Mean O2 Uptake Research Articles

Benthic O2 uptake by coral gardens at the Condor seamount (Azores)

Using the non-invasive aquatic eddy covariance technique, we provide the first oxygen (O2) uptake rates from within coral gardens at the Condor seamount (Azores). To explore some of the key drivers of the benthic O2 demand, we obtained benthic images, quantified local hydrodynamics, and estimated phototrophic biomass and deposition dynamics with a long-term moored sediment trap. The coral gardens were dominated by the octocorals Viminella flagellum and Dentomuricea aff. meteor. Daily rates of O2 uptake within 3 targeted coral garden sites (203 to 206 m depth) ranged from 10.0 ± 0.88 to 18.8 ± 2.0 mmol m-2 d-1 (mean ± SE) and were up to 10 times higher than 2 local sandy reference sites within the seamount summit area. The overall mean O2 uptake rate for the garden (13.4 mmol m-2 d-1) was twice the global mean for sedimentary habitats at comparable depths. Combined with parallel ex situ incubations, the results suggest that the octocorals might contribute just ~5% of the observed O2 uptake rates. Deposition of particulate organic matter (POM) assessed by the sediment trap accounted for less than 10% of the O2 demand of the coral garden, implying a substantial POM supply circumventing the deployed traps. Our results expand the database for carbon turnover rates in cold-water coral habitats by including the first estimates from these largely understudied coral gardens.

Cardiac Function and SMO2 During HIIT at Altitude and Sea Level with Oxygen Contrast Training

PURPOSE: This study investigated how high-intensity interval training (HIIT) at altitude (ALT) versus sea level (SL) with and without supplemental oxygen recovery (SRO2) affected cardiac function and skeletal muscle %O2 saturation (SMO2). METHODS: Eight cyclists aged 42.4 ± 7.7 (HT: 68.9 ± 4.6; WT: 177.9 ± 26.6; Body Fat: 19.3% ± 7.5%; VO2 max L/min 4.38 ± 1.01) performed a baseline cycling VO2max test and four treatment trials (TRA - ALTHIIT/SRO2; TRB - SLHIIT/SLrecovery; TRC - ALTHIIT/ SLrecovery; TRD - steady-state (SS) cycling). Each HIIT work period (n=3) was 75s with 120s recovery at 75% and 50% of VO2max, respectively. For TRD, subjects cycled at a workload equal to the mean O2 uptake equal of TRB (Control-Trial). O2 uptake was measured using a breath X breath metabolic cart for VO2 max and TRB. Cardiac function (HR, Cardiac Output (Q), Stroke Volume (SV)) was assessed using impedance cardiography. SMO2 was measured in the vastus-intermedius quadricep muscles using Moxy NIR devices. Data was analyzed using a w/in repeated measures design (Treatment (4) X 3 HIIT/Recovery Periods). RESULTS: Despite identical workloads, HR was significantly lower during SS cycling compared to the HIIT trials by 7.6% (SS: 118.0 ± 3.4; Mean HIIT TR HRs: 127.0 ± 3.7, p=0.002). ALTHIIT/SRO2 (TRA: 141.8 ± 9.2) showed a lower SV by 8.4% compared to the ALTHIIT/SLrecovery trial (TRC: 154.3 ± 9.2). Q was significantly lower during the HIITw/SRO2 (TRA:17.7 ± 1.1) compared to SLHIIT/SLrecovery & ALTHIIT/SLrecovery (TRB: 19.8 ± 1.1; TRC:19.8 ± 1.1) by 12% (P=0.04). SMO2 data showed a trend for ALTHIIT/SRO2 & SS cycling to have higher SMO2 values compared to the both HIIT trials without SRO2 (p=0.09). During recovery, ALTHIIT/SRO2 showed improved HR recovery 5.2% (p=0.01), increased SMO2 re- saturation rate 12.6% (p=0.01), and lowered Q 11.9% (p=0.01) compared to the altitude-sea level recovery trial. CONCLUSION: These results suggested that supplemental O2 recovery lowered cardiac demand (Q) at the same HIIT workload by maintaining HIIT SMO2 better by enhancing the overall recovery process. Supported by a grant from LiveO2 and Exercising Nutritionally, LLC

Does the Strength and Endurance Training Sequence Affect Cardiorespiratory Adaptations in Women?

Strenuous strength (S) protocols may lead to acute decreases in work economy during subsequent endurance (E) exercise. Therefore, when performing prolonged S and E training combined within the same-session, the exercise sequence may affect the magnitude of training-induced cardiorespiratory adaptations. PURPOSE: To investigate the differences of same-session combined training with different exercise sequences (S followed by E [SE] and ES) on maximal (VO2max) and sub-maximal (VO2sub) oxygen uptake (O2). METHODS: Physically active women (30±5 yrs, 166±6 cm, 66±10 kg) were assigned to an ES (n=15) or SE (n=13) group and trained for 2x12 wks. Subjects performed 2x SE or ES during wks 0-12 and 2.5x SE or ES during wks 13-24. S mainly focused on lower limbs with loads of 70-95% of 1RM. E consisted of steady-state and interval cycling (30-50 min/session) with increasing intensity throughout 24 wks. VO2max and VO2sub were measured during an incremental cycle test (2 min increments of 25 W). VO2sub was defined as the mean O2 uptake of the 2nd min at each load. RESULTS: VO2max increased similarly in SE and ES during wks 0-12 (from 34±5 to 36±5 and 31±4 to 33±4 ml·kg-1·min-1, p=0.072 and 0.030 respectively) and 0-24 (to 37±5 and 34±4 ml·kg-1·min-1, p=0.002 and 0.009 respectively). VO2sub of increasing loads completed by all subjects is presented in the Table.Table: No title available.CONCLUSION: This study showed that the exercise sequence did not affect adaptations in VO2max in women following 24 wks of training. However, during the first 12 wks, VO2sub was lower in ES compared to SE at 50, 100 and 125 W, but no btw-group differences were observed after 24 wks. These findings indicate that during the initial 12 wks of training S performed before E may attenuate the adaptations in VO2sub, while over long-term the training mode did not affect cardiorespiratory adaptations in women.

Effect of aerial O2 partial pressure on bimodal gas exchange and air-breathing behaviour inTrichogaster leeri

The effects of experimental alterations of aerial O2 partial pressure (PO2,air) on bimodal gas exchange and air-breathing behaviour were investigated in the aquatic air-breathing fish Trichogaster leeri in normoxic water. Fish responded to increasing PO2,air by decreasing air-breathing frequency, increasing aerial O2 consumption rate (VO2), increasing mean O2 uptake per breath (VO2/breath) and decreasing aquatic VO2 to maintain a constant total VO2. The rate of oxygen uptake from the air-breathing organ (ABO) during apnoea (VO2,ap) was derived on a breath-by-breath basis from VO2/breath and apnoea duration. VO2,ap and estimates of ABO volume were used to calculate the PO2 in the ABO at the end of apnoea. This increased with increasing PO2,air, suggesting that ABO-PO2 is not regulated at a constant level by internal chemoreceptors. Furthermore, mean VO2,ap increased with increasing PO2,air, indicating that the observed increase in VO2/breath with increasing PO2,air was facilitated not only by an increase in apnoea duration but also by an increase in the air-blood PO2 gradient.

Short-term Reliability of Oxygen Uptake On-kinetics in Apparently Healthy Subjects

The analysis of oxygen (O2) uptake on-kinetics at the onset of aerobic exercise has been shown to be reflective of cardiovascular and skeletal muscle health in a number of previous investigations. The purpose of the present investigation is to assess the short-term reliability of O2 uptake on-kinetics in a group of apparently healthy individuals. Forty apparently healthy subjects participated in 3 consecutive treadmill exercise sessions on 3 consecutive days. During each session, O2 uptake was collected at rest for 2 minutes and during ambulation at 2.2 miles per hour and a 6% grade for 6 minutes. The time constant (TC) for the O2 uptake response was calculated for each of the 3 sessions using the equation: O2(t) = O2(resting) + O2(steady-rate)[1 - e]. Two subjects did not adhere to the physical activity guidelines and were excluded from data analysis. The following data are representative of the remaining 38 subjects. The mean O2 uptake TC value for the 3 sessions was 33.67 +/- 7.87, 34.59 +/- 7.57, and 32.59 +/- 6.64 seconds, respectively. The intraclass correlation coefficient for the O2 uptake TC was 0.84 (P < .001). The results of the present study indicate O2 uptake on-kinetics may be reliably measured using a single testing session. Multiple testing sessions, which would limit the potential clinical application of O2 uptake on-kinetics, may therefore not be necessary. Future research should be directed toward determining if O2 uptake on-kinetics is equally reliable in patient populations.

Bioaugmentation as a method of biodegradation enhancement in oil hydrocarbons contaminated soil

Respirometry studies using the 10-chamber Micro-Oxymax respirometer (Columbus, Ohio) were conducted to determine the effect of adding bacterial consortium for enhancing biodegradation in soils contaminated with oil hydrocarbons from the former military airport. Bioaugmentation was carried out using both indigenous and extraneous bacteria able to degrade hydrocarbons. The potentials of intrinsic and enhanced biodegradation were evaluated by the mean O2 uptake and CO2 production rates. The results demonstrated that the highest biodegradation rates were achieved using bacterial consortium containing 4.8×1015 Colony Forming Units (CFU) cm−3. Generally, in all cases, enhanced biodegradation rates were four times higher than intrinsic biodegradation rates. Moreover, application of indigenous bacterial consortia was more efficient in comparison to the employment of extraneous bacterial consortia. This study showed that bioaugmentation could be an effective method for enhancing intrinsic biodegradation of oil hydrocarbons in soil.

Residual effects of prior exercise and recovery on subsequent exercise-induced metabolic responses

Data on the metabolic responses to repeated endurance exercise sessions are limited. Thus, the aims of this study were to examine (1) the impact of prior exercise on metabolic responses to a subsequent exercise session and (2) the effect of different recovery periods between two daily exercise sessions on metabolic responses to the second bout of exercise. Nine male elite athletes participated in four 25-h trials: one bout of exercise (ONE), two bouts of exercise separated by 3 h of rest and one meal (SHORT), two bouts of exercise separated by 6 h of rest and two meals (LONG), and a trial with no exercise (REST). All exercise bouts consisted of 10 min cycling at 50% followed by 65 min at 75% of maximal O2 uptake. Compared to no prior exercise (ONE), a previous bout of exercise (SHORT) was followed by higher mean O2 uptake, heart rate (HR), rectal temperature (TR), excess post-exercise oxygen consumption and lower respiratory exchange ratio (R) during and after a similar exercise session 3 h later. A longer rest interval between the two exercise bouts (6 h versus 3 h) and an additional meal resulted in a decrease in O2 uptake, HR, TR and an increase in R during the second bout of exercise, but no effects on post-exercise metabolism were found. Thus, augmented metabolic stress was observed when strenuous exercise was repeated after only 3 h of recovery, but this was attenuated when a longer recovery period including an additional meal was provided between the exercise sessions.

Muscle metabolism during exercise and heat stress in trained men: effect of acclimation

Exercise metabolism was examined in 13 endurance athletes who exercised on three occasions for 40 min at 70% of maximal O2 uptake in an environmental chamber at either 20 degrees C and 20% relative humidity (RTT) or 40 degrees C and 20% relative humidity before (PRE ACC) or after (POST ACC) 7 days of acclimation. Exercise in the heat resulted in a lower (P < 0.05) mean O2 uptake (0.13 l/min) and higher (P < 0.01) heart rate and respiratory exchange ratio. Acclimation resulted in a lower (P < 0.01) mean heart rate and respiratory exchange ratio. Postexercise rectal temperature, muscle temperature, muscle and blood lactate, and blood glucose were higher (P < 0.01) in the PRE ACC than in the RTT trial, but all were reduced (P < 0.01) in the POST ACC compared with the PRE ACC trial. Muscle glycogenolysis and percentage of type I muscle fibers showing glycogen depletion were greater (P < 0.05) in the PRE ACC than in the RTT trial. Muscle glycogenolysis was unaffected by acclimation during exercise in the heat, although the percentage of depleted type I fibers was higher (P < 0.05) in the unacclimated state. Plasma epinephrine was higher (P < 0.01) during exercise in the heat in the unacclimated individual relative to RTT but was lower (P < 0.01) in the POST ACC than in the PRE ACC trial. The greater reliance on carbohydrate as a fuel source during exercise in the heat appears to be partially reduced after acclimation. These alterations are consistent with the observed changes in plasma epinephrine concentrations.

Mechanisms of improved arterial oxygenation after peripheral chemoreceptor stimulation during hypoxic exercise.

Almitrine, a peripheral chemoreceptor agonist, has been reported to increase arterial O2 saturation (SaO2) without changing minute ventilation (VE) during hypoxic exercise (Giesbrecht et al. J. Appl. Physiol. 70: 1770-1774, 1991). To explain this finding, we studied pulmonary hemodynamics (right heart catheterization) and gas exchange (multiple inert gas elimination technique) in six healthy volunteers at rest and during heavy exercise in normobaric normoxia (fractional concentration of O2 in inspired air 0.21) or hypoxia (fractional concentration of O2 in inspired air 0.125), before and after 75 mg of almitrine taken orally. During normoxic exercise, at a mean O2 uptake (VO2) of 4.0 l/min, almitrine increased arterial PO2 (PaO2) (P < 0.05), SaO2 (P < 0.01), and VE (P < 0.05) and decreased arterial PCO2 (P < 0.01), without affecting pulmonary hemodynamics or ventilation-perfusion distributions. During hypoxic exercise, at a mean VO2 of 3.0 l/min, almitrine increased SaO2 (P < 0.01) and VE (P < 0.01) and decreased arterial PCO2 (P < 0.05), with no effect on PaO2 or on ventilation-perfusion distributions and with a slight pulmonary vasoconstriction (P < 0.01). Almitrine during hypoxia did not affect cardiac output or calculated O2 diffusing capacity, but it did increase the slope of the VE/VO2 relationship (P < 0.01). We conclude that during hypoxic exercise, a pharmacological stimulation of the peripheral chemoreceptors improves SaO2 but not PaO2 by means of increased ventilation and an associated leftward shift of the oxyhemoglobin dissociation curve.

Dependence of oxygen uptake on ambient PO2 in isolated perfused frog skin.

Rates of O2 uptake across isolated perfused skin of bullfrogs (Rana catesbeiana) were measured in relation to blood flow at three levels of ambient O2 tension: normoxia (O2 tension = 152 torr), hypoxia (12% O2, 87 torr) and hyperoxia (42% O2, 306 torr). At bulk perfusion rates ranging from 3.4 to 10.1 microliters.cm-2 x min-1, O2 uptake was positively correlated with hemoglobin delivery rate in both normoxia and hyperoxia, but was independent of delivery rate in hypoxia. Mean O2 uptake in normoxia was 3.8 nmol O2 x cm-2 x min-1 at a delivery rate of 9.8 nmol.cm-2 x min-1 and 6.5 nmol O2 x cm-2 x min-1 at a delivery rate of 28.3 nmol.cm-2 x min-1. At any given bulk perfusion rate, oxygen uptake averaged about 49% lower in hypoxia than in normoxia, decreasing in proportion to the reduction of O2 tension difference between medium and blood. In hyperoxia, O2 uptake did not increase proportionally with the difference in O2 tension between blood and medium, averaging only 50% higher at a 2.4-fold greater O2 tension difference. Cutaneous diffusing capacity for O2 averaged 0.041 nmol O2 x cm-2 x torr-1 x min-1 during the first hour of perfusion in normoxia, and was not affected by reduction of ambient O2 tension. The results indicate that cutaneous O2 uptake in hypoxia is highly diffusion limited, and consequently, increases in cutaneous perfusion can not effectively compensate for reduction of ambient O2 tension. In hyperoxia, O2 uptake may be substantially perfusion limited because of reduced blood O2 capacitance at high O2 saturations.

How Reliable are Short-term Measurements of Oxygen Uptake in Polytraumatized and Long-term Ventilated Patients?

O2-uptake was measured continuously in 18 polytraumatized and 21 long-term ventilated patients. All patients were on assisted ventilation with sufficient sedation and analgesia. O2-uptake was measured every minute, the values were recorded over 24 h and the mean O2-uptake/min was calculated. At the same time, the O2-uptake of the last 15 min of every hour was measured separately (e.g. 7.45-8.00, 8.45-9.00, etc.). The mean O2-uptake/min measured continuously was compared and correlated with the mean O2-uptake per day, calculated on the basis of each of the short-term measurements. There were only slight differences between the mean values of the two procedures: In the group of long-term ventilated patients the mean O2-uptake was found to be 364 ml/min in continuous measurements and 363 ml/min in short-term measurements. This O2-uptake corresponded to an energy expenditure of 2360 kcal/day. The mean correlation coefficient was 0.89 (range: 0.79-0.96). If O2-uptake was measured over 2 periods of 15 min each, e.g. in the late morning and in the afternoon, the mean correlation coefficient improved to 0.94 and the standard deviation was reduced. Comparable results were obtained in the group of polytraumatized patients. This study shows that under certain preconditions short-term measurements of O2-uptake of 2 x 15 min allow sufficiently reliable predictions of the daily O2-uptake and energy expenditure in severely traumatized or critically ill patients.

Automated systems for measurement of oxygen uptake during exercise testing.

We evaluated three automated systems for measurement of O2 uptake and compared them with the conventional Douglas bag method. One system (9000 IV Ergometric system) was only tested with respect to its oxygen kinetics, the other two (MMC-Horizon and EOS-Sprint) were tested during three exercise programs: (1) steady-state exercise at 50-W steps from 0 to 200 W, (2) progressive increasing exercise to maximal load, and (3) single-step exercise from 0 to 250 W. The regression lines of mean O2 uptake and load for six subjects were different for intercept (MMC-Horizon) or slope (EOS-Sprint) compared with the conventional method. The maximal O2 uptake values of six subjects were not significantly different for the two systems when compared with the Douglas bag method. The time constants of the exponential function describing oxygen kinetics during repeated (6 times) step changes in load in two subjects were different for the three systems. MMC-Horizon and 9000 IV Ergometric system had lower (51.8 s and 55.1 s, respectively, vs 62.5 s) and EOS-Sprint higher time constant (94.6 vs 47.7 s) than the conventional method. The automated systems were convenient and efficient for measurement of O2 uptake during steady-state and maximal exercise. When O2 uptake kinetics are essential, one has to take into account the response time of the system.

The influence of macrofauna on estuarine benthic community metabolism: a microcosm study

Effects of benthic macrofauna (Corophium volutator, Hydrobia sp., Nereis virens) on benthic community metabolism were studied over a 65-d period in microcosms kept in either light/dark cycle (L/D-system) or in continuous darkness (D-system). Sediment and animals were collected in January 1986 in the shallow mesohaline estuary, Norsminde Fjord, Denmark. The primary production in the L/D-system after 10 d acted as a stabilizing agent on the O2 and CO2 flux rates, whereas the D-system showed decreasing O2 and CO2 flux throughout the period. Mean O2 uptake over the experimental period ranged from 0.38 to 1.24 mmol m−2 h−1 and CO2 release varied from 0.80 to 1.63 mmol m−2 h−1 in both systems. The presence of macrofauna stimulated community respiration rates measured in darknes, 1.4 to 3.0 and 0.9 to 2.0 times for O2 and CO2, respectively. In contrast, macrofauna lowered primary production. Gross primary production varied from 1.06 to 2.26 mmol O2 m−2 h−1 and from 1.26 to 2.62 mmol CO2 m−2 h−1. The community respiratory quotient (CRQ, CO2/O2) was generally higher in the begining of the experiment (0–20 d, mean 1.89) than in the period from Days 20 to 65 (mean 1.38). The L/D-system exhibited lower CRQ (ca. 1) than the D-system. The community photosynthetic quotient varied for both net and gross primary production from 0.64 to 1.03, mean 0.81. The heterotrophic D-system revealed a sharp decrease in the sediment content of chlorophyll a as compared to the initial content. In the autotrophic L/D-system, a significant increase in chlorophyll a concentration was observed in cores lacking animals and cores with C. volutator (The latter species died during the experiment). Due to grazing and other macrofauna activities other cores of the L/D-system exhibited no significant change in chlorophyll a concentration. Community primary production was linearly correlated to the chlorophyll a content in the 0 to 0.5 cm layer. Fluxes of DIN (NH4++NO2−+NO3−) did not reveal significant temporal changes during the experiment. Highest rates were found for the cores containing animals, mainly because of an increased NH4+ flux. The release of DIN decreased significantly due to uptake by benthic microalgae in the L/D-system. No effects of the added macrofauna were found on particulate organic carbon (POC), particulate organic nitrogen (PON), total carbon dioxide (TCO2) and NH4+ in the sediment. The ratio between POC and PON was nearly constant (9.69) in all sediment dephts. The relationship between TCO2 and NH4+ was more complex, with ratios below 2 cm depth similar to those for POC/PON, but with low ratios (3.46) at the sediment surface.

The energy cost of aerobic exercise in fed and fasted normal subjects

It has been claimed that there is a prolonged thermogenic effect of aerobic exercise although the evidence is by no means conclusive. We have therefore studied the thermogenic effect of moderate aerobic exercise in the fasted and fed state in four lean subjects during weight maintenance. Exercise was performed at a constant rate on a bicycle ergometer during the initial 20 min for four successive hours. The first two exercise periods were in the fasted state while the last two followed an 800 kcal (3.4 MJ) mixed meal. Oxygen uptake increased 22% over the 165 min after the meal on rest days (p less than 0.001). There was a significant but similar elevation of mean O2 uptake during 40 min postexercise by 13.6% in both the fasted (p less than 0.001) and fed state (p less than 0.001). Sixty minutes after ceasing exercise mean O2 uptake was not different from preexercise levels (p greater than 0.05). We conclude that there is no prolonged thermogenic effect of moderate repeated aerobic exercise in weight-maintaining lean subjects. In addition there was no interaction between exercise and dietary induced thermogenesis.

High-sensitivity device for continuous measurements of tissue O2 uptake.

An analysis system for continuous measurements of O2 uptake by rat diaphragm during several hours is described. The tissue was set in a chamber where a medium was flowing at a known and constant flow rate, temperature, and partial pressure of oxygen (PO2). The decrease in PO2 of the medium was measured with a Clark O2 cathode at the outlet of the chamber. To increase the sensitivity of the system and the signal-to-noise ratio of the measurements, a sweeping device was designed. It provided homogenization of the medium in the chamber. The main characteristics of this analysis system are a) a sensitivity of +/-0.2% of the mean PO2 value of the perfused medium, +/-0.8% of the mean O2 uptake of rat diaphragm, b) a linearity of +/-1.75% in the range of 0+/-200 Torr, c) a stability of +/-0.38% of the initial PO2 value, and d) a time constant of 8 min 30 s. This type of system can be used for high-sensitivity measurements of O2 uptake of any tissue after adaptation of the chamber and of the medium flow rate.

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 &lt; 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 &lt; 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

Effect of body composition and weight gain on performance in the adult dog.

The effect of overfeeding and variations in body composition on resting metabolism and work performance has been examined in the adult dog. At rest, the mean O2 uptake was 85.5 cc/min. and the R.Q. was .65. These were not substantially altered by 20% gain in weight associated with variations of 12%–20% in body fat content. Work performance was tested during a 50-min. period of treadmill running at a fixed work intensity of 202.9 kg-m/min. Oxygen uptake, work and recovery pulse rates were constant. However, the respiratory quotient increased from .81 to .95 and water loss during work increased from 1.16 cc/Cal. to 1.84 cc/Cal. with gain in weight and adiposity. It is concluded that the most important effect of gain in weight is to promote increased water loss during constant steady-state work. Submitted on December 11, 1959

The Effect of Sodium Arsenite on the Respiration of Bovine Semen and the Relation of this Response to the Fertilizing Ability of Semen

Treatment of bovine semen with a low concentration of buffered sodium arsenite (5×10–10 M) increased the mean O2 uptake of the semen studied. A high concentration (10–5 M) slightly decreased the mean O2 uptake and a still higher concentration (10–3 M) decreased O2 uptake when compared to O2 uptake of untreated semen. The response of O2 uptake to sodium arsenite varied greatly according to the individual semen sample.When the individual semen sample response was related to the fertilizing capacity of the semen, a negative relationship was found. The degree of relationship was statistically significant but not close enough to be of practical value for accurate prediction of semen quality.