Partial Tissue Oxygen Tension Research Articles

Lower limb ischemia and microrheological alterations in patients with diabetic retinopathy.

Diabetes mellitus is frequently associated with vascular pathologies and hemorheological disorders. 105 patients with diabetic retinopathy (DRP) (mean age 64.64±9.01 years, 56 males, 49 females), 35 age-matched non-diabetic (mean age 61.65±7.6 years, 14 males and 21 females) and 42 young healthy volunteers (mean age 25.52±3.32 years, 22 males, 20 females) were recruited. Lower extremity artery disease (LEAD) and microcirculatory alterations were screened by hand-held Doppler, transcutaneous partial tissue oxygen tension (tcpO2), tuning fork test, 6-minute walk test, erythrocyte aggregation and deformability. High prevalence of LEAD was detected in diabetic population: 55.3% fulfilled the criteria of LEAD based on ankle-brachial index; severely impaired tcpO2 was measured in 18.6%. The results of non-invasive measurements of the diabetic patients were significantly worse than those of the control groups (p < 0.05). Hemorheological disturbances could be characterized by the significantly higher erythrocyte aggregation (p < 0.05) and lower erythrocyte deformability (p < 0.05) in the diabetic population. Macro- and microcirculatory lower limb disorders could be revealed at high prevalence in diabetic patients with retinopathy. Measurement of tcpO2 and hemorheological variables could be useful to discover patients at higher risk for diabetic foot complications.

The Effect of Perfluorocarbon-Based Artificial Oxygen Carriers on Tissue-Engineered Trachea

The biological effect of the perfluorocarbon-based artificial oxygen carrier (Oxygent) was investigated in tissue-engineered trachea (TET) construction. Media supplemented with and without 10% Oxygent were compared in all assessments. Partial tissue oxygen tension (PtO(2)) was measured with polarographic microprobes; epithelial metabolism was monitored by microdialysis inside the TET epithelium perfused with the medium underneath. Chondrocyte-DegraPol constructs were cultured for 1 month with the medium before glycosaminoglycan assessment and histology. Tissue reaction of TET epithelial scaffolds immersed with the medium was evaluated on the chick embryo chorioallantoic membrane. Oxygent perfusion medium increased the TET epithelial PtO(2) (51.2 +/- 0.3 mm Hg vs. 33.4 +/- 0.3 mm Hg at 200 microm thickness; 12.5 +/- 0.1 mm Hg vs. 3.1 +/- 0.1 mm Hg at 400 microm thickness, p < 0.01) and decreased the lactate concentration (0.63 +/- 0.08 vs. 0.80 +/- 0.06 mmol/L, p < 0.05), lactate/pyruvate (1.87 +/- 0.26 vs. 3.36 +/- 10.13, p < 0.05), and lactate/glucose ratios (0.10 +/- 0.00 vs. 0.29 +/- 0.14, p < 0.05). Chondrocyte-DegraPol in Oxygent group presented lower glycosaminoglycan value (0.03 +/- 0.00 vs. 0.13 +/- 0.00, p < 0.05); histology slides showed poor acid mucopolysaccharides formation. Orthogonal polarization spectral imaging showed no difference in functional capillary density between the scaffolds cultured on chorioallantoic membranes. The foreign body reaction was similar in both groups. We conclude that Oxygent increases TET epithelial PtO(2), improves epithelial metabolism, does not impair angiogenesis, and tends to slow cartilage tissue formation.

ERYTHROPOIETIN ENHANCES OXYGENATION IN CRITICALLY PERFUSED TISSUE THROUGH MODULATION OF NITRIC OXIDE SYNTHASE

The aim of this study was to investigate the effect of human recombinant erythropoietin (EPO) on the microcirculation and oxygenation of critically ischemic tissue and to elucidate the role of endothelial NO synthase in EPO-mediated tissue protection. Island flaps were dissected from the back skin of anesthetized male Syrian golden hamsters including a critically ischemic, hypoxic area that was perfused via a collateralized vasculature. Before ischemia, animals received an injection of epoetin beta at a dose of 5,000 U/kg body weight with (n = 7) or without (n = 7) blocking NO synthase by 30 mg/kg body weight L-NAME (Nomega-nitro-L-arginine methyl ester hydrochloride). Saline-treated animals served as control (n = 7). Ischemic tissue damage was characterized by severe hypoperfusion and inflammation, hypoxia, and accumulation of apoptotic cell nuclei after 5 h of collateralization. Erythropoietin pretreatment increased arteriolar and venular blood flow by 33% and 37%, respectively (P < 0.05), and attenuated leukocytic inflammation by approximately 75% (P < 0.05). Furthermore, partial tissue oxygen tension in the ischemic tissue increased from 8.2 to 15.8 mmHg (P < 0.05), which was paralleled by a 21% increased density of patent capillaries (P < 0.05) and a 50% reduced apoptotic cell count (P < 0.05). The improved microcirculation and oxygenation were associated with a 2.2-fold (P < 0.05) increase of endothelial NO synthase protein expression. Of interest, L-NAME completely abolished all the beneficial effects of EPO pretreatment. Our study demonstrates that, in critically ischemic and hypoxic collateralized tissue, EPO pretreatment improves tissue perfusion and oxygenation in vivo. This effect may be attributed to NO-dependent vasodilative effects and anti-inflammatory actions on the altered vascular endothelium.

Is hemoglobin in hemoglobin vesicles infused for isovolemic hemodilution necessary to improve oxygenation in critically ischemic hamster skin?

The aim of this study was to test the influence of hemoglobin, encapsulated in phospholipid vesicles as an oxygen carrier, given in the course of isovolemic hemodilution to improve oxygenation in critically ischemic hamster flap tissue. Capillary hemodynamics and macromolecular leakage were investigated with intravital microscopy and analyzed off-line with the CapImage software. Partial tissue oxygen tension was measured with fluorescence quenching electrodes. The occurrence of apoptosis was assessed with the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay. Vesicles with (HbV) or without (V) encapsulated Hb were suspended in 6% hydroxyethyl starch (HES) used for the 33% blood exchange. In the ischemic tissue, hemodilution led to an increase in functional capillary density by 31% for HES (P < 0.01 vs. other groups), 66% for V-HES, and 62% for HbV-HES (all P < 0.01 vs. control). Capillary diameters behaved inversely proportional to capillary microhemodynamics. The 20% increase in macromolecular leakage found over time in control animals was completely abolished in the vesicles groups (P < 0.01) but not with HES. Oxygen tension was improved from 10.7 to 16.0 mmHg after HbV-HES (P < 0.01 vs. baseline and other groups). Compared with the other groups, apoptosis was significantly reduced after HbV-HES (P < 0.01). We conclude that the encapsulation of Hb was essential to attenuate hypoxia and subsequent cell death in the critically ischemic tissue. However, the effect was partly attributed to the rheological changes exerted by the vesicles.

Preconditioning with Monophosphoryl Lipid A Improves Survival of Critically Ischemic Tissue

In this study we sought to assess the effects of preconditioning with monophosphoryl lipid A on critically ischemic wound margins and on systemic and local hemodynamics and oxygenation during prolonged anesthesia with volatile anesthetics and narcotics. Twenty large white pigs were randomly assigned to receive either monophosphoryl lipid A 35 mug/kg IV or saline 24 h before dissection of a buttock flap. The animals were anesthetized with isoflurane (end-tidal concentration approximately 1.25%) for surgery and subsequent monitoring of hemodynamics and oxygenation both systemically and in the flap tissue for 6 h. Preconditioning resulted in increased cardiac index and oxygen delivery (both P < 0.05) and in decreased central venous pressure and systemic vascular resistance (both P < 0.01). In the preconditioned flap tissue, microcirculatory blood flow (laser Doppler flowmetry) and partial tissue oxygen tension (polarographic microprobes) were up to 2.5-fold higher compared with control (both P < 0.05) and flap necrosis was reduced by 20% on postoperative day 14 (P < 0.05). Our results suggest that preconditioning with a single dose of monophosphoryl lipid A may attenuate ischemia-related wound healing complications, which may be related to an improvement in perfusion and oxygenation of this tissue. Furthermore, preconditioning exerted a systemic cardiovascular stabilization effect during prolonged isoflurane anesthesia.

New generation of hemoglobin-based oxygen carriers evaluated for oxygenation of critically ischemic hamster flap tissue

The aim of this study was to investigate and compare the effects of a traditionally formulated, low-viscosity, right-shifted polymerized bovine hemoglobin solution and a highly viscous, left-shifted hemoglobin vesicle solution (HbV-HES) on the oxygenation of critically ischemic peripheral tissue. Randomized, prospective study. University laboratory. A total of 40 male golden Syrian hamsters. Island flaps were dissected from the back skin of anesthetized hamsters. The flap included a critically ischemic, hypoxic area that was perfused via a collateralized vasculature. One hour after completion of the preparation, the animals received a 33% blood exchange with 6% hydroxyethyl starch 200/0.5 (HES, n = 9), HbV suspended in HES (HbV-HES, n = 8), or polymerized bovine hemoglobin solution (n = 9). Three hours after the blood exchange, microcirculatory blood flow (laser-Doppler flowmetry) was increased to 262% of baseline for HbV-HES (p < .01) and 197% for polymerized bovine hemoglobin solution (p < .05 vs. baseline and HbV-HES). Partial tissue oxygen tension (bare fiber probes) was only improved after HbV-HES (9.4 torr to 14.2 torr, p < .01 vs. baseline and other groups). The tissue lactate/pyruvate ratio (microdialysis) was elevated to 51 in the untreated control animals, and to 34 +/- 8 after HbV-HES (p < .05 vs. control) and 38 +/- 11 after polymerized bovine hemoglobin solution (not significant). Our study suggests that in critically ischemic and hypoxic collateralized peripheral tissue, oxygenation may be improved by normovolemic hemodilution with HbV-HES. We attributed this improvement to a better restoration of the microcirculation and oxygen delivery due to the formulation of the solution.

The Influence of Trauma and Ischemia on Carbohydrate Metabolites Monitored in Hamster Flap Tissue

To monitor hypoperfusion of the peripheral tissues in critical illness caused by injury, we measured the concentrations of glucose, pyruvate, and lactate in traumatized and ischemic hamster flap tissue with the use of microdialysis. The interruption of the anatomic blood supply led to a drastic decrease in microvascular blood flow (laser Doppler flowmetry) and partial tissue oxygen tension (dye fluorescence quenching technique) in the ischemic part of the flap (both P < 0.01). In the traumatized area, blood flow, oxygen tension, and pyruvate were similar to the healthy control tissue throughout the experiments, whereas pyruvate was reduced in the ischemic tissue (P < 0.05 versus baseline and other tissues). Lactate was increased in both parts of the flap (P < 0.01 versus baseline and other groups for ischemic, not significant for traumatized). The sensitivity to detect ischemic hypoxia was 62% for lactate and 93% for lactate/pyruvate ratio (L/P) (P < 0.01). The specificity to discern ischemia-related from trauma-related changes was 71% for lactate and 70% for L/P (not significant). Our results suggest that L/P is more accurate than lactate for monitoring ischemia-related hypoxia after trauma. However, the rate of increased values originating from normally perfused but traumatized tissue was high for both markers.

Evolution of a “falx lunatica” in demarcation of critically ischemic myocutaneous tissue

Using intravital microscopy in a chronic in vivo mouse model, we studied the demarcation of myocutaneous flaps and evaluated microvascular determinants for tissue survival and necrosis. Chronic ischemia resulted in a transition zone, characterized by a red fringe and a distally adjacent white falx, which defined the demarcation by dividing the proximally normal from the distally necrotic tissue. Tissue survival in the red zone was determined by hyperemia, as indicated by recovery of the transiently reduced functional capillary density, and capillary remodeling, including dilation, hyperperfusion, and increased tortuosity. Angiogenesis and neovascularization were not observed over the 10-day observation period. The white rim distal to the red zone, appearing as "falx lunatica," showed a progressive decrease of functional capillary density similar to that of the necrotic distal area but without desiccation, and thus transparency, of the tissue. Development of the distinct zones of the critically ischemic tissue could be predicted by partial tissue oxygen tension (Pt(O(2))) analysis by the time of flap elevation. The falx lunatica evolved at a Pt(O(2)) between 6.2 +/- 1.3 and 3.8 +/- 0.7 mmHg, whereas tissue necrosis developed at <3.8 +/- 0.7 mmHg. Histological analysis within the falx lunatica revealed interstitial edema formation and muscle fiber nuclear rarefaction but an absence of necrosis. We have thus demonstrated that ischemia-induced necrosis does not demarcate sharply from normal tissue but develops beside a fringe of tissue with capillary remodeling an adjacent falx lunatica that survives despite nutritive capillary perfusion failure, probably by direct oxygen diffusion.

Normovolemic hemodilution with Hb vesicle solution attenuates hypoxia in ischemic hamster flap tissue.

The aim of this study was to test whether oxygenation in acutely ischemic, collateralized tissue may be improved by normovolemic hemodilution with a solution containing liposome-encapsulated human Hb (HbV). A skin flap model in anesthetized hamsters was used, which consisted of two parts receiving either anatomic or collateral perfusion. Microhemodynamics were investigated with intravital microscopy. Partial tissue oxygen tension was measured with a Clark-type microprobe. Hemodilution was obtained by exchanging 50% of the total blood volume with HbV suspended in 8% human serum albumin (HSA8) or 6% Dextran 70 (Dx70). The size of the vesicles was 276 nm, the P(50) was 22 mmHg, and the Hb concentration of the solutions was 7.5 g/dl. Colloid osmotic pressure and viscosity were 49.9 mmHg and 8.7 cP for HbV-Dx70 and 40.0 mmHg and 2.9 cP for HbV-HSA8, respectively. Hemodilution with HbV-Dx70 led to an increase in microvascular blood flow in the ischemic microvessels to maximally 158% (median, P < 0.01), whereas blood flow remained virtually unchanged after hemodilution with HbV-HSA8. In the ischemic tissue, oxygen tension was improved from 11.9 to 17.0 mmHg (P < 0.01) after hemodilution with HbV-Dx70 but remained virtually unchanged after hemodilution with HbV-HSA8. Our study suggests that the oxygenation in acutely ischemic, collateralized tissue may be improved by normovolemic hemodilution with HbV suspended in Dx70. The effect was achieved by an increase in microcirculatory blood flow related to the rheological properties of the suspending medium.

Interrelations of laser doppler flowmetry and brain tissue oxygen pressure during ischemia and reperfusion induced by an experimental mass lesion.

The objective of this study was to assess interrelations between bilateral changes of cortical laser doppler flowmetry and intraparenchymal, subcortical partial tissue oxygen tension in the course of an experimental trauma. Ten animals served as a sham group, 8 Sprague-Dawley rats received an unilateral, focal parietal mass lesion. The bilateral course of cortical blood flow measured by laser doppler flowmetry (LDF) was correlated with subcortical, intraparenchymal partial tissue oxygen tension [p(ti)O2]. In the sham-operated group, laser doppler mean flow values drifted between 9.0% and 9.5% and showed no significant changes over time neither between the hemispheres nor within each hemisphere. Absolute mean p(ti)O2 in sham-operated animals was 32.4 mm Hg in the left and 30.5 mm Hg in the right hemisphere. In the trauma group, mean laser doppler flow values during maximum brain compression decreased ipsilateral to 20.3% and contralateral to 34.4% of the baseline values. P(ti)O2 decreased ipsilateral from 25.9 to 6.6 mm Hg (25.4%) and contralateral from 22.6 to 9.8 mm Hg (43.6%). After balloon deflation, cortical LDF was restored much faster compared to p(ti)O2, but did not reach baseline values [ipsilateral 61.6% (p < 0.05); contralateral 75.8% of baseline values]. The p(ti)O2 values reached 25.2 mm Hg (97%) ipsilateral and 23.7 mm Hg (105%) contralateral. A temporary phase of reactive hyperemia occurred sporadically shortly after decompression. Both parameters showed a significant but rather weak correlation (r = 0.56; p < 0.001). Based upon these findings, we conclude that intraparenchymal, subcortical p(ti)O2 measurements supplemented on-line cortical CBF monitoring and score out discontinuous alternative measurement techniques in detecting hemodynamically relevant events. The small spatial resolution of LDF and p(ti)O2 probes, however, which in the small animal model may be of negligible influence, does raise the question whether the values obtained represent the microcirculatory situation of the human brain.