Mechanical ventilatory constraint, breathing pattern and ventilatory responses in obese postmenopausal women during exercise
Date Issued
2009
Date
2009
Author(s)
Chen, Wen-Yu
Abstract
Background/Purpose: Obesity-related changes in lung volumes have shown to affect breathing mechanisms. During exercise, altered breathing mechanisms increase potential for expiratory flow limitation and compromise exercise capacity. Estrogen and progesterone are potent respiratory stimulants, and their effects in the physiologic regulation of breathing are down-regulated after menopause. Therefore, we theorized that the combined obesity and reduced sex hormone levels after menopause work as a double jeopardy to cause mechanical ventilatory constraint which aggravates dyspnea sensation during exercise, and thus a reduction in exercise capacity. The purpose of this study was to exam the dynamic lung volumes in obese post-menopausal women (without hormone replacement therapy) during exercise and their correlations with dyspnea. Methods and Analysis: From doctoral referral and advertisement, 24 obese (BMI ≧ 27 kg/m2) and 26 lean post-menopausal women were recruited for the study. Pulmonary function and body composition were measured at rest. A maximal flow volume loop (MFVL) was obtained at baseline. All subjects then performed an incremental exercise test on a cycle ergometer with workload increasing 25 watts every 3 min. During exercise, at each workload, the tidal exercise FV loops were obtained and an inspiratory capacity (IC) maneuver was conducted to assess changes in end-expiratory lung volume (EELV) and end inspiratory lung volume (EILV). Dyspnea and leg fatigue were assessed using the Borg scale. Analysis of variance with repeated measurements was used to test the significance of the mean differences between the two groups during exercise. Linear regression analysis was used to determine whether changes in dynamic lung volumes during exercise were related to changes in Borg scores. Statistical significance was established at p < 0.05. Results and Discussion: Functional residual capacity (FRC), expiratory reserved volume (ERV), and total lung capacity (TLC) were significantly lower in the obese group than those in the control group (all p < 0.05). Compared to control, relative peak oxygen consumption (VO2peak) and heart rate (HRpeak) were significantly lower in obese group. Obese subjects demonstrated mechanical ventilatory constraint with elevated EELV during exercise. Minute ventilation (VE), tidal volume (Vt), mean inspiratory flow (Vt/TI), and dyspnea score were significantly higher in the obese then those in the control group during exercise. In the obese group, moderate to severe obese subjects showed greater changes in EILV and EELV compared to those of mild obese. In obese group, changes EILV and EELV were found to have mild and moderate correlation with the dyspnea scores, respectively, and the obese severity could influence the correlation strength. Conclusions: Patterns of dynamic lung volume changes were different between obese and lean post-menopausal women. Obese post-menopausal women demonstrated mild degree of mechanical ventilatory constraint during exercise and changes in dynamic lung volumes were significant positively correlated with dyspnea sensation.
Subjects
Obesity
Postmenopausal women
Mechanical ventilatory constraints
Dynamic lung volume
Expiratory flow limitation
SDGs
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