AN INTEGRATED NONINVASIVE SYSTEM FOR MONITORING THE MICROCIRCULATORY EFFECTS OF VASOACTIVE DRUGS - AN EXPERIMENTAL-STUDY

Background: No information is available on the effects of vasoactive d rugs on the microcirculation and on the correlation between their effe cts on the capillary and the systemic circulation. Purpose: To charact erize the effects of nitroglycerin (NTG), nitroprusside (NP), and meta raminol infusion on microcirculatory variables using a noninvasive mon itoring system. Methods: Increasing doses of NTG (5-40 mu g/kg/min) an d NP (5-20 mu g/kg/min) were intravenously infused to eight rabbits. T he microcirculatory parameters were monitored by a combined noninvasiv e system which included laser Doppler flowmetry (LDF), photoplethysmog raph (PPG), and transcutaneous oxygen tension (tc-PO2). Mean blood pre ssure (MBP) was measured simultaneously. Results: At maximal rate of N TG infusion, the values of LDF, PPG, tc-PO2, and MBP were 72.2 +/- 23. 9, 234.7 +/- 165.6, 103.5 +/- 37.4, and 82.7 +/- 7.4% of baseline, res pectively. Following NP infusion the LDF, PPG, tc-PO2, and MBP reached 70.8 +/- 24.1, 190.5 +/- 68.9, 70.0 +/- 14.7, and 75.6 +/- 14.6% of b aseline, respectively. The tissue oxygenation was significantly reduce d during NP infusion compared to NTG (P < 0.05). The values gradually returned to the baseline 10 min after termination of NP infusion, but not after NTG. After injection of 1 mg metaraminol there was a steep d ecline in LDF, PPG, and tc-PO2 parallel to a significant increase in M BP. When metaraminol was administered after injection of 0.1 mg phenox ybenzamine, these changes were abolished. Conclusions: This noninvasiv e system effectively monitors microcirculatory hemodynamic changes ind uced by vasoactive drugs. NTG and NP cause similar changes in the syst emic and microcirculatory bed, with the exception of peripheral oxygen ation, which is reduced only during infusion of NP. The changes in the microcirculatory bed following metaraminol and phenoxybenzamine imply that their effects on the arterioles are mediated by adrenegic alpha- receptors. (C) 1997 Academic Press.