A Modified Method Of Evaluating Dynamic Hyperinflation In COPD Patients

Background:Chronic obstructive pulmonary disease(COPD)is a common airway disease that is characterized by constantly flow limitation.FFV1%prcd is usually used to evaluate severity of the diease in clinic.However,this term can not assess the treatment effect and symptoms.Dynamic lung hyperinflation plays a central role in the mechanisms underlying the development of dyspnoea,exercise capacity and exacerbations.Dynamic hyperinflation is defined by the temporary increase of the gas remaining in the lung at the end expiratory lung volume(EELV).Dynamic hyperinflation is usually assessed indirectly by the difference in inspiratory capacity between the end of exhaustive exercise and the rest under the assumption that the neural respiratory drive remained constant before and during the exercise.However,with the expiratory airflow.limited,patients with COP D have to increase breathing frequency during exercise,which result in the time to exhale decreased and carbon dioxide retention in the lung.Involuntary neural respiratory drive can be stimulated by the carbon dioxide storage so that the muscles of respiration may be reinforced.Therefore,inspiratory capacity that is in the end of exercise is greater than that in the rest in patients with COPD due to exercise related hypercapnia.Consequently,even if COPD patients feel obvious shortness of breath and dyspnea,the test result may show ’nonhyperinflator phenotype’.The study required subjects to inhale 8%CO2,ensuring that neural respiratory drive at the rest approached the level at the end of exercise.The difference between the IC at the end of exercise and that after inhalation of CO2 is used to replace the conventional method in the study.Methods:Seventeen stable COPD patients were studied(age62.24±5.64years,FEV1%pred 43.94±12.98%).Pulmonary function and demographic data were measured at the first visit.We also required subjects to practice IC maneuvers and the exercise at the same time.We carried out the exercise experiment and then conducted air or CO2 study at rest in a random order at the second visit.Results:IC,EMGdi-IC during inhaling CO2 were significantly greater than that during inhaling air(1.74±0.35 vs1.51±0.36 of 1C,P<0.01;152.21 ±70.18 vs 125.7±55.82,P<0.01).There was no significant dillerence in mET-CO2 at the end of exercise and that elicited by inhalation of 8%{58.80±7.43 vs 60.42±10.33,P=0.357).Compared with inhaling air,EMGd1-IC increased signiificantly(52.21±70.18 vs 125.7±55.82,P<0.05).The modified dynamic hyperinflation was found to be positive in all 17 subjects.Conclusions:Comparing the difference of IC and EMGdi-IC between rebreathing CO2 and rebreathing air,we confirmed that CO2 inhalation can further stimulate the neural respiratory drive.The modified dynamic hyperinflation method in patients with COPD is more reliable than conventional methods.