Changes In PO2 Research Articles

Lack of arterial PO2 downregulation in Atlantic salmon (Salmo salar L.) during long-term normoxia and hyperoxia

Regulation of arterial partial pressure of O2 (PaO2) in Atlantic salmon (Salmo salar) was investigated during resting conditions in normoxic and hyperoxic water. Dorsal aorta cannulated adult Atlantic salmon (1.2-1.6 kg, n=8) were exposed to 2 week sequential periods of normoxia [16.7±1.1 kPa (mean±SD)] and hyperoxia (34.1±4.9 kPa) in individual tanks containing seawater (33.7±0.2 ppt) at stable temperature conditions (8.7±0.7°C) and a light regime of L:D=12:12. Tank design and sampling procedures were optimized to provide suitable shelter and current for the fish, and to allow repeated, undisturbed sampling of blood from free-swimming fish. Fish were sampled regularly through the experimental period. PwO2, PaO2, blood ion composition (Na+, K+, Cl-), acid-base status (pH, PCO2, HCO3-), haematocrit and glucose were measured. The most frequently observed PaO2 values were in the range of 60-80% of PwO2, both during normoxia and hyperoxia, and PaO2 values were significantly lower during normoxia than during hyperoxia. Blood pH, PCO2 and HCO3- were significantly elevated during hyperoxia, while, Na+, Cl- and Hct were significantly lower. K+ and glucose showed no significant differences. This study demonstrates a lack PaO2 regulation in Atlantic salmon to low partial pressures, in contrast to previous reports for many aquatic gill breathing animals. Both during normoxia and hyperoxia, PaO2 reflects PwO2, and alterations in external PO2 consequently result in proportional arterial PO2 changes. Physiological adaptation to hyperoxia, as illustrated by changes in several blood parameters, does not include down-regulation of PaO2 in Atlantic salmon. The lack of PaO2 regulation may make Atlantic salmon vulnerable to the oxidative stress caused by increased free radical formation in hyperoxic conditions.

Mixed conduction and chemical diffusion in a Pb(Zr0.53,Ti0.47)O3 buried capacitor structure

Impedance spectroscopy is performed on a buried capacitor structure composed of a PZT-0.75% Nb ceramic with platinum electrodes. The ionic and electronic conductivities (σion,σelec) are extracted from the impedance spectra using an equivalent circuit based on the premise of mixed conduction. In the temperature range 500–700 °C, a change in local pO2 mainly affects σelec, suggesting that the samples are ionically compensated, i.e., [VO••]=[VPb″]. The chemical diffusion coefficient, D̃, is obtained by a conductivity relaxation technique assuming two-dimensional diffusion geometry. In comparison to BaTiO3, or SrTiO3, the chemical diffusivity is found to be relatively high, D̃=2.0×10−4 cm2 s−1 (700 °C, in air).

Rapid intravenous infusion of 20 ml/kg saline does not impair resting pulmonary gas exchange in the healthy human lung

Rapid infusion of intravenous saline, a model of pulmonary interstitial edema, alters the distribution of pulmonary perfusion, raises pulmonary capillary blood volume, and increases bronchial wall thickness in humans. We hypothesized that infusion would disrupt pulmonary gas exchange by increasing ventilation/perfusion ((.)VA/(.)Q) inequality as opposed to a diffusive impairment in O2 exchange. Seven males (26 +/- 3 yr; FEV1: 110 +/- 16% predicted.) performed spirometry and had (.)VA/(.)Q mismatch measured using the multiple inert gas elimination technique, before and after 20 ml/kg iv of normal saline delivered in approximately 30 min. Infusion increased thoracic fluid content from transthoracic impedance by 12% (P < 0.0001) and left FVC unchanged but reduced expiratory flows (FEF(25-75) falling from 5.1 +/- 0.4 to 4.2 +/- 0.4 l/s, P < 0.05). However, (.)VA/(.)Q mismatch as measured by the log standard deviation of the ventilation (LogSD(.)V) and perfusion (LogSD(.)Q) distributions remained unchanged; LogSD(.)V: 0.40 +/- 0.03 pre, 0.38 +/- 0.04 post, NS; LogSD(.)Q: 0.38 +/- 0.03 pre, 0.37 +/- 0.03 post, NS. There was no significant change in arterial PO2 (99 +/- 2 pre, 99 +/- 3 mmHg post, NS) but arterial PCO2 was decreased (38.7 +/- 0.6 pre, 36.8 +/- 1.2 mmHg post, P < 0.05). Thus, infusion compressed small airways and caused a mild degree of hyperventilation. There was no evidence for a diffusive limitation to O2 exchange, with the measured-predicted alveolar-arterial oxygen partial pressure difference being unaltered by infusion at FIO2 = 0.125 (4.3 +/- 1.0 pre, 5.2 +/- 1.0 post, NS). After infusion, the fraction of perfusion going to areas with (.)VA/(.)Q < 1 was increased when a subject breathed a hyperoxic gas mixture [0.72 +/- 0.06 (FIO2 = 0.21), 0.80 +/- 0.06 (FIO2 = 0.30), P < 0.05] with similar effects on ventilation in the face of unchanged (.)VA and (.)Q. These results suggest active control of blood flow to regions of decreased ventilation during air breathing, thus minimizing the gas exchange consequences.

Radiotherapy in Conjunction with 7-Hydroxystaurosporine: A Multimodal Approach with Tumor pO2as a Potential Marker of Therapeutic Response

Checkpoint inhibitors potentially could be used to enhance cell killing by DNA-targeted therapeutic modalities such as radiotherapy. UCN-01 (7-hydroxystaurosporine) inhibits S and G2 checkpoint arrest in the cells of various malignant cell lines and has been investigated in combination with chemotherapy. However, little is known about its potential use in combination with radiotherapy. We report the effect of 20 Gy radiation given in conjunction with UCN-01 on the pO2 and growth of subcutaneous RIF-1 tumors. Multisite EPR oximetry was used for repeated, non-invasive tumor pO2 measurements. The effect of UCN-01 and/or 20 Gy on tumor pO2 and tumor volume was investigated to determine therapeutic outcomes. Untreated RIF-1 tumors were hypoxic with a tissue pO2 of 5-7 mmHg. Treatment with 20 Gy or UCN-01 significantly reduced tumor growth, and a modest increase in tumor pO2 was observed in tumors treated with 20 Gy. However, irradiation with 20 Gy 12 h after UCN-01 treatment resulted in a significant inhibition of tumor growth and a significant increase in tumor pO2 to 16-28 mmHg from day 1 onward compared to the control, UCN-01 or 20-Gy groups. Treatment with UCN-01 12 h after 20 Gy also led to a similar growth inhibition of the tumors and a similar increase in tumor pO2. The changes in tumor pO2 observed after the treatment correlated inversely with the tumor volume in the groups receiving UCN-01 with 20 Gy. This multimodal approach could be used to enhance the outcome of radiotherapy. Furthermore, tumor pO2 could be a potential marker of therapeutic response.

ALTERAÇÕES HEMOGASOMÉTRICAS E ELETROLÍTICAS DE CAVALOS DA RAÇA ÁRABE DURANTE PROVA DE ENDURO DE 60 KM

Changes in venous blood pH, pCO2, pO2, HCO-3 and cBase, and in serum concentrations of sodium, potassium, ionized calcium and chloride were studied in eight Arabian horses during endurance ride of 60km, with controlled speed of 12km/h-. The blood samples were collected prior to the beginning (M0) of the exercise, immediately after the ride (M1) and one hour after the ride (M2), with the animals resting. Immediately after the end of the exercise (M1) the animals presented higher values for pH which, added to the increase of cHCO3- and cBase, characterized the metabolic alkalosis, probably due to losses of chloride ions in the sweat. The metabolic changes observed in M1 were quickly corrected by respiratory changes, characterized by increased pCO2 or hypoventilation. Additionally, the horses presented dehydration, hypocalcemia and hypokalemia. The metabolic disturbances observed were not associated with clinical changes. KEY WORDS: Acid-base, electrolytes, endurance, equine

BOLD MRI in sheep fetuses: a non‐invasive method for measuring changes in tissue oxygenation

The purpose of this descriptive study was to correlate changes in the blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) signal with direct measurements of fetal tissue oxygenation. Seven anesthetized ewes carrying singleton fetuses at 125 days' gestation (term 145 days) underwent BOLD MRI, covering the entire fetus in a multislice approach. The fetuses were subjected to normoxic, hypoxic and hyperoxic conditions by changing the O(2)/N(2)O ratio in the maternal ventilated gas supply. The partial pressure of oxygen (pO2) in the fetal liver was measured using an oxygen-sensitive optode. Maternal arterial blood samples were simultaneously withdrawn for blood gas analysis. These measurements were compared with BOLD MRI signals in the fetal liver, kidney, spleen and brain. We demonstrated a consistent increase in the BOLD MRI signal with increasing tissue pO(2). For the fetal liver, spleen and kidney we observed a clear association between changes in maternal arterial blood pO2 and changes in BOLD MRI signal. Interestingly, we found that the BOLD signal of the fetal brain remained unchanged during hypoxic, normoxic and hyperoxic conditions. This experimental study demonstrated that BOLD MRI is a reliable non-invasive method for measuring changes in tissue oxygenation in fetal sheep. The unchanged signal in the fetal brain during altered maternal oxygen conditions is probably explained by the brain-sparing mechanism.

Oxygen tension correlates with regional blood flow in obstructed rat kidney

As renal tissue oxygen tension (P(O(2))) is determined by the balance between oxygen supply and consumption, direct tissue P(O(2)) measurements are essential when evaluating the presence of hypoxia. The present study aimed at evaluating invasively and continuously the renal medullary and cortical tissue P(O(2)) by novel fibre-optic probes in rats subjected to acute unilateral ureteral obstruction (AUUO). In parallel, regional blood flow measurements were obtained by MRI to investigate the relationship between regional blood flow and tissue oxygen tension. The abundance of transport proteins was determined by immunoblotting. In the obstructed kidney, AUUO caused a prompt decrease in medullary tissue P(O(2)) to 60% of baseline level whereas cortical tissue P(O(2)) was unchanged. By contrast, tissue P(O(2)) slightly increased in the non-obstructed kidney. These changes developed during the first 30 min after AUUO and persisted for the 3 h observation period. Medullary blood flow declined 1.5-2 h after induction of AUUO to 61% of baseline level in the obstructed kidney. By contrast, cortical blood flow increased to 108% of baseline level in the non-obstructed kidney. Finally, the abundance of phosphorylated aquaporin 2 decreased significantly in the obstructed kidney medulla, but increased in the obstructed kidney cortex. The Na(+)/K(+)-ATPase abundance increased in the obstructed kidney medulla whereas the Na(+)/K(+)/2Cl(-) co-transporter abundance remained unchanged in the obstructed kidney. In conclusion, measurements of regional blood flow reflect tissue P(O(2)) changes during AUUO suggesting that reduced regional blood flow is a predictor of local hypoxia. Furthermore, the abundance of major transport protein is independent of tissue P(O(2)).

Compressible gas gills of diving insects: Measurements and models

Many diving insects collect a bubble of air from the surface to supply their oxygen requirements while submerged. It has been theorised that these air bubbles may also act as compressible gas gills, as the low oxygen partial pressure (PO2) within the bubble caused by the insect's respiration creates a gradient capable of driving the diffusion of oxygen from the water into the bubble. Under these conditions nitrogen diffuses in the opposite direction, resulting in a situation where the volume of the bubble is continually shrinking while oxygen is obtained. This study measures changes in volume and PO2 within the gas gills held by a tethered water bug, Agraptocorixa eurynome. Both gill volume and PO2 drop rapidly at the beginning of a dive, but eventually the PO2 reaches an apparently stable level while volume continually declines at a slower rate. Active ventilation of the gill is crucial to maintaining oxygen uptake. These measurements are used to calculate oxygen flux into the gas gill and the oxygen consumption rate (V˙O2) of the bug. The effectiveness of a gas gill as a respiratory organ is also demonstrated by determining the critical PO2 of the water bug and comparing this with measured gas gill PO2 and calculated V˙O2.

Physiological effects of the TASER® C2 conducted energy weapon

In previous studies, exposure to conducted energy weapons (CEWs) (such as TASER International's Advanced TASER X26 device) resulted in leg muscle contraction, acidosis, increased blood electrolytes, and other biochemical and physiological changes. In the current study, experiments were performed to examine the effects of exposures to TASER International's "C2" CEW, which is specifically marketed to civilian rather than law-enforcement users. Ten pigs (Sus scrofa) were sedated with an intramuscular injection of Telezol (tiletamine HCl and zolazepam HCl) and intubated. General anesthesia was maintained with an IV propofol infusion. Applications of the C2 device for 30 s resulted in extensive muscle contraction and significant increases in heart rate and hematocrit, and in blood levels of pCO2, lactate, glucose, and potassium, sodium, and calcium ions. Significant decreases were observed in blood oxygen saturation, pO2, and pH. Qualitatively, many of these changes were consistent with previous reports in the literature dealing with studies of muscle stimulation or exercise. The changes in blood pCO2, pO2, electrolytes, lactate, and pH, however, were greater than in a previous study of three repeated 5-s exposures to the X26 CEW commonly used by law-enforcement personnel. On the basis of the results, potential detrimental effects due to use of the "citizen-version" TASER C2 CEW may be more likely than limited intermittent applications of the X26 CEW.

Change In Intracellular Po2 During Muscle Contraction Under Hb-free Medium Perfusion

Change In Intracellular Po2 During Muscle Contraction Under Hb-free Medium Perfusion

Reduction of Erythrocyte (RBC) Deformability Attenuates Low Oxygen Tension (pO2) Induced ATP Release from the RBC

The mechanism by which decreased pO2 stimulates ATP release from RBCs has not been established. Here we evaluated the hypothesis that RBC deformability is required for ATP release from rabbit RBCs in response to exposure to low pO2. Deformability of RBCs, measured with a St. George's Blood Filtrometer, was decreased by incubation of RBCs with diamide, an agent that promotes cytoskeletal cross‐linking. Incubation of RBCs with diamide (100 uM) resulted in a 7.67 ± 1.19 % reduction in RBC deformability by 30 min that was stable for 1 hr (n=4). In untreated RBCs, changes in pO2 from 121.9 ± 2.7 to 13.7 ± 1.2 mmHg resulted in a significant 8.5 ± 2.9 fold increase in ATP release (p&lt;0.01, n=5). In contrast, in diamide treated RBCs, changes of pO2 from 125.8 ± 6.1 to 13.5 ± 0.6 mmHg resulted in only a 2.9 ± 1.0 fold increase in ATP release, which was significantly lower than the increase in untreated RBCs (p&lt;0.05, n=5). To ensure that effects of diamide on low pO2‐induced ATP release were selective for that signaling pathway and was not due to a general inhibition of ATP release, RBCs were incubated with iloprost (ILO), to stimulate ATP release in the absence or presence of diamide. Diamide did not inhibit ILO‐induced ATP release (n=2). These results are consistent with the hypothesis that membrane deformability is required for low pO2‐induced ATP release from rabbit RBCs. (ADA grant RA‐133 and NIH grants HL‐64180 &amp; HL‐89094)

Experimental gas embolism and tissue oxygenation using intravital microscopy

Little is known about microhemodynamic responses to arterial gas embolism (AGE) and associated local O2 tensions (PO2) have never been evaluated in vivo. Therefore, we assessed the adequacy of intravital microscopy to study the microcirculation during AGE, and investigated how bubble‐induced vaso‐occlusion and blood flow redistribution were associated with changes in arteriolar and tissue PO2. Blood pressure and heart rate were not significantly different before and after local AGE in the rat cremaster muscle. The first attempt of embolization did not result in arteriolar occlusion and multiple attempts were needed. Control diameter and blood flow averaged 53 ± 25 and 13 ± 10 nl/s, respectively. After AGE, these parameters changed to 53 ± 24 µm and 1 ± 3 nl/s. Arteriolar PO2 averaged 59 ± 19 mmHg during control and dropped to 34 ± 27 mmHg (upstream) and 24 ± 22 mmHg (downstream) after AGE. Interstitial PO2 changed from 44 ± 22 to 23 ± 20 mmHg and did not follow the drop recorded in the embolized arteriole when the PO2 in nearby flowing vessels remained high. We also measured in vivo bubble reabsorption (volume ≤ 20pL). Our findings suggest that blood redistribution in the muscle prevented severe hypoxia in some tissue areas after AGE and that arteriolar entrapment of air bubbles is associated with prior endothelial cell damage caused by the first bubble passage.Support: NIH, ONR.

Rapid change of PO2 promoted dendritic cells to induce a strong Th1 cell immune response with decreased Foxp3+Tregs (89.11)

Abstract Ischemia-reperfusion injury (IRI) can be found in transplantation and other ischemic syndromes in multiple organ systems including kindey, brain, heart and liver, this pathogenesis of IRI is complex and incompletely understood. It has been suggested that reoxygenation after hypoxia is a crucial mechanism mediating organ injury in IRI. Well, dendritic cells (DCs), the critical immune cells linking innate and adaptive immunity, are often exposed to various oxygen tensions under physiological and pathological conditions, such as ischemia-reperfusion. However, the effects of various oxygen tensions on DCs remain unclear. In this study, we showed that hypoxia-differentiated DCs expressed lower levels of MHC-|| molecule, co-stimulatory molecules (CD80, CD86) and pro-inflammatory cytokines (IL-1 β, IL-6, TNF-α and IL-12), but higher levels of immunoregulatory cytokine transforming growth factor-beta (TGF-b) than did normoxia-differentiated DCs. However, reoxygenation of the hypoxia-differentiated DCs dramatically upregulateed the aforementioned molecules leading to a mature phenotype. Significantly, these reoxygenated DCs induced syngeneic or allogeneic naïve CD4+ T cells to differentiate into Th1 effector cells. The generation of CD4+CD25+Foxp3+ regulatory T cells (Treg cells) induced by reoxygenated DCs was however down-regulated. These data indicate that hypoxic microenvironment suppresses the maturation and function of murine DCs. Re-exposure of the hypoxia-differentiated DCs to sutured oxygen however results in complete recovery of their mature phenotype and function and drives them to initiate Th1 cell differentiation, suggesting DCs play a critical role in inflammation in ischemia-reperfusion injury (IRI).

Implications of river damming: the influence of aquatic hypoxia on the diving physiology and behaviour of the endangered Mary River turtle

AbstractRiver impoundments are characterized by low oxygen levels as a result of reduced water velocity and increased water depth. Bimodally respiring turtle species are likely to be highly sensitive to changes in aquatic PO2 with decreases in oxygen levels impacting upon their diving ability. The acute and long‐term effects of aquatic hypoxia on dive duration, oxygen consumption and blood respiratory properties were examined in hatchlings of the endangered Mary River turtle Elusor macrurus. It was hypothesized that acute exposure to aquatic hypoxia would cause a decrease in dive duration as a consequence of a decrease in reliance on aquatic respiration. With long‐term exposure to hypoxia, we predicted that Elu. macrurus would have the capacity to compensate for the acute effect of hypoxia and that dive duration would increase due to an increase in aquatic respiration, haemoglobin concentration and oxygen affinity (P50). When exposed to hypoxic conditions, aquatic respiration in Elu. macrurus was substantially reduced resulting in a 51% decrease in dive duration. Contrary to our predictions, Elu. macrurus hatchlings did not acclimate, and long‐term exposure to hypoxic conditions caused Elu. macrurus to lose significantly more oxygen to the hypoxic water than the normoxic acclimated turtles. The exacerbation of long‐term hypoxia on the respiratory physiology and diving ecology of Elu. macrurus raises concerns about the impacts of long‐term environmental change as a result of habitat alteration on the survival of freshwater turtle populations.

Development of polymer-coated paramagnetic Implants for biomedical oximetry Applications

There are a variety of methods available for measuring and mapping of oxygen concentration in biological tissues. The particulate-based, electron paramagnetic resonance (EPR) oximetry is a powerful technology that allows non-invasive and repetitive monitoring of oxygenation in tissues. Lithium naphthalocyanine (LiNc) forms highly stable paramagnetic crystals which can be used for high resolution oximetry in tissues. To show efficient biocompatibility, long-term in vivo stability and responsiveness of LiNc oximetry probes, as well as for making the probes surgically implantable/ retrievable, we coated LiNc microcrystals with Teflon AF 2400 (TAF) polymeric materials. EPR linewidths of polymer-coated LiNc probes under anoxic conditions as well as at varying partial pressures of oxygen (pO2) did not show appreciable change relative to uncoated LiNc particulates, yet the linewidth of coated LiNc crystals was linearly dependent on varying pO2. The coated implantable probes responded to changes in pO2 quickly and reproducibly, enabling dynamic measurements of oxygenation in real time. The implants were unaffected by biological oxidoreductants. The oxygen sensitivity and stability of the coated LiNc was demonstrated in vivo in mice for more than two months. Thus, new TAF polymer-coated LiNc crystals are potential candidates for future in vivo studies including clinical trials for oxygen measurements in pathophysiological tissues.

Impact of cyclic hypoxia on HIF‐1α regulation in endothelial cells – new insights for anti‐tumor treatments

Heterogeneities in tumor blood flow are associated with cyclic changes in pO2 or cyclic hypoxia. A major difference from O2 diffusion-limited or chronic hypoxia is that the tumor vasculature itself may be directly influenced by the fluctuating hypoxic environment, and the reoxygenation phases complicate the usual hypoxia-induced phenotypic pattern. Here, we determined the cyclic hypoxia-driven pathways that modulate hypoxia inducible factor (HIF)-1alpha abundance in endothelial cells to identify possible therapeutic targets. We found that exposure of endothelial cells to cycles of hypoxia/reoxygenation led to accumulation of HIF-1alpha during the hypoxic periods and the phosphorylation of protein kinase B (Akt), extracellular regulated kinase (ERK) and endothelial nitric oxide synthase (eNOS) during the reoxygenation phases. We identified stimulation of mitochondrial respiration and activation of the phosphoinositide-3 kinase (PI3K)/Akt pathway during intervening reoxygenation periods as major triggers of the stabilization of HIF-1alpha. We also found that the NOS inhibitor nitro-l-arginine methyl ester further stimulated the cyclic hypoxia-driven HIF-1alpha accumulation and the associated gain in endothelial cell survival, thereby mirroring the effects of a PI3K/Akt inhibitor. However, combination of both drugs resulted in a net reduction in HIF-1alpha and a dramatic in decrease in endothelial cell survival. In conclusion, this study identified cyclic hypoxia, as reported in many tumor types, as a unique biological challenge for endothelial cells that promotes their survival in a HIF-1alpha-dependent manner through phenotypic alterations occurring during the reoxygenation periods. These observations also indicate the potential of combining Akt-targeting drugs with anti-angiogenic drugs, in particular those interfering with the NO pathway.

Polymer coating of paramagnetic particulates for in vivo oxygen-sensing applications

Crystalline lithium phthalocyanine (LiPc) can be used to sense oxygen. To enhance biocompatibility/stability of LiPc, we encapsulated LiPc in Teflon AF (TAF), cellulose acetate (CA), and polyvinyl acetate (PVAc) (TAF, previously used to encapsulate LiPc, was a comparator). We identified water-miscible solvents that don't dissolve LiPc crystals, but are solvents for the polymers, and encapsulated crystals by solvent evaporation. Oxygen sensitivity of films was characterized in vitro and in vivo. Encapsulation did not change LiPc oximetry properties in vitro at anoxic conditions or varying partial pressures of oxygen (pO2). EPR linewidth of encapsulated particles was linear with pO2, responding to pO2 changes quickly and reproducibly for dynamic measurements. Encapsulated LiPc was unaffected by biological oxidoreductants, stable in vivo for four weeks. Oximetry, stability and biocompatibility properties of LiPc films were comparable, but both CA and PVAc films are cheaper, and easier to fabricate and handle than TAF films, making them superior.

Continuous monitoring of pO2 and pCO2 by microdialysis indicates physiologic status of the critically ill patients

The monitoring of dissolved oxygen and carbon dioxide in blood or organic tissues is extremely useful for respiratory studies and can be valuable in determining the physiologic status of the critically ill patients. The measurement quantity for both O2 and CO2 sensors is the luminescence lifetime by phase modulation fluorometry. The properties and accuracy of both types of sensors have been firstly characterised in vitro using physiological solutions to demonstrate the fulfilment of the defined requirements for clinical applications. The presented sensors enable the measurement of pO2 in the range 0–300mmHg and of pCO2 in the range 0–150mmHg, respectively, with a resolution better than 1mmHg and accuracy better than 1mmHg. To verified the operating function of developed sensors in in vivo and to analyse the changes of interstitial pO2 and pCO2 in adipose tissue as indicators of critical ill conditions, several in vivo tests on animal and healthy volunteer have been successfully carried out using a microdialysis catheter CMA 60 for the extraction of interstitial fluid (ISF) from the subcutaneous adipose tissue. Critical conditions similar to intensive care patients have been provoked using two different models: an animal model of haemorrhagic shock and subministration of adrenaline, which causes a local vasoconstriction in the case of experiment with human subjects, respectively. Our results proved that changes in the interstitial pCO2 and pO2 are informative metabolic parameters for critical condition of the patients.

Sickle Cell Patients Have Exagerated Autonomic Response to Transient Hypoxia

Sickle cell anemia (SCA) is a devastating disorder that results from a single amino acid substitution in the beta chain of hemoglobin causing polymerization of hemoglobin S when oxygen is removed. This causes normally flexible sickle red cells (SRBC) to become rigid, obstruct vasculature resulting in ischemic organ damage and decreased longevity. Anything which decreases microvasculature flow will promote the sickling process. Inflammation and adhesion of cellular elements to the vessel wall are known to increase the probability of vasoocclusive crisis (VOC). However, the precise event that triggers the cascade called “crisis” is not known. Microvascular flow changes rapidly in response to autonomic signals which can be assessed by measurement of heart rate variability (HRV). These autonomic signals may be the trigger that causes regional decrease in flow and initiates the events resulting in crisis.We have established a model of induced hypoxia in human subjects that was designed to mimic the transient hypoxia occuring naturally during sleep. Calibrated tidal volume, O2 saturation, and electrocardiogram, were recorded up to 200 times per second using a LifeShirt physiological monitoring garment and tissue oxygenation and microvascular blood flow was assessed by laser Doppler flowmetry or magnetic resonance imaging. The report focuses on safety and on HRV results. Subjects breathed 5 breaths of 100% N2 twice separated by a 5 to 10 minte recovery period on up to 4 separate days per subject. 15 SCA had two hypoxic exposures on 38 days.Subjects were contacted 1, 12, and 24 hrs and 7 to 14 days later and symptom questionnaires completed. On only 4 occasions, subjects reported mild transient sicklelike pain that required no or non-narcotic treatment within 24 hours of hypoxia and was deemed possibly related to the hypoxic exposure. About sixty percent of the exposures were associated with lightheadedness lasting 10 to 15 seconds at the nadir of the SpO2. The drop in SpO2 was greater in the SCA patients (p<.05) and lasted 15 to 20 seconds. However, when we used the subjects' individually measured oxyhemoglobin saturation curve to calculate change in pO2, there was no difference between SCA and normals.Using a novel algorithm we developed which allows second to second comparison of autonomic nervous system (ANS) balance to change in SaO2, we found that the high frequency component of HRV representing parasympathetic (HFP) and low frequency component representing mixed sympathetic activity (LFP) were significantly different between SCA and control (p<.001). SCA patients have a dramatic loss of parasympathetic signal in response to transient hypoxia resulting in significant loss of heart rate variability. These data suggest than SCA patients have a greatly amplified autonomic nervous system response, at least to hypoxia. Since these same ANS signals are also responsible for control of regional microvascular blood flow, it is reasonable to speculate that this hyperactive ANS response leads to regional drop in perfusion which, on a background of hyper-adhesiveness, nitric oxide depletion, inflammation, and dehydration, triggers the sickling cascade. It is important to note that loss of HRV is a powerful predicator of sudden death in several other settings of vascular disease and that 15 to 20% of SCA deaths are otherwise unexplained sudden deaths.These data demonstrate thattransient hypoxia can be safely induced in SCA subjects and used to study the relation between hypoxia and physiological responses andSCA patients have a marked abnormality in autonomic nervous system regulation in response to transient hypoxia that likely plays a role in the pathophysiology of this disorder.

Impact of Arterial and Arteriovenous Renal Clamping with and without Intrarenal Cooling on Renal Oxygenation and Temperature in a Porcine Model

As laparoscopic partial nephrectomy increases in prominence, more needs to be understood about the combined effect of the pneumoperitoneum and renal ischemia during tumor resection. The purpose of this study is to investigate the effect of combined renal hilar clamping (arterial only versus arteriovenous) and retrograde intrarenal cooling on renal temperature and oxygenation in a porcine laparoscopic partial nephrectomy model. Under general anesthesia, laparoscopic access with intra-abdominal pressure of 15 mm Hg to the left renal hilum was obtained. Licox tissue oxygenation and temperature probes were placed into the kidney transcutaneously; measurements were taken every 30 seconds. After establishing baseline readings, either the artery alone (n=18) or the artery and vein (n=18) were clamped for 30, 60 or 90 minutes (n=12 each). During vascular clamping, retrograde, intrarenal cooling was performed with ice cold saline infused via a percutaneously placed ureteric catheter in 18 pigs. Changes in renal pO2 and temperature were analyzed with repeated measures ANCOVA in SPSS 16. Retrograde cooling decreased renal parenchyma to 75.8% of baseline temperature (27.9 degrees C) within 15 minutes. There were no differences in cooling whether arterial or arteriovenous clamping was used (p=0.79). In uncooled animals, there was no significant difference in the decrease in renal pO2 during the clamp phase (p=0.18) or during the recovery phase (p=0.52). During the recovery phase, renal pO2 in uncooled animals was significantly higher than in those who received cooling (p=0.01). Animals who underwent hilar clamping for extended periods (60 and 90 min) had a slower recovery of renal pO2 to baseline than those with hilar clamping for 30 minutes (p=0.04) Retrograde intrarenal cooling can reliably cool the porcine kidney to 28 degrees C, regardless of whether arterial or arteriovenous clamping is used. Renal pO2 is not significantly different between animals that undergo artery only versus en bloc hilar clamping. Pigs that were provided with retrograde cooling had a slower return of pO2 to baseline following release of hilar clamps, possibly due to hypothermic vasospasm. Clamp durations greater than 60 minutes were also associated with slower return of renal oxygenation to baseline.