Validation of a new calibration method for human muscle microdialysis at rest and during exercise

Abstract

Microdialysis presents the unique possibility to measure metabolite concentrations in human interstitial fluid. During exercise, the recovery of these metabolites should be precisely monitored since it is known to increase greatly with muscle blood flow. The loss of ethanol, perfused at low concentration, can be accurately measured and reflects the changes in dialysis conditions. We evaluated whether using the relationship determined in resting metabolic conditions between the loss of ethanol, as reference substance, and the recovery for lactate or glucose would allow us to calculate precisely the concentration of these substances and their variations during exercise. Using the new catheter calibration method (slope method), the error of estimation of lactate and glucose in vitro was limited to -0.6 (5.8)% and -0.7 (6.2)%, respectively. In resting human muscle, the slope method proved to be as accurate as an established calibration technique ("no net flux method") to evaluate interstitial lactate concentration [1.82 (0.58) vs 1.83 (0.47) mM, respectively]. During dynamic knee-extension exercise or light neuromuscular electrical stimulation, the estimated interstitial lactate and glucose concentrations varied differently, but their time course changes remained consistent with their respective plasma values. We conclude that, after an initial calibration step, the slope method allows accurate measurement of interstitial muscle metabolites and it could be used to monitor rapid metabolic changes during exercise.

Microdialysis of insulin-like growth factor-I in human muscle

“…The principle of our probe calibration method for IGF-I is similar to that previously described for glucose (Desvigne et al 2004). We first determined in vitro the relationship between recovery of lactate (RecLac) and recovery of IGF-I (RecIGF-I).…”

“…We previously validated in vitro and in vivo, the slope method, to calculate MI concentration for low molecular weight substances such as glucose and lactate (Desvigne et al 2004). In the present study, using the same method, we also showed a very close relationship in vitro between RecLac and RecIGF-I, which allowed us to estimate the in vivo IGF-I concentration from lactate measurements.…”

“…Microdialysis probes were designed as described previously (Desvigne et al 2004) and the same types of catheters were used for all in vitro and in vivo studies. Briefly, a microdialysis fibre, obtained from an artificial dialysis kidney (Nephral AN69XT, Hospal, France), was glued at both extremities to nylon tubes (Standard G, 0.5 mm ID, 0.63 mm OD, Portex UK).…”

“…Thus a calibration of the dialysis probes is required to determine the probe recoveries for every metabolite. To overcome that limitation, we developed an original calibration method, the slope method, to determine actual lactate and glucose concentrations in human muscle at rest and during exercise (Desvigne et al 2004). In the present study, we evaluated our ability to quantify the concentration of IGF-I in the interstitial fluid.…”

An assessment of calibration and performance of the microdialysis system

“…The NNF-method provides an option to determine the true interstitial concentration defined by the zero net flux point where concentrations in the dialysate and the perfusate are the same. To obtain the zero net flux point, the interstitial space should be perfused with a least four predefined concentrations [3,5,8,10,11]. The NNF-method is demanding and requires the metabolism to be stable [10].…”