PROPORTIONAL CHANGES IN BODY-FLUID WITH HEMODIALYSIS EVALUATED BY DUAL-ENERGY X-RAY ABSORPTIOMETRY AND TRANSTHORACIC BIOIMPEDANCE WITH PARTICULAR EMPHASIS ON THE THORACIC REGION

Alterations in body composition during extracorporeal hemodialysis (HD ) were investigated in 12 hemodialysis patients (9 males and 3 females , mean age 50 +/- 15 years) with a mean ultrafiltration of 2.6 +/- 1.0 L. Analysis was performed using a dual-energy x-ray absorptiometry te chnique (DXA), which measures 3 principal components of the body: fat mass (FM); lean body mass (LBM), i.e., all soft tissues excluding fat; and bone mineral content (BMC). These 3 components were calculated fo r the whole body and for different body regions (namely, the thorax, t runk, lower limbs, and upper limbs). The thoracic cage region could be defined manually, separately from the trunk, and its tissue compositi on was calculated. DXA analysis was performed concomitant with a measu rement of the basal thoracic impedance (TFI) by bioimpedance cardiogra phy prior to and 1 h after dialysis. We found a significant decrease i n the total LBM, from 55.8 +/- 8.8 to 53.3 +/- 9.3 kg (p < 0.05), but no change in either the FM or BMC. Moreover, there was a disproportion al reduction in the LBM in different regions, being significantly grea ter in the thorax (7.47 +/- 3.7%) than in the other body regions (trun k 4.3 +/- 2.0%, lower limbs 5.4 +/- 2.1%, and upper limbs 4.7 +/- 1.5% ). Regarding bioimpedance, a stronger significant correlation was dete cted between the percentage changes in the TFI and the changes in thor acic fluid (r = 0.80, p < 0.01) than between the changes in the TFI an d the changes in the total body fluid (r = 0.63, p < 0.01). The absolu te values of the TFI were also significantly and negatively correlated to the thoracic lean mass to fat mass ratio, both before and after HD (r = 0.82, p < 0.001 and r = 0.86, p < 0.001, respectively). In concl usion: DXA is a very sensitive technique to detect fluid changes durin g KD in the thorax when the thoracic cavity is defined as a region of interest as well as for the whole body. The data also indicate an extr acellular compartmental imbalance between different regions with a sig nificantly greater change in the thoracic region. Transthoracic bioimp edance is a useful technique for evaluating the HD induced changes in the thoracic fluid, rather than total body fluid.