Evaluation of the cerebral hemodynamic response to rhythmic handgrip

hemodynamic response to rhythmic handgrip. J Appl Physiol 88: 2205–2213, 2000.—The response of the cerebral circula-tion to exercise has been studied with transcranial Doppler ultrasound (TCD) because this modality provides continuous measurements of blood velocity and is well suited for the exercise environment. The use of TCD as an index of cerebral blood flow, however, requires the assumption that the diam-eter of the insonated vessel is constant. Here, we examine this assumption for rhythmic handgrip using a spectral index designed to measure trends in vessel flow. Nineteen normal subjects were studied during 5 min of volitional maximum rhythmic right handgrip at 1 Hz. TCD velocities from both middle arteries (left and right), blood pressure, and end-tidal PCO2 were recorded every 10 s. A spectral weighted sum was also calculated as a flow index (FI). Averages were compute