Relative recovery over time - an in vivo microdialysis study of human skeletal muscle

The microdialysis technique is a method for sampling endogenous molecules from the interstitial compartments of varying tissues and relies on diffusion of molecules between the tissue and a perfusate via a membrane. Such samples do not allow determination of the true interstitial concentration but only a certain percentage. This gives rise to one of the most crucial parameter that needs to be considered for a dependable microdialysis; the relative recovery. Relative recovery states the efficiency of which an analyte is extracted from its external medium. Aim. To investigate the relative recovery of small molecules (< 20 kDa) such as lactate, fluid recovery and the reproducibility of the relative recovery at group and individual level of the microdialysis technique applied in muscle.

Using in vivo microdialysis of the trapezius muscle of 65 women from two separate occasions 4-6 months apart. Relative recovery of small molecules was measured from samples collected every 20 min during a period of 220 min.

Good reproducibility at group level of catheters with cut-offs 100 and 20kDa were found. Furthermore, there was a high and steady relative recovery with an overall good fluid recovery. Poor reproducibility was found at the individual level for both catheters.

This study demonstrates that when using microdialysis in skeletal muscle relative recovery is stable over time and is not affected by low-force exercise. Although there is a good reproducibility at group level this is not the case at the individual level. Thus in vivo, the relative recovery should be determined for each test subject and at each test occasion.