Comparison of two methods to assess the tissue/blood partition coefficient for xenon in subcutaneous adipose tissue in man

Summary. A new method to calculate the tissue/blood partition coefficient (Λ) for xenon in studies on the subcutaneous adipose tissue blood flow was compared with a previously reported method based on local skinfold thickness (Λ_LSt). The former method included needle biopsies from the abdominal and femoral subcutaneous adipose tissue, and the mean fat cell diameter was measured (Λ_ECT)- The extracellular tissue fraction in subcutaneous tissue was then estimated from a diagram. The tissue lipid content was approximated to equal the relative intracellular volume and Ostwald's solubility coefficients for ¹³³Xe, based on the distribution of xenon in lipid, albumin and 0.9% saline were applied. Estimated Λ-values based on needle biopsies from the abdominal site were: 8.6±0.1 versus 9.9±0.4 ml g^-1 (meanæ) (P<0.05) and from the femoral site: 9.1±0.1 versus 9.6±0.2 in lean (n=10) and obese subjects (n=10), respectively. The corresponding Λ-values obtained from skinfold measurements were: 6.2±0.5 versus 11.0±0.4 (P<0.001) and 6.9±03 versus 11.4±0.4 (P<0.001) in lean and obese subjects, respectively. Pooled Λ_LsT-values correlated positively with estimated adipose tissue blood flow (ATBF) (r: 0.34, P<0.05, n=40) whereas no such correlation was found for Λ_ECT-values. In conclusion, a new method is presented which may allow an accurate determination of, and which may lead to reliable data on, subcutaneous ATBF in both lean and obese subjects. Comparative studies indicate that the widely used Λ-value of 10.0 in subcutaneous adipose tissue may be used as a rough estimate for subcutaneous blood flow studies in these patient groups.