Total O2 Uptake Research Articles

Skeletal muscle mitochondria: the aerobic gate?

At an animal's maximum aerobic capacity (VO2max), the O2 flowing through the respiratory system is consumed by a functionally exclusive sink, skeletal muscle mitochondria. Thus, O2 consumption will never exceed the muscles O2 demand. If the system is ideally designed, structures upstream to the skeletal muscle O2 sink must be built to insure adequate O2 delivery to the working muscle. There are a number of structure-function solutions available to supply the demanded O2 to the muscle; these have been found to vary, often ontogenetically, with hypoxia, training, etc. But there is one relationship that is invariant: Total O2 uptake can be predicted by the total (active) skeletal muscle mitochondrial volume. In aerobic and sedentary animals, across a range of body sizes, maximum (in vivo) mitochondrial O2 consumption is constant among mammals (at approximately 2000 O2 molecules per square micron of inner mitochondrial membrane per second). Because the volume of mitochondria is one of the most plastic of all respiratory structures, we interpret this relationship as suggesting that skeletal muscle mitochondria alone sets the demand for O2 and, thus, the volume of skeletal muscle mitochondria dictates an animal's maximum aerobic capacity.

Improved estimation of total oxygen uptake in exercise by evaluation of aerobic fitness.

The purpose of the present study was to contrive a new practical method for estimating total O2 uptake during exercise from total heart beats after individual evaluation of aerobic fitness levels. Twenty healthy male subjects participated in cycle ergometer tests, maximal O2 uptake (VO2max) tests and various simple tests including simple endurance tests. From the cycle ergometer results, the following formula for estimating total O2 uptake in exercise was determined: TVO2 (ml X kg-1) = SR125 X (45.8 X mean HR + 4268) X THB X 10(-4) where TVO2, THB, and mean HR are total O2 uptake, total heart beats, and mean heart rate (beats X min-1) in exercise, respectively, and SR125 is the slope of the regression line between accumulated heart beats and accumulated O2 uptake during exercise at 125 beats X min-1 of mean HR. SR125 had a significant correlation not only with VO2max but also with each score (X) in any simple endurance tests such as, for example, a step test for 2 min. In this case, accordingly, SR125 can be found as; SR125 = -0.00118X + 0.3478. These formulae indicate that the total O2 uptake of any exercising subject can be estimated from his total heart beats regardless of intensities of exercise when his aerobic fitness level is evaluated by the simple endurance test. The total O2 uptake estimated by our method was compared to that measured by the Douglas bag method, and the discrepancy between the two results was less than the errors of values estimated by traditional methods.

On the nature of the oxygen uptake in the light by Chondrus crispus. Effects of inhibitors, temperature and light intensity

The nature of the different processes of O2 uptake involved in the light in the red macroalga Chondrus crispus Stackhouse (Rhodophyta, Gigartinales) was investigated. At limiting CO2, INH (2.5 mM) did not alter the O2 uptake rate. Glycolate was not excreted and did not accumulate within the cells. KCN reduced the rate of O2 uptake in the light by 76% at limiting CO2 and by 43% at saturating CO2, but caused > 95% inhibition of O2 evolution. DCMU (5 μM) totally blocked the photosynthetic electron transport chain, but allowed a residual O2 uptake of 3.0±0.6 μmol O2 .h(-1).g(-1) FW, irrespective of the CO2 concentration. In saturating CO2, a high light intensity pretreatment significantly stimulated the rate of O2 uptake compared to net O2 evolution, suggesting the persistence, in the light, of mitochondrial respiration. Irrespective of the CO2 concentration, the optimum temperature for O2 evolution was 17°C whereas dark O2 uptake increased linearly with temperature. In contrast, O2 uptake in the light showed an optimum at 17°C in limiting CO2, and 21-25° C in saturating CO2; its Q10 was 2.4 at limiting CO2, a value close to that of RuBP oxygenase, and 3.1 at saturating CO2, a value close to that of dark respiration. It is concluded that: 1) mitochondrial respiration and Mehler reaction are both involved at all CO2 concentrations, 2) RuBP oxygenase activity cannot account for more than 45%, and Mehler reaction for less than 20%, of the total O2 uptake observed in the light at limiting CO2.

Cutaneous and gill O2 uptake in the European eel (Anguilla anguilla L.) in relation to ambient PO2, 10–400 Torr

The partition of O2 uptake between gills and skin was examined in the freshwater eel (Anguilla anguilla L.) at ambient PO2 ranging from hyperoxia (PO2 = 400 Torr) to severe hypoxia (PO2 = 10 Torr) using a technique of open-flow respirometry. All the expired water was collected, and the ventilatory flow and the mixed expired water PO2 were directly measured. The ventilatory water flow decreased moderately in hyperoxia, increased markedly between normoxia and 40 Torr, and below 40 Torr, hyperventilation was gradually reduced. Between PO2 400 and 70 Torr, the total O2 uptake was constant and the skin O2 uptake was lower than gill O2 uptake (32% of total uptake in normoxia). Between 70 and 10 Torr, the skin contribution to the total O2 uptake progressively increased, and was higher than gill O2 uptake in severe hypoxia. A possible facilitation of cutaneous O2 uptake in hypoxia is discussed from estimates of the O2 diffusing capacity of the skin.

Lactate as a cerebral metabolic fuel for glucose-6-phosphatase deficient children.

The main substrates for brain energy metabolism were measured in blood samples taken from the carotid artery and the internal jugular bulb of four children with glycogen storage disease caused by deficiency of glucose-6-phosphatase. Multiple paired arterial and venous blood samples were analyzed for glucose, lactate, pyruvate, D-beta-hydroxybutyrate, acetoacetate, glycerol and O2, and the arteriovenous differences of the concentrations were calculated. In the first three patients the substrates were measured in two successive conditions with lower and higher glucose-intake, respectively, inducing reciprocally higher and lower concentrations of blood lactate. In the fourth patient medium chain triglycerides were administered simultaneously with the glucose-containing gastric drip feeding. Lactate appeared to be taken up significantly. It consumed, if completely oxidized, between 40-50% of the total O2 uptake in most cases. Only once in one patient the uptake of lactate switched to its release, when the blood lactate level decreased to normal. D-beta-hydroxybutyrate and acetoacetate arteriovenous (A-V) differences were small to negligible and these ketone bodies, therefore, did not contribute substantially to the brain's energy expenditure. Glycerol was not metabolized by the brain. Lactate thus appeared to be the second brain fuel next to glucose. It may protect the brain against fuel depletion in case of hypoglycemia.

Cardiovascular and metabolic responses to carotid clamping in anemic dogs.

It has been observed that blood flow to the hindlimb was maintained or even increased in proportion to cardiac output during isovolemic hemodilution of anesthetized dogs with dextran (Grupp et al., 1972; Cain and Chapler, 1978; 1981). This was true even when the decrease in total O2 transport limited whole body O2 uptake. In one study, we infused norepinephrine to increase vasoconstrictor tone. The results suggested that the reduction in viscosity prevented any measurable increase in hindlimb resistance during anemia so that blood flow could not be redistributed to areas more essential than resting skeletal muscle. In these new experiments we have used a more physiologic cardiovascular challenge, clamping of the carotid arteries, to see if lowered blood viscosity alters the response to baroreceptor stimulation. As will be shown, the buffering effect of aortic baroreceptors prevented much change in the peripheral resistance but carotid clamping did alter O2 uptake.KeywordsCardiac OutputStroke VolumeStroke WorkSystemic Arterial Blood PressureLimb Blood FlowThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Physiological and Behavioural Aspects of Water Balance and Respiratory Function in the Terrestrial Slug, Limax Maximus

ABSTRACT A method is described for establishing a stable relationship between body weight and hydration (i.e. 100% hydrated) in terrestrial slugs. This allows the use of ‘% initial body weight’ as an indicator of relative body hydration. During progressive dehydration in the slug, Umax maximus (L.), the haemolymph osmolality increases exponentially. This, together with measurements of wet weight/dry weight ratios of various tissues, indicates that the water loss during the initial stages of dehydration is from the haemolymph. Although long-term (days) cyclical changes in body hydration were not observed, a daily cycle is described with highs at 12.00 midnight and lows at 12.00 noon. It is shown that the huddling behaviour of slugs can reduce evaporative water loss from individual slugs. Dehydration of a slug to about 90 % of its initial body weight initiates a rhythmic cycle of pneumostome closures. Further dehydration results in an increase in the duration of the closures and reduction of the diameter of the pneumostome when open. The absolute and relative O2 uptake by the integument and lung are presented. In quiet slugs, the lung is responsible for about 20 % of the total O2 uptake, while in active slugs it is responsible for 50 % of the total. During activity there is a greater increase of O2 uptake across the lung than across the integument.

Sustained branchial apnea in the Australian short‐finned eel, Anguilla australis

Branchial and cutaneous O2 uptake as well as branchial ventilatory stroke volume and frequency were measured by twin-chamber respirometry in conscious unoperated eels (Anguilla australis) at 20 degrees C. The branchial ventilatory pattern comprised alternating periods of apnea and eupnea, together constituting a "Standard Breathing Cycle" (SBC = 1 apneic period plus the ensuing period of eupnea). SBC time in 17 eels averaged 15.5 min of which only 23% was devoted to eupnea. Reduction of the PO2 of inspired water from 155 to 80 torr significantly increased the proportion of time devoted to eupnea to 49% of SBC time without significantly changing SBC time. Absolute cutaneous O2 uptake (5.8 ml O2 X h-1 X kg-1) was largely independent of the frequency or occurrence of eupnea, with the relative contribution of the skin to total O2 uptake averaging 47%. The histological appearance of the skin in A. australis is very similar to that described in A. anguilla: eel skin is only poorly vascularized. It was concluded that the skin may contribute to O2 requirements other than its own, and that this adaptation is a consequence of the unusual intermittent pattern of gill ventilation.

Total and hindlimb O2 uptake and blood flow in hypoxic dogs given dopamine.

Cardiovascular interactions between dopamine and hypoxia were examined in 8 anesthetized, paralyzed dogs ventilated at constant rates. Total and hindlimb (less paw) O2 uptake, blood flow, and vascular resistance were measured with and without dopamine infusion of 10 micrograms/kg . min during both normoxic and hypoxic ventilation. Another 8 dogs were similarly treated after beta-blockade with propranolol infusion (1 mg/kg). During the baseline period, normoxic dopamine significantly increased total O2 uptake, cardiac output, and stroke volume, and significantly decreased total vascular resistance in the control group. Hypoxia decreased total O2 uptake, cardiac output, and heart rate but increased total vascular resistance. Dopamine reversed each of these hypoxic changes and restored total O2 uptake to normoxic levels. Hindlimb measurements were not significantly changed by dopamine or hypoxia in the control group. During hypoxia, beta-blockade abolished dopamine's effects except for the decrease in total vascular resistance. The improvement in cardiac output and O2 transport by dopamine infusion resulted from increased stroke volume during normoxia and from increased heart rate during hypoxia.

Gastrointestinal tract O2 uptake and regional blood flows during digestion in conscious newborn lambs

We determined gastrointestinal tract O2 uptake, cardiac output, regional blood flows, and whole-body O2 uptake before and for 1-6 h after feeding in 10 chronically catheterized unanesthetized lambs (9-15 days of age). Total gastrointestinal blood flow (sum of blood flows to the stomach, small intestine, and colon, as calculated with the radioactive microsphere technique) increased 23% at 1 h postprandially. This increased flow at 1 h was due to a large increase in blood flow to the stomach, whereas blood flows to the small intestine and colon did not change significantly. By 2 h, stomach blood flow and thus total gastrointestinal blood flow had returned to fasting values. In contrast, total O2 uptake by the gastrointestinal tract organs (stomach, small intestine, and colon) increased 65% at 1 h, 51% at 2 h, and 28% at 3 h postprandially in association with increases in O2 extraction (O2 uptake/O2 delivery) of 41% at 1 h, 45% at 2 h, and 27% at 3 h. There were no digestion-related changes in whole-body O2 uptake or in cardiac output and its distribution to the brain, heart, kidney, liver (hepatic artery), and carcass. Our data indicate that postprandial increases in O2 demand by gastrointestinal tract organs of the newborn animal are met primarily by enhanced tissue O2 extraction, rather than by metabolic hyperemia, because the postprandial hyperemia observed in the neonate is of short duration and is confined to the stomach.

O2 extraction by canine hindlimb during alpha-adrenergic blockade and hypoxic hypoxia.

Hindlimb and total blood flow and O2 uptake were measured in anesthetized paralyzed dogs in which venous outflow from the left hindlimb (less paw) was directed through the femoral vein. After ventilation on room air, 10 dogs were given 3 mg/kg phenoxybenzamine + 10 ml/kg dextran and 10 other dogs were isovolemically exchanged with 10 ml/kg dextran without alpha-block while continuing to be ventilated on room air. All animals were then ventilated with 9.1% O2 in N2, followed by a recovery period on room air. Total and limb peripheral resistances were lowered by alpha-block, but total and limb blood flow changed little from control levels. Both total and limb O2 uptake were decreased below control values during hypoxia. Cardiac output and limb blood flow increased during hypoxia in both groups. Although alpha-block caused O2 extraction by the whole body to be less during hypoxia than in unblocked dogs, the hindlimb in both groups extracted O2 equally well. We concluded that skeletal muscle was not overperfused relative to O2 demand when alpha-blocked during hypoxia.

Temperature insensitive O2 in blood of the tree frogChiromantis petersi

Respiratory gas exchange and blood respiratory properties have been studied in the East-African tree frogChiromantis petersi. This frog is unusually xerophilous, occupies dry habitats and prefers body temperatures near 40°C and direct solar exposure. Total O2 uptake was low at 81 μl O2·g−1·h−1±19.0 (SD) at 25°C increasing to 253.5 μl O2·g−1·h−1±94.8 (SD) at 40°C giving aQ10 value of 2.1. Skin O2 uptake at 25°C was 38.5% of total. The gas exchange ratio was 0.71 for whole body gas exchange, 0.61 for the lungs and 1.02 for the skin at 25°C.

Oxygen extraction by canine hindlimb during hypoxic hypoxia

Regional and total blood flow and O2 uptake (VO2) were measured in 10 anesthetized paralyzed dogs in which venous outflow from the left hindlimb (less paw) was directed through the femoral vein. After being ventilated on room air during a 40-min control period, they were ventilated on 12.0% O2 for 40 min, 9.2% O2 for 40 min, and again on room air for 40 min. A second group of 10 was treated the same after they were given 1.0 mg/kg propranolol to block beta-adrenergic receptors. Neither limb blood flow nor cardiac output changed significantly during moderate hypoxia in either group; both increased in severe hypoxia but only in the no-beta-block group. Limb VO2 was not decreased significantly in either group during moderate hypoxia but total VO2 was decreased in the beta-block group. Total VO2 was decreased in both groups during severe hypoxia but limb VO2 was maintained in the beta-block group. beta-Block prevented the fall in total and limb peripheral resistance seen in severe hypoxia but did not alter the consistently more efficient utilization of total O2 delivery shown by the limb in comparison to the whole body by higher O2 extraction ratios and lower venous O2 pressure. beta-Vasodilator receptors evidently played an active part in the vasodilatation seen during severe hypoxia.

BIMODAL GAS EXCHANGE AND THE REGULATION OF OXYGEN UPTAKE IN HOLOTHURIANS

In air-saturated sea water, 60% of the total O2 uptake by Cucumaria frondosa (epifaunal) and Sclerodactyla briareus (infaunal) occurs through the respiratory trees. When the cloacal opening of C. frondosa is occluded, weight-specific O2 uptake decreases with weight more than in intact specimens, indicating an increasing dependence of large individuals on their respiratory trees. Likewise, cloaca occlusion results in a proportionately greater loss of oxyregulatory ability in large C. frondosa. Neither of these results occurs in S. briareus, which compensates for loss of the trees by increasing O2 uptake across the general body surface.In intact animals, the greater oxyregulatory ability of S. briareus relative to C. frondosa is also due to the former's having less of a decline in frequency combined with a more pronounced increase in volume per pumping cycle of the respiratory tree irrigation rhythm, resulting in an increase in total volume of water pumped, as Po2 declines; in C. frondosa, this volume decli...

Ventilation and gas exchange in the diamondback water snake,Natrix rhombifera

Simultaneous measurements of pulmonary and cutaneous oxygen and carbon dioxide exchange, pulmonary ventilation and heart rate were made on the diamondback water snake,Natrix rhombifera at 28°C using body plethysmography. Resting lung volume, maximum lung volume and tracheal volume were also measured. The following mean values were measured in undisturbed snakes breathing room air: total (pulmonary and cutaneous) O2 uptake 46 μmol · (kg min)−1; total CO2 output, 49 μmol · (kg min)−1; tidal volume, 12 ml (BTPS) · kg−1; ventilatory rate, 6.9 min−1; heart rate, 42 min−1. From the measurements of tracheal volume, the effective (alveolar) ventilation was estimated as approximately 70% of total ventilation resulting in effective pulmonary $$P_{O_2 }$$ and $$P_{CO_2 }$$ of 130 Torr and 20 Torr respectively. Cutaneous exchange accounted for 8.1% of the total $$\dot M_{O_2 }$$ and 12.4% of the total $$\dot M_{CO_2 }$$ . Resting lung volume of anaesthetized snakes was 75 ml (BTPS) · kg−1, maximum lung volume was 341 ml (BTPS) · kg−1 and tracheal volume was 3.9 ml (BTPS) · kg−1.

Effect of altered thyroid status induced by thyroid hormones, goitrogens and diet on intestinal electrogenic valine transfer.

The kinetics of the electrogenic transfer of valine across rat jejunum was studied in vitro with an electrical technique. The operational kinetic parameters of ‘apparent K m ’ and the p. d. max (maximum transfer potential difference generated) were calculated and used to characterize the effects of diet and thyroid status on the electrogenic valine transfer mechanism. Hypothyroidism induced by 6-propyl-2-thiouracil (PTU), potassium thiocyanate, surgery or diet significantly increased the p. d. max but not the ‘apparent K m ’. Triiodothyronine (T 3 ) treatment reduced the elevated p. d. max in both the PTU-treated and thyroidectomized rats but thyroxine (T 4 ) was ineffective in the PTU group. The p. d. max and ‘apparent K m ’ in euthyroid rats were decreased by T 3 and T 4 but were unaltered by a 3-day fast. Fasting hypothyroid rats, however, did prevent the enhancement of p. d. max observed in hypothyroidism. Significant differences were observed in the p. d. max , the percentage 131 I protein bound in the serum and percentage 131 I uptake by the thyroid in rats fed notionally similar diets manufactured by two different suppliers but no differences were observed in total body O 2 uptake. The results obtained on giving supplemental iodine indicated that one of the diets altered thyroid function which significantly affected electrogenic valine transfer but not total body oxygen uptake. Thus electrogenic valine transfer is a more sensitive index of change in thyroid status than its conventional measure by total body oxygen uptake.

Gas exchange and active ventilation in a starfish, Pteraster tesselatus

1. The oxygen uptake of the cushion star Pteraster tesselatus was independent of ambient tension down to about 70 mm Hg and showed an average value of 10.5 ml/kg/hr in normoxic water in the range 10–12° C. The average uptake decreased approximately 2.65 times when the temperature was lowered from 10–12 to 5° C. 2. Oxygen extraction from the respiratory water current averaged 18 % at normoxic conditions. Effectiveness of oxygen removal was slightly higher than 50%; this is a very high value when compared with those of the crab Cancer magister and the cephalopod Octopus dofleini. 3. The exceptional ability of Pteraster to regulate its O2 uptake is based on the active irrigation of the dermal branchiae in the nidamental cavity. About 90 % of the total O2 uptake is derived from the active ventilation, the remaining 10 % being ascribed to passive diffusion through the body surface and tube feet. Ventilation values, measured with a termal velocity probe directly over the osculum, averaged 70 ml/min. 4. The transfer factor for Pteraster at 10–12° C was 0.0048 ml O2/kg/min/mm Hg, as compared with 0.0062 for Octopus dofleini and 0.0043 for Cancer magister. 5. Normal CO2 tensions in the coelomic fluid ranged between 1.00–1.40 mm Hg; coelomic fluid pH values ranged between 7.33–7.46 when the animals were in well aerated water at 11–12° C. 6. An effective barrier exists between the large fluid compartment of the stomach and the coelomic fluid, as indicated by measurements in both compartments. 7. The ability of Pteraster to regulate O2 uptake and the values for coelomic fluid tensions under different conditions, indicate that the principal determinant of the O2 uptake rate is the O2 tension prevailing at the tissues level.

O2 consumption and metabolite balance in the dog gastrocnemius at rest and during exercise

In a gastrocnemius muscle “in situ” performing isotonic contractions, blood flow, O2 consumption, CO2 production, the balance of glucose, lactic acid, free fatty acids and total esterified fatty acids were measured. The RQ increased from a resting value of 0.75 to a value of 0.89 at the highest exercise levels. The net glucose uptake from blood (glucose uptake-lactic acid output) could account, at rest, for 53%, and during exercise, for 30% of the total O2 uptake. The uptake of free fatty acids was practically nil at rest, while it could account for about 15% of the O2 consumed at exercise. Comparison of the metabolites balance with the energy contributed by oxidation of carbohydrates and lipids, as computed from $$\dot V_{{\text{O}}_{\text{2}} }$$ and RQ, provides evidence for a sizable storage of carbohydrates in the resting muscle, for a depletion of the stores during exercise and for oxidation of a substrate, probably lipid stored in the muscle, resulting in a low RQ.

Circulatory and ventilatory effects of exercise in smokers and nonsmokers.

To evaluate the effects of cigarette smoking on some of the circulatory and ventilatory responses to exercise, a group of young male subjects, 18 smokers and 14 nonsmokers, was studied. Exercise consisted of a standard 5-min bicycle ergometer test that achieved a mean O2 uptake of 1.44 liters/ min in the 5th min of exercise. There was no difference between smokers and nonsmokers in the O2 uptake achieved during subsequent maximal exercise. Pulmonary function studies performed on the two groups revealed normal results for each group. There was an oxygen debt accumulation among smokers that was significantly greater ( P < 0.001) and this debt represented a greater per cent of the total O2 uptake. The heart rate at rest and 3 min after exercise in smokers was significantly faster ( P < 0.02). These differences do not appear to be related to ventilatory factors and may, therefore, be due to either circulatory or metabolic differences in the two groups. Submitted on August 17, 1962

Blood glucose metabolism in man during muscular work.

A resting human subject was given an intravenous injection of a “trace” dose of glucose-U-C14, and blood and respiratory CO2 samples were collected during ensuing rest, exercise, and rest periods. The CO2 was assayed for radioactivity, and the blood was assayed for total and radioactive glucose and lactate. Total O2 uptake and CO2 output were also measured. In the initial rest period, blood glucose and lactate remained constant while their specific activities declined exponentially. Immediately with onset of exercise, blood lactate level and CO2 excretion increased greatly, but their low specific activities in comparison with that of the blood glucose indicated their origin from endogenous substrates, presumably muscle glycogen. During the subsequent recovery period the specific activities of lactate and CO2 rose while the blood lactate and respiratory CO2 excretion dropped to normal levels. Although the level of blood glucose did not change markedly, its specific activity fell more rapidly during work than during rest, indicating a greater “turnover.” However, this increased turnover began some time after commencement of work and continued into the subsequent recovery period. These findings suggest that the stored muscle glycogen represents the immediate fuel for glycolysis and respiration of working muscle. Subsequently, there is an increased uptake of the blood glucose by working muscle, compensated in the present experiments by an increased hepatic glucose output. The data are in accord with previous suggestions that there is a mechanism whereby muscular work stimulates glucose uptake. Submitted on July 27, 1961