The effects of hemodilution with Hemolink upon hemodynamics and blood flow distribution in anesthetized dogs.

Hemoglobin based oxygen-carrying solutions (HBOCs) as hemoglobin replacement therapeutics are being tested for clinical use. Some of these products are associated with elevations in both systemic and pulmonary vascular resistances but their effect on the distribution of blood flow to major organs in larger animals have not been extensively described. We tested two formulations of o-raffinose cross-linked human hemoglobin, Hemolink (frozen-Hemolink-1 and refrigerated Hemolink-2) and compared them to Pentaspan, a colloid volume expander in extensive clinical use. Cardiovascular measurements and the distribution of blood flow (radionuclide-labeled microspheres) to the major organs were determined in Beagle dogs (n = 5 per group). After baseline measurements, either Hemolink-1, Hemolink-2, or Pentaspan was exchange transfused in an isovolemic manner (resulting in hematocrit reduction to approximately 20-25%); measurements were made 30, 60, 120 and 180 min post-exchange. There was no significant difference in cardiac output, mean arterial pressures and systemic or pulmonary vascular resistances after exchange in any of the three groups. Myocardial blood flow increased in all three groups post-exchange but the increase was more sustained in the Hemolink groups. Endocardial/epicardial flow ratios were also maintained after exchange in all groups. Thus, Hemolink is ideally suited for volume replacement when used in conjunction with acute normovolemic hemodilution because under these circumstances, the adverse hemodynamic effects are alleviated while extra hemoglobin is added to the blood.

The effects of hemodilution with Hemolink upon hemodynamics and blood flow distribution in anesthetized dogs.

Hemoglobin based oxygen-carrying solutions (HBOCs) as hemoglobin replacement therapeutics are being tested for clinical use. Some of these products are associated with elevations in both systemic and pulmonary vascular resistances but their effect on the distribution of blood flow to major organs in larger animals have not been extensively described. We tested two formulations of o-raffinose cross-linked human hemoglobin, Hemolink (frozen Hemolink-1 and refrigerated Hemolink-2) and compared them to Pentaspan, a colloid volume expander in extensive clinical use. Cardiovascular measurements and the distribution of blood flow (radionuclide-labeled microspheres) to the major organs were determined in Beagle dogs (n=5 per group). After baseline measurements, either Hemolink-1, or Hemolink-2, or Pentaspan was exchange transfused in an isovolemic manner (resulting in hematocrit reduction to approximately 20-25%); measurements were made 30, 60, 120 and 180 min post-exchange. There was no significant difference in cardiac output, mean arterial pressures and systemic or pulmonary vascular resistance after exchange in any of the three groups. Myocardial blood flow increased in all three groups post-exchange but the increase was more sustained in the Hemolink groups. Endocardial/epicardial flow ratios were also maintained after exchange in all groups. Thus, Hemolink is ideally suited for volume replacement when used in conjunction with acute normovolemic hemodilution because under these circumstances, the adverse hemodynamic effects are alleviated while extra hemoglobin is added to the blood.

A phase I study of oxidized raffinose cross-linked human hemoglobin.

OBJECTIVE: To evaluate the safety of oxidized-raffinose cross-linked human hemoglobin, Hemolink, in normal healthy volunteers. DESIGN: Randomized, placebo-controlled, double-blind study. SETTING: Clinical research facility of a contract research organization. PATIENTS: Forty-two healthy adult male volunteers of which 33 received Hemolink. INTERVENTIONS: Oxidized-raffinose cross-linked and polymerized hemoglobin as a 10% (w/v) solution, in doses of 0.025-0.6 g/kg or an equivalent volume of lactated Ringer's solution, was infused intravenously on day 1, and subjects were monitored for 3 days in the clinical facility with < or =6 wks follow-up. Major organ function was assessed pre- and postinfusion, by hemodynamic, electrocardiographic, pulmonary function, and clinical chemistry measurements. MEASUREMENTS AND MAIN RESULTS: Doses of 1.7-42 g of hemoglobin were administered with no serious adverse events noted. Abdominal pain of moderate to severe intensity was seen in some subjects at doses >0.4 g/kg and was alleviated with smooth muscle relaxants. There was a dose-dependent increase in mean arterial pressure with a plateau of approximately 14% above baseline at 0.1 g/kg. There was a concomitant reduction in heart rate, with no electrocardiographic abnormalities found. Respiratory function was not affected. There was a dose-dependent increase in serum bilirubin with values above the upper limit of normal at doses of > or =0.4 g/kg. Small increases in aspartate aminotransferase and alanine aminotransferase were noted in some patients, whereas alkaline phosphatase and gamma-glutamyltransferase remained in the normal range. Serum amylase concentrations were normal in 31 of 33 patients receiving Hemolink, whereas lipase was within the normal range in 21 of 33 patients. LDH was increased in a dose-dependent fashion. Two patients had increased creatine kinase concentrations, with a normal creatine kinase-MB mass fraction. All hematologic variables were within the normal range. The half-life of the oligomeric (>64 kDa) fraction of Hemolink was 18-20 hrs. CONCLUSION: Oxidized-raffinose cross-linked hemoglobin, Hemolink, at doses < or =0.6 g/kg were well tolerated in healthy volunteers with no evidence of organ dysfunction. Further investigation of its potential use in surgical and trauma settings appears warranted.

Haemodynamic response following a 10% topload infusion of HemolinkTM in conscious, anaesthetized and treated spontaneously hypertensive rats.

HemolinkTM (HLK), a haemoglobin-based oxygen carrier (HBOC), is currently undergoing Phase II/III clinical trials in surgical patients. It causes some blood pressure rise in animal and human tests. This study was designed to investigate the systemic haemodynamic response to HemolinkTM in spontaneously hypertensive rats (SHR rats). Conscious or anaesthetized SHR rats and control Wistar Kyoto rats (WKY rats) received either HemolinkTM or homologous plasma as a 10% topload infusion. Some awake animals were pretreated with nifedipine and followed by HLK infusion. In the conscious animal study, HLK induced a greater pressure rise and less bradycardia in SHR rats than in WKY rats. In the anaesthetized animal experiment, HLK-induced pressure rise and bradycardia were similar in both strains and less pronounced than in the conscious animals. In the nifedipine pretreated SHR rats, HLK-induced pressure rise was significantly smaller than that observed in nontreated SHR rats and was not different from that of nontreated WKY rats. The HLK-induced bradycardia was significantly smaller in nifedipine-treated animals than in the nontreated SHR or WKY rats. This study suggests that the pressor effect of HemolinkTM can be attenuated in hypertensive animals with general anaesthesia or treatment with antihypertensive agents.

Systemic responses to SFHS-infusion in hemorrhaged dogs.

Anesthetized mongrel (weight range: 16-27 Kg) dogs were prepared for monitoring hemodynamics, blood flow distribution, plasma colloid osmotic pressure and renal functional parameters at various intervals. Removal of 35 ml/Kg blood resulted in marked drop and only partial spontaneous recovery in systemic and pulmonary arterial pressures, cardiac output and organ blood flows (> 50% flow-decrements occurred in kidney, spleen, heart, gut and pancreas); plasma colloid osmotic pressure as well as urine output and creatinine clearance also fell. Group I (n = 6) of dogs was transfused after 45 minutes of hypovolemia with their own anticoagulated blood, while Group II (n = 6) received an equal volume of unmodified 6% stromafree hemoglobin solution (SFHS). Comparison of the two groups' responses to resuscitation yielded some differences. There was a significant overshoot (30 mmHg) in systemic arterial blood pressure accompanied by bradycardia in Group II only. Cardiac output recovered in both groups but was less well sustained in Group II. Cerebral blood flow rose higher and hepatic arterial flow-increment was less in Group II than in Group I; the responses to resuscitation in the other organs were comparable. Colloid osmotic pressure decreased in Group I whereas it rose immediately after resuscitation in Group II, declining thereafter with a converging trend and 30 minutes thereafter the differences were not significant between the groups. Urine excretion and creatinine clearance recovered to comparable extents in both groups, but N-acetyl-beta-D-glucosaminidase (N.A.G.) excretion rose over 10-fold higher in Group II than in Group I. These experiments have defined the response of bled animals to resuscitation with unmodified, unpurified SFHS, when compared to resuscitation with whole blood, showing a less well sustained but adequate hemodynamic and renal functional recovery while revealing indications of early renal tubular cellular injury, providing baseline comparison for testing highly purified and modified hemoglobin solutions.

Oxyradical generation after resuscitation of hemorrhagic shock with blood or stroma-free hemoglobin solution.

Hypovolemic states are characterized by inadequate tissue perfusion; when this state is reversed, the reintroduction of oxygen is accompanied by the excess generation of oxyradicals and these, in turn, may cause "reperfusion injury" in susceptible tissues. When hemoglobin solution is used to resuscitate the hypovolemic state, the generation of oxyradicals may be enhanced by catalytic means. The generation of oxyradicals was estimated in dogs subjected to the acute removal of 35 ml/Kg blood, and resuscitated 45 mins thereafter with an equal volume of either autologous blood (Group I, n = 6) or 6% stromafree hemoglobin solution (S.F.H.S.) (Group II, n = 6). Hepatic and pancreatic enzymes were measured in blood drawn at intervals. The hypovolemic state was characterized by profound hypotension which was reversed by resuscitation. Oxyradical generation in arterial blood samples, drawn at various times, was estimated by the generation of oxidation products (2,3- and 2,5-dihydroxybenzoic acid) of exogenously administered sodium salicylate, determined by HPLC in plasma samples extracted with diethyl ether. Salicylate oxidation products rose significantly above the baseline value in Group I dogs, whereas they rose 5-6-fold higher than the baseline values in those of Group II. The actual values attained and the increments were significantly (p < .05) greater in Group II than in Group I. In the group resuscitated with S.F.H.S., catalytically active iron concentration in plasma also rose 10-12-fold higher and was associated with spuriously elevated levels of gamma-glutamyl transferase due to interference with the assay. These findings are consistent with the hypothesis that blood-resuscitation of hypovolemic shock is accompanied by oxyradical generation of a modest degree; in contrast, S.F.H.S.-resuscitation introduces catalytically active iron and is accompanied by oxyradical generation of a significantly greater degree.

A convenient method for the determination of the solubility of hemoglobin and modified hemoglobins.

The removal of a single charged group can drastically alter the solubility of hemoglobin. Alterations in hemoglobin structure to make it of potential use as a blood substitute must produce derivatives which are sufficiently soluble to allow adequate oxygen delivery. We have developed a convenient method for examining modified hemoglobins. How the polymerization of Hemoglobin S is perturbed in the presence of modified hemoglobins is determined. To measure Hemoglobin S polymerization, a rapid temperature jump from 0 degree and a nitrogen atmosphere [1] are not required. In pH 7.4 phosphate buffers at concentrations greater than 2M containing sodium dithionite, dilute solutions (less than 1 mg/ml) of hemoglobin S aggregate at 30 degrees, or higher, after a delay time (minutes) which depends on the hemoglobin concentration. Light scattering can be used to quantify the extent of polymerization. Chemical modifications of Hemoglobin A can result in altered perturbation of Hemoglobin S polymerization as determined by this method. Modification of hemoglobin to provide suitable oxygen binding characteristics and crosslinking of subunits is a required preliminary to use of hemoglobin as an acellular blood substitute. These modifications often involve the elimination of charged groups from hemoglobin. Information on whether such modifications may have undesirable consequences with respect to solubility properties can be examined using the method described.

Central hemodynamics and blood flow distribution during infusion of perflubron emulsion or its vehicle: effects in anesthetized dogs.

Mongrel dogs were anesthetized and prepared for hemodynamic monitoring and the measurement of blood flow distribution using radionuclide-labelled microspheres (15 +/- 2 microns). Four dogs were infused with a perflubron emulsion (E) (90% w/v perflubron containing egg yolk phospholipid as a stabilizer) and five dogs were infused with the vehicle (V) (same composition without the perfluorocarbon). Both infusions were given at the dose of 3 ml/Kg over a 30-minute period. Measurements of blood pressures and cardiac output were made before, at 12 minutes of the infusion and at 5, 30 and 60 minutes post-infusion. Blood flow distribution was determined before, at the 15th minute of the infusion and at 2 and 60 minutes post-infusion. One dog infused with V exhibited a hypotensive reaction and urticaria; this was excluded from the group statistics. Neither group showed statistically significant hemodynamic changes during or after the infusion, although both E and V groups showed transient elevation of the stroke volume. Blood flows were raised consistently to the heart and renal cortex and transiently to some skeletal muscles by E treatment.

Perfluorocarbon-based red blood cell substitutes.

Since our review 5 years ago, a new generation of PFC emulsion has been developed and is undergoing extensive testing. This new generation is the result of the application of physicochemical principles, applied to both the choice of the PFC itself and the emulsifier, as well as advances in emulsion-producing technology. The efficacy of PFCs in general for oxygen transporting capability has been fully recognized, as exemplified by the limited license issued to Fluosol. The latter also represents the recognition of the relative absence of major toxicity of PFCs in general. The development of new products owes much to the lessons learned during the past 20 years and to advances made in the physical chemistry of PFCs. These advances now permit the rational selection or design of the most appropriate PFC and the design of emulsifiers best suited for the purpose. Perflubron represents a clear advance over the Fluosol-DA-type formulation. It is only one but the most advanced of the second-generation products. At least three other commercial entities (Hema-Gen/PFC, Green Cross, Adamantech) are also developing products based on the above principles. Five years ago we concluded that, in spite of the enormous complexity of PFC emulsions as large volume parenterals, they have shown remarkable biocompatibility. The advances in the past 5 years have confirmed this conclusion. The advances occurring during the past 5 years show that the application of the proper technology can lead to product improvement, and that PFC preparations with significant transfusional and nontransfusional potential are, in fact, feasible. It remains to be seen whether high PFC-content emulsion can be successfully deployed in initial, prehospital resuscitation situations. The high PFC content will reduce the absolute requirement for the maintenance of FIO2 > 0.8 in the case of Fluosol-DA for optimal efficacy. The second-generation products also seem to lend themselves to intraoperative use, because they can be removed from the blood postoperatively by plasmapheresislike methods. They are also suitable in combination with autologous blood donation/transfusion. All of these potential applications are in various stages of exploration and, if found to be efficacious, will likely conserve the supply of whole blood and blood components. The nontransfusional applications, particularly those in diagnostic imaging, seem to show substantial promise. Because they involve smaller doses than transfusional applications, they may enter clinical use earlier. The applications in radiation and chemotherapy of malignant diseases represent an intermediate position between the transfusional and nontransfusional uses.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of Ca++ on the preservation of myocardial energy and function with University of Wisconsin solution. A 31P nuclear magnetic resonance study of isolated blood perfused Langendorff pig hearts.

We have studied the effects of adding 0.5 mmol/L CaCl2 to University of Wisconsin solution (0.08 mmol/L free Ca++) on hypothermic heart preservation. Isolated pig hearts were subjected to 8 hours of preservation at 12 degrees C; eight hearts were arrested with Ca++ free University of Wisconsin solution, and seven hearts were arrested with Ca(++)-containing University of Wisconsin solution. The recovery of contractile function was evaluated by measuring isovolumic ventricular pressure development. 31P nuclear magnetic resonance spectroscopy was used to monitor the changes in high-energy phosphates. Compared to the hearts arrested with the Ca(++)-free University of Wisconsin solution, the heart arrested with the Ca(++)-containing University of Wisconsin solution showed significantly improved (p < 0.001) contractile functional recovery. No "stone heart" or loss of high-energy phosphates was observed on reperfusion. The hearts showed an increase in diastolic pressure during infusion of the Ca(++)-containing University of Wisconsin solution, however, to show the relationship between the addition of calcium and the increase in diastolic pressure, a second protocol was performed. A 30-minute period of ischemia was induced in thirteen hearts that were arrested at 12 degrees C with either Ca(++)-containing University of Wisconsin solution (n = 8) or Ca(++)-free University of Wisconsin solution (n = 5). Diastolic pressure was monitored during ischemia while ventricular volume was maintained constant with a balloon. The hearts arrested with the Ca(++)-containing University of Wisconsin solution showed a mean rise of 5 mm Hg in diastolic pressure and a rapid decline of phosphocreatine (p < 0.001). Our results suggest that, although 0.08 mmol/L free Ca++ improves functional recovery after 8 hours of heart preservation with University of Wisconsin solution at 12 degrees C, it can increase diastolic pressure during ischemia and accelerate breakdown of the high-energy phosphate stores in the myocardium, suggesting that use of University of Wisconsin solution containing 0.5 mmol/L CaCl2 may result in a significant increase in the intracellular calcium level.

Time course of myocardial bloodflow changes during healing of myocardial infarct in pigs.

OBJECTIVE: To define the time course of changes in bloodflow and microsphere content at intervals between one and 28 days after surgical ligation of the circumflex coronary artery. SUBJECTS AND METHODS: After the ligation, pigs were assigned to six groups; all pigs in a group were reanesthetized at either one, three, seven, 14, 21 or 28 days post ligation to determine myocardial bloodflow distribution using radionuclide-labelled (15 +/- 2 microns) microspheres. RESULTS: Bloodflow to the infarct zone, 10 mins post ligation, was 7.3 +/- 1.4% of the normal flow. At one and three days post occlusion, infarct bloodflow was about 50% of the 'normal', declining after day 7 to between 20 and 25%. Bloodflow in the noninfarct zone was significantly elevated during the initial 14 days, declining thereafter to within the normal range. Microspheres in the infarct zone injected prior to the occlusion became concentrated and were diluted in the noninfarct zone; the ratio of infarct:noninfarct microsphere content rose progressively, reaching a 2.5-fold rise by day 28. CONCLUSIONS: The initial stages of infarct healing are associated with a marked rise in bloodflow with a subsequent fall. A more prolonged augmentation of flow is evident in the noninfarct zone. Microspheres are useful in estimating the relative magnitude of changes in the myocardium accompanying the healing (shrinkage) of the infarct and hypertrophy occurring in the noninfarct zone after a coronary occlusion.

The effect of magnesium added to secondary cardioplegia on postischemic myocardial metabolism and contractile function--a 31P NMR spectroscopy and functional study in the isolated pig heart.

This study investigated whether increasing the magnesium concentration during secondary cardioplegia improves postischemic myocardial recovery. Twenty-four isolated pig hearts were divided into four groups. All hearts were initially subjected to control perfusion with modified Krebs-Henseleit solution for 30 min, followed by a single infusion of St. Thomas' solution #2. The hearts were then maintained without perfusion at 12 degrees C for 4 h. Following this hypothermic preservation, the hearts in group I were reperfused with modified Krebs-Henseleit solution for 50 min, while hearts in group II and III were reperfused with a secondary cardioplegic solution containing 16 or 0 mmol/L magnesium, respectively, for 20 min followed by 30 min of perfusion with modified Krebs-Henseleit solution. In group IV, the hearts were initially reperfused with Krebs-Henseleit solution containing 16 mmol/L potassium for 20 min, followed by 30 min of reperfusion with modified Krebs-Henseleit solution. The changes in high-energy phosphates and intracellular pH were monitored throughout the experiments using 31P nuclear magnetic resonance (NMR) spectroscopy. Heart rate, left-ventricular systolic developed pressure, and rates of pressure increase and decrease were measured during control perfusion and reperfusion to calculate the percent contractile functional recovery. Needle biopsies for measurement of energy metabolites with high performance liquid chromatography were performed at the end of preservation and reperfusion to confirm the NMR measurements. All six hearts in group I showed significantly less recovery of contractile function during reperfusion when compared to the hearts in groups II, III, IV (p less than 0.05). There was no difference in either recovery of metabolism or mechanical function among the latter three groups of hearts. None of hearts in groups II, III, and IV showed ventricular fibrillation, which occurred in all six hearts of group I upon reperfusion. The results suggest that a short period of re-arrest perfusion following ischemia ("secondary cardioplegia") improves postischemic contractile functional recovery and prevents reperfusion-induced ventricular fibrillation. Increased magnesium concentration in the secondary cardioplegia did not provide additional benefit to the ischemic myocardium, possibly due to the low permeability of the sarcolemmal membrane to magnesium.

Studies on blood substitutes based on hemoglobin and perfluorocarbon.

Unmodified, and to a lesser extent, modified stroma-free hemoglobin preparations have been reported to exhibit coronary and renal vasoconstrictor activity in isolated perfused hearts and kidneys. The physiological significance in vivo of such ex vivo demonstrated vasoconstriction has not yet been established. We have conducted a number of in vivo dog experiments designed to elucidate (a) whether free hemoglobin in the plasma phase contributes to diffusive oxygen supply to the tissues and (b) whether excessive vasoconstriction results in functional impairment. Our findings indicate that (a) the infusion of unmodified SFHS does not cause a significant disturbance of central hemodynamics, although it causes an elevation of the arterial blood pressure; the latter is accompanied by vasoconstriction in the skeletal muscle vascular bed and in the renal cortex; (b) there is no significant improvement of diffusive oxygen supply to the tissue at rest; and (c) that glutaraldehyde cross-linked SFHS administered to hypotensive dogs causes a brief further aggravation of hypotension as well as renal vasoconstriction accompanied by renal functional impairment. The findings suggest that coronary autoregulatory mechanisms in vivo can override the vasoconstrictor potency demonstrated in vitro, but the renal effects of SFHS containing unmodified hemoglobin can give rise to significant concern.

Resuscitation of bled dogs with pyridoxalated-polymerized hemoglobin solution.

We bled 25% of estimated total blood volume, then infused pyridoxalated polymerized human stroma-free hemoglobin solution (PP-SFH) (10 g/dl) to dogs under anesthesia in a volume equal to the blood removed. Central hemodynamics, blood flow distribution to organs, and renal function were studied up to 2-3 hours following the infusion. Mean arterial pressure was reduced from 120 +/- 3 to 86 +/- 7 mmHg at the end of the 30-minute hypovolumic period and the cardiac output was reduced by 27%. Immediately following the PP-SFH infusion we observed a further fall in blood pressure (43%) caused by a fall in cardiac output which lasted for 10 minutes. Blood pressure was restored gradually with the continuation of the infusion and the cardiac output was restored and maintained well. During the hypovolumic period, blood flow to the heart, renal cortex, and liver were reduced, whereas normal flow to the renal medulla and brain were maintained. After the resuscitation, blood flow to the heart, brain, liver, and renal medulla significantly exceeded the normal range, but remained subnormal in the renal cortex. Glomerular filtration rate (GFR), urine flow, and electrolyte excretion were all reduced during the hypovolumic period and were not restored to the pre-bleed levels after the infusion.

Systemic hemodynamic and renal effects of unmodified human SFHS in dogs.

Isovolumic exchange transfusion (25% of total estimated blood volume) was carried out in the anesthetized dogs using 9 g/dl of unmodified human stroma-free hemoglobin solution (SFHS). The objective was to determine the systemic hemodynamic, blood distribution and renal effects of SFHS over a 2-3 hour period post-exchange. At 30 minutes after the exchange, blood pressure rose from 114 +/- 117 to 133 +/- 22 mmHg, but this rise was not sustained thereafter. Mean pulmonary arterial blood pressure rose from 8 +/- 3 to 13 +/- 2 mmHg, and remained above the pre-exchange level up to 3 hours post-exchange. Cardiac output remained within normal limits. Significant flow-increments were seen at 30 minutes in heart, brain, liver, gut, and kidney, but these were also not sustained. A fall in glomerular filtration rate (GFR) occurred after the exchange and remained below the pre-exchange level. A reduction in urine flow at 150 minutes post-exchange was observed and was accompanied by a reduction in urinary electrolyte excretion. The findings suggest that the initial effects of the administration of unmodified stroma-free hemoglobin solution are those of peripheral vasoconstriction which does not appear to significantly restrict flow to the vital organs, such as heart and brain. Unmodified hemoglobin was found to cause a decrease in renal function.

Clearance of differentially labelled infused hemoglobin and polymerized hemoglobin from dog plasma and accumulation in urine and selected tissues.

Pyridoxalated hemoglobin polymerized with glutaraldehyde has been proposed as a hemoglobin based blood substitute. The preparations contain significant amounts of unpolymerized hemoglobin. We have prepared polymerized pyridoxalated hemoglobin labelled with 14C by reductive methylation free of unpolymerized hemoglobin and pyridoxalated hemoglobin labelled with 3H by reductive methylation to compare the handling of the two forms after infusion into dogs. Four dogs were examined sequentially. After three hours, 52.4 +/- 8.9% of the 3H label had disappeared from plasma whereas 21.7 +/- 5.8 of the 14C label had disappeared. The decrease of both labels occurred in a very close to linear fashion over the time period examined. From radioactivity in collected urine, it was calculated that 30.7 +/- 6.3% of the 3H and 9.0 +/- 2.7 of the 14C that had been cleared from plasma appeared in urine. The ratio of the specific radioactivity in tissue to the specific radioactivity of plasma indicated that extravascular accumulation of 3H label from unpolymerized hemoglobin occurred in kidney, heart and liver, with the kidney cortex exhibiting a very high concentration of the label. The specific radioactivity of both 3H and 14C label in liver suggested the substantial involvement of the reticuloendothelial system in the removal of both unpolymerized and polymerized hemoglobin from the circulation.

Changes in the myocardial area at risk, infarct size, and collateral flow following nicardipine infusion in dogs.

The area at risk of infarction after an acute occlusion of the left anterior descending coronary artery was defined in anesthetized dogs using the distribution of 99mTc-labelled albumin microaggregates and Monastral blue dye. In thirteen dogs, it was determined that these two particulate labels identified identical areas of unperfused myocardium. In a second group of dogs (n = 12), the risk areas determined at 10 (99mTc-labelled macroaggregates) and at 180 min (Monastral blue dye) were found to be identical, with no change in collateral blood flow, indicating the absence of a spontaneous change in underperfused myocardium over this time. In a third group of dogs (n = 17) nicardipine was infused (10 micrograms.kg-1.min-1 for 5 min, followed by 8 micrograms.kg-1.min-1 for 165 min). This resulted in a significant and sustained fall (32 +/- 4 mmHg; 1 mmHg = 133.32 Pa) in mean arterial blood pressure but no significant change in collateral blood flow was found, except for a marginal increase in the center of the ischemic zone. Area at risk and infarct sizes were also not significantly different between the latter two groups (18.2 +/- 4.1 vs. 21.6 +/- 4.0% of left ventricle). In this model, the magnitude of the area at risk appears to be determined early after a coronary occlusion and appears to be unmodified by treatment with nicardipine begun after the occlusion.

Stroma-free hemoglobin: its presence in plasma does not improve oxygen supply to the resting hindlimb vascular bed of hemodiluted dogs.

In hemodilution, red cell spacing in the microcirculation is increased, flow distribution may become more heterogeneous, and, as a result, oxygen supply to tissues may suffer. We tested the hypothesis that oxygen extraction from diluted blood may be enhanced by the presence of hemoglobin in the plasma phase in relatively low concentrations. In anesthetized dogs, the hindlimb vascular bed was isolated and perfused with the animal's own blood by a roller pump. One group of dogs (n = 6) was hemodiluted (hematocrit = 15.0 +/- 1.0%) with a 6% solution of dextran. A second group of dogs (n = 6) was similarly hemodiluted (hematocrit = 16.0 +/- 0.4%) with dextran containing stroma-free hemoglobin solution whereby plasma-phase hemoglobin concentration was raised to 1.1 +/- 0.1 g.dL-1. Systemic hemodynamic observations were made repeatedly over the subsequent 2.5 h, while blood flow to the hindlimb was progressively reduced in stepwise decrements. The hemoglobin-hemodiluted group showed increased systemic arterial blood pressure and total peripheral resistance when compared with the control (dextran diluted) group. The isolated hindlimb also showed evidence of increased vascular resistance in the hemoglobin-treated group. In each individual animal, critical oxygen delivery and extraction were determined by finding the intercept of the supply-independent and supply-dependent portions of the oxygen uptake/oxygen delivery relationship. Neither the critical oxygen delivery rates (5.75 +/- 0.83 vs. 6.41 +/- 0.53 mL.kg-1.min-1) nor critical oxygen extraction ratios (0.75 +/- 0.03 vs. 0.76 +/- 0.04) were found to be significantly different in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of high buffer cardioplegia and secondary cardioplegia on cardiac preservation and postischemic functional recovery: a 31P NMR and functional study in Langendorff perfused pig hearts.

High buffer cardioplegia may provide protection against ischemic damage by reducing the extent of intracellular acidosis. Secondary cardioplegia may improve postischemic recovery by restoration of high energy phosphates, ionic gradients, and intracellular pH. To test these hypotheses, pig hearts were arrested with high buffer (150 mM MOPS) cardioplegia or modified St. Thomas' solution II and then kept ischemic at 12 degrees C for 8 h. High energy phosphates and intracellular pH were followed during the period of ischemia, using 31P nuclear magnetic resonance spectroscopy, and functional recovery was followed during reperfusion. The hearts arrested by high buffer cardioplegia showed significantly higher intracellular pH than hearts preserved with St. Thomas' solution, but there were no significant differences in high energy phosphates. There were no significant differences in functional recovery. We found, however, that secondary cardioplegia abolished ventricular fibrillation, and resulted in improved functional recovery after 8 h of ischemic preservation compared with the hearts reperfused with Krebs-Henseleit solution alone. Our results suggest that despite attenuating the decreases in intracellular pH, high buffer cardioplegia does not improve recovery following 8 h of preservation at 12 degrees C. Secondary cardioplegia reduces the incidence of ventricular fibrillation and improves postischemic functional recovery of the myocardium.