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A M McKenzie

Publications and source records attributed to A M McKenzie.

3 recordsLinked to original sources
PubMed1993

Quantitative testing of sympathetic function with laser Doppler flowmetry.

OBJECTIVE: The objective of this study was to develop an indirect technique for evaluating dynamic changes in sympathetic function in humans. METHODS: We used laser Doppler to monitor sympathetic mediated vasoconstrictive responses (VRs) produced by 3 different provocative stimuli: 4-second inspiratory gasp (IG), ice-water immersion (Ice), and a spring-loaded pin prick (Pin). Skin perfusion on the thenar eminence was continuously monitored in 10 normal subjects (aged 25 to 36 years) using laser Doppler. Ten trials of the 3 stimuli were presented to each subject at 1-minute intervals. We determined the VR, the percent decrease in perfusion produced by each stimulus, and the 2 standard deviation variation in perfusion. RESULTS: No subject found the IG maneuver uncomfortable. In contrast, the Pin and Ice stimuli were reported to be uncomfortable by 8 and 10 subjects, respectively. Five subjects found Pin and Ice stimuli overtly painful. Vasoconstrictive response was 54.1 +/- 2.3% (mean +/- SEM) with IG, 49.2 +/- 2.0% with Ice, and 24.0 +/- 1.8% with Pin. Baseline variation was approximately 15% in all trials. CONCLUSION: Inspiratory gasp vasoconstrictive response (IGVR) is a sensitive indirect technique for evaluating sympathetic efferent function. We observed that the magnitude of the VR elicited by the IG stimuli was similar to that induced by cold water. Unlike the VR induced by Pin or Ice, IGVR is not dependent on noxious input via somatic afferents; therefore, it can be used in patients with diseases that produce a peripheral neuropathy, such as diabetes mellitus. Present uses of this technique and speculation on future uses are presented.

Adult↗
PubMedDate not supplied

Effects of epidural test dose volume on skin perfusion, temperature, and reflex vasoconstriction.

BACKGROUND AND OBJECTIVES: The authors sought to define the effects of differing volumes of epidural test dose on skin perfusion, skin temperature, and reflex vasoconstriction to a maximal inspiration (inspiratory gasp vasoconstrictive response, IGVR). METHODS: With informed consent and Institutional Review Board approval, the authors studied 40 patients undergoing epidural anesthesia. Skin perfusion was monitored in glabrous skin on the foot using laser Doppler. Inspiratory gasp vasoconstrictive response and temperature measurements were obtained at 1-minute intervals. After a baseline period, 5 patients received 60 mg intravenous lidocaine HCl; 5 received 5 mL normal saline, via epidural catheter; and 30 patients received 50 mg lidocaine HCl and 20 mcg epinephrine in 2.5, 5.0, or 7.5 mL normal saline (10 patients each). Inspiratory gasp vasoconstrictive response was defined as the percent change in perfusion from baseline produced by an inspiratory gasp. Perfusion was normalized by expressing each patient's value as a percentage of the respective baseline value. RESULTS: Significant increases in perfusion, of up to 169% of baseline, were seen 12 minutes after the test dose. Inspiratory gasp vasoconstrictive response showed significant changes from baseline in all test groups. The temperature change was insignificant. Control groups did not show perfusion or IGVR changes. CONCLUSIONS: Skin perfusion and IGVR changed significantly after epidural test dose; the minimal effect of volume appears to be 5 mL of lidocaine-epinephrine solution; the presence of IGVR or perfusion changes, or both, are positive predictors of successful placement of the catheter into the epidural space; and temperature changes as observed here were not reliable predictors of proper placement of epidural catheters.

Aged↗