Mechanisms of cough syncope as evaluated by the valsalva maneuver.

Transcranial Doppler is often employed for the assessment of cerebral hemodynamics. The study by Chao et al in the February 2007 issue of the journal raises some important issues regarding the understanding of the mechanisms involved in cough syncope. We suggest including some additional monitoring parameters, for example, end-tidal or arterial carbon dioxide levels, transcranial Doppler waveform patterns and their characteristics in studies of patients with orthostatic hypotension. Vasomotor reactivity testing, especially in stenotic cerebral arteries, under controlled circumstances, may provide a quantitative assessment of cerebral autoregulation.