Training improves divers' ability to detect increased CO2.
BACKGROUND
Elevated arterial PCO2 (hypercapnia) is a known risk in diving with closed circuit breathing apparatus. In a retrospective study, we determined CO2 retention and the ability to detect CO2 in novice divers who were either CO2-recognition-trained subjects (TS) or untrained subjects (UTS).


METHODS
Ventilatory and perceptual responses to variations in inspired CO2 (range 0-5.6 kPa, 0-42 mm Hg) during moderate exercise were assessed in novice Israeli Navy divers on active duty. Tests were carried out on 231 TS and 213 UTS.


RESULTS
The minimal mean inspired PCO2 that could be detected was 4.8 +/- 1.6 kPa (36 +/- 12 mm Hg) in UTS and 2.9 +/- 0.7 kPa (22 +/- 5 mm Hg) in TS (p < 0.0001). No significant changes were found in PETCO2 between the two groups during exposure to a PICO2 of 5.6 kPa (42 mm Hg). There were 46 TS who were found to be CO2 retainers (more than +1 SD above the mean) and 19 were classified as poor detectors (more than +1 SD above the mean). Seven subjects exhibited both traits. During actual oxygen diving performed later by this group, the only four cases of CNS-oxygen toxicity were among those seven subjects (p < 0.01).


CONCLUSIONS
We conclude that CO2 recognition training improves the diver's capability to detect CO2. We suggest that a diver who is both a poor CO2 detector and a CO2 retainer will be prone to CNS-oxygen toxicity.
Israel Naval Medical Institute, IDF Medical Corps, Haifa, Israel.
Mirit
M
Eynan
Yochanan I
YI
Daskalovic
Yehuda
Y
Arieli
Ran
R
Arieli
Avi
A
Shupak
Esther
E
Eilender
Dan H
DH
Kerem
D000328:Adult; D002245:Carbon Dioxide / Q000378:metabolism*; D016009:Chi-Square Distribution; D004242:Diving; D006801:Humans; D006935:Hypercapnia / Q000175:diagnosis*; D008297:Male; D008889:Military Personnel; D010465:Perception / Q000502:physiology*; D010806:Physical Education and Training / Q000379:methods*; D012189:Retrospective Studies; D018709:Statistics, Nonparametric
D002245:Carbon Dioxide