Carotid body chemosensitivity is not attenuated during cold water diving

Abstract

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 CO2 retention more than thermoneutral diving. Methods: Thirteen subjects (age: 26±4 y; BMI: 26±2 kg/m2) 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 (CBCO2) and hypoxic ventilatory response (CBO2) 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 CO2 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). CBCO2 was unchanged during the dive (p=0.24) and was not different between conditions (p=0.23). CBO2 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, CBO2 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 CO2 retention.