Exhaled nitric oxide during normoxic and hypoxic exercise in endurance athletes

Exercise-Induced Hypoxemia in Endurance Athletes: Consequences for Altitude Exposure

Exercise-induced hypoxemia (EIH) is well-described in endurance-trained athletes during both maximal and submaximal exercise intensities. Despite the drop in oxygen (O₂) saturation and provided that training volumes are similar, athletes who experience EIH nevertheless produce the same endurance performance in normoxia as athletes without EIH. This lack of a difference prompted trainers to consider that the phenomenon was not relevant to performance but also suggested that a specific adaptation to exercise is present in EIH athletes. Even though the causes of EIH have been extensively studied, its consequences have not been fully characterized. With the development of endurance outdoor activities and altitude/hypoxia training, athletes often train and/or compete in this stressful environment with a decrease in the partial pressure of inspired O₂ (due to the drop in barometric pressure). Thus, one can reasonably hypothesize that EIH athletes can specifically adapt to hypoxemic episodes during exercise at altitude. Although our knowledge of the interactions between EIH and acute exposure to hypoxia has improved over the last 10 years, many questions have yet to be addressed. Firstly, endurance performance during acute exposure to altitude appears to be more impaired in EIH vs. non-EIH athletes but the corresponding physiological mechanisms are not fully understood. Secondly, we lack information on the consequences of EIH during chronic exposure to altitude. Here, we (i) review research on the consequences of EIH under acute hypoxic conditions, (ii) highlight unresolved questions about EIH and chronic hypoxic exposure, and (iii) suggest perspectives for improving endurance training.

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.

The intranasal AlaxoLito Plus Nasal Stent: Improvement of NO-induced microrheology and oxygen uptake during exercise?

AIM

To investigate the influence of the intranasal AlaxoLito Plus Nasal Stent during exercise on nitric oxide (NO) synthesis, NO exhalation, red blood cell (RBC) deformability and oxygen uptake.

METHODS

Parameters were measured before and after acute cycle ergometer test at different intensities. Spirometric, microrheological and NO parameters were determined for oral (OB), nasal (NB) and nasal-stent breathing (SB). RBC deformability was measured and elongation indices for 3.87 Pa and maximal deformability were calculated. RBC/plasma/exhaled NO, oxygen uptake and respiratory rate were determined.

RESULTS

Exhaled NO was higher at rest during OB compared to SB and NB and decreased after exercise with NB and SB. Plasma and RBC NO remained unaltered during intervention. RBC deformability increased at moderate intensity during SB. Deformability decreased at moderate and medium intensity with NB. Respiratory rate for same oxygen uptake did not differ between breathing settings.

CONCLUSION

The AlaxoLito Plus Nasal Stent may modulate deformability during moderate exercise and increase NO exhalation without major effects on oxygen uptake and performance.

The pulmonary and autonomic effects of high-intensity and low-intensity exercise in diesel exhaust

BACKGROUND

Exposure to air pollution impairs aspects of pulmonary and autonomic function and causes pulmonary inflammation. However, how exercising in air pollution affects these indices is poorly understood. Therefore, the purpose of this study was to determine the effects of low-intensity and high-intensity cycling with diesel exhaust (DE) exposure on pulmonary function, heart rate variability (HRV), fraction of exhaled nitric oxide (FeNO), norepinephrine and symptoms.

METHODS

Eighteen males performed 30-min trials of low-intensity or high-intensity cycling (30 and 60% of power at VO_2peak) or a resting control condition. For each subject, each trial was performed once breathing filtered air (FA) and once breathing DE (300μg/m³ of PM_2.5, six trials in total). Pulmonary function, FeNO, HRV, norepinephrine and symptoms were measured prior to, immediately post, 1 h and 2 h post-exposure. Data were analyzed using repeated-measures ANOVA.

RESULTS

Throat and chest symptoms were significantly greater immediately following DE exposure than following FA (p < 0.05). FeNO significantly increased 1 h following high-intensity exercise in DE (21.9 (2.4) vs. 19.3 (2.2) ppb) and FA (22.7 (1.7) vs. 19.9 (1.4)); however, there were no differences between the exposure conditions. All HRV indices significantly decreased following high-intensity exercise (p < 0.05) in DE and FA. The exception to this pattern was LF (nu) and LF/HF ratio, which significantly increased following high-intensity exercise (p < 0.05). Plasma norepinephrine (NE) significantly increased following high-intensity exercise in DE and FA, and this increase was greater than following rest and low-intensity exercise (p < 0.05). DE exposure did not modify any effects of exercise intensity on HRV or norepinephrine.

CONCLUSIONS

Healthy individuals may not experience greater acute pulmonary and autonomic effects from exercising in DE compared to FA; therefore, it is unclear if such individuals will benefit from reducing vigorous activity on days with high concentrations on particulate matter.

The Influence of 17 Hours of Normobaric Hypoxia on Parallel Adjustments in Exhaled Nitric Oxide and Airway Function in Lowland Healthy Adults

Van Iterson, Erik H., Eric M. Snyder, and Bruce D. Johnson. The influence of 17 hours of normobaric hypoxia on parallel adjustments in exhaled nitric oxide and airway function in lowland healthy adults. High Alt Med Biol. 18:1-10, 2017.-Currently, there is a disparate understanding of the role that normobaric hypoxia plays in affecting nitric oxide (NO) measured in exhaled air (eNO) and airway function in lowland healthy adults. Compared to normobaric normoxia, this study aimed to test the effect of 17 hours of normobaric hypoxia on relationships between eNO and airway function in healthy adults. In a crossover study including 2 separate visits, 26 lowland healthy Caucasian adults performed eNO and pulmonary function tests on visit 1 in normobaric normoxia, while repeating all tests on visit 2 following 17 hours of normobaric hypoxia (12.5% O₂). Compared to normobaric normoxia, eNO (29 ± 24 vs. 36 ± 28 ppb), forced expiratory volume in one second (FEV₁) (4.1 ± 0.7 vs. 4.3 ± 0.8 L), mean forced expiratory flow between 25% and 75% FVC (FEF_25-75) (3.9 ± 1.0 vs. 4.2 ± 1.2 L/s), and forced expiratory flow at 75% FVC (FEF₇₅) (2.0 ± 0.7 vs. 2.3 ± 0.8 L/s) increased in normobaric hypoxia, respectively (all p < 0.05). Correlations at normoxia between eNO and FEV₁ (r = 0.39 vs. 0.44), FEF_25-75 (r = 0.51 vs. 0.51), and FEF₇₅ (r = 0.53 vs. 0.55) persisted as both parameters increased in hypoxia, respectively. For the first time, these data suggest that 17 hours of hypoxic breathing in the absence of low ambient pressure contribute to increased eNO and airway function in lowland healthy adults.

Exercise and NO production: relevance and implications in the cardiopulmonary system

This article reviews the existing knowledge about the effects of physical exercise on nitric oxide (NO) production in the cardiopulmonary system. The authors review the sources of NO in the cardiopulmonary system; involvement of three forms of NO synthases (eNOS, nNOS, and iNOS) in exercise physiology; exercise-induced modulation of NO and/or NOS in physiological and pathophysiological conditions in human subjects and animal models in the absence and presence of pharmacological modulators; and significance of exercise-induced NO production in health and disease. The authors suggest that physical activity significantly improves functioning of the cardiovascular system through an increase in NO bioavailability, potentiation of antioxidant defense, and decrease in the expression of reactive oxygen species-forming enzymes. Regular physical exercises are considered a useful approach to treat cardiovascular diseases. Future studies should focus on detailed identification of (i) the exercise-mediated mechanisms of NO exchange; (ii) optimal exercise approaches to improve cardiovascular function in health and disease; and (iii) physical effort thresholds.

Arterialised earlobe capillary blood gases in the COPD population

Arterialised ear lobe capillary blood (ELCB) gas sampling is a widely used clinical procedure undertaken across both primary and secondary care settings. The prevalence of this sampling method has grown among health professionals, coupled with a growing demand for domiciliary oxygen therapy in the UK, in particular for those who have chronic obstructive pulmonary disease (COPD). Research studies supporting arterialised ELCB gas sampling show inconsistencies in technique, and a survey of respiratory nurses' current practice demonstrated wider inconsistencies. In the absence of national clinical guidelines to direct this practice, and an acknowledged and accepted under-calculation of partial pressure of oxygen, this article investigates the sampling method used to obtain arterialised ELCB gas sampling and consequently questions its reliability in practice.

The adult patient with eisenmenger syndrome: a medical update after dana point part I: epidemiology, clinical aspects and diagnostic options

Eisenmenger syndrome is the most severe form of pulmonary arterial hypertension and arises on the basis of congenital heart disease with a systemic-to-pulmonary shunt. Due to the chronic slow progressive hypoxemia with central cyanosis, adult patients with the Eisenmenger syndrome suffer from a complex and multisystemic disorder including coagulation disorders (bleeding complications and paradoxical embolisms), renal dysfunction, hypertrophic osteoarthropathy, heart failure, reduced quality of life and premature death.For a long time, therapy has been limited to symptomatic options or lung or combined heart-lung transplantation. As new selective pulmonary vasodilators have become available and proven to be beneficial in various forms of pulmonary arterial hypertension, this targeted medical treatment has been expected to show promising effects with a delay of deterioration also in Eisenmenger patients. Unfortunately, data in Eisenmenger patients suffer from small patient numbers and a lack of randomized controlled studies.To optimize the quality of life and the outcome, referral of Eisenmenger patients to spezialized centers is required. In such centers, specific interdisciplinary management strategies of physicians specialized on congenital heart diseases and PAH should be warranted. This medical update emphasizes the current diagnostic and therapeutic options for Eisenmenger patients with particularly focussing on epidemiology, clinical aspects and specific diagnostic options.

Effect of acute hypoxia on respiratory muscle fatigue in healthy humans

Background

Greater diaphragm fatigue has been reported after hypoxic versus normoxic exercise, but whether this is due to increased ventilation and therefore work of breathing or reduced blood oxygenation per se remains unclear. Hence, we assessed the effect of different blood oxygenation level on isolated hyperpnoea-induced inspiratory and expiratory muscle fatigue.

Methods

Twelve healthy males performed three 15-min isocapnic hyperpnoea tests (85% of maximum voluntary ventilation with controlled breathing pattern) in normoxic, hypoxic (SpO₂ = 80%) and hyperoxic (FiO₂ = 0.60) conditions, in a random order. Before, immediately after and 30 min after hyperpnoea, transdiaphragmatic pressure (P_di,tw ) was measured during cervical magnetic stimulation to assess diaphragm contractility, and gastric pressure (P_ga,tw ) was measured during thoracic magnetic stimulation to assess abdominal muscle contractility. Two-way analysis of variance (time x condition) was used to compare hyperpnoea-induced respiratory muscle fatigue between conditions.

Results

Hypoxia enhanced hyperpnoea-induced P_di,tw and P_ga,tw reductions both immediately after hyperpnoea (P_di,tw : normoxia -22 ± 7% vs hypoxia -34 ± 8% vs hyperoxia -21 ± 8%; P_ga,tw : normoxia -17 ± 7% vs hypoxia -26 ± 10% vs hyperoxia -16 ± 11%; all P < 0.05) and after 30 min of recovery (P_di,tw : normoxia -10 ± 7% vs hypoxia -16 ± 8% vs hyperoxia -8 ± 7%; P_ga,tw : normoxia -13 ± 6% vs hypoxia -21 ± 9% vs hyperoxia -12 ± 12%; all P < 0.05). No significant difference in P_di,tw or P_ga,tw reductions was observed between normoxic and hyperoxic conditions. Also, heart rate and blood lactate concentration during hyperpnoea were higher in hypoxia compared to normoxia and hyperoxia.

Conclusions

These results demonstrate that hypoxia exacerbates both diaphragm and abdominal muscle fatigability. These results emphasize the potential role of respiratory muscle fatigue in exercise performance limitation under conditions coupling increased work of breathing and reduced O₂ transport as during exercise in altitude or in hypoxemic patients.