P. Vogelaere et al., CARDIAC-OUTPUT VARIATIONS IN SUPINE RESTING SUBJECTS DURING HEAD-OUT COLD-WATER IMMERSION, International journal of biometeorology, 39(1), 1995, pp. 40-45
Five men, aged 31.2 years (SD 2.3), under semi-nude conditions and res
ting in a dorsal reclining position, were exposed to thermoneutral air
for 30 min, followed immediately by a cold water (15 degrees C) immer
sion for 60 min. Cardiac output was measured using a dualbeam Doppler
flow meter. During immersion in cold water, cardiac frequency (f(c)) s
howed an initial bradycardia. The lowest values were reached at about
10 min after immersion, 58.3 (SD 2.5) to 48.3 (SD 7.8) beats min(-1) (
P < 0.05). By the 20th min of exposure, f(c) had gradually risen to 70
.0 beats min(-1) (SD 6.6, P < 0.05). This change could be due to the i
nhibition of the initial vagal reflex by increased catecholamine conce
ntration. Stroke volume (V-s) was significantly increased (P < 0.05) d
uring the whole cold immersion period. Cardiac output, increased from
3.57 (SD 0.50) to 6.26 (SD 1.33)l min(-1) (P < 0.05) and its change wi
th time was a function of both V-s and f(c). On the other hand, systol
ic flow acceleration was unchanged during the period of immersion. The
changes in the respiratory variables (ventilation, oxygen uptake, car
bon dioxide output and respiratory exchange ratio) during immersion sh
owed an initial hyperventilation followed, as immersion proceeded, by
a slower metabolic increase due to shivering.