Modulation of lung reperfusion injury by nitric oxide: impact of inspired oxygen fraction.

BACKGROUND: Attempts to attenuate lung reperfusion injury by administration of inhaled nitric oxide have yielded conflicting results. We hypothesized that the inspired oxygen fraction may play an important role in determining the outcome of nitric oxide therapy. METHODS: Rat lungs were reperfused in a circuit incorporating a support animal either immediately after flushing (group A) or after 24-hr hypothermic storage (groups B-D). During the first 10 min of reperfusion, grafts were ventilated with 95% oxygen in groups A and B, 95% oxygen and 20 ppm nitric oxide in group C, and 20% oxygen and 20 ppm nitric oxide in group D. Ventilation during the subsequent 50 min of reperfusion was with 100% oxygen only, in all groups. RESULTS: Graft function in group B was poor compared to group A in terms of blood flow and pulmonary artery and peak airway pressures. In group C, although 5 out of 10 grafts functioned at control levels, the remainder performed poorly. Function in group D, on the other hand, was uniformly good. CONCLUSIONS: Inhaled nitric oxide can prevent lung reperfusion injury, but this effect may be compromised by concurrent ventilation with high oxygen concentrations.

Pulmonary graft preservation: a worldwide survey of current clinical practice.

BACKGROUND: Flush perfusion of pulmonary grafts with cold modified EuroCollins solution supplemented by prostaglandin treatment was introduced clinically 10 years ago. Primary graft failure remains a major cause of morbidity and death after lung transplantation. During the last decade, much experimental work has led to reports of alternative storage solutions, differing storage conditions, and pharmacologic interventions that improve pulmonary graft performance. It is unclear how these findings have influenced current clinical practice. METHODS: A worldwide survey of the 125 centers performing lung transplantation was conducted by questionnaire. RESULTS: One hundred twelve replies were received (90%). Most centers (n = 86) continue to use EuroCollins solution (77%), of whom 69% include prostaglandin therapy and 32% donor steroid treatment. University of Wisconsin solution (UW) is used by 15 centers (13.5%), of which 10 (67%) use prostaglandin and seven (47%) use donor steroids. Nine centers use Papworth solution and one uses donor core cooling. The volume of flush used varied widely, from 20 to 120 ml/kg, with median volumes of 60, 60, and 30 ml/kg in centers using EuroCollins, UW, and Papworth solutions, respectively. Two thirds of centers using EuroCollins solution store grafts at 0 degrees to 5 degrees C, and one third at 5 degrees to 10 degrees C. One center that uses EuroCollins solution stores grafts at 10 degrees to 15 degrees C. Centers using UW solution are evenly split at 0 degrees to 5 degrees C and 5 degrees to 10 degrees C. Most centers that use Papworth solution store grafts at 5 degrees to 10 degrees C. Only six centers use superoxide radical scavengers. The maximum ischemic period accepted by centers varies from 4 to 12 hours, with median periods of 8, 7, 6, and 6 hours for the UW, EuroCollins, Papworth, and donor core cooling centers, respectively. All but one of the UW centers (93%) expressed satisfaction with the quality of graft preservation achieved by UW solution. Only 58 of the 86 centers using EuroCollins solution (67%) were satisfied. Six of nine centers using Papworth solution were satisfied. CONCLUSIONS: There has been a trend toward the use of UW solution and a slightly warmer storage temperature. However, for most centers, graft storage techniques have changed little over the last decade.

Controlled reperfusion protects lung grafts during a transient early increase in permeability.

BACKGROUND: We have previously shown that an initial 10-minute period of low-pressure reperfusion prevents the lung graft dysfunction that follows physiologic-pressure reperfusion. Possible mechanisms were investigated in this study. METHODS: Rat lungs were reperfused ex vivo using a parabiotic animal after 0-hour (groups A through C) or 24-hour (groups D through G) storage. Reperfusion pressure was either physiologic (groups A through D) or reduced by 50% for a specified time (groups E through G). The duration of reperfusion was 5 minutes (groups A, D, and E), 10 minutes (groups B and F), or 30 minutes (groups C and G), at which time endothelial permeability was measured through iodine 125-labeled albumin leakage and neutrophil sequestration through tissue myeloperoxidase activity. RESULTS: Graft function in group D deteriorated rapidly, whereas groups E through G performed at control levels. Albumin leakage was significantly elevated in group D; with controlled reperfusion, it was elevated after 5 minutes (group E) but had returned to baseline at 10 minutes (group F) and 30 minutes (group G). Myeloperoxidase levels were not significantly different between groups. CONCLUSIONS: Endothelial permeability is transiently elevated in the early phase of lung graft reperfusion. Initial low-pressure reperfusion may be protective by preventing irreversible edema formation during this period.

Intramural blood flow of skeletal muscle ventricles functioning as aortic counterpulsators.

BACKGROUND: Skeletal muscle ventricles (SMVs) working as aortic counterpulsators have provided long-term left ventricular assistance under experimental conditions. However, gradual deterioration of SMV pump function and rupture have been observed, and this may be related to compromised intramural blood flow during synchronized counterpulsation under systemic working conditions. METHODS: Transformed, double-layered SMVs in 6 sheep were stimulated for 3-minute periods (5 V, 30 Hz, burst duration and delay from QRS both 40% of the cardiac cycle) to work as diastolic counterpulsators in the systemic circulation at a 1:2 (SMV:heart) and 1:1 ratio, and on a mock circulation with low-pressure loading conditions at a 1:2 ratio. Thoracodorsal artery blood flow was monitored by ultrasonic flow probe, and intramural blood flow distribution was investigated by fluorescent microspheres. Thoracodorsal venous lactate concentrations were measured before and after each period of stimulation. RESULTS: Thoracodorsal artery blood flow increased significantly (p < 0.001) after stimulation. The magnitude of augmentation (89%; 95% confidence interval, 36% to 163%) was similar for all working conditions studied. Reactive hyperemia was observed after most 1:1 regimens but was rare after 1:2 regimens. A significant (p < 0.05) 15% increase in serum lactate levels was present after 1:1 regimens only. All regimens of stimulation resulted in a significant increase (p < 0.01) in blood flow to sections in the outer wall of the SMV, but a significant increase (p < 0.05) in blood flow to sections in the inner wall was observed only under low loading conditions. CONCLUSIONS: Skeletal muscle ventricles subjected to 1:1 systemic counterpulsation regimens work under partly anaerobic conditions. High loading conditions may compromise SMV inner wall blood flow.

Attenuation of lung graft reperfusion injury by a nitric oxide donor.

OBJECTIVE: One of the primary features of ischemia-reperfusion injury is reduced production of protective autocoids, such as nitric oxide, by dysfunctional endothelium. Administration of a nitric oxide donor during reperfusion of lung grafts may therefore be beneficial through modulation of vascular tone and leukocyte and platelet function. METHODS: Rat lung grafts were flushed with University of Wisconsin solution and reperfused for 1 hour in an ex vivo model incorporating a support animal. Group I grafts (n = 6) were reperfused immediately after explantation, group II (n = 6) and III (n = 5) grafts after 24 hours of storage at 4 degrees C. In group III, glyceryl trinitrate, a nitric oxide donor, was administered during the first 10 minutes of reperfusion at a rate of 200 micrograms/min. In an additional group (n = 5), 200 micrograms/min hydralazine was administered instead, to assess the effect of vasodilation alone. RESULTS: Graft function in group II deteriorated compared with that in group I, with significant reduction of graft effluent oxygen tension and blood flow and elevation of pulmonary artery pressure, peak airway pressure, and wet/dry weight ratio. In contrast, in group III, glyceryl trinitrate treatment improved graft function to baseline levels in all these parameters. Administration of hydralazine, meanwhile, produced mixed results with only two out of five grafts functioning at control levels. CONCLUSIONS: In this model, administration of glyceryl trinitrate to supplement the nitric oxide pathway in the early phase of reperfusion has a sustained beneficial effect on lung graft function after 24-hour hypothermic storage, probably through mechanisms beyond vasodilation alone.

Low-dose nitric oxide inhalation during initial reperfusion enhances rat lung graft function.

BACKGROUND: In ischemia-reperfusion injury, the production of nitric oxide by dysfunctional endothelium falls rapidly within minutes of the onset of reperfusion. Replenishment during this critical early period using inhaled nitric oxide may benefit lung grafts through modulation of vascular tone, endothelial permeability, neutrophil and platelet function, and availability of reactive oxygen species. METHODS: Rat lung grafts were flushed with 60 mL/kg cold University of Wisconsin solution and were reperfused either immediately (group I, n = 5) or after 24-hour 4 degrees C storage (groups II and III, n = 5 each), for 60 minutes in an ex vivo model incorporating a support animal. Graft ventilation was with room air. In group III, 20 parts per million inhaled nitric oxide was added during the initial 10 minutes of reperfusion, whereas in groups I and II, equivalent flows of nitrogen were added to standardize oxygen concentration. RESULTS: Compared with group I, graft function in group II was poor, with reductions in oxygenation and blood flow and elevations of mean pulmonary artery pressure, peak airway pressure, and wet to dry weight ratio. In contrast, during nitric oxide inhalation in group III, graft function improved to control levels. This improvement was subsequently sustained throughout the reperfusion period. CONCLUSIONS: Low-dose inhaled nitric oxide administration in the early phase of reperfusion of stored lung grafts can yield sustained improvement in function. There may be a role for inhaled nitric oxide in the prevention of reperfusion injury in transplanted lungs.

Relative importance of prostaglandin/cyclic adenosine monophosphate and nitric oxide/cyclic guanosine monophosphate pathways in lung preservation.

BACKGROUND: Modulation of vascular tone and platelet and neutrophil function through the prostaglandin/cyclic adenosine monophosphate or nitric oxide/cyclic guanosine monophosphate pathway can benefit lung graft function. The relative importance of these pathways is unclear. METHODS: Rat lung grafts (5 per group) were studied in an ex vivo reperfusion model. Group I grafts were pretreated with prostacyclin (20 ng.kg-1.min-1), flushed with cold Euro-Collins solution containing prostacyclin (200 micrograms/L), and reperfused immediately for 1 hour. Group II grafts were similarly procured but were stored at 4 degrees C for 6 hours before reperfusion. In group III, no prostacyclin therapy was used; instead, the nitric oxide donor glyceryl trinitrate (0.1 mg/mL) was added to the flush/storage solution, and the grafts were stored for 6 hours. RESULTS: Group II grafts performed poorly compared with those in group I, with substantial deterioration of oxygenation and blood flow and elevation of pulmonary artery pressure, peak airway pressure, and wet to dry weight ratio. In contrast, graft function in group III was similar to that in controls. CONCLUSIONS: Lung graft integrity after storage in Euro-Collins solution was better preserved by glyceryl trinitrate than by prostacyclin in this model.

Critical importance of the first 10 minutes of lung graft reperfusion after hypothermic storage.

BACKGROUND: We have shown previously that lung graft function can be improved by achieving reperfusion with stepwise increments of perfusion pressure over 60 minutes. This study aimed to establish whether similar benefit could be achieved with a shorter, simpler protocol and different storage conditions. METHODS: Rat lungs were flushed with University of Wisconsin or modified Euro-Collins solution and reperfused for 1 hour with blood from a support animal. Grafts were reperfused immediately or after storage at 4 degrees C for 24 hours (University of Wisconsin solution) or 6 hours (Euro-Collins solution). Stored-graft reperfusion was initiated with a 0-, 5-, or 10-minute period during which reperfusion pressure was reduced by 50%. RESULTS: Stored grafts receiving 0 to 5 minutes of initial low-pressure reperfusion performed poorly, with reduced oxygenation and blood flow and elevated pulmonary artery pressure, airway pressure, and wet/dry weight ratio. In contrast, 10 minutes of initial 50%-pressure reperfusion yielded function comparable with that in controls with both storage conditions. CONCLUSIONS: An initial 10-minute period of 50%-pressure reperfusion improves the function of stored rat lung grafts, whereas 5 minutes is insufficient.

Effects of cardiomyoplasty on cardiac growth in rats.

BACKGROUND AND AIM OF THE STUDY: Cardiomyoplasty (CMP) has been proposed as a treatment for pediatric patients, but restriction of cardiac growth by the muscle wrap is a potential source of concern. This possibility was investigated in an immature animal model. METHODS: Six-week-old rats (body weight 203.8 +/- 5.4 g, mean +/- SEM) underwent either left thoracotomy with CMP (group I, n = 7), or thoracotomy without CMP (group II, n = 8). A third group (group III, n = 7) served as untreated controls. Final measurements were made 20 weeks later after body weights had reached a plateau. RESULTS: Preoperative body weights were not significantly different between the groups. At elective sacrifice, the body weights of animals that underwent surgery did not differ significantly (group I, 558.0 +/- 21.5 g and group II, 617.3 +/- 20.3 g), but were significantly less than those of control animals (727.6 +/- 13.3 g, p < 0.001 and p < 0.01, respectively). Cardiac ventricular weights in the CMP group were significantly less than those of control animals (group I, 1.21 +/- 0.06 g; group III 1.45 +/- 0.04 g; p < 0.01), but were not statistically different from those of the sham thoracotomy group (group II, 1.36 +/- 0.05 g). Mean left ventricular end-diastolic volumes were similar in all groups (group I, 0.67 +/- 0.07 mL; group II, 0.66 +/- 0.07 mL; and group III, 0.69 +/- 0.10 mL; p = ns). CONCLUSIONS: A major surgical procedure impairs growth in juvenile rats. no evidence emerged from this study for additional restriction of cardiac development due to cardiac wrapping. However, studies that include stimulated muscle wraps are needed before CMP should be considered for the pediatric age group.

Controlled pressure reperfusion of rat pulmonary grafts yields improved function after twenty-four-hours' cold storage in University of Wisconsin solution.

BACKGROUND: Pulmonary graft recipients commonly have a degree of pulmonary hypertension. Immediate reperfusion of stored pulmonary grafts at supraphysiologic or even physiologic pressures may be detrimental to subsequent function. We wished to test the hypothesis that initial reperfusion of pulmonary grafts at low pressures may be beneficial. METHODS: We used an isolated, ventilated rat lung model, perfused by an extracorporeal veno-venous circuit from a support animal. Three groups of donor lungs (n = 5 each) were flushed with cold University of Wisconsin solution. Group I was reperfused immediately at physiologic pressure to provide control values. Group II grafts were stored at 4 degrees C for 24 hours and reperfused at physiologic pressure. Group III grafts were also stored at 4 degrees C for 24 hours but reperfused according to a protocol of reduced pressure initially, with increments every 15 minutes up to physiologic levels by 60 minutes. Grafts and support animals were ventilated with room air. Graft function was assessed over a 2-hour period with regard to oxygenation, vascular resistance, peak airway pressure, and the wet/dry weight ratio. RESULTS: Grafts in group II functioned poorly at 2 hours compared with control values: group II: oxygen tension 68 +/- 4 mm Hg; pulmonary vascular resistance 2488 +/- 675 x 10(3) dyne.sec/cm5; peak airway pressure 32 +/- 1 mm Hg wet/dry wright ratio 9.1 +/- Group I: oxygen tension 136 +/- 2 mm Hg; pulmonary vascular resistance 120 +/- 3 x 10(3) dyne.sec/cm5; peak airway pressure 13 +/- 1 mm Hg and wet/dry weight ratio 3.6 +/- 0.3; p < 0.001 all parameters except pulmonary vascular resistance: p < 0.05. In contrast, grafts undergoing controlled pressure reperfusion (group III) achieved function comparable with baseline values at 2 hours: oxygen tension 137 +/- 3 mm Hg; pulmonary vascular resistance 132 +/- 7 x 10(3) dyne. sec/cm5; peak airway pressure 13 +/- 1 mm Hg; wet/dry weight ratio 4.1 +/- 0.3 (p = Not significant). CONCLUSIONS: The pressure at which pulmonary grafts are initially reperfused appears to be critical to their subsequent integrity. A protocol of controlled reperfusion may reduce reperfusion injury and improve graft function in clinical practice.

Latissimus dorsi muscle blood flow during synchronized contraction: implications for cardiomyoplasty.

BACKGROUND: Damage in latissimus dorsi muscle flaps has been reported after clinical and experimental cardiomyoplasty, and an ischemic origin has been suggested. METHOD: In situ, preconditioned latissimus dorsi muscles in 5 sheep were stimulated in either 1:1 (muscle: heart) or 1:2 synchrony with the systolic phase of the cardiac cycle, using a burst duration of either 21% or 35% of the cycle. Thoracodorsal artery blood flow and thoracodorsal venous lactate concentrations were measured before and immediately after a 3-minute period of stimulation. RESULTS: The exercise-induced augmentation of thoracodorsal artery blood flow was significantly (p < 0.05) less with a 1:2 regimen than a 1:1 regimen, for both a 21% (88%; 95% confidence interval [CI], 55.6% to 127.3% versus 138.9%; CI, 97.6% to 188.8%) and 35% burst duration (123.2%; CI, 84.7% to 169.9% versus 167.0; CI, 120.8% to 222.6%). After cessation of stimulation, reactive hyperaemia was observed in 3 of 5 animals with 1:1 21% burst stimulation, and in 5 of 5 animals with a 35% burst duration, but was not seen after 1:2 regimens. A significant (p < 0.01) increase in thoracodorsal venous lactate levels was present after 1:1 35% burst stimulation (34.9%; CI, 9.9% to 65.6%), but lactate levels tended to fall when a 1:2 ratio was used (15.9%; CI, -3.2% to 31.5%; p < 0.1). CONCLUSIONS: One-to-one stimulation regimens may be detrimental to latissimus dorsi blood flow, and an adaptive, rather than fixed, burst duration may be preferable. These findings have important implications for the cardiomyoplasty procedure.