Effects Of Body Mass Index On Lung Function In Patients With Chronic Obstructive Pulmonary Disease

Objective:Chronic obstructive pulmonary disease（COPD）is a pulmonary ventilation and parenchymal disease characterized by airflow limitation in response to chronic inflammation,which is one of the four common chronic diseas-es in China and often accompanied by varying degrees of malnutrition and wei-ght loss.Body mass index（BMI）is one of the most important indicators used to assess nutritional status of human body.The study aimed to investigate the effects of body mass index（BMI）on lung function in patients chronic obstructive pulmonary disease（COPD）in stable and acute exacerbation period.Methods:A total of 3312 patients with COPD were selected from outpatient and inpatient in department of gerontal respiratory medicine of the first hospit-al of Lanzhou University from August 2016 to August 2020,including 1103 patients in stable period and 2 209 patients in acute exacerbation period.Acco-rding to BMI,these COPD patients were divided into four groups:low weight（56 cases,131 cases）,normal weight（448 cases,945 cases）,overweight（424 cases,773 cases）and obesity groups（175 cases,360 cases）respectively in sta-ble stage and in acute exacerbation stage.The lung function of inspiratory cap-acity（IC）,vital capacity（VC）,residual volume（RV）,total lung capacity（TLC）,RV/TLC,forced expiratory volume in 1 second（FEV1）,forced vital capacity（FVC）,FEV1/FVC,PEF（peak expiratory flow）,maximal mid-expiratory flow（MMEF）,diffusing capacity of the lung for carbon monoxide（DLCO）,DLCO normalized per liter alveolar volume（DLCO/VA）,respiratory impedance（Zrs）,respiret-ory resistance at 5 Hz（R5）,respiratory resistance at 20 Hz（R20）and respiratory reactance at 5 Hz（X5）were measured using Master Screen PFT in allpatients,and the influence of BMI on lung function were analyzed respectively.The risk factors of lung function were analyzed by ordered logistic regression with lung function grade as dependent variable and age,gender,smoking histo-ry,smoking index and BMI as independent variables（“%pred”represents the percentage of predicted value）.Results:（1）1103 patients in stable period were aged from 41 to 89 years,with a median age of 66 years.Among them,698（63.3%）were males and 599（54.3%）were smokers.There were 397 patients with grade Ⅰ,492 patients with grade Ⅱ,182 patients with grade Ⅲ and 32 patients with grade Ⅳ.There were 56（5.1%）,448（40.6%）,424（38.4%）and 175（15.9%）patients in low weight,normal weight,overweight and obese groups,respectively.There were no statis-tically significant differences in age and smoking index among different BMI groups,while there were statistically significant differences in gender and prop-ortion of smoking patients（all P<0.001）.2209 patients in acute exacerbation were aged from 41 to 95 years,with a median age of 70 years.There were 1424 males（64.5%）and 1215 smokers（55.0%）.There were477 patients with grade Ⅰ,997 patients with grade Ⅱ,562 patients with grade Ⅲ,and173 patients with grade Ⅳ.There were131（5.9%）,945（42.8%）,945（42.8%）and 773（35.0%）patients in low weight,normal weight,overweight and obese groups,respectively.There were no statistically significant differences in age and smoking index among different BMI groups,while there were statistically significant differences in gender and proportion of smoking patients.The higher grade of the lung function in COPD patients,the lower the BMI,the patients of low BMI with lung function Ⅲ/Ⅳ was more,while the patients of overweight and obese with lung function Ⅰ/Ⅱ were more.（2）The proportion of patients with lung function grade Ⅲ/Ⅳ in acute exacerbation period（64.9%,37%,27.4%,24.4%）was higher than that in stable stage（42.9%,25.9%,13.7%,9.1%）,while the proportion of patients with lung function grade Ⅰ in stable stage（21.4%,34.2%,38.2%,40.0%）was higher thanthat in acute exacerbation period（7.6%,20.0%,25.4%,22.8%）（all P<0.05）.（3）The IC%pred,VC%pred,FEV1%pred,FVC%pred,FEV1/FVC,MMEF%pred,DLCO%pred,DLCO/VA%pred and R20 in low weight group were signif-icantly lower than other groups both in stable period and acute exacerbation p eriod（all P<0.05）.The RV/TLC was higher in low weight group than that of n ormal weight and overweight groups in both periods（all P<0.05）.The IC%pred,FEV₁%pred,FEV1/FVC,DLCO%pred,DLCO/VA%pred,R5 and R20 in over-weight and obesity groups were higher than that of normal weight group（all P<0.05）.The RV/TLC,FEV1/FVC,DLCO%pred,DLCO/VA%pred,Zrs,R5 and R20 in obesity group were higher than that of overweight group（all P<0.05）.（4）The ordered logistic regression analysis showed that low BMI was independent risk factors for impaired lung function of COPD both in stable period[OR（95%CI）:2.316（1.206-3.554）]and acute exacerbation period[OR（95%CI）:2.457（1.647-3.669）].Conclusion:With the deterioration of lung function,BMI decline in COPD patients,lung ventilation and diffusion function of patients with low BMI are the lowest.Therefore,increasing nutritional support for patients with low BMI should be an important part of comprehensive treatment for COPD.