Introduction
Cold-water immersion (CWI) elicits the cold shock response (CSR). The hyperventilatory component of the CSR causes a decrease in cerebral blood flow velocity (CBFv) potentially causing sensations of dizziness and increasing the risk of becoming unconscious and consequently drowning [1]. In these early minutes of CWI the current advice is to 'float first' and remain stationary [2] yet this strategy may not have any effect on ventilation and therefore brain CBFv. We tested the hypothesis that leg only exercise could offset the reduction in CBFv in a resting CWI (H1) and be absent in warm water immersion.
Methods
Seventeen participants consented and visited the laboratory 3 times; mean [SD]: age 21 [3]yrs; height 1.71 [.01]m; mass 70.9 [10.1]kg. All immersions were standardised by depth, duration, clothing (bathing suit) and time of day. Test conditions were a) a resting warm water immersion (WWI; 34.7 [2.6] °C), b) a resting CWI (CWI-R: 12.2 [0.5] °C), c) a CWI (12.1 [0.5] °C) where light exercise (leg kicking/treading water; 80 bpm-1) commenced 30-seconds after water entry (CWI-K). CBFv was measured using a transcranial Doppler at a fixed depth (61 [1] mm) over the middle cerebral artery. Oxygen uptake and ventilation were measured using an online gas analysis system. Perceptions of breathlessness were measured after 1, 3 and 5 minutes using an 11-point categorical scale (0-not at all breathless, 10-extremely breathless). ANOVA was used to analyse the data to an alpha level of 0.05.
Results
CWI induced significant changes in contrast to WWI (see Table 1).
Table 1.
Mean [SD] perceived breathlessness, CBFv, oxygen uptake, and carbon dioxide production in WWI (condition a), CWI-R (b) and CWI-K (c); letters denote differences between the corresponding condition.
| CBFv (Δ%) | VO2 (mL.kg-1.min-1) | VCO2 (mL.kg-1.min-1) | |||||||
|---|---|---|---|---|---|---|---|---|---|
| WWIa | CWI-Rb | CWI-Kc | WWIa | CWI-Rb | CWI-Kc | WWIa | CWI-Rb | CWI-Kc | |
| PRE | - | - | - | 387[96] | 407[58] | 405[90] | 335[80] | 377[75] | 365[87] |
| 1 MIN | 5[4]b | -6[9]a | -3[16] | 633[117]c | 671[129] | 692[137]a | 518[97]b,c | 837[253]a | 880[343]a |
| 2 MIN | 3[6]b | -6[9]a | 2[20] | 424[84]c | 437[94]c | 534[89]a,b | 375 [79]c | 482[212]c | 623[216]ab |
| 3 MIN | 3[4] | 1[10] | 3[16] | 390[76]bc | 432[84]ac | 537[79]a,b | 347 [76]c | 405[173]c | 497[133]ab |
| 4 MIN | 3[4] | 7[11] | 8 [21] | 359[66]bc | 436[101]ac | 543[84]a,b | 321[60]c | 368[135]c | 460[120]ab |
| 5 MIN | 5[6] | 7[10] | 4[17] | 362[72]bc | 454 [85]ac | 570[99]ab | 322[66]c | 372[108]c | 455[99]ab |
Discussion
Leg kicking on CWI partially offset the reduction in CBFv that normally occurs on CWI; in contrast to a warm water control. WWI CBFv was only different to the CWI-R condition. This did not alleviate symptoms of breathlessness despite increased oxygen uptake and carbon dioxide production in the CWI-K condition; the hypothesis is only partially supported.
References
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