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Journal of Applied Physiology... Oct 2017High altitude is physiologically challenging for vertebrate life for many reasons, including hypoxia (low environmental oxygen); yet, many birds thrive at altitude.... (Review)
Review
High altitude is physiologically challenging for vertebrate life for many reasons, including hypoxia (low environmental oxygen); yet, many birds thrive at altitude. Compared with mammals, birds have additional enhancements to their oxygen transport cascade, the conceptual series of steps responsible for acquiring oxygen from the environment and transporting it to the mitochondria. These adaptations have allowed them to inhabit a number of high-altitude regions. Waterfowl are a taxon prolific at altitude. This minireview explores the physiological responses of high-altitude waterfowl (geese and ducks), comparing the strategies of lifelong high-altitude residents to those of transient high-altitude performers, providing insight into how birds champion high-altitude life. In particular, this review highlights and contrasts the physiological hypoxia responses of bar-headed geese (), birds that migrate biannually through the Himalayas (4,500-6,500 m), and Andean geese (), lifelong residents of the Andes (4,000-5,500 m). These two species exhibit markedly different ventilatory and cardiovascular strategies for coping with hypoxia: bar-headed geese robustly increase convective oxygen transport elements (i.e., heart rate and total ventilation) whereas Andean geese rely predominantly on enhancements that are likely morphological in origin (i.e., increases in lung oxygen diffusion and cardiac stroke volume). The minireview compares the short- and long-term cardiovascular and ventilatory trade-offs of these different physiological strategies and offers hypotheses surrounding their origins. It also draws parallels to high-altitude human physiology and research, and identifies a number of areas of further research. The field of high-altitude avian physiology offers a unique and broadly applicable insight into physiological enhancements in hypoxia.
Topics: Acclimatization; Adaptation, Physiological; Altitude; Animal Migration; Animals; Birds; Hypoxia; Oxygen Consumption
PubMed: 28839002
DOI: 10.1152/japplphysiol.00110.2017 -
Experimental Physiology Dec 2020
Topics: Exercise; Exercise Test; Humans; Oxygen; Oxygen Consumption; Respiratory Muscles
PubMed: 33372725
DOI: 10.1113/EP089199 -
International Journal of Environmental... Sep 2022Uphill running induces a higher physiological demand than level conditions. Although many studies have investigated this locomotion from a psychological point of view,...
Uphill running induces a higher physiological demand than level conditions. Although many studies have investigated this locomotion from a psychological point of view, there is no clear position on the effects of the slope on the physiological variables during an incremental running test performed on a slope condition. The existing studies have heterogeneous designs with different populations or slopes and have reported unclear results. Some studies observed an increase in oxygen consumption, whereas it remained unaffected in others. The aim of this study is to investigate the effect of a slope on the oxygen consumption, breathing frequency, ventilation and heart rate during an incremental test performed on 0, 15, 25 and 40% gradient slopes by specialist trail runners. The values are compared at the first and second ventilatory threshold and exhaustion. A one-way repeated measures ANOVA, with a Bonferroni post-hoc analysis, was used to determine the effects of a slope gradient (0, 15, 25 and 40%) on the physiological variables. Our study shows that all the variables are not affected in same way by the slopes during the incremental test. The heart rate and breathing frequency did not differ from the level condition and all the slope gradients at the ventilatory thresholds or exhaustion. At the same time, the ventilation and oxygen consumption increased concomitantly with the slope ( < 0.001) in all positions. The post-hoc analysis highlighted that the ventilation significantly increased between each successive gradient (0 to 15%, 15% to 25% and 25% to 40%), while the oxygen consumption stopped increasing at the 25% gradient. Our results show that the 25 and 40% gradient slopes allow the specialist trail runners to reach the highest oxygen consumption level.
Topics: Exercise Test; Heart Rate; Oxygen Consumption; Respiration; Running
PubMed: 36231513
DOI: 10.3390/ijerph191912210 -
International Journal of Sports... Nov 2021Since its publication in 2012, the W' balance model has become an important tool in the scientific armamentarium for understanding and predicting human physiology and... (Review)
Review
Since its publication in 2012, the W' balance model has become an important tool in the scientific armamentarium for understanding and predicting human physiology and performance during high-intensity intermittent exercise. Indeed, publications featuring the model are accumulating, and it has been adapted for popular use both in desktop computer software and on wrist-worn devices. Despite the model's intuitive appeal, it has achieved mixed results thus far, in part due to a lack of clarity in its basis and calculation. Purpose: This review examines the theoretical basis, assumptions, calculation methods, and the strengths and limitations of the integral and differential forms of the W' balance model. In particular, the authors emphasize that the formulations are based on distinct assumptions about the depletion and reconstitution of W' during intermittent exercise; understanding the distinctions between the 2 forms will enable practitioners to correctly implement the models and interpret their results. The authors then discuss foundational issues affecting the validity and utility of the model, followed by evaluating potential modifications and suggesting avenues for further research. Conclusions: The W' balance model has served as a valuable conceptual and computational tool. Improved versions may better predict performance and further advance the physiology of high-intensity intermittent exercise.
Topics: Exercise; Exercise Test; High-Intensity Interval Training; Humans; Oxygen Consumption
PubMed: 34686611
DOI: 10.1123/ijspp.2021-0205 -
BMC Anesthesiology Jun 2023Body temperature (BT) is thought to have associations with oxygen consumption (VO). However, there have been few studies in which the association between systemic VO and...
BACKGROUND
Body temperature (BT) is thought to have associations with oxygen consumption (VO). However, there have been few studies in which the association between systemic VO and BT in humans was investigated in a wide range of BTs. The aims of this study were 1) to determine the association between VO and age and 2) to determine the association between VO and BT.
METHODS
This study was a retrospective study of patients who underwent surgery under general anesthesia at a tertiary teaching hospital. VO was measured by the Dräger Perseus A500 anesthesia workstation (Dräger Medical, Lubeck, Germany). The associations of VO with age and BT were examined using spline regression and multivariable regression analysis with a random effect.
RESULTS
A total of 7,567 cases were included in this study. A linear spline with one knot shows that VO was reduced by 2.1 ml/kg/min with one year of age (p < 0.001) among patients less than 18 years of age and that there was no significant change in VO among patients 18 years of age or older (estimate: 0.014 ml/kg/min, p = 0.08). VO in all bands of BT < 36.0 °C was not significantly different from VO in BT > = 36 °C and < 36.5 °C. Multivariable linear regression analysis showed that compared with VO in BT > = 36 °C and < 36.5 °C as a reference, VO levels were significantly higher by 0.57 ml/kg/min in BT > = 36.5 °C and < 37 °C (p < 0.001), by 1.8 ml/kg/min in BT > = 37 °C and < 37.5 °C (p < 0.001), by 3.6 ml/kg/min in BT > = 37.5 °C and < 38 °C (p < 0.001), by 4.9 ml/kg/min in BT > = 38 °C and < 38.5 °C (p < 0.001), and by 5.7 ml/kg/min in BT > = 38.5 °C (p < 0.001). The associations between VO and BT were significantly different among categorized age groups (p = 0.03).
CONCLUSIONS
VO increases in parallel with increase in body temperature in a hyperthermic state but remains constant in a hypothermic state. Neonates and infants, who have high VO, may have a large systemic organ response in VO to change in BT.
Topics: Infant; Infant, Newborn; Humans; Adolescent; Adult; Child, Preschool; Body Temperature; Retrospective Studies; Anesthesia, General; Fever; Oxygen Consumption; Oxygen
PubMed: 37340340
DOI: 10.1186/s12871-023-02182-1 -
Medicine and Science in Sports and... Jun 2022Determine 1) if adults with facioscapulohumeral muscular dystrophy (FSHD) exhibit exercise intolerance and 2) potential contributing mechanisms to exercise intolerance,...
PURPOSE
Determine 1) if adults with facioscapulohumeral muscular dystrophy (FSHD) exhibit exercise intolerance and 2) potential contributing mechanisms to exercise intolerance, specific to FSHD.
METHODS
Eleven people with FSHD (47 ± 13 yr, 4 females) and 11 controls (46 ± 13 yr, 4 females) completed one visit, which included a volitional peak oxygen consumption (V̇O2peak) cycling test. Breath-by-breath gas exchange, ventilation, and cardiovascular responses were measured at rest and during exercise. The test featured 3-min stages (speed, 65-70 rpm) with incremental increases in intensity (FSHD: 20 W per stage; control: 40-60 W per stage). Body lean mass (LM (kg, %)) was collected via dual-energy x-ray absorptiometry.
RESULTS
V̇O2peak was 32% lower (24.5 ± 9.7 vs 36.2 ± 9.3 mL·kg-1·min-1, P < 0.01), and wattage was 55% lower in FSHD (112.7 ± 56.1 vs 252.7 ± 67.7 W, P < 0.01). When working at a relative submaximal intensity (40% of V̇O2peak), wattage was 55% lower in FSHD (41.8 ± 30.3 vs 92.7 ± 32.6 W, P = 0.01), although ratings of perceived exertion (FSHD: 11 ± 2 vs control: 10 ± 3, P = 0.61) and dyspnea (FSHD: 3 ± 1 vs control: 3 ± 2, P = 0.78) were similar between groups. At an absolute intensity (60 W), the rating of perceived exertion was 63% higher (13 ± 3 vs 8 ± 2, P < 0.01) and dyspnea was 180% higher in FSHD (4 ± 2 vs 2 ± 2, P < 0.01). V̇O2peak was most strongly correlated with resting O2 pulse in controls (P < 0.01, r = 0.90) and percent leg LM in FSHD (P < 0.01, r = 0.88). Among FSHD participants, V̇O2peak was associated with self-reported functionality (FSHD-HI score; activity limitation: P < 0.01, r = -0.78), indicating a strong association between perceived and objective impairments.
CONCLUSIONS
Disease-driven losses of LM contribute to exercise intolerance in FSHD, as evidenced by a lower V̇O2peak and elevated symptoms of dyspnea and fatigue during submaximal exercise. Regular exercise participation may preserve LM, thus providing some protection against exercise tolerance in FSHD.
Topics: Adult; Dyspnea; Exercise; Exercise Test; Exercise Tolerance; Female; Humans; Muscular Dystrophy, Facioscapulohumeral; Oxygen Consumption
PubMed: 35195100
DOI: 10.1249/MSS.0000000000002882 -
Experimental Eye Research Oct 2018Light flicker stimulation has been shown to increase inner retinal oxygen metabolism and supply. The purpose of the study was to test the hypothesis that sustained light...
Light flicker stimulation has been shown to increase inner retinal oxygen metabolism and supply. The purpose of the study was to test the hypothesis that sustained light flicker stimulation of various durations alters the depth profile metrics of oxygen partial pressure in the retinal tissue (tPO) but not the outer retinal oxygen consumption rate (QO). In 17 rats, tPO depth profiles were derived by phosphorescence lifetime imaging after intravitreal injection of an oxyphor. tPO profile metrics, including mean inner retinal tPO, maximum outer retinal tPO and minimum outer retinal tPO were determined. QO was calculated using a one-dimensional oxygen diffusion model. Data were acquired at baseline (constant light illumination) and during light flicker stimulation at 10 Hz under the same mean illumination levels, and differences between values obtained during flicker and baseline were calculated. None of the tPO profile metrics or QO differences depended on the duration of light flicker stimulation (R ≤ 0.03). No significant change in any of the tPO profile metrics was detected with light flicker compared with constant light (P ≥ 0.08). Light flicker decreased QO from 0.53 ± 0.29 to 0.38 ± 0.30 mL O/(min*100 gm), a reduction of 28% (P = 0.02). The retinal compensatory responses to the physiologic challenge of light flicker stimulation were effective in maintaining the levels of oxygen at or near baseline in the inner retina. Oxygen availability to the inner retina during light flicker may also have been enhanced by the decrease in QO.
Topics: Animals; Light; Male; Oxygen; Oxygen Consumption; Photic Stimulation; Rats; Rats, Long-Evans; Retina
PubMed: 30121195
DOI: 10.1016/j.exer.2018.08.007 -
Redox Biology May 2024Mitochondrial respiration extends beyond ATP generation, with the organelle participating in many cellular and physiological processes. Parallel changes in components of...
Mitochondrial respiration extends beyond ATP generation, with the organelle participating in many cellular and physiological processes. Parallel changes in components of the mitochondrial electron transfer system with respiration render it an appropriate hub for coordinating cellular adaption to changes in oxygen levels. How changes in respiration under functional hypoxia (i.e., when intracellular O levels limit mitochondrial respiration) are relayed by the electron transfer system to impact mitochondrial adaption and remodeling after hypoxic exposure remains poorly defined. This is largely due to challenges integrating findings under controlled and defined O levels in studies connecting functions of isolated mitochondria to humans during physical exercise. Here we present experiments under conditions of hypoxia in isolated mitochondria, myotubes and exercising humans. Performing steady-state respirometry with isolated mitochondria we found that oxygen limitation of respiration reduced electron flow and oxidative phosphorylation, lowered the mitochondrial membrane potential difference, and decreased mitochondrial calcium influx. Similarly, in myotubes under functional hypoxia mitochondrial calcium uptake decreased in response to sarcoplasmic reticulum calcium release for contraction. In both myotubes and human skeletal muscle this blunted mitochondrial adaptive responses and remodeling upon contractions. Our results suggest that by regulating calcium uptake the mitochondrial electron transfer system is a hub for coordinating cellular adaption under functional hypoxia.
Topics: Humans; Calcium; Oxygen Consumption; Cell Respiration; Hypoxia; Muscle, Skeletal; Oxygen
PubMed: 38401291
DOI: 10.1016/j.redox.2024.103037 -
Journal of the International Society of... Dec 2023Rectal distension increases regulatory burden to autonomic nervous system in the brain.
BACKGROUND
Rectal distension increases regulatory burden to autonomic nervous system in the brain.
PURPOSE
To determine the effect of rectal defecation on endurance performance and blood supply to the prefrontal brain and sub-navel regions of elite triathletes.
METHODS
Thirteen elite triathletes completed a cycling time trial (80% VO) under defecated and non-defecated conditions, using a counterbalanced crossover design. Oxygenation and blood distribution in prefrontal brain and sub-navel regions were monitored by near-infrared spectroscopy (NIRS) during cycling.
RESULTS
Defecation moderately decreased systolic blood pressure (-4 mmHg, < 0.05, d = 0.71), suggesting an alleviation of autonomic nervous activity. During the exercise trials, fatigue (cycling time to exhaustion) occurred when cerebral oxygenation decreased to ~ 5 % below baseline regardless of treatment conditions, suggesting a critical deoxygenation point for sustaining voluntary exertions. Cerebral blood (estimated by total hemoglobin) increased progressively throughout the entire exercise period. Defecation decreased sub-navel oxygenation levels below the non-defecated level, suggesting an increased sub-navel oxygen consumption. Exercise also decreased sub-navel blood distribution, with minimal difference between non-defecated and defecated conditions. Defecation improved blood pooling in the prefrontal brain during exercise ( < 0.05) and enhanced cycling performance in triathletes (Non-defecated: 1624 ± 138 s vs. defecated: 1902 ± 163 s, d = 0.51, < 0.05).
CONCLUSION
Our results suggest that improved exercise performance after defecation is associated with greater blood availability to compensate deoxygenation in the prefrontal brain region during exercise. Further investigation is needed to examine the role of increasing sub-navel oxygen consumption in the performance improvement after defecation.
Topics: Humans; Defecation; Exercise; Oxygen Consumption; Fatigue; Cerebrovascular Circulation
PubMed: 37102434
DOI: 10.1080/15502783.2023.2206380 -
PloS One 2021Maximum oxygen uptake (VO2max) is a "gold standard" in aerobic capacity assessment, playing a vital role in various fields. However, ratio scaling ([Formula: see text]),... (Review)
Review
Maximum oxygen uptake (VO2max) is a "gold standard" in aerobic capacity assessment, playing a vital role in various fields. However, ratio scaling ([Formula: see text]), the present method used to express relative VO2max, should be suspected due to its theoretical deficiencies. Therefore, the aim of the study was to revise the quantitative relationship between VO2max and body weight (bw). Dimensional analysis was utilized to deduce their theoretical relationship, while linear or nonlinear regression analysis based on four mathematical models (ratio scaling, linear function, simple allometric model and full allometric model) were utilized in statistics analysis to verify the theoretical relationship. Besides, to investigate the effect of ratio scaling on removing body weight, Pearson correlation coefficient was used to analyze the correlation between [Formula: see text] and bw. All the relevant data were collected from published references. Dimensional analysis suggested VO2max be proportional to [Formula: see text]. Statistics analysis displayed that four mathematical expressions were VO2max = 0.047bw (p<0.01, R2 = 0.68), VO2max = 0.036bw+0.71 (p<0.01, R2 = 0.76), VO2max = 0.10bw0.82 (p<0.01, R2 = 0.93) and VO2max = 0.23bw0.66-0.48 (p<0.01, R2 = 0.81) respectively. Pearson correlation coefficient showed a significant moderately negative relation between [Formula: see text] and bw (r = -0.42, p<0.01), while there was no correlation between [Formula: see text] and bw (r = 0.066, p = 0.41). Although statistics analysis did not fully verify the theoretical result, both dimensional and statistics analysis suggested ratio scaling distort the relationship and power function be more appropriate to describe the relationship. Additionally, we hypothesized that lean mass, rather than body weight, plays a more essential role in eliminating the gap between theoretical and experimental b values, and is more appropriate to standardize VO2max, future studies can focus more on it.
Topics: Body Weight; Humans; Models, Biological; Oxygen Consumption
PubMed: 34932594
DOI: 10.1371/journal.pone.0261519