Anomalous oxygen uptake by flowing blood

It is found that oxygen uptake by whole blood flowing in rectangular channels greatly excedes theoretical predictions, despite the fact that such predictions are accurate when used with other channel geometries. An “optimum” rectangular channel aspect ratio for oxygen uptake improvement, relative to theory, is found and the possible use of the anomalous gas transfer in membrane oxygenator construction is indicated.     

Use of oxygen uptake recovery curve to predict peak oxygen uptake in upper body exercise

A group of 18 well-trained white-water kayakers performed maximal upper body exercise in the laboratory and during.a field test. Laboratory direct peak oxygen uptake ( ) values were compared, firstly by a backward extrapolation estimation and secondly by an estimation calculated from measured during the first 20 s of exercise recovery. Direct peak correlated with backward extrapolation (r=0.89), but the results of this study showed that the backward extrapolation method tended to overestimate significantly peak by [0.57 (SD 0.31) 1·min^–1 in the laboratory, and 0.66 (SD 0.33) 1·min^–1 in the field,P<0.001]. The measured during the first 20 s of recovery, whether the exercise was performed in the laboratory or in the field, correlated well with the laboratory direct peak (r=0.92 andr=0.91, respectively). The use of the regression equation obtained from field data _2f20s, that is peak ₂=0.23+1.08 _2f20s, gave an estimated peak ₂, the mean difference of which compared with direct peak was 0.22 (SD 0.13) 1·min^–1. In conclusion, we propose the use of a regression equation to estimate peak from a single sample of the gas expired during the first 20 s of recovery after maximal exercise involving the upper part of the body.     

Estimation of maximal oxygen uptake by bioelectrical impedance analysis

Previous non-exercise models for the prediction of maximal oxygen uptake VO(2max) have failed to accurately discriminate cardiorespiratory fitness within large cohorts. The aim of the present study was to evaluate the feasibility of a completely indirect method for predicting VO(2max) that was based on bioelectrical impedance analysis (BIA) in 66 young, healthy fit men and women. Multiple, stepwise regression analysis was used to determine the usefulness of BIA and additional covariates to estimate VO(2max) (ml min(-1)). BIA was highly correlated to VO(2max) (r = 0.914; P < 0.001) and entered the regression equation first. The inclusion of gender and a physical activity rating further improved the model which accounted for 88% of the variance in VO(2max) and resulted in a relative standard error of the estimate (SEE) of 7.2%. Substantial agreement between the methods was confirmed by the fact that nearly all the differences were within +/-2 SD. Furthermore, in contrast to previously published non-exercise models, no trend of a reduction in prediction accuracy with increasing VO(2max) values was apparent. It was concluded that a non-exercise model based on BIA might be a rapid and useful technique to estimate VO(2max), when a direct test does not seem feasible. However, though the present results are useful to determine the viability of the method, further refinement of the BIA approach and its validation in a large, diverse population is needed before it can be applied to the clinical and epidemiological settings.     

Contribution of oxygen extraction fraction to maximal oxygen uptake in healthy young men

We analysed the importance of systemic and peripheral arteriovenous O₂ difference ( difference and a‐v_fO₂ difference, respectively) and O₂ extraction fraction for maximal oxygen uptake ( ). Fick law of diffusion and the Piiper and Scheid model were applied to investigate whether diffusion versus perfusion limitations vary with . Articles (n = 17) publishing individual data (n = 154) on , maximal cardiac output ( ; indicator‐dilution or the Fick method), difference (catheters or the Fick equation) and systemic O₂ extraction fraction were identified. For the peripheral responses, group‐mean data (articles: n = 27; subjects: n = 234) on leg blood flow (LBF; thermodilution), a‐v_fO₂ difference and O₂ extraction fraction (arterial and femoral venous catheters) were obtained. and two‐LBF increased linearly by 4.9‐6.0 L · min^–1 per 1 L · min^–1 increase in (R² = .73 and R² = .67, respectively; both P < .001). The difference increased from 118‐168 mL · L^–1 from a of 2‐4.5 L · min^–1 followed by a reduction (second‐order polynomial: R² = .27). After accounting for a hypoxemia‐induced decrease in arterial O₂ content with increasing (R² = .17; P < .001), systemic O₂ extraction fraction increased up to ~90% ( : 4.5 L · min^–1) with no further change (exponential decay model: R² = .42). Likewise, leg O₂ extraction fraction increased with to approach a maximal value of ~90‐95% (R² = .83). Muscle O₂ diffusing capacity and the equilibration index Y increased linearly with (R² = .77 and R² = .31, respectively; both P < .01), reflecting decreasing O₂ diffusional limitations and accentuating O₂ delivery limitations. In conclusion, although O₂ delivery is the main limiting factor to , enhanced O₂ extraction fraction (≥90%) contributes to the remarkably high in endurance‐trained individuals.     

The influence of inspired oxygen on the oxygen uptake response to ramp exercise

The relation between and work rate (WR) was examined in seven male subjects who performed ramp (1 W·3 s^–1) two-legged cycle ergometry to exhaustion while inspiring either hypoxic (12% O₂), normoxic (21% O₂), or hyperoxic (40% O₂) air. The anaerobic threshold was estimated from respiratory gas exchange data and is thus referred to as the respiratory gas exchange threshold (RGET). Prior to the RGET, the was greater under normoxic [mean (SD); 10. 19(1.04) ml O₂·min^–1·W^–1] and hyperoxic [10.44 (0.72)] conditions compared with hypoxia [9.34 (0.89)]. Above the RGET, the for hypoxia [8.91 (0.63)], normoxia [10.40 (0.77)], and hyperoxia [11.08 (0.48)] were all significantly different from each other. These data indicated that for two-legged, cycle, ramp ergometry in normoxia below the RGET, both the and response time was constant. Above the RGET, the normoxic response was the net result of a declining and a longer response time to the unsteady state character of a ramp exercise protocol.     

Depressed melatonin secretion in patients with nightmares due to beta-adrenoceptor blocking drugs

Nocturnal urinary melatonin excretion was evaluated in six patients with nightmares and hallucinations during treatment with beta-adrenoceptor blocking agents, and compared to six control patients with similar diagnoses and treatment but without such symptoms from the central nervous system (CNS). Nightly melatonin excretion was lower in all cases with nightly CNS-symptoms than in the control patients. The results also suggest drug differences and dose dependency. It is concluded that in predisposed patients CNS side-effects induced by beta-adrenoceptor antagonists are related to depressed nightly melatonin secretion.     

Fusion of interleukin-2 to subunit antigens increase their antigenicity in vitro due to an interleukin-2 receptor beta-mediated antigen uptake mechanism

Subunit vaccines, based on one or more epitopes, offer advantages over whole vaccines in terms of safety but are less antigenic. We investigated whether fusion of the cytokine interleukin-2 (IL-2) to influenza-derived subunit antigens could increase their antigenicity. The fusion of IL-2 to the subunit antigens increased their antigenicity in vitro. Encapsulation of the subunit antigen in liposomes also increased its antigenicity in vitro, yet encapsulation of the subunit IL-2 fusion did not. The use of anti-IL-2 receptor beta (IL-2Rbeta) antibody to block the receptor subunit on macrophages suggested that the adjuvancy exerted by IL-2 in our in vitro system is due to, at least in part, a previously unreported IL-2Rbeta-mediated antigen uptake mechanism.     

Reliability of measurement of oxygen uptake by a portable telemetric system

Summary The purpose of the present study was to check the reliability of measurements of oxygen uptake (VO₂) using a newly developed portable telemetry system. This system (K2) consisted of a face mask, a flow meter, a gas analyser with a transmitter, and a receiver. The total mass for the subject to carry was about 850 g. Three experiments were carried out, firstly to check the reliability and reproducibility of the flow meter and the K2 gas analyser, secondly to check the accuracy of K2 by comparing it with the Douglas bag method (DB), and thirdly to apply K2 to sports activities. In the first experiment, the flow meter was highly accurate up to 180 l·min^–1 with good reproducibility. The measurement error of the gas analyser was less than 2%. In the second experiment, there was no significant difference in the calculated ventilation between K2 and DB. The VO₂ showed no significant difference between K2 and DB with some exceptions. In the third experiment, we succeeded in the measurement of VO₂ during rowing on water. The measurement of VO₂ during running and playing soccer was also possible. It would seem that the present system could well be a powerful tool in the field measurement of VO₂ during various sports activities.     

Fitness as a determinant of oxygen uptake response to constant-load exercise

Summary Exercise performed above the lactate threshold (Θ _La) produces a slowly-developing phase of oxygen uptake ( ) kinetics which elevates above that predicted from the sub-Θ _La -work rate relationship. This phenomenon has only been demonstrated, to date, in subjects who were relatively homogeneous with respect to fitness. This investigation therefore examined whether this behaviour occurred at a given absolute or whether it was a characteristic of supra-Θ _La exercise in a group of subjects with over a threefold range ofΘ _La (990–3000 ml O₂·min⁻¹) and peak (1600–5260 ml O₂·min⁻¹). Twelve healthy subjects performed: 1) exhausting incremental cycle ergometer exercise for estimation ofΘ _La ( ) and peak , and 11) a series of constant-load tests above and below for determination of the profile and efficiency of work. During all tests expired ventilation, and carbon dioxide production were monitored breath-by-breath. The efficiency of work determined during incremental exercise (28.1±0.7%, ,n=12) did not differ from that determined during sub- constant-load exercise (27.4±0.5%,p>0.05). For constant-load exercise, rose above that predicted, from the sub- -work rate relationship, for all supra- work rates. This was evident above 990 ml O₂·min⁻¹ in the least fit subject but only above 3000 ml O₂·min⁻¹ in the fittest subject. As a consequence the efficiency of work was reduced from 27.4±0.5% for sub- exercise to 22.6±0.4% (p<0.05) at the lowest supra- work rate (i.e. +20 W, on average). The efficiency of work generally decreased further at the higher supra- work rates. We conclude that the response to constant-load exercise includes an additional slow phase of the kinetics for all exercise intensities above irrespective of the fitness of the subject. Consequently, measurements of the aerobic efficiency of work during constant-load exercise must rigorously constrain the exercise intensity to the sub- domain. Supported by grants from the John D. and Catherine T. Mac-Arthur Foundation, USPHS RR 00865-15, and NIH HL 07694-01     

Use of temperature and water immersion to control the human body louse (Anoplura: Pediculidae)

Physical methods such as high and low temperatures were used in the past for the control of human body louse, Pediculus humanus humanus L. (Anoplura: Pediculidae). In the current study, the minimum time necessary to kill all lice after exposing them to temperatures other than those described in the literature, the mortality of lice after immersing them in water, and the survival of lice whose legs were amputated were studied. All lice died after 6 d at 6 degrees C, after 11 d at 24 degrees C, and after 9 d at 31 degrees C. At -17 degrees C, all lice were dead after 35 min, whereas at -70 degrees C, all lice were dead after 1 min. All lice died after immersion in water within 19 h. The differences in mortality were significant but borderline between controls and lice whose two legs were amputated immediately or 24 h after feeding (3.3 versus 13.3% and 8.3 versus 21.7%). For lice whose leg was amputated 48 h after feeding, significant differences were found between controls and lice with one amputated leg (13.3 versus 48.3%), between controls and lice with two amputated legs (13.3 versus 68.3%), and between lice with one and two amputated legs (48.3 versus 68.3%).     

Water immersion delays the oxygen uptake response to sitting arm-cranking in humans

We investigated the effect of central hypervolaemia during water immersion up to the xiphoid process on the oxygen uptake (V˙O₂) and heart rate (HR) response to arm cranking. Seven men performed a 6-min arm-cranking exercise at an intensity requiring a V˙O₂ at 80% ventilatory threshold both in air [C trial, 29 (SD 9)?W] and immersed in water [WI trial, 29 (SD 11)?W] after 6 min of sitting. The V˙O₂ (phase 2) and HR responses to exercise were obtained from a mono-exponential fit [f(t)=baseline+gain·(1?e^{?( t ? TD )/})]. The response was evaluated by the mean response time [MRT; sum of time constant () and time delay (TD)]. No significant difference in V˙O₂ and HR gains between the C and WI trials was observed [V˙O₂ 0.78 (SD 0.1) vs 0.80 (SD 0.2) l?·?min^?1, HR 36 (SD 7) vs 37 (SD 8) beats?·?min^?1, respectively]. Although the HR MRT was not significantly different between the C and WI trials [17 (SD 3), 19 (SD 8)?s, respectively), V˙O₂ MRT was greater in the WI trial than in the C trial [40 (SD 6), 45 (SD 6)?s, respectively; P<0.05]. Assuming no difference in V˙O₂ in active muscle between the two trials, these results would indicate that an increased oxygen store and/or an altered response in muscle blood distribution delayed the V˙O₂ response to exercise.     

Severe hypoxia decreases oxygen uptake relative to intensity during submaximal graded exercise

Summary The effect of severe acute hypoxia (fractional concentration of inspired oxygen equalled 0.104) was studied in nine male subjects performing an incremental exercise test. For power outputs over 125 W, all the subjects in a state of hypoxia showed a decrease in oxygen consumption ( O₂) relative to exercise intensity compared with normoxia (P < 0.05). This would suggest an increased anaerobic metabolism as an energy source during hypoxic exercise. During submaximal exercise, for a given O₂, higher blood lactate concentrations were found in hypoxia than in normoxia (P < 0.05). In consequence, the onset of blood lactate accumulation (OBLA) was shifted to a lower O₂ ( O₂ 1.77 l·min^–1 in hypoxia vs 3.10 l·min^–1 in normoxia). Lactate concentration increases relative to minute ventilation ( _E) responses were significantly higher during hypoxia than in normoxia (P < 0.05). At OBLA, _E during hypoxia was 25% lower than in the normoxic test. This study would suggest that in hypoxia subjects are able to use an increased anaerobic metabolism to maintain exercise performance.     

Alveolar to arterial transmission of oxygen fluctuations due to respiration in anesthetized dogs

Summary The amplitudes of respiratory oxygen fluctuations in the alveoli obtained by calculation were compared with those of the arterial blood measured by a catheterP _{O 2} electrode in vivo in anesthetized and artificially ventilated dogs. It is shown that there is a significant correlation between them in general in bothP _{O 2} andS _{O 2} though the latter correlates better. Amplitude ratio of arterial to alveolar O₂ fluctuations was calculated from two factors, i.e., dispersion of circulation time in the pulmonary vein and mixing in the left heart. The results of calculation agree satisfactorily with those obtained experimentally. The reduction of the amplitude of respiratory fluctuations of oxygen seems to be quite small in the aorta.     

Relating pulmonary oxygen uptake to muscle oxygen consumption at exercise onset: in vivo and in silico studies

Assessment of the rate of muscle oxygen consumption, UO_2m, in vivo during exercise involving a large muscle mass is critical for investigating mechanisms regulating energy metabolism at exercise onset. While UO_2m is technically difficult to obtain under these circumstances, pulmonary oxygen uptake, VO_2p, can be readily measured and used as a proxy to UO_2m. However, the quantitative relationship between VO_2p and UO_2m during the nonsteady phase of exercise in humans, needs to be established. A computational model of oxygen transport and utilization—based on dynamic mass balances in blood and tissue cells—was applied to quantify the dynamic relationship between model-simulated UO_2m and measured VO_2p during moderate (M), heavy (H), and very heavy (V) intensity exercise. In seven human subjects, VO_2p and muscle oxygen saturation, StO_2m, were measured with indirect calorimetry and near infrared spectroscopy (NIRS), respectively. The dynamic responses of VO_2p and StO_2m at each intensity were in agreement with previously published data. The response time of muscle oxygen consumption, estimated by direct comparison between model results and measurements of StO_2m was significantly faster (P < 0.001) than that of pulmonary oxygen uptake, (M: 13 ± 4 vs. 65 ± 7 s; H: 13 ± 4 vs. 100 ± 24 s; V: 15 ± 5 vs. 82 ± 31 s). Thus, by taking into account the dynamics of oxygen stores in blood and tissue and determining muscle oxygen consumption from muscle oxygenation measurements, this study demonstrates a significant temporal dissociation between UO_2m and VO_2p at exercise onset.     

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

Summary 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 ( ) 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: (ml·kg^–1)=SR₁₂₅×(45.8× mean HR+4268)×THB×10^–4 where , THB, and mean HR are total O₂ uptake, total heart beats, and mean heart rate (beats · 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 · min^–1 of mean HR. SR₁₂₅ had a significant correlation not only with 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.Supported in part by Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan (grant no. 57780095)