The effects of age and sex on mechanical ventilatory constraint and dyspnea during exercise in healthy humans

Assessing the repeatability of expiratory flow limitation during incremental exercise in healthy adults

We sought to determine the repeatability of EFL in healthy adults during incremental cycle exercise. We hypothesized that the repeatability of EFL would be "strong" when assessed as a binary variable (i.e., absent or present) but "poor" when assessed as a continuous variable (i.e., % tidal volume overlap). Thirty-two healthy adults performed spirometry and an incremental cycle exercise test to exhaustion on two occasions. Standard cardiorespiratory variables were measured at rest and throughout exercise, and EFL was assessed by overlaying tidal expiratory flow-volume and maximal expiratory flow-volume curves. The repeatability of EFL was determined using Cohen's κ for binary assessments of EFL and intraclass correlation (ICC) for continuous measures of EFL. During exercise, n = 12 participants (38%) experienced EFL. At peak exercise, the repeatability of EFL was "minimal" (κ = 0.337, p = 0.145) when assessed as a binary variable and "poor" when measured as a continuous variable (ICC = 0.338, p = 0.025). At matched levels of minute ventilation during high-intensity exercise (i.e., >75% of peak oxygen uptake), the repeatability of EFL was "weak" when measured as a binary variable (κ = 0.474, p = 0.001) and "moderate" when measured as a continuous variable (ICC = 0.603, p < 0.001). Our results highlight the day-to-day variability associated with assessing EFL during exercise in healthy adults.

Sex- and age-adjusted reference values for dynamic inspiratory constraints during incremental cycle ergometry

Activity-related dyspnea in chronic lung disease is centrally related to dynamic (dyn) inspiratory constraints to tidal volume expansion. Lack of reference values for exertional inspiratory reserve (IR) has limited the yield of cardiopulmonary exercise testing in exposing the underpinnings of this disabling symptom. One hundred fifty apparently healthy subjects (82 males) aged 40-85 underwent incremental cycle ergometry. Based on exercise inspiratory capacity (ICdyn), we generated centile-based reference values for the following metrics of IR as a function of absolute ventilation: IRdyn1 ([1-(tidal volume/ICdyn)] x 100) and IRdyn2 ([1-(end-inspiratory lung volume/total lung capacity] x 100). IRdyn1 and IRdyn2 standards were typically lower in females and older subjects (p<0.05 for sex and age versus ventilation interactions). Low IRdyn1 and IRdyn2 significantly predicted the burden of exertional dyspnea in both sexes (p<0.01). Using these sex and age-adjusted limits of reference, the clinician can adequately judge the presence and severity of abnormally low inspiratory reserves in dyspneic subjects undergoing cardiopulmonary exercise testing.

Effects of inspiratory muscle training on thoracoabdominal volume regulation in older adults: A randomised controlled trial

OBJECTIVES

We investigated the effect of inspiratory muscle training (IMT) on inspiratory muscle strength, functional capacity and respiratory muscle kinematics during exercise in healthy older adults.

METHODS

24 adults were randomised into an IMT or SHAM-IMT group. Both groups performed 30 breaths, twice daily, for 8 weeks, at intensities of ∼50 % maximal inspiratory pressure (PImax; IMT) or <15 % PImax (SHAM-IMT). Measurements of PImax, breathing discomfort during a bout of IMT, six-minute walk distance, physical activity levels, and balance were assessed pre- and post-intervention. Respiratory muscle kinematics were assessed via optoelectronic plethysmography (OEP) during constant work rate cycling.

RESULTS

PImax was significantly improved (by 20.0±11.9 cmH2O; p=0.001) in the IMT group only. Breathing discomfort ratings during IMT significantly decreased (from 3.5±0.9-1.7±0.8). Daily sedentary time was decreased (by 28.0±39.8 min; p=0.042), and reactive balance significantly improved (by 1.2±0.8; p<0.001) in the IMT group only. OEP measures showed a significantly greater contribution of the pulmonary and abdominal rib cage compartments to total tidal volume expansion post-IMT.

CONCLUSIONS

IMT significantly improves inspiratory muscle strength and breathing discomfort in this population. IMT induces greater rib cage expansion and diaphragm descent during exercise, thereby suggesting a less restrictive effect on thoracic expansion and increased diaphragmatic power generation.

The metabolic cost of breathing for exercise ventilations: effects of age and sex

Given that there are both sex-based structural differences in the respiratory system and age-associated declines in pulmonary function, the purpose of this study was to assess the effects of age and sex on the metabolic cost of breathing (V̇o2RM) for exercise ventilations in healthy younger and older males and females. Forty healthy participants (10 young males 24 ± 3 yr; 10 young females 24 ± 3 yr; 10 older males 63 ± 3 yr, 10 older females 63 ± 6 yr) mimicked their exercise breathing patterns (voluntary hyperpnea) in the absence of exercise across a range of exercise intensities. At peak exercise, V̇o2RM represented a significantly greater fraction of peak oxygen consumption (V̇o2peak) in young females, 12.7 ± 4.0%, compared with young males, 10.7 ± 3.0% (P = 0.027), whereas V̇o2RM represented 13.5 ± 2.3% of V̇o2peak in older females and 13.2 ± 3.3% in older males. At relative ventilations, there was a main effect of age, with older males consuming a significantly greater fraction of V̇o2RM (6.6 ± 1.9%) than the younger males (4.4 ± 1.3%; P = 0.012), and older females consuming a significantly greater fraction of V̇o2RM (6.9 ± 2.5%) than the younger females (5.1 ± 1.4%; P = 0.004) at 65% V̇emax. Furthermore, both younger and older males had significantly better respiratory muscle efficiency than their female counterparts at peak exercise (P = 0.011; P = 0.015). Similarly, younger participants were significantly more efficient than older participants (6.5 ± 1.5% vs. 5.5 ± 2.0%; P = 0.001). Normal age-related changes in respiratory function, in addition to sex-based differences in airway anatomy, appear to influence the ventilatory responses and the cost incurred to breathe during exercise.NEW & NOTEWORTHY Here we show that at moderate and high-intensity exercise, older individuals incur a higher cost to breathe than their younger counterparts. However, as individuals age, the sex difference in the cost of breathing narrows. Collectively, our findings suggest that the normative age-related changes in respiratory structure and function, and sex differences in airway anatomy, appear to influence the ventilatory responses to exercise and the oxygen cost to breathe.

The pulmonary physiology of exercise

The pulmonary system is the first and last "line of defense" in terms of maintaining blood gas homeostasis during exercise. Our review provides the reader with an overview of how the pulmonary system responds to acute exercise. We undertook this endeavor to provide a companion article to "Cardiovascular Response to Exercise," which was published in Advances in Physiological Education. Together, these articles provide the readers with a solid foundation of the cardiopulmonary response to acute exercise in healthy individuals. The intended audience of this review is level undergraduate or graduate students and/or instructors for such classes. By intention, we intend this to be used as an educational resource and seek to provide illustrative examples to reinforce topics as well as highlight uncertainty to encourage the reader to think "beyond the textbook." Our treatment of the topic presents "classic" concepts along with new information on the pulmonary physiology of healthy aging.NEW & NOTEWORTHY Our narrative review is written with the student of the pulmonary physiology of exercise in mind, be it a senior undergraduate or graduate student or those simply refreshing their knowledge. We also aim to provide examples where the reader can incorporate real scenarios.

Functionality, muscular strength and cardiorespiratory capacity in the elderly: relationships between functional and physical tests according to sex and age

Introduction: There are several tests that provide information about physical fitness and functionality in older adults. The aims of this study were: (i) to analyze the differences between sex and age in functional, strength and cardiorespiratory tests; and (ii) to study the correlations between functional, strength and cardiorespiratory tests according to sex and age. Methods: A total of 171 older adults (72.09 ± 13.27 kg; 1.59 ± 0.09 m; 72.72 ± 6.05 years) were divided according to sex (men: n = 63; women: n = 108) and age (≥60 <70: n = 65; ≥70 <80: n = 89; ≥80: n = 18). Anthropometry, body composition, upper limb strength (hand grip; HG), lower limb strength (countermovement jump; CMJ), cardiorespiratory capacity (6 min walking test; 6MWT), timed up and go test (TUG) and Short Physical Performance Battery (SPPB) were assessed. Results: Men showed higher values in CMJ height, HG and expired volume (VE) (p < 0.05). There were no significant differences between sexes in TUG and SPPB. Regarding age, there were significant differences in CMJ, VE and peak oxygen uptake (VO2peak), TUG, gait speed, chair and stand test and SPPB total (p < 0.05). The test times were higher in older people. Regarding correlations, the TUG showed significant correlations in all strength and cardiorespiratory tests, regardless of sex and age. The CMJ correlated more significantly with functional tests compared to HG. Discussion: There were sex and age differences in functional, strength, and cardiorespiratory tests. The execution of quick and low-cost tests such as the CMJ and TUG could provide information on overall physical fitness in older adults.

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.

Dysanapsis is not associated with exertional dyspnoea in healthy male and female never-smokers aged 40 years and older

In healthy adults, airway-to-lung (i.e., dysanapsis) ratio is lower and dyspnoea during exercise at a given minute ventilation (V̇E) is higher in females than in males. We investigated the relationship between dysanapsis and sex on exertional dyspnoea in healthy adults. We hypothesized that females would have a smaller airway-to-lung ratio than males and that exertional dyspnoea would be associated with airway-to-lung ratio in males and females. We analyzed data from n = 100 healthy never-smokers aged ≥40 years enrolled in the Canadian Cohort Obstructive Lung Disease (CanCOLD) study who underwent pulmonary function testing, a chest computed tomography scan, and cardiopulmonary exercise testing. The luminal area of the trachea, right main bronchus, left main bronchus, right upper lobe, bronchus intermedius, left upper lobe, and left lower lobe were 22%-37% smaller (all p < 0.001) and the airway-to-lung ratio (i.e., average large conducting airway diameter relative to total lung capacity) was lower in females than in males (0.609 ± 0.070 vs. 0.674 ± 0.082; p < 0.001). During exercise, there was a significant effect of V̇E, sex, and their interaction on dyspnoea (all p < 0.05), indicating that dyspnoea increased as a function of V̇E to a greater extent in females than in males. However, after adjusting for age and total lung capacity, there were no significant associations between airway-to-lung ratio and measures of exertional dyspnoea, regardless of sex (all r < 0.34; all p > 0.05). Our findings suggest that sex differences in airway size do not contribute to sex differences in exertional dyspnoea.

Time-Efficient, High-Resistance Inspiratory Muscle Strength Training Increases Exercise Tolerance in Midlife and Older Adults

PURPOSE

This study aimed to determine if time-efficient, high-resistance inspiratory muscle strength training (IMST), comprising 30 inhalation-resisted breaths per day, improves cardiorespiratory fitness, exercise tolerance, physical function, and/or regional body composition in healthy midlife and older adults.

METHODS

We performed a double-blind, randomized, sham-controlled clinical trial (NCT03266510) testing 6 wk of IMST (30 breaths per day, 6 d·wk -1 , 55%-75% maximal inspiratory pressure) versus low-resistance sham training (15% maximal inspiratory pressure) in healthy men and women 50-79 yr old. Subjects performed a graded treadmill exercise test to exhaustion, physical performance battery (e.g., handgrip strength, leg press), and body composition testing (dual x-ray absorptiometry) at baseline and after 6 wk of training.

RESULTS

Thirty-five participants (17 women, 18 men) completed high-resistance IMST ( n = 17) or sham training ( n = 18). Cardiorespiratory fitness (V̇O 2peak ) was unchanged, but exercise tolerance, measured as treadmill exercise time during a graded exercise treadmill test, increased with IMST (baseline, 539 ± 42 s; end intervention, 606 ± 42 s; P = 0.01) but not sham training (baseline, 562 ± 39 s; end intervention, 553 ± 38 s; P = 0.69). IMST increased peak RER (baseline, 1.09 ± 0.02; end intervention, 1.13 ± 0.02; P = 0.012), peak ventilatory efficiency (baseline, 25.2 ± 0.8; end intervention, 24.6 ± 0.8; P = 0.036), and improved submaximal exercise economy (baseline, 23.5 ± 1.1 mL·kg -1 ⋅min -1 ; end intervention, 22.1 ± 1.1 mL·kg -1 ⋅min -1 ; P < 0.001); none of these factors were altered by sham training (all P > 0.05). Changes in plasma acylcarnitines (targeted metabolomics analysis) were consistently positively correlated with changes in exercise tolerance after IMST but not sham training. IMST was associated with regional increases in thorax lean mass (+4.4%, P = 0.06) and reductions in trunk fat mass (-4.8%, P = 0.04); however, peripheral muscle strength, muscle power, dexterity, and mobility were unchanged.

CONCLUSIONS

These data suggest that high-resistance IMST is an effective, time-efficient lifestyle intervention for improving exercise tolerance in healthy midlife and older adults.

Ventilatory limitations in patients with HFpEF and obesity

Heart failure with preserved ejection fraction (HFpEF) patients have an increased ventilatory demand. Whether their ventilatory capacity can meet this increased demand is unknown, especially in those with obesity. Body composition (DXA) and pulmonary function were measured in 20 patients with HFpEF (69 ± 6 yr;9 M/11 W). Cardiorespiratory responses, breathing mechanics, and ratings of perceived breathlessness (RPB, 0-10) were measured at rest, 20 W, and peak exercise. FVC correlated with %body fat (R2 =0.51,P = 0.0006), V̇O2peak (%predicted,R2 =0.32,P = 0.001), and RPB (R2 =0.58,P = 0.0004). %Body fat correlated with end-expiratory lung volume at rest (R2 =0.76,P < 0.001), 20 W (R2 =0.72,P < 0.001), and peak exercise (R2 =0.74,P < 0.001). Patients were then divided into two groups: those with lower ventilatory reserve (FVC<3 L,2 M/10 W) and those with higher ventilatory reserve (FVC>3.8 L,7 M/1 W). V̇O2peak was ∼22% less (p < 0.05) and RPB was twice as high at 20 W (p < 0.01) in patients with lower ventilatory reserve. Ventilatory reserves are limited in patients with HFpEF and obesity; indeed, the margin between ventilatory demand and capacity is so narrow that exercise capacity could be ventilatory limited in many patients.

Attenuating intrathoracic pressure swings decreases cardiac output at different intensities of exercise

Intrathoracic pressure (ITP) swings that permit spontaneous ventilation have physiological implications for the heart. We sought to determine the effect of respiration on cardiac output (Q ̇ $\dot Q$ ) during semi-supine cycle exercise using a proportional assist ventilator to minimize ITP changes and lower the work of breathing (Wb ). Twenty-four participants (12 females) completed three exercise trials at 30%, 60% and 80% peak power (Wmax ) with unloaded (using a proportional assist ventilator, PAV) and spontaneous breathing. Intrathoracic and intraabdominal pressures were measured with balloon catheters placed in the oesophagus and stomach. Left ventricular (LV) volumes andQ ̇ $\dot Q$ were determined via echocardiography. Heart rate (HR) was measured with electrocardiogram and a customized metabolic cart measured oxygen uptake (V ̇ O 2 ${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}}}$ ). Oesophageal pressure swings decreased from spontaneous to PAV breathing by -2.8 ± 3.1, -4.9 ± 5.7 and -8.1 ± 7.7 cmH2 O at 30%, 60% and 80% Wmax , respectively (P = 0.01). However, the decreases in Wb were similar across exercise intensities (27 ± 42 vs. 35 ± 24 vs. 41 ± 22%, respectively, P = 0.156). During PAV breathing compared to spontaneous breathing,Q ̇ $\dot Q$ decreased by -1.0 ± 1.3 vs. -1.4 ± 1.4 vs. -1.5 ± 1.9 l min-1 (all P < 0.05) and stroke volume decreased during PAV breathing by -11 ± 12 vs. -9 ± 10 vs. -7 ± 11 ml from spontaneous breathing at 30%, 60% and 80% Wmax , respectively (all P < 0.05). HR was lower during PAV breathing by -5 ± 4 beats min-1 at 80% Wmax (P < 0.0001). Oxygen uptake decreased by 100 ml min-1 during PAV breathing compared to spontaneous breathing at 80% Wmax (P < 0.0001). Overall, attenuating ITPs mitigated LV preload and ejection, thereby suggesting that the ITPs associated with spontaneous respiration impact cardiac function during exercise. KEY POINTS: Pulmonary ventilation is accomplished by alterations in intrathoracic pressure (ITP), which have physiological implications on the heart and dynamically influence the loading parameters of the heart. Proportional assist ventilation was used to attenuate ITP changes and decrease the work of breathing during exercise to examine its effects on left ventricular (LV) function. Proportional assist ventilation with progressive exercise intensities (30%, 60% and 80% Wmax ) led to reductions in cardiac output at all intensities, primarily through reductions in stroke volume. Decreases in LV end-diastolic volume (30% and 60% Wmax ) and increases in LV end-systolic volume (80% Wmax ) were responsible for the reduction in stroke volume. The relationship between cardiac output and oxygen uptake is disrupted during respiratory muscle unloading.

A Systematic Review of Methods Used to Determine the Work of Breathing during Exercise

INTRODUCTION

Measurement of the work of breathing (Wb) during exercise provides useful insights into the energetics and mechanics of the respiratory muscles across a wide range of minute ventilations. The methods and analytical procedures used to calculate the Wb during exercise have yet to be critically appraised in the literature.

PURPOSE

The aim of this systematic review was to evaluate the quality of methods used to measure the Wb during exercise in the available literature.

METHODS

We conducted an extensive search of three databases for studies that measured the Wb during exercise in adult humans. Data were extracted on participant characteristics, flow/volume and pressure devices, esophageal pressure (P oes ) catheters, and methods of Wb analysis.

RESULTS

A total of 120 articles were included. Flow/volume sensors used were primarily pneumotachographs ( n = 85, 70.8%), whereas the most common pressure transducer was of the variable reluctance type ( n = 63, 52.5%). Esophageal pressure was frequently obtained via balloon-tipped catheters ( n = 114, 95.0%). Few studies mentioned calibration, frequency responses, and dynamic compensation of their measurement devices. The most popular method of measuring the Wb was pressure-volume integration ( n = 51, 42.5%), followed by the modified Campbell ( n = 28, 23.3%) and Dean & Visscher diagrams ( n = 26, 21.7%). Over one-third of studies did not report the methods used to process their pressure-volume data, and the majority (60.8%) of studies used the incorrect Wb units and/or failed to discuss the limitations of their Wb measurements.

CONCLUSIONS

The findings of this systematic review highlight the need for the development of a standardized approach for measuring Wb, which is informative, practical, and accessible for future researchers.

The effects of age on dyspnea and respiratory mechanical and neural responses to exercise in healthy men

The respiratory muscle pressure generation and inspiratory and expiratory neuromuscular recruitment patterns in younger and older men were compared during exercise, alongside descriptors of dyspnea. Healthy younger (n = 8, 28 ± 5 years) and older (n = 8, 68 ± 4 years) men completed a maximal incremental cycling test. Esophageal, gastric (Pga ) and transdiaphragmatic pressures, and electromyography (EMG) of the crural diaphragm were measured using a micro-transducer and EMG catheter. EMG of the parasternal intercostals, sternocleidomastoids, and rectus abdominis were measured using skin surface electrodes. After the exercise test, participants completed a questionnaire to evaluate descriptors of dyspnea. Pga at end-expiration, Pga expiratory tidal swings, and the gastric pressure-time product (PTPga ) at absolute and relative minute ventilation were higher (p < 0.05) for older compared to younger men. There were no differences in EMG responses between older and younger men. Younger men were more likely to report shallow breathing (p = 0.005) than older men. Our findings showed younger and older men had similar respiratory neuromuscular activation patterns and reported different dyspnea descriptors, and that older men had greater expiratory muscle pressure generation during exercise. Greater expiratory muscle pressures in older men may be due to compensatory mechanisms designed to offset increasing airway resistance due to aging. These results may have implications for exercise-induced expiratory muscle fatigue in older men.

Distinguishing science from pseudoscience in commercial respiratory interventions: an evidence-based guide for health and exercise professionals

Respiratory function has become a global health priority. Not only is chronic respiratory disease a leading cause of worldwide morbidity and mortality, but the COVID-19 pandemic has heightened attention on respiratory health and the means of enhancing it. Subsequently, and inevitably, the respiratory system has become a target of the multi-trillion-dollar health and wellness industry. Numerous commercial, respiratory-related interventions are now coupled to therapeutic and/or ergogenic claims that vary in their plausibility: from the reasonable to the absurd. Moreover, legitimate and illegitimate claims are often conflated in a wellness space that lacks regulation. The abundance of interventions, the range of potential therapeutic targets in the respiratory system, and the wealth of research that varies in quality, all confound the ability for health and exercise professionals to make informed risk-to-benefit assessments with their patients and clients. This review focuses on numerous commercial interventions that purport to improve respiratory health, including nasal dilators, nasal breathing, and systematized breathing interventions (such as pursed-lips breathing), respiratory muscle training, canned oxygen, nutritional supplements, and inhaled L-menthol. For each intervention we describe the premise, examine the plausibility, and systematically contrast commercial claims against the published literature. The overarching aim is to assist health and exercise professionals to distinguish science from pseudoscience and make pragmatic and safe risk-to-benefit decisions.

Combining hypoxia with thermal stimuli in humans: physiological responses and potential sex differences

Increasing prevalence of native lowlanders sojourning to high altitudes (>2,500 m) for recreational, occupational, military, and competitive reasons has generated increased interest in physiological responses to multistressor environments. Exposure to hypoxia poses recognized physiological challenges that are amplified during exercise and further complicated by environments that might include combinations of heat, cold, and high altitude. There is a sparsity of data examining integrated responses in varied combinations of environmental conditions, with even less known about potential sex differences. How this translates into performance, occupational, and health outcomes requires further investigation. Acute hypoxic exposure decreases arterial oxygen saturation, resulting in a reflex hypoxic ventilatory response and sympathoexcitation causing an increase in heart rate, myocardial contractility, and arterial blood pressure, to compensate for the decreased arterial oxygen saturation. Acute altitude exposure impairs exercise performance, for example, reduced time to exhaustion and slower time trials, largely owing to impairments in pulmonary gas exchange and peripheral delivery resulting in reduced V̇o2max. This exacerbates with increasing altitude, as does the risk of developing acute mountain sickness and more serious altitude-related illnesses, but modulation of those risks with additional stressors is unclear. This review aims to summarize and evaluate current literature regarding cardiovascular, autonomic, and thermoregulatory responses to acute hypoxia, and how these may be affected by simultaneous thermal environmental challenges. There is minimal available information regarding sex as a biological variable in integrative responses to hypoxia or multistressor environments; we highlight these areas as current knowledge gaps and the need for future research.

Sex differences in blood pressure and inactive limb blood flow responses during dynamic leg exercise with increased inspiratory muscle work

We hypothesized that, compared with young males, young females have a smaller decrease in blood flow to the inactive limb, accompanied by a smaller increase in arterial blood pressure, during dynamic exercise with increased inspiratory muscle work. Young males and females performed dynamic knee-extension and -flexion exercises for 10 min (spontaneous breathing for 5 min and voluntary hyperpnoea with or without inspiratory resistance for 5 min). Mean arterial blood pressure (MAP) and mean blood flow (MBF) in the brachial artery were continuously measured by means of finger photoplethysmography and Doppler ultrasound, respectively. No sex differences were found in the ΔMAP and ΔMBF (Δ: from baseline) during exercise without inspiratory resistance. In contrast, the ΔMAP during exercise with inspiratory resistive breathing was greater (P < 0.05) in males (+31.3 ± 2.1 mmHg, mean ± SE) than females (+18.9 ± 3.2 mmHg). The MBF during exercise with inspiratory resistance did not change in males (-4.4 ± 10.6 mL/min), whereas it significantly increased in females (+25.2 ± 15.4 mL/min). These results suggest that an attenuated inspiratory muscle-induced metaboreflex in young females affects blood flow distribution during submaximal dynamic leg exercise.

The effect of trait self-control on dyspnoea and tolerance to a CO2 rebreathing challenge in healthy males and females

BACKGROUND

High trait self-control is associated with greater tolerance of unpleasant sensations including effort and pain. Dyspnoea and pain have several commonalities and this study aimed to investigate for the first time whether trait self-control influences responses to a hypercapnic rebreathing challenge designed to induce dyspnoea. As sex also influences tolerance to dyspnoea, we also sought to investigate whether this moderated the role of trait self-control.

METHODS

Participants (n = 65, 32 females) scoring high or low for trait self-control, performed a standardised rebreathing challenge, in which inspired carbon dioxide (CO₂) gradually increased over a period of 6 min or until an intolerable level of dyspnoea. Air hunger (AH) intensity - a distinctive quality of dyspnoea, was measured every 30 s. The multidimensional dyspnoea profile (MDP) was completed after the rebreathing challenge for a more complete overview of breathing discomfort.

RESULTS

Males high in trait self-control (SCHIGH) (302 ± 42 s), tolerated the rebreathing challenge for longer than males low in self-control (SCLOW) (252 ± 66 s, P = 0.021), experienced slower increases in AH intensity during the rebreathing challenge (0.03 ± 0.01 cm^.s ^- 1 vs. 0.04 ± 0.01 cm^.s ^- 1,P = 0.045) and reported lower perceived mental effort on the MDP (4.94 ± 2.46 vs. 7.06 ± 1.60, P = 0.007). There was no difference between SCHIGH and SCLOW females for challenge duration. However, SCHIGH females (9.29 ± 0.66 cm) reported greater air hunger at the end of the challenge than SCLOW females (7.75 ± 1.75 cm, P = 0.003). It is possible that SCLOW females were unwilling to tolerate the same perceptual intensity of AH as the SCHIGH females.

CONCLUSIONS

These results indicate that individuals high in trait self-control are more tolerant of dyspnoea during a CO₂ rebreathing challenge than low self-control individuals. Tolerance of the stimulus was moderated by the sex of the participant, presenting an interesting opportunity for future research.

Considerations for Sex-Cognizant Research in Exercise Biology and Medicine

As the fields of kinesiology, exercise science, and human movement developed, the majority of the research focused on male physiology and extrapolated findings to females. In the medical sphere, basing practice on data developed in only males resulted in the removal of drugs from the market in the late 1990s due to severe side effects (some life-threatening) in females that were not observed in males. In response to substantial evidence demonstrating exercise-induced health benefits, exercise is often promoted as a key modality in disease prevention, management, and rehabilitation. However, much like the early days of drug development, a historical literature knowledge base of predominantly male studies may leave the exercise field vulnerable to overlooking potentially key biological differences in males and females that may be important to consider in prescribing exercise (e.g., how exercise responses may differ between sexes and whether there are optimal approaches to consider for females that differ from conventional approaches that are based on male physiology). Thus, this review will discuss anatomical, physiological, and skeletal muscle molecular differences that may contribute to sex differences in exercise responses, as well as clinical considerations based on this knowledge in athletic and general populations over the continuum of age. Finally, this review summarizes the current gaps in knowledge, highlights the areas ripe for future research, and considerations for sex-cognizant research in exercise fields.

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

Impact of aging on the work of breathing during exercise in healthy men

This study examined the impact of aging on the elastic and resistive components of the work of breathing (W_b) during locomotor exercise at a given 1) ventilatory rate, 2) metabolic rate, and 3) operating lung volume. Eight healthy younger (25 ± 4 yr) and 8 older (72 ± 6 yr) participants performed incremental bicycle exercise, from which retrospective analyses identified similar ventilatory rates (approximately 40, 70, and 100 L·min^-1), similar metabolic rates (V̇o₂: approximately 1.2, 1.6, and 1.9 L·min^-1), and similar lung volumes [inspiratory and expiratory reserve volumes (IRV/ERV: approximately 25/34%, 16/33%, and 13-34% of vital capacity]. W_b at each level was quantified by integrating the averaged esophageal pressure-volume loop, which was then partitioned into elastic and resistive components of inspiratory and expiratory work using the modified Campbell diagram. IRV was smaller in the older participants during exercise at ventilations of 70 and 100 L·min^-1 and during exercise at the three metabolic rates (P < 0.05). Mainly because of a greater inspiratory elastic and resistive W_b in the older group (P < 0.05), total W_b was augmented by 40%-50% during exercise at matched ventilatory and matched metabolic rates. When examined during exercise evoking similar lung volumes, total W_b was not different between the groups (P = 0.86). Taken together, although aging exaggerates total W_b during locomotor exercise at a given ventilatory or a given metabolic rate, this difference is abolished during exercise at a given operating lung volume. These findings highlight the significance of operating lung volume in determining the age-related difference in W_b during locomotor exercise.NEW & NOTEWORTHY This study evaluated the impact of aging on the work of breathing (W_b) during locomotor exercise evoking similar ventilatory rates, metabolic rates, and operating lung volumes in young and older individuals. Mainly because of a greater inspiratory elastic and resistive W_b in older participants, total W_b was higher during exercise at any given ventilatory and metabolic rate with aging. However, this age-related difference was abolished during exercise evoking similar operating lung volumes in both age groups. These findings highlight the significance of lung volumes in determining the age-related difference in total W_b.

Does Regular Physical Activity Mitigate the Age-Associated Decline in Pulmonary Function?

Whereas the negative effects of aging and smoking on pulmonary function are undisputed, the potential favorable effects of physical activity on the aging process of the otherwise healthy lung remain controversial. This question is of particular clinical relevance when reduced pulmonary function compromises aerobic exercise capacity (maximal oxygen consumption) and thus contributes to an increased risk of morbidity and mortality. Here, we discuss whether and when the aging-related decline in pulmonary function limits maximal oxygen consumption and whether, how, and to what extent regular physical activity can slow down this aging process and preserve pulmonary function and maximal oxygen consumption. Age-dependent effects of reduced pulmonary function (i.e., FEV₁, the volume that has been exhaled after the first second of forced expiration) on maximal oxygen consumption have been observed in several cross-sectional and longitudinal studies. Complex interactions between aging-related cellular and molecular processes affecting the lung, and structural and functional deterioration of the cardiovascular and respiratory systems account for the concomitant decline in pulmonary function and maximal oxygen consumption. Consequently, if long-term regular physical activity mitigates some of the aging-related decline in pulmonary function (i.e., FEV₁ decline), this could also prevent a steep fall in maximal oxygen consumption. In contrast to earlier research findings, recent large-scale longitudinal studies provide growing evidence for the beneficial effects of physical activity on FEV₁. Although further confirmation of those effects is required, these findings provide powerful arguments to start and/or maintain regular physical activity.

Time to Move Beyond a "One-Size Fits All" Approach to Inspiratory Muscle Training

Inspiratory muscle training (IMT) has been studied as a rehabilitation tool and ergogenic aid in clinical, athletic, and healthy populations. This technique aims to improve respiratory muscle strength and endurance, which has been seen to enhance respiratory pressure generation, respiratory muscle weakness, exercise capacity, and quality of life. However, the effects of IMT have been discrepant between populations, with some studies showing improvements with IMT and others not. This may be due to the use of standardized IMT protocols which are uniformly applied to all study participants without considering individual characteristics and training needs. As such, we suggest that research on IMT veer away from a standardized, one-size-fits-all intervention, and instead utilize specific IMT training protocols. In particular, a more personalized approach to an individual's training prescription based upon goals, needs, and desired outcomes of the patient or athlete. In order for the coach or practitioner to adjust and personalize a given IMT prescription for an individual, factors, such as frequency, duration, and modality will be influenced, thus inevitably affecting overall training load and adaptations for a projected outcome. Therefore, by integrating specific methods based on optimization, periodization, and personalization, further studies may overcome previous discrepancies within IMT research.

Airway luminal area and the resistive work of breathing during exercise in healthy young females and males

We examined the relationship between the work of breathing (W_b) during exercise and in vivo measures of airway size in healthy females and males. We hypothesized that sex differences in airway luminal area would explain the larger resistive W_b during exercise in females. Healthy participants (n = 11 females and n = 11 males; 19-30 yr) completed a cycle exercise test to exhaustion where W_b was assessed using an esophageal balloon catheter. On a separate day, each participant underwent a bronchoscopy procedure for optical coherence tomography measures of seven airways. In vivo measures of luminal area were made for the fourth to eighth airway generations. A composite index of airway size was calculated as the sum of the luminal area for each generation, and the total area was calculated based on Weibel's model. We found that index of airway size (males: 37.4 ± 6.3 mm² vs. females: 27.5 ± 7.4 mm²) and airway area calculated based on Weibel's model (males: 2,274 ± 557 mm² vs. females: 1,594 ± 389 mm²) were significantly larger in males (both P = 0.003). When minute ventilation was greater than ∼60 L·min^-1, the resistive W_b was higher in females. At the highest equivalent flow achieved by all subjects, resistance to inspired flow was larger in females and significantly associated with two measures of airway size in all subjects: index of airway size (r = 0.524, P = 0.012) and Weibel area (r = 0.525, P = 0.012). Our findings suggest that innate sex differences in luminal area result in a greater resistive W_b during exercise in females compared with males.NEW & NOTEWORTHY We hypothesized that the higher resistive work of breathing in females compared with males during high-intensity exercise is due to smaller airways. In vivo measures of the fourth to eighth airway generations made using optical coherence tomography show that females tend to have smaller airway luminal areas of the fourth to sixth airway generations. Sex differences in airway luminal area result in a greater resistive work of breathing during exercise in females compared with males.

A comparison of methods used to quantify the work of breathing during exercise

The mechanical work of breathing (Wb) is an insightful tool used to assess respiratory mechanics during exercise. There are several different methods used to calculate the Wb, however, each approach having its own distinct advantages/disadvantages. To date, a comprehensive assessment of the differences in the components of Wb between these methods is lacking. We therefore sought to compare the values of Wb during graded exercise as determined via the four most popular methods: 1) pressure-volume integration; 2) the Hedstrand diagram; 3) the Otis diagram; and the 4) modified Campbell diagram. Forty-two participants (30 ± 15 yr; 16 women) performed graded cycling to volitional exhaustion. Esophageal pressure-volume loops were obtained throughout exercise. These data were used to calculate the total Wb and, where possible, its subcomponents of inspiratory and expiratory, resistive and elastic Wb, using each of the four methods. Our results demonstrate that the components of Wb were indeed different between methods across the minute ventilations engendered by graded exercise. Importantly, however, no systematic pattern in these differences could be observed. Our findings indicate that the values of Wb obtained during exercise are uniquely determined by the specific method chosen to compute its value-no two methods yield identical results. Because there is currently no "gold-standard" for measuring the Wb, it is emphasized that future investigators be cognizant of the limitations incurred by their chosen method, such that observations made by others may be interpreted with greater context, and transparency.NEW & NOTEWORTHY The measurement of the work of breathing (Wb) during exercise provides us with deep insights into respiratory (patho)physiology, and sheds light on the putative factors which lead to respiratory muscle fatigue. There are 4 popular methods available to determine the Wb. Our study demonstrates that no two of these methods produce identical values of Wb during exercise. This paper also discusses the practical and theoretical limitations of each method.

Evaluation of sex-based differences in airway size and the physiological implications

Recent evidence suggests healthy females have significantly smaller central conducting airways than males when matched for either height or lung volume during analysis. This anatomical sex-based difference could impact the integrative response to exercise. Our review critically evaluates the literature on direct and indirect techniques to measure central conducting airway size and their limitations. We present multiple sources highlighting the difference between male and female central conducting airway size in both pediatric and adult populations. Following the discussion of measurement techniques and results, we discuss the functional implications of these differences in central conducting airway size, including work of breathing, oxygen cost of breathing, and how these impacts will continue into elderly populations. We then discuss a range of topics for the future direction of airway differences and the benefits they could provide to both healthy and diseased populations. Specially, these sex-differences in central conducting airway size could result in different aerosol deposition or how lung disease manifests. Finally, we detail emerging techniques that uniquely allow for high-resolution imaging to be paired with detailed physiological measures.

Impact of ageing and pregnancy on the minute ventilation/carbon dioxide production response to exercise

Ventilatory efficiency can be evaluated using the relationship between minute ventilation (V′_E) and the rate of CO₂ production (V′_CO2). In accordance with the modified alveolar ventilation equation, this relationship is determined by changes in dead space volume (V_D) and/or the arterial CO₂ tension (P_aCO2) equilibrium point. In this review, we summarise the physiological factors that may account for normative ageing and pregnancy induced increases in V′_E/V′_CO2 during exercise. Evidence suggests that age-related increases in V_D and pregnancy-related decreases in the P_aCO2 equilibrium point are mechanistically linked to the increased V′_E/V′_CO2 during exercise. Importantly, the resultant increase in V′_E/V′_CO2 (ratio or slope), with normal ageing or pregnancy, remains below the critical threshold for prognostic indication in cardiopulmonary disease, is not associated with increased risk of adverse health outcomes, and does not affect the respiratory system's ability to fulfil its primary role of eliminating CO₂ and maintaining arterial oxygen saturation during exercise.

The minute ventilation/carbon dioxide production response to exercise is elevated with advancing age and in healthy pregnancy due to increased dead space and lowering of the arterial partial pressure of carbon dioxide equilibrium point, respectively.https://bit.ly/2GJXm0o

An integrative approach to the pulmonary physiology of exercise: when does biological sex matter?

Historically, many studies investigating the pulmonary physiology of exercise (and biomedical research in general) were performed exclusively or predominantly with male research participants. This has led to an incomplete understanding of the pulmonary response to exercise. More recently, important sex-based differences with respect to the human respiratory system have been identified. The purpose of this review is to summarize current findings related to sex-based differences in the pulmonary physiology of exercise. To that end, we will discuss how morphological sex-based differences of the respiratory system affect the respiratory response to exercise. Moreover, we will discuss sex-based differences of the physiological integrative responses to exercise, and how all these differences can influence the regulation of breathing. We end with a brief discussion of pregnancy and menopause and the accompanying ventilatory changes observed during exercise.

The Oxygen Cascade During Exercise in Health and Disease

The oxygen transport cascade describes the physiological steps that bring atmospheric oxygen into the body where it is delivered and consumed by metabolically active tissue. As such, the oxygen cascade is fundamental to our understanding of exercise in health and disease. Our narrative review will highlight each step of the oxygen transport cascade from inspiration of atmospheric oxygen down to mitochondrial consumption in both healthy active males and females along with clinical conditions. We will focus on how different steps interact along with principles of homeostasis, physiological redundancies, and adaptation. In particular, we highlight some of the parallels between elite athletes and clinical conditions in terms of the oxygen cascade.

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.

Face Masks and the Cardiorespiratory Response to Physical Activity in Health and Disease

To minimize transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the novel coronavirus responsible for coronavirus disease (COVID-19), the U.S. Centers for Disease Control and Prevention and the World Health Organization recommend wearing face masks in public. Some have expressed concern that these may affect the cardiopulmonary system by increasing the work of breathing, altering pulmonary gas exchange and increasing dyspnea, especially during physical activity. These concerns have been derived largely from studies evaluating devices intentionally designed to severely affect respiratory mechanics and gas exchange. We review the literature on the effects of various face masks and respirators on the respiratory system during physical activity using data from several models: cloth face coverings and surgical masks, N95 respirators, industrial respirators, and applied highly resistive or high-dead space respiratory loads. Overall, the available data suggest that although dyspnea may be increased and alter perceived effort with activity, the effects on work of breathing, blood gases, and other physiological parameters imposed by face masks during physical activity are small, often too small to be detected, even during very heavy exercise. There is no current evidence to support sex-based or age-based differences in the physiological responses to exercise while wearing a face mask. Although the available data suggest that negative effects of using cloth or surgical face masks during physical activity in healthy individuals are negligible and unlikely to impact exercise tolerance significantly, for some individuals with severe cardiopulmonary disease, any added resistance and/or minor changes in blood gases may evoke considerably more dyspnea and, thus, affect exercise capacity.

Age and sex differences in blood pressure responses during hyperpnoea

NEW FINDINGS

What is the central question of this study? Increased respiratory muscle activation is associated with neural and cardiovascular consequences via the respiratory muscle-induced metaboreflex. Does ageing and/or sex influence the arterial blood pressure response during voluntary normocapnic incremental hyperpnoea? What is the main finding and its importance? The increase in blood pressure during hyperpnoea was smaller in younger females than in older females, whereas no difference was found between older males and older females. The blunted respiratory muscle-induced metaboreflex in younger females is normalized with advancing age, whereas ageing has no such effect in males.

ABSTRACT

We hypothesized that older females (OF) have a greater arterial blood pressure response to increased respiratory muscle work compared with younger females (YF) and that no such difference exists between older males (OM) and younger males (YM). To test these hypotheses, cardiovascular responses during voluntary normocapnic incremental hyperpnoea were evaluated and compared between older and younger subjects. An incremental respiratory endurance test (IRET) was performed as follows: target minute ventilation was initially set at 30% of the maximal voluntary ventilation (MVV12) and was increased by 10% of MVV12 every 3 min. The test was terminated when the subject could not maintain the target percentage of MVV12. Heart rate and mean arterial blood pressure (MAP) were recorded continuously. The increase in MAP from baseline (ΔMAP) during the IRET in OM (+24.0 ± 14.7 mmHg, mean ± SD) did not differ (P = 0.144) from that in YM (+24.3 ± 13.4 mmHg), but it was greater (P = 0.004) in OF (+31.2 ± 11.6 mmHg) than in YF (+10.3 ± 5.5 mmHg). No significant difference in ΔMAP during the IRET was observed between OM and OF (P = 0.975). These results suggest that the respiratory muscle-induced metaboreflex is blunted in YF, but it could be normalized with advancing age. In males, ageing has little effect on the respiratory muscle-induced metaboreflex. These results show no sex difference in the respiratory muscle-induced metaboreflex in older adults.

Physiological sex differences affect the integrative response to exercise: acute and chronic implications

NEW FINDINGS

What is the topic of this review? We review sex differences within physiological systems implicated in exercise performance; specifically, how they integrate to determine metabolic thresholds and fatigability. Thereafter, we discuss the implications that these sex differences might have for long-term adaptation to exercise. What advances does it highlight? The review collates evidence from recent physiological studies that have investigated sex as a biological variable, demonstrating that the physiological response to equivalent 'dosages' of exercise is not the same in males and females; thus, highlighting the need to research diversity in physiological responses to interventions.

ABSTRACT

The anatomical and physiological differences between males and females are thought to determine differences in the limits of human performance. The notion of studying sex as a biological variable has recently been emphasized in the biosciences as a vital step in enhancing human health. In this review, we contend that the effects of biological sex on acute and chronic responses must be studied and accounted for when prescribing aerobic exercise, much like any intervention targeting the optimization of physiological function. Emerging evidence suggests that the response of physiological systems to exercise differs between males and females, potentially mediating the beneficial effects in healthy and clinical populations. We highlight evidence that integrative metabolic thresholds during exercise are influenced by phenotypical sex differences throughout many physiological systems. Furthermore, we discuss evidence that female skeletal muscle is more resistant to fatigue elicited by equivalent dosages of high-intensity exercise. How the different acute responses affect the long-term trainability of males and females is considered, with discussion about tailoring exercise to the characteristics of the individual presented within the context of biological sex. Finally, we highlight the influence of endogenous and exogenous sex hormones on physiological responses to exercise in females. Sex is one of many mediating influences on the outcomes of exercise, and with careful experimental designs, physiologists can advance the collective understanding of diversity in physiology and optimize outcomes for both sexes.

Evaluation of Dynamic Respiratory Mechanical Abnormalities During Conventional CPET

Assessment of the ventilatory response to exercise is important in evaluating mechanisms of dyspnea and exercise intolerance in chronic cardiopulmonary diseases. The characteristic mechanical derangements that occur during exercise in chronic respiratory conditions have previously been determined in seminal studies using esophageal catheter pressure-derived measurements. In this brief review, we examine the emerging role and clinical utility of conventional assessment of dynamic respiratory mechanics during exercise testing. Thus, we provide a physiologic rationale for measuring operating lung volumes, breathing pattern, and flow-volume loops during exercise. We consider standardization of inspiratory capacity-derived measurements and their practical implementation in clinical laboratories. We examine the evidence that this iterative approach allows greater refinement in evaluation of ventilatory limitation during exercise than traditional assessments of breathing reserve. We appraise the available data on the reproducibility and responsiveness of this methodology. In particular, we review inspiratory capacity measurement and derived operating lung volumes during exercise. We demonstrate, using recent published data, how systematic evaluation of dynamic mechanical constraints, together with breathing pattern analysis, can provide valuable insights into the nature and extent of physiological impairment contributing to exercise intolerance in individuals with common chronic obstructive and restrictive respiratory disorders.

Is the healthy respiratory system built just right, overbuilt, or underbuilt to meet the demands imposed by exercise?

In the healthy, untrained young adult, a case is made for a respiratory system (airways, pulmonary vasculature, lung parenchyma, respiratory muscles, and neural ventilatory control system) that is near ideally designed to ensure a highly efficient, homeostatic response to exercise of varying intensities and durations. Our aim was then to consider circumstances in which the intra/extrathoracic airways, pulmonary vasculature, respiratory muscles, and/or blood-gas distribution are underbuilt or inadequately regulated relative to the demands imposed by the cardiovascular system. In these instances, the respiratory system presents a significant limitation to O₂ transport and contributes to the occurrence of locomotor muscle fatigue, inhibition of central locomotor output, and exercise performance. Most prominent in these examples of an "underbuilt" respiratory system are highly trained endurance athletes, with additional influences of sex, aging, hypoxic environments, and the highly inbred equine. We summarize by evaluating the relative influences of these respiratory system limitations on exercise performance and their impact on pathophysiology and provide recommendations for future investigation.

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.

Modelling the effects of age and sex on the resistive and viscoelastic components of the work of breathing during exercise

NEW FINDINGS

What is the central question of this study? What is the effect of age and sex on the resistive and viscoelastic components of work of breathing (W_b ) during exercise? What is the main finding and its importance? The resistive and viscoelastic components of W_b were higher in older adults, regardless of sex. The resistive, but not viscoelastic, component of W_b was higher in females than in males, regardless of age. These findings contribute to improving our understanding of the effects of ageing and sex on the mechanical ventilatory response to exercise.

ABSTRACT

Healthy ageing and biological sex each affect the work of breathing (W_b ) for a given minute ventilation ( V ̇ E ). Age-related structural changes to the respiratory system lead to an increase in both the resistive and viscoelastic components of W_b ; however, it is unclear whether healthy ageing differentially alters the mechanics of breathing in males and females. We analysed data from 22 older (60-80 years, n = 12 females) and 22 younger (20-30 years, n = 11 females) males and females that underwent an incremental cycle exercise test to exhaustion. V ̇ E and W_b were assessed at rest and throughout exercise. W_b - V ̇ E data for each participant were fitted to a non-linear equation (i.e. W_b  = a V ̇ E ³ + b V ̇ E ² ) that partitions W_b into resistive (i.e. a V ̇ E ³ ) and viscoelastic (i.e. b V ̇ E ² ) components. We then modelled the effects of healthy ageing and biological sex on each component of W_b . Overall, the model fit was excellent (r² : 0.99 ± 0.01). There was a significant main effect of age and sex on the resistive component of W_b (both P < 0.05), and a significant main effect of age (P < 0.001), but not sex (P = 0.309), on the viscoelastic component of W_b . No significant interactions between age and sex on a V ̇ E ³ or b V ̇ E ² were noted (both P > 0.05). Our findings indicate that during exercise: (i) the higher total W_b in females relative to males is due to a higher resistive, but not viscoelastic, component of W_b , and (ii) regardless of sex, the higher W_b in older adults relative to younger adults is due to higher resistive and viscoelastic components of W_b .

Analysis of maximal expiratory flow-volume curves in adult survivors of preterm birth

Adult survivors of very preterm (≤32 wk gestational age) birth without (PRE) and with bronchopulmonary dysplasia (BPD) have variable degrees of airflow obstruction at rest. Assessment of the shape of the maximal expiratory flow-volume (MEFV) curve in PRE and BPD may provide information concerning their unique pattern of airflow obstruction. The purposes of the present study were to 1) quantitatively assess the shape of the MEFV curve in PRE, BPD, and healthy adults born at full-term (CON), 2) identify where along the MEFV curve differences in shape existed between groups, and 3) determine the association between an index of MEFV curve shape and characteristics of preterm birth (i.e., gestational age, mass at birth, duration of oxygen therapy) in PRE and BPD. To do so, we calculated the average slope ratio (SR) throughout the effort-independent portion of the MEFV curve and at increments of 5% of forced vital capacity (FVC) between 20 and 80% of FVC in PRE (n = 19), BPD (n = 25), and CON (n = 20). We found that average SR was significantly higher in PRE (1.34 ± 0.35) and BPD (1.33 ± 0.45) compared with CON (1.03 ± 0.22; both P < 0.05) but similar between PRE and BPD (P = 0.99). Differences in SR between groups occurred early in expiration (i.e., 20-30% of FVC). There was no association between SR and characteristics of preterm birth in PRE and BPD groups (all P > 0.05). The mechanism(s) of increased SR during early expiration in PRE/BPD relative to CON is unknown but may be due to differences in the structural and mechanical properties of the airways.

Intercostal muscle blood flow is elevated in old rats during submaximal exercise

BACKGROUND

Respiratory muscle blood flows (BF) increase substantially during exercise in younger adult rats. As aging is associated with altered pulmonary function, we hypothesized that old rats will have greater intercostal muscle BF and vascular conductances (VC) than young rats during submaximal exercise.

METHODS

Mean arterial pressure and respiratory muscle BFs (via carotid artery catheter and radiolabeled microspheres, respectively) were measured at rest and during submaximal exercise in young (n = 9) and old (n = 7) Fischer 344 X Brown Norway rats.

RESULTS

At rest, diaphragm, intercostal, and transversus abdominis BFs and VCs were not different between groups (all, p > 0.10). During submaximal exercise, old compared to young rats had greater intercostal BF (40 ± 6 vs 25 ± 2 mL/min/100 g) and VC (0.30 ± 0.05 vs 0.18 ± 0.02 mL/min/mmHg/100 g) (both, p ≤ 0.01). Diaphragm and transversus abdominis BFs and VCs were not different between groups during exercise (all, p > 0.24).

CONCLUSIONS

These data demonstrate that intercostal muscle BF and VC are increased in old compared to young rats during submaximal exercise.

Expiratory flow limitation under moderate hypobaric hypoxia does not influence ventilatory responses during incremental running in endurance runners

We tested whether expiratory flow limitation (EFL) occurs in endurance athletes in a moderately hypobaric hypoxic environment equivalent to 2500 m above sea level and, if so, whether EFL inhibits peak ventilation ( V ˙ Epeak ), thereby exacerbating the hypoxia-induced reduction in peak oxygen uptake ( V ˙ O2peak ). Seventeen young male endurance runners performed incremental exhaustive running on separate days under hypobaric hypoxic (560 mmHg) and normobaric normoxic (760 mmHg) conditions. Oxygen uptake ( V ˙ O2 ), minute ventilation ( V ˙ E), arterial O2 saturation (SpO2 ), and operating lung volume were measured throughout the incremental exercise. Among the runners tested, 35% exhibited EFL (EFL group, n = 6) in the hypobaric hypoxic condition, whereas the rest did not (Non-EFL group, n = 11). There were no differences between the EFL and Non-EFL groups for V ˙ Epeak and V ˙ O2peak under either condition. Percent changes in V ˙ Epeak (4 ± 4 vs. 2 ± 4%) and V ˙ O2peak (-18 ± 6 vs. -16 ± 6%) from normobaric normoxia to hypobaric hypoxia also did not differ between the EFL and Non-EFL groups (all P > 0.05). No differences in maximal running velocity, SpO2 , or operating lung volume were detected between the two groups under either condition. These results suggest that under the moderate hypobaric hypoxia (2500 m above sea level) frequently used for high-attitude training, ~35% of endurance athletes may exhibit EFL, but their ventilatory and metabolic responses during maximal exercise are similar to those who do not exhibit EFL.

Manipulation of mechanical ventilatory constraint during moderate intensity exercise does not influence dyspnoea in healthy older men and women

KEY POINTS

The perceived intensity of exertional breathlessness (i.e. dyspnoea) is higher in older women than in older men, possibly as a result of sex-differences in respiratory system morphology. During exercise at a given absolute intensity or minute ventilation, older women have a greater degree of mechanical ventilatory constraint (i.e. work of breathing and expiratory flow limitation) than their male counterparts, which may lead to a greater perceived intensity of dyspnoea. Using a single-blind randomized study design, we experimentally manipulated the magnitude of mechanical ventilatory constraint during moderate-intensity exercise at ventilatory threshold in healthy older men and women. We found that changes in the magnitude of mechanical ventilatory constraint within the physiological range had no effect on dyspnoea in healthy older adults. When older men and women perform moderate intensity exercise, mechanical ventilatory constraint does not contribute significantly to the sensation of dyspnoea.

ABSTRACT

We aimed to determine the effect of manipulating mechanical ventilatory constraint during submaximal exercise on dyspnoea in older men and women. Eighteen healthy subjects (aged 60-80 years; nine men and nine women) completed two days of testing. On day 1, subjects were assessed for pulmonary function and performed a maximal incremental cycle exercise test. On day 2, subjects performed three 6-min bouts of cycling at ventilatory threshold, in a single-blind randomized manner, while breathing: (i) normoxic helium-oxygen (HEL) to reduce the work of breathing (W_b ) and alleviate expiratory flow limitation (EFL); (ii) through an inspiratory resistance (RES) of ∼5 cmH₂ O L^-1  s^-1 to increase W_b ; and (iii) ambient air as a control (CON). Oesophageal pressure, diaphragm electromyography, and sensory responses (category-ratio 10 Borg scale) were monitored throughout exercise. During the HEL condition, there was a significant decrease in W_b (men: -21 ± 6%, women: -17 ± 10%) relative to CON (both P < 0.01). Moreover, if EFL was present during CON (four men and five women), it was alleviated during HEL. Conversely, during the RES condition, W_b (men: 42 ± 19%, women: 50 ± 16%) significantly increased relative to CON (both P < 0.01). There was no main effect of sex on W_b (P = 0.59). Across conditions, women reported significantly higher dyspnoea intensity than men (2.9 ± 0.9 vs. 1.9 ± 0.8 Borg scale units, P < 0.05). Despite significant differences in the degree of mechanical ventilatory constraint between conditions, the intensity of dyspnoea was unaffected, independent of sex (P = 0.46). When older men and women perform moderate intensity exercise, mechanical ventilatory constraint does not contribute significantly to the sensation of dyspnoea.

Exertional Dyspnea in Childhood: Is There an Iceberg Beneath the Apex?

This essay expounds on fundamental, quantitative elements of the exercise ventilation in children, which was the subject of the Tom Rowland Lecture given at the NASPEM 2018 Conference. Our knowledge about how much ventilation rises during aerobic exercise is reasonably solid; our understanding of its governance is a work in progress, but our grasp of dyspnea and ventilatory limitation in children (if it occurs) remains embryonic. This manuscript summarizes ventilatory mechanics during dynamic exercise, then proceeds to outline our current understanding of mechanisms of dyspnea, particularly during exercise (exertional dyspnea). Most research in this field has been done in adults, and the vast majority of these studies in patients with chronic obstructive pulmonary disease. To what extent conclusions drawn from this literature apply to children and adolescents-both healthy and those with cardiopulmonary disease-will be discussed. The few, recent, pertinent, pediatric studies will be reviewed in an attempt to provide an empirical basis for proposing a hypothetical model to study exertional dyspnea in youth. Just as somatic growth will have consequences for ventilatory and exercise capacity, so too will neural developmental plasticity and experience affect perception of dyspnea. Our path to understand how these evolving inputs and influences summate during a child's life will be Columbus' India.

Resistive and elastic work of breathing in older and younger adults during exercise

It is unknown whether the greater total work of breathing (WOB) with aging is due to greater elastic and/or resistive WOB. We hypothesized that older compared with younger adults would exhibit a greater total WOB at matched ventilations (V̇e) during graded exercise, secondary to greater inspiratory resistive and elastic as well as expiratory resistive WOB. Older (OA: 60 ± 8 yr; n = 9) and younger (YA: 38 ± 7 yr; n = 9) adults performed an incremental cycling test to volitional fatigue. Esophageal pressure, inspiratory (IRV) and expiratory reserve volumes (ERV), expiratory flow limitation (EFL), and ventilatory variables were measured at matched V̇e (i.e., 25, 50, and 75 l/min) during exercise. The inspiratory resistive and elastic as well as expiratory resistive WOB were quantified using the Otis method. At V̇e of 75 l/min, older adults had greater %EFL and larger tidal volumes to inspiratory capacity but smaller relative IRV ( P ≤ 0.03) than younger adults. Older compared with younger adults had greater total WOB at V̇_E of 50 and 75 l/min (OA: 90 ± 43 vs. YA: 49 ± 21 J/min; P < 0.04 for both). At V̇e of 75 l/min, older adults had greater inspiratory elastic and resistive WOB (OA: 44 ± 27 vs. YA: 24 ± 22 and OA: 23 ± 15 vs. YA: 11 ± 3 J/min, respectively, P < 0.03 for both) and expiratory resistive WOB (OA: 23 ± 19 vs. YA: 14 ± 9 J/min, P = 0.02) than younger adults. These data demonstrate that aging-induced pulmonary alterations result in greater inspiratory elastic and resistive as well as expiratory resistive WOB, which may have implications for the integrated response during exercise. NEW & NOTEWORTHY Aging-induced changes to the pulmonary system result in increased work of breathing (WOB) during exercise. However, it is not known whether this higher WOB with aging is due to differences in elastic and/or resistive WOB. Herein, we demonstrate that older adults exhibited greater inspiratory elastic and resistive as well as expiratory resistive WOB during exercise.