Predictors of Expiratory Flow Limitation during Exercise in Healthy Males and Females

Difference in expiratory flow limitations development in normoxia and hypoxia in healthy individuals

The present study investigated the maintenance/repeatability of expiratory flow limitation (EFL) between normoxia and hypoxia. Fifty-one healthy active individuals (27 men and 24 women) performed a lung function test and a maximal incremental cycling test in both normoxia and hypoxia (inspired oxygen fraction = 0.14) on two separate visits. During exercise in normoxia, 28 participants exhibited EFL (55 %). In hypoxia, another cohort of 28 participants exhibited EFL. The two groups only partly overlapped. Individuals with EFL only in normoxia reported lower maximal ventilation values in hypoxia than in normoxia (n=5; -13.5 ± 7.8 %) compared to their counterparts with EFL only in hypoxia (n=5; +6.7 ± 6.3 %) or without EFL (n=18; +5.1 ± 10.3 %) (p=0.004 and p<0.001, respectively). EFL development may be induced by different mechanisms in hypoxia vs. normoxia since the individuals who exhibited flow limitation were not the same between the two environmental conditions. This change seems influenced by the magnitude of the maximal ventilation change.

Effects of Obesity and Sex on Ventilatory Constraints during a Cardiopulmonary Exercise Test in Children

PURPOSE

Ventilatory constraints are common during exercise in children, but the effects of obesity and sex are unclear. The purpose of this study was to investigate the effects of obesity and sex on ventilatory constraints (i.e., expiratory flow limitation (EFL) and dynamic hyperinflation) during a maximal exercise test in children.

METHODS

Thirty-four 8- to 12-yr-old children without obesity (18 females) and 54 with obesity (23 females) completed pulmonary function testing and maximal cardiopulmonary exercise tests. EFL was calculated as the overlap between tidal flow-volume loops during exercise and maximal expiratory flow-volume loops. Dynamic hyperinflation was calculated as the change in inspiratory capacity from rest to exercise.

RESULTS

Maximal minute ventilation was not different between children with and without obesity. Average end-inspiratory lung volumes (EILV) and end-expiratory lung volumes (EELV) were significantly lower during exercise in children with obesity (EILV: 68.8% ± 0.7% TLC; EELV: 41.2% ± 0.5% TLC) compared with children without obesity (EILV: 73.7% ± 0.8% TLC; EELV: 44.8% ± 0.6% TLC; P < 0.001). Throughout exercise, children with obesity experienced more EFL and dynamic hyperinflation compared with those without obesity ( P < 0.001). Also, males experienced more EFL and dynamic hyperinflation throughout exercise compared with females ( P < 0.001). At maximal exercise, the prevalence of EFL was similar in males with and without obesity; however, the prevalence of EFL in females was significantly different, with 57% of females with obesity experiencing EFL compared with 17% of females without obesity ( P < 0.05). At maximal exercise, 44% of children with obesity experienced dynamic hyperinflation compared with 12% of children without obesity ( P = 0.002).

CONCLUSIONS

Obesity in children increases the risk of developing mechanical ventilatory constraints such as dynamic hyperinflation and EFL. Sex differences were apparent with males experiencing more ventilatory constraints compared with females.

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.

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.

Fitness Level- and Sex-Related Differences in Pulmonary Limitations to Maximal Exercise in Normoxia and Hypoxia

PURPOSE

Both maximal-intensity exercise and altitude exposure challenge the pulmonary system that may reach its maximal capacities. Expiratory flow limitation (EFL) and exercise-induced hypoxemia (EIH) are common in endurance-trained athletes. Furthermore, because of their smaller airways and lung size, women, independently of their fitness level, may be more prone to pulmonary limitations during maximal-intensity exercise, particularly when performed in hypoxic conditions. The objective of this study was to investigate the impact of sex and fitness level on pulmonary limitations during maximal exercise in normoxia and their consequences in acute hypoxia.

METHODS

Fifty-one participants were distributed across four different groups according to sex and fitness level. Participants visited the laboratory on three occasions to perform maximal incremental cycling tests in normoxia and hypoxia (inspired oxygen fraction = 0.14) and two hypoxic chemosensitivity tests. Pulmonary function and ventilatory capacities were evaluated at each visit.

RESULTS

EIH was more prevalent (62.5% vs 22.2%, P = 0.004) and EFL less common (37.5% vs 70.4%, P = 0.019) in women than men. EIH prevalence was different ( P = 0.004) between groups of trained men (41.7%), control men (6.7%), trained women (50.0%), and control women (75.0%). All EIH men but only 40% of EIH women exhibited EFL. EFL individuals had higher slope ratio ( P = 0.029), higher ventilation (V̇ E ) ( P < 0.001), larger ΔVO 2max ( P = 0.019), and lower hypoxia-related V̇ E increase ( P < 0.001).

CONCLUSIONS

Women reported a higher EIH prevalence than men, regardless of their fitness level, despite a lower EFL prevalence. EFL seems mainly due to the imbalance between ventilatory demands and capacities. It restricts ventilation, leading to a larger performance impairment during maximal exercise in hypoxic conditions.

Tidal expiratory flow limitation during exercise is unrelated to peripheral hypercapnic chemosensitivity

We sought to determine if peripheral hypercapnic chemosensitivity is related to expiratory flow limitation (EFL) during exercise. Twenty participants completed one testing day which consisted of peripheral hypercapnic chemosensitivity testing and a maximal exercise test to exhaustion. The chemosensitivity testing consisting of two breaths of 10% CO2 (O2∼21%) repeated 5 times during seated rest and the first 2 exercise intensities during the maximal exercise test. Following chemosensitivity testing, participants continued cycling with the intensity increasing 20 W every 1.5 minutes till exhaustion. Maximal expiratory flow-volume curves were derived from forced expiratory capacity maneuvers performed before and after exercise at varying efforts. Inspiratory capacity maneuvers were performed during each exercise stage to determine EFL. There was no difference between the EFL and non-EFL hypercapnic chemoresponse (mean response during exercise 0.96 ± 0.46 and 0.91 ± 0.33 l min-1 mmHg-1, p=0.783). Peripheral hypercapnic chemosensitivity during mild exercise does not appear to be related to the development of EFL during exercise.

Ventilatory Responses to Exercise by Age, Sex, and Health Status

ABSTRACT

An understanding of the normal pulmonary responses to incremental exercise is requisite for appropriate interpretation of findings from clinical exercise testing. The purpose of this review is to provide concrete information to aid the interpretation of the exercise ventilatory response in both healthy and diseased populations. We begin with an overview of the normal exercise ventilatory response to incremental exercise in the healthy, normally trained young-to-middle aged adult male. The exercise ventilatory responses in two nonpatient populations (females, elderly) are then juxtaposed with the responses in healthy males. The review concludes with overviews of the exercise ventilatory responses in four patient populations (obesity, chronic obstructive pulmonary disease, asthma, congestive heart failure). Again, we use the normal response in healthy adults as the framework for interpreting the responses in the clinical groups. For each healthy and clinical population, recent, impactful research findings will be presented.

Functional assessment of respiratory muscles and lung capacity of CrossFit athletes

CrossFit is a high-intensity training related to physical fitness and respiratory capacity that can promote changes in lung function. This cross-sectional study was aimed at evaluating respiratory muscle strength, electromyographic (EMG) activity, and lung capacity in CrossFit athletes. Thirty subjects aged between 25 and 35 years were divided into groups: CrossFit athletes (n=15) and sedentary individuals without comorbidities (n=15). Respiratory muscle strength was evaluated using maximal inspiratory and expiratory pressures, lung capacity, and EMG of the sternocleidomastoid, serratus anterior, external intercostal, and diaphragm muscles at respiratory rest, maximal inspiration and expiration, and respiratory cycle. Data were tabulated and subjected to statistical analyses (t-test and Spearman test, P<0.05). Respiratory muscle strength on EMG of the sternocleidomastoid, serratus, external intercostal, and diaphragm muscles at the respiratory cycle and maximal forced inspiration and expiration were higher in the CrossFit athletes group than in the sedentary group without comorbidities. CrossFit athlete group showed significantly strong positive correlation between maximal inspiratory and expiratory muscle strengths (Spearman rho= 0.903, P=0.000), with increasing muscle strength during inspiration favoring an increase in strength during expiration. The forced vital capacity (FVC) and forced expiratory volume in 1 sec (FEV₁) also showed a significantly high positive correlation (Spearman rho=0.912, P=0.000) in the CrossFit athletes group, showing that higher FVC favors higher FEV₁. The results of this study suggest that improved fitness is based on increased respiratory muscle strength on EMG in CrossFit athletes.

Influence of graded hypercapnia on endurance exercise performance in healthy humans

Military and/or emergency services personnel may be required to perform high-intensity physical activity during exposure to elevated inspired carbon dioxide (CO2). Although many of the physiological consequences of hypercapnia are well characterized, the effects of graded increases in inspired CO2 on self-paced endurance performance have not been determined. The aim of this study was to compare the effects of 0%, 2%, and 4% inspired CO2 on 2-mile run performance, as well as physiological and perceptual responses during time trial exercise. Twelve physically active volunteers (peak oxygen uptake = 49 ± 5 mL·kg-1·min-1; 3 women) performed three experimental trials in a randomized, single-blind, crossover manner, breathing 21% oxygen with either 0%, 2%, or 4% CO2. During each trial, participants completed 10 min of walking at ∼40% peak oxygen uptake followed by a self-paced 2-mile treadmill time trial. One participant was unable to complete the 4% CO2 trial due to lightheadedness during the run. Compared with the 0% CO2 trial, run performance was 5 ± 3% and 7 ± 3% slower in the 2% and 4% CO2 trials, respectively (both P < 0.001). Run performance was significantly slower with 4% versus 2% CO2 (P = 0.046). The dose-dependent performance impairments were accompanied by stepwise increases in mean ventilation, despite significant reductions in running speed. Dyspnea and headache were significantly elevated during the 4% CO2 trial compared with both the 0% and 2% trials. Overall, our findings show that graded increases in inspired CO2 impair endurance performance in a stepwise manner in healthy humans.

Sex differences in the ventilatory responses to exercise in mild-moderate obesity

NEW FINDINGS

What is the central question of the study? What are the sex differences in ventilatory responses during exercise in adults with obesity. What is the main finding and its importance? Tidal volume and expiratory flows are lower in females when compared with males at higher levels of ventilation despite small increases in end-expiratory lung volumes. Since dyspnea on exertion is a frequent complaint, particularly in females with obesity, careful attention should be paid to unpleasant respiratory symptoms and mechanical ventilatory constraints before prescribing exercise.

ABSTRACT

Obesity is associated with altered ventilatory responses, which may be exacerbated in females due to the functional consequences of sex-related morphological differences in the respiratory system. This study examined sex differences in ventilatory responses during exercise in adults with obesity. Healthy adults with obesity (n = 73; 48 females) underwent pulmonary function testing, underwater weighing, magnetic resonance imaging, a graded exercise test to exhaustion, and two constant work rate exercise tests; one at a fixed work rate (60W for females and 105W for males) and one at a relative intensity (50% of peak oxygen uptake, V̇O_2peak ). Metabolic, respiratory, and perceptual responses were assessed during exercise. Compared with males, females used a smaller proportion of their ventilatory capacity at peak exercise (69.13 ± 14.49 vs. 77.41 ± 17.06 % maximum voluntary ventilation, P = 0.0374). Females also utilized a smaller proportion of their forced vital capacity (FVC) at peak exercise (tidal volume: 48.51±9.29 vs. 54.12±10.43 %FVC, P = 0.0218). End-expiratory lung volumes were 2-4% higher in females compared with males during exercise (P<0.05), while end-inspiratory lung volumes were similar. Since the males were initiating inspiration from a lower lung volume, they experienced greater expiratory flow limitation during exercise. Ratings of perceived breathlessness during exercise were similar between females and males at comparable levels of ventilation. In summary, sex differences in the manifestations of obestity-related mechanical ventilatory constraints were observed. Since dyspnea on exertion is a common complaint in patients with obesity, particularly in females, exercise prescriptions should be tailored with the goal of minimizing unpleasant respiratory sensations. This article is protected by copyright. All rights reserved.