Onset Of Anaerobic Metabolism Research Articles

Evaluation of respiratory exchange ratio (RER) for predicting postoperative outcomes in elderly patients undergoing oncological resection for gastrointestinal malignancies - A prospective cohort study.

Predicting complications after major oncosurgery is particularly daunting in the elderly subcategory of patients owing to factors like preexisting age-related immune cellular senescence and a significant imbalance of oxygen delivery (DO2) and consumption (VO2) characteristic of major oncological surgeries. The respiratory exchange ratio (RER) indicates DO2-VO2 balance and onset of anaerobic metabolism. We evaluated the ability of RER in predicting the occurrence of postoperative complications following geriatric oncosurgery. In the study, we enrolled 96 patients aged 65 years and above undergoing definitive surgery for gastrointestinal malignancy. The RER was calculated at predefined time points by a non-volumetric method from the respiratory parameters as RER = (end-tidal fractional carbon dioxide [FetCO2] - fraction of inspired carbon dioxide [FiCO2]/fraction of inspired oxygen [FiO2] - end-tidal fractional oxygen [FetO2]). Other indices of tissue perfusion, like central venous oxygen saturation and lactate levels, were also recorded. The patients were followed up for postsurgical complications. The predictive value of RER and other perfusion parameters was assessed and compared by appropriate statistical methods. The patients who sustained major complications had a higher RER than the patients who did not sustain complications (1.47 ± 0.99 vs. 0.90 ± 0.31, P = 0.001). An intraoperative cutoff value of RER ≥0.89 was found to best predict postoperative complications at a specificity and sensitivity rate of 81.2% and 76%, respectively. End-operative partial pressure of carbon dioxide (pCO2) gap of >5.2 mm and elevated arterial lactate could also predict postsurgical complications in this age group. The RER can serve as a noninvasive, real-time and sensitive indicator of tissue hypoperfusion and postoperative complications in geriatric gastrointestinal oncosurgery.

A Personal Biography of a Physiological Misnomer: The Anaerobic Threshold.

In 1973 Wasserman, Whipp, Koyal, and Beaver published a groundbreaking study titled "Anaerobic threshold and respiratory gas analysis during exercise". At that time, respiratory gas analysis and laboratory computers had evolved such that more advanced respiratory exercise physiology studies were possible. The initial publications from this group on the onset of anaerobic metabolism in cardiac patients, the first breath-by-breath VO2 system, the first description of the anaerobic threshold, and then later new methods to detect the anaerobic threshold have been and continue to be highly cited. In fact, their 1973 anaerobic threshold paper is the sixth and their 1986 paper is the second most cited paper ever published in the Journal of Applied Physiology. The anaerobic threshold concept has also generated>5500 publications with the rates increasing over time. The publication of two papers that help to refute the "anaerobic" explanation for this phenomenon had no effect on the rates of citations of the original anaerobic threshold papers or the number of anaerobic threshold papers published since. Thus, despite now substantial evidence refuting the proposed anaerobic mechanisms underlying this phenomenon, these papers continue to be highly influential in the discipline of exercise physiology and, perhaps even more explicitly, clinical exercise physiology.

Lactic acidosis, hyperlactatemia and sepsis

Among hospitalized patients, lactic acidosis represents the most common cause of metabolic acidosis. Lactate is not just a metabolic product of anaerobic glycolysis but is triggered by a variety of metabolites even before the onset of anaerobic metabolism as part of an adaptive response to a hypermetabolic state. On the basis of such considerations, lactic acidosis is divided into two classes: inadequate tissue oxygenation (type A) and absence of tissue hypoxia (type B). Lactic acidosis is characterized by non-specific symptoms but it should be suspected in all critical patients who show hypovolemic, hypoxic, in septic or cardiogenic shock or if in the presence of an unexplained high anion gap metabolic acidosis. Lactic acidosis in sepsis and septic shock has traditionally been explained as a result of tissue hypoxia when whole-body oxygen delivery fails to meet whole body oxygen requirements. In sepsis lactate levels correlate with increased mortality with a poor prognostic threshold of 4 mmol/L. In hemodynamically stable patients with sepsis, hyperlactatemia might be the result of impaired lactate clearance rather than overproduction. In critically ill patients the speed at which hyperlactatemia resolves with appropriate therapy may be considered a useful prognostic indicator. The measure of blood lactate should be performed within 3 h of presentation in acute care setting. The presence of lactic acidosis requires early identification of the primary cause of shock for the best appropriate treatment. Since most cases of lactic acidosis depend on whole-body oxygen delivery failure, the maximization of systemic oxygen delivery remains the primary therapeutic option. When initial resuscitation does not substantially or completely correct lactic acidosis, it is also essential to consider other causes. The treatment of acidosis with buffering agents (specifically bicarbonate) is generally advocated only in the setting of severe acidosis. Ongoing research into lactate clearance and probable noninvasive surrogate measures may add further insight into outcome-based practices.

Anaerobic Metabolism at Thermal Extremes: A Metabolomic Test of the Oxygen Limitation Hypothesis in an Aquatic Insect

Thermal limits in ectotherms may arise through a mismatch between supply and demand of oxygen. At higher temperatures, the ability of their cardiac and ventilatory activities to supply oxygen becomes insufficient to meet their elevated oxygen demand. Consequently, higher levels of oxygen in the environment are predicted to enhance tolerance of heat, whereas reductions in oxygen are expected to reduce thermal limits. Here, we extend previous research on thermal limits and oxygen limitation in aquatic insect larvae and directly test the hypothesis of increased anaerobic metabolism and lower energy status at thermal extremes. We quantified metabolite profiles in stonefly nymphs under varying temperatures and oxygen levels. Under normoxia, the concept of oxygen limitation applies to the insects studied. Shifts in the metabolome of heat-stressed stonefly nymphs clearly indicate the onset of anaerobic metabolism (e.g., accumulation of lactate, acetate, and alanine), a perturbation of the tricarboxylic acid cycle (e.g., accumulation of succinate and malate), and a decrease in energy status (e.g., ATP), with corresponding decreases in their ability to survive heat stress. These shifts were more pronounced under hypoxic conditions, and negated by hyperoxia, which also improved heat tolerance. Perturbations of metabolic pathways in response to either heat stress or hypoxia were found to be somewhat similar but not identical. Under hypoxia, energy status was greatly compromised at thermal extremes, but energy shortage and anaerobic metabolism could not be conclusively identified as the sole cause underlying thermal limits under hyperoxia. Metabolomics proved useful for suggesting a range of possible mechanisms to explore in future investigations, such as the involvement of leaking membranes or free radicals. In doing so, metabolomics provided a more complete picture of changes in metabolism under hypoxia and heat stress.

Bymixer system can measure O2 uptake and CO2 elimination in the anesthesia circle circuit

The ability to measure carbon dioxide elimination (Vco(2)), oxygen uptake (Vo(2)), and R (respiratory exchange ratio, Vco(2)/Vo(2)) during anesthesia may help the non-invasive detection of critical events (e.g., abrupt decrease in cardiac output) and metabolic upset (e.g., onset of anaerobic metabolism). We have developed a new clinical bymixer (inline mixing chamber) that can measure mixed inspired and expired gas fractions in the anesthesia circle circuit. The addition of a standard anesthesia gas analyzer and flowmeter, and a new airway temperature and humidity sensor, allow determinations of Vco(2) and Vo(2) at the airway opening of the circle circuit. Over a range of tidal volume and frequency, Vco(2) and Vo(2) were compared to reference values generated by the combustion of metered liquid ethanol in a new metabolic lung simulator. By linear regression, bymixer-flow measurements of Vco(2) (slope = 1.02, Y-intercept = -5.31, coefficient of determination, R(2) = 0.998) and Vo(2) (slope = 1.05, Y-intercept = -4.34, R(2) = 0.993) correlated closely to the reference values generated by the metabolic lung simulator. Limits of agreement analysis generated percent errors (mean +/- 1.96 SD) of -1.2 +/- 7.2% for Vco(2) and 2.5 +/- 9.8% for Vo(2). The new clinical bymixer is compact, lightweight, disposable, inexpensive, and has a fast and adjustable response time (time constant about 14 sec). Anesthesia circle circuit integrity is maintained. Bymixer-flow measurements of Vco(2) and Vo(2) are accurate and may add to clinical monitoring under anesthesia and surgery.

Description of trophic status, hyperautotrophy and dystrophy of a coastal lagoon through a potential oxygen production and consumption index—TOSI: Trophic Oxygen Status Index

Abstract Seasonal changes of trophic status of the Sacca di Goro lagoon (northern Italy) are analysed through time series of oxygen metabolism for two stations in which separate measures of planktonic, macroalgal ( Ulva rigida ), and benthic exchange are available. These component results and their sums (i.e. total ecosystem metabolism) are compared using conventional analyses and an index obtained from oxygen fluxes (Trophic Oxygen Status Index, TOSI). The TOSI is derived from the Benthic Trophic Status Index (BTSI) proposed earlier by Rizzo et al. [Estuaries 19 (1996) 247] and basically represents the net potential metabolism. The index results from the relationship between net maximum productivity (NP), measured at saturating light, and dark respiration (DR). The index was developed to provide a simple portrayal of oxygen processing over time and space for shallow aquatic systems and has two modes: a categorical classification and a graphical representation. The categorical classification of the index from autotrophy to heterotropy provides a rapid assessment of the potential oxygen balance and thus evidences critical situations in the lagoonal metabolism. In the graphical representation of the TOSI, three pieces of information are given: the categorical TOSI, the magnitude of flux for both NP and DR and the time line of the fluxes. Where flushing is slow, the TOSI reflects dissolved oxygen dynamics since the NP:|DR| ratio clearly correlates with both the maximum oxygen concentration (MOC) and the daily quantity of oxygen remaining in the water column (RO). However, TOSI is less well related to MOC and RO in open systems in which oxygen concentrations are dominated by physical factors. The graphical representation of TOSI seems also suitable to represent the degree of intrasystem disturbance that is related to the excess of primary production and changes in oxygen availability. It can also discriminate among different photoautotrophic conditions, including hyperautotrophy, as an abnormal oxygen production with respect to the biomass build up, and dystrophy, as the subsequent abnormal oxygen deficit which causes prolonged anoxia and the onset of anaerobic metabolism. Overall, the index provides a tool for rapid assessment of system metabolism and potentially its consequences.

Bench-to-bedside review: lactate and the lung.

The ability of the isolated lung tissue to take up glucose and to release lactate is potentially similar to that of other body tissues. Nonetheless, when lung lactate exchange was assess in vivo in normal humans, no measurable lactate production could be detected. Lung lactate production may become clinically evident in disease states especially in the patients with acute lung injury or with acute respiratory distress syndrome. Potential mechanisms of lactate production by the injured lung may include not only the onset of anaerobic metabolism in hypoxic zones, but also direct cytokine effects on pulmonary cells and an accelerated glucose metabolism in both the parenchymal and the inflammatory cells infiltrating lung tissue. In addition, as skeletal muscle, lung tissue may show metabolic adaptations in response to systemic mediators and may contribute to the systemic metabolic response to severe illness even in the absence of direct tissue abnormalities.

Gut luminal lactate release during gradual intestinal ischemia

Gut ischemia induced by occlusion of the superior mesenteric artery (SMA) results in release of lactate into the gut lumen. We studied the threshold of SMA flow reduction that leads to increased gut luminal lactate during stepwise reduction in SMA blood flow. A randomized, controlled animal experiment in a university experimental research laboratory. Anesthetized, normoventilated, normovolemic domestic pigs were randomized to ischemia ( n=7) and sham groups ( n=7). SMA blood flow was reduced stepwise at 15-min intervals by 22%, 44%, 66%, and 88% and kept constant thereafter for 60 min. Jejunal luminal microdialysate lactate and mucosal pCO(2) were measured every 15 min. The luminal lactate increased over the upper normal limit of 0.2 mmol/l at a median SMA blood flow of 9.6 ml kg(-1) min(-1) (range 7.5-23.7). In five of seven animals the increase in luminal lactate was preceded by or accompanied by an increase in the mucosal-arterial pCO(2) gradient. There is a threshold of SMA blood flow below which gut luminal lactate increases, indicating mucosal anaerobic metabolism. Measurement of gut luminal lactate by microdialysis can be used to assess the adequacy of gut perfusion and the onset of anaerobic metabolism.

Physiological adaptations to high intertidal life involve improved water conservation abilities and metabolic rate depression in Littorina saxatilis

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 224:171-186 (2001) - doi:10.3354/meps224171 Physiological adaptations to high intertidal life involve improved water conservation abilities and metabolic rate depression in Littorina saxatilis I. M. Sokolova1,2,*, H. O. Pörtner1 1Alfred-Wegener Institute for Polar and Marine Research, Columbusstrasse 3, 27568 Bremerhaven, Germany 2White Sea Biological Station, Zoological Institute of Russian Academy of Sciences, Universitetskaya nab., 1, 199034 St. Petersburg, Russia *Present address: Department of Zoology, University of Guelph, Guelph, Ontario N1G 2W1, Canada. E-mail: innas@bms.bc.ca ABSTRACT: Mortality, rates of water loss, aerobic and anaerobic metabolic rates and changes in the parameters of cellular energy status were monitored in the intertidal gastropod Littorina saxatilis from different latitudes and shore levels during prolonged air exposure at elevated temperatures (30°C). Prolonged air exposure, imitating environmental conditions during summer low tide at high-shore levels, resulted in the onset of anaerobic metabolism, as indicated by the significant accumulation of succinate and alanine and a considerable depletion of high-energy phosphates (ATP and phospho-l-arginine, PLA). However, anaerobic metabolism accounted for only 1 to 2% of total ATP turnover in all groups, the remainder being supplied by aerobic metabolism. Snails from the White Sea population, which were more resistant to prolonged air exposure at 30°C than North Sea specimens, demonstrated higher anaerobic capacity and a depression of overall metabolic rate by ca 20% in air, whereas the less-resistant North Sea animals displayed very low anaerobic metabolic rates and elevated aerial oxygen consumption rates (110 to 125% of the rate observed in water). Within the White Sea population, high-shore periwinkles demonstrated higher resistance to prolonged air exposure than low-shore specimens associated with lower evaporation water loss, reduced rates of anaerobic ATP turnover, higher stores of l-aspartate and lower defended values of ATP and PLA. In contrast, no differences were found between high- and low-shore snails in the North Sea. This may reflect environmental conditions at the 2 study sites, with stronger contrasts between high- and low shore habitats in the White Sea than in the North Sea. In general, our data show that adaptation to prolonged air exposure at elevated temperatures, which may occur at high-shore levels during summer low tide, does not necessarily involve increased anaerobic capacity in L. saxatilis. Instead, enhanced abilities for water conservation and metabolic rate depression combined with increased stores of fermentable substrate seem to be crucial for survival during prolonged periods of emersion. KEY WORDS: Intertidal · Air exposure · Anaerobiosis · Respiration · Water loss · Metabolic rate · Littorina saxatilis Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 224. Online publication date: December 18, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

Oxygen limitation of thermal tolerance defined by cardiac and ventilatory performance in spider crab, Maja squinado.

Geographic distribution limits of ectothermal animals appear to be correlated with thermal tolerance thresholds previously identified from the onset of anaerobic metabolism. Transition to these critical temperatures was investigated in the spider crab (Maja squinado) with the goal of identifying the physiological processes limiting thermal tolerance. Heart and ventilation rates as well as PO(2) in the hemolymph were recorded on-line during progressive temperature change between 12 and 0 degrees C (1 degrees C/h) and between 12 and 40 degrees C (2 degrees C/h). Lactate and succinate were measured in tissues and hemolymph after intermediate or final temperatures were reached. High levels of hemolymph oxygenation suggest that an optimum range of aerobic performance exists between 8 and 17 degrees C. Thermal limitation may already set in at the transition from optimum to pejus (pejus = turning worse, progressively deleterious) range, characterized by the onset of a decrease in arterial PO(2) due to reduced ventilatory and cardiac performance. Hemolymph PO(2) values fell progressively toward both low and high temperature extremes until critical temperatures were reached at approximately 1 and 30 degrees C, as indicated by low PO(2) and the onset of anaerobic energy production by mitochondria. In conclusion, the limited capacity of ventilation and circulation at extreme temperatures causes insufficient O(2) supply, thereby limiting aerobic scope and, finally, thermal tolerance.

Behavioural responses and biochemical correlates in Solea solea to gradual hypoxic exposure

The common sole, Solea solea, a benthic flatfish, is frequently exposed to environmental hypoxic conditions. A succession of behavioural responses to oxygen depletion can be observed. Under moderate hypoxia (80-20% air saturation) the fish reduce spontaneous activity and the scope for activity is lowered. At the onset of anaerobic metabolism (at 20% air saturation) the fish lie still on the bottom, but with increasing severity of hypoxia they start bending the body so as to lift the mouth above the bottom and to reach water layers with higher oxygen concentrations. Between 20 and 6% air saturation, the sole applies two different metabolic strategies: (i) it activates anaerobic metabolism and (ii) it depresses its metabolism below standard metabolic rate. At 5% air saturation or lower the fish swim up with burst- and panic-like movements and lose balance and swim in an uncoordinated manner (below 3%), finally remaining paralysed at the bottom. The correlation of behavioural and metabolic responses clearly shows that under unfavourable oxygen conditions, escape behaviour and burst activity are induced as a last response when other energy-saving alternatives (anaerobic metabolism and metabolic depression) seem to become insufficient.

Myocardial anaerobic metabolism occurs at a critical coronary venous PO2 in pigs.

We tested the hypothesis that the onset of myocardial anaerobic metabolism is fundamentally different from the whole body and other organs, where the onset of anaerobic metabolism occurs at a critical oxygen extraction ratio--not at a critical venous PO2. We measured oxygen saturation and PO2 of arterial and coronary venous blood at the onset of global myocardial anaerobic metabolism during progressive hypoxic hypoxia (n = 7) compared with carbon monoxide hypoxia (n = 7), which left-shifted the oxygen-hemoglobin dissociation curve. The onset of global myocardial anaerobic metabolism was defined by decreased myocardial lactate consumption and left ventricular contractility. Coronary venous PO2 was no different during hypoxic hypoxia and carbon monoxide hypoxia at equivalent arterial oxygen saturations, particularly at the onset of myocardial anaerobic metabolism (PO2 17.0 +/- 1.7 torr versus 15.9 +/- 2.2 torr, p = NS). However, the myocardial oxygen extraction ratio was significantly greater during hypoxic hypoxia than during carbon monoxide hypoxia at the onset of myocardial anaerobic metabolism (0.88 +/- 0.02 versus 0.65 +/- 0.04, p < 0.01). Thus, in contrast to the whole body where the onset of anaerobic metabolism occurs at a critical oxygen extraction ratio, the onset of myocardial anaerobic metabolism occurs at a critical coronary venous PO2.

Energy metabolism and ATP free-energy change of the intertidal wormSipunculus nudus below a critical temperature

The intertidal wormSipunculus nudus was exposed to various temperatures for an analysis of the integrated changes in energy and acid-base status. Animals were incubated in sea water or maintained for up to 8 days at 4 and 0°C while dwelling in the sediment. Cannulation of the animals prior to experimentation allowed the analysis of blood gas parameters (\(P_{O_2 } \),\(P_{CO_2 } \) and pH).\(P_{O_2 } \) fell to 0 torr within 8 days at 0°C. A simultaneous reduction of ventilatory activity was derived from measurements of the pattern of coelomic fluid pressure changes associated with ventilatory movements. The increase in\(P_{CO_2 } \) and an onset of anaerobic metabolism, indicated by the accumulation of end products like acetate and propionate both in the coelomic fluid and the body wall musculature, led to the development of a progressive acidosis and a deviation from the alphastat regulation of intracellular pH seen in unburied animals. The drop in intracellular pH together with the depletion of the adenylates and the phosphagen, phospho-l-arginine, reflect a significant decrease in the Gibb's free-energy change of ATP hydrolysis. These changes are interpreted to indicate lethal cold injuries, because recovery was not possible when the animals were returned to 12°C after more than 2 days of exposure to 0°C. A low critical temperature indicating the onset of cold-induced anaerobiosis is concluded to exist below 4°C owing to the insufficient response of the ventilatory system to the developing hypoxia.

Oxygen deficit and blood lactate in prepubertal boys during exercise above the anaerobic threshold

Recent studies have shown that in boys a steady-state of blood lactate is maintained at exercise levels above the anaerobic threshold. Therefore, the explanation hitherto provided for the steeper increase in blood lactate beyond the anaerobic threshold, i.e. the onset of anaerobic metabolism, needs modification. Investigations were carried out in ten boys, aged 11-12 years, during treadmill running. Maximal oxygen uptake (VO2max) and maximal blood lactate were determined during incremental exercise. Subsequently each boy performed four runs at different high constant speeds of 16 min duration, in order to determine maximal steady-state blood lactate. The underlying data also served to estimate roughly the lactate anaerobic threshold. Oxygen uptaken (VO2) was measured at 0.5 min intervals during the initial 7.5 min of each constant-speed run. Maximal steady-state blood lactate was 5.6 mmol/l corresponding to 92% of VO2max. The mean blood lactate at which the anaerobic threshold was reached or just exceeded was 2.7 mmol/l corresponding to 82% of VO2max. Oxygen transport transient kinetics were computed from the mean 0.5 min VO2-values during the constant-speed runs near the maximal steady-state blood lactate and from runs near the anaerobic threshold. Half-times of VO2 response were shorter than values previously reported for adults due to a faster increase in VO2 at the onset of exercise. Half-times increased with increasing work rates as did the oxygen deficit, due to a slower increase in VO2 along with a longer time required to attain a steady-state at higher work rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Gastric intramucosal pH: a noninvasive method for the indirect measurement of tissue oxygenation

Monitoring the adequacy of tissue oxygenation is an important goal in the care of the critically ill patient. Global alterations in tissue oxygenation are inferred from changes in systemic oxygen transport (defined as the product of cardiac output and arterial oxygen content) and total oxygen consumption. These parameters, however, cannot measure the level of oxygenation of specific tissue beds, in particular those that are first affected by hypoxia, such as the gastrointestinal tract and the kidneys. Gastrointestinal tonometry is a new method for measuring the partial pressure of carbon dioxide of the gastrointestinal mucosa. This information can be used in conjunction with the arterial blood bicarbonate to calculate the pH of the mucosa. Mucosal acidosis correlates well with the onset of anaerobic metabolism in response to hypoxia or sepsis. This review discusses the basic principles of tonometry, the results of experimental and clinical studies, and the practical aspects related to the implementation and use of tonometers in patients in the critical care unit. Gastrointestinal tonometry is a relatively noninvasive device that appears capable of measuring metabolic changes produced by hypoxia. Because of the sensitive nature of the gastrointestinal mucosa, these changes often occur well in advance of other, more common, indices of hypoxia. The use of the tonometer may become a routine procedure in the overall monitoring of critically ill patients.

Metabolic Rates at Different Oxygen Levels Determined by Direct and Indirect Calorimetry in the Oxyconformer Sipunculus Nudus

ABSTRACT Oxygen uptake and the mode of energy production in Sipunculus nudus L. were determined at different oxygen levels by means of direct and indirect calorimetry. Oxygen consumption declined linearly with decreasing ambient . A similar decrease in heat production was observed down to a of 8.66 kPa. At lower oxygen tensions, a discrepancy between aerobic and total heat production indicated the onset of anaerobic metabolism. The occurrence of the critical between 8.66 and 2.66 kPa was confirmed by estimation of anaerobic end products in the body wall musculature. The contributions of aerobic and anaerobic metabolism to total ATP production were determined at a of 2.66 kPa and were found to be 48 and 52 %, respectively. Measured heat dissipation under extreme hypoxia ( nominally zero) (21.5±3.5mJh-1g-1) agreed with the enthalpy changes calculated from the rates of formation of anaerobic end products (17.9±4.7mJh-1g-1). For the sake of redox balance maintenance, saturation of fatty acids was assumed; this would be accompanied by an additional heat production of 3.3mJh-1g-1, so that the total calculated enthalpy change amounted to 21.2mJh-1g-1.

Metabolic Responses of the ToadBufo marinusto Environmental Hypoxia: An Analysis of the Critical Po2

Characteristics of the critical Po₂ have been investigated by analyzing both O₂ uptake rates and modes of energy production during hypoxic exposure in the toad Bufo marinus. After preacclimatization to moderate hypoxia, this oxyregulator exhibits constant rates of O₂ consumption in a wide range of Po₂. Below 30-37 Torr, an increase in O₂ consumption coincides with the onset of anaerobic metabolism. Consequently, a Po₂ in this range is concluded to be equivalent to the critical Po₂. The early decrease in the levels of high-energy phosphates and the accumulation of large amounts of lactate in the kidney and, even more so, the heart indicate that limits in the O₂ supply to aerobic organs determine the hypoxia tolerance of the animal. The appearance of lactate in the plasma and the concomitant increase in O₂ consumption suggest that lactate may mediate this increase, thus eliciting a stress response.

Comparison of 6-min ???all-out??? and incremental exercise tests in elite oarsmen

A high aerobic capacity is an important criterion for rowing success. Two exercise protocols, the 6-min "all-out" (6M-AO) and progressive incremental (PI) tests, have been used to evaluate physiological performance in rowers and to select team members. We measured heart rate (HR), minute ventilation (VE), oxygen consumption (VO2), and carbon dioxide production (VCO2) every 30 s, and obtained ratings of perceived exertion (RPE) from 12 candidates for the 1983 United States Men's Lightweight Rowing Team. Testing was randomized and each oarsman performed a different test on the rowing ergometer on consecutive days. For the group, age was 23 +/- 2 yr (mean +/- SD), height was 183 +/- 3 cm, and weight was 72.2 +/- 1.4 kg. Peak physiological values were achieved in the first 2 min of exercise for the 6M-AO test, but in the last 2 min for the PI test. There were no statistically significant differences among peak values for HR, VE, VO2, VCO2, and RPE with each test. The peak ventilatory equivalent for oxygen (VE/VO2) was also similar. The onset of anaerobic metabolism was observed at 83 +/- 4% of peak VO2 during the PI test, while anaerobic metabolism has been shown to occur within the first minute of the 6M-AO test. We conclude that physiological values at peak exercise were similar for the 6M-AO and PI tests. Because the onset of anaerobic metabolism can only be determined by noninvasive means using the PI test, this method of testing is preferable for the physiological assessment of rowing performance.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerobic parameters of exercise as a function of body size during growth in children.

To examine the relationship between body weight in children and aerobic parameters of exercise, we determined the anaerobic threshold (AT), maximum O2 uptake (VO2max), work efficiency, and response time for O2 uptake (RT-VO2) in 109 healthy children (51 girls and 58 boys, range 6-17 yr old) using a cross-sectional study design. Gas exchange during exercise was measured breath by breath. The protocol consisted of cycle ergometry and a linearly increasing work rate (ramp) to the limit of the subject's tolerance. Both AT and VO2max increased systematically with body weight, whereas work efficiency and RT-VO2 were virtually independent of body size. The ratio of AT to VO2max decreased slightly with age, and its mean value was 60%. AT scaled to body weight to the power of 0.92, not significantly different from the power of 1.01 for VO2max. Thus both the AT and the VO2max increase in a highly ordered manner with increasing size, and as judged by AT/VO2max, the onset of anaerobic metabolism during exercise occurred at a relatively constant proportion of the overall limit of the gas transport system. We conclude that in children cardiorespiratory responses to exercise are regulated at optimized values despite overall change in body size during growth.

Oxygen uptake and heat production in a metabolic conformer (Littorina irrorata) and a metabolic regulator (Uca pugnax)

The heat production of Littorina irrorata and Uca pugnax in air was measured with a twin calorimeter while oxygen tension was measured with a pO2 electrode. Both L. irrorata, an oxyconformer, and U. pugnax, a metabolic regulator, showed a rapid decrease in oxygen uptake (below 1.3 mm Hg in L. irrorata and 13.4 mm Hg in U. pugnax) while heat production decreased more slowly. Consequently, during the period of minimum oxygen uptake, the oxycalorific coefficient increased from about 4.8 for both species to an average value of 8.3 in L. irrorata and 19.9 cal ml-1 O2 in U. pugnax, indicating the onset of anaerobic metabolism and accumulation of metabolic and products. Above their respective critical pO2, the oxycalorific coefficient was the same as the commonly used conversion factor of 4.8 cal ml-1 O2. From one time interval to the next, however, the coefficient varied from 3.8 to 5.4 in L. irrorata and from 2.9 to 6.0 in U. pugnax, indicating, that the processes of oxygen consumption and heat production are more or less independent of each other and usually not in phase.