Sorbitol clearance during exercise as a measure of hepatic and renal blood flow

1 Institute of Sports Medicine, University of Leipzig
3 Ilmtalklinik, Pfaffenhofen
2 Center of Sports Medicine, Hannover Medical School
4 Department of Anesthesiology I, Hannover Medical School

Abstract

Busse M, Tegtbur U, Machold H, Panning B. Sorbitol clearance during exercise as a measure of hepatic and renal blood flow. Clinical Sports Medicine International (CSMI) 2004, 1: 1-8

Background: To measure total and hepatic sorbitol clearance during moderate and intense constant load exercise.

Methods: Plasma sorbitol concentration was measured during a constant rate sorbitol infusion (40%, 8ml/min) at rest and during 40% and 60% of the individual maximum work load (W max ). From the respective sorbitol clearance and the hepatic extraction rate for sorbitol, hepatic and renal sorbitol clearance were calculated.

Results: Mean values for hepatic and renal sorbitol clearance at rest were 1.01 ± 0.22 l/min and 0.13 ± 0.07 l/min. The respective exercise values were: 40% VO2-max: 0.59 ± 0.13 l/min and 0.08 ± 0.05 l/min; 60% VO2-max: 0.35 ± 0.07 l/min and 0.05 ± 0.03 l/min. No steady state sorbitol clearance was obtained during the 44 ( ± 15) min of the 60% VO2-max level, and thus the estimated functional hepatic blood flow may still overestimate the real values. Hepatic sorbitol clearance (CL hep ) was calculated from exercise heart rate (HR): CL hep = 0.0048 . HR + 1.2. From total sorbitol clearance (CL tot ), hepatic sorbitol clearance (CL hep ), estimated hepatic blood flow (EHBF) and estimated hepatic plasma flow (EHPF) can be calculated as follows: CL hep = 0.87 . Cl tot ; EHBF = 1.58 . Cl tot ; EHPF = 0.91 . Cl tot .

Conclusions: The results correspond well with former measurements of hepatic and renal blood flow, using indocyanine green, PAH or sorbitol, respectively. Moderate exercise reduces liver blood flow to a minor extent, whereas intense constant load exercise slightly below the anaerob threshold reduces liver blood flow markedly without an apparent steady-state end-point. Drawback of the method is a long equilibration time and the necessity of frequent urine sampling, when high precision is desired.

Key words: exercise, sorbitol, liver blood flow, liver plasma flow