The cerebrovascular response to graded Valsalva maneuvers while standing

Abstract

The Valsalva maneuver (VM) produces large and abrupt increases in mean arterial pressure (MAP) at the onset of strain (Phase I), however, hypotension, sufficient to induce syncope, occurs upon VM release (phase III). We examined the effect of VM intensity and duration on middle cerebral artery blood velocity (MCAv) responses. Healthy men (n =10; mean ± SD: 26 ± 4 years) completed 30%, 60%, and 90% of their maximal VM mouth pressure, for 5 and 10 sec (order randomized) while standing. Beat-to-beat MCAv and MAP during phase I (peak), at nadir (phase III), and recovery are reported as the change from standing baseline. During phase I, MCAv rose 15 ± 6 cm·s(-1) (P <0.001), which was not reliably different between intensities (P =0.11), despite graded increases in MAP (P <0.001; e.g., +12 ± 9 mmHg vs. +35 ± 14 for 5 sec 30% and 90% VM, respectively). During Phase III, the MCAv response was duration- (P = 0.045) and intensity dependent (P < 0.001), with the largest decrease observed following the 90% VM (e.g., -19 ± 13 and -15 ± 11 cm·s(-1) for 5 and 10 sec VM, respectively) with a concomitant decrease in MAP (P <0.001, -23 ± 11 and -23 ± 9 mmHg). This asymmetric response may be attributable to the differential modulators of MCAv throughout the VM. The mechanical effects of the elevated intrathoracic pressure during phase I may restrain increases in cerebral perfusion via related increases in intracranial pressure; however, during phase III the decrease in MCAv arises from an abrupt hypotension, the extent of which is dependent upon both the duration and intensity of the VM.

Keywords: Cerebral blood flow; Valsalva maneuver; orthostasis; syncope.

Figure 1.

The response of mean middle cerebral artery blood flow velocity (MCAv_mean), mean arterial pressure (MAP) and cerebrovascular conductance (CVC) during and following a Valsalva maneuver (VM) at 30%, 60%, and 90% of maximal VM pressure, displayed every second. The vertical dashed lines represent the initiation and completion of the VM. All values are means ± SE.

Figure 2.

The percentage change from baseline for mean middle cerebral artery blood flow velocity (MCAv_mean) and the absolute change in mean arterial pressure (MAP) during and following a Valsalva maneuver (VM) at 30%, 60%, and 90% of maximal VM pressure, displayed every second. The zero time point represents the initiation of the VM with the vertical dashed lines representing the completion. All values are means ± SE.

Figure 3.

Representative trace of middle cerebral artery blood flow velocity (MCAv), arterial blood pressure (ABP) and mouth pressure during a 90% 5 sec VM in one participant.