Evaluation of impaired cerebral autoregulation by the Valsalva maneuver

Transcranial Doppler sonography has recently been used to describe cerebral hemodynamics during the Valsalva maneuver in normal human subjects. Since some changes in flow velocity during the Valsalva maneuver seem to reflect the brain's autoregulatory response to a decrease in cerebral perfusion pressure during the strain, we hypothesized that this method could identify vascular territories with impaired autoregulatory capacity.

Eight patients with unilateral (n=7) or bilateral (n=1) severe obstruction of the internal carotid artery and impaired vascular responses to the CO2 reactivity test and to dynamic autoregulation testing were studied. We compared changes in flow velocities and blood pressures during defined phases of the Valsalva maneuver in the patients with the results in a group of 17 normal volunteers. We defined two indices to evaluate autoregulatory capacity based on the response to the Valsalva maneuver.

During the Valsalva maneuver, changes in flow velocity in the middle cerebral arteries ipsilateral to the lesions showed characteristic abnormalities compared with the normal pattern. Autoregulatory indices of these vessels as defined by the Valsalva maneuver were significantly different from those with normal vascular reactivity to CO2 (P<.0001). There were good correlations between an index based on the changes in flow velocity and blood pressure in phase II and the results of the CO2 test (r=.78; P<.0001) or those of dynamic autoregulatory testing (r=.6; P<.0001).

Vascular territories with severely impaired vasomotor reactivity due to carotid obstruction can be identified by transcranial Doppler sonography by their pattern of flow velocity changes if their autoregulatory capacity is challenged during the Valsalva maneuver.