Apnea-induced changes in time estimation and its relation to bradycardia.
BACKGROUND
Both exercise and hypoxia affect human ability to estimate time, an alteration thought to be induced by changes in subjects' level of arousal. Apnea induces cardiovascular changes and a decrease in oxygen uptake that indicate changes in physiological arousal. We tested time estimation (TE) during brief periods of voluntary apnea. We hypothesized that there would be a relationship between TE and heart rate (HR), a physiological indicator of arousal.


METHODS
Subjects were two different groups of seven triathletes. To measure TE, the target time interval (20 or 30 s) was demonstrated and the subject was then asked to reproduce it under various conditions. Experiment 1 required 1 min of breath-holding while immersed in a pool at 31 degrees C. Experiment 2 was performed seated on a cycle ergometer in a laboratory and involved short periods of apnea at rest and during exercise.


RESULTS
TE during apnea was significantly greater than baseline during both immersion and at rest on the cycle (+27% and +17% compared with their respective baselines). A significant linear negative correlation was demonstrated between TE and HR. Training in apnea during exercise had no effect on TE.


CONCLUSIONS
Although this study revealed a relationship between TE and HR, our results should be interpreted with caution. Further studies are needed to confirm the relationship between HR and TE. A misperception of elapsed time may be a contributing factor in diving accidents which involve inexperienced breath-hold divers.
Jamin
Thibaud
T
Laboratoire E.S.P. (EA 3162), Université du Sud Toulon-Var, La Garde, France.
Joulia
Fabrice
F
Fontanari
Pierre
P
Giacomoni
Magali
M
Bonnon
Michel
M
Vidal
Franck
F
Crémieux
Jacques
J
D000059:Accidents; D000328:Adult; D001049:Apnea / Q000150:complications*; D001288:Attention; D001919:Bradycardia / Q000150:complications* / Q000209:etiology*; D004242:Diving / Q000293:injuries*; D005080:Exercise Test; D006801:Humans; D008297:Male; D013998:Time Perception