Recovery of the hypoxic ventilatory drive of rats from the toxic effect of hyperbaric oxygen.

Hyperbaric oxygen (HBO) exposure reduces the hypoxic ventilatory drive (HVD), probably by damaging the carotid bodies. The recovery of the HVD from HBO exposure was studied. The HVD was calculated from whole body plethysmographic recordings of the ventilatory response to greater than 85% and 2% O2 in N2 mixtures. Five groups of rats were exposed to HBO for 9 h at pressures of 1.9, 2.0, 2.1, 2.2, and 2.4 ATA, respectively. Each rat underwent three control measurements on different days prior to HBO exposures and then at various intervals following the exposure. Postexposure HVD was reduced to 28% of control values in the high PO2s. Ninety percent recovery of pre-exposure HVD was evident by 12-48 h although in some animals exposed to relatively low PO2s (1.9 and 2.0 ATA) HVD stabilized at a level lower than 100%. The recovery of the HVD in percent during the first 4 d following exposure can be expressed as an exponential function of the time from the termination of HBO: HVD = 28 + 72(1 - exp-0.053t) (t in hours). This information may be of importance in cases of repeated exposures to HBO where one tries to avoid cumulative damage to the carotid bodies, and in the care of the poorly oxygenated patient after HBO treatment.