A comparison of hydrostatic weighing and air displacement plethysmography in adults with spinal cord injury

Objectives: To compare (1) total body volume (V_b) and density (D_b) measurements obtained by hydrostatic weighing (HW) and air displacement plethysmography (ADP) in adults with spinal cord injury (SCI); (2) measured and predicted thoracic gas volume (V_TG); and (3) differences in percentage of fat measurements using ADP-obtained D_b and HW-obtained D_b measures that were interchanged in a 4-compartment body composition model (4-comp %fat). Design: Twenty adults with SCI underwent ADP and V_TG, and HW testing. In a subgroup (n=13) of subjects, 4-comp %fat procedures were computed. Setting: Research laboratories in a university setting. Participants: Twenty adults with SCI below the T3 vertebrae and motor complete paraplegia. Interventions: Not applicable. Main Outcome Measures: Statistical analyses, including determination of group mean differences, shared variance, total error, and 95% confidence intervals. Results: The 2 methods yielded small yet significantly different V_b and D_b. The groups' mean V_TG did not differ significantly, but the large relative differences indicated an unacceptable amount of individual error. When the 4-comp %fat measurements were compared, there was a trend toward significant differences (P=.08). Conclusions: ADP is a valid alternative method of determining the V_b and D_b in adults with SCI; however, the predicted V_TG should be used with caution.