Skeletal Muscle PO2 Research Articles

The impact of mild hypoxia exposure on myokine secretion in human obesity.

Compelling evidence indicates that myokines act in an autocrine, paracrine and endocrine manner to alter metabolic homeostasis. The mechanisms underlying exercise-induced changes in myokine secretion remain to be elucidated. Since exercise acutely decreases oxygen partial pressure (pO2) in skeletal muscle (SM), the present study was designed to test the hypothesis that (1) hypoxia exposure impacts myokine secretion in primary human myotubes and (2) exposure to mild hypoxia in vivo alters fasting and postprandial plasma myokine concentrations in humans. Differentiated primary human myotubes were exposed to different physiological pO2 levels for 24 h, and cell culture medium was harvested to determine myokine secretion. Furthermore, we performed a randomized single-blind crossover trial to investigate the impact of mild intermittent hypoxia exposure (MIH: 7-day exposure to 15% O2, 3x2h/day vs. normoxia: 21% O2) on in vivo SM pO2 and plasma myokine concentrations in 12 individuals with overweight and obesity (body-mass index ≥ 28 kg/m2). Hypoxia exposure (1% O2) increased secreted protein acidic and rich in cysteine (SPARC, p = 0.043) and follistatin like 1 (FSTL1, p = 0.021), and reduced leukemia inhibitory factor (LIF) secretion (p = 0.009) compared to 3% O2 in primary human myotubes. In addition, 1% O2 exposure increased interleukin-6 (IL-6, p = 0.004) and SPARC secretion (p = 0.021), whilst reducing fatty acid binding protein 3 (FABP3) secretion (p = 0.021) compared to 21% O2. MIH exposure in vivo markedly decreased SM pO2 (≈40%, p = 0.002) but did not alter plasma myokine concentrations. Hypoxia exposure altered the secretion of several myokines in primary human myotubes, revealing hypoxia as a novel modulator of myokine secretion. However, both acute and 7-day MIH exposure did not induce alterations in plasma myokine concentrations in individuals with overweight and obesity. This study is registered at the Netherlands Trial Register (NL7120/NTR7325).

Application of a Second‐Order Control‐Systems Model to Investigate Effects of Impaired Capillary Signalling in Skeletal Muscle on Regulation of Capillary Blood Flow Velocity and Tissue Oxygenation

Microcirculation is the main region of the vasculature where oxygen (O2) is transferred directly from blood to metabolically active tissue. Tissue O2 partial pressure (PO2) in the microcirculation has been historically infeasible to measure, but critical as an indicator of capillary and surrounding tissue health. Thus, theoretical modelling of capillary‐tissue O2 transport is crucial as a complement to in vivo experiments in exploring structure‐function relationships in microvascular networks (Ellis et al, Microcirc 2012, 19:5). To properly complement experiments which stimulate O2 flow‐dependent regulation systems, modelling of microcirculatory O2 transport requires incorporation of knowledge on regulatory mechanisms.Capillary networks modulate their blood velocity to recruit sufficient O2 delivery in many local O2 conditions; this has led to the conclusion that endothelium signals upstream to arterioles in an O2‐dependent manner (Ghonaim et al, Microcirc 2021, e12699). Recently, a second‐order control systems model was developed to investigate the interaction between capillary‐tissue O2 transport and O2‐dependent blood flow regulation under an externally applied O2 stimulus. This utilized elements from previous arteriolar diameter alteration models in response to skeletal muscle O2 gradients, as well as elements from a recently developed continuous‐capillary O2 transport model (Afas et al, Math Biosci 2021, 333:108535).The control systems model aimed to predict modulations in blood velocity through endothelial signalling which homogenized outlet capillary PO2 in skeletal muscle. The model demonstrated that variations in O2 transport parameters such as capillary network density and tissue O2 consumption rate had varying effects on the averaged blood velocity in a small skeletal muscle segment perfused by a capillary network. In addition, the externally supplied PO2 had an effect on both blood velocity and the tissue‐capillary O2 balance. While the tissue‐capillary PO2 balance and velocity adaptation were investigated, the endothelial signalling parameters were not reported (Afas & Goldman, Vasc. Bio. 2021, conference).The present study investigates implications of capillary network metric variations on the endothelial signal communicated upstream to modulate capillary blood flow in response to various muscle surface PO2 levels. Constraints imposed by pathogenic impairment of endothelial signalling will be investigated and interpreted in the context of capillary flow regulation.

Pulmonary Hypertension Induces Sex Differences in Control of Contracting Rat Skeletal Muscle Oxygen Pressures

Pulmonary hypertension (PH) is a disease characterized by pulmonary vascular remodeling, cardiac impairments, and skeletal muscle dysfunction. Males and females display different features of the disease, including a higher incidence in females, while males present with greater mortality. Exercise intolerance is a cardinal manifestation of PH, but any potential differences regarding skeletal muscle function during contractions between males and females have not been studied. This investigation tested the hypothesis that sexual dimorphism exists in the oxygen delivery (Q̇O2)‐to‐oxygen utilization (V̇O2) matching with PH as represented by oxygen partial pressures (PO2) at rest and following the onset of contractions. Considering that females display greater reliance upon nitric oxide (NO) for vascular function and PH decreases NO bioavailability, we hypothesized that PH would attenuate the skeletal muscle PO2 response to a greater extent in females than males.MethodsThirty‐three Sprague‐Dawley rats were randomly assigned to healthy (HC) or PH groups. PH rats (male: n=7; female: n=9) were administered monocrotaline (MCT; 50 mg/kg, i.p.) while HC rats (male: n=9; female: n=8) were given saline. Disease progression was monitored via echocardiography. Phosphorescence quenching determined the O2 partial pressure in the interstitial space (PO2is) in the spinotrapezius muscle at rest and during contractions.ResultsAll PH rats displayed criteria for disease including right ventricular (RV) hypertrophy, elevated RV systolic pressure, and pulmonary congestion compared to HC. Indicators of PH severity did not differ between males and females (P>0.05). Females displayed a greater reduction in baseline PO2is in PH versus HC when compared to male counterparts (‐29 ± 3% vs. ‐18 ± 2%; P<0.05). No sex differences were present in PO2is kinetics (i.e., tau, amplitude) throughout contractions. However, females with PH reached a lower nadir in PO2is than PH males (4.2 ± 0.3 vs. 7.4 ± 0.4 mmHg; P<0.05).ConclusionsThese findings support that Q̇O2‐to‐V̇O2 matching is impaired in a sex specific manner in skeletal muscle. Individual contributions of O2 delivery and utilization, as well as biochemical analysis of NO in skeletal muscle will be invaluable to elucidating the mechanistic bases for the effects seen herein.

Mild intermittent hypoxia exposure induces metabolic and molecular adaptations in men with obesity

ObjectiveRecent studies suggest that hypoxia exposure may improve glucose homeostasis, but well-controlled human studies are lacking. We hypothesized that mild intermittent hypoxia (MIH) exposure decreases tissue oxygen partial pressure (pO2) and induces metabolic improvements in people who are overweight/obese. MethodsIn a randomized, controlled, single-blind crossover study, 12 men who were overweight/obese were exposed to MIH (15 % O2, 3 × 2 h/day) or normoxia (21 % O2) for 7 consecutive days. Adipose tissue (AT) and skeletal muscle (SM) pO2, fasting/postprandial substrate metabolism, tissue-specific insulin sensitivity, SM oxidative capacity, and AT and SM gene/protein expression were determined. Furthermore, primary human myotubes and adipocytes were exposed to oxygen levels mimicking the hypoxic and normoxic AT and SM microenvironments. ResultsMIH decreased systemic oxygen saturation (92.0 ± 0.5 % vs 97.1 ± 0.3, p < 0.001, respectively), AT pO2 (21.0 ± 2.3 vs 36.5 ± 1.5 mmHg, p < 0.001, respectively), and SM pO2 (9.5 ± 2.2 vs 15.4 ± 2.4 mmHg, p = 0.002, respectively) compared to normoxia. In addition, MIH increased glycolytic metabolism compared to normoxia, reflected by enhanced fasting and postprandial carbohydrate oxidation (pAUC = 0.002) and elevated plasma lactate concentrations (pAUC = 0.005). Mechanistically, hypoxia exposure increased insulin-independent glucose uptake compared to standard laboratory conditions (~50 %, p < 0.001) and physiological normoxia (~25 %, p = 0.019) through AMP-activated protein kinase in primary human myotubes but not in primary human adipocytes. MIH upregulated inflammatory/metabolic pathways and downregulated extracellular matrix-related pathways in AT but did not alter systemic inflammatory markers and SM oxidative capacity. MIH exposure did not induce significant alterations in AT (p = 0.120), hepatic (p = 0.132) and SM (p = 0.722) insulin sensitivity. ConclusionsOur findings demonstrate for the first time that 7-day MIH reduces AT and SM pO2, evokes a shift toward glycolytic metabolism, and induces adaptations in AT and SM but does not induce alterations in tissue-specific insulin sensitivity in men who are overweight/obese. Future studies are needed to investigate further whether oxygen signaling is a promising target to mitigate metabolic complications in obesity. Clinical trial registrationThis study is registered at the Netherlands Trial Register (NL7120/NTR7325).

Skeletal muscle interstitial Po2 kinetics during recovery from contractions.

The oxygen partial pressure in the interstitial space (Po2 is) drives O2 into the myocyte via diffusion, thus supporting oxidative phosphorylation. Although crucial for metabolic recovery and the capacity to perform repetitive tasks, the time course of skeletal muscle Po2 is during recovery from contractions remains unknown. We tested the hypothesis that Po2 is would recover to resting values and display considerable on-off asymmetry (fast on-, slow off-kinetics), reflective of asymmetric capillary hemodynamics. Microvascular Po2 (Po2 mv) was also evaluated to test the hypothesis that a significant transcapillary gradient (ΔPo2 = Po2 mv - Po2 is) would be sustained during recovery. Po2 mv and Po2 is (expressed in mmHg) were determined via phosphorescence quenching in the exposed rat spinotrapezius muscle during and after submaximal twitch contractions (n = 12). Po2 is rose exponentially (P < 0.05) from end-contraction (11.1 ± 5.1), such that the end-recovery value (17.9 ± 7.9) was not different from resting Po2 is (18.5 ± 8.1; P > 0.05). Po2 is off-kinetics were slower than on-kinetics (mean response time: 53.1 ± 38.3 versus 18.5 ± 7.3 s; P < 0.05). A significant transcapillary ΔPo2 observed at end-contraction (16.6 ± 7.4) was maintained throughout recovery (end-recovery: 18.8 ± 9.6; P > 0.05). Consistent with our hypotheses, muscle Po2 is recovered to resting values with slower off-kinetics compared with the on-transient in line with the on-off asymmetry for capillary hemodynamics. Maintenance of a substantial transcapillary ΔPo2 during recovery supports that the microvascular-interstitium interface provides considerable resistance to O2 transport. As dictated by Fick's law (V̇o2 = Do2 × ΔPo2), modulation of O2 flux (V̇o2) during recovery must be achieved via corresponding changes in effective diffusing capacity (Do2; mainly capillary red blood cell hemodynamics and distribution) in the face of unaltered ΔPo2.NEW & NOTEWORTHY Capillary blood-myocyte O2 flux (V̇o2) is determined by effective diffusing capacity (Do2; mainly erythrocyte hemodynamics and distribution) and microvascular-interstitial Po2 gradients (ΔPo2 = Po2 mv - Po2 is). We show that Po2 is demonstrates on-off asymmetry consistent with Po2 mv and erythrocyte kinetics during metabolic transitions. A substantial transcapillary ΔPo2 was preserved during recovery from contractions, indicative of considerable resistance to O2 diffusion at the microvascular-interstitium interface. This reveals that effective Do2 declines in step with V̇o2 during recovery, as per Fick's law.

Blood Flow Restricted Exercise and Reduced Oxygen Tension Decrease Mitochondrial ROS Emission in Human Muscle

Low volume blood flow restricted (BFR) training has been proposed to induce comparable adaptations to traditional resistance training, however the underlying mechanisms remain unknown. Despite the absence of direct support, a suggested mechanism of BFR is an increase in reactive oxygen species (ROS). PURPOSE: We aimed to determine if the rate of mitochondrial ROS emission was altered following an acute bout of occluded (BFR) or non-occluded resistance training (RT), and to mechanistically investigate the role of skeletal muscle O2 partial pressure (pO2) in this response. METHODS: Ten males (25±1yrs) performed 3 sets of single leg squats to failure at 30% 1RM, with either BFR (60-70% occlusion), or without occlusion (RT), while skeletal muscle tissue oxygenation was estimated using near-infrared spectroscopy. Muscle biopsies were obtained at rest and 2-hours post-exercise to determine mitochondrial respiration and ROS emission in permeabilized muscle fibers. In a separate cohort, muscle biopsies were obtained from six males (25±2yrs) to examine the effects of pO2 on in vitro mitochondrial bioenergetics. RESULTS: Resistance exercise, with or without BFR, did not alter maximal respiratory capacity or mitochondrial sensitivity to ADP. While maximal mitochondrial ROS emission was unchanged following RT, BFR decreased this response compared to rest (66.6 vs. 86.2 pmol min-1 mg dry wt-1, p<0.05). Skeletal muscle oxygenation was lower in the BFR compared to RT leg, both during (41.4% vs. 46.1% saturation respectively, p<0.01) and between (50.3% vs. 61.1% saturation respectively, p<0.01) exercise sets. Further evaluation of mitochondrial bioenergetics in vitro revealed that mild O2 restriction (50μM) dramatically attenuated maximal mitochondrial ROS emission (~4-fold), and fraction electron leak to ROS (~3-fold) compared to room air (200μM). This effect was especially evident in the presence of non-saturating ADP, as submaximal ROS emission was almost completely suppressed during O2 restriction, without a reduction in submaximal respiration. CONCLUSIONS: These data indicate that a reduction in skeletal muscle pO2 attenuates the propensity of mitochondria to produce ROS, a mechanism which may contribute to the acute responses to BFR training. This research is supported by NSERC funding.

Managing the power grid: how myoglobin can regulate PO2 and energy distribution in skeletal muscle.

Managing the power grid: how myoglobin can regulate PO2 and energy distribution in skeletal muscle.

Skeletal muscle and glioma oxygenation by carbogen inhalation in rats: a longitudinal study by EPR oximetry using single-probe implantable oxygen sensors.

The feasibility of EPR oximetry using a single-probe implantable oxygen sensor (ImOS) was tested for repeated measurement of pO₂ in skeletal muscle and ectopic 9L tumors in rats. The ImOS (50 mm length) were constructed using nickel-chromium alloy wires, with lithium phthalocyanine (LiPc, oximetry probe) crystals loaded in the sensor loop and coated with AF 2400(®) Teflon. These ImOS were implanted into the skeletal muscle in the thigh and subcutaneous 9L tumors. Dynamic changes in tissue pO₂ were assessed by EPR oximetry at baseline, during tumor growth, and repeated hyperoxygenation with carbogen breathing. The mean skeletal muscle pO₂ of normal rats was stable and significantly increased during carbogen inhalation in experiments repeated for 12 weeks. The 9L tumors were hypoxic with a tissue pO₂ of 12.8 ± 6.4 mmHg on day 1; however, the response to carbogen inhalation varied among the animals. A significant increase in the glioma pO₂ was observed during carbogen inhalation on day 9 and day 14 only. In summary, EPR oximetry with ImOS allowed direct and longitudinal oxygen measurements in deep muscle tissue and tumors. The heterogeneity of 9L tumors in response to carbogen highlights the need to repeatedly monitor pO₂ to confirm tumor oxygenation so that such changes can be taken into account in planning therapies and interpreting results.

S-nitrosylation therapy to improve oxygen delivery of banked blood

From the perspectives of disease transmission and sterility maintenance, the world's blood supplies are generally safe. However, in multiple clinical settings, red blood cell (RBC) transfusions are associated with adverse cardiovascular events and multiorgan injury. Because ∼85 million units of blood are administered worldwide each year, transfusion-related morbidity and mortality is a major public health concern. Blood undergoes multiple biochemical changes during storage, but the relevance of these changes to unfavorable outcomes is unclear. Banked blood shows reduced levels of S-nitrosohemoglobin (SNO-Hb), which in turn impairs the ability of stored RBCs to effect hypoxic vasodilation. We therefore reasoned that transfusion of SNO-Hb-deficient blood may exacerbate, rather than correct, impairments in tissue oxygenation, and that restoration of SNO-Hb levels would improve transfusion efficacy. Notably in mice, administration of banked RBCs decreased skeletal muscle pO2, but infusion of renitrosylated cells maintained tissue oxygenation. In rats, hemorrhage-induced reductions in muscle pO2 were corrected by SNO-Hb-repleted RBCs, but not by control, stored RBCs. In anemic awake sheep, stored renitrosylated, but not control RBCs, produced sustained improvements in O2 delivery; in anesthetized sheep, decrements in hemodynamic status, renal blood flow, and kidney function incurred following transfusion of banked blood were also prevented by renitrosylation. Collectively, our findings lend support to the idea that transfusions may be causally linked to ischemic events and suggest a simple approach to prevention (i.e., SNO-Hb repletion). If these data are replicated in clinical trials, renitrosylation therapy could have significant therapeutic impact on the care of millions of patients.

Effects of Exchange Transfusion With Liposome-Encapsulated Hemoglobin on VO2/DO2

We clarified the effect of exchange transfusion with liposome-encapsulated hemoglobin (neo red cells, NRCs) with low O₂ affinity (P₅₀O₂ = 50 mm Hg) on O₂ metabolism. Rabbits were randomly assigned to receive serial exchange transfusions with NRC (NRC group, n = 5), shed blood diluted 1:1 with saline (red blood cell (RBC) group, n = 5), or saline alone (plasma group, n = 4) under hemodynamic monitoring. Cardiac tamponade was then induced and successively reversed to determine relationships between O₂ consumption (VO₂) and O₂ delivery (DO₂) using the dual-line method. Mean values of Hb concentration after exchange transfusion were 5.7 (NRC), 6.0 (RBC), and 1.5 (plasma) g/dL. The plasma group could not even survive the initial exchange hemodilution due to a critical decrease in DO₂. The NRC, but not the RBC group, developed progressive metabolic acidosis and lactatemia, as well as increases in PaCO₂ and decreases in tissue PO₂ in skeletal muscle after exchange transfusion. Nonetheless, systemic O₂ uptake indices obtained from an analysis of the VO₂/DO₂ relationship in the NRC and RBC groups were comparable. These findings suggested that systemic O₂ uptake was maintained in rabbits after exchange transfusion with NRC, although progressive tissue hypoxia with systemic acidosis is indicative of inadequate peripheral circulation and insufficient aerobic metabolism during extended hemodilution in which 86% of the circulating blood is replaced.

Tissue gas tensions and tissue metabolites for detection of organ hypoperfusion and ischemia

The aim of this study was to evaluate how tissue gas tensions and tissue metabolites measured in situ can detect hypoperfusion and differentiate between aerobic and anaerobic conditions during hemorrhagic shock. We hypothesized that tissue PCO(2) (PtCO(2)) would detect hypoperfusion also under aerobic conditions and detect anaerobic metabolism concomitantly with or earlier than other markers. Prospective experimental animal study with eight anesthetized pigs subjected to a continuous blood loss ∼8% of total blood volume per hour until death. We measured cardiac index, organ blood flows, and tissue levels of PO(2), PCO(2), glucose, pyruvate, lactate, and glycerol in intestine, liver, kidney, and skeletal muscle. With reduction in blood flow to the organs under aerobic conditions, PtCO(2) increased ∼1-4 kPa from baseline. With the onset of tissue hypoxia there was a pronounced increase of PtCO(2), lactate, lactate-pyruvate (LP) ratio, and glycerol. Tissue pH and bicarbonate decreased significantly, indicating that metabolic acid was buffered by bicarbonate to generate CO(2). Moderate tissue hypoperfusion under aerobic conditions is associated with increased PtCO(2), in contrast to metabolic parameters of ischemia (lactate, LP ratio, and glycerol) which remain low. From the onset of ischemia there is a much more rapid and pronounced increase in PtCO(2), lactate, and LP ratio. PtCO(2) can be used as a marker of hypoperfusion under both aerobic and anaerobic conditions; it gives an earlier warning of hypoperfusion than metabolic markers and increases concomitantly with or earlier than other markers at the onset of tissue anaerobiosis.

Microvascular PO2 Kinetics in Hindlimb Skeletal Muscle of Obese Diabetic Zucker Rats

Microvascular PO2 (PO2mv) in skeletal muscle reflects the dynamic balance between oxygen delivery and oxygen uptake. PO2mv on-kinetics in the rat spinotrapezius muscle during the rest-contraction transition are faster in both streptozotocin (STZ) and Goto-Kazazaki (GK) diabetic rats. Reduced nitric oxide (NO) availability has been implicated in these diabetic sequelae. PURPOSE: The purpose of this study was to determine the impact of insulin-resistant diabetes on PO2mv kinetics in a hindlimb locomotory muscle, and to assess the role of NO. METHODS: PO2mv (phosphorescence quenching) was measured in the extensor digitorum longus muscle (EDL) of female lean control (LC, n=10, 194 ± 3 g) and obese diabetic (OD, n=9, 356 ± 11 g) Zucker rats. PO2mv was monitored at rest and through the rest-contraction transition. PO2mv on-kinetics were determined using a monoexponential plus time delay model. EDL blood flow (radiolableled microspheres) was measured at the end of the 150 s contraction period. The experimental protocol included; 1) a pre-stimulation, 2) a control stimulation, 3) administration of L-NAME (30 mg/kg), and 4) a post-L-NAME stimulation. RESULTS: OD rats had elevated blood glucose levels (LC, 5.9 ± 0.4; OD, 25.4 ± 1.8 mmol/L). Resting PO2mv was not different in LC and OD rats (LC, 29 ± 2; OD, 23 ± 3 mmHg). During contractions, PO2mv fell to the same level in both groups (LC, 16 ± 2; OD, 17 ± 2 mmHg). OD rats had both a shorter time delay (LC, 9 ± 2; OD, 7 ± 1 s; P<0.05) and shorter mean response time (LC, 24 ± 2; OD, 17 ± 1 s; P<0.05). EDL blood flow during contractions was not different (LC, 70 ± 15; OD, 67 ± 17 ml/ min/100 g). PO2mv was lower after L-NAME in both LC and OD rats. Both time delay and mean response time were shorter in LC and OD rats, but the PO2mv time constant was shorter only in LC rats. Blood flow during contractions was not reduced by L-NAME, but the vascular conductance was reduced. CONCLUSIONS: The faster PO2mv on-kinetics observed in the EDL of OD rats is consistent with previous reports in STZ and GK rats, and may be due to a slower rise in blood flow and oxygen delivery at the onset of contractions. These data also suggest that impaired NO production in OD rats may contribute to the more rapid fall in PO2mv at the onset of muscle contractions. (Supported by the AHA, Heartland Affiliate and the KCOM Graduate Program.)

Quantifying the role of oxygen pressure in tissue function

it has been suggested that oxygen had reached significant levels in the earth's oceans as early as 2.5 billion years ago and has rapidly increased to near current levels about 50 million years later ([6][1]). The appearance of oxygen dramatically changed the chemical composition of the oceans and

MONITORING SKELETAL MUSCLE AND SUBCUTANEOUS TISSUE ACID-BASE STATUS AND OXYGENATION DURING HEMORRHAGIC SHOCK AND RESUSCITATION

Gastric tonometry correlates with the severity of blood loss during shock. However, tonometry is cumbersome, has a slow response time, and is not practical to apply in the acute resuscitation setting. We hypothesized that subcutaneous tissue (SC) and skeletal muscle (SM) pH, pCO2, and pO2 changes are comparable with changes seen in bowel tonometry during shock and resuscitation. Thirteen male mini-swine (25-35 kg; n = 4 control, n = 9 shock) underwent laparotomy and jejunal tonometry. A multisensor probe (Diametrics Medical, Roseville, MN) was placed in the carotid artery, the chest SC, and the adductor muscle of the leg (SM). PaCO2 was maintained between 40 and 45 mmHg. Shocked animals were hemorrhaged and kept at mean arterial pressure of 40 mmHg. Animals were bled until a reinfusion of >10% of the total shed blood was needed to maintain the mean arterial pressure at 40 mmHg. Animals were resuscitated with shed blood plus 2x shed volume in lactated Ringer's solution (20 min) and were observed for 3 h. The average blood loss was 47.2% +/- 8.7% of calculated blood volume. During the hemorrhagic phase, SM and SC displayed tissue acidosis (r2 = 0.951), tissue hypercapnea (r2 = 0.931), and tissue hypoxia (r2 = 0.748). Overall, pH displayed the best correlation between SM and SC during shock and resuscitation. PCO2 in the jejunum (tonometry), SM, and SC increased during decompensation. However, during resuscitation as tonometric pCO2 normalized, only SC pCO2 decreased to its baseline value, whereas the SM pCO2 decrease tended to lag behind. Bland-Altman analyses demonstrated that the variability of the tissue pH changes in SM and SC are predictable according to the phases of hemorrhage and resuscitation. Changes in tissue pH correlated during bleeding and during resuscitation among SC and SM, and these changes followed the trends in gut tonometry as well. Continuous pCO2 and pO2 monitoring in the SM and SC tissues had significant correlations during the induction of shock only. SM and SC continuous pH and pCO2 monitoring reflect bowel pCO2 values during hemorrhagic shock. The response of these indicators as potential surrogates of impaired tissue metabolism varies among tissues and according to the phases of hemorrhage or resuscitation.

Effect of mild hyperglycemia +/- meta-iodo-benzylguanidine on the radiation response of R3230 Ac tumors.

The effects of glucose or meta-iodo-benzylguanidine (MIBG) on oxygen utilization (QO2) of several tumor cell lines were studied using a Clark-type electrode chamber. For in vivo studies, rats bearing R3230 Ac rat mammary adenocarcinomas were utilized. To evaluate changes in tumor oxygenation induced by glucose or MIBG, intratumoral pO2 and skeletal muscle pO2 were measured using Eppendorf Histography. To find the effect of mild hyperglycemia (i.p., 1 g/kg) +/- MIBG (i.p., 20 mg/kg) on the radiation response, a growth delay assay was used. Glucose alone produced a approximately 20% inhibition of QO2 in several tumor cells we tested except Q7 tumor cells. MIBG inhibited QO2 in R3230 Ac tumors. The median tumor pO2 for glucose + MIBG was increased from 5.3 mm Hg to 13.8 mm Hg. We hypothesized that combined treatment with glucose + MIBG significantly enhanced radiation-induced tumoricidal effects on R3230 Ac tumors, mainly due to reduction in QO2 and increase in tumor pO2.

Skeletal muscle acidosis correlates with the severity of blood volume loss during shock and resuscitation.

Continuous assessment of tissue perfusion and oxygen utilization may allow for early recognition and correction of hemorrhagic shock. We hypothesized that continuously monitoring skeletal muscle (SM) PO2, PCO2, and pH during shock would provide an easily accessible method for assessing the severity of blood loss and the efficacy of resuscitation. Thirteen anesthetized pigs (25-35 kg) underwent laparotomy and femoral vessel cannulation. Multiparameter fiberoptic sensors were placed in the deltoid (SM) and femoral artery. Ventilation was maintained at a PaCO2 of 40-45 mm Hg. Total blood volume (TBV) was measured using an Evans blue dye technique. Animals were bled for 15 minutes, maintained at a mean arterial pressure (MAP) of 40 mm Hg for 1 hour, resuscitated (shed blood + 2 times shed volume in normal saline) and observed for 1 hour. Four animals served as controls (sham hemorrhage). Blood and tissue samples were taken at each time point. Blood loss ranged from 28.5-56% of TBV. SM pH and SM PO2 levels fell rapidly with shock. SM PO2 returned to normal with resuscitation; however, SM pH did not return to baseline. SM PCO2 significantly rose with shock, but returned to baseline promptly with resuscitation. There was a significant correlation between SM pH and blood volume loss at end shock (r2 = 0.73, p < 0.001) and recovery (r2 = 0.84, p < 0.001). Animals (n = 2) whose SM pH did not recover to 7.2 were found to have ongoing blood loss from biopsy sites and persistent tissue hypercarbia despite normal MAP. Continuous multiparameter monitoring of SM provides a minimally invasive method for assessing severity of shock and efficacy of resuscitation. Both PCO2 and PO2 levels change rapidly with shock and resuscitation. SM pH is directly proportional to lost blood volume. Persistent SM acidosis (pH < 7.2) and elevated PCO2 levels suggest incomplete resuscitation despite normalized hemodynamics.

Comparison of skeletal muscle PO2, PCO2, and pH with gastric tonometric P(CO2) and pH in hemorrhagic shock.

To monitor PO2, PCO2, and pH in the interstitium of skeletal muscle (PmO2, PmCO2, and pHm) during hemorrhage, shock, and resuscitation using fiber-optic sensors and to compare Pco2 and pH in the interstitium of gastric mucosa (PrCO2 and pHi) obtained using gastric CO2 tonometry. Prospective, controlled observational study in an acute experimental preparation. Physiology laboratory in a university medical school. Nine mongrel dogs (20 to 35 kg). Anesthesia was induced with pentobarbital (25 mg/kg iv) and maintained (10 mg/hr) after hemorrhagic shock. Mechanical ventilation was established to maintain baseline PaCO2 approximately 35 torr. Arterial, venous, and pulmonary artery catheters were placed. Blood flow probes were placed around the right femoral artery and vein. A probe (0.5 mm in diameter) with fiber-optic PO2, PCO2, and pH sensors was placed percutaneously in the adductor muscle of the right thigh. A gastric tonometer catheter was placed in the stomach lumen. After baseline data collection, controlled hemorrhage to mean arterial pressure (MAP) of 45 to 50 mm Hg was maintained for 1 hr. Shed blood was then reinfused. Blood gas, hemodynamic, and gastric tonometric data were collected during shock and reinfusion at 30-min intervals and hourly after reinfusion for 4 hrs. Normothermia was maintained. PmO2 decreased rapidly from 42 +/- 13 torr (mean +/- sD) to 13 +/- 9 torr within 15 mins and to 6 +/-4 torr within 30 mins of MAP reaching 45 mm Hg, and it recovered to baseline with reinfusion. pHm decreased gradually from 7.23 +/-0.09 to 6.89 +/- 0.25 during the 1-hr shock period and increased slowly toward baseline after reinfusion. pHi decreased from 7.43 +/- 0.14 to 6.91 +/- 0.23, and on average it returned to baseline 2 hrs after reinfusion. PmCO2 increased from 50 +/- 12 to 113 +/- 49 torr, increased further to 124 +/- 73 torr during reinfusion, and returned slowly toward baseline after reinfusion. PrCO2 increased from 35 +/- 8 to 60 +/- 19 torr and returned to baseline within 15 mins after reinfusion. During shock and reinfusion, oxygen delivery, mixed venous PO2, mixed venous oxygen saturation, and PmO2 responded with similar time courses. After reinfusion, on average, PmO2 exceeded baseline PmO2 and mixed venous PO2, and oxygen availability exceeded demand, suggesting an oxygen consumption defect. On average, PmCO2 and pHm did not return to baseline values 4 hrs after reinfusion, suggesting the persistence of anaerobic metabolic effects in skeletal muscle beyond the relatively short time that is required to reestablish baseline MAP, blood flow rates, oxygen delivery, PrCO2, and pHi. PmO2, PmCO2, and pHm, monitored simultaneously using fiber-optic sensors in a single, small probe placed percutaneously, appear to indicate greater severity of shock and more prolonged resuscitation than conventional systemic or gastric tonometric variables.

Skeletal muscle PO2, PCO2, and pH in hemorrhage, shock, and resuscitation in dogs.

To test fiber-optic PO2, PCO2, and pH sensors placed in skeletal muscle as monitors of hemorrhage, shock, and resuscitation, compared with mean arterial blood pressure, cardiac output, and blood gas variables. Observational study in physiology laboratory, using a canine controlled hemorrhagic shock model. Mongrel dogs (20-35 kg; n = 10) were monitored with arterial, venous, and pulmonary artery catheters. A probe (0.5 mm in diameter) with fiber-optic PO2, PCO2, and pH sensors was placed percutaneously in the adductor muscle of the right medial thigh. Mean arterial blood pressure of 45 to 50 mm Hg was maintained for 1 hour with controlled hemorrhage, after which shed blood was reinfused. The animals were monitored for 4 hours after reinfusion. Skeletal muscle PO2 (PmO2) decreased from 31+/-9 to 5+/-4 mm Hg during shock and recovered with reinfusion. Skeletal muscle pH (pHm) decreased from 7.24+/-0.10 to 6.94+/-0.12 during shock, to 6.90+/-0.13 with reinfusion, and recovered to near baseline 2 hours after reinfusion. PmCO2 increased from 48+/-14 to 134+/-86 mm Hg during shock, to 138+/-92 mm Hg with a time course inverse to pHm, and recovered to near baseline 30 minutes after reinfusion. On average, skeletal muscle PCO2 (PmCO2) and pHm did not recover to baseline, possibly indicating persistent anaerobic metabolic effects. O2 delivery, mixed venous PO2, mixed venous O2, saturation and PmO2 responded with similar time courses. PmO2, PmCO2, and pHm can be monitored simultaneously for several hours with fiber-optic sensors in a single, small probe. PmO2 may provide information comparable to O2 delivery. PmCO2 may reflect adequacy of perfusion. pHm may indicate success of resuscitation. This technology may offer new insight into the extent of injury and refinement of shock resuscitation and monitoring.

Hypertonic Saline Treatment of Acid Aspiration-Induced Lung Injury

Airway acid aspiration leads to severe microvascular lung injury and pulmonary edema. Recent studies have demonstrated that other conditions associated with microvascular injury such as sepsis and burns can be effectively treated with low-volume hypertonic saline (HTS). Thus, the present study aimed to test whether HTS attenuates aspiration-induced lung injury in the rat. Intratracheal administration of 0.2 ml of 0.1NHCl (n= 7) induced pulmonary leukosequestration [myeloperoxidase (MPO) activity +446 ± 34%,P< 0.05; bronchoalveolar lavage (BAL) fluid neutrophil count +178 ± 23%,P< 0.05], edema (+43 ± 6%,P< 0.01), and microvascular permeability defect (BAL protein concentration +675 ± 34%,P< 0.01). These changes were associated with tissue hypoxia (skeletal muscle PO2, 49 ± 8 mm Hg,P< 0.05) and elevated serum TNFα (750 ± 38 pg/ml,P< 0.01). HTS (2400 mosmole/liter) at 5 ml/kg, administered 20 min after aspiration (n= 7), reduced lung pulmonary edema by 58 ± 7% (P< 0.05) and improved tissue oxygen tension (PO2, 85 ± 7 mm Hg,P< 0.05) but failed to alter lung MPO and BAL fluid protein and leukocyte count response. Also, HTS did not reduce TNFα response to aspiration. These data point to a potential therapeutic role for low-volume HTS in treating aspiration-induced lung injury. In addition, our data suggest that HTS is acting by rapidly shifting fluid from the pulmonary interstitium to the intravascular compartment because it did not inhibit the inflammatory response to aspiration.

Dopexamine hydrochloride in septic shock: Effects on oxygen delivery and oxygenation of gut, liver, and muscle: J Trauma Inj Infect Crit Care 1995; 38/5: 767–775

It has been suggested that septic shock is a disorder of microvascular autoregulation. Tissue blood flow is modulated by the state of activation of upstream endothelial receptors controlling the vascular smooth muscle tone. Because vascular receptor populations vary between organs, it should be expected that vasoactive drugs affect tissue oxygenation differently in different organs. We studied the effects of dopexamine HCl (a novel inotrope) and septic shock on oxygen delivery as well as tissue Po2 in gut, liver, and skeletal muscle in anesthetized rabbits. Employing the thermodilution technique, cardiac output was measured across the pulmonary bed and used to calculate oxygen delivery. Three eight-channel Mehrdraht Dortmund Oberflache oxygen electrodes were placed on gut serosa, liver, and skeletal muscle surfaces, respectively, and sufficient readings were obtained to calculate tissue Po2 distributions. During septic shock mean arterial pressure, cardiac output, oxygen delivery, and mean tissue Po2 decreased in all organs. Our results suggest that the observed changes in tissue oxygenation during septic shock were caused by defective regulation of microvascular blood flow. In conclusion, during baseline conditions dopexamine HCl caused no statistically significant changes in tissue oxygenation in any organ, except in skeletal muscle at 10 micrograms/kg/min when tissue Po2 increased. During septic shock, however, dopexamine HCl improved oxygenation in all three organs in a dose-dependent manner.