Focal cerebral ischemia in rats: effect of hemodilution with alpha-alpha cross-linked hemoglobin on CBF

Association of Blood Pressure with Neurological Function Decline and Functional Outcome in Patients of Watershed Infarction

Background and Aims

The association between acute-phase blood pressure (BP) and outcomes in watershed infarction (WI) remains unclear. This study aimed to investigate the relationships between BP and BP changes with neurological functional decline (NFD) and functional outcome at 90 days.

Methods

We included patients with WI from a prospective, observational, single-center study (Effect of Cardiac Function on Short-Term Functional Prognosis in Patients with Acute Ischemic Stroke, SPARK). We recorded data of systolic blood pressure (SBP) and diastolic blood pressure (DBP) on the day of admission, as well as on day 2 and day 3. In logistic regression models, both the baseline BP and BP changes were assessed.

Results

Among the 207 patients with WI, 147 (71%) had concurrent cortical and internal infarcts. After adjusting for relevant factors, higher baseline SBP (OR:1.17; 95% CI:1.01-1.37) and DBP (OR:1.04; 95% CI:1.01-1.09) were associated with an increased risk of NFD. However, the restricted cubic spline (RCS) curve indicated that this association was statistically significant only when SBP was >180 mmHg or DBP was >100 mmHg. Additionally, an elevation in DBP of ≥4 mmHg on day 3 was associated with a reduced risk (OR:0.28; 95% CI: 0.08-0.97), whereas an elevation of DBP ≥10 mmHg was not. Neither baseline BP nor BP changes were associated with functional outcome.

Conclusion

In patients with WI, the risk of NFD increases when baseline SBP >180 mmHg or DBP >100 mmHg. However, raising DBP by ≥4 mmHg but <10 mmHg on day 3 is associated with a reduced risk of NFD. BP may not be associated with functional outcome.

Trial Registration

https://www.chictr.org.cn/, ChiCTR2300067696.

Red Blood Cell Transfusion

Red blood cell (RBC) transfusions are necessary to increase a patient's oxygen carrying capacity. The optimal transfusion trigger remains elusive, but a restrictive transfusion trigger of 7 g/dL has been shown in studies to reduce RBC transfusions without adversely affecting patient outcomes. Patient blood management programs have been shown effective at reducing RBC transfusions. Hemoglobin-based oxygen carriers and induced pluripotent stem cell derived RBCs are being developed to help mitigate RBC shortages and RBC transfusion limitations. Numerous challenges still exist that need to be overcome before they can have widespread clinical use.

Endothelin rather than 20-HETE contributes to loss of pial arteriolar dilation during focal cerebral ischemia with and without polymeric hemoglobin transfusion

Partial exchange transfusion with a cell-free hemoglobin (Hb) polymer during transient middle cerebral artery occlusion (MCAO) reduces infarct volume but fails to increase blood flow, as might be expected with the induced decrease in hematocrit. In ischemic brain, endothelin antagonists are known to produce vasodilation. In nonischemic brain, pial arterioles constrict after Hb exchange transfusion, and the constriction is blocked by an inhibitor of 20-HETE synthesis. We tested the hypothesis that a 20-HETE synthesis inhibitor and an endothelin A receptor antagonist increase pial arteriolar dilation after Hb exchange transfusion during MCAO. Pial arteriolar diameter was measured in the ischemic border region of the distal MCA border region through closed cranial windows in anesthetized rats subjected to the filament model of MCAO. During 2 h of MCAO, pial arteriolar dilation gradually subsided from 37 +/- 3 to 7 +/- 5% (+/-SE). Compared with residual dilation at 2 h of MCAO with vehicle superfusion (14 +/- 3%), loss of dilation was not prevented by superfusion of a 20-HETE synthesis inhibitor (21 +/- 5%), partial Hb exchange transfusion (7 +/- 5%) that decreased hematocrit to 23%, or a combination of the two (5 +/- 5%). However, loss of dilation was prevented by superfusion of an endothelin A receptor antagonist with (35 +/- 4%) or without (32 +/- 5%) Hb transfusion. Pial artery constriction during reperfusion was attenuated by HET0016 alone and by BQ610 with or without Hb transfusion. Systemic administration of the endothelin antagonist during prolonged MCAO increased blood flow in the border region. Thus loss of pial arteriolar dilation in the ischemic border region during prolonged MCAO depends on endothelin A receptor activation, and this effect was independent of the presence of cell-free Hb polymers in the plasma. In contrast to previous work in nonischemic brain, inhibition of oxygen-dependent 20-HETE synthesis does not significantly influence the pial arteriolar response to polymeric Hb exchange transfusion during focal ischemia.

The Role of Nitric Oxide Synthase Inhibition in the Adverse Effects of Etomidate in the Setting of Focal Cerebral Ischemia in Rats

We evaluated the effect of N(G)-nitro-L-arginine-methyl-ester (l-NAME, a nitric oxide synthase [NOS] inhibitor) and L-arginine (nitric oxide substrate) on cerebral mitochondrial dysfunction (hereafter referred to as "injury") after temporary middle cerebral artery occlusion (MCAo) during halothane or etomidate anesthesia in spontaneously hypertensive rats. Sixty minutes before MCAo, rats were randomized to 1 of 5 regimens (n = 8 per group): h/control, 1.2 minimum alveolar anesthetic concentration of halothane; h/L-NAME, 1.2 minimum alveolar anesthetic concentration of halothane and L-NAME (30 mg/kg); etomidate, an electroencephalographic (EEG) burst suppression dose of etomidate; e/L-NAME, an EEG burst suppression dose of etomidate and L-NAME (30 mg/kg); or e/L-NAME/arg, an EEG burst suppression dose of etomidate, L-NAME (30 mg/kg), and L-arginine (bolus of 300 mg/kg with an infusion at 35 mg x kg(-1) x min(-1)). After 180 min of MCAo and 120 min of reperfusion, volume of injury was determined using 2,3,5-triphenytetrazolium stain. Injury volume (mm(3), mean +/- sd) was larger in the etomidate group (153 +/- 17) than the halothane anesthetized h/control group (93 +/- 16) (P < 0.05) but did not differ between the e/L-NAME (162 +/- 17) and h/L-NAME groups (155 +/- 26). Injury volume in the e/L-NAME/arg group (88 +/- 15) was not different from the h/control group (93 +/- 16) and was less than that in either the etomidate or the e/L-NAME groups (P < 0.05). The data reproduce our previous observation that, relative to a halothane-anesthetized control state, etomidate has an adverse effect on ischemic injury in the setting of temporary focal cerebral ischemia. Prior inhibition of NOS with L-NAME resulted in no difference in the volume of injury between groups receiving etomidate or halothane (162 +/- 17 versus 155 +/- 26). Administration of a large dose of L-arginine prevented the adverse effect of etomidate. The data were obtained after only 2 h of reperfusion and therefore cannot be construed as representative of final neurologic outcome. They nonetheless suggest that etomidate produces an adverse effect on mitochondrial function early in the course of focal cerebral ischemia, in part, by inhibition of NOS.

Physiologic aspects of anemia

The most important adaptive responses from a physiological stance involved the cardiovascular system, consisting in particular of elevation of the cardiac output and its redistribution to favor the coronary and cerebral circulations, at the expense of the splanchnic vascular beds. The evidence regarding these physiological responses, especially in experimental studies that permit the control of many variables, is particularly powerful and convincing. On the other hand, there is a remarkable lack, in quality and quantity, of clinical studies addressing how normal physiological adaptive responses may be affected by a variety of diseases and conditions that often accompany and may complicate anemia, and interactions with other such compounding variables as age and different patient populations. For these reasons, it is not possible to offer guidelines on how to increase, maintain, or even to determine optimal DO2 in high-risk patients and how best transfusion strategies might be used under these conditions. From the brief review of physiological principles and the strong consensus in the literature, it is evident that cardiac function must be a central consideration in decisions regarding transfusion in anemia, because of the critical role it plays in assuring adequate oxygen supply of all vital tissues. Particular attention should be paid to the possible presence of CAD or incipient or cardiac failure, as these conditions may require careful transfusions to improve DO2 at levels that may not necessitate such interventions when cardiac disease is absent. Although the cerebral circulation also serves an obligate aerobic organ unable to tolerate significant hypoxia, there is little convincing evidence to support the notion that cerebral ischemia is aggravated by anemia and that this can be prevented by improved DO2 through rapid correction of anemia. Consequently, the arguments favoring transfusions in the presence of ischemic heart disease do not appear to apply to occlusive cerebrovascular disease. Because firm evidence is lacking on the interactions of concurrent diseases and anemia in various patient populations, understanding of the physiological consequences of anemia, and of the diseases concerned, is useful but not fully sufficient to provide firm and rational guidance to transfusion practice in specific complex clinical instances. A good deal of clinical and experimental investigation is required to support fully rational and comprehensive guidelines. In the meantime, prudent and conservative management, based on awareness of risks and sound understanding of the normal and pathological physiology, must remain the guiding principle.

Clinical trials for cytoprotection in stroke

To date, many cytoprotective drugs have reached the stage of pivotal phase 3 efficacy trials in acute stroke patients. (Table 1) Unfortunately, throughout the neuroprotective literature, the phrase "failure to demonstrate efficacy" prevails as a common thread among the many neutral or negative trials, despite the largely encouraging results encountered in preclinical studies. The reasons for this discrepancy are multiple, and have been discussed by Dr. Zivin in his review. Many of the recent trials have addressed deficiencies of the previous ones with more rigorous trial design, including more specific patient selection criteria (ensure homogeneity of stroke location and severity), stratified randomization algorithms (time-to-treat), narrowed therapeutic time-window and pharmacokinetic monitoring. Current trials have also incorporated biologic surrogate markers of toxicity and outcome such as drug levels and neuroimaging. Lastly, multi-modal therapies and coupled cytoprotection/reperfusion strategies are being investigated to optimize tissue salvage. This review will focus on individual therapeutic strategies and we will emphasize what we have learned from these trials both in terms of trial design and the biologic effect (or lack thereof) of these agents.

Regional cerebral blood flow in cats with cross-linked hemoglobin transfusion during focal cerebral ischemia

The beneficial effect of hemodilution on cerebral blood flow (CBF) during focal cerebral ischemia is mitigated by reduced arterial oxygen content (CaO2). In anesthetized cats subjected to permanent middle cerebral artery occlusion, the time course of regional CBF was evaluated after isovolemic exchange transfusion with either albumin or a tetrameric hemoglobin-based oxygen carrier. The transfusion started 30 min after arterial occlusion. We tested the hypothesis that bulk oxygen transport (CBF x CaO2) to ischemic tissue is increased by hemoglobin transfusion at a hematocrit of 18% compared with albumin-transfused cats at a hematocrit of 18% or control cats at a hematocrit of 30% and equivalent arterial pressure. In the nonischemic hemisphere, CBF increased selectively after albumin transfusion, and oxygen transport was similar among groups. In the ischemic cortex, albumin transfusion increased CBF, but oxygen transport was not increased above that of the control group. Hemoglobin transfusion increased both CBF and oxygen transport in the ischemic cortex above values in the control group, but the increase was delayed until 4 h of ischemia. Consequently, acute injury volume measured at 6 h of ischemia was not significantly attenuated. In contrast to the cortex, CBF in the ischemic caudate nucleus was not substantially increased by either albumin or hemoglobin transfusion. Therefore, in a large animal model of permanent focal ischemia in which transfusion starts 30 min after ischemia, tetrameric cross-linked hemoglobin transfusion can augment oxygen transport to the ischemic cortex, but the increase can be delayed and not necessarily provide protection. Moreover, an end-artery region such as the caudate nucleus is less likely to benefit from hemodilution.

Cross-linked polyhemoglobin-superoxide dismutase-catalase supplies oxygen without causing blood-brain barrier disruption or brain edema in a rat model of transient global brain ischemia-reperfusion

In strokes, myocardial infarctions, severe sustained hemorrhagic shock, and donor organs, inadequate blood supply results in lack of oxygen to the tissue (ischemia). If ischemia is sustained, reperfusion with the needed oxygen can result in tissue injury (ischemia-reperfusion injury) due to formation of reactive oxygen species. We are studying an oxygen-carrying solution with anitoxidant activity formed by cross-linking hemoglobin, superoxide dismutase, and catalase to form PolyHb-SOD-CAT. The present report studies its effect on the blood-brain barrier and cerebral edema when used in a transient global brain ischemia-reperfusion rat model. We compare this solution to sham-control, oxygenated saline, stroma-free hemoglobin (SF-Hb), polymerized hemoglobin (PolyHb), and a mixture of SF-Hb, SOD, and CAT in free solution. The results show that the cross-linked PolyHb-SOD-CAT solution, unlike the other solutions, can supply oxygen to ischemic tissues without causing reperfusion injury in the transient global brain ischemia-reperfusion model.

Thiopentone and methohexital, but not pentobarbitone, reduce early focal cerebral ischemic injury in rats

PURPOSE

Although barbiturates are considered to be cerebral protectants, little is known regarding the relative efficacy of different barbiturates to reduce ischemic brain injury. In a model of middle cerebral artery occlusion (MCAo), we compared the relative effects of 1.0 and 0.4 burst-suppression doses of thiopentone, methohexital, and pentobarbitone on cerebral infarct.

METHODS

During isoflurane anesthesia, MCAo was achieved via a temporal craniotomy. Thirty minutes before MCAo the rats were randomized to receive one of the following which was maintained throughout the study. Halothane (n=20)-1.2 MAC halothane, thiopentone (n=20), methohexital (n=20), or pentobarbitone (n=20). The first ten animals in each barbiturate group received the respective barbiturate in a dose sufficient to maintain burst-suppression of the electroencephalogram (3-5 bursts x min(-1)). The subsequent ten animals in each barbiturate group received 40% of the burst-suppression dose. After 180 min of MCAo and 120 min of reperfusion, cerebral injury was assessed.

RESULTS

For the burst-suppression animals, injury volume (mm3, mean +/- SD) was less in the thiopentone group (88 +/- 14) than the halothane (133 +/- 17), methohexital (126 +/- 19), or pentobarbitone (130 +/- 17) groups (P <0.05). For 0.4 burst-suppression animals, injury volume was less for the methohexital group (70 +/- 22) than the halothane (124 +/- 24), thiopentone (118 +/- 15), or pentobarbitone (121 +/- 20) groups (P <0.05).

CONCLUSIONS

These data are inconsistent with the longstanding assumption that electrophysiologically comparable doses of the various classes of barbiturates have equivalent protective efficacy. They in turn suggest that mechanisms other than, or at least in addition to, metabolic suppression may contribute to the protective effect of barbiturates.

Avaliação da isquemia cerebral pela respiração mitocondrial: modelo experimental

A isquemia cerebral acontece em várias doenças. Um dos fatores críticos para a recuperação de um paciente é a duração do processo isquêmico. A atividade cerebral depende do suprimento de energia, isto sugere que o estudo da função mitocondrial pode ser utilizado para a avaliação do dano neuronal. O objetivo deste trabalho foi o de estudar a respiração mitocondrial pela oclusão da artéria cerebral média esquerda pela técnica do fio intraluminal. Ratos da raça Wistar foram subdivididos em 4 grupos: controle e 15, 30 e 60 minutos de oclusão. Os resultados mostraram que não há diferença estatisticamente significativa entre o grupo de 15 minutos e o grupo controle. O grupo de 30 minutos teve diminuição do estado III da respiração mitocondrial comparado com o grupo controle. O grupo de 60 minutos teve diminuição dos estados III e IV comparados com o grupo controle. A respiração mitocondrial permitiu uma avaliação efetiva e precoce do processo isquêmico focal no cérebro do rato.

Controlled safety study of a hemoglobin-based oxygen carrier, DCLHb, in acute ischemic stroke

BACKGROUND AND PURPOSE

Diaspirin cross-linked hemoglobin (DCLHb) is a purified, cell-free human hemoglobin solution. In animal stroke models its use led to a significant reduction in the extent of brain injury. The primary objective of this study was to evaluate the safety of DCLHb in patients with acute ischemic stroke.

METHODS

DCLHb or saline was administered to 85 patients with acute ischemic stroke in the anterior circulation, within 18 hours of onset of symptoms, in a multicenter, randomized, single-blind, dose-finding, controlled safety trial, consisting of 3 parts: 12 doses of 25, 50, and 100 mg/kg DCLHb over 72 hours.

RESULTS

DCLHb caused a rapid rise in mean arterial blood pressure. The pressor effect was not accompanied by complications or excessive need for antihypertensive treatment. Two patients in the 100 mg/kg group had adverse events that were possibly drug related: one suffered fatal brain and pulmonary edema, the other transient renal and pancreatic insufficiency. Multivariate logistic regression analysis showed that a severe stroke at baseline and treatment with DCLHb (OR, 4.0; CI, 1.4 to 12.0) were independent predictors of a worse outcome (Rankin Scale score of 3 to 6) at 3 months.

CONCLUSIONS

Outcome scale scores were worse in the DCLHb group, and more serious adverse events and deaths occurred in DCLHb-treated patients than in control patients. We recommend that additional safety studies be performed, preferably with a second generation, genetically engineered hemoglobin.

Subarachnoid hemorrhage in rats: effect of singular or sustained hemodilution with alpha-alpha diaspirin crosslinked hemoglobin on cerebral hypoperfusion

OBJECTIVE

To evaluate the effect of singular or sustained hemodilution, with alpha-alpha diaspirin crosslinked hemoglobin (DCLHb), on the area of hypoperfusion after subarachnoid hemorrhage.

DESIGN

Prospective animal study.

SETTING

Animal research laboratory.

SUBJECTS

Isoflurane anesthetized, mechanically ventilated rats.

INTERVENTIONS

Subarachnoid hemorrhage was induced by injecting 0.3 mL of blood into the cisterna magna. The animals were randomly assigned to one of the following groups (n = 16 in each hemodilution group; eight animals received a single treatment of hemodilution after subarachnoid hemorrhage; and, for eight animals, treatment was sustained for 48 hrs): control group (n = 8), no hematocrit (45%) manipulation; DCLHb group (n = 16), hematocrit decreased to 30% with DCLHb; or Alb group (n = 16), hematocrit decreased to 30% with human serum albumin. After 48 hrs, the area of hypoperfusion (cerebral blood flow < 40 ml/100g/min) was determined with 14C-iodoantipyrine in five coronal brain sections.

MEASUREMENTS AND MAIN RESULTS

For both singular and sustained treatment, the area of hypoperfusion was less in both hemodilution groups than in the control group (p<.05). For four of the five coronal brain sections, no differences were found between the DCLHb and Alb groups within a given hemodilution protocol. In addition, in four of the five coronal brain sections for the DCLHb hemodilution groups and in all five sections for the albumin hemodilution groups, the area of hypoperfusion was less for rats that received sustained hemodilution compared with their respective groups in the singular treatment protocol (p<.05).

CONCLUSIONS

These data support the hypothesis that hemodilution with molecular hemoglobin decreases hypoperfusion after subarachnoid hemorrhage and that sustained hemodilution is more effective than singular treatment. The data do not support the notion that intravascular DCLHb has an adverse effect on cerebral ischemia after subarachnoid hemorrhage.

Effect of diaspirin cross-linked hemoglobin on endothelin-1 and blood pressure in acute ischemic stroke in man

OBJECTIVE

For almost 50 years it has been known that hemolysed blood can increase blood pressure. Although preclinical studies suggest that this pressor response is due to an interaction of hemoglobin with endothelium-derived vasoactive substances, its mechanism in humans is unknown. We investigated the involvement of endothelin-1 in the blood pressure response to the oxygen carrier diaspirin cross-linked hemoglobin (DCLHb) in stroke patients.

DESIGN

In a randomized phase II study, increasing doses of DCLHb (25, 50 and 100 mg/kg, n=8, 8 and 11, respectively) or placebo (n=26) were infused intravenously every 6 h for 72 h to patients with an acute ischemic stroke. Blood pressure and heart rate were measured every 15 min and plasma concentrations of endothelin-1, catecholamines, renin, vasopressin and atrial natriuretic peptide were measured before and 24 and 66 h after the start of the infusions.

RESULTS

In the placebo group, mean arterial pressure (MAP) was 112 (109-115) mmHg (mean and 95% confidence interval) at baseline and decreased spontaneously by 11.4 (5.4-17.5) and 12.5 (5.4-19.5) mmHg after 24 and 66 h, respectively. This decrease in MAP was attenuated in patients treated with DCLHb, reaching statistical significance in the highest dose group. The plasma endothelin-1 concentration decreased slightly in the placebo group, from 4.2 (3.1-5.3) pg/ml (median and range) at baseline to 2.4 (1.9-3.7) pg/ml after 24 h (P=0.0044) and 2.8 (1.9-3.7) pg/ml after 66 h (P=0.0042), but increased dose-dependently in response to DCLHb infusion. With the highest dose of DCLHb, the plasma endothelin-1 concentration rose from 4.8 (0.1-7.8) pg/ml at baseline to 21.2 (13.4-53.2) pg/ml after 24 h (P< 0.001) and to 27.6 (11.9-47.8) pg/ml after 66 h (P< 0.001). The increases in the plasma endothelin-1 concentration and in MAP were correlated (r=0.30, P=0.02). Other vasoactive hormones were not affected by the DCLHb infusion.

CONCLUSIONS

Infusion of DCLHb in patients with acute ischemic stroke was associated with a dose-dependent increase in plasma endothelin-1 concentration. This may underlie the attenuation by DCLHb of the natural decrease in blood pressure that we observed in these patients.

Effects of a synthetic allosteric modifier of hemoglobin oxygen affinity on outcome from global cerebral ischemia in the rat

BACKGROUND AND PURPOSE

Neuronal injury results from an insufficient supply of oxygen to the brain. This experiment examined whether a pharmacologically induced rightward shift of the partial pressure of oxygen at which 50% of hemoglobin is saturated (P50) would improve outcome from either incomplete and/or near-complete forebrain ischemia-induced hypoxia in the rat.

METHODS

For incomplete ischemia (attenuated electroencephalogram), fasted rats (n = 17 to 19 per group) were given a synthetic allosteric modifier of hemoglobin affinity for oxygen (RSR13; 150 mg/kg IV) before or immediately after 20 minutes of bilateral carotid occlusion combined with a decrease in mean arterial pressure to 40 mm Hg. For near-complete ischemia (isoelectric electroencephalogram), rats (n = 15 per group) were given RSR13 (150 mg/kg) at onset of reperfusion after 10 minutes of bilateral carotid occlusion combined with a decrease in mean arterial pressure to 30 mm Hg. In both experiments, control rats were given vehicle (0.9% NaCl IV) only. Outcome (defined as percent dead hippocampal CA1 neurons) was determined at 5 days after ischemia.

RESULTS

RSR13 (150 mg/kg) produced a 68% rightward shift of P50 (34+/-3 to 57+/-8 mm Hg). RSR13 reduced CA1 damage resulting from incomplete ischemia by 28% (P=0.02), but only when administered at the onset of reperfusion. RSR13 had no effect on outcome from near-complete ischemia.

CONCLUSIONS

A postischemic pharmacologically induced increase in P50 may improve outcome from incomplete global cerebral ischemia. More severe (near-complete) ischemia negates this benefit.

Hypervolemic hemodilution in acute ischemic stroke: the Multicenter Austrian Hemodilution Stroke Trial (MAHST)

BACKGROUND AND PURPOSE

Experimental studies suggest a beneficial effect of hemodilution on acute ischemic stroke. This was not proven by previous multicenter trials in the clinical setting. Various reasons have been suggested for the failure of these studies, which we attempted to consider in the Multicenter Austrian Hemodilution Stroke Trial (MAHST).

METHODS

MAHST is a randomized, double-blind, placebo-controlled study of hypervolemic hemodilution (HHD) within 6 hours of a clinically first ischemic stroke localized in the middle cerebral artery territory. The treatment consisted of 10% hydroxyethyl starch 200/0.5 (HES) and was tested against pure rehydration with Ringer's lactate over a period of 5 days. Our primary outcome measure was clinical improvement within 7 days as measured by the Graded Neurologic Scale (GNS). We performed an adaptive interim analysis to reevaluate the study goal after entering half of the projected number of patients (n = 200). At least 600 patients per group would have been required for significant results, and therefore we decided to terminate the trial.

RESULTS

Ninety-eight patients received HHD and 102 patients placebo. The baseline characteristics were comparable between both groups. In the HHD group the absolute reduction of the hematocrit was 2.5% on day 2 with a maximum of 3.7% on day 5, which compares with a reduction in the placebo group of 1% and 1.9%, respectively. Intention-to-treat analysis showed no significant difference of the change of the GNS scores between HHD-treated (median, -8.5; 95% confidence interval, -14.2 to -4.0) and placebo-treated patients (median, -6.0; 95% confidence interval, -11.0 to 0.0) on day 7, and GNS scores remained similar in both treatment groups throughout the trial. At 3 months, slightly more HHD patients showed complete independence on the Barthel Index (28 versus 24), and fewer HHD than placebo patients had died (13 versus 17), but these differences were not statistically significant. HHD treatment was not associated with any specific adverse event.

CONCLUSIONS

Mild HHD is safe but failed to demonstrate a significant beneficial effect over the pure rehydration regimen in patients with acute ischemic stroke.

Effects of diaspirin-cross-linked hemoglobin (DCLHb) on the microcirculation of striated skin muscle in the hamster: a study on safety and toxicity

Hemoglobin-based oxygen-carrying solutions are reported to exert vasoconstrictor effects and to enhance oxygen radical formation, particularly during ischemia-reperfusion. This study investigates whether diaspirin-cross-linked hemoglobin (DCLHb) affects the microvascular integrity of striated skin muscle. The microcirculation model in the hamster and intravital fluorescence microscopy were applied for investigation of the microvascular changes in striated skin muscle. Hypervolemic infusion (500 mg x kg(-1), I.V.) and isovolemic exchange transfusion (3.3 gm x kg(-1) I.V.; hematocrit 30%) with DCLHb (1) led to a short-lasting (0 to 2 minutes) arteriolar constriction (approximately 20% reduction in baseline diameter), (2) significantly influenced arteriolar vasomotion, (3) increased venular red blood cell velocity by 1.5-fold (p < 0.05 vs dextran, Mr 60,000), and (4) did not enhance microvascular leukocyte-endothelium interaction or endothelial permeability. Resuscitation from severe hemorrhagic shock with autologous blood (AuB) or DCLHb (33 ml x kg(-1), I.V.) immediately restored mean arterial pressure and heart rate, whereas 6% dextran (60 kd)(Dx-60) did not return these parameters to baseline. Venular red blood cell velocity was restored to 110% of baseline after DCLHb, to 90% of baseline after AuB, and to 45% of baseline after Dx-60. Leukocyte-endothelium interaction was significantly enhanced after resuscitation with AuB and Dx-60, whereas this phenomenon was absent after DCLHb. These data demonstrate that DCLHb increases venular red blood cell velocity under both nonischemic and postischemic conditions without inducing enhanced leukocyte-endothelium interaction in the microcirculation of striated skin muscle.

Alpha-alpha diaspirin crosslinked hemoglobin, nitric oxide, and cerebral ischemic injury in rats

Prior studies indicate that alpha-alpha diaspirin crosslinked hemoglobin (DCLHb) decreases cerebral ischemia. One mechanism whereby DCLHb may ameliorate cerebral ischemia is by binding nitric oxide (NO), which has been implicated as neurotoxic. We assessed the effect of L-NAME (NO synthase inhibitor) and L-arginine (NO substrate) on ischemic brain injury after DCLHb infusion. Rats were randomized to one of the following groups: Control-no hematocrit manipulation; DCLHb-hematocrit decreased to 16% with 10% DCLHb; DCLHb/L-NAME-hematocrit decreased to 16% with DCLHb, and L-NAME given; DCLHb/L-arg-hematocrit decreased to 16% with DCLHb, and L-arginine given. After 90-min of middle cerebral artery occlusion and 4-hr of reperfusion, infarct volume was determined with TTC stain. Infarct volume (mm3, mean +/- SD) was greater in the Control group (142 +/- 16) than the DCLHb (43 +/- 12), DCLHb/L-NAME (45 +/- 14), and DCLHb/L-arg (71 +/- 18) groups (p < 0.05); was greater in the DCLHb/L-arg group than the DCLHb and DCLHb/L-NAME groups (p < 0.05); but was not different between the DCLHb and DCLHb/L-NAME groups. These data indicate that DCLHb decreases ischemic brain injury, and that binding NO may be one mechanism by which DCLHb decreases ischemic brain injury.

Effect of subarachnoid administration of alpha-alpha diaspirin crosslinked hemoglobin on cerebral blood flow in rats

As extravasated red blood cells have been implicated in the pathogenesis of perfusion deficits after subarachnoid hemorrhage, alpha-alpha diaspirin crosslinked hemoglobin (DCLHb) might have a detrimental effect on cerebral perfusion after subarachnoid hemorrhage. We evaluated the effect of subarachnoid administration of DCLHb on cerebral blood flow (CBF). Rats were randomized to receive one of the following solutions into the cisterna magna: Control-0.3 ml of mock cerebrospinal fluid; Blood-0.3 ml of autologous blood; DCLHb-0.3 ml of 10% DCLHb. After 20-min, the area of cerebral hypoperfusion was determined (CBF < 40 ml.100g-1.min-1). The area of hypoperfusion (% area of a coronal brain section, mean +/- SD) was greater in the Blood group (58 +/- 16) than the DCLHb (16 +/- 7) and Control (5 +/- 5) groups (p < 0.05), and was greater in the DCLHb group than the Control group (p < 0.05). These data support a hypothesis that extravasation of blood from the intravascular to the subarachnoid space induces cerebral hypoperfusion. Moreover, the data support the hypothesis that although extravasated molecular hemoglobin decreases CBF, the adverse effect is not as severe as a similar volume of blood.

Cellular responses to surgical trauma, hemorrhage, and resuscitation with diaspirin cross-linked hemoglobin in rats

BACKGROUND

Resuscitation with acellular oxygen carrier solutions offers the potential advantage of improved oxygen delivery compared with crystalloid solutions, but the detailed consequences of improved resuscitation have not been fully evaluated. This study evaluated local and systemic cellular effects of trauma, hemorrhage, and resuscitation in a model of hemorrhage and surgical trauma.

METHODS

Rats with a 10 cm full-thickness incisional wound and a 15 mL/kg hemorrhage were either not resuscitated or resuscitated with blood or diaspirin cross-linked hemoglobin (DCLHb). Cellular proliferative responses were evaluated at 1.5, 6, 24, and 48 hours after wounding by labeling in vivo with 5-bromo-2'-deoxyuridine. Plasma levels of interleukin-6, tumor necrosis factor-alpha, and interferon-gamma were measured by bioassay or enzyme-linked immunosorbent assay (ELISA). Bacterial translocation was measured by culturing liver homogenates.

RESULTS

Trauma inhibited keratinocyte and hepatocyte proliferation at 1.5 and 6 hours, and stimulated subsequent proliferation of keratinocytes and liver nonparenchymal cells. DCLHb stimulated wound keratinocyte proliferation, attenuated the inhibition of hepatocyte proliferation, eliminated bacterial translocation to the liver, protected the intestine from ischemic damage, and induced a rapid increase of interleukin-6 during the early phase of injury.

CONCLUSIONS

Surgical trauma alone, or in combination with hemorrhage, modulated cell proliferation both in the wound and in the remote organs of intestine and liver. DCLHb enhanced wound healing and cell proliferation as well as, or better than, freshly drawn blood, which may be beneficial for trauma care.

Combined neuroprotection and reperfusion therapy for stroke. Effect of lubeluzole and diaspirin cross-linked hemoglobin in experimental focal ischemia

BACKGROUND AND PURPOSE

In search of a better treatment for acute ischemic stroke, we evaluated the use of lubeluzole and hemodilution with diaspirin cross-linked hemoglobin (DCLHb) therapy to test whether treatment with two complementary acting compounds provides more potent protection than either treatment alone.

METHODS

We used unilateral reversible middle cerebral artery (MCA) and common carotid artery (CCA) occlusion of various durations in Long-Evans rats to produce ischemic cortical lesions. We calculated the average maximal lesion volume (Volmax) and the time required to produce half maximal lesion size (T50) in control animals (n = 31) and evaluated the effects on cerebral perfusion and infarct size of treatment with lubeluzole (n = 23), hemodilution (to 30% hematocrit) with albumin (n = 17) or DCLHb (n = 23), and combined lubeluzole + DCLHb therapy initiated 15 minutes after MCA/CCA occlusion.

RESULTS

The Volmax produced by MCA/CCA occlusion in control animals was 138.5 +/- 7.7 mm3, and T50 was 98.5 +/- 10.2 minutes. Lubeluzole alone reduced Volmax by 53% with no significant effect on T50. In contrast to lubeluzole, DCLHb hemodilution prolonged T50 by 68% with no significant effect on Volmax. Prolongation of T50 by DCLHb was not due to hemodilution itself, since a similar degree of hemodilution with albumin had no effect. Finally, combined lubeluzole+DCLHb rescued 72% of the tissue and augmented the effect of lubeluzole alone by 40% (Volmax, 66.3 +/- 13.0 versus 39.4 +/- 12.2 mm3) while prolonging T50 by 31%.

CONCLUSIONS

Combination therapy for acute stroke using compounds with complementary action can result in more complete attenuation of neuronal damage and demonstrates the possible clinical utility of combined neuroprotective and reperfusion therapies.

Effect of oncotic pressure of diaspirin cross-linked hemoglobin (DCLHb) on brain injury after temporary focal cerebral ischemia in rats

Previous studies have shown that diaspirin cross-linked hemoglobin (DCLHb, 10 g/dL) decreases cerebral ischemia and the resultant injury in a dose-dependent manner, requiring large volumes of DCLHb for maximum efficacy. We assessed the effect of a more concentrated (20 g/dL) and more hyperoncotic preparation of DCLHb on cerebral infarction volume. Immediately after middle cerebral artery occlusion, rats were randomized to one of the following groups: Control, hematocrit not manipulated; 10/Hb, hematocrit decreased to 30% with 10% DCLHb (oncotic pressure 43 mm Hg); 7.5/Alb, hematocrit decreased to 30% with 7.5% albumin (oncotic pressure 43 mm Hg); 20/Hb, the same dose of DCLHb (20%, oncotic pressure 129 mm Hg) as the 10/HB group (half the volume); or 15/Alb, the same dose of albumin (15%, oncotic pressure 130 mm Hg) as the 7.5/Alb group half the volume). After 90 min of ischemia, 72 h of reperfusion was allowed. Infarction volume (mm3, mean +/- sd) was less in the DCLHb groups (10/Hb = 79 +/- 17; 20/HB = 51 +/- 14) than the oncotically matched albumin groups (7.5/Alb = 124 +/- 21; 15/Alb = 85 +/- 18) and the Control group (135 +/- 17) (P < 0.05). These data indicate that in this model of cerebral ischemia, DCLHb decreases ischemic brain injury more effectively than albumin, and that a hyperoncotic preparation of DCLHb is preferable.

Optimal timing of hemodilution for brain protection in a canine model of focal cerebral ischemia

BACKGROUND AND PURPOSE

Hemodilution is known to ameliorate the effects of focal ischemia when used shortly after cerebral arterial occlusion; however, it remains to be proved whether hemodilution will be effective when used at more clinically relevant times, ie, with some delay between the onset of ischemia and initiation of therapy.

METHODS

Thirty-two dogs were selected for inclusion in this study. Cerebral infarction was induced by permanent occlusion of the middle cerebral and the azygos anterior cerebral arteries. The animals were allocated to 1 of 4 groups of eight animals each: arterial occlusion without hemodilution (group 1); hemodilution immediately after occlusion (group 2); hemodilution 3 hours after occlusion (group 3); and hemodilution 6 hours after occlusion (group 4). Isovolemic hemodilution to a hematocrit of 30% was performed. The animals were killed 6 days after induction of ischemia, and the infarct size was determined.

RESULTS

Groups 2 and 3 showed significant reduction of infarct size (P < .0001) when compared with group 1. The neurological grade of group 3 on postoperative days 4, 5, and 6 was significantly better than those of groups 1 and 4 (P < .01). Group 4 showed a significant increase in the incidence of hemorrhagic infarction when compared with groups 1 and 2 (P < .01).

CONCLUSIONS

The current study indicates that hemodilution administered as much as 3 hours after ischemia is effective in reducing infarct size and improving neurological status. When administered 6 hours after ischemia, hemodilution is not helpful and may be harmful.

Regional blood flow alterations after bovine fumaryl beta beta-crosslinked hemoglobin transfusion and nitric oxide synthase inhibition

OBJECTIVES

a) To determine whether isovolemic exchange transfusion with cell-free, bovine fumaryl beta beta-crosslinked hemoglobin results in a different pattern of regional blood flow distribution than transfusion with a poor oxygen-carrying, colloidal solution. b) Because of potential nitric oxide scavenging by plasma-based hemoglobin, to determine whether blood flow differences are reduced after nitric oxide synthase inhibition.

DESIGN

A prospective, randomized design with repeated blood flow measurements within groups.

SETTING

Experimental physiology laboratory in a university medical center.

SUBJECTS

Pentobarbital-anesthetized female cats.

INTERVENTIONS

Three groups of eight cats were studied: a) a control group with no transfusion (hematocrit of 32%); b) an anemia group in which exchange transfusion with an albumin-containing solution reduced hematocrit to 18% over a 40- to 50-min period; and c) a group in which cell-free hemoglobin was exchanged transfused to reduce hematocrit to 18%, without a proportional reduction in oxygen-carrying capacity. Bovine hemoglobin was covalently crosslinked intramolecularly between the 81-lysine residues on the beta-subunits to stabilize the tetramer. Regional blood flow was measured by the radiolabeled microsphere technique before transfusion and at 10, 100, and 180 mins from the start of transfusion. At 190 mins, N omega-nitro-L-arginine methyl ester (L-NAME; 10mg/kg) was infused to inhibit nitric oxide synthase and blood flow was measured 30 mins later.

MEASUREMENTS AND MAIN RESULTS

Mean arterial pressure was unchanged in the control and albumin-transfused groups. However, mean arterial pressure increased rapidly in the hemoglobin-transfused group. With hemoglobin transfusion, there were marked reductions in blood flow to the intestines, kidneys and adrenal glands. Administration of L-NAME after hemoglobin transfusion failed to increase arterial pressure or cause further reductions in intestinal, renal, or adrenal blood flow. Administration of L-NAME to the control and albumin-transfused groups increased arterial pressure and reduced intestinal, renal, and adrenal blood flows to values attained with hemoglobin transfusion. In contrast, in skeletal muscle and left ventricle, blood flow rates increased in the albumin-transfused group and were greater than those values found in the control group and hemoglobin-transfused group. The greater flow in the albumin-transfused group persisted after L-NAME administration. There was no difference in renal sodium, potassium, or osmolar excretion, or in urine flow between groups.

CONCLUSIONS

Transfusion with cell-free, bovine crosslinked hemoglobin in cats can selective reductions in blood flow in the intestines, kidneys, and adrenal glands without evidence of renal dysfunction by a mechanism consistent with nitric oxide scavenging. In skeletal and cardiac muscle, the increase in blood flow persisted after nitric oxide inhibition in the albumin group relative to the hemoglobin-transfused group at equivalent hematocrit values. This finding is consistent with compensatory vasoconstriction with hemoglobin transfusion due to improved oxygenation by this oxygen carrier.

Blood substitutes: fluids, drugs, or miracle solutions?

Oxygen-carrying volume-expanding solutions that can sustain life in the absence of red blood cells have been developed. Concerns about side effects, sources of hemoglobin, and the ultimate demonstration of efficacy will have to be satisfactorily addressed before anesthesiologists routinely administer such solutions in place of red cells during surgery.

Role of endothelin in the cardiovascular effects of diaspirin crosslinked and stroma reduced hemoglobin

OBJECTIVES

Diaspirin crosslinked hemoglobin is a resuscitative solution with excellent oxygen-carrying capacity. Diaspirin crosslinked hemoglobin produces an immediate increase in blood pressure and marked regional circulatory changes in rats and pigs. Our objective was to determine the role of endothelin in the cardiovascular actions of diaspirin crosslinked hemoglobin (modified) and (unmodified) stroma reduced hemoglobin solutions.

DESIGN

Prospective, randomized comparison of cardiovascular effects of diaspirin crosslinked and stroma reduced hemoglobin in control rats and in rats pretreated with cyclo(D-Asp-Pro-D-Val-Leu-D-Trp) (BQ-123), an endothelin-A receptor antagonist.

SETTING

Research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Modified, highly purified, and heat pasteurized (diaspirin crosslinked) and unmodified (stroma reduced) hemoglobin in control (untreated) and BQ-123 (5 mg/kg/hr iv)-treated rats.

MEASUREMENTS AND MAIN RESULTS

Infusion of stroma reduced hemoglobin (400 mg/kg iv) in control rats produced an increase in blood pressure (43%) and total peripheral resistance (65%) without any change in heart rate, cardiac output, and stroke volume. Stroma reduced hemoglobin decreased blood flow to the kidneys and liver, increased blood flow to the heart, and had no effect on blood flow to the brain, gastrointestinal tract, spleen, musculoskeletal system, skin, and mesentery and pancreas. Infusion of stroma reduced hemoglobin in rats treated with BQ-123 (5 mg/kg/hr iv) increased the blood pressure to a similar degree when compared with control rats, but the increase in total peripheral resistance was significantly attenuated. The stroma reduced hemoglobin-induced decrease in blood flow to the kidneys and liver was significantly attenuated in BQ-123-treated rats as compared with control rats. However, the stroma reduced hemoglobin-induced increase in blood flow to the heart of BQ-123-treated rats was similar to the increase in control rats. Infusion of diaspirin crosslinked hemoglobin (400 mg/kg iv) produced increases in blood pressure (81%), cardiac output (36%), stroke volume (30%), and total peripheral vascular resistance (45%), along with increases in blood flow to the heart, spleen, gastrointestinal tract, and skin of control rats. The blood flows to the brain, kidneys, liver, musculoskeletal system, and mesentery and pancreas were not altered by diaspirin crosslinked hemoglobin in control rats. The increases in blood pressure, cardiac output, stroke volume, and total peripheral vascular resistance by diaspirin crosslinked hemoglobin were significantly blocked in BQ-123-treated rats as compared with control rats. The increases in blood flow to the heart, spleen, and skin by diaspirin crosslinked hemoglobin were significantly blocked in BQ-123-treated rats as compared with control rats. Diaspirin crosslinked hemoglobin produced an increase in the blood flow to the brain and a decrease in blood flow to the kidney and musculoskeletal system of BQ-123-treated rats as compared with control rats. Blood plasma endothelin-1-like immunoreactivity was found to be significantly increased after treatment with diaspirin crosslinked hemoglobin or stroma reduced hemoglobin.

CONCLUSIONS

The endothelin-A receptor antagonist, BQ-123, could attenuate the systemic hemodynamic and regional circulatory effects of diaspirin crosslinked hemoglobin and stroma reduced hemoglobin. However, the increase in blood flow to the heart induced by stroma reduced hemoglobin could not be attenuated by BQ-123.

Focal cerebral ischemia during anesthesia with etomidate, isoflurane, or thiopental: a comparison of the extent of cerebral injury

An investigation was performed to compare the cerebral protective properties of etomidate, isoflurane, and thiopental. In separate groups of spontaneously hypertensive rats, etomidate, isoflurane, or thiopental was administered to achieve and maintain burst-suppression of the electroencephalogram (3-5 bursts/min) for the duration of the experiment. A fourth group received 1.2 minimal alveolar concentration halothane. All groups underwent 3 hours of middle cerebral artery occlusion and then 2 hours of reperfusion. Thereafter, the animals were killed and the volume of injured brain was determined by staining with 2,3,5-triphenyltetrazolium. Physiological parameters did not differ among the four groups during the investigation, with the exception that hemolysis occurred in the etomidate group (free hemoglobin levels, approximately 0.4 g.dl-1). The volume of injured brain in the thiopental group (56 +/- 10 mm3) was significantly smaller than that in the halothane control group (99 +/- 13 mm3). The volumes of injured brain in the etomidate and isoflurane groups (145 +/- 11 mm3 and 139 +/- 14 mm3, respectively) were significantly larger than those in the control and thiopental groups. We speculate that the apparently detrimental effect of etomidate may be the result of the binding of nitric oxide of cerebral endothelial origin by the iron component of free hemoglobin. Intracranial pressure was not recorded, and in the isoflurane group, there may have been adverse effects on cerebral perfusion pressure associated with vasodilation caused by high concentrations of isoflurane. The results are consistent with a protective effect by barbiturates.

Yohimbine modulates diaspirin crosslinked hemoglobin-induced systemic hemodynamics and regional circulatory effects

OBJECTIVE

Diaspirin crosslinked hemoglobin, a hemoglobin-based blood substitute, is proposed to be an effective resuscitative solution. It produces an immediate, but limited increase in blood pressure when administered to conscious or anesthetized rats. This vasoactivity is associated with an increase in blood flow to several major organs. It has been shown that alpha-adrenergic receptors in the peripheral vascular system are sensitized by diaspirin crosslinked hemoglobin in rats. The present study was conducted to determine the effect of yohimbine, an alpha 2-adrenergic receptor antagonist on systemic hemodynamics and regional circulatory effects of diaspirin crosslinked hemoglobin.

DESIGN

Prospective, randomized comparison of cardiovascular effects of diaspirin crosslinked hemoglobin in control and yohimbine-pretreated rats.

SETTING

Laboratory of experimental medicine.

SUBJECTS

Male Sprague-Dawley rats weighing 300 to 350 g.

INTERVENTIONS

Modified, highly purified, and heat-pasteurized hemoglobin (diaspirin crosslinked hemoglobin) in control and yohimbine-treated (2 mg/kg i.v.) rats.

MEASUREMENTS AND MAIN RESULTS

The systemic hemodynamics and regional circulation were measured using a radioactive microsphere technique. Diaspirin crosslinked hemoglobin (400 mg/kg i.v.) produced an increase in blood pressure and total peripheral resistance, while heart rate, cardiac output, and stroke volume were not significantly altered in control rats. In yohimbine-pretreated (2 mg/kg i.v.) animals, diaspirin crosslinked hemoglobin did not produce any change in heart rate, stroke volume, cardiac output, and total peripheral resistance, but a slight increase in blood pressure was observed compared with baseline values obtained after the administration of yohimbine. The increase in blood pressure induced by diaspirin crosslinked hemoglobin was significantly blocked by pretreatment with yohimbine. Yohimbine (2 mg/kg i.v.) per se decreased blood pressure, while other systemic hemodynamic parameters were not affected. Diaspirin crosslinked hemoglobin increased blood flow to the heart, gastrointestinal tract (stomach, small intestine, cecum, and large intestine), portal (spleen, mesentery, and pancreas) and skin, while blood flow to the brain (cerebral hemispheres, diencephalon, cerebellum, and brain stem), liver, kidneys, and musculoskeletal system was not affected in control rats. In yohimbine-pretreated animals, diaspirin crosslinked hemoglobin produced an increase in blood flow to the heart, brain (cerebellum and brain stem), liver, small intestine, cecum, spleen, mesentery and pancreas, kidneys, skin and musculoskeletal system, while blood flow to the stomach and large intestine was not affected. Yohimbine pretreatment significantly attenuated the diaspirin crosslinked hemoglobin-induced increase in blood flow to the large intestine, mesentery, and pancreas.

CONCLUSIONS

The cardiovascular actions of diaspirin crosslinked hemoglobin are partially mediated through alpha 2-adrenergic receptors. Adrenergic receptor antagonists may be useful in attenuating the pressor effect of diaspirin crosslinked hemoglobin while maintaining the regional perfusion.

Diaspirin crosslinked hemoglobin (DCLHb) does not affect the anesthetic potency of isoflurane in rats

Hemoglobin solutions are being developed as oxygen carrying fluids for multiple clinical indications. Despite an early report of accentuation of ether anesthesia, the effect of hemoglobin on anesthetic potency has not been assessed. We assessed the effect of alpha-alpha diaspirin crosslinked hemoglobin (DCLHb) on the anesthetic requirement of isoflurane necessary to keep rats unresponsive to noxious stimuli (1.0 MAC [minimum alveolar concentration]). During isoflurane administration, each rat received one of the following fluid regimens: 44Hct/N-normal hematocrit and volume; 44Hct/H-8.0 ml of donor blood given as a hypervolemic bolus; 30Hct/H-5.0 ml of DCLHb given as an exchange transfusion and 8.0 ml as a hypervolemic bolus; or 16Hct/H-15.0 ml of DCLHb given as an exchange transfusion and 8.0 ml as a hypervolemic bolus. MAC was determined using a standard tail clamp technique. The isoflurane requirement to achieve 1.0 MAC was not different between the four groups. These results are consistent with a hypothesis that DCLHb does not change the anesthetic state.

Diaspirin cross-linked hemoglobin improves neurological outcome following reversible but not irreversible CNS ischemia in rabbits

BACKGROUND AND PURPOSE

Hemodilution using modified hemoglobin solutions may reduce ischemic central nervous system injury. Purified diaspirin cross-linked hemoglobin (DCLHb) is a cell-free hemoglobin that is intramolecularly cross-linked between the two alpha subunits, resulting in enhanced oxygen offloading to tissues and increased half-life. In the present experiments, we evaluated the ability of DCLHb to reduce neurological damage in two rabbit stroke models.

METHODS

In a reversible spinal cord ischemia model, ischemia of the caudal lumbar spinal cord was produced by temporary occlusion of the abdominal aorta. In an irreversible model of cerebral ischemia, plastic microspheres (50 microns) were injected into the internal carotid artery and lodged in the cerebral microvasculature. DCLHb was administered 5 minutes after initiation of ischemia as either a 10-mL/kg infusion, 10-mL/kg exchange transfusion, or a 20-mL/kg infusion. Control animals received human serum albumin that was oncotically matched to the DCLHb.

RESULTS

In the spinal cord model, DCLHb significantly increased the duration of ischemia required to produce permanent paralysis from 27.33 +/- 8.71 minutes (mean +/- SD) in controls to 42.59 +/- 10.10 minutes in the 10-mL/kg exchange transfusion group and to 40.82 +/- 18.16 minutes in the 20-mL/kg infusion condition (P < .05). DCLHb did not significantly reduce neurological damage in the microsphere embolization model.

CONCLUSIONS

These data suggest that cross-linked hemoglobin reduces neurological damage after reversible central nervous system ischemia and that this is not attributable to hemodilution or hypervolemia only.

Effects of viscosity and oxygen content on cerebral blood flow in ischemic and normal rat brain

The mechanism of hemodilution-induced increases in cerebral blood flow (CBF) was investigated. Hemodilution was achieved with a molecular hemoglobin solution (DCLHb) and albumin which have similar viscosities but different oxygen carrying capacities. Part A: CBF was assessed in rats after one of the following regimens: (1) control-hematocrit not manipulated, (2) 30/Alb-hematocrit decreased to 30% with albumin, (3) 30/DCLHb-hematocrit decreased to 30% with DCLHb, or (4) 16/Alb/DCLHb-hematocrit decreased to 30% with albumin and then 16% with DCLHb. For viscosity matched groups (30/Alb and 30/DCLHb), CBF was greater in animals with decreased oxygen content (30/Alb); while in oxygen content matched groups (30/Alb and 16/Alb/DCLHb), CBF was greater in animals with decreased viscosity (16/Alb/DCLHb) (p < 0.05). Part B: Middle cerebral artery occlusion was performed, hemodilution achieved as in Part A, and CBF determined. For viscosity matched groups (30/Alb and 30/DCLHb), CBF was less in rats with decreased oxygen content (30/Alb); while in oxygen content matched groups (30/Alb and 16/Alb/DCLHb), CBF was greater in animals with decreased viscosity (16/Alb/DCLHb) (p < 0.05). This data supports the premise, that in normal brain, both viscosity and oxygen content effect CBF; while in ischemic brain, a decrease in viscosity but not oxygen content increases CBF.

Acute myocardial ischemia: effects of reperfusion with arterial blood

Periods of severe ischemia of 15 minutes or less injure myocytes of the dog heart reversibly in that reperfusion of the affected tissue with arterial blood salvages all myocytes destined to die if the ischemia is not relieved. While the myocytes are ischemic, they develop numerous changes as a consequence of ischemic metabolism including depletion of approximately P and accumulation of glycolytic intermediates, H+, and the end-products of adenine nucleotide pool degradation. With restoration of arterial flow, aerobic respiration resumes. Lactate and other intermediates are reutilized or are washed to the systemic circulation. If the period of severe ischemia is extended to 40-60 minutes, the injury becomes irreversible. Such myocytes cannot be salvaged by reperfusion with arterial blood and are necrotic. When reperfused, irreversibly injured myocytes develop contraction-band necrosis and accumulate calcium phosphate. Although unproved, it is possible that some myocytes, alive at the time of reperfusion, may die as a consequence of successful reperfusion. This phenomenon is termed lethal reperfusion injury. Sublethal forms of reperfusion injury, such as stunning, also occur.

Prazosin blocks the pressor but not the regional circulatory effects of diaspirin crosslinked hemoglobin

Diaspirin crosslinked hemoglobin (DCLHb) (400 mg/kg, i.v.) produces an increase in blood pressure and blood flow to the heart, spleen, stomach, small intestine, skin, mesentery and pancreas when administered to rats. The present study was conducted to determine (1) whether prazosin, an alpha 1-adrenergic antagonist, can block the pressor effect of DCLHb and (2) the effect of prazosin pretreatment on regional circulatory changes induced by DCLHb in rats. DCLHb (400 mg/kg, i.v.) produced an increase in blood pressure (64%), cardiac output (20%) and total peripheral resistance (65%) when administered to control rats. Infusion of DCLHb in prazosin (1 mg/kg, i.v.) treated rats did not show any significant pressor effect, but reversed the hypotensive effect of prazosin. Cardiac output and stroke volume were significantly increased and total peripheral resistance decreased in prazosin treated rats as compared to control (untreated) rats. DCLHb significantly increased blood flow to the heart, gastrointestinal tract, portal system (spleen), and skin of control rats. Blood flow to the brain, kidneys, and musculo-skeletal system was not altered following the infusion of DCLHb in controls rats. Infusion of DCLHb in prazosin treated rats produced a significant increase in blood flow to the brain, heart, kidneys, gastrointestinal tract, portal system, skin and musculoskeletal system. In summary, prazosin pretreatment blocked the pressor effect of DCLHb, however, blood flow to the heart, brain, gastrointestinal tract, portal system, kidneys, skin and musculoskeletal system was increased by DCLHb. It is concluded that blood flow to most of the organs is increased by DCLHb but the pressor effect of DCLHb is blocked by prazosin pretreatment.

Regional circulatory and systemic hemodynamic effects of diaspirin cross-linked hemoglobin in the rat

Diaspirin cross-linked hemoglobin (DCLHb) (Baxter Healthcare Corporation) is a promising resuscitative fluid. The effect of DCLHb (400 mg/kg, i.v.), on regional circulation and systemic hemodynamics was studied in male Sprague-Dawley rats using a radioactive microsphere technique. Systemic hemodynamics, distribution of cardiac output, regional blood flow and vascular resistance were determined before (baseline) and 15, 30 and 60 min after the administration of DCLHb. Infusion of an equal volume of saline did not produce any significant change in systemic hemodynamics or regional circulation. DCLHb produced an increase (79%) in the mean blood pressure which lasted for more than 60 min. Heart rate, cardiac output and stroke volume were not significantly affected, while total peripheral resistance was increased after the administration of DCLHb. DCLHb produced significant increases in blood flow to the heart, gastrointestinal tract (GIT), portal system and skin. The blood flow to the kidney, brain and musculoskeletal system was not significantly affected by DCLHb. The vascular resistance was not altered in the heart, brain, GIT, portal system, kidney or skin, but there was a marked increase in the vascular resistance in the musculoskeletal system. There was a significant increase in the percentage of cardiac output to visceral organs like heart, GIT and portal system, while a marked decrease in the percent cardiac output to musculoskeletal system was observed with DCLHb. It is concluded that the blood flow to most of the organs is either increased or is not affected by DCLHb.

Nitric oxide mediates the hypertensive response to a modified hemoglobin solution (DCLHb) in rats

We investigated the effect of nitric oxide synthase inhibition with L-NAME, and L-arginine (nitric oxide synthase substrate), on the hemodynamic response to a modified hemoglobin solution (DCLHb). Rats were given one of the following regimens (all groups hypervolemic except Control): Control-8.0 ml of donor blood (isovolemic exchange); HV-8.0 ml of donor blood; DCLHb-8.0 ml of DCLHb; L-NAME-30 mg.kg-1 of L-NAME followed by 8.0 ml of DCLHb; or L-Arg-8.0 ml of DCLHb followed by L-arginine (600 mg.kg-1). Mean arterial blood pressure (MABP) was continuously recorded and the change compared to baseline and expressed as delta MABP. delta MABP was greater in the HV and DCLHb groups versus the Control and L-NAME groups; and was greater in the DCLHb group versus the HV group. delta MABP was not different between the Control and L-NAME group. In the L-Arg group the initial delta MABP (after DCLHb) was similar to the DCLHb group; however, after L-arginine administration delta MABP was not different from the Control group. This study supports a hypothesis that DCLHb effects an increase in MABP by a nitric oxide related mechanism.

Diaspirin cross-linked hemoglobin (DCLHB): involvement of adrenergic mechanisms in the pressor effect

Diaspirin cross-linked Hemoglobin (DCLHb) (400 mg/kg, i.v.), a resuscitative solution, produces a pressor effect in rats and several other species. Studies were conducted to determine the role of the central nervous system and adrenal medulla in the pressor effect of DCLHb in rats. Intravenous administration of DCLHb produced an increase in blood pressure in cervical sectioned animals, which was comparable to that observed in normal rats. This indicates that the pressor effect of DCLHb was mediated through the peripheral vascular system rather than through the central nervous system. DCLHb produced a pressor effect in bilateral adrenal demedullated rats that was similar to normal rats, suggesting that the pressor effect is not through the release of catecholamines or other pressor substance from the adrenal medulla. The effects of DCLHb pretreatment on norepinephrine (0.5 microgram/kg), phenylephrine (5 micrograms/kg) and clonidine induced blood pressure and heart rate responses were also studied. DCLHb significantly potentiated the pressor response to norepinephrine and phenylephrine. Clonidine normally produces a fall in blood pressure by acting on the central alpha-adrenoceptors, and a rise in blood pressure by stimulating the peripheral vascular alpha-adrenoceptors. DCLHb produced a marked potentiation of the pressor response to clonidine (75 micrograms/kg, i.v.), that masked the central depressor effect. The specificity of the potentiation was confirmed by using phenoxybenzamine, prazosin, and yohimbine. In order to exclude the contribution of a centrally induced cardiovascular effect of clonidine, further studies were carried out in cervical sectioned rats. DCLHb markedly potentiated the pressor effect of clonidine (25 micrograms/kg, i.v.) in cervical sectioned rats. This potentiation could be attenuated by prazosin and yohimbine.(ABSTRACT TRUNCATED AT 250 WORDS)

Focal cerebral ischemia in rats: effect of hemodilution with alpha-alpha cross-linked hemoglobin on brain injury and edema

The effect of hemodilution, with alpha-alpha cross-linked hemoglobin (DCLHb), on brain injury and edema was assessed after temporary middle cerebral artery occlusion in rats. Injury was analyzed with 2,3,5-triphenyltetrazolium chloride (TTC) stain and edema by microgravimety. Part A: DCLHb was given to maintain one of the following hematocrits (Hct) and normotension: 1) 45/Hct, 2) 30/Hct, 3) 16/Hct, or 4) 9/Hct. Brain injury (% of ischemic hemisphere, mean +/- SD) was less in the 30/Hct group (31 +/- 4) versus the 45/Hct group (42 +/- 5); and in the 16/Hct (20 +/- 3) and 9/Hct (19 +/- 4) groups versus the 45/Hct and 30/Hct groups. Edema was less in the hemodiluted groups versus the 45/Hct group. Part B: DCLHb was given to maintain one of the following hematocrits and hyper (HTN)-or normotension (Norm): 1) 45/Norm, 2) 30/Norm, 3) 30/HTN, 4) 16/Norm, or 5) 16/HTN. In hematocrit matched groups hypertension decreased brain injury (30/HTN-24 +/- 2 < 30/Norm-34 +/- 4; and 16/HTN-17 +/- 3 < 16/Norm-24 +/- 4). Edema was not effected by hypertension. These results suggest that hemodilution with DCLHb decreases focal ischemic injury, and is most effective when given in a manner that induces hypertension.