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This study examined the effect of repetitive apnea on brain oxygen pressure in newborn piglets. Each animal was given 10 episodes of apnea, initiated by disconnecting them from the ventilator and completed by reconnecting them to the ventilation circuit. The apneic episodes were ended 30 sec after the heart rate reached the bradycardic threshold of 60 beats per min. The oxygen pressure in the microvasculature of the cortex was measured by oxygen-dependent quenching of the phosphorescence. In all experiments, the blood pressure, body temperature, and heart rate were continuously monitored. Arterial blood samples were taken throughout the experiment and the blood pH, PaO and PaCO were measured.

During pre-apnea, cortical oxygen was 55.1 ± 6.4 (SEM, n = 7) mm Hg and decreased during each apnea to 8.1 ± 2.8 mm Hg. However, the values of cortical oxygen varied during recovery periods. Maximal oxygen levels during recovery from the first two apneic episodes were 76.8 ± 12 mm Hg and 69.6 ± 9 mm Hg, respectively, values higher than pre-apnea. Cortical oxygen pressure then progressively decreased following consequent apnea.

In conclusion, the data show that repetitive apnea caused a progressive decrease in cortical oxygen levels in the brain of newborn piglets. This deficit in brain oxygenation can be at least partly responsible for the neurological side effects of repetitive apnea.

This paper investigates the optimal placement of NIRS optodes in order to maximise the detection of haemoglobin changes in cortical grey matter resulting from an evoked response in neonates. The analysis is based upon predictions of optical signal at the surface of the head, using a Finite Element based model of light diffusion in tissue. Using the generated intensity data, the combination of optode positions, which maximise the signal from cortical grey matter whilst minimising that from surface tissue or cerebral white matter, is determined using a Chemometric statistical analysis. The neonatal head is modelled as a 2 dimensional circle with 3 layers corresponding to the skin/scalp, and grey and white matter. A wide range of absorption coefficients for each layer is simulated, based upon physiologically reasonable values for parameters. Surface intensity at 10 different optode positions have been generated for a total of 31,250 combinations of these variables for the 3 layers. It was found that with 3 optodes at 5, 15, and 50 mm apart from the source, the smallest root-mean-square error between the estimated and modelled values can be obtained. Increasing the number of optodes further does not improve the performance.

We simulated the effects of compression of the breast on blood volume and tissue oxygenation. We sought to answer the question: how does the compression during breast examination impact on the circulatory systems of the breast tissue, namely blood flow, blood pooling, and oxygen concentration? We assumed that the blood was distributed in two compartments, arterial and venous. All the parameters were expressed with oxy- and deoxyhemoglobin quantities and were measured with a non-invasive method, Near Infrared Spectroscopy (NIRS). The simulated data showed that the blood volume pool in the breast decreased due to lower arterial flow and higher venous outflow, as the breast was squeezed under 100 cm HO with a 10 cm diameter probe (or 78 cm). The blood volume was reversed when the pressure was released. The breast venous oxygen saturation dropped, but overall tissue saturation (presenting NIRS signal, volume weighted average saturation) was increased. The results showed that simulation can be used to obtain venous and average oxygen saturation as well as blood flow in compressed breast tissues.

Increased formation of ROS on reperfusion after ischemia underlies ischemia reperfusion (I/R) damage. We measured, in real time, both oxygen tension in microvessels and tissue and oxidant stress during postischemic reperfusion in hamster cheek pouch microcirculation. We measured PO by using phosphorescence quenching microscopy and oxygen radical species (ROS) production in the systemic blood. We evaluated the effects of a NOS inhibitor (L-NMMA) and superoxide dismutase (SOD) on the oxidative stress during reperfusion. Microvascular injury was assessed by measuring diameter change, the perfused capillary length (PCL), and leukocyte adhesion.

Our findings demonstrate that early reperfusion is characterized by low concentration of oxygen linked to increased production of ROS. After this initial transience in arterioles, the oxygen tension and production of ROS return to normal after reperfusion, while the blood flow and capillary perfusion decrease. The early increased ROS production, in turn, may impair oxygen consumption by endothelial cells, thus further promoting activation of oxygen to ROS. This event is substantiated by the finding that treatment with SOD maintains ROS at normal levels, which, in turn, should be effective to increase the production of endothelial NO. Conversely, a decrease in NO levels led to decreased ROS production during early reperfusion, which increased later during reperfusion, ultimately causing vasoconstriction and greatly increasing venular leukocyte adhesion on postcapillary venules during hypoxic conditions. Therefore, low-flow hypoxia is primarily responsible for vascular endothelial damage during reperfusion through changes in ROS and NO production.

Hypoxia is a well-recognized feature of human solid tumors. It is also well recognized, by both physicians and investigators, that malignant disease in various organs/tissues in the same patient, or the same tumor cells implanted in different sites or organs in the preclinical host, have different levels of hypoxia and different levels of response to systemic therapies. Over the past 10 years, it has been established that normal cells involved in the malignant disease process can be important targets for therapeutic attack. A prime example of ‘normal’ cells that have come to the fore as anticancer therapeutic targets is endothelial cells.

The field of antiangiogenic therapies was fueled by the early hypothesis which held that angiogenesis was the same no matter where it occurred. The corollary to this hypothesis was that models of normal embryo development, as well as models working with mature well-differentiated endothelial cells in culture, would be sufficient and satisfactory models for tumor endothelial cells. However, the current hypothesis is that angiogenesis occurring during malignant disease is abnormal, and that therapeutic targets identified by studying endothelial cells isolated from fresh samples of human cancers will be most relevant in developing therapeutic agents to treat human malignant disease.

We report in this article a new method for oxygen measurement using green fluorescence protein (GFP). COS7 cells were transiently transfected with an expression vector, pCMX-GFP, using a polyethylenimine reagent and cultured for 48 hrs. After exposure of the cell to anoxic gas (O<.001%), a 1 min illumination of the cell to strong 470–490 nm light evoked a significant red fluorescence (excitation 520–550 nm, emission >580 nm) that had been negligible before the photoactivation. This red shift of (green) GFP fluorescence was never observed in normoxia. We then examined the validity of this method in transgenic mice in which GFP is stably expressed (green mice). All the ventricular myocytes isolated from the green mice showed significant green fluorescence, although the intensity was ∼1/200 of the transiently GFP-expressing COS7 cells. The photoactivation in anoxia increased the red fluorescence in these cells, but the magnitude was much smaller than expected. In summary, GFP can be used as an probe for hypoxia. In GFP-expressing transgenic animals, imaging of anoxic loci with a submicron spatial resolution may be possible.

The purpose of this study is to identify the best perfusate after blood for maintaining skeletal muscle inotropy, muscle peak oxygen consumption (peak VO), and oxygen consumption at rest (resting VO) in isolated canine gastrocnemius-plantaris muscle. Rejuvenated red cells suspended in perfusate at hematocrit 30% and 45%, perfusate contained insulin (100 µU·ml), adrenalin (0.3 and 3 ng·ml), and noradrenaline (3 ng·ml). Insulin significantly augmented resting VO and contracting muscle peak VO, and developed isometric twitch tension at 4 Hz, compared with control. Insulin-induced increase in resting muscle VO was abrogated by catecholamines. In addition to insulin and catecholamines, the developed twitch tension increased significantly by 178% with the accompanied increase in flow rate. O cost (peak VO / tension) significantly decreased by 52%. The developed tension did not correlate with O delivery but with flow rate and peak VO of contracting muscle. We successfully identified the characteristics of the best perfusate after blood. Our results suggest that the positive inotropy by insulin and catecholamines is attributed partly to an O delivery-independent increase in flow to contracting muscle and redistribution of flow within the contracting muscle, which suffered from low perfusion by perfusate containing rejuvenated red cells.

It is recognized that brain oxygen deprivation results in increased glycolysis and lactate accumulation. Moreover, glucose metabolism is altered during starvation or diet, resulting in increased plasma ketones (acetoacetate + β-hydroxybutyrate; BHB). We investigated glucose and lactate adaptation to hypoxia in concurrence with diet-induced ketosis. Male Wistar rats were fed standard (STD), ketogenic (high fat; KG), or carbohydrate-rich (low fat; CHO) diets for 3 wks and then exposed to hypobaric (0.5 ATM) or normobaric atmosphere for 3 wks while on their diets. Lactate, ketones, and glucose concentrations were measured in plasma (mM) and brain tissue (mmol/g). Plasma and tissue ketone levels were elevated up to 12-fold in the KG fed groups compared with other groups (STD and CHO), with the hypoxic KG group reaching the highest levels (2.6 ± 1.3 mM and 0.3 ± 0.1 mmol/g; mean ± SD). Tissue lactate levels in the hypoxic ketotic rats (4.7 ± 1.3 mM) were comparable with normoxic STD (5.0 ± 0.7 mM) and significantly lower (ANOVA <.05) than the hypoxic STD rats (6.1 ± 1.0 mM). These data indicate that adaptation to hypoxia did not interfere with ketosis, and that ketosis during hypoxia may lower lactate levels in brain, suggesting decreased glycolysis or increased glucose disposal.

Since conventional therapies are directly dependent on the supply of either drugs or oxygen, a key question is whether antiangiogenic agents produce detrimental effects on tumor vascular function, thus compromising combination therapies. A second question is whether experimental results based on fast-growing, transplanted tumors mimic those in slowly developing spontaneous tumors, which may be more representative of response in human primary tumors. To investigate changes in tumor pathophysiology, three antiangiogenic agents were compared: a) endostatin, b) anti-VEGFR-2 (DC101), and c) celecoxib. Total blood vessels were identified using anti-CD31, perfused vessels using DiOC, and hypoxia by EF5 uptake. Although individual tumor growth rates varied substantially, DC101 produced the most striking inhibition. DC101 increased total and perfused vessel spacing as well as overall hypoxia, while endostatin increased total vessel spacing, and hypoxia and celecoxib had no marked effects. These results reinforce the idea that pathophysiological changes in spontaneous tumors are in general reflective of response in transplanted tumors. Furthermore, although DC101 inhibited growth in roughly half of the spontaneous tumors, the remaining tumors were unaffected. A key focus of future studies will be to investigate the underlying rationale for the widely varying antiangiogenic response among tumors that outwardly appear so similar.

We have developed a novel procedure for monitoring of oxygen concentration in growing tumors by electron paramagnetic resonance (EPR)-based oximetry using embedded paramagnetic particulates. The new approach uses spin probes that are permanently embedded or implanted in the tumor. A particular advantage of this procedure is that it is non-invasive, both in terms of implantation of the probe as well as readouts of oxygen. We implanted a mixture of RIF-1 tumor cells and microparticulates of lithium phthalocyanine (LiPc) in the upper hind leg of C3H mice to grow as solid tumor. This enabled repeated measurements of oxygen concentration from the implanted site (tumor) for more than two weeks during the progression of the tumor. The particulates that were embedded in the tumor were stable and non-toxic to tumor cells. There was no apparent inhibitory effect to cell proliferation or tumor growth rate. The measurements indicated that the pO of the tumor decreased exponentially with tumor growth (size) and reached hypoxia (< 4 mm Hg). EPR imaging was used to identify the distribution of the particles in the tumor. The data showed a heterogeneous distribution of the probe particles within the tumor volume. Imaging of oxygen in the growing tumor demonstrated the development of significant hypoxia in the tumor within 4–6 days after inoculation. In summary, the EPR spectroscopy and imaging using embedded spin probe enabled accurate and repeated measurements of pO under non-perturbing conditions in growing tumors.