Mechanical Ventilatory Constraints Research Articles

Physiological mechanisms of sex differences in exertional dyspnoea: role of neural respiratory motor drive

What is the central question of this study? Does the combination of a higher neural respiratory drive and greater dynamic mechanical ventilatory constraints during exercise in healthy women versus men form the mechanistic basis of sex differences in activity-related dyspnoea? What is the main finding and its importance? Sex differences in activity-related dyspnoea in health primarily reflected the awareness of a higher neural respiratory drive needed to achieve any given ventilation during exercise in the setting of relatively greater dynamic mechanical ventilatory constraints in women. These findings may have implications for our understanding of the mechanisms of sex differences in exertional dyspnoea in variants of health (e.g. the elderly) and in patients with cardiorespiratory disease. The purpose of this study was to elucidate the physiological mechanisms of sex differences in exertional dyspnoea. We compared detailed measures of neural respiratory motor drive [diaphragmatic EMG (EMGdi) expressed as a percentage of maximal EMGdi (EMGdi%max)], breathing pattern, operating lung volumes, dynamic respiratory mechanics [tidal oesophageal (P(oes,tida)l%peak) and transdiaphragmatic pressure swings (P(di,tidal)%peak) expressed as a percentage of their respective peak values] and sensory intensity and unpleasantness ratings of dyspnoea during symptom-limited incremental cycle exercise in healthy young women (n = 25) and men (n = 25). The tidal volume to forced vital capacity ratio (V(T)%FVC), breathing frequency, EMGdi%max, P(oes,tidal)%peak, P(di,tidal)%peak and sensory intensity and unpleasantness ratings of dyspnoea were higher, while dynamic inspiratory capacity and inspiratory reserve volume were lower at a standardized absolute ventilation of 55 l min(-1) during submaximal exercise in women versus men (all P < 0.05). In contrast, sex had no demonstrable effect on the inter-relationships between exercise-induced increases in V(T)%FVC, EMGdi%max and sensory intensity and unpleasantness ratings of dyspnoea. The results of this study suggest that sex differences in the intensity and unpleasantness of exertional dyspnoea in health are likely to reflect the awareness of a relatively higher neural respiratory motor drive (or EMGdi%max) needed to achieve any given ventilation during exercise in the setting of relatively greater dynamic mechanical constraints on V(T) expansion in women.

Ventilatory Responses at Peak Exercise in Endurance-Trained Obese Adults

Alterations in respiratory mechanics predispose healthy obese individuals to low lung volume breathing, which places them at risk of developing expiratory flow limitation (EFL). The high ventilatory demand in endurance-trained obese adults further increases their risk of developing EFL and increases their work of breathing. The objective of this study was to investigate the prevalence and magnitude of EFL in fit obese (FO) adults via measurements of breathing mechanics and ventilatory dynamics during exercise. Ten (seven women and three men) FO (mean ± SD, 38 ± 5 years, 38% ± 5% body fat) and 10 (seven women and three men) control obese (CO) (38 ± 5 years, 39% ± 5% body fat) subjects underwent hydrostatic weighing, pulmonary function testing, cycle exercise testing, and the determination of the oxygen cost of breathing during eucapnic voluntary hyperpnea. There were no differences in functional residual capacity (43% ± 6% vs 40% ± 9% total lung capacity [TLC]), residual volume (21% ± 4% vs 21% ± 4% TLC), or FVC (111% ± 13% vs 104% ± 15% predicted) between FO and CO subjects, respectively. FO subjects had higher FEV1 (111% ± 13% vs 99% ± 11% predicted), TLC (106% ± 14% vs 94% ± 7% predicted), peak expiratory flow (123% ± 14% vs 106% ± 13% predicted), and maximal voluntary ventilation (128% ± 15% vs 106% ± 13% predicted) than did CO subjects. Peak oxygen uptake (129% ± 16% vs 86% ± 15% predicted), minute ventilation (128 ± 35 L/min vs 92 ± 25 L/min), and work rate (229 ± 54 W vs 166 ± 55 W) were higher in FO subjects. Mean inspiratory (4.65 ± 1.09 L/s vs 3.06 ± 1.21 L/s) and expiratory (4.15 ± 0.95 L/s vs 2.98 ± 0.76 L/s) flows were greater in FO subjects, which yielded a greater breathing frequency (51 ± 8 breaths/min vs 41 ± 10 breaths/min) at peak exercise in FO subjects. Mechanical ventilatory constraints in FO subjects were similar to those in CO subjects despite the greater ventilatory demand in FO subjects. FO individuals achieve high ventilations by increasing breathing frequency, matching the elevated metabolic demand associated with high fitness. They do this without developing meaningful ventilatory constraints. Therefore, endurance-trained obese individuals with higher lung function are not limited by breathing mechanics during peak exercise, which may allow healthy obese adults to participate in vigorous exercise training.

Mechanical ventilatory constraints during incremental exercise in healthy and cystic fibrosis children

To analyze breathing pattern and mechanical ventilatory constraints during incremental exercise in healthy and cystic fibrosis (CF) children. Thirteen healthy children and 6 children with cystic fibrosis volunteered to perform an incremental test on a treadmill. Exercise tidal flow/volume loops were plotted every minute within a maximal flow/volume loop (MFVL). Expiratory flow limitation (expFL expressed in %Vt) was evaluated and end-expiratory and end-inspiratory lung volumes (EELV and EILV) were estimated from expiratory reserve volume relative to vital capacity (ERV/FVC) and from inspiratory reserve volume relative to vital capacity (IRV/FVC). During the incremental exercise, expFL was first observed at 40% of maximal aerobic speed in both groups. At maximal exercise, 46% of healthy children and 83% of CF children presented expFL, without significant effect of cystic fibrosis on the severity of expFL. According to the two-way ANOVA results, both groups adopted similar breathing pattern and breathing strategies as no significant effect of CF has been revealed. But, according to one-way ANOVA results, a significant increase of ERV/FVC associated with a significant decrease of IRV/FVC from resting value shave been observed in healthy children at maximal exercise, but not in CF children. The hypothesis of this study was based on the assumption that mild cystic fibrosis could induce more frequent and more severe mechanical ventilatory constraints due to pulmonary impairment and breathing pattern disturbances. But, this study did not succeed to highlight an effect of mild cystic fibrosis on the mechanical ventilatory constraints (expFL and dynamic hyperinflation) that occur during an incremental exercise. This absence of effect could be due to the absence of an impact of the disease on spirometric data, breathing pattern regulation during exercise and breathing strategy.

Exercise‐induced arterial hypoxaemia and the mechanics of breathing in healthy young women

The purpose of this study was to characterize exercise-induced arterial hypoxaemia (EIAH), pulmonary gas exchange and respiratory mechanics during exercise, in young healthy women. We defined EIAH as a >10 mmHg decrease in arterial oxygen tension ( ) during exercise compared to rest. We used a heliox inspirate to test the hypothesis that mechanical constraints contribute to EIAH. Subjects with a spectrum of aerobic capacities (n = 30; maximal oxygen consumption ( ) = 49 ± 1, range 28-62 ml kg(-1) min(-1)) completed a stepwise treadmill test and a subset (n = 18 with EIAH) completed a constant load test (~85% ) with heliox gas. Throughout exercise arterial blood gases, oxyhaemoglobin saturation ( ), the work of breathing (WOB) and expiratory flow limitation (EFL) were assessed. Twenty of the 30 women developed EIAH with a nadir and ranging from 58 to 88 mmHg and 87 to 96%, respectively. At maximal exercise, was inversely related to (r = -0.57, P < 0.05) with notable exceptions where some subjects with low aerobic fitness levels demonstrated EIAH. Subjects with EIAH had a greater (51 ± 1 vs. 43 ± 2 ml kg(-1) min(-1)), lower end-exercise (93.2 ± 0.5 vs. 96.1 ± 0.3%) and a greater maximal energetic WOB (324 ± 19 vs. 247 ± 23 J min(-1)), but had similar resting pulmonary function compared to those without EIAH. Most subjects developed EIAH at submaximal exercise intensities, with distinct patterns of hypoxaemia. In some subjects with varying aerobic fitness levels, mechanical ventilatory constraints (i.e. EFL) were the primary mechanism associated with the hypoxaemia during the maximal test. Mechanical ventilatory constraints also prevented adequate compensatory alveolar hyperventilation in most EIAH subjects. Minimizing mechanical ventilatory constraints with heliox inspiration partially reversed EIAH in subjects who developed EFL. In conclusion, healthy women of all aerobic fitness levels can develop EIAH and begin to do so at submaximal intensities. Mechanical ventilatory constraints are a primary mechanism for EIAH in some healthy women and prevent reversal of hypoxaemia in women for whom it is not the primary mechanism.

Repeated exercise-induced arterial hypoxemia in a healthy untrained woman

A healthy 36-year-old untrained (maximal oxygen consumption (V˙O2max): 39mL/kg/min) woman completed multiple graded exercise tests on a treadmill. Temperature-corrected arterial blood samples were obtained in addition to esophageal pressure. Significant hypoxemia (−13mmHg arterial oxygen tension decrease) and arterial oxyhemoglobin desaturation (−6% decrease) was observed relative to rest and occurred during submaximal exercise and worsened at maximal intensities. Expiratory flow limitation (28–40% intersection of tidal volume) was present at near-maximal intensities. Relieving mechanical ventilatory constraints with a helium inspirate (79% He:21% O2) partially reversed the hypoxemia. Conversely, increasing chemical ventilatory stimuli, with hypercapnia (3.5% CO2), failed to increase ventilation. Maintaining oxyhemoglobin saturation, via a mildly hyperoxic (26% O2) inspirate, increased exercise duration (+45s) and V˙O2max (+5mL/kg/min). We attribute the hypoxemia to an excessive A–aO2 resulting from ventilation–perfusion mismatch and secondarily to mechanical ventilatory constraints. We conclude that a healthy untrained woman can develop EIAH and this remains stable over a period of 6 months.

Comparison of mechanical ventilatory constraints between continuous and intermittent exercises in healthy prepubescent children

The aim of this study was to evaluate the occurrence and severity of mechanical ventilatory constraints in healthy prepubescent children during continuous and intermittent exercise. Twelve prepubescent children (7-11 years old) performed 7 exercises on a treadmill: one graded test for the determination of maximal aerobic speed (MAS), three continuous exercises (CE) at 60, 70, and 80% of MAS and three intermittent exercises (IE), alternating 15 sec of exercise with 15 sec of passive recovery, at 90, 100, and 110% of MAS. During each CE and IE, tidal flow/volume loops were plotted within a maximal flow/volume loop (MFVL) measured at rest before each exercise. Expiratory flow limitation (expFL expressed in %Vt) was defined as the part of exercise tidal volume (Vt) meeting the boundary of MFVL. Breathing strategy was estimated by measuring inspiratory capacity relative to forced vital capacity and tidal volume relative to inspiratory capacity. Other breathing pattern parameters (ventilation VE, Vt, respiratory frequency f) were continuously recorded during exercise. An "intensity" effect was found for VE during CE (P < 0.001) but not during IE (P = 0.08). The increase in VE was predominantly assumed by an increase in f for both exercise modalities. During each exercise, several children heterogeneously experienced expFL ranging between 10 and 90%Vt. For all exercises, Vt was predominantly regulated by an increase in Vt/IC with no change in IC/FVC from rest to exercise. Finally, no significant "modality" effect was found for mechanical ventilatory constraint parameters (expFL, Vt/IC, and IC/FVC). We could conclude that neither of the modalities studied induced more mechanical ventilatory constraints than the other, but that exercise intensities specific to each modality might be greater sources of exacerbation for mechanical ventilatory constraints.

No effect of arm-crank exercise on diaphragmatic fatigue or ventilatory constraint in Paralympic athletes with cervical spinal cord injury

Cervical spinal cord injury (CSCI) results in a decrease in the capacity of the lungs and chest wall for pressure, volume, and airflow generation. We asked whether such impairments might increase the potential for exercise-induced diaphragmatic fatigue and mechanical ventilatory constraint in this population. Seven Paralympic wheelchair rugby players (mean + or - SD peak oxygen uptake = 16.9 + or - 4.9 ml x kg(-1) x min(-1)) with traumatic CSCI (C(5)-C(7)) performed arm-crank exercise to the limit of tolerance at 90% of their predetermined peak work rate. Diaphragm function was assessed before and 15 and 30 min after exercise by measuring the twitch transdiaphragmatic pressure (P(di,tw)) response to bilateral anterolateral magnetic stimulation of the phrenic nerves. Ventilatory constraint was assessed by measuring the tidal flow volume responses to exercise in relation to the maximal flow volume envelope. P(di,tw) was not different from baseline at any time after exercise (unpotentiated P(di,tw) = 19.3 + or - 5.6 cmH(2)O at baseline, 19.8 + or - 5.0 cmH(2)O at 15 min after exercise, and 19.4 + or - 5.7 cmH(2)O at 30 min after exercise; P = 0.16). During exercise, there was a sudden, sustained rise in operating lung volumes and an eightfold increase in the work of breathing. However, only two subjects showed expiratory flow limitation, and there was substantial capacity to increase both flow and volume (<50% of maximal breathing reserve). In conclusion, highly trained athletes with CSCI do not develop exercise-induced diaphragmatic fatigue and rarely reach mechanical ventilatory constraint.

Effects of Aerobic Fitness and Pulmonary Function on Mechanical Ventilatory Constraints During Exercise in Healthy Women

Females with a higher maximal aerobic capacity (Vo2max) have higher ventilatory requirements during exercise relative to their untrained counterparts. The higher ventilatory loads in trained females might make them more susceptible to developing expiratory flow limitation (EFL) during exercise. However, the interrelationship between aerobic fitness, pulmonary function and EFL has not been well characterized in women. PURPOSE: To determine the effect of Vo2max and maximal expiratory flow-volume (MEFV) curve characteristics on EFL in healthy women. METHODS: A progressive stepwise cycle test to exhaustion was completed by 22 healthy females (age=28±5; Vo2max=49±8, range 31-62 ml·kg-1·min-1). A MEFV curve was generated by having subjects perform several expirations from total lung capacity to residual volume at different efforts before and after exercise. Tidal breaths at each exercise stage were superimposed within the MEFV curve by having subjects perform inspiratory capacity maneuvers. The magnitude of EFL was calculated as the percent of the tidal breath that met or exceeded the outer boundary of the MEFV curve. Subjects were partitioned into those with EFL (n=10) and those with no EFL (NEFL; n=12). RESULTS: There was no difference in Vo2max between the EFL group and the NEFL group (47±5 vs. 51±10 ml·kg-1·min-1, respectively, P >0.05). There was no relationship between the degree of EFL and Vo2max (r=0.18, P>0.05). Absolute values were different between the EFL and NEFL groups for: peak expiratory flow (PEF) (6.9±0.9 vs. 8.5±1.0 l·sec-1, P < 0.05), and for forced expiratory flows at 75% of vital capacity (FEF75%) (6.0±0.6 vs. 7.6±0.9 l·sec-1, P<0.05), 50% of vital capacity (FEF50%) (3.5±0.4 vs. 5.6±1.0 l·sec-1, P<0.05) and 25% of vital capacity (FEF25%) (1.8±0.2 vs. 3.0±0.9 l·sec-1, P<0.05). The forced vital capacity was significantly larger in the NEFL group compared to the EFL group (4.4±0.5 vs. 3.8±0.4 l, P<0.05). When expressed as a percentage of PEF, FEF75% was not different between groups (87±7 vs. 90±6%, P>0.05) while FEF50% (52± 8 vs. 66±6%, P<0.05) and FEF25% (26±6 vs. 35±7.39%, P<0.05) were different. CONCLUSION: The degree of EFL experienced by women appears to be more associated with lung size and the characteristics of their MEFV curve rather than aerobic fitness. Funding: BC Lung Association and NSERC

Mechanical ventilatory constraints during incremental cycle exercise in human pregnancy: implications for respiratory sensation

The aim of this study was to identify the physiological mechanisms of exertional respiratory discomfort (breathlessness) in pregnancy by comparing ventilatory (breathing pattern, airway function, operating lung volumes, oesophageal pressure (P(oes))-derived indices of respiratory mechanics) and perceptual (breathlessness intensity) responses to incremental cycle exercise in 15 young, healthy women in the third trimester (TM(3); between 34 and 38 weeks gestation) and again 4-5 months postpartum (PP). During pregnancy, resting inspiratory capacity (IC) increased (P < 0.01) and end-expiratory lung volume decreased (P < 0.001), with no associated change in total lung capacity (TLC) or static respiratory muscle strength. This permitted greater tidal volume (V(T)) expansion throughout exercise in TM(3), while preserving the relationship between contractile respiratory muscle effort (tidal P(oes) swing expressed as a percentage of maximum inspiratory pressure (P(Imax))) and thoracic volume displacement (V(T) expressed as a percentage of vital capacity) and between breathlessness and ventilation . At the highest equivalent work rate (HEWR = 128 +/- 5 W) in TM(3) compared with PP: , tidal P(oes)/P(Imax) and breathlessness intensity ratings increased by 10.2 l min(-1) (P < 0.001), 8.8%P(Imax) (P < 0.05) and 0.9 Borg units (P < 0.05), respectively. Pulmonary resistance was not increased at rest or during exercise at the HEWR in TM(3), despite marked increases in mean tidal inspiratory and expiratory flow rates, suggesting increased bronchodilatation. Dynamic mechanical constraints on V(T) expansion (P < 0.05) with associated increased breathlessness intensity ratings (P < 0.05) were observed near peak exercise in TM(3) compared with PP. (1) pregnancy-induced increases in exertional breathlessness reflected the normal awareness of increased and contractile respiratory muscle effort; (2) mechanical adaptations of the respiratory system, including recruitment of resting IC and increased bronchodilatation, accommodated the increased V(T) while preserving effort-displacement and breathlessness-VE relationships; and (3) dynamic mechanical ventilatory constraints contributed to respiratory discomfort near the limits of tolerance in late gestation.

Difference in breathing strategies during exercise between trained elderly men and women

This study compared the ventilatory responses and exercise tidal flow-volume (Vt) loops during exercise in order to analyze the influence of gender on breathing strategy in a fit aging population. Sixteen trained elderly men (63.0+/-2.9 years) and eight peer women (62.3 +/- 5.5 years) performed an incremental test on a cycle ergometer. At 90% maximal oxygen consumption (VO2max), the women presented a significantly higher expiratory flow limitation (EFL) than the men (38 +/- 10 vs 17 +/- 8% of Vt, respectively) (P<0.01) and a lower value of expiratory reserve volume relative to forced vital capacity (FVC) compared with the men (16.8 +/- 5.3% vs 23.0 +/- 5.2%, respectively) (P<0.05). Inspiratory reserve volume relative to FVC was significantly higher in women than men at 50% (P<0.05), 70% (P<0.01) and 90%VO2max (25.2 +/- 5.4% vs 12.2 +/- 4.2%, respectively, at 90%VO2max) (P<0.01). Mechanical ventilatory constraints occurred in trained elderly men and women. However, different breathing strategies were observed relative to gender. A significantly higher EFL was measured in women, whereas men rather presented a dynamic hyperinflation. This specific breathing strategy measured in trained elderly women would induce lower ventilatory efficiency than in peer men.

Breathing strategy in master athletes and untrained elderly subjects according to the incremental protocol

To analyze the influence of step-duration protocol (1 vs. 3 min) on breathing strategy according to the physical fitness of healthy elderly subjects, this study compared the ventilatory responses and exercise tidal flow-volume loops (ETFVL) at the first and second ventilatory thresholds (VT(1) and VT(2)). Nineteen master athletes (mean age (+/- SD), 63.1 +/- 3.2 y; (.)VO(2)(max), 41.5 mL x (min x kg)(-1)) and 8 untrained elderly subjects (age, 65.5 +/- 2.3 y; (.)VO(2)(max), 25.8 mL x (min x kg)(-1)) performed 2 exhaustive exercise tests on a cycle ergometer. In untrained subjects, at VT(1) and VT(2), no significant difference was measured in ventilatory responses and ETFVL between protocols. Master athletes, at VT(2), presented a significantly higher (.)VCO(2) (P < 0.01), ventilation ((.)VE; P < 0.01), breathing frequency (f(b); P < 0.05), tidal volume relative to inspiratory capatcity (V(t)/IC) (P < 0.01),V(t) relative to forced vital capacity (V(t)/FVC; P < 0.05), and lower inspiratory reserve volume relative to FVC (IRV/FVC; P < 0.01) during the 1 min protocol than during the 3 min protocol. Master athletes, at maximal exercise, expressed significantly higher (.)VCO(2) (P < 0.01) and dyspnea (P < 0.05) with the shorter protocol. We concluded that, in untrained subjects, neither incremental exercise test had an impact on respiratory responses during exercise. Nevertheless, in master athletes, breathing strategy seems to be protocol dependent. The short test induced higher mechanical ventilatory constraints and dyspneic feeling than the long protocol, which could be explained by a higher (.)VE itself linked to a greater (.)VCO(2) and a higher blood lactate concentration.

Exercise flow-volume loops in prepubescent aerobically trained children

We studied mechanical ventilatory constraints in 13 aerobically trained (Tr) and 11 untrained (UT) prepubescent children by plotting the exercise flow-volume (F-V) loops within the maximal F-V loop (MFVL) measured at rest. The MFVL allowed to determine forced vital capacity (FVC) and maximal expiratory flows. Expiratory and inspiratory reserve volumes relative to FVC (ERV/FVC and IRV/FVC, respectively) were measured during a progressive exercise test until exhaustion. Breathing reserve (BR) and expiratory flow limitation (expFL), expressed in percentage of tidal volume (V(T)) and defined as the part of the tidal breath meeting the boundary of the MFVL, were measured. Higher FVC and maximal expiratory flows were found in Tr than UT (P < 0.05) at rest. Our results have shown that during exercise, excepting one subject, all Tr regulated their V(T) within FVC similarly during exercise, by breathing at low lung volume at the beginning of exercise followed breathing at high lung volume at strenuous exercise. In UT, ERV/FVC and IRV/FVC were regulated during exercise in many ways. The proportion of children who presented an expFL was nearly the same in both groups (approximately 70% with a range of 14 to 65% of V(T)), and no significant difference was found during exercise concerning expFL. However, higher ventilation (V(E)), ERV/FVC, and dyspnea associated with lower BR, IRV/FVC, and SaO2 were reported at peak power in Tr than UT (P < 0.05). These results suggest that, because of their higher Ve level, trained children presented higher ventilatory constraints than untrained. These may influence negatively the SaO2 level and dyspnea during strenuous exercise.

Ventilatory response to exercise in simulated obesity by chest loading.

Obesity-related increases of weight on the chest wall are known to decrease lung volume and chest wall compliance, but the effect of this mass loading, independent of other obesity-related complications on the ventilatory response to exercise is unknown. The purpose of this study was to investigate the effect of chest mass loading on the ventilatory response to exercise. External chest loading (CL) was used to simulate the effect of moderate obesity (BMI = 32 kg x m). Eight healthy nonobese subjects performed two incremental exercise tests on a cycle ergometer with work rate increasing 25 W every 3 min once without (control; CON) and once with CL. Expiratory reserve volume (ERV), forced vital capacity (FVC), and forced expiratory volume in 1 s (FEV1) were measured before each test. During exercise, inspiratory capacity (IC), to estimate changes in end-expiratory lung volume, and inspiratory (TI) and expiratory (TE) duration, tidal volume (Vt), breathing frequency (Fb), minute ventilation (VE), mean inspiratory (Vt/TI) and expiratory (Vt/TE) flow rates, and oxygen consumption (VO2) were measured. Baseline ERV, FVC and FEV1 were lower with CL (P < 0.05). Compared with CON, the peak work rate achieved during exercise with CL was lower and VO2, VE, Fb, Vt/TI, and Vt/TE were higher, and Vt was lower at work rates > or = 100 W (P < 0.05). IC increased progressively in CON during exercise but remained unchanged with CL. Obesity-related chest loading decreases lung volumes and increases the mechanical ventilatory constraints during exercise and is likely a critical factor in reducing exercise capacity in obesity.

Progressive mechanical ventilatory constraints with aging.

To investigate the progressive nature of mechanical ventilatory constraints with aging, we studied 20 young (age 39 +/- 3 yr), 14 senior (70 +/- 2 yr), and 11 elderly (88 +/- 2 yr) men and women during exercise. All subjects had normal pulmonary function and performed graded cycle ergometry to exhaustion. Minute ventilation (V E), lung volume, and expiratory airflow limitation (EAFL) were measured during each 1-min increment in work rate. Data were analyzed by two-way analysis of variance (ANOVA; age x gender) at rest, ventilatory threshold (VTh), and peak exercise. If an interaction was present, each gender was analyzed with a one-way ANOVA. Aging resulted in an increased V E for a given submaximal work rate, although V E during peak exercise was lowest in the elderly group (p < 0.01). End-expiratory lung volume (EELV, % of TLC) in men increased progressively with age and all groups were different at VTh (p < 0.01) and peak exercise (p < 0.01). In women, EELV (% of TLC) also increased with aging, the senior and elderly subjects had a greater EELV at VTh (p < 0.01) and peak exercise (p < 0.01) than the young group. Additionally, the normal decrease in EELV during the early stages of exercise was not observed in elderly subjects. End-inspiratory lung volume (EILV) also progressively increased with aging; senior and elderly subjects had a higher EILV at rest (p < 0.05), VTh (p < 0.01), and peak exercise (p < 0.01) than young subjects. EAFL (% of VT) increased with aging; elderly subjects experienced greater EAFL at rest (p < 0.05), VTh (p < 0.01), and peak exercise (p < 0.01) than both young and senior subjects. We conclude that mechanical ventilatory constraints are progressive with aging, elderly subjects demonstrating marked mechanical ventilatory constraints during exercise. The impact of these constraints on exercise tolerance cannot be determined from this investigation and remains unclear.

Mechanical ventilatory constraints in aging, lung disease, and obesity: perspectives and brief review.

Mechanical ventilatory constraints in aging, lung disease, and obesity; perspectives and brief review. Med. Sci. Sports Exerc., Vol. 31, No. 1 (Suppl.), pp. S12-S22, 1999. One of the most difficult tasks of cardiopulmonary exercise testing is to determine the influence of ventilatory limitations on the ventilatory response to exercise. Currently there is no generally accepted method in which to quantify the magnitude of mechanical ventilatory constraints during exercise. Nor is there agreement on how to quantify maximal ventilatory capacity. To address these issues, this article focuses on the evaluation of mechanical ventilatory constraints during exercise and provides an overview of the mechanical ventilatory constraints that are encountered with aging, lung disease, and obesity.

Ventilation and respiratory mechanics during exercise in younger subjects breathing CO 2 or HeO 2

To determine if ventilation (V̇ e) during maximal exercise would be increased as much by 3% CO 2 loading as by resistive unloading of the airways, we studied seven subjects (39±5 years; mean±S.D.) during graded cycle ergometry to exhaustion while breathing: (1) room air (RA); (2) 3% CO 2, 21% O 2, and 76% N 2; or (3) 79% He and 21% O 2). V̇ e and respiratory mechanics were measured during each 1-min increment (20 or 30 W) in work rate. V̇ e during maximal exercise was increased 21±17% when breathing 3% CO 2 and 23±16% when breathing HeO 2 ( P<0.01). Further, the ventilatory response to exercise above ventilatory threshold (VTh) was increased ( P<0.05) when breathing HeO 2 (0.89±0.26 L/min/W) as compared with breathing RA (0.65±0.12). When breathing HeO 2, end-expiratory lung volume (%total lung capacity, TLC) was lower during maximal exercise (46±7) when compared with RA (53±6, P<0.01). In conclusion, V̇ e during maximal exercise can be augmented equally by 3% CO 2 loading as by resistive unloading of the airways in younger subjects. This suggests that in younger subjects with normal lung function there are minimal mechanical ventilatory constraints on V̇ e during maximal exercise.

Ventilatory response to exercise in subjects breathing CO2 or HeO2.

To investigate the effects of mechanical ventilatory limitation on the ventilatory response to exercise, eight older subjects with normal lung function were studied. Each subject performed graded cycle ergometry to exhaustion once while breathing room air; once while breathing 3% CO2-21% O2-balance N2; and once while breathing HeO2 (79% He and 21% O2). Minute ventilation (VE) and respiratory mechanics were measured continuously during each 1-min increment in work rate (10 or 20 W). Data were analyzed at rest, at ventilatory threshold (VTh), and at maximal exercise. When the subjects were breathing 3% CO2, there was an increase (P < 0.001) in VE at rest and at VTh but not during maximal exercise. When the subjects were breathing HeO2, VE was increased (P < 0.05) only during maximal exercise (24 +/- 11%). The ventilatory response to exercise below VTh was greater only when the subjects were breathing 3% CO2 (P < 0.05). Above VTh, the ventilatory response when the subjects were breathing HeO2 was greater than when breathing 3% CO2 (P < 0.01). Flow limitation, as percent of tidal volume, during maximal exercise was greater (P < 0.01) when the subjects were breathing CO2 (22 +/- 12%) than when breathing room air (12 +/- 9%) or when breathing HeO2 (10 +/- 7%) (n = 7). End-expiratory lung volume during maximal exercise was lower when the subjects were breathing HeO2 than when breathing room air or when breathing CO2 (P < 0.01). These data indicate that older subjects have little reserve for accommodating an increase in ventilatory demand and suggest that mechanical ventilatory constraints influence both the magnitude of VE during maximal exercise and the regulation of VE and respiratory mechanics during heavy-to-maximal exercise.

Relative contribution of rib cage and abdomen to ventilation during exercise.

Relative contribution of rib cage and abdomen to ventilation during exercise.