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Hypoxic Respiratory Response during Acute Stable Hypocapnia

Hypoxic Respiratory Response during Acute Stable Hypocapnia,Stephen Corne,Kim Webster,Magdy Younes

Hypoxic Respiratory Response during Acute Stable Hypocapnia   (Citations: 5)
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The hypoxic ventilatory response during hypocapnia has been stud- resume spontaneous breathing in the event of a ventilator ied with divergent results. We used volume-cycled ventilation in malfunction (e.g., disconnect) or when a central apnea devel- spontaneously breathing normal subjects to study their hypoxic ops after sleep in recently tracheostomized previously hyper- ventilatory response under conditions of stable hypocapnia. Sub- capnic patients. jects were studied at three different levels of end-tidal (partial) car- The ventilatory response to hypoxia is augmented when bon dioxide pressure (PETCO2), eucapnia and 6 and 12 mm Hg below Pco2 is increased above eucapnia (8-10). Although it is clear eucapnia (mild and moderate hypocapnia, respectively). The response from previous human studies that the hypoxic response de- to hypoxia was assessed by changes in muscle pressure output (Pmus) creases during hypocapnia, there are uncertainties about the and respiratory rate. Compared with the Pmus response at eucapnia magnitude of this depression and, in particular, whether there (0.53 0.59 cm H2O/percentage oxygen saturation (% O2sat)), the is aP co2 level below which hypoxic response is lost and, if response at mild hypocapnia was attenuated (0.26 0.33 cm H2O/ so, what is this level. Thus, some studies demonstrated persis- %O 2sat), whereas the response at moderate hypocapnia was negli- tence of a vigorous response at end-tidal (partial) carbon gible (0.003 0.09 cm H2O/% O2sat). Similar reductions were seen dioxide pressure (Pet CO2) up to the mid 20s (e.g., 8), whereas with the respiratory rate (eucapnia, 0.17 0.2 breaths/minute/ others reported that hypoxic response disappeared at Pet CO2 %O 2sat; mild hypocapnia, 0.11 0.11 breaths/minute/% O2sat; levels only a few mm Hg lower than eupneic Pco 2 (11). In
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