Systemic Oxygen Transport Research Articles

Early warning: End-tidal carbon dioxide is associated with central venous oxygenation under continuous cardiorespiratory monitoring in a porcine model of hemorrhagic shock and resuscitation

BackgroundEnd-tidal carbon dioxide (ETCO2) has previously shown promise as a predictor of shock severity and mortality in trauma. ETCO2 monitoring is non-invasive, real-time, and readily available in prehospital settings, but the temporal relationship of ETCO2 to systemic oxygen transport has not been thoroughly investigated in the context of hemorrhagic shock. MethodsA validated porcine model of hemorrhagic shock and resuscitation was used in male Yorkshire swine (N ​= ​7). Both ETCO2 and central venous oxygenation (SCVO2) were monitored and recorded continuously in addition to other traditional hemodynamic variables. ResultsLinear regression analysis showed that ETCO2 was associated with ScvO2 both throughout the experiment (β ​= ​1.783, 95% confidence interval (CI) [1.552–2.014], p ​< ​0.001) and during the period of most rapid hemorrhage (β ​= ​4.896, 95% CI [2.416–7.377], p ​< ​0.001) when there was a marked decrease in ETCO2. ConclusionsETCO2 and ScvO2 were closely associated during rapid hemorrhage and continued to be temporally associated throughout shock and resuscitation.

Microcirculatory effects of rewarming in experimental hemorrhagic shock.

Rewarming is a recommended therapy during the resuscitation of hypothermic patients with hemorrhagic shock. In experimental models, however, it increases inflammatory response and mortality. Although microcirculation is potential target of inflammation, the microvascular effects of rewarming during the resuscitation of hemorrhagic shock have not been studied. Our goal was to assess the systemic and microcirculatory effects of an increase in core temperature (T°) during the retransfusion of hemorrhagic shock in sheep. Our hypothesis was that rewarming could hamper microcirculation. In anesthetized and mechanically ventilated sheep, we measured systemic, intestinal, and renal hemodynamics and oxygen transport. O2 consumption (VO2) and respiratory quotient were measured by indirect calorimetry. Cortical renal, intestinal villi and sublingual microcirculation were assessed by IDF-videomicroscopy. After basal measurements, hemorrhagic shock was induced and T° was reduced to ~33°C. After 1h of shock and hypothermia, blood was retransfused and Ringer lactate solution was administered to prevent arterial hypotension. In the control group (n=12), T° was not modified, while in the intervention (rewarming) group, it was elevated ~3°C. Measurements were repeated after 1h. During shock, both groups showed similar systemic and microvascular derangements. After retransfusion, VO2 remained decreased compared to baseline in both groups, but was lower in the control compared to the rewarming group. Perfused vascular density has a similar behavior in both groups. Compared to baseline, it remained reduced in peritubular (control vs. rewarming group, 13.8 [8.7-17.5] vs. 15.7 [10.1-17.9] mm/mm2, PNS) and villi capillaries (14.7 [13.6-16.8] vs. 16.3 [14.2-16.9] mm/mm2, PNS), and normalized in sublingual mucosa (19.1 [16.0-20.3] vs. 16.6 [14.7-17.2] mm/mm2, PNS). This is the first experimental study assessing the effect of rewarming on systemic, regional, and microcirculatory perfusion in hypothermic hemorrhagic shock. We found that a 3°C increase in T° neither improved nor impaired the microvascular alterations that persisted after retransfusion. In addition, sublingual mucosa was less susceptible to reperfusion injury than villi and renal microcirculation.

Postpartum haemorrhage: minimum allowable haemoglobin level

Despite defining the acceptable postpartum haemoglobin levels, there is neither consensus, nor a strong statistically proven analysis of its minimum safe level and its influence on systemic haemodynamic and oxygen metabolism in particular.&#x0D; The aim. Therefore, this study aimed to determine statistically minimal allowable haemoglobin levels in postpartum women in case of postpartum haemorrhage which allows the cardiac functional status and oxygen metabolism to be maintained on the lower margin of the physiological range.&#x0D; Materials and methods: Clinical research was on 113 postpartum women who had received blood transfusions for postpartum haemorrhages were selected for this study. The following circulation parameters were assessed: heart rate (HR), systolic blood pressure (BPs), diastolic blood pressure (BPD), mean arterial pressure (MAP), central venous pressure (CVP), cardiac index (СІ), contractility index (ΔS), systemic vascular resistance index (SVRI), systemic oxygen delivery index (IDО2), systemic oxygen consumption index (IVО2), tissue oxygen extraction ratio (O2ER).&#x0D; Results: Through a comparison of hemodynamic parameters depending on haematocrit and haemoglobin levels in patients with postpartum blood loss it was discovered that in case of blood loss and consequent intensive therapy aimed at TBV (total blood volume) restoration statistically significant changes of BPs, MAP, СІ and SVRI were observed. Also, during this study linear high-degree correlations between СІ, ΔS and Hb levels were found.&#x0D; Analysis of systemic oxygen transport dependence on haematocrit and haemoglobin levels for patients during the early postpartum period demonstrates significant differences in cardiac indexes with a strong positive statistically significant correlation between these parameters and haemoglobin levels.&#x0D; Conclusion. From the calculation of the minimum allowable haemoglobin level in postpartum women in case of blood loss using linear regression with coefficients calculated through the method of least squares the Hb=82.5 g/L value was obtained, which can be considered the minimum allowable level in postpartum women in case of postpartum blood loss which allows the cardiac functional status and oxygen metabolism to be on safety physiological range

Study of the effect of Occlutech Atrial Flow Regulator on symptoms, hemodynamics, and echocardiographic parameters in advanced pulmonary arterial hypertension.

Optimal sized balloon atrial septostomy improves hemodynamics in advanced pulmonary arterial hypertension. Occlutech Atrial Flow Regulator is designed to provide an atrial septal fenestration diameter titrated according to the age and right atrial pressures. This observational study analyzed symptoms, exercise distance, oxygen saturations, hemodynamics and echocardiographic parameters after Atrial Flow Regulator implantation in patients with syncope or right-heart failure. Patients with high-risk predictors of mortality during septostomy were scrutinized. Thirty-nine patients (9 children) with syncope (34/39) or right-heart failure (27/39) underwent Atrial Flow Regulator implantation without procedural complications. Six-minute walk distance increased from 310 ± 158.2 to 376.4 ± 182.6 m, none developed syncope. Oxygen saturations reduced from 96.4 ± 6.4% to 92 ± 4.9% at rest and further to 80.3 ± 5.9% on exercise. Right atrial pressures reduced from 9.4 ± 5 (2–27) mmHg to 6.9 ± 2.6 (1–12) mmHg, while cardiac index increased from 2.4 ± 0.8 (0.98–4.3) to 3 ± 1 (1.1–5.3) L/min/m2 and systemic oxygen transport increased from 546.1 ± 157.9 (256.2–910.5) to 637.2 ± 191.1 (301.3–1020.2) ml/min. Echocardiographic improvement included significant reduction of pericardial effusion and inferior caval congestion at a median follow-up of 37 months. Overall survival improved except two early and one late deaths in high-risk patients. Five of seven patients with advanced disease and key hemodynamic predictors of mortality survived. Acute hemodynamic benefits in pulmonary arterial hypertension after Atrial Flow Regulator were improved cardiac output, systemic oxygen transport, and reduced right atrial pressures. Improvement of symptoms especially syncope, exercise duration, and right ventricular systolic function as well as device patency were sustained on mid-term follow-up. Implantation was safe in all including young children without procedural complications. Mortality was noted only in patients who had high-risk predictors and patients at advanced stage of the disease.

The role of metabolic adaptation of the functional state of circulating erythron in determining the course of traumatic disease in patients with massive blood loss in polytrauma

Annotation. Metabolic adaptation of the functional state of circulating erythron is an important criterion for predicting the course of traumatic disease in patients with polytrauma, which is accompanied by heavy blood loss. The aim of the study was to increase the effectiveness of treatment of patients with polytrauma with hemorrhagic shock by developing and implementing a differentiated approach to infusion and transfusion therapy, based on elucidation of the mechanisms of systemic oxygen transport in the postoperative period. The index of erythrocyte transformation index, oxygen delivery index as a leading indicator of oxygen transport system in patients of group I who received intensive therapy according to the classical algorithm, in patients of group II who were additionally prescribed ceruloplasmin solution, in patients of group III who were additionally prescribed a solution of D-fructose-1,6-diphosphate sodium salt hydrate. To determine the functional state of erythrocytes and their ability to deform, we used the method of scanning electron microscopy. Statistical data processing was performed using Student’s t-test (for n&lt;100) at a given level of reliability p=0.95. The statistical analysis of the obtained data revealed a probable reduction in the number of doses of heterogeneous erythrocytes received by patients with high blood loss in polytrauma in patients of group II on the background of maximum ability of erythrocytes to transform while maintaining the oxygen delivery index at a satisfactory level. In the future it is planned to study the morphofunctional parameters of erythrocytes in this group of patients.

Effects of Acute Subdural Hematoma-Induced Brain Injury On Energy Metabolism in Peripheral Blood Mononuclear Cells.

In activated immune cells, differentiation and function are determined by cell type-specific modifications of metabolic patterns. After traumatic brain injury both immune cell activation and suppression were reported. Therefore, we sought to explore immune cell energy metabolism in a long-term, resuscitated porcine model of acute subdural hematoma (ASDH)-induced acute brain injury devoid of impaired systemic hemodynamics and oxygen transport.Before and up to 50 h after induction of ASDH, peripheral blood mononuclear cells (PBMCs) were separated by density gradient centrifugation, and cell metabolism was analyzed using high-resolution respirometry for mitochondrial respiration and electron spin resonance for reactive oxygen species production. After incubation with stable isotope-labeled 1,2-13C2-glucose or 13C5-glutamine, distinct labeling patterns of intermediates of glycolysis or tricarboxylic acid (TCA) cycle and 13CO2 production were measured by gas chromatography-mass spectroscopy. Principal component analysis was followed by a varimax rotation on the covariance across all measured variables and all measured time points.After ASDH induction, average PBMC metabolic activity remained unaffected, possibly because strict adherence to intensive care unit guidelines limited trauma to ASDH induction without any change in parameters of systemic hemodynamics, oxygen transport, and whole-body metabolism. Despite decreased glycolytic activity fueling the TCA cycle, the principal component analysis indicated a cell type-specific activation pattern with biosynthetic and proliferative characteristics.

Indicators of oxygen transport in acute and early periods of traumatic disease with multistage surgical correction at polytrauma

Disorders of the oxygen transport play an important role in the development of multiple organ disfunction syndrome and are a marker of tissue hypoxia and ischemia. Disorders of the oxygen transport could be use for predicting patient survival and as criteria for the severity of the pathological process. The aim of this study was to explore the indicators of systemic oxygen transport in the perioperative period in patients with traumatic deases in multi-stage surgical correction at polytrauma in terms of standard and advanced intensive care. Materials and methods. A prospective study of 88 patients with traumatic deases was conducted. The dynamics of indices of oxygen delivery (iDО2) and oxygen consumption (iVO2), oxygen extraction coefficient (KEO2) at different variants of intensive care was studied. Results. The patients in both groups was noted iDO2 decline, which was due to massive blood loss and decreased cardiac output on admission to the operation room. Despite the fact that during the acute period was held stop bleeding, correction of hypovolemia and posthemorrhagic anemia, the average level of iDО2 was quite low. iDO2 was multidirectional nature of the changes in the studied groups at the second and third stages of the study. In turn, the average values KEO2 characterized the degree of tension compensatory mechanisms and metabolic changes caused by hypoxia and hypoperfusion. Normalization of oxygen homeostasis parameters was achieved in the fourth stage of the study. Conclusions. The maximal intensity of development of compensatory mechanisms and changes of oxygen transport occurs within the first 5 days after the injury. The optimized intensive care which has been used in the treatment patients of Group II, has positive effect on the ability to potentiate adaptive defense mechanisms and reduce oxygen debt.

Comparison of Oxygen Uptake Kinetics During Severe-intensity Laboratory and Field Cycling

The O2-kinetic response to constant work rate exercise provides an insight into the adjustment of systemic oxygen transport and muscle metabolism. Whether O2-kinetics measured in laboratory conditions reflect O2-kinetics in field conditions has not yet been analysed. The aim of this study was to compare O2-kinetics between field and laboratory conditions. Thirteen competitive male cyclists (mean±SD age 23.3±4.1 years; V̇O2peak 68.2±4.7 mL.min-1.kg-1) completed two 6-min severe-intensity trials at 60 and 90 rev.min-1 in both conditions. Power output was measured with an SRM power meter and V̇O2 was measured with a portable gas analyser. The time constant (τ), the time delay (TD) and the amplitude (Amp) were resolved by least square regression, and the V̇O2 slow component (SC) was calculated as the difference between the end-exercise V̇O2 and Amp. To determine differences between the trials, a repeated-measure ANOVA was conducted. The Amp and end-exercise V̇O2 were significantly higher during field cycling whereas the SC were significantly higher during laboratory cycling (all at p<0.001). No significant differences were found for τ (p=0.24). Laboratory measures tend to underestimate the oxygen demand in field cycling. A higher cadence leads to greater oxygen demand in laboratory and field cycling.

The Creation of an Interatrial Right-To-Left Shunt in Patients with Severe, Irreversible Pulmonary Hypertension: Rationale, Devices, Outcomes.

Targeted pharmacotherapies did improve survival rates, exercise capacity, and quality of life (QoL) of PAH patients. However, these pharmacological interventions are expensive and not always accessible. In addition, not all patients do respond similarly to these medications and many will continue to deteriorate. This review aims to discuss the beneficial role of an artificial right-to-left shunt and highlights current interventional devices and outcomes. Since patients with preexisting atrial shunts or patients with Eisenmenger's disease show better survival rates, improved exercise capacity, and QoL, PAH patients clinically do benefit from an atrial septostomy by reducing signs of right heart failure, improving left heart filling, cardiac output, and systemic oxygen transport despite hypoxia. However, an uncontrolled septostomy with unrestricted right-to-left shunt bears the risk of acute severe desaturation and death. The Atrial Flow Regulator (AFR device, Occlutech®, Sweden) provides an adjustable shunt size with restricted flow and excellent short-term outcomes. Interventional strategies for PAH palliation are on the rise. The novel AFR device provides a durable and safe option for a controlled right-to-left shunting, thus enabling an individualized management.

Systemic Oxygen Transport with Rest, Exercise, and Hypoxia: A Comparison of Humans, Rats, and Mice.

The objective of this article is to compare and contrast the known characteristics of the systemic O2 transport of humans, rats, and mice at rest and during exercise in normoxia and hypoxia. This analysis should help understand when rodent O2 transport findings can-and cannot-be applied to human responses to similar conditions. The O2 -transport system was analyzed as composed of four linked conductances: ventilation, alveolo-capillary diffusion, circulatory convection, and tissue capillary-cell diffusion. While the mechanisms of O2 transport are similar in the three species, the quantitative differences are naturally large. There are abundant data on total O2 consumption and on ventilatory and pulmonary diffusive conductances under resting conditions in the three species; however, there is much less available information on pulmonary gas exchange, circulatory O2 convection, and tissue O2 diffusion in mice. The scarcity of data largely derives from the difficulty of obtaining blood samples in these small animals and highlights the need for additional research in this area. In spite of the large quantitative differences in absolute and mass-specific O2 flux, available evidence indicates that resting alveolar and arterial and venous blood PO2 values under normoxia are similar in the three species. Additionally, at least in rats, alveolar and arterial blood PO2 under hypoxia and exercise remain closer to the resting values than those observed in humans. This is achieved by a greater ventilatory response, coupled with a closer value of arterial to alveolar PO2 , suggesting a greater efficacy of gas exchange in the rats. © 2018 American Physiological Society. Compr Physiol 8:1537-1573, 2018.

Atrial septostomy with a predefined diameter using a novel occlutech atrial flow regulator improves symptoms and cardiac index in patients with severe pulmonary arterial hypertension.

A novel Occlutech atrial flow regulator (AFR) implantation gives an atrial septal predefined predictable fenestration. Atrial septostomy relieves syncope in pulmonary arterial hypertension (PAH) by improving left heart filling, cardiac output and systemic oxygen transport despite hypoxia. Symptoms recur when small fenestrations close spontaneously. AFR was implanted after informed consent in patients with severe PAH presenting with syncope and right heart failure. Symptoms, hemodynamics, echocardiographic parameters, brain natriuretic peptide (BNP) levels and device patency were serially documented. Twelve patients aged 28.3 ± 8.5 years with severe PAH underwent AFR implantation. All procedures were successful without any major complications. All patients had relief of syncope and 6-min walk distance improved significantly from 377.3 ± 33.2 to 423 ± 31.32 m. The cardiac index (2.36 ± 0.52 to 2.89 ± 0.56 L/min/m2 ) and systemic oxygen transport (367.5 ± 75.5 to 428.0 ± 67.1 ml/min/m2 ) also showed a significant improvement. Inferior caval vein congestion and pericardial effusion reduced due to improvement in heart failure, but other echocardiographic parameters of right ventricular function did not show significant change. The reduction in BNP levels too did not reach statistical significance. The device was patent in all patients at a median follow-up of 189 days (range 10-296 days) resulting in a significant reduction of oxygen saturations from 98 ± 0.18 to 85.26 ± 2.86% after exercise. AFR implantation was feasible and safe in all patients with PAH. There was a significant improvement of symptoms, six-minute walk distance, cardiac index and systemic oxygen transport. The device maintained patency in short-term follow-up and the resultant hypoxia was tolerated well.

Blood rheology and systemic oxygen transport

Blood rheology and systemic oxygen transport

AltitudeOmics: Red Blood Cell Metabolic Adaptation to High Altitude Hypoxia.

Red blood cells (RBCs) are key players in systemic oxygen transport. RBCs respond to in vitro hypoxia through the so-called oxygen-dependent metabolic regulation, which involves the competitive binding of deoxyhemoglobin and glycolytic enzymes to the N-terminal cytosolic domain of band 3. This mechanism promotes the accumulation of 2,3-DPG, stabilizing the deoxygenated state of hemoglobin, and cytosol acidification, triggering oxygen off-loading through the Bohr effect. Despite in vitro studies, in vivo adaptations to hypoxia have not yet been completely elucidated. Within the framework of the AltitudeOmics study, erythrocytes were collected from 21 healthy volunteers at sea level, after exposure to high altitude (5260 m) for 1, 7, and 16 days, and following reascent after 7 days at 1525 m. UHPLC-MS metabolomics results were correlated to physiological and athletic performance parameters. Immediate metabolic adaptations were noted as early as a few hours from ascending to >5000 m, and maintained for 16 days at high altitude. Consistent with the mechanisms elucidated in vitro, hypoxia promoted glycolysis and deregulated the pentose phosphate pathway, as well purine catabolism, glutathione homeostasis, arginine/nitric oxide, and sulfur/H2S metabolism. Metabolic adaptations were preserved 1 week after descent, consistently with improved physical performances in comparison to the first ascendance, suggesting a mechanism of metabolic memory.

Effects of erythropoietin on systemic hematocrit and oxygen transport in the splenectomized horse

To test the hypotheses that erythropoietin (rhuEPO) treatment increases systemic hematocrit, maximal O2 uptake (V˙O2max, by elevated perfusive and diffusive O2 conductances) and performance five female horses (4–13 years) received 15IU/kg rhuEPO (erythropoietin) three times per week for three weeks. These horses had been splenectomized over 1 year previously to avoid confounding effects from the mobilization of splenic red blood cell reserves. Each horse performed three maximal exercise tests (one per month) on an inclined (4°) treadmill to the limit of tolerance; two control trials and one following EPO treatment. Measurements of hemoglobin concentration ([Hb] and hematocrit), plasma and blood volume, V˙O2, cardiac output as well as arterial and mixed venous blood gases were made at rest and during maximal exercise. EPO increased resting [Hb] by 18% from 13.3±0.6 to 15.7±0.8g/dL (mean±SD) corresponding to an increased hematocrit from 36±2 to 46±2% concurrent with 23 and 10% reductions in plasma and blood volume, respectively (all P<0.05). EPO elevated V˙O2max by 20% from 25.7±1.7 to 30.9±3.4L/min (P<0.05) via a 17% increase in arterial O2 content and 18% greater arteriovenous O2 difference in the face of an unchanged cardiac output. To achieve the greater V˙O2max after EPO, diffusive O2 conductance increased ∼30% (from 580±76 to 752±166mL O2/mmHg/min, P<0.05) which was substantially greater than the elevation of perfusive O2 conductance. These effects of EPO were associated with an increased exercise performance (total running time: control, 216±72; EPO, 264±48s, P<0.05). We conclude that EPO substantially increases V˙O2max and performance in the splenectomized horse via improved perfusive and diffusive O2 transport.

Metabolism at the Max: How Vertebrate Organisms Respond to Physical Activity.

Activity metabolism is supported by phosphorylated reserves (adenosine triphosphate, creatine phosphate), glycolytic, and aerobic metabolism. Because there is no apparent variation between vertebrate groups in phosphorylated reserves or glycolytic potential of skeletal muscle, variation in maximal metabolic rate between major vertebrate groups represents selection operating on aerobic mechanisms. Maximal rates of oxygen consumption in vertebrates are supported by increased conductive and diffusive fluxes of oxygen from the environment to the mitochondria. Maximal CO2 efflux from the mitochondria to the environment must be matched to oxygen flux, or imbalances in pH will occur. Among vertebrates, there are a variety of modes of locomotion and vastly different rates of metabolism supported by a variety of cardiorespiratory architectures. However, interclass comparisons strongly implicate systemic oxygen transport as the rate-limiting step to maximal oxygen consumption for all vertebrate groups. The key evolutionary step that accounts for the approximately 10-fold increase in maximal oxygen flux in endotherms versus ectotherms appears to be maximal heart rate. Other variables such as ventilation, pulmonary/gill, and tissue diffusing capacity, have excess capacity and thus are not limiting to maximal oxygen consumption. During maximal activity, the ratio of ventilation to respiratory system blood flow is remarkably similar among vertebrates, and CO2 extraction efficiency increases while oxygen extraction efficiency decreases, suggesting that the respiratory system provides the largest resistance to maximal CO2 flux. Despite the large variation in modes of activity and rates of metabolism, maximal rates of oxygen and CO2 flux appear to be limited by the cardiovascular and respiratory systems, respectively.

Sex differences in cardiovascular function during submaximal exercise in humans.

Differences in cardiovascular function between sexes have been documented at rest and maximal exercise. The purpose of this study was to examine the sex differences in cardiovascular function during submaximal constant-load exercise, which is not well understood.Thirty-one male and 33 female subjects completed nine minutes moderate and nine minutes vigorous intensity submaximal exercise (40 and 75% of peak watts determined by maximal exercise test). Measurements included: intra-arterial blood pressure (SBP and DBP), cardiac index (QI), heart rate (HR), oxygen consumption (VO2) and arterial catecholamines (epinephrine = EPI and norepinephrine = NE), and blood gases. Mean arterial pressure (MAP), stroke volume index (SVI), systemic vascular resistance index (SVRI), arterial oxygen content (CaO2), arterial to venous O2 difference (AVO2) and systemic oxygen transport (SOT) were calculated.At rest and during submaximal exercise QI, SVI, SBP, MAP, NE, CaO2, and SOT were lower in females compared to males. VO2, AVO2, EPI were lower in females throughout exercise. When corrected for wattage, females had a higher Q, HR, SV, VO2 and AVO2 despite lower energy expenditure and higher mechanical efficiency.This study demonstrates sex differences in the cardiovascular response to constant-load submaximal exercise. Specifically, females presented limitations in cardiac performance in which they are unable to compensate for reductions in stroke volume through increases in HR, potentially a consequence of a female’s blunted sympathetic response and higher vasodilatory state. Females demonstrated greater cardiac work needed to meet the same external work demand, and relied on increased peripheral oxygen extraction, lower energy expenditure and improvements in mechanical efficiency as compensatory mechanisms.

Clinical Hemodynamic Parameters Do Not Accurately Reflect Systemic Oxygen Transport in Neonates after the Norwood Procedure.

Clinical hemodynamic parameters (heart rate, systolic arterial pressure [SAP], and arterial and venous oxygen saturation saturations [SaO2 and SvO2 ]) are commonly used to guide management to optimize oxygen transport after the Norwood procedure. The adequacy of this practice has not been demonstrated. We examined the correlations between these clinical parameters and direct measurements of oxygen transport in these patients. Oxygen consumption (VO2 ) was measured using respiratory mass spectrometry for 72 hours in 17 neonates after the Norwood procedure. Arterial, superior vena caval, and pulmonary venous blood gases and pressures were measured at intervals of 2-4 hours to calculate cardiac output (CO), systemic and pulmonary blood flows (Qs , Qp), systemic vascular resistance (SVR), total pulmonary vascular resistance including the Blalock-Taussig shunt (tPVR), oxygen delivery (DO2), and extraction ratio (ERO2 ). Heart rate and SAP were also recorded. Heart rate was positively correlated with VO2 (P = .004) and ERO2 (P = .005). SAP was positively correlated with CO (P = .006), VO2 (P = .02), ERO2 (P = .01), and SVR (P = .08). SaO2 was negatively correlated with tPVR, Qs, and DO2 but positively with Qp and SVR (P < .05 for all). SvO2 was positively correlated with CO, Qs , and DO2 (P < .0001 for all) and negatively correlated with SVR, VO2, and ERO2 (P < .05 for all). Routine clinical hemodynamic parameters do not accurately reflect oxygen transport after the Norwood procedure, except for SvO2, which does not differentiate between VO2 and DO2. Higher heart rate and SAP are correlated with a worse balance of oxygen transport. The results of clinical hemodynamic monitoring should be interpreted with caution. Direct measurements of oxygen transport parameters are important in the care of neonates after the Norwood procedure.

Elevated Plasma B-type Natriuretic Peptide and C-reactive Protein Levels in Children with Restrictive Right Ventricular Physiology Following Tetralogy of Fallot Repair

This study aimed to compare the levels of plasma B-type natriuretic peptide (BNP) and C-reactive protein (CRP) in relation to oxygen transport between patients with restrictive right ventricle (rRV) and those without (non-rRV) early after tetralogy of Fallot (TOF) repair. Eighty patients (30 in the rRV group) underwent TOF repair in 2011 and 2012. BNP and CRP were repeatedly measured during postoperative day (POD) 7, along with oxygen transport variables including arterial and superior vena cava oxygen saturation (SaO2 and SvO2 ), oxygen extraction ratio (ERO2 ), and lactate. Demographic data included age and durations of cardiopulmonary bypass (CPB), aortic cross-clamping (ACC), mechanical ventilation, and ICU and hospital stays. During POD 7, BNP did not change in either of the two groups but was consistently higher in the rRV group (P < .0001). CRP increased from POD 1 to POD 2 and decreased thereafter. The decrease was slower in the rRV group (P = .04). The increase in SvO2 and the decrease in ERO2 were slower in the rRV group (P < .05). Lactate decreased in both groups (P < .05) but was consistently higher in the rRV group (P = .03). BNP was negatively correlated with SvO2 and preoperative SaO2 and positively correlated with ERO2 and lactate (P < .05). No correlation was found between CRP and oxygen transport variables. The rRV group was older and required longer CPB, ACC, mechanical ventilation, and ICU and hospital stays compared with the non-rRV group (P < .05 for all). rRV physiology is associated with significantly higher BNP and CRP levels with poorer balance of systemic oxygen transport. Information about these pathophysiological changes may help to identify appropriate treatment strategies in this difficult group of patients.

Haemoglobin concentration and mass as determinants of exercise performance and of surgical outcome

The ability of the cardiorespiratory system (heart, lungs, blood) to deliver oxygen to exercising skeletal muscle constrains maximum oxygen consumption , with cardiac output and the concentration of oxygen-carrying haemoglobin ([Hb]) being key limiting parameters. Total blood volume (BV) is the sum of the plasma volume (PV) and the total red cell volume. The measured [Hb] is dependent upon the total circulating mass of haemoglobin (tHb-mass) and plasma volume (PV). While the proportion of oxygen carried in plasma is trivial (0.3 mL of oxygen per 100 mL of plasma), each gram of Hb, contained in red blood cells, binds 1.39 mL of oxygen. As a result, the relationship between and tHb-mass is stronger than that observed between and [Hb] or BV. The glycoprotein hormone erythropoietin drives red cell synthesis and, like simple transfusion of packed red blood cells, can increase tHb-mass. An iron-containing haem group lies at the centre of the Hb molecule and, in situations of actual or functional iron deficiency, tHb-mass will also rise following iron administration. However achieved, an increase in tHb-mass also increases circulating oxygen-carrying capacity, and thus the capacity for aerobic phosphorylation. It is for such reasons that alterations in and exercise performance are proportional to those in arterial oxygen content and systemic oxygen transport, a change in tHb-mass of 1 g being associated with a 4 mL · min−1 change in . Similarly, increases by approximately 1% for each 3 g · L−1 increase in [Hb] over the [Hb] range (120 to 170 g · L−1). Surgery, like exercise, places substantial metabolic demands on the patient. Whilst subject to debate, oxygen supply at a rate inadequate to prevent muscle anaerobiosis may underpin the occurrence of the anaerobic threshold (AT), an important submaximal marker of cardiorespiratory fitness. Preoperatively, cardiopulmonary exercise testing (CPET) can be used to determine AT and peak exertional oxygen uptake ( peak) as measures of ability to meet increasing oxygen demands. The degree of surgical insult and the ability to meet the resulting additional postoperative oxygen demand appear to be fundamental determinants of surgical outcome: individuals in whom such ability is impaired (and thus those with reduced peak and AT) are at greater risk of adverse surgical outcome. This review provides an overview of the relationships between [Hb], tHb-mass, exercise capacity, and surgical outcome and discusses the potential value of assessing tHb-mass over [Hb].

Intensity of daily physical activity is associated with central hemodynamic and leg muscle oxygen availability in COPD

In chronic obstructive pulmonary disease (COPD), daily physical activity is reported to be adversely associated with the magnitude of exercise-induced dynamic hyperinflation and peripheral muscle weakness. There is limited evidence whether central hemodynamic, oxygen transport, and peripheral muscle oxygenation capacities also contribute to reduced daily physical activity. Nineteen patients with COPD (FEV1, 48 ± 14% predicted) underwent a treadmill walking test at a speed corresponding to the individual patient's mean walking intensity, captured by a triaxial accelerometer during a preceding 7-day period. During the indoor treadmill test, the individual patient mean walking intensity (range, 1.5 to 2.3 m/s2) was significantly correlated with changes from baseline in cardiac output recorded by impedance cardiography (range, 1.2 to 4.2 L/min; r = 0.73), systemic vascular conductance (range, 7.9 to 33.7 ml·min(-1)·mmHg(-1); r = 0.77), systemic oxygen delivery estimated from cardiac output and arterial pulse-oxymetry saturation (range, 0.15 to 0.99 L/min; r = 0.70), arterio-venous oxygen content difference calculated from oxygen uptake and cardiac output (range, 3.7 to 11.8 mlO2/100 ml; r = -0.73), and quadriceps muscle fractional oxygen saturation assessed by near-infrared spectrometry (range, -6 to 23%; r = 0.77). In addition, mean walking intensity significantly correlated with the quadriceps muscle force adjusted for body weight (range, 0.28 to 0.60; r = 0.74) and the ratio of minute ventilation over maximal voluntary ventilation (range, 38 to 89%, r = -0.58). In COPD, in addition to ventilatory limitations and peripheral muscle weakness, intensity of daily physical activity is associated with both central hemodynamic and peripheral muscle oxygenation capacities regulating the adequacy of matching peripheral muscle oxygen availability by systemic oxygen transport.