Profound hyperventilation and development of periodic breathing during exceptional orthostatic stress in a 21-year-old man

In this case report we describe a trial of experimentally induced syncope in a healthy young volunteer that produced abnormal periods of hyperventilation (V˙A=57   L/min) and periodic breathing; the latter persisting for approximately 60 min following termination of the trial. In this example, independent of systemic hypotension, the severe hyperventilation and related hypocapnia (end-tidal PETCO2∼5   mm   HgPETCO2∼5   mm   Hg) induced by orthostatic stress (lower body negative pressure) resulted in a ∼65% reduction in cerebral blood flow velocity. Potential mechanisms underlying these striking cardiorespiratory patterns are discussed.