Alveolar gas composition before and after maximal breath-holds in competitive divers.
The urge to breathe, as stimulated by hypercapnia, is generally considered to cause a breath-hold diver to end the breath-hold, and pre-breath hold hyperventilation has been suggested to cause hypoxic loss of consciousness (LOC) due to the reduced urge to breathe. Competitors hyperventilate before "Static Apnea", yet only 10% surface with symptoms of hypoxia such as loss of motor control (LMC) or LOC. We hypothesized that the extensive hyperventilation would prevent hypercapnia even during prolonged breath-holding and we also recorded breaking-point end-tidal PO2 in humans. Nine breath-hold divers performed breath-holds of maximal duration according to their chosen "Static Apnea" procedure. They floated face down in a swimming pool (28 degrees C). The only non-standard procedure was that they exhaled into a sampling tube for end-expiratory air, before starting the breath-hold and before resuming breathing. Breath-hold duration was 284 +/- 25 (SD) seconds. End-tidal PCO2 was 18.9 +/- 2.0 mmHg before apnea and 38.3 +/- 4.7 mmHg at apnea termination. End-tidal PO2 was 131.7 +/- 2.7 mmHg before apnea and 26.9 +/- 7.5 mmHg at apnea termination. Two of the subjects showed LMC after exhaling into the sampling tube; their end-tidal PAO2 values were 19.6 and 21.0 mmHg, respectively. End-tidal CO2 was normocapnic or hypocapnic at the termination of breath-holds. These data suggest that the athletes rely primarily on the hypoxic stimuli, probably in interaction with CO2 stimuli to determine when to end breath-holds. The severity of hypoxia close to LOC was similar to that reported for acute hypobaric hypoxia in humans.
Lindholm
P
P
Center for Research and Education in Special Environments, and Department of Physiology and Biophysics, University at Buffalo (SUNY), Buffalo, NY, USA.
Lundgren
C E G
CE
D000328:Adult; D000368:Aged; D001049:Apnea / Q000097:blood / Q000503:physiopathology; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000032:analysis*; D004242:Diving / Q000502:physiology*; D006801:Humans; D006985:Hyperventilation / Q000097:blood / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D019957:Motor Skills Disorders / Q000097:blood / Q000503:physiopathology; D010100:Oxygen / Q000032:analysis*; D012119:Respiration; D013997:Time Factors
D002245:Carbon Dioxide; D010100:Oxygen