Journal of applied physiology
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Clinical Trial
Influence of arterial O2 on the susceptibility to posthyperventilation apnea during sleep.
To investigate the contribution of the peripheral chemoreceptors to the susceptibility to posthyperventilation apnea, we evaluated the time course and magnitude of hypocapnia required to produce apnea at different levels of peripheral chemoreceptor activation produced by exposure to three levels of inspired P(O2). We measured the apneic threshold and the apnea latency in nine normal sleeping subjects in response to augmented breaths during normoxia (room air), hypoxia (arterial O2 saturation = 78-80%), and hyperoxia (inspired O2 fraction = 50-52%). Pressure support mechanical ventilation in the assist mode was employed to introduce a single or multiple numbers of consecutive, sigh-like breaths to cause apnea. ⋯ Torr(-1); P < 0.05) compared with normoxia (0.79 +/- 0.05 l.min(-1). Torr(-1)). These findings indicate that posthyperventilation apnea is initiated by the peripheral chemoreceptors and that the varying susceptibility to apnea during hypoxia vs. hyperoxia is influenced by the relative activity of these receptors.
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Clinical Trial
Pulse transit time measured from the ECG: an unreliable marker of beat-to-beat blood pressure.
The arterial pulse-wave transit time can be measured between the ECG R-wave and the finger pulse (rPTT), and has been shown previously to have a linear correlation with blood pressure (BP). We hypothesized that the relationship between rPTT, preejection period (PEP; the R-wave/mechanical cardiac delay), and BP would vary with different vasoactive drugs. Twelve healthy men (mean age 22 yr) were studied. ⋯ However, the relationship is not reliable enough for rPTT to be used as a surrogate marker of SBP, although it may be useful in assessing BP variability. DBP and MAP cannot be predicted from rPTT without correction for PEP. The significant contribution of PEP to rPTT means that rPTT should not be used as a marker of purely vascular function.