Ventilatory behavior after hypoxia in C57BL/6J and A/J mice

Given the environmental forcing by extremes in hypoxia-reoxygenation, there might be no genetic effect on posthypoxic short-term potentiation of ventilation. Minute ventilation ((V) over dot E), respiratory frequency (f), tidal volume ((V) over dot T), and the airway resistance during chemical loading were assessed in unanesthetized unrestrained C57BL/6J (B6) and A/J mice using whole body plethysmography. Static pressure-volume curves were also performed. In 12 males for each strain, after 5 min of 8% O-2 exposure, B6 mice had a prominent decrease in V E on reoxygenation with either air (-11%) or 100% O-2 (-20%), due to the decline of f. In contrast, A/J animals had no ventilatory undershoot or f decline. After 5 min of 3% CO2- 10% O-2 exposure, B6 exhibited significant decrease in (V) over dot E (-28.4 vs. -38.7%, air vs. 100% O-2) and f (-13.8 vs. -22.3%, air vs. 100% O-2) during reoxygenation with both air and 100% O-2; however, A/J mice showed significant increase in (V) over dot E (+116%) and f (+62.2%) during air reoxygenation and significant increase in V E (+68.2%) during 100% O-2 reoxygenation. There were no strain differences in dynamic airway resistance during gas challenges or in steady-state total respiratory compliance measured postmortem. Strain differences in ventilatory responses to reoxygenation indicate that genetic mechanisms strongly influence posthypoxic ventilatory behavior.