Carotid body chemosensitivity is not attenuated during cold water diving

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. Thirteen subjects [age: 26 ± 4 yr; body mass index (BMI): 26 ± 2 kg/m2) completed two 4-h 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 with brief hypercapnic ventilatory response (CBCO2 ) and hypoxic ventilatory response (CBO2 ) tests before dive, 80 and 160 min into the dive (D80 and D160, respectively), and immediately after and 60 min after dive. Data are reported as an absolute mean (SD) change from predive. End-tidal CO2 pressure increased during both the thermoneutral water dive [D160: 2 (3) mmHg; P = 0.02] and the cold water dive [D160: 1 (2) mmHg; P = 0.03]. Ventilation increased 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 thermoneutral 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). In 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.