Heliox breathing equally influences respiratory mechanics and cycling performance in trained males and females

Breathing a low-density gas reduces respiratory muscle force development and marginally improves exercise performance in master athletes

INTRODUCTION

We tested the hypothesis that breathing heliox, to attenuate the mechanical constraints accompanying the decline in pulmonary function with aging, improves exercise performance.

METHODS

Fourteen endurance-trained older men (67.9 ± 5.9 year, [Formula: see text]O2max: 50.8 ± 5.8 ml/kg/min; 151% predicted) completed two cycling 5-km time trials while breathing room air (i.e., 21% O2-79% N2) or heliox (i.e., 21% O2-79% He). Maximal flow-volume curves (MFVC) were determined pre-exercise to characterize expiratory flow limitation (EFL, % tidal volume intersecting the MFVC). Respiratory muscle force development was indirectly determined as the product of the time integral of inspiratory and expiratory mouth pressure (∫Pmouth) and breathing frequency. Maximal inspiratory and expiratory pressure maneuvers were performed pre-exercise and post-exercise to estimate respiratory muscle fatigue.

RESULTS

Exercise performance time improved (527.6 ± 38 vs. 531.3 ± 36.9 s; P = 0.017), and respiratory muscle force development decreased during inspiration (- 22.8 ± 11.6%, P < 0.001) and expiration (- 10.8 ± 11.4%, P = 0.003) with heliox compared with room air. EFL tended to be lower with heliox (22 ± 23 vs. 30 ± 23% tidal volume; P = 0.054). Minute ventilation normalized to CO2 production ([Formula: see text]E/[Formula: see text]CO2) increased with heliox (28.6 ± 2.7 vs. 25.1 ± 1.8; P < 0.001). A reduction in MIP and MEP was observed post-exercise vs. pre-exercise but was not different between conditions.

CONCLUSIONS

Breathing heliox has a limited effect on performance during a 5-km time trial in master athletes despite a reduction in respiratory muscle force development.

Cardiorespiratory Fitness and Performance Adaptations to High-Intensity Interval Training: Are There Differences Between Men and Women? A Systematic Review with Meta-Analyses

BACKGROUND

It is important to consider biological sex as a variable that might influence exercise adaptation in order to optimize exercise prescription for men and women.

OBJECTIVE

The aim of this study was to quantify the impact of biological sex on maximal oxygen uptake ([Formula: see text]O2max) and performance outcomes after high-intensity interval training (HIIT).

METHODS

A systematic search and review was conducted by two independent reviewers up to 8 September 2022 using MEDLINE, SPORTDiscus, and Sports Medicine & Education Index in ProQuest. Trials including healthy adults were included if they presented data for or compared male and female [Formula: see text]O2max or performance outcomes in response to HIIT. Performance outcomes included measures of exercise performance and concurrently measured physiological adaptations. Where appropriate, a random-effects, pre-post meta-analysis was undertaken. Data were sub-grouped for men and women, baseline training level, mean age, intervention type, and intervention length. Heterogeneity was assessed using Chi2, Cochran's Q, and Higgins I2 and sensitivity analyses, where required. Study quality was assessed using the Newcastle-Ottawa Scale and publication bias was assessed through visual inspection of funnel plots.

RESULTS

Thirty-three references from 28 trials were included in the review (n = 965; 462 women and 503 men). Meta-analyses included 19 studies for [Formula: see text]O2max, eight for peak power output from [Formula: see text]O2max testing (PPO), and five for threshold power (powerAT). Meta-analyses revealed similar increases in [Formula: see text]O2max in women (g = 0.57; 95% CI 0.44-0.69) and men (g = 0.57; 95% CI 0.42-0.72), and powerAT in women (g = 0.38; 95% CI 0.13-0.64) and men (g = 0.38; 95% CI 0.11-0.64). Raw mean differences for change in [Formula: see text]O2max were Δ 0.32 L·min-1 and 3.50 mL·kg-1·min-1 in men, versus Δ 0.20 L·min-1 and 3.34 mL·kg-1·min-1 for women. No significant sex differences were present for the primary analysis of any outcome. After sub-grouping, significant differences were present for PPO where the effect size was higher for well-trained women (g = 0.37) compared with well-trained men (g = 0.17), and for [Formula: see text]O2max where interventions with a duration of 4 weeks or less had significantly smaller effect sizes compared with those longer than 4 weeks (p < 0.001). Unweighted mean percentage change in [Formula: see text]O2max, PPO, and powerAT across studies was 11.16 ± 7.39%, 11.16 ± 5.99%, and 8.07 ± 6.55% for women, and 10.90 ± 5.75%, 8.22 ± 5.09%, and 7.09 ± 7.17% for men, respectively. Significant heterogeneity was present for both [Formula: see text]O2max and PPO (I2, range: 62.06-78.80%). Sub-grouping by baseline training status and intervention length decreased heterogeneity in most groups. A qualitative synthesis of other outcomes indicated similar improvements in fitness and performance for men and women with some evidence suggesting differences in the mechanisms of adaptation.

LIMITATIONS AND RISK OF BIAS

Publication bias is unlikely to have significantly influenced results for [Formula: see text]O2max or powerAT, but the meta-analysis of PPO could have benefitted from additional study data to strengthen results. The overlap in age categories and sensitivity of the analysis limits the accuracy of the results of the sub-grouping by age.

CONCLUSIONS

Findings indicated no sex-specific differences for any fitness or performance outcomes. Baseline training status and intervention length accounted for most variability in outcomes. PROSPERO registration number: CRD42021272615.

Sex Differences in VO2max and the Impact on Endurance-Exercise Performance

It was not until 1984 that women were permitted to compete in the Olympic marathon. Today, more women than men participate in road racing in all distances except the marathon where participation is near equal. From the period of 1985 to 2004, the women’s marathon record improved at a rate three times greater than men’s. This has led many to question whether women are capable of surpassing men despite the fact that there remains a 10–12% performance gap in all distance events. The progressive developments in sports performance research and training, beginning with A.V. Hill’s establishment of the concept of VO_2max, have allowed endurance athletes to continue performance feats previously thought to be impossible. However, even today women are significantly underrepresented in sports performance research. By focusing more research on the female physiology and sex differences between men and women, we can better define how women differ from men in adapting to training and potentially use this information to improve endurance-exercise performance in women. The male advantage in endurance-exercise performance has commonly been attributed to their higher VO_2max, even when expressed as mL/kg/min. It is widely known that oxygen delivery is the primary limiting factor in elite athletes when it comes to improving VO_2max, but little research has explored the sex differences in oxygen delivery. Thus, the purpose of this review is to highlight what is known about the sex differences in the physiological factors contributing to VO_2max, more specifically oxygen delivery, and the impacts on performance.

Sex, gender and the pulmonary physiology of exercise

In this review, we detail how the pulmonary system's response to exercise is impacted by both sex and gender in healthy humans across the lifespan. First, the rationale for why sex and gender differences should be considered is explored, and then anatomical differences are highlighted, namely that females typically have smaller lungs and airways than males. Thereafter, we describe how these anatomical differences can impact functional aspects such as respiratory muscle energetics and activation, mechanical ventilatory constraints, diaphragm fatigue, and pulmonary gas exchange in healthy adults and children. Finally, we detail how gender can impact the pulmonary response to exercise.

Biological sex can influence the pulmonary response to exercise in healthy individuals across the lifespanhttps://bit.ly/3ejMDrv

A randomized single-center controlled trial of synchronized intermittent mandatory ventilation with heliox in newborn infants with meconium aspiration syndrome

OBJECTIVE

This study aimed to investigate the beneficial effects of synchronized intermittent mandatory ventilation (SIMV) with heliox in newborn infants with meconium aspiration syndrome (MAS).

METHODS

Seventy-one newborn infants with MAS in the neonatal intensive care unit (NICU) of Daping Hospital of Army Medical University were enrolled in the trial. Infants treated with SIMV were randomized and divided into the heliox group (n = 35) and control group (n = 36). The heliox group received heliox for 6 h followed by air-oxygen mixed gas, and the control group received air-oxygen mixed gas. The primary outcome measures were PaO₂ /FiO₂ (P/F) and the extubation time. The secondary outcome measures were the incidence of mechanical ventilation complications, hospital length of stay in the NICU, blood gas analysis, and inflammation markers.

RESULTS

The P/F in the heliox group was significantly better than that in the control group (p < .001). The extubation time and hospital length of stay in the NICU in the heliox group were shorter than those in the control group (p < .001). The inflammation markers at 6 h and myocardial injury markers at 24 h were decreased compared with those at 0 h, and those in the heliox group were more significantly decreased than those in the control group ([interleukin {IL}-6/IL-8/tumor necrosis factor α] p < .001, [C-reaction protein] p = .012; [creatine kinase] p < .001, [CK-MB] p = .041).

CONCLUSION

Heliox appears to be more effective in reducing the length of ventilation and increasing carbon dioxide eliminations than an air-oxygen mixture in infants with MAS under the support of SIMV.

The effect of estimating chest wall compliance on the work of breathing during exercise as determined via the modified Campbell diagram

The modified Campbell diagram provides one of the most comprehensive assessments of the work of breathing (Wb) during exercise, wherein the resistive and elastic work of inspiration and expiration are quantified. Importantly, a necessary step in constructing the modified Campbell diagram is to obtain a value for chest wall compliance (C_CW). To date, it remains unknown whether estimating or directly measuring C_CW impacts the Wb, as determined by the modified Campbell diagram. Therefore, the purpose of this study was to evaluate whether the components of the Wb differ when the modified Campbell diagram is constructed using an estimated versus measured value of C_CW. Forty-two participants (n = 26 men, 16 women) performed graded exercise to volitional exhaustion on a cycle ergometer. C_CW was measured directly at rest via quasistatic relaxation. Estimated values of C_CW were taken from prior literature. The measured value of C_CW was greater than that obtained via estimation (214 ± 52 mL/cmH₂O vs. 189 ± 18 mL/cmH₂O; P < 0.05). At modest-to-high minute ventilations (i.e., 50-200 L/min), the inspiratory elastic Wb was greater and expiratory resistive Wb was lower, when modified Campbell diagrams were constructed using estimated compared with measured values of C_CW (P = 0.001). These differences were however small and never exceeded ±5%. Thus, although our findings demonstrate that estimating C_CW has a measurable impact on the determination of the Wb, its effect appears relatively small within a cohort of healthy adults during graded exercise.

Effects of the Turbine™ on Ventilatory and Sensory Responses to Incremental Cycling

INTRODUCTION

The Turbine™ is a nasal dilator marketed to athletes to increase airflow, which may serve to reduce dyspnea and improve exercise performance, presumably via reductions in the work of breathing (WOB). However, the unpublished data supporting these claims were collected in individuals at rest that were exclusively nasal breathing. These data are not indicative of how the device influences breathing during exercise at higher ventilations when a larger proportion of breathing is through the mouth. Accordingly, the purpose of this study was to empirically test the efficacy of the Turbine™ during exercise. We hypothesized that the Turbine™ would modestly reduce the WOB at rest and very low exercise intensities but would have no effect on the WOB at moderate to high exercise intensities.

METHODS

We conducted a randomized crossover study in young, healthy individuals (7M:1F; age = 27 ± 5 yr) with normal lung function. Each participant performed two incremental cycle exercise tests to exhaustion with the Turbine™ device or under a sham control condition. For the sham control condition, participants were told they were breathing a low-density gas to reduce the WOB, but they were actually breathing room air. The WOB was determined through the integration of ensemble averaged esophageal pressure-volume loops. Standard cardiorespiratory measures were recorded using a commercially available metabolic cart. Dyspnea was assessed throughout exercise using the 0-10 Borg scale.

RESULTS

Peak V˙O2 and work rate were not different between conditions (P = 0.70 and P = 0.35, respectively). In addition, there was no interaction or main effect of condition on dyspnea, ventilation, or WOB throughout the exercise (all P > 0.05).

CONCLUSION

These findings suggest that the Turbine™ does not reduce the WOB and has no effect on dyspnea or exercise capacity.

Minimizing airflow turbulence in women lowers the work of breathing to levels similar to men

Smaller airways increase resistance and the propensity toward turbulent airflow, both of which are thought to be mechanisms behind greater resistive and total work of breathing (Wb) in females. Previous research examining the effect of airway size on the Wb between the sexes is limited by the inability to experimentally manipulate airway size. Heliox (21% oxygen, balance helium) is less dense than room air, which reduces turbulent airflow and airway resistance. The purpose of our study was to utilize heliox inspiration in women to provide a stimulus physiologically similar to increasing airway size. We hypothesized that when breathing heliox women would have a Wb similar to men breathing room air. Eighteen healthy young subjects (n = 9 women, 9 men) completed two maximal exercise tests on a cycle ergometer over 2 days. Subjects breathed room air for one test and heliox for the other. Wb was assessed with an esophageal balloon catheter. During the room air trial, when ventilations were >65 L/min, women had a significantly greater Wb compared with men (P < 0.05). The greater Wb in women was due to greater resistance to turbulent flow. For both sexes, breathing heliox resulted in increased expiratory flow (+132 ± 18% of room air), an elimination of expiratory flow limitation, and a reduction in Wb (69 ± 12% of room air) (all P < 0.05). When the women were breathing heliox, Wb was not different from that in the men breathing room air. Our findings support the idea that the smaller conducting airways in females are responsible for a greater total and resistive Wb.NEW & NOTEWORTHY When healthy young women breathe heliox gas during exercise, their work of breathing is not different from men breathing room air. Heliox inspiration reduces airway resistance and promotes laminar flow, which is a physiologically similar effect of increasing airway size. Our findings provide experimental evidence that smaller airways in women are responsible for the greater work of breathing during exercise.

Sex Differences in the Pulmonary System Influence the Integrative Response to Exercise

Healthy women have proportionally smaller lungs and airways compared with height-matched men. These anatomical sex-based differences result in greater mechanical ventilatory constraints and may influence the integrative response to exercise. Our review will examine this hypothesis in healthy humans in the context of dynamic whole-body exercise.

Ventilatory Limitation of Exercise in Pediatric Subjects Evaluated for Exertional Dyspnea

Purpose: Attribution of ventilatory limitation to exercise when the ratio of ventilation (V˙E) at peak work to maximum voluntary ventilation (MVV) exceeds 0.80 is problematic in pediatrics. Instead, expiratory flow limitation (EFL) measured by tidal flow-volume loop (FVL) analysis – the method of choice – was compared with directly measured MVV or proxies to determine ventilatory limitation.

Methods: Subjects undergoing clinical evaluation for exertional dyspnea performed maximal exercise testing with measurement of tidal FVL. EFL was defined when exercise tidal FVL overlapped at least 5% of the maximal expiratory flow-volume envelope for > 5 breaths in any stage of exercise. We compared this method of ventilatory limitation to traditional methods based on MVV or multiples (30, 35, or 40) of FEV₁. Receiver operating characteristic curves were constructed and area under curve (AUC) computed for peak V˙E/MVV and peak V˙E/x⋅FEV₁.

Results: Among 148 subjects aged 7–18 years (60% female), EFL was found in 87 (59%). Using EFL shown by FVL analysis as a true positive to determine ventilatory limitation, AUC for peak V˙E/30⋅FEV₁ was 0.84 (95% CI 0.78–0.90), significantly better than AUC 0.70 (95% CI 0.61–0.79) when 12-s sprint MVV was used for peak V˙E/MVV. Sensitivity and specificity were 0.82 and 0.70 respectively when using a cutoff of 0.85 for peak V˙E/30⋅FEV₁ to predict ventilatory limitation to exercise.

Conclusion: Peak V˙E/30⋅FEV₁ is superior to peak V˙E/MVV, as a means to identify potential ventilatory limitation in pediatric subjects when FVL analysis is not available.

Effects of macro- and micronutrients on exercise-induced hepcidin response in highly trained endurance athletes

Iron deficiency has ergolytic effects on athletic performance. Exercise-induced inflammation impedes iron absorption in the digestive tract by upregulating the expression of the iron regulatory protein, hepcidin. Limited research indicates the potential of specific macro- and micronutrients on blunting exercise-induced hepcidin. Therefore, we investigated the effects of postexercise supplementation with protein and carbohydrate (CHO) and vitamins D3 and K2 on the postexercise hepcidin response. Ten highly trained male cyclists (age: 26.9 ± 6.4 years; maximal oxygen uptake: 67.4 ± 4.4 mL·kg–1·min–1 completed 4 cycling sessions in a randomized, placebo-controlled, single-blinded, triple-crossover study. Experimental days consisted of an 8-min warm-up at 50% power output at maximal oxygen uptake, followed by 8 × 3-min intervals at 85% power output at maximal oxygen uptake with 1.5 min at 60% power output at maximal oxygen uptake between each interval. Blood samples were collected pre- and postexercise, and at 3 h postexercise. Three different drinks consisting of CHO (75 g) and protein (25 g) with (VPRO) or without (PRO) vitamins D3 (5000 IU) and K2 (1000 μg), or a zero-calorie control drink (PLA) were consumed immediately after the postexercise blood sample. Results showed that the postexercise drinks had no significant (p ≥ 0.05) effect on any biomarker measured. There was a significant (p < 0.05) increase in hepcidin and interleukin-6 following intense cycling intervals in the participants. Hepcidin increased significantly (p < 0.05) from baseline (nmol·L–1: 9.94 ± 8.93, 14.18 ± 14.90, 10.44 ± 14.62) to 3 h postexercise (nmol·L–1: 22.27 ± 13.41, 25.44 ± 11.91, 22.57 ± 15.57) in VPRO, PRO, and PLA, respectively. Contrary to our hypothesis, the drink compositions used did not blunt the postexercise hepcidin response in highly trained athletes.

Effect of Regular Yoga Practice on Respiratory Regulation and Exercise Performance

Yoga alters spontaneous respiratory regulation and reduces hypoxic and hypercapnic ventilatory responses. Since a lower ventilatory response is associated with an improved endurance capacity during whole-body exercise, we tested whether yogic subjects (YOGA) show an increased endurance capacity compared to matched non-yogic individuals (CON) with similar physical activity levels. Resting ventilation, the ventilatory response to hypercapnia, passive leg movement and exercise, as well as endurance performance were assessed. YOGA (n = 9), compared to CONTROL (n = 6), had a higher tidal volume at rest (0.7±0.2 vs. 0.5±0.1 l, p = 0.034) and a reduced ventilatory response to hypercapnia (33±15 vs. 47±15 l·min^-1, p = 0.048). A YOGA subgroup (n = 6) with maximal performance similar to CONTROL showed a blunted ventilatory response to passive cycling (11±2 vs. 14±2 l·min^-1, p = 0.039) and a tendency towards lower exercise ventilation (33±2 vs. 36±3 l·min^-1, p = 0.094) while cycling endurance (YOGA: 17.3±3.3; CON: 19.6±8.5 min, p = 0.276) did not differ. Thus, yoga practice was not associated with improved exercise capacity nor with significant changes in exercise ventilation despite a significantly different respiratory regulation at rest and in response to hypercapnia and passive leg movement.