A standardized analysis of ventilatory and cardiovascular responses to a hypoxic stimulus

Objective Apply a standardized analysis to describe the dynamic responses of the ventilatory & cardiovascular systems to standardized hypoxic challenges. Method I used a repeated, steady state, isocapnic hypoxic stimulus for chemoreflex characterization as proposed by Duffin1. Subjects experienced three hypoxic exposures, each at a different level of isocapnia. End‐tidal PO 2 and PCO 2 were controlled by using a RespirAct™, while ventilation, cerebral blood flow (CBF), heart rate, and blood pressure were recorded. Results 18 subjects completed the study; the patterns of response for each parameter fell into 4 categories: Decline, Plateau, Double, and no response (Fig 1). As a consequence, the classic hypoxic ventilatory decline (HVD) analysis could not be applied to all responses. Furthermore, CBF responses differed from those previously published. Therefore a new analysis, standardized across all responses, was developed and applied. The “acute” response phase is characterized by the peak response value and time to reach this peak. The “adaptative” response phase is expressed as the average value of the 2 last minutes of hypoxia, which approximates the usual HVD calculation in case of a decline response, but should be more accurate in describing a Double response. In most subjects the patterns of response were similar for all measures. Conclusion The pattern of response to isocapnic hypoxia varies between subjects and is reflected in all measures. This study is funded by Thornhill Research Inc.