The cerebrovascular response to graded Valsalva maneuvers while standing

Area of Science:

• Cardiovascular Physiology
• Cerebrovascular Regulation
• Autonomic Nervous System Function

Background:

• The Valsalva maneuver (VM) is a physiological test involving forceful attempted exhalation against a closed glottis.
• VM acutely increases mean arterial pressure (MAP) during strain (Phase I) but causes hypotension upon release (Phase III).
• Understanding the impact of VM intensity and duration on cerebral blood flow, specifically middle cerebral artery velocity (MCAv), is crucial.

Purpose of the Study:

• To investigate how varying intensities and durations of the Valsalva maneuver affect middle cerebral artery blood velocity (MCAv) responses.
• To analyze the relationship between VM parameters and the resulting changes in mean arterial pressure (MAP) and MCAv during different phases of the maneuver.

Main Methods:

• Ten healthy men performed VM at 30%, 60%, and 90% of their maximal mouth pressure for 5 and 10 seconds.
• Beat-to-beat measurements of MCAv and MAP were recorded during standing baseline, VM Phase I peak, Phase III nadir, and recovery.
• Data were analyzed to determine changes in MCAv and MAP relative to baseline, examining effects of VM intensity and duration.

Main Results:

• During VM Phase I, MCAv increased significantly, but this rise was not reliably different across VM intensities despite graded MAP increases.
• Phase III revealed significant duration- and intensity-dependent decreases in MCAv, with the greatest reduction following 90% VM.
• Concomitant significant decreases in MAP were observed during Phase III, correlating with the magnitude of MCAv reduction.

Conclusions:

• The study demonstrates an asymmetric cerebral blood flow response to the Valsalva maneuver, with significant MCAv reduction upon release.
• The extent of MCAv decrease during Phase III is critically dependent on both the intensity and duration of the VM.
• Hypotension during VM Phase III is a primary driver for the observed reduction in middle cerebral artery blood velocity.