Protocol to measure acute cerebrovascular and ventilatory responses to isocapnic hypoxia in humans

This study describes a protocol to determine acute cerebrovascular and ventilatory (AHVR) responses to hypoxia. Thirteen subjects undertook a protocol twice, 5 days apart. The protocol started with 8 min of eucapnic euoxia (end-tidal Pco(2) (PETco(2) = 1.5 Torr) above rest- end-tidal Po-2 (PETo(2)) = 88 Torr) followed by six descending 90 s hypoxie steps (PETo(2) = 75.2, 64.0, 57.0. 52.0. 48.2. 45.0 Torr). Then, PETo(2) was elevated to 300 Torr for 10 min while PETo(2) remained at eucapnia (5 min) then raised by 7.5 Torr (5 min). Peak blood flow velocity in the middle cerebral artery (MCA) and regional cerebral oxygen saturation (Sro(2)) were measured with transcranial Doppler ultrasound and near-infrared spectroscopy, respectively, and indices of acute hypoxic sensitivity were calculated (AHRCBF and AHRSro(2)). Values for AHRCBF, AHRSro(2) and AHVR were 0.43 cm s(-1) % desaturation(-1), 0.80% % desaturation(-1) and 1.241 min(-1) % desaturation(-1), respectively. Coefficients of variation for AHR(CBF), AHRSro(2) and AHVR were small (range = 8.0-15.2%). This protocol appears suitable to quantify cerebrovascular and ventilatory responses to acute isocapnic hypoxia. (C) 2004 Elsevier B.V. All rights reserved.