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 PCO2 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 PCO2, 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.