Central chemoreflex sensitivity and sympathetic neural outflow in elite breath-hold divers.
Level 4 - case-series / case-control
Small cross-sectional physiological case-control study comparing divers to non-divers
PubMed 17991789 · doi:10.1152/japplphysiol.00844.2007
What was done
Researchers compared 11 experienced elite breath-hold divers (who participated in 7.3 ± 1.2 competitions and 76.4 ± 14.6 training sessions in the preceding season) with 9 healthy non-diver controls. Measurements included beat-by-beat blood pressure, heart rate, femoral artery blood flow, respiration, end-tidal CO2, and muscle sympathetic nerve activity (MSNA) at baseline and during hyperoxic rebreathing designed to raise end-tidal CO2 to 60 Torr.
What was found
Baseline MSNA burst frequency was 31 ± 11 bursts/min in divers compared with 33 ± 13 bursts/min in controls. Total baseline MSNA activity was 1.8 ± 1.5 AU/min in divers and 1.8 ± 1.3 AU/min in controls. During hyperoxic rebreathing, arterial oxygen saturation did not change, and the slopes of the hypercapnic ventilatory response and MSNA response were similar between both groups.
Why it matters
These findings suggest that repeated severe hypoxemic episodes in healthy elite breath-hold divers do not lead to chronic sympathetic activation or hypertension, in contrast to what is observed in obstructive sleep apnea.
Limits
Sample size was very small (11 divers and 9 controls), which limits statistical power. Measurements were taken 3 to 5 days after the last apnea exposure rather than acutely, and resting blood pressure values were not quantified in the abstract.
Cited by
- contradicts The brainstem's ventilatory sensitivity and tolerance to elevated carbon dioxide levels can be trained and adapted through intentional breath-holding exercises.