Mantoni T, Rasmussen JH, Belhage B, Pott FC. Voluntary respiratory control and cerebral blood flow velocity upon ice-water immersion. Aviat Space Environ Med 2008; 79:765–8.Introduction: In non-habituated subjects, cold-shock response to cold-water immersion causes rapid reduction in cerebral blood flow velocity (∼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°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%. Discussion: 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.