Hours Of Normothermic Ischemia Research Articles

ISCHEMIC AND PEROXYNITRITE PRECONDITIONING EFFECTS IN CHRONIC HYPOXIC RAT LUNG

Chronic hypoxic pulmonary hypertension is characterized by vasoconstriction and vascular remodeling and impaired endothelial nitric oxide (NO) production. Although ischemic preconditioning of the lung leads to protective effect against ischemic reperfusion injury, the mechanisms of this protection are not well documented in the lung. The aim of this study was to investigate the effects of chronic hypoxia on preconditioning induced by ischemia or peroxynitrite in isolated rat lungs. The isolated rat lung, from exposed to hypobaric hypoxia for 21 days, was mounted on a modified Langendorff perfusion apparatus. Lungs were preconditioned by either 5 minutes' ischemia and 5 minutes' reperfusion or 10 μ M peroxynitrite prior to 2 hours of normothermic ischemia. Although ischemia-reperfusion or peroxynitrite preconditioning markedly reduced KCl responses on perfusion pressure, phenylephrine-induced responses were not significantly modified. Pretreatment of the hypoxic lungs with peroxynitrite scavenger, uric acid, or poly (ADP-ribose) synthase inhibitors (PARS), 3-aminobenzamide (3-AB) or nicotinamide, did not modify the KCl- and phenylephrine-induced responses in chronic hypoxic lungs. There were also no marked differences either in wet to dry weight ratio or malondialdehyde levels of chronic hypoxic lungs. These results imply that preconditioning does not occur in the chronic hypoxic rat lungs.

The role of taurine added to pulmonary reperfusion solutions in isolated guinea pig lungs.

An experimental comparative study on isolated guinea pig-lungs has been undertaken to determine the probable beneficial effects of adding taurine to pulmonary reperfusion solutions in lung ischemia-reperfusion. 20 guinea pigs were used. The isolated lungs (n = 10 in each group) previously being perfused by oxygenated Krebs-Henseleit solution were put in normothermic ischemic conditions. After 3 hours of normothermic ischemia the lungs were reperfused (with Krebs-Henseleit solution in the control group, Krebs-Henseleit solution plus taurine 10(-2) M in the experiment group) for 20 minutes. Pulmonary artery pressures, tissue malondialdehyde (MDA) and glutathione (GSH) levels were measured before and after the ischemic period and also at the end of reperfusion. Malondialdehyde and glutathione levels of the pefusate were measured before ischemic period and at the end of reperfusion. An electron microscopic analysis was performed on the lung tissues before and after the ischemic period and also at the end of reperfusion. Decreased pulmonary artery pressure, tissue perfusate MDA levels and increased perfusate GSH levels were observed in taurine added group. Electron microscopic evaluation supported our findings indicating preservation of lamellar bodies of type II pneumocytes. It is concluded that taurine may play an important role in protecting tissue against ischemia-reperfusion injury by functioning as an antioxidant.

Prevention of reperfusion induced lung injury by L-carnitine

L-Carnitine plays an important role in the transmembrane transport of long chain fatty ascids for it's oxidation and supresses the development of free radical damage. An experimental comparative study isolated guinea pig lungs has been undertaken to determine the probable beneficial effects of adding L-Carnitine to preischemic pulmonary perfusion solutions in lung ischemia-reperfusion. The isolated lungs (n=10 in control group) previously being perfused by oxygenated Krebs Henseleit solution were put in normothermic ischemic conditions. 1 O mmol of L-Carnitine was added into a Krebs-Henseleit solution in the experimental group (n= 10) and after 20 min., perfusion was completed and the lungs were then exposed to normothermic ischemia. After 3 hours of normothermic ischemia, the lungs were perfused with Krebs-Henseleit solution for 20 minutes. Tissue malondialdehyde (MDA), glutathione (GSH) levels and electron microscopic evaluations were held on before the ischemic period and also at the end of reperfusion. MDA and GSH levels of the perfusate were measured before ischemic period and at the end of reperfusion. L-Carnitine administration reduced MDA levels both in tissues and perfusates. in contrast to glutathione levels which is increased. According to our data, the addition of L Carnitine to preischemic pulmonary perfusion solution showed a significant protective effect regarding both ischemic and reperfusion injury.

Perfusão pulmonar anterógrada "versus" retrógrada na preservação pulmonar para transplante em modelo canino de viabilidade pulmonar pós-morte

A doação pulmonar após parada cardiocirculatória tem sido estudada experimentalmente na obtenção de órgãos para transplante, porém a severa lesão isquêmica/reperfusão exigem métodos de preservação que permitam viabilidade pulmonar. A perfusão do enxerto com solução cristalóide hipotérmica via anterógrada (artéria pulmonar) é o método de preservação mais utilizado, porém esta via não perfunde a circulação brônquica, permitindo a retenção sanguínea neste território capaz de desencadear fenômenos de lesão de reperfusão. Isto nos levou a testar os efeitos da perfusão anterógrada versus retrógrada (via átrio esquerdo, capaz de perfundir a circulação brônquica) em modelo canino de transplante unilateral cujos pulmões foram extraídos 3 horas após parada cardiorrespiratória. Doze cães doadores foram sacrificados com tiopental sódico e mantidos à temperatura ambiente sob ventilação mecânica durante 3 horas, após as quais os animais foram randomizados e os blocos cardiopulmonares perfundidos via retrógrada (n = 6) ou anterógrada (n = 6) com solução de Euro-Collins modificada e extraídos. Os receptores (n = 12) foram anestesiados, pneumonectomizados e submetidos a transplante pulmonar esquerdo recebendo enxertos perfundidos por via retrógrada (grupo I) ou anterógrada (grupo II). Após a reperfusão do enxerto, os animais foram mantidos sob ventilação mecânica (FiO2 = 1) por 6 horas, sendo então sacrificados. Durante este período obtiveram-se medidas hemodinâmicas e gasometrias arteriais, além de amostras de tecido pulmonar para dosagem de ATP intracelular. As medidas hemodinâmicas não diferiram entre os grupos. Nos animais do grupo I a PaO2 e PaCO2 foram superiores às do grupo II (p = 0,016 e p = 0,008, respectivamente). O ATP intracelular não diferiu entre os grupos, embora tenha se reduzido nas amostras obtidas na extração do enxerto do doador quando comparados aos valores após a reperfusão (p = 0,01) e ao término do período de avaliação (p = 0,01). Os autores concluem que, neste modelo experimental, a perfusão retrógrada hipotérmica resulta em função superior do enxerto após 3 horas de isquemia normotérmica sob ventilação mecânica.

Primary critical ischemia time in the hairless mouse ear.

The primary critical ischemia time of the hairless mouse ear was determined using a probit analysis. An atraumatic clamp was used across the pedicle base of the ear to induce total ischemia at 0, 2, 4, 6, 7, 7.5, 8.0, 8.5, 9.0, 9.5, and 12 hours of normothermic ischemia. Seventy-seven ears were examined 7 days after the ischemic interval for evidence of necrosis. The median critical ischemia time was determined to be 8.2 hours with 95 percent fiducial limits of 7.74 hours and 8.69 hours.

Endothelium-dependent vasodilatation produced by the L-arginine/nitric oxide pathway in normal and ischemic bone.

We used an experimental model of the perfused isolated rabbit tibia to investigate the vasodilatation produced by nitric oxide in the circulation of bone. Tibiae were perfused at a constant flow rate while the perfusion pressure was monitored continuously. Perfusion pressure was raised by the addition of noradrenaline to the perfusate, and dose responses were measured for bolus doses of acetylcholine and sodium nitroprusside. N omega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthesis, was then added to the perfusate at a concentration of 10(-4) M, and the dose responses to acetylcholine and sodium nitroprusside were repeated. Measurements were performed on groups of bones after 0, 6, 12, and 24 hours of normothermic ischemia (n 5, 4, 6, and 9, respectively). Both acetylcholine and sodium nitroprusside produced significant vasodilatation after 0 and 6 hours' ischemia, but no significant response was observed after 12 or 24 hours of ischemia. The vasodilatation produced by acetylcholine was significantly attenuated when L-NAME was added to the perfusate, but the vasodilatation produced by sodium nitroprusside remained unchanged. These findings confirm endothelial production of NO by stimulation of muscarinic receptors on the endothelial cells in bone and indicate that vasodilatation via the L-arginine/NO pathway remains viable for 6 hours after normothermic ischemia.

Deleterious effects of xanthine oxidase on rat liver endothelial cells after ischemia/reperfusion

Previous studies have demonstrated that reactive oxygen species are involved in ischemic injury. The present work was undertaken to determine in vivo the role of xanthine oxidase in the oxygen free radical production during rat liver ischemia and to examine the activity of antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase) during the same period. Our results indicate a 4-fold increase in xanthine oxidase activity between 2 and 3 hours of normothermic ischemia, in parallel with a decrease in cell viability. Moderate hypothermia delays both events. Under the same conditions, the activity of oxygen radical scavenging enzymes remains unchanged. Moreover, we have compared in vitro the susceptibility of isolated liver cells to an oxidative stress induced by O 2 ·−, H 2O 2 and OH. Our results reveal that endothelial cells are much more susceptible to reactive oxygen species than hepatocytes, probably because they lack H 2O 2-detoxifying enzymes. These findings suggest that xanthine oxidase might play a major role in the ischemic injury mainly at the level of the sinusoidal space where most endothelial cells are located.

Pharmacologic support with high-energy phosphate preservation in the postischemic neonatal heart

Milrinone improves function in failing adult hearts. This study examined its effect on immature myocardium. Using an isolated working neonatal rabbit heart preparation, we measured myocardial function, high-energy compounds, and cyclic adenosine monophosphate. Hearts were subjected to 1 hour of normothermic ischemia, 10 minutes of reperfusion with Ringer's solution, and 30 minutes of reperfusion with either unaltered Ringer's, Ringer's with dobutamine (0.1 microgram/mL), or Ringer's with milrinone (1 microgram/mL). These hearts were compared with each other, with a control group continuously perfused for 70 minutes, and with a group of hearts that were made ischemic and reperfused for only 10 minutes. There was a progressive decline in adenosine triphosphate levels measured in hearts from the groups receiving 10 and 40 minutes of reperfusion with unaltered perfusate, and cardiac output fell to 82% +/- 4% of preischemic control in the latter group. When either dobutamine or milrinone was added to the reperfusion solution, postischemic myocardial function was restored completely, and the loss of adenosine triphosphate with reperfusion was halted. Cyclic adenosine monophosphate level was highest in ischemic/40-minute reperfused hearts, and there was no measurable increase in cyclic adenosine monophosphate level in the group of hearts receiving milrinone. The mechanism of preservation of high-energy stores with inotropic agents is not known but may involve potentiation of mitochondrial oxidative phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of selenium added to pulmonary preservation solutions in isolated guinea pig lungs

An experimental comparative study on isolated guinea pig lungs has been undertaken to determine the probable beneficial effects of adding selenium to pulmonary preservation solutions in lung ischemia. The isolated lungs (n = 10 in each group) previously being perfused by oxygenated Krebs-Henseleit solution were put in normothermic ischemic conditions just after the infusion of 30 ml of pulmonary preservation solution (Euro-Collins in the control group, Euro-Collins plus selenium 10(-3) mol in the experiment group). After 3 hours of normothermic ischemia the lungs were reperfused with the same buffer for 20 minutes. Pulmonary artery pressures, tissue malondialdehyde levels, and adenosine deaminase levels of the perfusate were measured before and after the ischemic period and also at the end of reperfusion. An electron microscopic analysis was performed on the lung tissues at the end of the experimental procedure. According to our data, the addition of selenium to pulmonary preservation solution showed a significant protective effect regarding both ischemic and reperfusion injury.

Effect of inflation on adenosine triphosphate catabolism and lactate production during normothermic lung ischemia

Although few biochemical data comparing adenosine triphosphate (ATP) catabolism or lactate production in isolated deflated versus inflated lung tissue are available, most transplant centers preserve their donor lungs inflated. We measured ATP level (using high-performance liquid chromatography), energy charge, and lactate level during 2 hours of normothermic ischemia in deflated lung tissue (n = 6), in lung tissue inflated with room air (n = 6), and in lung tissue inflated with 100% oxygen (n = 6). To determine the onset of anaerobic metabolism in lung issue inflated with 100% O 2, ATP and lactate levels were measured in another group (n = 6) during 8 hours of normothermic ischemia. Rabbit lungs were flushed in situ with a modified Krebs-Henseleit solution (60 mL/kg). They were isolated and immersed in 0.9% Nacl at 37 °C. In deflated lung tissue, ATP level (control value, 9.4 ± 0.58 μmol/g dry wt) decreased and lactate level (control value, 5.6 ± 1.16 μmol/g dry wt) increased after 15 minutes of ischemia (ATP, 5.2 ± 0.86 μmol/g dry wt; lactate, 13.3 ± 1.58 μmol/g dry wt). When the lung was stored inflated with room air, ATP breakdown and increase of lactate concentration only occurred after 90 minutes of normothermic ischemia (at 60 minutes: ATP, 8.0 ± 0.58 μmol/g dry wt; lactate, 6.3 ± 1.1 μmol/g dry wt). In lungs stored inflated with 100% O 2, ATP breakdown and lactate accumulation only occurred after 5 hours of normothermic ischemia (at 4 hours: ATP, 8.1 ± 0.74 μmol/g dry wt; lactate, 5.9 ± 1.28 μmol/g dry wt). These data suggest that the breakdown of ATP and the onset of anaerobic metabolism in lung tissue is related to the alveolar oxygen concentration during storage, and that in the isolated inflated lung, aerobic metabolism continues for 4 hours even when perfusion has stopped.

The effect of hypothermia on changes in isometric contractile function in skeletal muscle after tourniquet ischemia

The effect of hypothermia on changes in contractile function of skeletal muscle observed after an episode of tourniquet ischemia has been investigated. Male Wistar rats were subjected to 2 hours of unilateral hypothermic ( n = 33) or normothermic ( n = 39) pneumatic tourniquet ischemia of a hind limb. Isometric contractile function was measured bilaterally from the gastrocnemius muscles after 1, 7, 14, 28, or 42 days of recovery. Compared to muscle subjected to normothermic ischemia, muscle that underwent hypothermic ischemia demonstrated more twitch tension at 1 day postischemia, higher maximum tetanic tension at all time periods, including 6 weeks after ischemia, and greater muscle weight at 6 weeks. Rat gastrocnemius muscle function is much better 1 day to 6 weeks after 2 hours of hypothermic ischemia than after 2 hours of normothermic ischemia. The results thus document the benefit of hypothermia during tourniquet ischemia in preventing or minimizing the changes in isometric contractile function observed after normothermic ischemia.

Reduction of the extent of ischemic skeletal muscle necrosis by perfusion with oxygenated perfluorocarbon

Oxygenated perfluorocarbon emulsion has been shown to preserve feline cerebral function after ischemia. The postulated protective effects of perfluorocarbons include improvement of blood rheology and prevention of neutrophil adherence by nonchemical inhibition of surface receptors. In this study, we used a well-described gracilis muscle model to investigate whether oxygenated perfluorocarbon can minimize skeletal muscle necrosis by mitigating the degree of leuko-sequestration. In eight adult mongrel dogs, both gracilis muscles were weighed and then subjected to 6 hours of normothermic ischemia followed by 48 hours of normothermic reperfusion. However, one randomly selected side (experimental side) was infused with oxygen (O2) Fluosol-DA 20% (4.4 +/- 0.2 mL O2/100 mL) intra-arterially at 12 mL/min for 40 minutes immediately after ischemia. Muscle biopsy specimens were obtained before ischemia and after 1 hour and 48 hours of reperfusion to estimate myeloperoxidase (MPO) activity, a marker of neutrophil infiltration. After 48 hours, both gracilis muscles were harvested and weighed in all animals. Muscle necrosis was measured by serial transections, nitroblue tetrazolium staining, and computerized planimetry. The transmuscular oxygen tension (pO2) of the gracilis muscle on the experimental side increased from 2 to 4 mm Hg during ischemia to 315 +/- 50 mm Hg during O2 Fluosol-DA 20% infusion. The percentage of muscle necrosis on the control side was 48.08% +/- 8.46%, compared with 27.62% +/- 6.96% on the experimental side (p less than 0.001). MPO activity was significantly higher at 48 hours of reperfusion compared with pre-ischemic and 1-hour reperfusion values (5.46 +/- 1.52 U/mg tissue protein versus 0.06 +/- 0.01 U/mg tissue protein and 0.16 +/- 0.06 U/mg tissue protein, respectively, in the control group; 1.78 +/- 0.60 U/mg tissue protein versus 0.16 +/- 0.08 U/mg tissue protein and 0.27 +/- 0.10 U/mg tissue protein, respectively, in the experimental group, p less than 0.05). However, MPO activity at 48 hours of reperfusion in the experimental group was significantly lower than in the control group (p less than 0.05). There was no difference in the percentage of weight gain between the control and the experimental groups (38.31% +/- 9.36% and 28.34% +/- 7.35%, respectively, p greater than 0.05). These data show that perfluorocarbons minimize the extent of skeletal muscle necrosis in this canine model. Based on our data on MPO activity, we believe t hat the protective effect of perfluorocarbons is in part due to th e decreased leuko-sequestration in the muscle during the the periods of ischemia and reperfusion.(ABSTRACT TRUNCATED AT 400 WORDS)

Electrode-derived myocardial pH measurements reflect intracellular myocardial metabolism assessed by phosphorus 31-nuclear magnetic resonance spectroscopy during normothermic ischemia

To determine the ability of extracellular myocardial tissue pH measured with an intramural electrode to reflect myocardial intracellular metabolic status during normothermic ischemia, we studied 14 open-chest dogs with in vivo phosphorus 31-nuclear magnetic resonance spectroscopy during left anterior descending coronary artery occlusion (experimental group, group I, n = 7) or after a sham operation (control group, nonischemic, group II, n = 7). Phosphorus nuclear magnetic resonance spectra were acquired every 5 minutes at 4.7 tesla (256 averages, TR = 1000 msec, pulse width = 30 microseconds) with a 2 cm two-turn radiofrequency surface coil. Intracellular myocardial adenosine triphosphate peak area was normalized to an external phosphate standard. The change in adenosine triphosphate peak area was expressed as percent of baseline value. During 3 hours of normothermic ischemia the observed extracellular myocardial pH correlated with nuclear magnetic resonance-calculated myocardial pH in the ischemic dogs with an average r value of 0.94 (p less than 0.0001). During this same interval, the fall in extracellular myocardial pH correlated with the loss of adenosine triphosphate peak in each ischemic dog, with an average r value of 0.91 (p less than 0.0001). Thus extracellular myocardial pH, measured with an intramural electrode, correlated with nuclear magnetic resonance-derived myocardial pH and loss of myocyte adenosine triphosphate peak content and reflected the metabolic status of the myocyte during ischemia. These data validate the use of extracellular myocardial pH to assess the adequacy of myocardial preservation during aortic crossclamping for cardiac operations.

Studies of myocardial protection in the immature heart: V. Safety of prolonged aortic clamping with hypocalcemic glutamate/aspartate blood cardioplegia

This study tests the hypothesis that multidose, hypocalcemic aspartate/glutamate-enriched blood cardioplegia provides safe and effective protection during prolonged aortic clamping of immature hearts. Of 17 puppies (6 to 8 weeks of age, 3 to 5 kg) placed on vented cardiopulmonary bypass, five were subjected to 60 minutes of 37 degrees C global ischemia without cardioplegic protection and seven underwent 120 minutes of aortic clamping with 4 degrees C multidose aspartate/glutamate-enriched blood cardioplegia ([Ca++] = 0.2 mmol/L), preceded and followed by 37 degrees C blood cardioplegic induction and reperfusion. Five puppies underwent blood cardioplegic perfusion for 10 minutes without intervening ischemia to assess the effect of the cardioplegic solution and the delivery techniques. Left ventricular performance was assessed 30 minutes after bypass was discontinued (Starling function curves). Hearts were studied for high-energy phosphates and tissue amino acids. One hour of normothermic ischemia resulted in profound functional depression, with peak stroke work index only 43% of control (0.7 +/- 0.1 versus 1.7 +/- 0.2 gm x m/kg, p less than 0.05). There was 70% depletion of adenosine triphosphate (7.6 +/- 1 versus control 20.3 +/- 1 mumol/gm dry weight, p less than 0.05) and 75% glutamate loss (6.6 +/- 1 versus control 26.4 +/- 3 mumol/gm, p less than 0.05). In contrast, after 2 hours of aortic clamping with multidose blood cardioplegia preceded and followed by 37 degrees C blood cardioplegia, there was complete recovery of left ventricular function (peak stroke work index 1.6 +/- 0.2 gm x m/kg) and maintenance of adenosine triphosphates, glutamate, and aspartate levels at or above control levels adenosine triphosphate 18 +/- 2 mumol/gm, aspartate 21 +/- 1 versus control 2 mumol/gm, and glutamate 25.4 +/- 2 mumol/gm). Puppy hearts receiving blood cardioplegic perfusion without ischemia had complete recovery of control stroke work index. We conclude that methods of myocardial protection used in adults, with amino acid-enriched, reduced-calcium blood cardioplegia, can be applied safely to the neonatal heart and allow for complete functional and metabolic recovery after prolonged aortic clamping.

Critical Ischemia Times and Survival Patterns of Experimental Pig Flaps

Previous work on critical ischemia time suggested (1) a greater susceptibility of myocutaneous flaps over skin flaps to the ischemia reperfusion injury and (2) that duration of ischemia may affect the survival area of a flap. Using a pig model, 55 animals were operated on and the critical ischemia times and survival patterns of the buttock skin (n = 85) and latissimus dorsi myocutaneous (n = 88) island flaps were determined after being submitted to 0, 2, 4, 6, 8, 10, 12, 14, and 16 hours of normothermic ischemia. The average critical ischemia times (CIT50) were determined to be 9 and 10 hours for the buttock skin and latissimus dorsi myocutaneous flaps, respectively. Percentage of total area surviving (%TAS) in those flaps which did survive was adversely affected by increases in the ischemic interval in both flap models. A statistically significant decrease in percentage of total area surviving was found after 6 and 8 hours of ischemia for the buttock skin and latissimus dorsi myocutaneous flaps, respectively.

Critical Ischemia Times and Survival Patterns of Experimental Pig Flaps

Previous work on critical ischemia time suggested (1) a greater susceptibility of myocutaneous flaps over skin flaps to the ischemia reperfusion injury and (2) that duration of ischemia may affect the survival area of a flap. Using a pig model, 55 animals were operated on and the critical ischemia times and survival patterns of the buttock skin (n = 85) and latissimus dorsi myocutaneous (n = 88) island flaps were determined after being submitted to 0, 2, 4, 6, 8, 10, 12, 14, and 16 hours of normothermic ischemia. The average critical ischemia times (CIT50) were determined to be 9 and 10 hours for the buttock skin and latissimus dorsi myocutaneous flaps, respectively. Percentage of total area surviving (%TAS) in those flaps which did survive was adversely affected by increases in the ischemic interval in both flap models. A statistically significant decrease in percentage of total area surviving was found after 6 and 8 hours of ischemia for the buttock skin and latissimus dorsi myocutaneous flaps, respectively.

Exogenous magnesium chloride-adenosine triphosphate administration during reperfusion reduces the extent of necrosis in previously ischemic skeletal muscle

The lower extremity may be exposed to prolonged periods of ischemia, resulting in depletion of intracellular energy stores in the affected skeletal muscle. The role of adenine nucleotide reduction and failure of resynthesis on reperfusion in determining the extent of muscle necrosis was investigated in this study, in addition to the possible beneficial effects of the addition of exogenous adenosine triphosphate-magnesium chloride during early reperfusion. The isolated paired canine gracilis muscle model was used. After 4 hours of normothermic ischemia in group I, a perfusate Krebs-Henseleit solution plus the gradual reintroduction of oxygenated blood flow was compared to standard reperfusion. In group II, a similar infusion protocol was used, with the addition of 2 mmol/L adenosine triphosphate-magnesium choride and compared to normal reperfusion. Adenosine triphosphate-magnesium chloride resulted in the salvage of skeletal muscle, 57% ± 12% versus 44% ± 14% (p < 0.05, n = 6 pairs). Reperfusion with the solution alone increased the resulting necrosis (42% ± 13% vs 60% ± 20%, n = 6 pairs). Adenine nucleotide stores were not increased, but oxygen consumption was increased by magnesium chloride-adenosine triphosphate (p < 0.05, analysis of variance [ANOVA]). A clear relationship was demonstrated between the fall in energy stores, as measured by a change in energy charge potential from preischemia to end ischemia levels, and the extent of resulting necrosis (p < 0.01). In summary, the addition of 2 mmol/L to an infusion of Krebs-Henseleit solution during reperfusion results in significant salvage of skeletal muscle. The fall in intracellular energy stores as measured by change in energy charge potential can accurately predict the resulting extent of muscle necrosis and is not influenced by exogenous magnesium chloride-adenosine triphosphate.

The rate and distribution of muscle blood flow after prolonged ischemia

The magnitude and distribution of muscle blood flow in the lower extremity after relief of an acute arterial occlusion may influence the extent of the resulting necrosis. The object of this study was to document the distribution of blood flow in the resting state and after prolonged periods of complete ischemia, and to assess the relationship between the degree of reactive hyperemia and subsequent necrosis. The isolated bilateral canine gracilis muscle preparation that we have previously characterized was used for microsphere studies. Total blood flow was measured by means of timed venous collections, and the distribution of flow was determined by means of a multiple microsphere injection technique. Measurements of microsphere distribution and blood flow were made before ischemia and during the initial 48 minutes of reperfusion after both 4 and 5 hours of normothermic ischemia, which resulted in 46.7% ± 6% and 71.2% ± 7% necrosis, respectively. The muscle was harvested and sectioned transversely into six slices approximately 1.5 cm thick, and the extent of necrosis was quantified by means of nitroblue tetrazolium staining 48 hours after reperfusion. Blood flow distribution during the early reperfusion phase was determined in each muscle slice and in both the alive and dead portions of each slice by use of the microsphere injection technique. Preischemic blood flow was distributed homogeneously throughout the muscle and was 4.5 ± 0.8 ml/100 gm/min (mean ± SEM, n = 8). On reperfusion total flow was 6 to 10 times higher than it was before ischemia and was distributed predominantly to the middle slices (p < 0.05, n = 12). In both the 4- and 5-hour ischemia groups there was no correlation between blood flow in each slice and the extent of necrosis (p > 0.1). The degree of reactive hyperemia was greater after 4 hours of ischemia than after 5 hours (20.3 ± 2.5 ml/100 gm/min vs 12.5 ± 1.6 ml/100 gm/min, p < 0.05). On reperfusion, blood flow is not distributed homogeneously throughout the muscle and the extent of reactive hyperemia is inversely related to the length of ischemia. Hyperemic blood flow reaches the maximum rate in the center portions of the muscle belly closest to the inflow and does not seem to be related to the distribution of necrosis.

Preischemic Flap Washout and Its Effect on the No-Reflow Phenomenon

Preischemic perfusion washout with an acellular physiologic solution delays the no-reflow phenomenon and improves tissue survival in rat epigastric free flaps following 18 and 24 hours of normothermic ischemia. This implies that stagnating blood may be a causative agent in the no-reflow phenomenon. A possible mechanism for this is capillary endothelial damage secondary to the presence of formed blood cells or their products of hemolysis. Perfusion washout may improve ischemic tolerance by preventing this blood cell-induced endothelial damage and by the prevention of sludge and thrombus. Whether any of the metabolic components of the perfusate actively enhance ischemic tolerance cannot be definitively stated.

The effect of adenosine and allopurinol on the tolerance of the collapsed lung to warm ischemia.

The collapsed left lungs of dogs were subjected to 1 hour of normothermic ischemia in situ followed by immediate ligation of the contralateral pulmonary artery. Adenosine in a dose of 50 mg/kg prolonged the survival of the dogs significantly. In the survivors only transient changes in the chest x-ray were seen, and no changes in arterial oxygenation were observed. The pulmonary architecture was well preserved on histological studies 14 days after operation. Animals whose ischemic lungs were not protected by adenosine showed an immediate drop in arterial oxygenation and a massive infiltrate of the ischemic lung. Histological study of the lungs showed a complete breakdown of the capillary-alveolar barrier. Allopurinol alone was ineffective by itself and was not able to improve the survival achieved with adenosine further. We conclude that it is possible to prolong the tolerance of a deflated lung to normothermic ischemia by pretreatment with adenosine.