The Relationship Between Functional Residual Capacity And Ventilation Function Parameters In Patients With Chronic Obstructive Pulmonary Disease

ObjectiveCOPD (Chronic obstructive pulmonary diseases) is a chronic disease characterized by continuous airflow which is slowly progressing. As the disease develops, the end expiratory lung volume also increases.FRC (Function residual capacity) is the volume of the residual gas in the lungs at the end of expiratory and reflects the change of EELV in COPD patients. Researches show that increased FRC as well as airflow obstruction plays an important role in affecting the exercise capacity. Therefore there is obvious significance in measuring FRC accurately in COPD patients.Since FRC contains RV (residual volume) in it, those methods of indirect measurement is necessary. In clinical practice, the common way is by means of gas notation and there are two different methods, single breath method and repeated breathing method.Some studies pointed out that there are certain differences between those two methods which means they cannot replace each other randomly.Because COPD patients has enlarged airflow resistance and prolonged time of gas distribution, single breath method would not guarantee accurate determination on FRC, while rebreathing method provides long enough time to allow gas distribute evenly. So it is why the later method can precisely determine FRC in COPD patients.The goal of this study is to measure FRC and some other indexes of lung function test by repeated rebreathing method in COPD patients and compared with the results got from the single breath method, thus provides objective evidence for clinical practice. MethodThere are totally34patients enrolled who accepted lung function tests and were clearly diagnosed as COPD in Zhongshan Hospital. We use single breath method and repeated rebreathing method as well to measure FRC, RV, TLC and other lung function indexes, then compare them respectively and look for their differences. ResultThere are significant difference between the results of these two methods in FRC, RV, TLC (total lung capacity) and other lung function indexes. Paired t tests shows that the measured values of FRC, RV, TLC and other lung function indexes determined by single breath method and repeated rebreathing method are statistically significant (p<0.05). And compared with those of the single breath method, the values of FRC, RV and TLC measured by repeated rebreathing method are higher obviously. ConclusionIn COPD patients, there are significant differences between the values of FRC, RV, TLC and other lung function indexes determined by single breath method and repeated rebreathing method. FRC measured by repeated rebreathing method are much higher than that of single breath method. So are TLC, RV and some other indexes. Therefore, in COPD patients it is impropriate to determine FRC by single breath method although it is more convenient and swift and much more widely used in clinical. But single breath method may lead to underestimated FRC and the severity of hyperinflation in COPD patients, which is why it is not good for objectively evaluate the exercise capacity and the degree of dypnea of those patients. In a word, rather than single breath method in COPD patient the right way to measure FRC and some other lung function test indexes is to choose the repeated rebreathing method. ObjectiveCOPD (Chronic obstructive pulmonary diseases) is a chronic disease characterized by continuous airflow which is slowly progressing. As the disease develops, the end expiratory lung volume also increases. At present FEV1is the indices of lung function in COPD patients, while fact is that those patients exercise capacity does not match their lung function degree as well as FEV1so well. And studies show that enlarged EELV as well as airflow obstruction plays an important role in progressive loss of exercise capacity in COPD patients and FRC is the most important index that reflecting the increased EELV. Because of incapable of measuring FRC precisely in COPD patients by means of single breath method, this study is designed to explore the relationship between FRC and FEV, by repeated rebreathing method in COPD patients thus adding proof to clinical practice. Method155COPD patients who used to get lung function tests and detailed history in Zhongshan Hospital and28bronchial asthma patients as a control group were enrolled and accepted lung function test for such indexes as FEV1and FVC, and some volume indicators as FRC and TLC by means of repeated rebreathing method, and correlation analysis and comparations were carried out on those measured values. ResultIn those155COPD patients, FRC increases as their lung function level going up and the difference of measured values was statistically significant between groups. FRC and FEV1, FRC%pred and FEV,%pred both have statistical correlation(p<0.05). FRC%pred and FVC%pred have statistical correlation too and the correlation coefficient is-0.289(p<0.01) while there is no significant correlation between FRC and FVC. The correlation coefficient is as high as0.866(p<0.01) between FRC%pred and RV%pred, which indicates that RV and FRC increase in good consistency. And the coefficient is-0.256between FRC%pred and IC%pred (p<0.01)In28asthma patients, FEV1%pred and FRC%pred have statistical correlation, whose correlation coefficient is-0.587. FRC and RV, FRC%pred and RV%pred also both have statistical correlation (p<0.05), whose correlation coefficient were0.716and0.714. IC%pred and FEV1%pred have statistical correlation and the correlation coefficient is0.884. But there is no statistical correlation between FRC%pred and FVC%pred ConclusionFRC is the sum of RV and ERV. In both COPD patients and bronchial asthma patients, FRC and RV rises synchronously as the lung function decreases. The elevated FRC is mainly caused by the increased RV, which is mostly because of the exhaled gas or advanced exhale termination caused by increased airway resistance or air trapping in small airways; hence FRC reflects the severity of hyperinflation of the lung objectively.The primary lesion in bronchial asthma patients is a wide range of small airway edema and spasm that lead to the drastically narrowed small bronchials and incapable of complete gas exhale, which causes the enlarged RV and FRC. So the extent of the increase of FRC has a good correlation with the indexes reflecting the severity of airway obstruction as FEV1and FEV1/FVC.But in COPD patients, FRC%pred and FEV1%pred show statistically correlation in a low extension, which indicates that elevated FRC partially reflects the severity of airway obstruction in COPD patients, but the correlation coefficient is not high because air trapping instead of airway obstruction plays the main role in COPD patients pathophysiological changes. So such ventilation indexes as FEV1%pred and FEV1/FVC does not reflect the hyperinflation in COPD patients quite fully and precisely, and it is necessary to also take the indexes into consideration who can objectively indicate the hyperinflation of the lungs such as FRC, RV and RV/TLC while trying to evaluate the degree of airflow obstruction and hyperinflation and estimate the degree of dypnea and exercise capacity loss in COPD patient.