Carotid body chemosensitivity at 1.6 ATA breathing air versus 100% oxygen

Abstract

Carotid body chemosensitivity at 1.6 ATA breathing air versus 100% oxygen. J Appl Physiol 129: 247–256, 2020. First published June 25, 2020; doi:10.1152/japplphysiol.00275.2020.—Hyperoxia reduces the ventilatory response to hypercapnia by suppressing carotid body (CB) activation. This effect may contribute to CO2 retention during underwater diving due to the high arterial O2 content associated with hyperbaria. We tested the hypothesis that CB chemosensitivity to hypercapnia and hypoxia is attenuated during hyperbaria. Ten subjects completed two, 4-h dry dives at 1.6 atmosphere absolute (ATA) breathing either 21% O2 (Air) or 100% O2 (100% O2). CB chemosensitivity was assessed using brief hypercapnic ventilatory response (CBCO2) and hypoxic ventilatory response (CBO2) tests predive, 75 and 155 min into the dives, and 15 and 55 min postdive. End-tidal CO2 pressure increased during the dive at 75 and 155 min [Air: +9 (SD 4) mmHg and +8 (SD 4) mmHg versus 100% O2: +6 (SD 4) mmHg and +5 (SD 3) mmHg; all P < 0.01] and was higher while breathing Air (P < 0.01). CBCO2 was unchanged during the dive (P = 0.73) and was not different between conditions (P = 0.47). However, CBO2 was attenuated from predive during the dive at 155 min breathing Air [0.035 (SD 0.037) L·min·mmHg1; P = 0.02] and at both time points while breathing 100% O2 [0.035 (SD 0.052) L·min·mmHg 1 and 0.034 (SD 0.064) L·min·mmHg 1; P = 0.02 and P = 0.02, respectively]. These data indicate that the CB chemoreceptors do not appear to contribute to CO2 retention in hyperbaria.