Body composition by air-displacement plethysmography by using predicted and measured thoracic gas volumes

Abstract

The BOD POD, a new air-displacement plethysmograph for measuring human body composition, utilizes the inverse relationship between pressure and volume (Boyle's law) to measure body volume directly. The quantity of air in the lungs during tidal breathing, the average thoracic gas volume (Vtg), is also measured by the BOD POD by using a standard plethysmographic technique. Alternatively, the BOD POD provides the use of a predicted Vtg (Vtgpred). The validity of using Vtgpred in place of measured Vtg (Vtgmeas) to determine the percentage of body fat (%BF) was evaluated in 50 subjects (36 women, 14 men; ages 18-56 yr). There was no significant difference between Vtgmeas and Vtgpred (mean difference +/- SE, 53.5 +/- 63.3 ml) nor in %BF by using Vtgmeas vs. Vtgpred (0.2 +/- 0.2 %BF). On an individual basis, %BF measured by using Vtgmeas vs. Vtgpred differed within +/-2.0% BF for 82% of the subjects; maximum differences were -2.9 to +3.0% BF. For comparison, data from 24 subjects who had undergone hydrostatic weighing were evaluated for the validity of using predicted vs. measured residual lung volume (VRpred vs. VRmeas, respectively). Differences between VRmeas and VRpred and in %BF calculated by using VRmeas vs. VRpred were significant (187 +/- 46 ml and 1.4 +/- 0.3% BF, respectively; P < 0.001). On an individual basis, %BF determined by using VRmeas vs. VRpred differed within +/-2.0% BF for 46% of the subjects; maximum differences were -2.9 to +3.8% BF. With respect to %BF measured by air displacement, our findings support the use of Vtgpred for group mean comparisons and for purposes such as screening in young to middle-aged individuals. This contrasts with the use of VRpred in hydrostatic weighing, which leads to significant errors in the estimation of %BF. Furthermore, although the use of Vtgpred has some application, determining Vtgmeas is relatively simple in most cases. Therefore, we recommend that the use of Vtgmeas remain as standard experimental and clinical practice.

Body composition in children and adults by air displacement plethysmography

“…A detailed description of the procedure is given in earlier reports (Dempster & Aitkens, 1995;McCrory et al, 1995). Since McCrory et al found no signi®cant difference between measured and predicted V TG in adults (McCrory et al, 1998), a predicted estimate of V TG based on age, sex, and height was used in cases where an accurate measurement of V TG was not possible. The between-day CV for B d estimates by ADP in our laboratory was determined in four adult subjects measured on four consecutive days.…”

Short-Term Moderate Weight Loss and Resistance Training Do Not Affect Insulin-Stimulated Glucose Disposal in Postmenopausal Women

“…Caucasian women, aged 63 Ϯ 2 years (range 55-79), with a BMI of 29.9 Ϯ 0.7 kg/m 2 (25)(26)(27)(28)(29)(30)(31)(32)(33)(34), and who were not actively involved in any physical training, volunteered to participate in this 7-week outpatient study. The women were recruited from the Little Rock, Arkansas, region via advertisements in local newspapers.…”

“…Body density was determined via airdisplacement plethysmography using BOD POD (Life Measurements Instruments, Concord, CA) (30). Percent body fat (BF), FM, and fat-free mass (FFM) were estimated from body density using the Siri two-compartment model equation (31).…”

Changes in thoracic gas volume with air-displacement plethysmography after a weight loss program in overweight and obese women

“…Alternatively, the BOD POD provides the use of a predicted V TG (V TGPredicted ) (Crapo et al, 1982). The validity of using the V TGPredicted in place of the measured V TG (V TGMeasured ) to determine %FM was studied in a few cross-sectional studies with mixed results (McCrory et al, 1998;Demerath et al, 2002). Accordingly, no differences were found between measured vs predicted V TG in different adult age groups.…”