Changes In Oxygen Transport Research Articles

Cerebral Oxygen Saturation Associates with Changes in Oxygen Transport Parameters during Cardiopulmonary Bypass.

(1) Background: Adequate organ perfusion during cardiopulmonary bypass (CPB) requires accurate estimation and adjustment of flow rates which conventional methods may not always achieve. Perioperative monitoring of cerebral oxygen saturation (ScO2) may detect changes in oxygen transport. This study aims to compare estimated and measured perfusion flow rates and assess the capacity of ScO2 to detect subtle changes in oxygen transport during CPB. (2) Methods: This observational study included 50 patients scheduled for elective coronary artery bypass grafting (CABG) surgery, all of whom provided written informed consent. Perfusion flow rates were estimated using the DuBois formula and measured using echocardiography and a flow probe in the arterial line of the CPB system. ScO2 was continuously monitored, alongside intermittent measurements of oxygen delivery and extraction ratios. (3) Results: Significant discrepancies were found between estimated flow rates (5.2 [4.8-5.5] L/min) and those measured at the start of the surgery (4.6 [4.0-5.0] L/min). These discrepancies were flow rate-dependent, being more pronounced at lower perfusion rates and diminishing as rates increased. Furthermore, ScO2 showed a consistent correlation with both oxygen delivery (r = 0.48) and oxygen extraction ratio (r = 0.45). (4) Conclusions: This study highlights discrepancies between estimated and actual perfusion flow rates during CPB and underscores the value of ScO2 monitoring as a continuous, noninvasive tool for maintaining adequate organ perfusion, suggesting a need for improved, patient-tailored perfusion strategies.

第２回 Response to Exercise after Bed Rest and after Training : A Longitudinal Study of Adaptive Changes in Oxygen Transport and Body Composition

第２回 Response to Exercise after Bed Rest and after Training : A Longitudinal Study of Adaptive Changes in Oxygen Transport and Body Composition

Acute Blood Loss: Regional Blood Flow and Microcirculation (Review, Part II)

The first part of the review highlights the data on the structural and functional organization of the microvas culature; regulation of vascular tone including local (metabolic and myogenic mechanisms, role of endothelium and red blood cells) and systemic (nervous, humoral) factors; general issues of microcirculatory alterations in blood loss and shock. Acute blood loss is considered as a phasic development of compensatory and adaptive processes involving the blood system, cardiovascular, nervous and endocrine systems. Changes in oxygen transport, the pathogenesis of hypoxia and metabolic abnormalities in blood loss and hemorrhagic shock are described. Examples of the vicious circles contributing to acute blood loss pathogenesis are considered as a base for developing decompensated hemorrhagic shock in which the role of hemostasis and blood rheology alterations are also considered.

Low haemoglobin concentration in Tibetan males is associated with greater high-altitude exercise capacity.

Tibetans living at high altitude have adapted genetically such that many display a low erythropoietic response, resulting in near sea-level haemoglobin (Hb) concentration. We hypothesized that absence of the erythropoietic response would be associated with greater exercise capacity compared to those with high [Hb] as a result of beneficial changes in oxygen transport. We measured, in 21 Tibetan males with [Hb] ranging from 15.2 g dl(-1) to 22.9 g dl(-1) (9.4 mmol l(-1) to 14.2 mmol l(-1) ), [Hb], ventilation, volumes of O2 and CO2 utilized at peak exercise (V̇O2 and V̇CO2), heart rate, cardiac output and arterial blood gas variables at peak exercise on a cycle ergometer at ∼4200 m. Lung and muscle O2 diffusional conductances were computed from these measurements. [Hb] was related (negatively) to V̇O2 kg(-1) (r = -0.45, P< 0.05), cardiac output kg(-1) (QT kg(-1) , r = -0.54, P < 0.02), and O2 diffusion capacity in muscle (DM kg(-1) , r = -0.44, P<0.05), but was unrelated to ventilation, arterial partial pressure of O2 (PaO2) or pulmonary diffusing capacity. Using multiple linear regression, variance in peak V̇O2 kg(-1) was primarily attributed to QT, DM, and PCO2 (R(2) = 0.88). However, variance in pulmonary gas exchange played essentially no role in determining peak V̇O2. These results (1) show higher exercise capacity in Tibetans without the erythropoietic response, supported mostly by cardiac and muscle O2 transport capacity and ventilation rather than pulmonary adaptations, and (2) support the emerging hypothesis that the polycythaemia of altitude, normally a beneficial response to low cellular PO2, may become maladaptive if excessively elevated under chronic hypoxia. The cause and effect relationships among [Hb], QT, DM, and PCO2 remain to be elucidated.

Variability in subtropical‐tropical cells drives oxygen levels in the tropical Pacific Ocean

AbstractPrevious studies found a negative trend in oxygen concentrations in tropical regions during the last decades. Employing a biogeochemical circulation model, we highlight the importance of wind‐driven ocean transport associated with the Subtropical‐Tropical Cells (STCs) in setting the oxygen levels in the tropical ocean. The observed and simulated slowdown of the STCs by 30% from the 1960s to the 1990s caused a decrease in oxygen transport to the tropics. Transport of phosphate was similarly reduced, decreasing export production and respiration. The effects of physical transport and biological consumption partly compensate, damping oxygen interannual and decadal variability. Our results suggest that the observed residual oxygen trend in the tropical Pacific is mainly driven by changes in oxygen transport. Accordingly, the observed recent strengthening of the STCs leads us to expect a pause in the oxygen decrease or even an increase of tropical Pacific oxygen values in the near future.

Hemodynamics and oxygen transport dynamics during hepatic resection at different central venous pressures in a pig model

Although low central venous pressure (CVP) has been used to minimize blood loss during hepatectomy, the impact of variations of CVP on the rate of blood loss and on the perfusion of end-organs has not been evaluated. This animal study aimed to evaluate the hemodynamics and oxygen transport changes during hepatic resection at different CVP levels. Forty-eight anesthetized Bama miniature pigs were divided into 8 groups with CVP during hepatic resection controlled at 0 to <1, 1 to <2, 2 to <3, 3 to <4, 4 to <5, 5 to <6, 6 to <7, and 7 to <8 cmH2O. Intergroup comparisons were made for hemodynamic parameters, oxygen transport dynamics, and the rate of blood loss. The rate of blood loss and the hepatic venous pressure during hepatic resection were almost linearly related to the CVP. A significant drop in the mean arterial pressure, cardiac output, and cardiac index occurred between CVP ≥2 and <2 cmH2O. Oxygen delivery (DO2), oxygen consumption (VO2) and oxygen extraction ratio (ERO2) remained relatively constant between CVPs of 2 to <8 cmH2O. There was a significant drop in DO2 when the CVP was <2 cmH2O. There was also a significant drop in VO2 and ExO2 when the CVP was <1 cmH2O. The optimal CVP for hepatic resection is 2 to 3 cmH2O.

Oxygen transport characterization of a human model of progressive hemorrhage

Background Hemorrhage continues to be a leading cause of death from trauma sustained both in combat and in the civilian setting. New models of hemorrhage may add value in both improving our understanding of the physiologic responses to severe bleeding and as platforms to develop and test new monitoring and therapeutic techniques. We examined changes in oxygen transport produced by central volume redistribution in humans using lower body negative pressure (LBNP) as a potential mimetic of hemorrhage. Methods and results In 20 healthy volunteers, systemic oxygen delivery and oxygen consumption, skeletal muscle oxygenation and oral mucosa perfusion were measured over increasing levels of LBNP to the point of hemodynamic decompensation. With sequential reductions in central blood volume, progressive reductions in oxygen delivery and tissue oxygenation and perfusion parameters were noted, while no changes were observed in systemic oxygen uptake or markers of anaerobic metabolism in the blood (e.g., lactate, base excess). While blood pressure decreased and heart rate increased during LBNP, these changes occurred later than the reductions in tissue oxygenation and perfusion. Conclusions These findings indicate that LBNP induces changes in oxygen transport consistent with the compensatory phase of hemorrhage, but that a frank state of shock (delivery-dependent oxygen consumption) does not occur. LBNP may therefore serve as a model to better understand a variety of compensatory physiological changes that occur during the pre-shock phase of hemorrhage in conscious humans. As such, LBNP may be a useful platform from which to develop and test new monitoring capabilities for identifying the need for intervention during the early phases of hemorrhage to prevent a patient's progression to overt shock.

Impacto hemodinâmico de manobra de recrutamento alveolar em pacientes evoluindo com choque cardiogênico no pós-operatório imediato de revascularização do miocárdio

Alveolar recruitment maneuver (ARM) with pressures of 40 cmH2O in the airways is effective in the reversal of atelectasis after myocardial revascularization (MR); however, there is a lack of studies evaluating the hemodynamic impact of this maneuver in patients who evolve with cardiogenic shock after MR. The objective of this study was to test the hemodynamic tolerance to ARM in patients who develop cardiogenic shock after MR.Ten hypoxemic patients in cardiogenic shock after MR were evaluated after admission to the ICU and hemodynamic stabilization. Ventilatory adjustments included tidal volume of 8 mL x kg(-1), PEEP 5 cmH2O, RR 12, and FiO2 0.6. Continuous pressure of 40 cmH2O was applied to the airways for 40 seconds in three cycles. Between cycles, patients were ventilated for 30 seconds, and after the last cycle, PEEP was set at 10 cmH2O. Hemodynamic measurements were obtained 1, 10, 30, and 60 minutes after ARM, and arterial and venous blood samples were drawn 10 and 60 minutes after the maneuver to determine lactate levels and blood gases. ANOVA and the Friedman test were used to analyze the data. A p of 0.05 was considered significant.Alveolar recruitment maneuver increased the ratio PaO2/ FiO2 from 87 to 129.5 after 10 minutes and to 120 after 60 minutes (p < 0.05) and reduced pulmonary shunting from 30% to 20% (p < 0.05). Hemodynamic changes or changes in oxygen transport immediately after or up to 60 minutes after the maneuver were not detected.In patients who evolved to cardiogenic shock and hypoxemia after MR, ARM improved oxygenation and was well tolerated hemodynamically.

Development of a Biomimetic Root Oxygen Bioavailability Sensor

Low oxygen availability in soil can impair root function, thereby decreasing agronomic productivity. Without oxygen to support mitochondrial respiration, energy levels in roots may limit mineral nutrient (N, P, K) transport. Traditional methods for measuring soil oxygenation include the use of redox electrodes and polarographic oxygen sensors. These approaches are limited to measuring oxygen concentrations at specific locations and cannot determine the bio-availability of that oxygen to a growing root. An innovative approach has been developed for direct measurement of oxygen bioavailability. Instead of building the sensor to measure oxygen concentrations, it is possible to construct an electrochemical system in a manner that makes it sensitive to changes in oxygen transport and availability in the soil. Furthermore, it is even possible to construct the sensor to match the oxygen consumption characteristics of a specific root tip, which is important because most metabolism and nutrient uptake occurs here. This is accomplished by using a conductive-gel membrane system that allows sensor profiles to be engineered to match the metabolic profiles of specific species. If constructed to these standards, the sensor will biomimetically replicate biophysical oxygen depletion profiles that are analogous to those found in the rhizosphere of a growing root tip. The biomimetic root oxygen bio-availability (ROB) sensor integrates all biotic and abiotic factors in the soil that limit oxygen transport to the root, while providing real-time sensing. This new sensor technology could be used as a research tool or as a closed-loop control system for field and greenhouse irrigation.

High-Intensity Kayak Performance After Adaptation to Intermittent Hypoxia

Live-high train-low altitude training produces worthwhile gains in performance for endurance athletes, but the benefits of adaptation to various forms of artificial altitude are less clear. To quantify the effects of intermittent hypoxic exposure on kayak performance. In a crossover design with a 6-week washout, we randomized 10 subelite male sprint kayak paddlers to hypoxia or control groups for 3 weeks (5 days/week) of intermittent hypoxic exposure using a nitrogen-filtration device. Each day's exposure consisted of alternately breathing hypoxic and ambient air for 5 minutes each over 1 hour. Performance tests were an incremental step test to estimate peak power, maximal oxygen uptake, exercise economy, and lactate threshold; a 500-m time trial; and 5 x 100-m sprints. All tests were performed on a wind-braked kayak ergometer 7 and 3 days pretreatment and 3 and 10 days posttreatment. Hemoglobin concentration was measured at 1 day pretreatment, 5 and 10 days during treatment, and 3 days after treatment. Relative to control, at 3 days posttreatment the hypoxia group showed the following increases: peak power 6.8% (90% confidence limits, + or - 5.2%), mean repeat sprint power 8.3% (+ or - 6.7%), and hemoglobin concentration 3.6% (+ or - 3.2%). Changes in lactate threshold, mean 500-m power, maximal oxygen uptake, and exercise economy were unclear. Large effects for peak power and mean sprint speed were still present 10 days posthypoxia. These effects of intermittent hypoxic exposure should enhance performance in kayak racing. The effects might be mediated via changes in oxygen transport.

Counterpoint: In health and in a normoxic environment, V̇o2 max is not limited primarily by cardiac output and locomotor muscle blood flow

Counterpoint: In health and in a normoxic environment, V̇<scp>o</scp>_{2 max} is not limited primarily by cardiac output and locomotor muscle blood flow

Errors of measurement for blood volume parameters: a meta-analysis

The volume of red blood cells (V(RBC)) is used routinely in the diagnostic workup of polycythemia, in assessing the efficacy of erythropoietin administration, and to study factors affecting oxygen transport. However, errors of various methods of measurement of V(RBC) and related parameters are not well characterized. We meta-analyzed 346 estimates of error of measurement of V(RBC) for techniques based on Evans blue (V(RBC,Evans)), 51chromium-labeled red blood cells (V(RBC,51Cr)), and carbon monoxide (CO) rebreathing (V(RBC,CO)), as well as hemoglobin mass with the carbon-monoxide method (M(Hb,CO)), in athletes and active and inactive subjects undergoing various experimental and control treatments lasting minutes to months. Subject characteristics and experimental treatments had little effect on error of measurement, but measures with the smallest error showed some increase in error with increasing time between trials. Adjusted to 1 day between trials and expressed as coefficients of variation, mean errors for M(Hb,CO) (2.2%; 90% confidence interval 1.4-3.5%) and V(RBC,51Cr) (2.8%; 2.4-3.2%) were much less than those for V(RBC,Evans) (6.7%; 4.9-9.4%) and V(RBC,CO) (6.7%; 3.4-14%). Most of the error of V(RBC,Evans) was due to error in measurement of volume of plasma via Evans blue dye (6.0%; 4.5-7.8%), which is the basis of V(RBC,Evans). Most of the error in V(RBC,CO) was due to estimates from laboratories with a relatively large error in M(Hb,CO), the basis of V(RBC,CO). V(RBC,51Cr) and M(Hb,CO) are the best measures for research on blood-related changes in oxygen transport. With care, V(RBC,Evans) is suitable for clinical applications of blood-volume measurement.

Metabolic and Ventilatory Acclimatization to Cold Stress in House Sparrows (Passer domesticus)

Passerines that overwinter in temperate climates undergo seasonal acclimatization that is characterized by metabolic adjustments that may include increased basal metabolic rate (BMR) and cold-induced summit metabolism (M(sum)) in winter relative to summer. Metabolic changes must be supported by equivalent changes in oxygen transport. While much is known about the morphology of the avian respiratory system, little is known about respiratory function under extreme cold stress. We examined seasonal variation in BMR, M(sum), and ventilation in seasonally acclimatized house sparrows from Wisconsin. BMR and M(sum) increased significantly in winter compared with summer. In winter, BMR increased 64%, and M(sum) increased 29% over summer values. The 64% increase in winter BMR is the highest recorded for birds. Metabolic expansibility (M(sum)/BMR) was 9.0 in summer and 6.9 in winter birds. The metabolic expansibility of 9.0 in summer is the highest yet recorded for birds. Ventilatory accommodation under helox cold stress was due to changes in breathing frequency (f), tidal volume, and oxygen extraction efficiency in both seasons. However, the only significant difference between summer and winter ventilation measures in helox cold stress was f. Mean f in helox cold stress for winter birds was 1.23 times summer values.

SEASONAL AND DIURNAL VARIATION IN METABOLISM AND VENTILATION IN HOUSE SPARROWS

Abstract Passerines that are year-round residents in temperate climates undergo seasonal acclimatization that facilitates maintenance of thermoregulatory homeostasis. These changes in thermoregulatory metabolism must be supported by equivalent changes in oxygen transport. We measured the effects of ambient temperature and time of day on metabolism and ventilation in House Sparrows (Passer domesticus) in summer and winter. House Sparrows were exposed to ambient temperatures (Ta) ranging from −12°C to 15.5°C in summer and 17.5°C in winter. Open-circuit respirometry was used to measure oxygen consumption (VO2) and ventilation was recorded using whole-body plethysmography. In both summer and winter, VO2 increased with decreasing Ta. VO2 was significantly higher during the active phase compared to the resting phase of the daily cycle in both summer and winter. Thermal conductance was significantly lower in nighttime birds compared to daytime birds. With increased oxygen demands, minute volume (VI) increase...

Modification of the cardiovascular response to hemorrhage by somatic afferent nerve stimulation with special reference to gut and skeletal muscle blood flow.

Tissue injury modifies heart rate and blood pressure responses to hemorrhage. The effect of concomitant injury on the hemorrhage-induced redistribution of cardiac output is much less clear. However, if injury elicits the visceral alerting response of the defense reaction, then a change in this redistribution of peripheral blood flow might be expected. If such a change compromised the gut circulation, then it might explain the deleterious effects of injury on the ability to withstand hemorrhage. Immature pigs anesthetized with Saffan were bled 30% of blood volume with or without concomitant somatic afferent (brachial) nerve stimulation (to mimic injury). In addition to global cardiovascular and oxygen transport variables, blood flow was measured in the cranial mesenteric (gut) and right femoral (skeletal muscle) arteries after a 60-minute stabilization period after surgery, at the end of the 30-minute hemorrhage, and after a 30-minute shock period. Hemorrhage induced the expected cardiovascular and oxygen transport changes accompanied by a reduction in skeletal muscle blood flow and a 55% increase in skeletal muscle vascular resistance, but gut blood flow and vascular resistance were unchanged. However, in the presence of brachial nerve stimulation, the pattern of response to hemorrhage was modified, such that gut blood flow was now reduced and gut vascular resistance increased. The sparing of the gut circulation after hemorrhage was abolished in the presence of "injury." This finding is consistent with injury eliciting the defense reaction and may help explain the deleterious effects of injury on resistance to hypovolemia.

The Effect of Oxygen Delivery-Directed Resuscitation on Splanchnic and Hepatic Oxygen Transport after Hemorrhagic Shock

Background: Gut and hepatic dysfunction, during and after hypovolemic shock, have been implicated as causative mechanisms in the development of multiple system organ failure in the trauma patient. Current techniques of assessment of perfusion only detect changes in systemic oxygen transport. We designed an animal model that can measure changes in oxygen transport in the liver and gut during hypovolemic shock and resuscitation. Materials and methods: Animals were hemorrhaged to a mean arterial pressure (MAP) of 60 mm Hg and maintained at 60 mm Hg for 60 min. Animals were then assigned to one of three groups. Group I served as nontreatment controls. Group II received shed blood and saline in sufficient volumes to restore MAP to baseline. Group III animals were resuscitated with shed blood, saline, and donor blood to restore systemic oxygen delivery to the preshock value. Results: The animals resuscitated to their baseline systemic oxygen delivery, Group III, had significantly higher systemic, hepatic, and splanchnic oxygen delivery than the remaining groups. In addition, Group III had higher oxygen consumption, portal flow, and hepatic artery flow than the blood pressure-directed group, Group II. The decrease in oxygen extraction ratio in the gut and liver was significantly greater in Group III than in Group II. Conclusions: These data show that hepatic and gut vascular beds are better perfused when resuscitation from hemorrhage is guided by systemic oxygen transport measurements compared to resuscitation guided by blood pressure.

MODS/SIRS: result of an overwhelming inflammatory response?

Multiple organ dysfunction syndrome and the systemic inflammatory response syndrome are expressions of an inappropriate, generalized inflammatory response to severe inflammatory stimuli, which may be bacterial or nonbacterial in nature. The clinical signs and symptoms, morphologic alterations, and changes in oxygen transport seem to be the direct effect of phagocyte activation. So far, identifying the microorganisms and neutralizing their toxins has not been helpful in improving prognosis. As an essential adjunct to treating the bacterial or nonbacterial causes, finding safe ways of modulating the phagocyte response should be considered.

Oxygen transport and hemodynamics during retrograde whole-body perfusion

The changes in oxygen transport and hemodynamics during retrograde whole-body extracorporeal perfusion (retro-ECC) were studied in six mongrel dogs. Oxygen consumption during retro-ECC, in which the blood flow rate was set at 25% and 50% of the flow during antegrade extracorporeal perfusion (ante-ECC), respectively, was relatively high compared with that during ante-ECC. These changes were caused by an increase in the oxygen extraction ratio to 71.5% +/- 8.2% and 51.2% +/- 12.4% during retro-ECC/25% and retro-ECC/50%, respectively. Thus, tissue perfusion was apparently well maintained by retrograde perfusion on the basis of the oxygen transport data. However, central venous pressure increased markedly to 29.5 +/- 11.6 mmHg and 56.2 +/- 24.5 mmHg during retro-ECC/25% and retro-ECC/50%, respectively, because of massive venous congestion caused by insufficient arterial return of perfused blood. The great venous compliance and increased systemic vascular resistance were the main causes of circulatory failure during retro-ECC. The risk of serious complications owing to the venous congestion must be considered during retrograde perfusion, especially during the clinical application of retrograde cerebral perfusion.

Oxygen delivery and oxygen consumption

AnaesthesiaVolume 48, Issue 8 p. 732-733 Free Access Oxygen delivery and oxygen consumption G.R. Nimmo, G.R. Nimmo Western General Infirmary, Edinburgh EH4 2XUSearch for more papers by this authorS.J. Mackenzie, S.J. Mackenzie Western General Infirmary, Edinburgh EH4 2XUSearch for more papers by this authorI.S. Grant, I.S. Grant Western General Infirmary, Edinburgh EH4 2XUSearch for more papers by this author G.R. Nimmo, G.R. Nimmo Western General Infirmary, Edinburgh EH4 2XUSearch for more papers by this authorS.J. Mackenzie, S.J. Mackenzie Western General Infirmary, Edinburgh EH4 2XUSearch for more papers by this authorI.S. Grant, I.S. Grant Western General Infirmary, Edinburgh EH4 2XUSearch for more papers by this author First published: August 1993 https://doi.org/10.1111/j.1365-2044.1993.tb07196.xCitations: 4AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. References 1 Vincent JL, Roman A, De-Backer D, Kahn RJ. Oxygen uptake/supply dependency. Effects of short term dobutamine infusion. American Review of Respiratory Disease 1990; 142: 2– 7. 2 Kruse JA, Haupt MT, Puri VK, Carlson RW. Lactate levels as predictors of the relationship between oxygen delivery and consumption in Ards. Chest 1990; 98: 959– 62. 3 Nimmo GR, Mackenzie SJ, Nightingale P, Grant IS, Edwards JD. Changes in oxygen transport and lactate during shock. Proceedings of Intensive Care Society 1991 (abstract). 4 Lorente JA, Renes E, Gomez-Aguinaga MA, Landin L, Morena JL, Liste D. Oxygen delivery-dependent oxygen consumption in acute respiratory failure. Critical Care Medicine 1991; 19: 770– 5. 5 Tuchschmidt J, Fried J, Astiz M, Rackow E. Elevation of cardiac output and oxygen delivery improves outcome in septic shock. Chest 1992; 102: 216– 20. Citing Literature Volume48, Issue8August 1993Pages 732-733 ReferencesRelatedInformation

Integrated Function of the Respiratory Pigment Hemocyanin in Crabs

A large number of factors are now known to influence the oxygen affinity of hemocyanins in crabs. In this article I review several case studies in which a number of different variables, including pH, CO2, calcium ions, lactate, urate, dopamine, and temperature, act together on hemocyanin oxygen affinity to bring about adaptive changes in oxygen transport. These changes act in tandem with ventilatory and cardiovascular adjustments to stabilize oxygen uptake during hypoxia or to increase oxygen uptake during exercise in a swimming crab. It is important, however, that the effects of the different modulators be examined at very low concentrations, where their effects are large, to assess their importance in resting crabs where their concentrations may be low. Temperature effects among hemocyanins in crabs are variable and the magnitude may be inversely related to the magnitude of the Bohr effect. Several examples are presented of acclimation effects where oxygen affinity increases significantly at cold temperatures. The acclimation response may be important in partially regulating the metabolic responses of crabs to seasonal changes in temperature.