Comparison of Skeletal Muscle Laser Doppler Flowmetry to Changes in Central Hemodynamics in Detecting the Physiological Response to Moderate Hemorrhage

Abstract

Previous studies have demonstrated that laser Doppler (LD) flowmetry is a useful technique for following changes in blood flow in a tissue bed, but the potential role of LD flowmetry in management of the critically ill patient is unclear. This study sought to establish the sensitivity of LD flowmetry compared to changes in centrally measured hemodynamic parameters in response to a mild hemorrhagic episode. In order to establish the correlation between LD flow and actual blood flow, livers from Sprague-Dawley rats were isolated and perfused via the portal vein with citrate anticoagulated rat blood. Changes in LD flow were recorded while changing blood flow via the perfusion pump. There was a strong correlation between pump flow and LD flow (for N = 5 livers, r > 0.9; P < 0.05). This relationship was stable at hematocrits >20. The second part of this study tested the sensitivity of LD flowmetry in anesthesized baboons. An LD probe was placed on the surface of the gracilis muscle of the adult male baboons. LD flow and hemodynamic parameters were measured following two episodes of bleeding and reinfusing 250 cc of blood. During the first bleed there were significant changes in heart rate (97 + 8 to 159 + 12), mean arterial pressure (125 + 6 to 105 + 9), and LD flow (20.6 + 4.6 to 11.9 + 3.6); these parameters returned to normal after reinfusion of blood. During the second bleed, the only parameters that showed significant changes were heart rate (118 + 5 to 135 + 12) and LD flow (17.5 + 8 to 10.7 + 3.4). Cardiac output, pulmonary artery wedge pressure, and arterial blood pH by blood gas determination did not change significantly during either bleeding episode. This study suggests that LD flowmetry is more sensitive to tissue hypoperfusion than commonly measured central parameters and may be useful in aiding the resuscitation of critically ill patients.