High pressure reduces pH sensitivity of respiratory center in isolated rat brainstem

We examined the effect of high pressure (10.1 MPa) on the sensitivity of the respiratory center to alterations in pH (range 5.8-7.6) which were obtained by varying either P_CO2 or [HCO₃^-] in superfused Krebs solution. Isolated rat brainstem-spinal cord preparations were placed in a pressure chamber and respiratory-related motor neuron activity was recorded from severed ventral roots C₁ and C₅. At atmospheric pressure, respiratory burst frequency in both C₁ and C₅ varied inversely with pH. Only the time integral of a single C₅ response was sensitive to acidification. High helium pressure reduced by 60% the sensitivity of the respiratory frequency to alteration in pH, while the time integral of both C₁ and C₅ responses became independent of P_CO2, causing the relative respiratory drive between the two roots to change. These modifications in the chemoresponse of the respiratory center may contribute to the respiratory difficulties encountered under high pressure conditions.