Carotid body chemosensitivity is not attenuated during cold water diving

Introduction: Tonic carotid body (CB) activity is reduced during exposure to cold and hyperoxia. We tested the hypotheses that cold water diving lowers CB chemosensitivity and augments CO 2 retention more than thermoneutral diving. Methods: Thirteen subjects (age: 26±4 y; BMI: 26±2 kg/m 2 ) completed two, four-hour head out water immersion protocols in a hyperbaric chamber (1.6 ATA) in cold (15°C) and thermoneutral (25°C) water. CB chemosensitivity was assessed using brief hypercapnic ventilatory response (CB CO 2 ) and hypoxic ventilatory response (CB O 2 ) tests pre-dive, 80 and 160 min into the dives (D80 and D160, respectively), immediately following and 60 min post-dive. Data are reported as an absolute mean (SD) change from pre-dive. Results: End-tidal CO 2 pressure increased during both the thermoneutral water dive (D160: +2(3) mmHg; p=0.02) and cold water dive (D160: +1(2) mmHg; p=0.03). Ventilationincreased during the cold water dive (D80: 4.13(4.38) and D160: 7.75(5.23) L·min -1 ; both p<0.01) and was greater than the thermoneutral water dive at both time points (both p<0.01). CB CO 2 was unchanged during the dive (p=0.24) and was not different between conditions (p=0.23). CB O 2 decreased during the thermonutral water dive (D80: -3.45(3.61) and D160: -2.76(4.04) L·min·mmHg -1 ; p<0.01 and p=0.03, respectively), but not the cold water dive. However, CB O 2 was not different between conditions (p=0.17). Conclusion: CB chemosensitivity was not attenuated during the cold stress diving condition and does not appear to contribute to changes in ventilation or CO 2 retention.