Diaphragmatic microcirculation measured by laser-Doppler flowmetry in the rat.

The applicability of laser-Doppler flowmetry (LDF) in measuring regional blood flow of the diaphragm (Qdi) was evaluated in anesthetized and mechanically ventilated rats. Specifically, we assessed the issues of the degree of tissue perfusion, spatial variations of Qdi signals, and the correlation between these signals and total Qdi. Qdi was detected from an area 1 mm in diameter and 0.5 mm in depth. With Ringer solution continuously suffusing the abdominal surface of the left hemidiaphragm, drugs were applied to the surface of the diaphragm at 1/100 of the flow rate of the suffusing fluid. In 13 rats, resting Qdi and the response of Qdi to a single concentration of adenosine (10(-4) M) remained unchanged over a 2-h period. Increasing adenosine concentrations (10(-9) to 10(-3) M) in eight rats elicited a progressive rise in Qdi. In six rats, the variability of Qdi in a given rat was assessed over five different sites at 2-mm intervals in a line on the diaphragm. A wide range of variability in Qdi was noticed among different sites. The depth of tissue penetration of LDF was little affected when a piece of freshly diaphragm was interposed between the probe and the perfused diaphragm, suggesting that LDF signals arise from complete penetration of the perfused diaphragm. Finally, significant linear relationships between mean Qdi and total Qdi were observed in all animals; however, the slopes of these relationships varied significantly between animals. In conclusion, LDF provides a stable and continuous method for monitoring regional microvascular diaphragmatic perfusion.(ABSTRACT TRUNCATED AT 250 WORDS)