Reduced arterial O2 saturation during supine exercise in highly trained cyclists

Differences in Peak Oxygen Uptake in Bicycle Exercise Test Caused by Body Positions: A Meta-Analysis

Background: As demand for cardiopulmonary exercise test using a supine position has increased, so have the testing options. However, it remains uncertain whether the existing evaluation criteria for the upright position are suitable for the supine position. The purpose of this meta-analysis is to compare the differences in peak oxygen uptake (VO_2peak) between upright and supine lower extremity bicycle exercise. Methods: We searched PubMed, Web Of Science and Embase from inception to March 27, 2021. Self-control studies comparing VO_2peak between upright and supine were included. The quality of the included studies was assessed using a checklist adapted from published papers in this field. The effect of posture on VO_2peak was pooled using random/fixed effects model. Results: This meta-analysis included 32 self-control studies, involving 546 participants (63% were male). 21 studies included only healthy people, 9 studies included patients with cardiopulmonary disease, and 2 studies included both the healthy and cardiopulmonary patients. In terms of study quality, most of the studies (n = 21, 66%) describe the exercise protocol, and we judged theVO_2peak to be valid in 26 (81%) studies. Meta-analysis showed that the upright VO_2peak exceeded the supine VO_2peak [relative VO_2peak: mean difference (MD) 2.63 ml/kg/min, 95% confidence interval (CI) 1.66-3.59, I ² = 56%, p < 0.05; absolute VO_2peak: MD 0.18 L/min, 95% CI 0.10-0.26, I ² = 63%, p < 0.05). Moreover, subgroup analysis showed there was more pooled difference in healthy people (4.04 ml/kg/min or 0.22 L/min) than in cardiopulmonary patients (1.03 ml/kg/min or 0.12 L/min). Conclusion: VO_2peak in the upright position is higher than that in supine position. However, whether this difference has clinical significance needs further verification. Systematic Review Registration: identifier, CRD42021233468.

Noninvasive Pulmonary Hemodynamic Evaluation in Athletes With Exercise-Induced Hypoxemia

BACKGROUND

Pulmonary capillary stress failure is potentially involved in exercise-induced hypoxemia (ie, a significant fall in hemoglobin oxygen saturation [Spo₂]) during sea level exercise in endurance-trained athletes. It is unknown whether there are specific properties of pulmonary vascular function in athletes exhibiting oxygen desaturation.

METHODS

Ten endurance-trained athletes with exercise-induced hypoxemia (EIH), nine endurance-trained athletes with no exercise-induced hypoxemia (NEIH), and 10 untrained control subjects underwent an incremental exercise stress echocardiography coupled with lung diffusion capacity for carbon monoxide (Dlco) and lung diffusion capacity for nitric oxide (Dlno) testing. Functional adaptation of the pulmonary circulation was evaluated with measurements of mean pulmonary arterial pressure (mPAP), pulmonary capillary pressure, pulmonary vascular resistance (PVR), cardiac output (Qc), and pulmonary vascular distensibility (alpha) mathematically determined from the curvilinearity of the multi-point mPAP/Qc relation.

RESULTS

EIH athletes exhibited a lower exercise-induced PVR decrease compared with the untrained and NEIH groups (P < .001). EIH athletes showed higher maximal mPAP compared with NEIH athletes (45.4 ± 0.9 mm Hg vs 41.6 ± 0.9 mm Hg, respectively; P = .003); there was no difference between the NEIH and untrained subjects. Alpha was lower in the EIH group compared with the NEIH group (P < .05). Maximal mPAP, Pcap, and alpha were correlated with the fall of Spo₂ during exercise (P < .01, P < .01, and P < .05). Dlno and Dlco increased with exercise in all groups, with no differences between groups. Dlno/Qc was correlated to the exercise-induced Spo₂ changes (P < .05).

CONCLUSIONS

EIH athletes exhibit higher maximal pulmonary vascular pressures, lower vascular distensibility, or exercise-induced changes in PVR compared with NEIH subjects, in keeping with pulmonary capillary stress failure or intrapulmonary shunting hypotheses.

Regulation of increased blood flow (hyperemia) to muscles during exercise: a hierarchy of competing physiological needs

This review focuses on how blood flow to contracting skeletal muscles is regulated during exercise in humans. The idea is that blood flow to the contracting muscles links oxygen in the atmosphere with the contracting muscles where it is consumed. In this context, we take a top down approach and review the basics of oxygen consumption at rest and during exercise in humans, how these values change with training, and the systemic hemodynamic adaptations that support them. We highlight the very high muscle blood flow responses to exercise discovered in the 1980s. We also discuss the vasodilating factors in the contracting muscles responsible for these very high flows. Finally, the competition between demand for blood flow by contracting muscles and maximum systemic cardiac output is discussed as a potential challenge to blood pressure regulation during heavy large muscle mass or whole body exercise in humans. At this time, no one dominant dilator mechanism accounts for exercise hyperemia. Additionally, complex interactions between the sympathetic nervous system and the microcirculation facilitate high levels of systemic oxygen extraction and permit just enough sympathetic control of blood flow to contracting muscles to regulate blood pressure during large muscle mass exercise in humans.

High-dose inhaled salbutamol has no acute effects on aerobic capacity or oxygen uptake kinetics in healthy trained men

The prevalence of asthma is higher among elite athletes than in the general population. This has resulted in the frequent use of anti-asthmatic medication such as beta2-agonists among asthmatic athletes. Beta2-agonists are on the prohibited list of WADA. The use of the beta2-agonist salbutamol is only permitted in therapeutic inhaled doses. Most studies have reported the lack of ergogenic effects of therapeutic doses of inhaled beta2-agonists measured in maximal oxygen uptake. No previous studies have examined any possible effects of high-dose inhaled salbutamol on oxygen uptake kinetics. We enrolled nine healthy well-trained men in a randomized, blinded, placebo-controlled crossover study. Subjects were randomized to inhalation of 40 puffs of 0.2 mg salbutamol or two placebo tablets and performed an incremental test to exhaustion and three submaximal tests at 75% of peak power to determine oxygen uptake kinetics. During the incremental test, there were no effects of inhaled salbutamol on VO(2max) in absolute or relative terms, and no effect on peak power and lactate threshold. During the submaximal test, we found no effects on the time constant, time delay, the mean response time or O(2) deficit related to oxygen uptake kinetics. In conclusion, no ergogenic effect of a high dose of salbutamol on aerobic capacity was found.

Arterial desaturation during exercise in man: implication for O2 uptake and work capacity

Exercise-induced arterial hypoxaemia is defined as a reduction in the arterial O2 pressure (PaO2) by more than 1 kPa and/or a haemoglobin O2 saturation (SaO2) below 95%. With blood gas analyses ideally reported at the actual body temperature, desaturation is a consistent finding during maximal ergometer rowing. Arterial desaturation is most pronounced at the end of a maximal exercise bout, whereas the reduction in PaO2 is established from the onset of exercise. Exercise-induced arterial hypoxaemia is multifactorial. The ability to maintain a high alveolar O2 pressure (PAO2) is critical for blood oxygenation and this appears to be difficult in large individuals. A large lung capacity and, in turn, diffusion capacity seem to protect PaO2. A widening of the PAO2-PaO2 difference does indicate that a diffusion limitation, a ventilation-perfusion mismatch and/or a shunt influence the transport of O2 from alveoli to the pulmonary capillaries. An inspired O2 fraction of 0.30 reduces the widened PAO2-PaO2 difference by 75% and prevents a reduction of PaO2 and SaO2. With a marked increase in cardiac output, diffusion limitation combined with a fast transit time dominates the O2 transport problem. Furthermore, a postexercise reduction in pulmonary diffusion capacity suggests that the alveolo-capillary membrane is affected. An antioxidant attenuates oxidative burst by neutrophilic granulocytes, but it does not affect PaO2, SaO2 or O2 uptake (VO2), and the ventilatory response to maximal exercise also remains the same. It is proposed, though, that increased concentration of certain cytokines correlates to exercise-induced hypoxaemia as cytokines stimulate mast cells and basophilic granulocytes to degranulate histamine. The basophil count increases during maximal rowing. Equally, histamine release is associated with hypoxaemia and when the release of histamine is prevented, the reduction in PaO2 is attenuated. During maximal exercise, an extreme lactate spill-over to blood allows pH decrease to below 7.1 and according to the O2 dissociation curve this is critical for SaO2. When infusion of sodium bicarbonate maintains a stable blood buffer capacity, acidosis is attenuated and SaO2 increases from 89% to 95%. This enables exercise capacity to increase, an effect also seen when O2 supplementation to inspired air restores arterial oxygenation. In that case, exercise capacity increases less than can be explained by VO2 and CaO2. Furthermore, the change in muscle oxygenation during maximal exercise is not affected when hyperoxia and sodium bicarbonate attenuate desaturation. It is proposed that other organs benefit from enhanced O2 availability, and especially the brain appears to increase its oxygenation during maximal exercise with hyperoxia.

Exercise-induced arterial hypoxaemia in athletes: a review

During exercise, healthy individuals are able to maintain arterial oxygenation, whereas highly-trained endurance athletes may exhibit an exercise-induced arterial hypoxaemia (EIAH) that seems to reflect a gas exchange abnormality. The effects of EIAH are currently debated, and different hypotheses have been proposed to explain its pathophysiology. For moderate exercise, it appears that a relative hypoventilation induced by endurance training is involved. For high-intensity exercise, ventilation/perfusion (V(A)/Q) mismatching and/or diffusion limitation are thought to occur. The causes of this diffusion limitation are still under debate, with hypotheses being capillary blood volume changes and interstitial pulmonary oedema. Moreover, histamine is released during exercise in individuals exhibiting EIAH, and questions persist as to its relationship with EIAH and its contribution to interstitial pulmonary oedema. Further investigations are needed to better understand the mechanisms involved and to determine the long term consequences of repetitive hypoxaemia in highly trained endurance athletes.

The influence of PaO2, pH and SaO2 on maximal oxygen uptake

Influence of arterial oxygen pressure (PaO2) and pH on haemoglobin saturation (SaO2) and in turn on O2 uptake (VO2) was evaluated during ergometer rowing (156, 276 and 376 W; VO2max, 5.0 L min-1; n = 11). During low intensity exercise, neither pH nor SaO2 were affected significantly. In response to the higher work intensities, ventilations (VE) of 129 +/- 10 and 155 +/- 8 L min-1 enhanced the end tidal PO2 (PETO2) to the same extent (117 +/- 2 mmHg), but PaO2 became reduced (from 102 +/- 2 to 78 +/- 2 and 81 +/- 3 mmHg, respectively). As pH decreased during maximal exercise (7.14 +/- 0.02 vs. 7.30 +/- 0.02), SaO2 also became lower (92.9 +/- 0.7 vs. 95.1 +/- 0.1%) and arterial O2 content (CaO2) was 202 +/- 3 mL L-1. An inspired O2 fraction (F1O2) of 0.30 (n = 8) did not affect VE, but increased PETO2 and PaO2 to 175 +/- 4 and 164 +/- 5 mmHg and the PETO2-PaO2 difference was reduced (21 +/- 4 vs. 36 +/- 4 mmHg). pH did not change when compared with normoxia and SaO2 remained within 1% of the level at rest in hyperoxia (99 +/- 0.1%). Thus, CaO2 and VO2max increased to 212 +/- 3 mL L-1 and 5.7 +/- 0.2 L min-1, respectively. The reduced PaO2 became of importance for SaO2 when a low pH inhibited the affinity of O2 to haemoglobin. An increased F1O2 reduced the gradient over the alveolar-arterial membrane, maintained haemoglobin saturation despite the reduction in pH and resulted in increases of the arterial oxygen content and uptake.