18 Aquatic Physical Therapy
KEY POINTS
Hydrotherapy and aquatic therapy are often used interchangeably to refer to physical therapy performed in water. Spa therapy refers to physical modalities applied in a relaxing atmosphere that may be purely commercial, devoid of oversight from a licensed practitioner at point of delivery. Spa therapies can include land-based modalities such as massage and electrotherapy, as well as water-based forms such as balneotherapy and whirlpool. Spa treatments, even when water-based, are typically passive.1 Studies of spa interventions prove difficult. Balneotherapy refers to the immersion of patient or limb in a natural thermal mineral water, defined as at least 20° C, and containing a concentration of specific salts in excess of 1 g/L.1
Basic Science
Water is nearly 800 times as dense as air.2 The bottom of a mass of material exerts a pressure based on the density of the material. For example, at sea level, effectively at the “bottom” of the earth’s atmosphere, patients are exposed to the pressure of air. When a patient enters a body of water, be it a hot tub, swimming pool, or ocean, the water exerts pressure that increases with increasing depth. Water affects the cardiovascular and renal systems. Water’s hydrostatic pressure compresses veins, increasing venous return and pushing blood centrally, leading to a rise in central blood volume, cardiac blood volume, and cardiac output.3 Compression of veins can reduce edema. Healthy individuals seated for 2 hours in water from the renowned spa at Bath, England, showed a doubling of diuresis and 50% increase in cardiac index. The increase in diuresis is not due to an increase in creatinine clearance, though alteration of renally active hormones may play a role.4 It is unclear if hydrostatic pressure is the primary mechanism underlying all of these systemic effects.
