Multiparameter fiber optic sensor for the assessment of intramyocardial perfusion.

OBJECTIVES: The objective of this study was to characterize a multiparameter fiber optic sensor for detection of changes in intramyocardial perfusion and to demonstrate a method of determining critical values for pH, PCO2, and PO2 to indicate onset of anaerobic metabolism. METHODS: Six swine underwent a 20-minute occlusion of the left anterior descending coronary artery (LAD). Myocardial pH, PCO2, and PO2 were measured continuously in the LAD and left circumflex coronary artery (CFX) territories. Critical values for each parameter were calculated from these data. RESULTS: During occlusion LAD myocardial pH declined from 7.36 +/- 0.04 to 6.85 +/- 0.04; PCO2 rose from 57.0 +/- 2.9 to 154.0 +/- 18.0 torr, PO2 fell from 78 +/- 20 to 6 +/- 5 torr. No myocardial pH or PCO2 changes were observed in the CFX region, however, CFX PO2 was affected in some animals during LAD occlusion and release. Methods for determining the ischemic threshold from these sensor data are presented. CONCLUSIONS: Multiparameter fiber optic sensors reliably respond to coronary occlusion and thus have the potential to help guide myocardial protection strategies for both on- and off-pump cardiac surgery.

Investigation of muscle pH as an indicator of liver pH and injury from hemorrhagic shock.

BACKGROUND: During hemorrhagic shock blood flow to vital organs is maintained by the diversion of blood from both the splanchnic organs and skeletal muscle. In this swine study, we tested the hypotheses that (1). liver and muscle pH are correlated during both shock and resuscitation and (2). muscle pH during shock is an indicator of potential liver injury after resuscitation. MATERIALS AND METHODS: Hemorrhagic shock was induced over 15 min to lower systolic blood pressure to 40 mm Hg and was maintained for 60 (n = 5) or 90 (n = 5) min. Resuscitation was achieved with shed blood and warm saline to maintain mean pressure >60 mm Hg for 120 min. Liver and muscle pH were measured with microelectrodes throughout the entire shock and resuscitation periods, along with hepatic venous oxygen saturation. Arterial lactate and aspartate aminotransferase were measured at baseline, end of shock, and resuscitation. Correlation between muscle and liver pH was determined. The ability of muscle pH to predict liver injury (40% increase in arterial aspartate aminotransferase) was compared with other predictors: liver pH, arterial lactate, and tonometric-arterial PCO(2) gap. RESULTS: pH values and rates of change were similar in both muscle and liver tissue. Liver pH was well correlated with muscle pH during both shock and resuscitation, R(2) = 0.84. Muscle pH predicts potential liver injury with the same sensitivity as blood lactate in this swine shock model. CONCLUSIONS: Minimally invasive measurement of muscle pH warrants further study as a method to assess splanchnic hypoperfusion and resultant injury.

Experimental coronary artery occlusion: relevance to off-pump cardiac surgery.

Mechanical coronary artery occlusion is required for minimally invasive direct coronary artery bypass and off-pump coronary artery bypass surgery. It is important that the method of occlusion be minimally traumatic. Chronic effects of these methods have never been studied. Temporary occlusion of coronaries utilizing suture snare, silastic loop snare, and bulldog clamp was carried out in 12 Yucatan pigs. Three animals each were sacrificed acutely and at 3, 6, and 12 months. The area of occlusion of each vessel was examined by light microscopy and the degree of damage recorded. In the animals sacrificed acutely, there was more damage using the suture snare than with the other 2 methods, but there was minimal damage at longer intervals. There was slight damage acutely and chronically with the bulldog technique. No damage was seen acutely with the silastic loop technique, but some late damage was found. The techniques of coronary artery dissection and occlusion used for minimally invasive and off-pump bypass surgery may contribute to early postoperative graft occlusion.