Aquatic Therapy – Relevant Thermoregulatory Effects and Pregnancy

Clinical Review by Bruce E. Becker, MD, MS

The two major compensatory mechanisms that assist cooling in warm air temperatures are peripheral vasodilatation combined with increased cardiac output. These mechanisms work to counter purposes in warm water (greater than 37°C), because they facilitate heat gain when the surrounding environment does not allow evaporative and radiant cooling.

Immersion at 40°C (104°F), which is a common hot tub temperature, produces a rectal (core) temperature rise which equates to approximately 0.1°F/min of immersion [178].

This is not a problem in the neurologically intact human, as somatic awareness warns when core temperature rises much beyond a degree centigrade or even less. But when alcohol or other drugs alter awareness, there is a serious risk of hyperthermia in a relatively brief period. There is also a risk when the metabolic ability of the tissues to respond is impaired, such as in vascular insufficiency.

Pregnancy creates a special problem, as small rises of core temperature (1.5°C) have been noted to alter the growth of fetal neuronal tissue, although in the study quoted, the temperature increases were the result of infectious processes, which may not be entirely relevant to short-term warm water immersion [179].

There have been no reports of fetal abnormalities associated with short low-level increases in core temperature lower than 38.9°C [180]. In general, pregnant women are quite sensitive to core temperature elevations, and usually depart the hot tub well before core temperature increases are near teratogenic levels [180].

McMurray et al have demonstrated the safe maintenance of core temperature during pregnancy when performing aquatic exercise in 30°C water [181-184].

A prudent guideline might be to limit hot tub immersion in 40°C tubs to periods of less than 15 minutes for pregnant women. Aquatic exercise at conventional pool temperatures has been shown to be safe during all trimesters of pregnancy, and facilitate aerobic conditioning, while reducing joint loading [185]. Aquatic exercise at conventional temperatures has also been shown to improve amniotic fluid production, which may be a useful side effect [186].

Typical prenatal programs should include cool to neutral temperature pool aerobic exercise at chest or deeper depth, along with spinal stabilization drills.

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