Investigators examined adults who had been exposed to perinatal hyperoxia as infants and report that such people may have diminished hypoxic and hyperoxic ventilatory responses.

Alteration of mitochondrial biogenesis promotes disease progression in multiple myeloma Alteration of mitochondrial biogenesis promotes disease progression in multiple myeloma

We evaluated several methods for characterizing hypoxic chemosensitivity in the conscious rat. Adult Sprague-Dawley rats ( n = 30) were exposed to normobaric hypoxia [inspired oxygen fraction (Fio₂) 0.15, 0.12, and 0.09]. We measured ventilation (V̇e; barometric plethysmography), arterial oxygen saturation (SpO₂; pulse oximeter), and oxygen consumption and carbon dioxide production (V̇o₂and V̇co₂; analysis of expired air). Linear regression analysis was used to define stimulus-response relationships. Testing was performed on 2 days to assess day-to-day reproducibility. Exposure to graded, steady-state hypoxia caused progressive reductions in SpO₂that were, for any given Fio₂, quite variable (SpO₂range, 20–30%) among individuals. Hypoxia produced progressive increases in V̇e caused by increases in both tidal volume (VT) and breathing frequency. Hypoxia also increased the VT:inspiratory time (T_i) ratio, an indicator of central respiratory “drive.” Hypoxia caused consistent, progressive declines in V̇o₂, V̇co₂, and core temperature (>20% at the lowest SpO₂). We propose that optimal quantification of carotid chemoreceptor hypoxic sensitivity in the unanesthetized rodent should employ SpO₂[a surrogate for arterial Po₂(PaO₂)] as the stimulus variable and the ventilatory equivalent for V̇co₂(V̇e/V̇co₂) and/or mean inspiratory flow rate (VT/T_i) normalized for V̇co₂as the response variables. Both metrics take into account not only the important influence of a falling metabolic rate, but also SpO₂, which represents the hypoxic stimulus at the carotid body. Because of the somewhat curvilinear nature of these responses, exposure to multiple levels of graded hypoxia provides the most complete characterization of hypoxic chemosensitivity.