Effect of graded water immersion on vital capacity and plasma volume in patients with cervical spinal cord injury.

STUDY DESIGN: A case-control study was conducted. OBJECTIVE: The aim of the study was to test the hypothesis that the increase in hydrostatic pressure on the abdominal wall may be the major determinant of vital capacity (VC) improvement in tetraplegic subjects during water immersion, despite the blood volume shifts from the legs and abdomen to the thorax. SETTING: The study was carried out in the Rehabilitation Center, Brasília/DF, Brazil. METHODS: In total, 11 men with tetraplegia (complete motor lesion, C4-7, 30.4 years old) and 12 healthy controls were studied. Hematocrit level and spirometry values were obtained on dry land and at each level of immersion (the pelvis, xiphoid and neck). RESULTS: Baseline spirometry value of tetraplegic subjects showed reduced VC (53.3+/-17.4% of predicted), whereas all control subjects had >80% of predicted values. Neither group showed significant changes in VC at the pelvic and xiphoid levels of immersion. In tetraplegic subjects, VC increased by 27.2% at the neck level (+/-25.8, P<0.008), whereas in healthy subjects it decreased by 6.3% (+/-5.0, P<0.008). Both groups showed significantly increased inspiratory capacity only when immersed to the neck. Hematocrit level of tetraplegic subjects fell significantly with immersion to the xiphoid and neck levels (P<0.017), which occurred in controls only at the xiphoid level (P<0.017). CONCLUSIONS: Hydrostatic compression may be the main contributor to improving VC in tetraplegic subjects immersed in water. This improvement occurs despite increased plasma volume during immersion.