Mechanical ventilatory constraint, breathing pattern and ventilatory responses in obese postmenopausal women during exercise
|Keywords:||肥胖;停經後婦女;機械性換氣限制現象;動態肺容量;吐氣氣流限制;Obesity;Postmenopausal women;Mechanical ventilatory constraints;Dynamic lung volume;Expiratory flow limitation||Issue Date:||2009||Abstract:||
背景與目的：肥胖相關的肺容積變化會改變呼吸機械機制（mechanism）。在運動過程中，這些機械機制的改變會增加產生吐氣氣流限制的機會進而影響運動能力。雌激素和黃體素對呼吸是正向的刺激因子，這些荷爾蒙對呼吸的調控會隨著停經狀態而調降。因此，我們推論肥胖合併停經造成性荷爾蒙的下降會導致這些婦女更容易在運動中產生呼吸機械性限制，進而惡化運動呼吸困難的感覺及降低運動能力。本研究目的是探討肥胖停經後婦女在運動過程中的動態肺功能變化，及這些變化與呼吸困難之間的關係。方法及分析：經由醫師轉介及廣告徵集，本研究有24位肥胖（身體質量指數 ≧ 27公斤/尺2）及26位非肥胖停經後婦女參與。所有受試者均接受以下測量╱試。休息狀態下先進行肺功能及身體組成的分析測量。接著測量基線的最大氣流-容積曲線。進行漸進式漸進式最大運動測試以固定式腳踏車進行，運動強度每3分鐘增加25瓦。在運動測試的每個運動強度，會以運動中吸氣容積（inspiratory capacity, IC）來計算吐氣末肺容積（end-expiratory lung volume, EELV）與吸氣末肺容積（end-inspiratory lung volume, EILV）變化，並以視覺等比量表測量呼吸困難及下肢疲乏程度。兩組間基本資料及運動測試結果（連續性變相）以t檢定來分析組別間是否有差異。運動中的變相改變則以重覆量數兩因子變異數分析及Bonferroni檢定作事後分析來分析組間及組內的差異。定義p < 0.05有統計上的意義。結果與討論：肥胖組全肺總容積、吐氣保留容積、功能貯備、用力呼氣肺活量、第一秒用力呼氣容積、及相對最高攝氧量（relative VO2peak）與最高心跳均顯著小於控制組（p < 0.05）。肥胖組EELV會隨著運動強度上升而逐漸上升並產生機械性換氣限制。運動過程中，每分鐘換氣量（minute ventilation, VE）、潮氣量（tidal volume, Vt）、平均吸氣流速（mean inspiratory flow, Vt/TI）與呼吸困難程度有顯著組間差異（肥胖組 > 控制組）肥胖組中，中重度的EELV變化幅度較輕度者為大。EILV及EELV的變化與呼吸困難分別呈低及中度顯著相關且相關強度會受肥胖嚴重度的影響。結論：停經後婦女在運動中，動態肺容積的變化模式在肥胖和正常體重的受試者有所不同。肥胖的停經後婦女在運動過程中會發生機械性換氣限制現象。且呼吸困難程度和動態肺容積變化具顯著正相關。
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.
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