Modest effect of temperature on the porcine oxygen dissociation curve

Effects of Carbon Dioxide and Temperature on the Oxygen-Hemoglobin Dissociation Curve of Human Blood: Implications for Avalanche Victims

Completely avalanche-buried patients are frequently exposed to a combination of hypoxia and hypercapnia with a risk of normothermic cardiac arrest. Patients with a long burial time and an air pocket are exposed to a combination of hypoxia, hypercapnia, and hypothermia which may lead to the development of the “triple H syndrome”. This specific combination has several pathophysiological implications, particularly on the cardiovascular system and oxygen transport (oxygen supply and oxygen consumption). To examine the effects on hemoglobin oxygen affinity, we investigated venous blood samples from 15 female and 15 male healthy subjects. In a factorial design of four different carbon dioxide partial pressure (PCO2) levels (20, 40, 60, and 80 mmHg) and five different temperature levels (13.7°C, 23°C, 30°C, 37°C, and 42°C), 30 unbuffered whole blood samples were analyzed in a newly developed in vitro method for high-throughput oxygen dissociation curve (ODC) measurements. P50s, Hill coefficients, CO2-Bohr coefficients, and temperature coefficients were analyzed using a linear mixed model (LMM). Mean P50 at baseline (37°C, 40 mmHg PCO2) was 27.1 ± 2.6 mmHg. Both CO2-Bohr (p < 0.001) and temperature coefficients (p < 0.001) had a significant effect on P50. The absolute CO2 effect was still pronounced at normothermic and febrile temperatures, whereas at low temperatures, the relative CO2 effect (expressed by CO2-Bohr coefficient; p < 0.001, interaction) was increased. The larger impact of PCO2 on oxygen affinity at low temperature may be caused by the competition of 2,3-BPG with PCO2 and the exothermic binding characteristic of 2,3-BPG. In a model of an avalanche burial, based on published data of CO2 levels and cooling rates, we calculated the resulting P50 for this specific condition based on the here-reported PCO2 and temperature effect on ODC. Depending on the degree of hypercapnia and hypothermia, a potentially beneficial increase in hemoglobin oxygen affinity in the hypoxic condition might ensue.

A compact integrated microfluidic oxygenator with high gas exchange efficiency and compatibility for long-lasting endothelialization

We have developed and tested a novel microfluidic device for blood oxygenation, which exhibits a large surface area of gas exchange and can support long-term sustainable endothelialization of blood microcapillaries, enhancing its hemocompatibility for clinical applications. The architecture of the parallel stacking of the trilayers is based on a central injection for blood and a lateral injection/output for gas which allows significant reduction in shear stress, promoting sustainable endothelialization since cells can be maintained viable for up to 2 weeks after initial seeding in the blood microchannel network. The circular design of curved blood capillaries allows covering a maximal surface area at 4 inch wafer scale, producing high oxygen uptake and carbon dioxide release in each single unit. Since the conventional bonding process based on oxygen plasma cannot be used for surface areas larger than several cm², a new "wet bonding" process based on soft microprinting has been developed and patented. Using this new protocol, each 4 inch trilayer unit can be sealed without a collapsed membrane even at reduced 15 μm thickness and can support a high blood flow rate. The height of the blood channels has been optimized to reduce pressure drop and enhance gas exchange at a high volumetric blood flow rate up to 15 ml min^-1. The simplicity of connecting different units in the stacked architecture is demonstrated for 3- or 5-unit stacked devices that exhibit remarkable performance with low primary volume, high oxygen uptake and carbon dioxide release and high flow rate of up to 80 ml min^-1.

A Randomized Porcine Study in Low Cardiac Output of Vasoactive and Inotropic Drug Effects on the Gastrointestinal Tract

BACKGROUND

Splanchnic vasodilation by inodilators is an argument for their use in critical cardiac dysfunction. To isolate peripheral vasoactivity from inotropy, such drugs were investigated, and contrasted to vasopressors, in a fixed low cardiac output (CO) model resembling acute cardiac dysfunction effects on the gastrointestinal tract. We hypothesized that inodilators would vasodilate and preserve the aerobic metabolism in the splanchnic circulation in low CO.

METHODS

In anesthetized pigs, CO was lowered to 60% of baseline by partial inferior caval vein balloon inflation. The animals were randomized to placebo (n = 8), levosimendan (24 μg kg-1 bolus, 0.2 μg kg-1 min-1, n = 7), milrinone (50 μg kg-1 bolus, 0.5 μg kg-1 min-1, n = 7), vasopressin (0.001, 0.002 and 0.006 U kg-1 min-1, 1 h each, n = 7) or norepinephrine (0.04, 0.12, and 0.36 μg kg-1 min-1, 1 h each, n = 7). Hemodynamic variables including mesenteric blood flow were collected. Systemic, mixed-venous, mesenteric-venous, and intraperitoneal metabolites were analyzed.

RESULTS

Cardiac output was stable at 60% in all groups, which resulted in systemic hypotension, low superior mesenteric artery blood flow, lactic acidosis, and increased intraperitoneal concentrations of lactate. Levosimendan and milrinone did not change any circulatory variables, but levosimendan increased blood lactate concentrations. Vasopressin and norepinephrine increased systemic and mesenteric vascular resistances at the highest dose. Vasopressin increased mesenteric resistance more than systemic, and the intraperitoneal lactate concentration and lactate/pyruvate ratio.

CONCLUSION

Splanchnic vasodilation by levosimendan and milrinone may be negligible in low CO, thus rejecting the hypothesis. High-dose vasopressors may have side effects in the splanchnic circulation.

Pulmonary Vasodilation by Intravenous Infusion of Organic Mononitrites Of 1,2-Propanediol in Acute Pulmonary Hypertension Induced by Aortic Cross Clamping and Reperfusion: A Comparison With Nitroglycerin in Anesthetized Pigs

INTRODUCTION

Suprarenal aortic cross clamping (SRACC) and reperfusion may cause acute pulmonary hypertension and multiple organ failure.

HYPOTHESIS

The organic mononitrites of 1,2-propanediol (PDNO), an nitric oxide donor with a very short half-life, are a more efficient pulmonary vasodilator and attenuator of end-organ damage and inflammation without significant side effects compared with nitroglycerin and inorganic nitrite in a porcine SRACC model.

METHODS

Anesthetized and instrumented domestic pigs were randomized to either of four IV infusions until the end of the experiment (n = 10 per group): saline (control), PDNO (45 nmol kg min), nitroglycerin (44 nmol kg min), or inorganic nitrite (a dose corresponding to PDNO). Thereafter, all animals were subjected to 90 min of SRACC and 10 h of reperfusion and protocolized resuscitation. Hemodynamic and respiratory variables as well as blood samples were collected and analysed.

RESULTS

During reperfusion, mean pulmonary arterial pressure and pulmonary vascular resistance were significantly lower, and stroke volume was significantly higher in the PDNO group compared with the control, nitroglycerin, and inorganic nitrite groups. In parallel, mean arterial pressure, arterial oxygenation, and fraction of methaemoglobin were similar in all groups. The serum concentration of creatinine and tumor necrosis factor alpha were lower in the PDNO group compared with the control group during reperfusion.

CONCLUSIONS

PDNO was an effective pulmonary vasodilator and appeared superior to nitroglycerin and inorganic nitrite, without causing significant systemic hypotension, impaired arterial oxygenation, or methaemoglobin formation in an animal model of SRACC and reperfusion. Also, PDNO may have kidney-protective effects and anti-inflammatory properties.

Effects of hypothermia, hypoxia, and hypercapnia on brain oxygenation and hemodynamic parameters during simulated avalanche burial: a porcine study

Avalanche patients who are completely buried but still able to breathe are exposed to hypothermia, hypoxia, and hypercapnia (triple H syndrome). Little is known about how these pathological changes affect brain physiology. The study aim was to investigate the effect of hypothermia, hypoxia, and hypercapnia on brain oxygenation and systemic and cerebral hemodynamics. Anesthetized pigs were surface cooled to 28°C. Fraction of inspiratory oxygen ([Formula: see text]) was reduced to 17% and hypercapnia induced. Hemodynamic parameters and blood gas values were monitored. Cerebral measurements included cerebral perfusion pressure (CPP), brain tissue oxygen tension ([Formula: see text]), cerebral venous oxygen saturation ([Formula: see text]), and regional cerebral oxygen saturation (rSo₂). Tests were interrupted when hemodynamic instability occurred or 60 min after hypercapnia induction. ANOVA for repeated measures was used to compare values across phases. There was no clinically relevant reduction in cerebral oxygenation ([Formula: see text], [Formula: see text], rSo₂) during hypothermia and initial [Formula: see text] reduction. Hypercapnia was associated with an increase in pulmonary resistance followed by a decrease in cardiac output and CPP, resulting in hemodynamic instability and cerebral desaturation (decrease in [Formula: see text], [Formula: see text], rSo₂). Hypercapnia may be the main cause of cardiovascular instability, which seems to be the major trigger for a decrease in cerebral oxygenation in triple H syndrome despite severe hypothermia.NEW & NOTEWORTHY Avalanche patients who are completely buried but still able to breathe are exposed to hypothermia, hypoxia, and hypercapnia (triple H syndrome). In a porcine model, there was no clinically relevant reduction in cerebral oxygenation during hypothermia and initial reduction of fraction of inspiratory oxygen ([Formula: see text]), as observed during hypercapnia. Hypercapnia may be the main cause of cardiovascular instability, which seems to be the major trigger for a decrease in cerebral oxygenation in triple H syndrome despite severe hypothermia.

Non-invasive optical neuromonitoring of the temperature-dependence of cerebral oxygen metabolism during deep hypothermic cardiopulmonary bypass in neonatal swine

Management of deep hypothermic (DH) cardiopulmonary bypass (CPB), a critical neuroprotective strategy, currently relies on non-invasive temperature to guide cerebral metabolic suppression during complex cardiac surgery in neonates. Considerable inter-subject variability in temperature response and residual metabolism may contribute to the persisting risk for postoperative neurological injury. To characterize and mitigate this variability, we assess the sufficiency of conventional nasopharyngeal temperature (NPT) guidance, and in the process, validate combined non-invasive frequency-domain diffuse optical spectroscopy (FD-DOS) and diffuse correlation spectroscopy (DCS) for direct measurement of cerebral metabolic rate of oxygen (CMRO₂). During CPB, n = 8 neonatal swine underwent cooling from normothermia to 18℃, sustained DH perfusion for 40 min, and then rewarming to simulate cardiac surgery. Continuous non-invasive and invasive measurements of intracranial temperature (ICT) and CMRO₂ were acquired. Significant hysteresis (p < 0.001) between cooling and rewarming periods in the NPT versus ICT and NPT versus CMRO₂ relationships were found. Resolution of this hysteresis in the ICT versus CMRO₂ relationship identified a crucial insufficiency of conventional NPT guidance. Non-invasive CMRO₂ temperature coefficients with respect to NPT (Q₁₀ = 2.0) and ICT (Q₁₀ = 2.5) are consistent with previous reports and provide further validation of FD-DOS/DCS CMRO₂ monitoring during DH CPB to optimize management.

Splanchnic Circulation and Intraabdominal Metabolism in Two Porcine Models of Low Cardiac Output

The impact of acute cardiac dysfunction on the gastrointestinal tract was investigated in anesthetized and instrumented pigs by sequential reductions of cardiac output (CO). Using a cardiac tamponade (n = 6) or partial inferior caval vein balloon inflation (n = 6), CO was controllably reduced for 1 h each to 75% (CO_75%), 50% (CO_50%), and 35% (CO_35%) of the baseline value. Cardiac output in controls (n = 6) was not manipulated and maintained. Mean arterial pressure, superior mesenteric arterial blood flow, and intestinal mucosal perfusion started to decrease at CO_50% in the intervention groups. The decrease in superior mesenteric arterial blood flow was non-linear and exaggerated at CO_35%. Systemic, venous mesenteric, and intraperitoneal lactate concentrations increased in the intervention groups from CO_50%. Global and mesenteric oxygen uptake decreased at CO_35%. In conclusion, gastrointestinal metabolism became increasingly anaerobic when CO was reduced by 50%. Anaerobic gastrointestinal metabolism in low CO can be detected using intraperitoneal microdialysis.

Organic mononitrites of 1,2-propanediol act as an effective NO-releasing vasodilator in pulmonary hypertension and exhibit no cross-tolerance with nitroglycerin in anesthetized pigs

Purpose

Clinically available intravenous (IV) nitric oxide (NO) donor drugs such as nitroglycerin (GTN) cause systemic hypotension and/or tolerance development. In a porcine model, novel NO donor compounds – the organic mononitrites of 1,2-propanediol (PDNO) – were compared to GTN with regard to pulmonary selectivity and tolerance development. The vasodilatory effects of inorganic nitrite were investigated.

Materials and methods

In anesthetized piglets, central hemodynamics were monitored. At normal pulmonary vascular resistance (PVR), IV infusions of PDNO (15–60 nmol kg⁻¹ min⁻¹), GTN (13–132 nmol kg⁻¹ min⁻¹), and inorganic nitrite (dosed as PDNO) were administered. At increased PVR (by U46619 IV), IV infusions of PDNO (60–240 nmol kg⁻¹ min⁻¹) and GTN (75–300 nmol kg⁻¹ min⁻¹) before and after a 5 h infusion of GTN (45 nmol kg⁻¹ min⁻¹) were given.

Results

At normal PVR, PDNO (n=12) and GTN (n=7) caused significant dose-dependent decreases in mean systemic and pulmonary arterial pressures, whereas inorganic nitrite (n=13) had no significant effect. At increased PVR, PDNO (n=6) and GTN (n=6) significantly decreased mean systemic and pulmonary pressures and resistances, but only PDNO reduced the ratio between pulmonary and systemic vascular resistances significantly. After the 5 h GTN infusion, the hemodynamic response to GTN infusions (n=6) was significantly suppressed, whereas PDNO (n=6) produced similar hemodynamic effects to those observed before the GTN infusion.

Conclusion

PDNO is a vasodilator with selectivity for pulmonary circulation exhibiting no cross-tolerance to GTN, but GTN causes non selective vasodilatation with substantial tolerance development in the pulmonary and systemic circulations. Inorganic nitrite has no vasodilatory properties at relevant doses.

Hypoxia delays hematopoiesis: retention of embryonic hemoglobin and erythrocytes in larval rainbow trout, Oncorhynchus mykiss, during chronic hypoxia exposure

In rainbow trout development, a switch occurs from high-affinity embryonic hemoglobin (Hb) and round, embryonic erythrocytes to lower-affinity adult Hb and oval, adult erythrocytes. Our study investigated the early ontogeny of rainbow trout blood properties and the hypoxia response. We hypothesized that hypoxia exposure would delay the ontogenetic turnover of Hb and erythrocytes because retention of high-affinity embryonic Hb would facilitate oxygen loading. To test this hypothesis we developed a method of efficiently extracting blood from individual embryos and larvae and optimized several techniques for measuring hematological parameters on microliter (0.5 - 2.0 μl) blood samples. In chronic hypoxia (30% of oxygen saturation), stage-matched embryos and larvae possessed half the Hb concentration, erythrocyte counts, and hematocrit observed in normoxia. Hypoxia-reared larvae also had 3 to 6 fold higher mRNA expression of the embryonic Hb α-1, β-1, and β-2 subunits relative to stage-matched normoxia-reared larvae. Furthermore, in hypoxia the round embryonic erythrocytic shape persisted into later developmental stages. Despite these differences, Hb-oxygen affinity (P50), cooperativity, and the Root effect were unaltered in hypoxia-reared O. mykiss. The data support our hypothesis that chronic hypoxia delays the ontogenetic turnover of Hb and erythrocytes but without the predicted functional consequences (i.e. higher than expected P50). These results also suggest that the Hb-oxygen affinity is protected during development in chronic hypoxia to favour oxygen unloading at the tissues. We conclude that in early trout development, the blood-oxygen transport system responds very differently to chronic hypoxia relative to adults, possibly because respiration depends relatively more on oxygen diffusion than convection.

Respiratory properties of blood in the harbor porpoise, Phocoena phocoena

Harbor porpoises are active divers that exchange O2 and CO2 with the environment during a fast single breath upon surfacing. We investigated blood O2-transporting properties, buffer characteristics, Cl– transport via the erythrocyte anion exchanger (AE1), circulating nitric oxide metabolites and hemoglobin nitrite reduction in harbor porpoises with the aim to evaluate traits that are adaptive for diving behavior. Blood O2 affinity was higher in harbor porpoises than in similar sized terrestrial mammals, as supported by our parallel recordings of O2 equilibria in sheep and pig blood. Further, O2 affinity tended to increase with increasing body mass. A high O2 affinity favors O2 extraction from the lungs, but a normal Bohr effect (ΔlogP50/ΔpH=–0.46) gradually lowers O2 affinity during dives (where CO2 accumulates) to assist O2 off-loading to perfused tissues. The true plasma non-bicarbonate buffer value was moderately higher than in terrestrial mammals and increased upon deoxygenation. Plasma bicarbonate was also relatively high, contributing to increase the overall buffer capacity. The apparent Cl– permeability of harbor porpoise erythrocytes was similar to the human value at 37°C, showing absence of a comparative increase in the velocity of erythrocyte HCO –3/Cl– exchange to aid CO2 excretion. The Q10 for AE1-mediated Cl– transport in harbor porpoises was lower than in humans and seemed to match the Q10 for metabolism (Q10≈2). Plasma nitrite, plasma nitrate and hemoglobin-mediated nitrite reduction were elevated compared with mammalian standards, suggesting that increased nitric oxide bioavailability and nitrite-derived nitric oxide could play important roles in diving physiology.

Predicted oxygenation efficacy of a thoracic artificial lung

A thoracic artificial lung (TAL) provides respiratory support for lung disease. How well a TAL improves blood oxygenation for a specific pathology depends on how the TAL is attached to the pulmonary circulation: in series with the natural lungs (NLs), in parallel, or in a hybrid series/parallel combination. A computational model, including hemodynamic and O(2) and CO(2) exchange components, predicts TAL effects on blood flow rates and gas transport in pulmonary disease states modeled by elevated pulmonary vascular resistance (PVR) or reduced oxygen diffusivity in the NLs. In most cases, parallel and series TAL attachment provide comparable, maximal oxygenation. Series, with passage of total cardiac output (CO) through the NLs, is preferred for its filtration of emboli. Hybrid TAL attachment is more complicated, requiring a third graft, yet oxygenates less well than parallel and series. With extreme elevations of PVR, as in primary pulmonary hypertension, parallel TAL attachment provides an oxygenating shunt around the high resistance of the NLs, thus unloading the right ventricle, normalizing CO, and maximizing oxygenation.

Temperature dependence of haemoglobin-oxygen affinity in heterothermic vertebrates: mechanisms and biological significance

As demonstrated by August Krogh et al. a century ago, the oxygen-binding reaction of vertebrate haemoglobin is cooperative (described by sigmoid O(2) equilibrium curves) and modulated by CO(2) and protons (lowered pH) that - in conjunction with later discovered allosteric effectors (chloride, lactate and organic phosphate anions) - enhance O(2) unloading from blood in relatively acidic and oxygen-poor tissues. Based on the exothermic nature of the oxygenation of the haem groups, haemoglobin-O(2) affinity also decreases with rising temperature. This thermal sensitivity favours oxygen unloading in warm working muscles, but may become detrimental in regionally heterothermic animals, for example in cold-tolerant birds and mammals and warm-bodied fish, where it may perturb the balance between O(2) unloading and O(2) requirement in organs with substantially different temperatures than at the respiratory organs and thus commonly is reduced or obliterated. Given that the oxygenation of haemoglobin is linked with the endothermic release of allosteric effectors, increased effector interaction is an effective strategy that is widely exploited to achieve adaptive reductions in the temperature dependence of blood-O(2) affinity. The molecular mechanisms implicated in heterothermic vertebrates from different taxonomic groups reveal remarkable variability, both as regards the effectors implicated (protons in tunas, organic phosphates in sharks and billfish, chloride ions in ruminants and chloride and phosphate anions in the extinct woolly mammoth, etc.) and binding sites for the same effectors, indicating multiple evolutionary origins, but convergent physiological functionality (reductions in temperature dependence of O(2) -binding affinity that safeguard tissue O(2) supply).

Effect of melatonin on the blood oxygen transport during hypothermia and rewarming in rats

PURPOSE

We aimed to study effect of melatonin on the blood oxygen transport during hypothermia and rewarming in rats.

MATERIAL/METHODS

Cold exposure was performed on male rats (body weight 220-270 g, n=48) for 120 minutes under the box water temperature of 19 degrees C; rewarming took the next 120 min, with a mean rate of 0.06 degrees C/min. Melatonin was administered intraperitoneally 30 min before the cold exposure (bolus doses of 0.1, 1 or 10 mg/kg, or 1 mg/kg*day for 4 days). Haemoglobin-oxygen affinity was evaluated by p50 (blood pO2 at its 50% O2 saturation) determined by the "mixing" method at 37 degrees C, pH 7.4 and pCO2 40 mm Hg (p50stand) and at actual pH, pCO2 and temperature (p50act).

RESULTS

After hypothermia and rewarming, the values of p50stand and p50act were 31.5+/-0.28 and 30.2+/-0.61 mm Hg, respectively. The 0.1 mg/kg of melatonin virtually did not change these values, whereas the larger doses increased them. This effect was maximal after the prolonged (4 days) melatonin administration: p50stand rose by 5.4% (p<0.05) and p50act--by 12.9 (p<0.05) compared with rats without the melatonin treatment. Melatonin affected the mechanisms of O2 transport by decreasing the haemoglobin-oxygen affinity (shifting the oxygen dissociation curve of haemoglobin rightwards) and promoting the tissue oxygenation, thereby enhancing the body's resistance to cold.

CONCLUSIONS

The melatonin effect mediated by haemoglobin-oxygen affinity change may be used for the correction of metabolic disorders and the improvement of the body's resistance to low environmental temperature.

Hypoxia has a greater effect than exercise on the redistribution of pulmonary blood flow in swine

Strenuous exercise combined with hypoxia is implicated in the development of high-altitude pulmonary edema (HAPE), which is believed to result from rupture of pulmonary capillaries secondary to high vascular pressures. The relative importance of hypoxia and exercise in altering the distribution of pulmonary blood flow (PBF) is unknown. Six chronically catheterized specific pathogen-free Yorkshire hybrid pigs (25.5 +/- 0.7 kg, means +/- SD) underwent incremental treadmill exercise tests in normoxia (Fi(O(2)) = 0.21) and hypoxia (Fi(O(2)) = 0.125, balanced order), consisting of 5 min at 30, 60, and 90% of the previously determined Vo(2max). At steady state (~4 min), metabolic and cardiac output data were collected and fluorescent microspheres were injected over approximately 30 s. Later the fluorescent intensity of each color in each 2-cm(3) lung piece was determined and regional perfusion was calculated from the weight-normalized fluorescence. Both hypoxia and exercise shifted PBF away from the ventral cranial lung regions toward the dorsal caudal regions of the lung, but hypoxia caused a greater dorsal caudal shift in PBF at rest than did near-maximal exercise in normoxia. The variance in PBF due to hypoxia, exercise, and vascular structure was 16 +/- 4.2, 4.0 +/- 4.4, and 59.4 +/- 11.4%, respectively, and the interaction between hypoxia and exercise represented 12 +/- 6.5%. This observation implies that there is already a maximal shift with in PBF with hypoxia in the dorsal-caudal regions in pigs that cannot be exceeded with the addition of exercise. However, exercise greatly increases the pulmonary arterial pressures and therefore the risk of capillary rupture in high flow regions.

Contribution of Cooperativity and the Bohr Effect to Efficient Oxygen Transport by Hemoglobins from Five Mammalian Species

By using published experimental values of the standard oxygen (O2) equilibrium curve and the in vivo arterial and venous O2 pressure (PO2) of fetal and maternal blood in five mammalian species (human, cow, pig, sheep, and horse), we investigated the relationship between the efficiency of O2 delivery and the effectiveness of the Bohr shift, and discussed the significance of cooperativity for mammalian Hb. The O2 delivery of fetal blood was more efficient than that of maternal blood, and the effectiveness of the Bohr shift at both O2 loading and release sites of fetal blood was high. A linear relationship was observed between the efficiency of O2 delivery and the effectiveness of the Bohr shift at O2 loading sites of the five mammalian species. In both fetal and maternal blood, the theoretically obtained optimal P50 value for O2 delivery (optP50(OD)) was nearly equal to the optimal P50 value for the effectiveness of the Bohr shift at the O2 loading site (optP50(BS)(loading)). This phenomenon was favorable for fetal blood to uptake O2 from maternal blood with the aid of the Bohr shift and to deliver a large amount of O2 to the tissues. The optP50s for the effectiveness of the Bohr shift at given arterial PO2 (PaO2) and venous PO2 (PvO2) were derived as follows: optP50(BS)(loading) = PaO2((n+1)/(n-1))(1/n), and optP50(BS)(release) = PvO2((n+1)/(n-1))(1/n). The relationship between in vivo PO2s and n, PaO2/PvO2 = ((n+1)/(n-1))(2/n), was derived by letting optP50 for the efficiency of O2 delivery be equal to that for the effectiveness of the Bohr shift.

Haemoglobin oxygen affinity and regulating factors of the blood oxygen transport in canine and feline blood

Complete dynamic oxygen equilibrium curves (OEC) on dogs and cats whole blood were measured at 33, 37 and 41 degrees C. OEC were also run at three partial carbon dioxide pressures (20, 40 and 80 mmHg) as well as at five pH levels (7.2, 7.3, 7.4, 7.5 and 7.6). 2,3- diphosphoglycerate (DPG) concentrations were determined. Results were compared to those previously published in humans, using the same experimental method [Comp. Biochem. Physiol. 106 (1993) 687]. In standard conditions (pH 7.4, pCO2 40 mmHg and temperature 37 degrees C), the partial oxygen pressure at half-saturation of haemoglobin (p50) was 30.0+/-1.3 mmHg for dogs and 34.1+/-1.8 mmHg for cats. Cat's OEC was thus rightshifted compared to dog's OEC, itself rightshifted compared to human OEC. 2,3-DPG concentrations were higher in dogs than in men until they were very low in cats. Contrary to that observed in human medicine, no significant correlation was identified between standard p50 and canine 2,3-DPG values. Influence of pH, pCO2 and temperature on the OEC was saturation dependent. In dogs, Delta log p50/Delta pH was equal to -0.370, Delta log p50/Delta log pCO2 was 0.093 and Delta log p50/Delta T was 0.020. In cats, Delta log p50/Delta pH was equal to -0.405, Delta log p50/Delta log pCO2 was 0.080 and Delta log p50/Delta T was 0.016. Practically, temperature and pH variations exert a lesser influence in domestic carnivores than in humans, effect of pCO2 being similar in both.

Effect of nitric oxide synthase inhibition on hemoglobin-oxygen affinity and lipid peroxidation in rabbits during fever

BACKGROUND

Nitric oxide (NO) is one of the most important biologic messengers and takes part in the development of fever. It can influence on the body prooxidant-antioxidant balance by different ways including interaction with hemoglobin (Hb).

METHODS

The effects of nitric oxide synthesis inhibition on the febrile response, hemoglobin-oxygen affinity and parameters of lipid peroxidation were studied in rabbits with fever. The fever was induced by intravenous administration of lipopolysaccharide from Salmonella typhi (0.6 microg/kg). Mixed venous blood was taken before the administration and 60, 120 and 180 min after it. The following parameters were measured: half-saturation oxygen pressure (P(50)), concentrations of conjugated dienes, Schiff bases and alpha-tocopherol in plasma and red blood cells, and activity of catalase in red blood cells.

RESULTS

The intravenous administration of the nitric oxide synthase inhibitor (N(omega)-nitro-L-arginine; 5x10(-3) M) reduced the lipopolysaccharide-induced rise in body temperature. After 180 min the actual P(50) had decreased from 35.0+/-1.7 to 29.4+/-1.3 mm Hg. An increase in the lipid peroxidation parameters and a decrease of the antioxidant system indices were observed. The administration of L-arginine to prevent nitric oxide synthase inhibition was accompanied by a shift of the oxyhemoglobin dissociation curve rightwards, more marked activation of the free radical processes and a greater elevation of body temperature. The multiple regression analysis showed a close linear correlation between P(50) and conjugated dienes, Schiff bases, alpha-tocopherol and catalase.

CONCLUSION

These results suggest that the increased hemoglobin-oxygen affinity found after the inhibition of nitric oxide synthesis lowers the oxygen flow to tissues and its fraction utilized in free radical oxidations, which finally causes a reduction of the fever response to the lipopolysaccharide.

Monitoring respiratory function and sleep in the obese Vietnamese pot-bellied pig

Development of drug treatments for obstructive sleep-disordered breathing has been impeded by the lack of animal models. The obese pig may be a suitable animal model, as it has been reported to experience sleep-disordered breathing resembling human obstructive sleep apnea. The purpose of this paper is to describe in detail techniques for chronic instrumentation of the obese Vietnamese pot-bellied pig and to study respiratory function during sleep. Under general anesthesia, four obese pigs were instrumented for long-term recording of intrapleural and tracheal pressures, genioglossal EMG, and bioelectric signals related to sleep. A custom-fitted face mask was used to record respiratory variables including airflow, snoring, and expired CO(2). Most chronic instrumentation provided robust signals for up to 6 wk after installation. All pigs displayed sleep-disordered breathing characterized by increased resistance to airflow, snoring, inspiratory flow limitation, and possible sleep disruption. Apneas and hypopneas were not a feature of breathing during sleep in these animals. Nonetheless, this animal preparation may be useful for exploring possible drug treatments for obstructive sleep-disordered breathing.

Pulmonary gas-exchange analysis by using simultaneous deposition of aerosolized and injected microspheres

Numerical methods for determining end-capillary gas contents for ventilation-to-perfusion ratios were first developed in the late 1960s. In the 1970s these methods were applied to validate distributions of ventilation-to-perfusion ratios measured by the multiple inert-gas-elimination technique. We combined numerical gas analysis and fluorescent-microsphere measurements of ventilation and perfusion to predict gas exchange at a resolution of approximately 2.0-cm3 lung volume in pigs. Oxygen, carbon dioxide, and inert gas exchange were calculated in 551-845 compartments/animal before and after pulmonary embolization with 780-micrometers beads. Whole lung gas exchange was estimated from the perfusion- and ventilation-weighted end-capillary gas contents. Before lung injury, no significant difference existed between microsphere-estimated arterial PO2 and PCO2 and measured values. After lung injury, the microsphere method predicted a decrease in arterial PO2 but consistently underestimated its magnitude. Correlation between predicted and measured inert gas retentions was 0.99. Overestimation of low-solubility inert gas retentions suggests underestimation of areas with low ventilation-to-perfusion ratios by microspheres after lung injury. Regional deposition of aerosolized and injected microspheres is a valid method for investigating regional gas exchange with high spatial resolution.

Chemical restraint by medetomidine-ketamine and its cardiopulmonary effects in pigs

Chemical restraint induced by medetomidine-ketamine (M-K) combination was evaluated compared with that by xylazine-ketamine (X-K) in pigs. The duration of restraint by M-K was 49.4 +/- 13.5 min (mean +/- SD) and longer than that by X-K (34.6 +/- 17.2 min), but the difference was not significant. The effect of X-K was not stable, since one of five pigs was restrained only for 6 min. Both combinations produced muscle relaxation. The duration of muscle relaxation in M-K was 43.6 +/- 12.7 min and was significantly longer than that in X-K (21.0 +/- 14.0 min). M-K combination had a slightly stimulative effect on the cardiovascular system, but scarcely changed the respiratory parameters. This limited effect on cardiopulmonary system was an advantage of M-K combination for chemical restraint in pigs. These results indicated that M-K combination is suitable for chemical restraint with prolonged muscle relaxation and has limited cardiopulmonary effects in pigs.

Temperature and pH effects on the oxygen equilibrium curve of the thoroughbred horse

A new oxygen equilibrium curve is defined for the Thoroughbred horse under standard conditions of 37 degrees C, pH = 7.4 and PCO2 = 5.33 kPa. The "standard" P50 for the Thoroughbred is, at 2.83 +/- 0.04 (SE of mean) kPa, significantly lower than that found for the Hanoverian horse (3.17 +/- 0.03 kPa) by Clerbaux et al. (Can. J. Vet. Res. 50: 188-192, 1986), and lower than other values for horses in the literature. Using data from Butler et al. (J. Exp. Biol. 179: 159-180, 1993), curves were also constructed, in vitro, under simulated conditions of intense exercise to examine the individual effects of pH, temperature and PCO2 on the standard curve. The fixed acid Bohr coefficient is similar to that in humans (-0.41) whereas the temperature coefficient is, at 0.019, lower than that for humans. The coefficients were shown to be saturation dependent.

Comparative study of the oxyhaemoglobin dissociation curve of four mammals: man, dog, horse and cattle

1. The entire oxygen dissociation curve (ODC) and the effects of temperature, pH and 2,3-diphosphoglycerate (DPG) on this curve, have been compared in four mammalians: man, dog, horse and cattle. 2. If the oxyphoric capacities are similar between these species (around 1.39 ml O2/gHb), their P50, measured in standard conditions, i.e. at pH 7.4; pCO2 40 mmHg and T 37 degrees C, varies between 23.8 (+/- 0.8) mmHg for the horse, 25.0 (+/- 1.4) mmHg for cattle, 26.6 (+/- 1.2) for man and 28.8 (+/- 2.6) mmHg for the dog. 3. The higher dispersion of the dog's P 50 is due to difference between breeds; in seven breeds investigated, the P 50 ranges from 25.8 (spaniel) to 35.8 (hound). 4. We noted no sex difference in the four species. 5. The DPG level is confirmed to be low in cattle (< 1 mumol/gHb) as compared to man (13.5 +/- 2.1 mumol/gHb), horse (16.9 +/- 1.1 mumol/gHb) and dog (19.4 +/- 2.8 mumol/gHb). 6. The oxygen exchange fraction defined as the difference in vol% between a pO2 of 80 and 35 mmHg is, respectively, 3.6 (+/- 0.6) vol% for cattle, 4.0 (+/- 0.4) vol% for the horse, 5.5 (+/- 0.5) vol% for man and 6.6 (+/- 1.7) vol% for the dog. 7. The position and shape of the ODC, as well as T, DPG and pH effects, indicate that the haemoglobin of man and dog seem better adapted to O2 delivery as compared to the horse and cattle.

Effects of hypothermia in hypercapnia and hypercapnic hypoxemia

Anesthetized, paralyzed and mechanically ventilated pigs were hypoventilated to extreme hypercapnia (PaCO2 approximately 20 kPa) at FiO2 0.5, and allotted to a hypothermic group (31.5 +/- 0.1 degrees C, n = 6) or a control group (39.6 +/- 0.2 degrees C, n = 6). Compared with the controls, the hypothermic animals had higher PaO2 (19.2 vs 15.6 kPa, P < 0.05), SaO2 (97.2 vs 89.3%), SvO2 (78.7 vs 68.2%), end-tidal O2 (34.5 vs 24.8 kPa) and arterial pH (7.01 vs 6.91), (P < 0.01), but lower PvO2 (7.0 vs 10.2 kPa) and PaCO2 (13.2 vs 23.5 kPa), (P < 0.01). Hypothermia reduced O2 delivery (DO2), O2 consumption (VO2) and CO2 production by 40-45% (P < 0.05), but O2 extraction ratio, i.e. VO2.DO(2)-1 x 100(%), did not differ between groups. Hypothermic animals had lower heart rate (127 vs 223 beats.min-1, P < 0.05) and cardiac output (2.5 vs 3.9 l.min-1, P < 0.01). Subsequently, the inspired oxygen fraction (FiO2) was decreased stepwise (0.3, 0.25, 0.21, 0.15, 0.10) at 30-min intervals. At FiO2 0.3, the hypothermic group had higher PaO2 (10.0 vs 5.7 kPa), SaO2 (91.3 vs 28.5%), PvO2 (5.8 vs 3.4 kPa), SvO2 (70.7 vs 10.3%), end-tidal O2 (16.7 vs 8.5 kPa), O2 delivery (344 vs 155 ml.min-1), arterial pH (7.02 vs 6.94) and systemic vascular resistance (3850 vs 1652 dyn.s.cm-5 (38,500 vs 16,520 microN.s.cm-5)) compared with the controls (P < 0.01), while PaCO2 was lower (12.4 vs 22.7 kPa), as well as O2 extraction ratio (23 vs 63%) and O2 half saturation tension (4.3 vs 8.0 kPa) (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular basis of low-temperature sensitivity in pig hemoglobins

It has been generally assumed that mammals have blood with a greater temperature sensitivity than ectothermic organisms. Recent results have shown that in some species of mammals, Hb displays a value of overall oxygenation enthalpy (delta H) much less exothermic than that observed for most mammalian hemoglobins, including human adult Hb. In this respect, a very interesting case is represented by porcine blood which shows a modest effect of temperature, the temperature coefficient of its oxygen-dissociation curve being significantly lower than that of human blood. Here we report a detailed functional characterization of pig Hb, which, interpreted on the basis of the amino acid sequence of the alpha and beta chains of the molecule, sheds some light on the molecular basis of the phenomenon.

Changes in oxygen-haemoglobin affinity and myocardial function during extracorporeal perfusion in immature pigs

An alteration in oxygen-haemoglobin affinity, as indicated by the partial pressure of oxygen at 50% haemoglobin saturation (P50), may theoretically affect oxygen delivery to the myocardium and, thus, alter myocardial tissue PO2 and possibly myocardial function. We studied the effect of changes in P50 on heart function, metabolism, and coronary sinus PO2 in 10 anaesthetized immature domestic pigs. To facilitate exchange transfusions and control of preload (left ventricular end diastolic pressure, LVEDP), afterload (mean arterial pressure), cardiac output, and heart rate, the animals were placed on right heart bypass. Stroke work (SW), myocardial oxygen consumption (MVO 2), coronary blood flow (CBF), arterial-coronary sinus O2 content difference (CaO2 -CcsO2), and P50 were measured with a control blood prime and after an exchange transfusion with blood having either a low (Group I) or high (Group II) affinity for oxygen. Results (Mean ± SEM, Control versus Test): P50 (mmHg) at 37°C and pH 7.4 increased in Group 1 (35.5 ± 0.7 versus 40.1 ± 1.2, p <0.01) and decreased in Group II (34.7 ± 1.3 versus 26.3 ± 0.5, P <0.001). At 8mmHg LVEDP, SW (gram·metres, g.m) remained constant in Group I (12.2 ± 1.1 versus 11.7 ± 0.8 g·m), but decreased (p <0.05) in Group II (11.7 ± 0.9 versus 8.6 ± 0.61 g.m). In addition, Starling curves relating SW to LVEDP between 4 and 18mmHg were uniformly depressed in Group II but not Group I. No significant change in MVO2 occurred in either group. Group II demonstrated decreased CaO2- CcsO2 (9.3 ± 0.8 versus 6.0 ± 0.3ml O2/dl, p <0.05) and increased CBF (121.6 ± 16.5 versus 188.9 ± 16.9ml/min/1 00gm, p <0.01). PcsO2 increased significantly in Group I (26.6 ± 4.2 versus 36.1 ± 2.7, P <0.02) but not Group II. In conclusion, a decrease in P50 appeared to decrease myocardial function despite a lack of change in PcsO2 or MVO2. A decrease in P50 also led to an increase in CBF. An increase in P50 did not alter function, but did increase coronary sinus and, presumably, tissue PO2.

Temperature modulation of bovine hemoglobins

The functional properties of hemoglobin from Egyptian water buffalo have been characterized as a function of pH, temperature and chloride concentration. Alongside overall similarities shared with ox and Arctic ruminant hemoglobins, hemoglobin from buffalo shows significant differences with respect to the effect of temperature. The results obtained may suggest that the limited effect of temperature on oxygen binding recently reported for ox hemoglobin could be regarded as an interesting case of a reminiscence of a past glacial age.

Temperature and the oxygen-hemoglobin dissociation curve of the harbor seal, Phoca vitulina

To determine the effect of temperature and pH on oxygen-hemoglobin affinity of the harbor seal, we measured 61 biotonometric oxygen-hemoglobin dissociation curves on blood from 5 seals at 3 temperatures and a range of pH values. The average (+/- SEM) hemoglobin concentration was 3.44 +/- 0.15 mM, nearly 50% greater than found in normal humans. At pH 7.4 the P50 (partial pressure of O2 at 50% hemoglobin saturation) +/- SEM values were 22.4 +/- 0.6,25.3 +/- 0.5, and 28.5 +/- 0.4 Torr at 33, 37 and 41 degrees C, respectively. The effect of temperature on oxygen-hemoglobin affinity, (delta log P50/delta T) was 0.014 +/- 0.001 at pH 7.4, significantly lower than that observed in human and dog blood. This low temperature sensitivity may facilitate oxygen off-loading from hemoglobin when temperature gradients exist within the animal or as tissue temperature decreases during a dive. Temperature did not significantly affect the Hill coefficient 'n' (shape) of the dissociation curve which averaged 2.43 +/- 0.04 at 37 degrees C. The fixed-acid Bohr coefficient (delta log P50/delta pH) was -0.606 +/- 0.032 at 37 degrees C and increased with temperature. This relatively large value for the Bohr coefficient was similar to those previously reported for the Northern Elephant, Bladdernose, and Weddell Seals, and may facilitate oxygen off-loading as acidosis develops during a dive.

Oxygen carriage and carbonic anhydrase activity in the blood of a marsupial, the Tammar wallaby (Macropus eugenii), during early development

Blood O2 transport and Hb type have been studied in pouch young and adult of a marsupial, the Tammar Wallaby. The O2-Hb equilibrium curves (at 35.5 degrees C and PCO2 = 34 Torr) had a high P50 in the first few days of life, up to 49 Torr. This fell to 32 Torr by 2 weeks of age. Also (delta log P50/delta PCO2) was low but it rose to adult levels by 2 weeks of age. The curves in these early pouch young showed a change in Hill coefficient (nH) at between 32 and 62% saturation, nH rising to more than 4.0 at higher O2 saturations. This indicates interaction between more than 4 Hb subunits. Model calculations showed that such curves could be produced by a mixture of 2 Hb components; one with a low P50 and low nH, and one with a high P50 and high nH. In this model the nH values were different from the nH values of either component. The temperature effect on P50 in early pouch young was higher than in adult Tammars and similar to that reported for adult eutherians. In the first 4 days all red cells were nucleated and four Hb types were present. Carbonic anhydrase activity in the blood before birth was about 30% of the adult levels. These levels remained until 2 days after birth, when a rapid rise in activity began, near-adult levels being reached at 5 days despite the animals being still very immature.

Oxygen transport properties of blood in two different bovine breeds

1. The whole oxygen dissociation curve of oxyhemoglobin has been determined in double-muscled cattle of the Belgian White Blue breed and in Friesian cattle of different body weight. 2. In calves, P50 values are low and DPG level is high (4-20 mumol/g Hb). 3. P50 values of 25 +/- 1.4 mm Hg (mean +/- SD) and a level of DPG less than 1.5 mumol/g Hb have been found in animals weighing more than 80 kg. 4. Effects of temperature and pH on the oxygen dissociation curve have been measured at all levels of saturation. The temperature coefficient (dlog P50/dT) and the Bohr effect expressed as dlog P50/dpH were 0.017 and -0.40, respectively. 5. Hematocrit, hemoglobin concentrations and oxygen capacity of hemoglobin have been measured. 6. No difference between both breeds has been observed. 7. These data can be used to correct measured values of oxygen tension for temperature and pH and to measure oxygen content of blood in cattle.

Embryonic pig hemoglobins Gower I (zeta 2 epsilon 2), Gower II (alpha 2 epsilon 2), Heide I (zeta 2 theta 2) and Heide II (alpha 2 theta 2): oxygen-binding functions related to structure and embryonic oxygen supply

The common pig lacks a fetal hemoglobin but has four embryonic hemoglobins: Gower I (zeta 2 epsilon 2), Gower II (alpha 2 epsilon 2), Heide I (zeta 2 theta 2) and Heide II (alpha 2 theta 2) as well as adult Hb A (alpha 2 beta 2) and the amino acid sequence for each of the five constituent polypeptide chains has been established. The oxygenation characteristics of the five components, measured in relation to pH, temperature and the erythrocytic ligand 2,3-diphosphoglycerate (DPG), together with the changes in their relative concentrations during early embryonic life, are given. The findings indicate a progressive decrease in maternal-fetal oxygen affinity difference and thus in oxygen transfer efficacy at a given diffusion gradient that correlates with the development of the gas exchange structures. The functional properties of the individual hemoglobins are additionally discussed in relation to molecular structure.

Decreased critical mixed venous oxygen tension and critical oxygen transport during induced hypothermia in pigs

The effects of hypothermia on oxygen delivery and tolerance to hypoxia were studied in 8 normothermic (36.8 degrees C) and 10 hypothermic (29.3 degrees C) pigs that had been anesthetized and surgically implanted with instruments. Cardiac output (QT), VO2 [oxygen consumption, or QT X C(a-v)O2, where C(a-v)O2 is arteriovenous oxygen content difference], arterial and mixed venous blood gas values, and lactate concentrations were measured as the animals were made progressively hypoxic. Under control, normoxic conditions, mixed venous oxygen tension (PvO2) was 41.4 +/- 2.1 mm Hg (mean +/- SE) in the normothermic animals and 26.1 +/- 1.6 mm Hg in the hypothermic animals; these values are close to those predicted in our previous theoretical analysis. To study tolerance to hypoxia during hypothermia, critical PvO2 and critical total oxygen transport (TOT = QT X CaO2, where CaO2 is oxygen content of arterial blood) were determined by decreasing the inspired oxygen concentration (FIO2) in steps and measuring the point where VO2 and blood lactate levels became PO2 or TOT dependent. Again as predicted, the critical PVO2 was lower in the hypothermic animals (15.5 +/- 1.0 mm Hg at 29.3 degrees C compared with 22.0 +/- 1.4 mm Hg at 36.8 degrees C), but critical venous oxyhemoglobin saturation values were not statistically different at the two temperatures. Critical TOT was also decreased during hypothermia, as was the margin of reserve in both PVO2 and TOT (the difference between the normoxic and the critical values).