockade, CBF velocity still increased by 55%, and CVCI by 33%. Both were significantly greater than before blockade. CONCLUSIONS: These data indicate that 1) after ganglionic blockade, cerebral autoregulation is unable to prevent the substantial fall in CBF induced by the marked reduction in BP during the VM. 2) Enhanced phase IV increases in both CBF velocity and CVCI reflect the intrinsic characteristics of cerebral hyperemic responses, which are likely Modified in part by the removal of vasoconstrictor effects of autonomic neural activity elicited during the VM.