A mathematical model of tumor oxygen and glucose mass transport and metabolism with complex reaction kinetics

Hypoxia imparts radioresistance to tumors, and various approaches have been developed to enhance oxygenation, thereby improving radiosensitivity. This study explores the influence of kinetic and physical factors on substrate metabolism in a tumor model, based on a Krogh cylinder. In tissue, aerobic metabolism is assumed to depend on glucose and oxygen, represented by the product of Michaelis-Menten expressions. For the base case, an inlet pO(2) of 40 mmHg, a hypoxic limit of 5 mmHg, and a tissue/capillary radius ratio of 10 are used. For purely aerobic metabolism, a hypoxic fraction of 0.16 and volume-average pO(2) of 8 mmHg are calculated. Reducing the maximum oxygen rate constant by 9%, decreasing the tissue cylinder radius by 5%, or increasing the capillary radius by 8% abolishes the hypoxic fraction. When a glycolytic term is added, concentration profiles are similar to the base case. Using a distribution of tissue/capillary radius ratios increases the hypoxic fraction and reduces sensitivity to the oxygen consumption rate, compared to the case with a single tissue/capillary radius ratio. This model demonstrates that hypoxia is quite sensitive to metabolic rate and geometric factors. It also predicts quantitatively the effects of inhibited oxygen metabolism and enhanced mass transfer on tumor oxygenation.     

Pyoderma gangrenosum: skin grafting after preparation with hyperbaric oxygen

Four patients with pyoderma gangrenosum were treated with hyperbaric oxygen to prepare the wounds for skin grafting. Each wound responded to a course of daily hyperbaric oxygen with reduction of infection and increased capillary angiogenesis. During follow-up periods of 12 to 30 months, all wounds remained healed. Although the exact etiology of pyoderma gangrenosum is unknown, vasculitis with wound ischemia and infection are prominent components. Inspired oxygen partial pressures of 1100 to 1300 mmHg elevate wound oxygen tension despite relative ischemia. The impaired intracellular bacterial killing of hypoxic leukocytes is corrected during each day's 2-hour bolus of hyperbaric oxygen. Daily wound oxygenation increases collagen production by fibroblasts to support capillary angiogenesis.     

Role of nitric oxide in capillary perfusion and oxygen delivery regulation during systemic hypoxia

The role of nitric oxide (NO) and reactive oxygen species (ROS) in regulating capillary perfusion was studied in the hamster cheek pouch model during normoxia and after 20 min of exposure to 10% O2-90% N2. We measured PO2 by using phosphorescence quenching microscopy and ROS production in systemic blood. Identical experiments were performed after treatment with the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA) and after the reinfusion of the NO donor 2,2'-(hydroxynitrosohydrazono)bis-etanamine (DETA/NO) after treatment with L-NMMA. Hypoxia caused a significant decrease in the systemic PO2. During normoxia, arteriolar intravascular PO2 decreased progressively from 47.0 +/- 3.5 mmHg in the larger arterioles to 28.0 +/- 2.5 mmHg in the terminal arterioles; conversely, intravascular PO2 was 7-14 mmHg and approximately uniform in all arterioles. Tissue PO2 was 85% of baseline. Hypoxia significantly dilated arterioles, reduced blood flow, and increased capillary perfusion (15%) and ROS (72%) relative to baseline. Administration of L-NMMA during hypoxia further reduced capillary perfusion to 47% of baseline and increased ROS to 34% of baseline, both changes being significant. Tissue PO2 was reduced by 33% versus the hypoxic group. Administration of DETA/NO after L-NMMA caused vasodilation, normalized ROS, and increased capillary perfusion and tissue PO2. These results indicate that during normoxia, oxygen is supplied to the tissue mostly by the arterioles, whereas in hypoxia, oxygen is supplied to tissue by capillaries by a NO concentration-dependent mechanism that controls capillary perfusion and tissue PO2, involving capillary endothelial cell responses to the decrease in lipid peroxide formation controlled by NO availability during low PO2 conditions.     

Tumor PO(2) changes during photodynamic therapy depend upon photosensitizer type and time after injection

In this study, the vascular and tissue oxygen changes induced by photodynamic therapy in the RIF-1 tumor were examined, using electron paramagnetic resonance (EPR) oximetry. Two photosensitizers, including verteporfin (BPD-MA in a lipid-based formulation) and aminolevulinic acid-induced protoporphyrin IX (ALA-PPIX), were investigated with optical irradiation, sufficient to induce sub-curative damage in the tumor tissue, and the transient changes in PO(2) and vascular perfusion were examined. A large increase in tissue oxygenation (from 3 up to 9.5 mmHg) was observed when treated with ALA-PPIX based photodynamic therapy, which lasted during the treatment and a small residual increase that returned back to baseline levels by 48 h after treatment. With verteporfin-based photodynamic therapy, one group of animals was irradiated 15 min after injection and exhibited a small decrease in oxygenation relative to pre-irradiation levels. The second group was irradiated at 3 h after injection and exhibited a large increase in the average PO(2), (from 3 to 15 mmHg) by the end of the treatment. These observations indicate that photodynamic therapy significantly increases tissue PO(2) under certain treatment conditions, with the potential cause being either increased local blood flow or decreased local oxygen metabolic consumption due to cellular damage.     

A computational model that links non-periodic vasomotion to enhanced oxygenation in skeletal muscle

We propose a model of a capillary network in which chaotic capillary activity is crucial for efficient oxygenation of a muscle fiber. Tissue oxygenation by microcirculation is controlled by a complex pattern of opening and closing of precapillary sphincters, a phenomenon known as vasomotion. We model the individual precapillary sphincter as a non-linear oscillator that exhibits perfectly periodic vasomotion in isolation. The precapillary sphincters surrounding an active fiber are considered as a network; specific modes of interaction within this network result in complex patterns of vasomotion. In our model, efficient oxygenation of the fiber depends crucially on the mode of interaction among the vasomotions of the individual capillaries. Network interactions that lead to chaotic vasomotion are found to be essential for meeting the tissue oxygen demands precisely. Interactions that cause regular rhythmic patterns of vasomotion fail to meet oxygenation demands accurately.     

Negative-Pressure Wound Therapy Enhances Local Inflammatory Responses in Acute Infected Soft-Tissue Wound

Clinical studies found that negative-pressure wound therapy (NPWT) displayed significant clinical benefits in the healing of infected wounds. However, the effect of NPWT on local inflammatory responses in acute infected soft-tissue wound has not been investigated thoroughly. The purpose of this study was to test the impact of NPWT on local expression of proinflammatory cytokines, amount of neutrophils, and bacterial bioburden in wound from acute infected soft-tissue wounds. Full-thickness wounds were created on the back of rabbits, and were inoculated with Staphylococcus aureus strain ATCC29213. The wounds were treated with sterile saline-moistened gauze dressings and NPWT with continuous negative pressure (?125 mmHg). Wound samples were harvested on days 0 (6 h after bacterial inoculation), 2, 4, 6, and 8 at the center of wound beds before irrigation for real-time PCR analysis of gene expression of IL-1β, IL-8, and TNF-α. Wound biopsies were examined histologically for neutrophil quantification in different layers of tissue. Quantitative bacterial cultures at the same time point were analyzed for bacterial clearance. Application of NPWT to acute infected wounds in rabbits was compared with treatment with sterile saline-moistened gauze, over an 8-day period. NPWT-treated wounds exhibited earlier and greater peaking of IL-1β and IL-8 expression and decrease in TNF-α expression over the early 4 days (P < 0.05). Furthermore, histologic examination revealed that significantly increased neutrophil count was observed in the shallow layer in wound biopsies of NPWT treatment at day 2 (P < 0.001). In addition, there was a statistically significant decrease of bacteria load from baseline (day 0) at days 2 and 8 in NPWT group (P < 0.05). In conclusion, this study demonstrates that NPWT of acute infected soft-tissue wounds leads to increased local IL-1β and IL-8 expression in early phase of inflammation, which may trigger accumulation of neutrophils and thus accelerate bacterial clearance. Meanwhile, the success of NPWT in the treatment of acute wounds can attenuate the expression of TNF-α, and the result may partly explain how NPWT can avoid significantly impairing wound healing.     

负压创面治疗技术对水通道蛋白4表达变化的研究

目的：研究爆炸伤后肌肉组织中AQP4蛋白表达变化的规律,以及应用创面负压吸引技术后AQP4蛋白表达的变化影响,探讨创面负压吸引技术的可能作用机制。方法：在猪软组织爆炸伤模型基础上将10只家猪的双侧臀部随机分为实验组和对照组,爆炸致伤造成的创面分别应用传统纱布爆炸治疗及负压创面治疗。应用Western-Blot技术和RT-PCR技术检测创面组织中AQP4蛋白和AQP4 mRNA的表达水平,并对两者的相关性进行分析。结果：致伤3天后对照组和实验组创面组织AQP4蛋白和AQP4 mRNA表达均达到峰值,随后逐渐降低,对照组创面AQP4蛋白和AQP4 mRNA水平显著高于实验组（P〈0.05）。实验组及对照组AQP4 mRNA与AQP4蛋白表达呈正相关。结论：负压创面治疗技术可减低创面组织AQP4蛋白表达。AQP4蛋白表达变化可能是负压创面治疗技术促进创面愈合的机制之一。     

Negative pressure wound therapy reduces the motility of <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> and enhances wound healing in a rabbit ear biofilm infection model

Pseudomonas aeruginosa motility, virulence factors and biofilms are known to be detrimental to wound healing. The efficacy of negative pressure wound therapy (NPWT) against P. aeruginosa has been little studied, either in vitro or in vivo. The present study evaluated the effect of negative pressure (NP) on P. aeruginosa motility in vitro, and the effect of NPWT on virulence factors and biofilms in vivo. P. aeruginosa motility was quantified under different levels of NP (atmospheric pressure, ? 75, ? 125, ? 200 mmHg) using an in vitro model. Swimming, swarming and twitching motility were significantly inhibited by NP (? 125 and ? 200 mmHg) compared with atmospheric pressure (p = 0.05). Virulence factors and biofilm components were quantified in NPWT and gauze treated groups using a rabbit ear biofilm model. Biofilm structure was studied with fluorescence microscopy and scanning electron microscopy. Additionally, viable bacterial counts and histological wound healing parameters were measured. Compared with the control, NPWT treatment resulted in a significant reduction in expression of all virulence factors assayed including exotoxin A, rhamnolipid and elastase (p = 0.01). A significant reduction of biofilm components (eDNA) (p = 0.01) was also observed in the NPWT group. The reduction of biofilm matrix was verified by fluorescence- and scanning electron-microscopy. NPWT lead to better histologic parameters (p = 0.01) and decreased bacterial counts (p = 0.05) compared with the control. NPWT treatment was demonstrated to be an effective strategy to reduce virulence factors and biofilm components, which may explain the increased wound healing observed.     

Metabolic models of microcirculatory regulation.

The functions and integrity of body tissues are critically dependent on an adequate oxygen supply. Because the transport of oxygen to the cells is intimately linked to the microcirculation, the concept of microcirculation-metabolism coupling has received much attention. In essence, the metabolic theory of intrinsic control of the microcirculation states that microvascular tone is locally modulated to maintain adequate oxygen levels in the parenchymal cells. We propose a two-component control system for the regulation of tissue O2 delivery in accordance with metabolic needs. A precapillary sphincter control mechanism maintains tissue PO2 by governing the number of perfused capillaries. Functional capillary density in turn determines surface area available for diffusion and capillary-to-cell diffusion distance. On the other hand, the arteriolar control system modulates local blood flow in accordance with parenchymal O2 utilization and thereby minimizes changes in capillary PO2 when the O2 availability/demand ratio is decreased. We propose that the precapillary sphincters are more sensitive to changes in tissue PO2 than are the flow-regulating arterioles. Consequently, for mild stresses, adequate tissue oxygenation is maintained mainly by precapillary sphincter control of diffusion parameters without the need for changes in blood flow. However, as metabolic stresses become greater, blood flow regulation becomes the dominant factor in the control of tissue O2 delivery. Thus, by working in concert, the local mechanisms regulating microvascular resistance and effective capillary density provide a wide margin of safety against the development of cellular hypoxia.     

A computational study of the effect of vasomotion on oxygen transport from capillary networks

The objective of this study was to investigate the effect of arteriolar vasomotion on oxygen transport from capillary networks. A computational model was used to calculate blood flow and oxygen transport from a simulated network of striated muscle capillaries. For varying tissue oxygen consumption rates, the importance of the frequency and amplitude of vasomotion-induced blood flow oscillations was studied. The effect of myoglobin on oxygen delivery during vasomotion was also examined. In the absence of myoglobin, it was found that when consumption is high enough to produce regions of hypoxia under steady flow conditions, vasomotion-induced flow oscillations can significantly increase tissue oxygenation and decrease oxygen transport heterogeneity. The largest effect was seen for low-frequency, high-amplitude oscillations (1.5-3 cycles min(-1), 90% of steady-state velocity). By contrast, at physiological tissue myoglobin concentrations, vasomotion did not improve tissue oxygenation. This unexpected finding is due to the buffering effect of myoglobin, suggesting that in highly aerobic muscles short-term storage of oxygen is more important than the possibility of increasing transport through vasomotion.     

Longitudinal oxygen gradients in cerebra micro vessels in acute anaemia in rats

Using a fine-tip oxygen microelectrodes the longitudinal gradients of oxygen tension (pO2) have been studied in small arterioles (with lumen diameter in control of 5 +/- 20 microm) and in capillaries of the rat brain cortex during stepwise decrease of the blood haemoglobin concentration [Hb] from control [Hb]--14.4 +/- 0.3 g/dl to 10.1 +/- 0.2 g/dl (step 1), 7.0 +/- 0.2 g/dl (step 2) and 3.7 +/- 0.2 g/dl (step 3). All data are presented as "mean +/- standard error". Oxygen tension was measured in arteriolar segments in two locations distanced deltaL = 265 +/- 34 microm, n = 30. Mean diameter of studied arterioles was 10.7 +/- 0.5 microm, n = 71. Length of studied capillary segments was about deltaL = 201 +/- 45 Mm, n = 18. The measured longitudinal pO2 gradient (deltapO2/deltaL) in arterioles amounted 0.03 +/- 0.01 mmHg/microm, n = 15 in control; 0.06 +/- 0.01 mmHg/microm, n = 16 (step 1); 0.07 +/- +/- 0.01 mmHg/microm, n = 14 (step 2); 0.1 +/- 0.01 mmHg/microm, n = 30 (step 3). In the capillaries, the deltapO2/deltaL amounted to: 0.07 +/- 0.01 mmHg/microm, n = 17 (control); 0.09 +/- 0.02 mmHg/microm, n = 16 (step 1); 0.08 +/- 0.01 mmHg/microm, n = 15 (step 2); 0.1 +/- 0.02 mmHg/microm, n = 18 (step 3). An over threefold decrease in the system blood oxygen capacity did not result in significant changes (p > 0.05) of the deltapO2/deltaL in capillaries that might result in relatively homogeneous oxygen flux from blood to tissue in acute anaemia. The longitudinal gradients of blood O2 saturation (deltaSO2/deltaL) in studied arterioles and capillaries were obtained using oxygen dissociation curve (ODC) of haemoglobin in the system blood. The gradients deltaSO2/deltaL in capillaries was shown to be threefold higher than the corresponding gradients in arterioles. The data show that anatomic capillaries are the main source of oxygen to brain tissue as in control and in hypoxic conditions. Sufficient oxygen delivery to brain tissue in acute anaemia is maintained by compensatory mechanisms of cardiovascular and respiratory systems. The data presented are the first measurements of the longitudinal pO, gradients in capillaries and minute cortical arterioles at acute anaemia.     

A naphthalocyanine-based EPR probe for localized measurements of tissue oxygenation.

A new electron paramagnetic resonance (EPR) oximetry probe, based on a naphthalocyanine macrocycle, is reported to exhibit high oxygen sensitivity and favorable EPR characteristics for biological applications. The free radical probe, lithium naphthalocyanine (LiNc), is synthesized as fine microcrystalline powder with particle size less than 1 microm and high spin density. It exhibits a single sharp EPR peak, whose width varies linearly with oxygen partial pressure (pO2). The EPR spectrum is nonsaturable at typical microwave power levels (< 25 mW at X-band). These unique characteristics make this probe ideal for measuring oxygen concentration in biological tissues, in vivo. The peak-to-peak width under anoxic conditions is 0.51 G (at X-band), and it increases linearly with increase in oxygen partial pressure and reaches 26.0 G for 100% oxygen (760 mmHg), showing an oxygen sensitivity of 34 mG/mmHg. The probe responds to changes in pO2 quickly and reproducibly, thus enabling dynamic measurements of regional oxygenation in real time. The application of this probe for oximetry is demonstrated in an in vivo biological system. The changes in pO2 were monitored in the leg muscle tissue of a living mouse breathing room air and carbogen (95% oxygen + 5% CO2), alternatively. The mean pO2 measured with this probe in muscle tissues was consistent with values reported previously using other methods. Overall, the probe shows very desirable characteristics for localized measurements of tissue oxygenation.     

Tissue oxygenation and perfusion in inferior pedicle reduction mammaplasty by near-infrared reflection spectroscopy and color-coded duplex sonography

Near-infrared reflection spectroscopy has been used in various experimental and clinical settings to investigate tissue perfusion and oxygenation noninvasively. Its application in plastic surgery has only recently been reported. The current study used near-infrared reflection spectroscopy to monitor cutaneous microcirculation in breast skin flaps after inferior pedicle reduction mammaplasty. Thirty patients underwent bilateral reduction mammaplasty by a modified Robbins technique. Near-infrared reflection spectroscopy measurements were performed preoperatively and postoperatively at several defined positions of the breast. The reflection spectroscopy system was capable of detecting absolute values of total hemoglobin in milligrams per milliliter of tissue and tissue hemoglobin oxygen saturation in percent. Color-coded duplex sonography was used to visualize nutrient vessels of the inferior dermoglandular pedicle and to measure systolic peak flow in the arteries supplying the nipple-areola complex. Reflection spectroscopy values were examined for changes during the postoperative course. Reflection spectroscopy and duplex sonography values were analyzed for differences between patients with normal and compromised skin flap perfusion and wound healing, which was assessed clinically and by ultrasound. Preoperative reflection spectroscopy values demonstrated local, regional, and interindividual variations. Postoperatively, characteristic changes of tissue hemoglobin oxygen saturation and total hemoglobin were observed in all patients during the 2-week follow-up. Reflection spectroscopy values differed significantly between breast and nipple-areola skin. Tissue hemoglobin oxygen saturation was significantly lower, and total hemoglobin significantly higher, in patients with impaired wound healing compared with patients having normal wound healing. However, systolic peak flow in arteries of the inferior dermoglandular pedicle did not reveal differences between patients with impaired or normal wound healing of the nipple-areola complex. Near-infrared reflection spectroscopy allows the detection of hemoglobin content and oxygenation in skin flaps. Changes in tissue hemoglobin oxygen saturation and total hemoglobin reflect hemodynamic changes in skin flaps during normal and pathological wound healing. Because of considerable intraindividual and interindividual variations, trend values seem to be superior to single measurements. Although in this study, near-infrared reflection spectroscopy was capable of distinguishing between normal and impaired perfusion in skin flaps in a clinical model, its future implication may be the early detection of vascular compromise in free flaps.     

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.     

Effect of oxygen consumption by measuring method on PO2 transients associated with the passage of erythrocytes in capillaries of rat mesentery

Mathematical models have predicted the existence of Po(2) gradients between erythrocytes in capillaries in the usual case where plasma contributes substantial resistance to oxygen diffusion. According to theoretical predictions, these gradients could be detected as rapid Po(2) fluctuations (erythrocyte-associated transients, EATs) along the capillary. However, verification of a model and correct choice of its parameters can be made only on the basis of direct experimental measurements. We used phosphorescence quenching microscopy to measure Po(2) in 52 capillaries of rat mesentery to obtain plasma Po(2) values 100 times/s at a given point along a capillary. A 532-nm laser generated 10-mus pulses of light, concentrated by a x100 objective, onto a spot 0.9 mum in diameter. The presence of erythrocytes in the excitation region was detected on the basis of phosphorescence amplitude (PA), proportional to the amount of plasma encountered by the laser beam, and on the basis of the intensity of transmitted laser light (LT), detected by a photodiode placed under the capillary. The data revealed correlated waveforms in PA, LT, and Po(2) in capillaries. The magnitude of the Po(2) gradients between erythrocytes and plasma was correlated with average capillary Po(2). EATs in Po(2) were more readily detected in capillaries with relatively low oxygenation. The correlation coefficients between PA and Po(2) for the half of the capillaries (n = 26) below the median Po(2) (mean Po(2) = 17 mmHg; R = -0.72) was higher than that for the other half (mean Po(2) = 39 mmHg; R = -0.38). These results support the theoretical predictions of EATs and plasma Po(2) gradients in capillaries.     

Erythrocyte-associated transients in PO2 revealed in capillaries of rat mesentery

Mathematical models have predicted the existence of Po(2) gradients between erythrocytes in capillaries in the usual case where plasma contributes substantial resistance to oxygen diffusion. According to theoretical predictions, these gradients could be detected as rapid Po(2) fluctuations (erythrocyte-associated transients, EATs) along the capillary. However, verification of a model and correct choice of its parameters can be made only on the basis of direct experimental measurements. We used phosphorescence quenching microscopy to measure Po(2) in 52 capillaries of rat mesentery to obtain plasma Po(2) values 100 times/s at a given point along a capillary. A 532-nm laser generated 10-micros pulses of light, concentrated by a x100 objective, onto a spot 0.9 microm in diameter. The presence of erythrocytes in the excitation region was detected on the basis of phosphorescence amplitude (PA), proportional to the amount of plasma encountered by the laser beam, and on the basis of the intensity of transmitted laser light (LT), detected by a photodiode placed under the capillary. The data revealed correlated waveforms in PA, LT, and Po(2) in capillaries. The magnitude of the Po(2) gradients between erythrocytes and plasma was correlated with average capillary Po(2). EATs in Po(2) were more readily detected in capillaries with relatively low oxygenation. The correlation coefficients between PA and Po(2) for the half of the capillaries (n = 26) below the median Po(2) (mean Po(2) = 17 mmHg; R = -0.72) was higher than that for the other half (mean Po(2) = 39 mmHg; R = -0.38). These results support the theoretical predictions of EATs and plasma Po(2) gradients in capillaries.     

VAC 技术治疗兔耳缺血性创面的实验研究

目的:观察间歇和持续负压下缺血创面不同处理与愈合的关系。方法:实验前1天,用脱毛剂(Nair,美国)对兔耳背脱毛。动物用1%戊巴比妥钠耳缘静脉注射麻醉(30 mg/kg体重),固定于手术台。75%乙醇消毒双侧耳背皮肤。距耳根3-3.5cm处分离、结扎兔耳中央神经血管束。在耳背中部形成直径2.5cm全层皮肤缺损创面(保留软骨膜)[1]。止血后置动物于特制木盒内。42只大白兔共84个创面,随机分为-50mmHg-75mmHg和-100mmHg 3大组,分别施以间歇负压(运行2分钟,停1分钟)和持续负压组。实验分别运用-50mmHg,-75mmHg,-100mmHg三个不同负压值进行连续、间歇治疗兔耳缺血性创面,观察伤后1,3,7,10,14,20d创面愈合情况,取伤后7d组织标本进行Western blot、HE染色,观察VEGF(vascular endothelial growth factor)的表达及创面上皮的再生和肉芽组织生长情况[1]。以及各时间点细胞凋亡的检测。结果:-50mmHg(纱布+海绵)间歇负压引流技术治疗兔耳缺血性创面的愈合最快,-75mmHg治疗组次之,-100mmHg治疗组创面愈合最慢。在同一时间点上,-50mmHg治疗组与-75mmHg,-100mmHg治疗组和空白对照组之间相比,能够更快地促进创面VEGF的表达和肉芽组织的再生,毛细血管增多。封闭负压治疗能够降低创面组织细胞的凋亡的发生。结论:(1)封闭负压治疗能够促进缺血创面的肉芽组织再生及VEGF的表达,减少创面组织细胞的凋亡的发生;(2)-50mmHg间歇封闭负压治疗效果最好。     

Influence of Oxygen on Wound Healing Dynamics: Assessment in a Novel Wound Mouse Model under a Variable Oxygen Environment

Introduction

Although oxygen is essential for the wound healing process, tissue hypoxia is known to stimulate angiogenesis. To explore these inconsistent findings, we estimated the influence of the oxygen environment on wound healing with our original model.

Methods

Experiment 1 (Establishment of the model): To modify the topical oxygen tension, oxygen impermeable (polyvinylidene chloride) and permeable (polymethylpentene) membranes were applied to symmetrical excisional wounds in ddy mice (n = 6). Oxygen tension under the membrane was quantified with a device using photo-quenching technique. Experiment 2 (Influence of oxygen environment on wound healing): The wound area, granulation thickness and vascular density were analyzed under different oxygen environments (n = 24).

Results

Experiment 1: The permeable group maintained equivalent oxygen level to atmosphere (114.1±29.8 mmHg on day 7), while the impermeable group showed extremely low oxygen tension (5.72±2.99 mmHg on day 7). Accordingly, each group was defined as the normoxia group and the hypoxia group. Experiment 2: Percent decrease in wound size was significantly enhanced in the normoxia group (11.1±1.66% on day 7) in comparison with the hypoxia group (27.6±3.47% on day 7). The normoxia group showed significantly thicker granulation tissue than the hypoxia group (491.8±243.2 vs. 295.3±180.9 µm). Contrarily, the vascular density of the hypoxia group significantly increased on day 7 (0.046±0.025 vs. 0.011±0.008 mm²/mm²).

Conclusions

Our original model successfully controlled local oxygen concentration around the wound, and the hypoxic wounds showed increased angiogenesis but with a smaller amount of granulation tissue and delayed wound closure. Enhanced neovascularization in the hypoxic group likely implies compensative response to an insufficient ambient oxygen supply.