Voluntary respiratory control and cerebral blood flow velocity upon ice-water immersion.
BACKGROUND
In non-habituated subjects, cold-shock response to cold-water immersion causes rapid reduction in cerebral blood flow velocity (approximately 50%) due to hyperventilation, increasing risk of syncope, aspiration, and drowning. Adaptation to the response is possible, but requires several cold immersions. This study examines whether thorough instruction enables non-habituated persons to attenuate the ventilatory component of cold-shock response.


METHODS
There were nine volunteers (four women) who were lowered into a 0 degrees C immersion tank for 60 s. Middle cerebral artery mean velocity (CBFV) was measured together with ventilatory parameters and heart rate before, during, and after immersion.


RESULTS
Within seconds after immersion in ice-water, heart rate increased significantly from 95 +/- 8 to 126 +/- 7 bpm (mean +/- SEM). Immersion was associated with an elevation in respiratory rate (from 12 +/- 3 to 21 +/- 5 breaths, min(-1)) and tidal volume (1022 +/- 142 to 1992 +/- 253 ml). Though end-tidal carbon dioxide tension decreased from 4.9 +/- 0.13 to 3.9 +/- 0.21 kPa, CBFV was insignificantly reduced by 7 +/- 4% during immersion with a brief nadir of 21 +/- 4%.


CONCLUSIONS
Even without prior cold-water experience, subjects were able to suppress reflex hyperventilation following ice-water immersion, maintaining the cerebral blood flow velocity at a level not associated with impaired consciousness. This study implies that those susceptible to accidental cold-water immersion could benefit from education in cold-shock response and the possibility of reducing the ventilatory response voluntarily.
Mantoni
Teit
T
Department of Anaesthesia and Intensive Care, Bispebjerg Hospital, Copenhagen, Denmark. temantoni@hotmail.com
Rasmussen
Jakob Højlund
JH
Belhage
Bo
B
Pott
Frank Christian
FC
D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D000704:Analysis of Variance; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003080:Cold Temperature / Q000009:adverse effects*; D005260:Female; D006801:Humans; D007035:Hypothermia / Q000209:etiology*; D007053:Ice / Q000009:adverse effects*; D007101:Immersion / Q000503:physiopathology*; D008297:Male; D010806:Physical Education and Training; D015656:Respiratory Mechanics / Q000502:physiology*; D012307:Risk Factors; D017585:Ultrasonography, Doppler, Transcranial
D007053:Ice