Biomedical subjects

Michael R Davis

Publications and source records attributed to Michael R Davis.

7 recordsLinked to original sources

PubMed2006

Bovine hemoglobin-based oxygen-carrying solution (HBOC-201) improves flap survival in a rat model of epigastric flap failure.

Despite continued improvements in surgical technique and postoperative management of pedicled flaps, partial flap necrosis continues to be a substantial problem. Several researchers sought interventions that would decrease the incidence of this complication. The hypothesis of this study is that a bovine hemoglobin-based, oxygen-carrying solution (HBOC-201) will increase oxygen delivery, thus decreasing the area of necrosis of the marginally perfused portions of a pedicled flap. Eighty male Sprague-Dawley rats were randomly assigned to one of four groups (20 animals in each group): group 1, controls (surgical creation of flap only); group 2, HBOC-201, 2 g i.v., administered preoperatively and on days 3 and 5; group 3, HBOC-201, 4 g i.v., administered preoperatively and on days 3 and 5; and group 4, hemodilution (lactated Ringer's solution) administered preoperatively and on days 3 and 5. A ventral fasciocutaneous flap (5 x 7 cm) was elevated, based on unilateral superficial inferior epigastric vessels, and the flap was replaced and sutured. Animals were examined daily and euthanized on day 7. Prior to euthanasia, digital photographs were taken of each subject, and the images were analyzed for total area of the flap and area of necrosis, using ImagePro software. Using the calculated percentage of necrosis for each animal, a mean value of percent necrosis was obtained for each animal group and used for statistical analysis. Animals in group 2 demonstrated a decreased area of necrosis when compared with the control group (9.14% vs. 22.24%, P = 0.014). In conclusion, the oxygen therapeutic HBOC-201, at a dose of 2 g, administered preoperatively and on days 3 and 5, decreased the area of necrosis in a rat model of epigastric skin-flap failure. Further investigation of this drug and its effects on flap survival is warranted.

Animals↗

PubMed2004

Thrombus-induced endothelial dysfunction: Hemoglobin and fibrin decrease nitric oxide bioactivity without altering eNOS.

BACKGROUND: Arterial thrombosis is associated with endothelial dysfunction. The purpose of this study was to determine which components of thrombus induce endothelial dysfunction and to determine their effect on endothelial nitric oxide synthase (eNOS) activity and expression. MATERIALS AND METHODS: Human aortic endothelial cells were grown to confluence. Group 1 consisted of control cells exposed to media. Group 2 was exposed to cellular components of thrombus, including erythrocytes (RBCs) (1.5, 3, and 6 x 10(4) cells/ml) and platelets (0.5, 1, and 2 x 10(5) platelets/ml). Group 3 was exposed to extracellular thrombus components, including hemoglobin (1.25, 2.5, and 5.0 g/dl), thrombin (0.4, 4.0, and 10.0 units/ml), and fibrin. The exposure time was 20 h. Nitric oxide (NO) levels were measured following exposure. Global cellular integrity was evaluated by MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) conversion. eNOS mRNA expression was measured using semiquantitative PCR and eNOS protein activity evaluated via a l-citrulline conversion assay. Studies were done in replicates of six and expressed as percentages of controls. RESULTS: NO levels decreased following exposure to hemoglobin (1.25 g/dl = 59 +/- 5%, 2.5 g/dl = 38 +/- 3%, 5 g/dl = 37 +/- 6%, P < 0.001). MTS metabolism was likewise suppressed (1.25 g/dl = 57 +/- 2%, 2.5 g/dl = 55 +/- 3%, 5 g/dl = 44 +/- 6%, P < 0.001). Fibrin diminished NO levels (37 +/- 5%, P < 0.01) and MTS metabolism (49 +/- 5%, P < 0.01). RBCs and platelets had no effect on NO production or MTS metabolism (P > 0.05). Thrombin's effect was concentration dependent, inhibiting nitric oxide production at low doses while stimulating it at high doses (P < 0.01). All thrombin doses enhanced MTS metabolism (P < 0.05). eNOS activity was not altered by fibrin, thrombin, or hemoglobin exposure (P > 0.05). Moreover, eNOS mRNA expression was unaffected (P > 0.05). CONCLUSIONS: Intact cellular components of thrombus do not cause endothelial dysfunction in vitro. However, free hemoglobin and fibrin diminish NO bioactivity, likely via scavenging. Thrombin affects NO levels in a concentration-dependent manner. Neither eNOS expression nor eNOS activity is diminished, indicating that thrombus does not cause permanent changes in NO generation capability.

Aorta↗

PubMed2003

Endothelial dysfunction after arterial thrombosis is ameliorated by L-arginine in combination with thrombolysis.

PURPOSE: To assess endothelial function after arterial thrombosis creation and after administration of a novel thrombolytic regimen in a new porcine model. MATERIALS AND METHODS: Untreated arteries that had undergone thrombosis for 90 minutes were compared to arteries treated with tissue plasminogen activator (tPA, 4 mg) and a combination of tPA and L-arginine (L-arg; 600 mmol/L). External iliac artery luminal diameter was measured with use of duplex ultrasonography. Endothelial-dependent relaxation (EDR) and endothelial-independent relaxation (EIR) were measured with use of acetylcholine chloride (ACh) and sodium nitroprusside (NTP), respectively. Endothelial integrity was confirmed by scanning electron microscopy (SEM). Nitric oxide (NO) levels were determined with use of a chemiluminescent assay of its nitrite/nitrate metabolites (NO(x)). RESULTS: After thrombosis, EDR was decreased (69% +/- 9.5; ACh = 15 micro g/min; n = 6). EDR remained unchanged after thrombolysis with tPA despite complete dissolution of thrombus (67% +/- 5.7; ACh = 15 micro g/min; n = 5). Thrombolysis with use of tPA coupled with L-arg resulted in an increase in EDR (95% +/- 4.9; ACh = 15 micro g/min; n = 5; P =.007). EIR was preserved in all groups, with uniform response to NTP. SEM analysis revealed intact endothelium in all groups. Local NO(x) levels were diminished after 90 minutes of thrombosis (49.3 micro mol/L vs 40.8 micro mol/L; P =.0002), but increased to 55.7 micro mol/L after thrombolysis with tPA and L-arg (P = NS). CONCLUSIONS: Thrombus induces arterial dysfunction acutely without altering endothelial integrity. This dysfunction is ameliorated through regional administration of L-arg in combination with standard thrombolytic therapy, which increases local NO levels. This model allows the in-vivo study of thrombosis and alternative thrombolytic regimens. Regional enhancement of NO levels may prove to be an attractive adjunct in thrombolytic therapy.

Animals↗

PubMed2003

A comparison of the hemoglobin-based oxygen carrier HBOC-201 to other low-volume resuscitation fluids in a model of controlled hemorrhagic shock.

BACKGROUND: The ideal resuscitation fluid for military applications would be effective at low volumes, thereby reducing logistical constraints. We have previously shown that the bovine hemoglobin-based oxygen carrier HBOC-201 is an effective low-volume resuscitation fluid. The goal of this experiment was to evaluate the effectiveness of HBOC-201 in comparison with other low-volume resuscitation fluids in a swine model of controlled hemorrhagic shock. METHODS: Forty-two immature female Yorkshire swine (55-70 kg) were divided into seven groups of six. Animals were hemorrhaged to a mean arterial pressure of 30 mm Hg. After 45 minutes, animals were resuscitated to a mean arterial pressure of 60 mm Hg with one of the following agents: hypertonic saline 7.5% (HTS), hypertonic saline 7.5%/Dextran-70 6% (HSD), pentastarch 6%, hetastarch 6%, or HBOC-201. Lactated Ringer's (LR) solution was used as a standard resuscitation control. Another group of animals received no resuscitation. Resuscitation was continued for 4 hours. Hemodynamic variables and oxygen consumption were measured continuously. Arterial and mixed venous blood gases and serum lactate levels were measured at intervals throughout the experiment. Data were analyzed using analysis of variance with Tukey's post hoc test when appropriate. Significance was defined as p < 0.05. RESULTS: Five of six animals in the no-resuscitation control group, six of six in the HTS group, and one animal in the HSD group died before completion of the study. All other animals survived to completion. Animals receiving resuscitation with HBOC-201 had significantly lower cardiac output, mixed venous oxygen saturation levels, and urinary output throughout the resuscitation period; however, there were no differences with regard to lactate, base excess, or oxygen consumption. Animals receiving HBOC-201 required significantly less fluid than any other group. CONCLUSION: In this model, hypotensive resuscitation with HBOC-201 restores tissue oxygenation and reverses anaerobic metabolism at significantly lower volumes when compared with HTS, HSD, pentastarch, or hetastarch solutions. These data suggest that HBOC-201 would be an effective primary resuscitation fluid for far-forward military or rural trauma settings where logistic constraints and prolonged transport times are common. However, when HBOC-201 is administered as a primary resuscitation fluid in hypotensive protocols, common clinical markers for determining adequacy of resuscitation may not be useful.

Analysis of Variance↗

PubMed2002

Luminal thrombus disrupts nitric oxide-dependent endothelial physiology.

BACKGROUND: The goals of this study were: (1) to develop a large animal model to study endothelial function, and (2) to determine if arterial thrombosis induces endothelial dysfunction in vivo. METHODS: Surgical exposure of the porcine iliac and femoral arteries was performed. Normal porcine arteries were compared with arteries subjected to 90 min of arterial thrombosis. External iliac artery (EIA) luminal diameters were measured using M- and B-mode duplex ultrasound. Endothelium-dependent relaxation (EDR) and endothelium-independent relaxation (EIR) were measured using acetylcholine (ACh) and sodium nitroprusside (NTP), respectively. Endothelial integrity was determined by factor VIII immunohistochemistry (F8) and scanning electron microscopy (SEM). Nitric oxide levels were determined using a chemiluminescence assay of nitrite/nitrate metabolites (NO(x)). Continuous variables were analyzed using the two-tailed Student t test. RESULTS: Control artery EDR was 80 +/- 7.1% (+/- SE), while arteries exposed to luminal thrombus for 90 min had an EDR of 55.2 +/- 5.7% (ACh = 15 microg/min, n = 11, P = 0.0231). EIR was preserved in normal and thrombosis groups with uniform response to NTP (4.92 +/- 0.1 cm vs 5.07 +/- 0.42 cm, P = 0.76). F8 staining identified endothelium in all groups. SEM analysis revealed an intact monolayer of endothelium after thrombosis. Local NO(x) levels were 17.3% lower after 90 min of thrombosis (49.3 microM vs 40.8 microM, n = 16, P < 0.001). CONCLUSIONS: Luminal thrombus induces arterial dysfunction acutely without causing endothelial cell loss. EIR remains unaffected, indicating normal smooth muscle cell function. NO(x) levels suggest that nitric oxide levels are decreased acutely after thrombosis. The development of this porcine large animal model allows the in vivo study of vasospasm and alternative thrombolytic regimens.

Acetylcholine↗

PubMed2002

The polymerized bovine hemoglobin-based oxygen-carrying solution (HBOC-201) is not toxic to neural cells in culture.

BACKGROUND: Recent data suggest that a neurotoxic effect of blood or its components may contribute to secondary neural cell dysfunction. This study investigated the effects of HBOC-201 (Hemopure) and purified human hemoglobin (hHgb) on rat fetal neural cell culture. METHODS: Neural cell cultures were exposed to HBOC-201 and hHgb (0.02, 0.2, 2.0, and 6.5 g/dL) for 24 hours, and then analyzed for proliferation, metabolism, and neurolysis. RESULTS: Cultures exposed to HBOC-201 maintained levels of proliferation and metabolism similar to controls while demonstrating no cellular lysis. However, cultures exposed to hHgb demonstrated decreased proliferation after exposure to 0.2, 2.0, and 6.5 g/dL hHgb (14,252.14, 3,221.89, and 343.12 vs. 19,509.53; p< 0.05) when compared with controls. In addition, cultures exposed to hHgb demonstrated decreased metabolic activity and increased cell lysis when compared with controls (p < 0.05). CONCLUSION: Cultures exposed to HBOC-201 displayed sustained metabolic activity and proliferation, and demonstrated no neurolysis, suggesting that HBOC-201 does not display the toxic characteristics of hHgb.

Analysis of Variance↗

PubMed2002

Trends in endovascular surgery training.

PURPOSE: To gather vascular surgery fellows' opinions on various issues related to endovascular surgery (EVS) over a 2-year period and analyze the responses to identify trends in EVS training. METHODS: Vascular surgery fellows in 2 consecutive years were given a 2-page questionnaire inquiring about training protocols and local practice habits. Respondents included 64 vascular fellows from the academic year 1998-1999 (F98) and 52 vascular fellows from the academic year 1999-2000 (F99) (78% men in the entire population; mean age 34 years), representing a significant fraction of trainees in North America. Data from F98 and F99 were compared and analyzed. RESULTS: The majority (66%) of vascular surgery fellows were trained at university hospitals and performed EVS at the time of the survey: 83% in the F98 class and 92% in the F99 group (p=0.17). Utilization rates among the 9 interventions surveyed ranged from angiography (83%) and angioplasty (77%) to intravascular ultrasound (33%) and atherectomy (15%). Performance of endovascular grafting significantly increased among trainees (50% versus 81%, p<0.005), while atherectomy and angioscopy decreased. EVS performed in the operating room with portable imaging equipment decreased (67% versus 42%, p=0.02) as access to the radiology and cardiology suites increased. In most communities (63%), radiology specialists performed most of the EVS procedures, but the portion of communities where vascular surgery performed the majority of EVS procedures increased from 20% to 35% (p=0.10) from F98 to F99. Responders (90%) believed that EVS would become a major component of vascular surgery and comprise 30% of their future practice. The proportion of fellows who believed they were sufficiently trained in endovascular techniques increased from 30% to 50% (p=0.04), with the remainder willing to devote a short period (<3 months) for further training. CONCLUSIONS: The vast majority of vascular trainees perform EVS and believe that it will have an increasing role in their practice. Trends include increased endovascular grafting and performance of EVS by vascular surgeons in interventional suites.

Adult↗