| BackgroundBronchodilators, the most commonly used drugs in COPD, have been shown to reduce dyspnea, improve exercise tolerance and improve health status. However, conventional lung function parameters such as forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) frequently fail to detect significant functional responses to bronchodilators in patients with chronic airflow obstruction. It is necessary for clinical and scientific reasons to develop a new tool to objectively assess the effect of different treatments including bronchodilator on COPD. Because dyspnea relates to respiratory effort, neural respiratory drive and its efficiency as expressed by a ratio of ventilation to the diaphragm electromyogram (EMGdi) may be useful to evaluate treatment benefits in Patients with COPD.Part 1. Neural respiratory drive during rest and constant treadmill exercise in COPD compared with healthyObjectiveDetermined whether efficiency of neural drive in patients with COPD is lower than that in healthy subjects, and whether it changes during exercise.Subjects and methodsWe studied 12 male patients with COPD (mean±SD age 62.8±10.3 years, FEV1 28.1±10.2% predicted) and 12 age- and gender-matched healthy subjects (age 61.1±7.2 years, FEV1 101.5±11.9% predicted). EMGdi was recorded from a multipair esophageal electrode during a constant work (80% of maximal oxygen consumption derived from a previous incremental exercise test) treadmill exercise. Minute ventilation (Ve) and oxygen consumption (VO2) were also measured. Borg Scale and IC maneuver is performed at 1-minute interval during exercise.ResultsRoot mean square (RMS) of the EMGdi increased initially and reached a plateau at submaximal drive during constant load exercise in both COPD patients and healthy subjects. The ratio of ventilation to EMGdi remained stable during exercise in healthy subjects from beginning to the end (1.0±0.7 at the beginning and 1.0±0.4 at the end, p>0.05), whereas the ratio decreased gradually during exercise in patients with COPD ( from 0.9±0.7 to 0.4±0.1, p<0.05).Part 2. Effect of tiotropium on neural respiratory drive in COPDObjectiveAssess the effect t of tiotropium on exercise, in particular on neural respiratory drive and its efficiency.Subjects and methodsTwenty stable severed COPD patients were recruited and were divided into two groups. Group 1 (ten subjects, mean age, 66.5±5.4 years, FEV1 33.1±11.1%pred) received Tiotropium (18ug/day) for one month and group 2 ( ten subjects, mean age, 63.6±4.6 years, FEV1 35.0±13.6%pred) as usual. Both groups were permitted to use all respiratory medications except inhaled anticholinergic drugs. All subjects visited laboratory three times. The first visit was to determine maximal workload during exhaustive incremental cycle exercise. A constant cycling exercise with 75% of maximal workload derived from visit 1 was performed on visits 2 (before treatment) and visit 3 (after treatment for one month). EMGdi , Pes, Pga and Pdi recorded from multipair esophageal electrode-balloon combined catheter were recorded. I also measured ventilation including Ve, VO2, and VCO2 during exercise. Efficiency of neural respiratory drive as expressed by VE/EMGdi%max was also measured during exercise. Inspiratory capacity was measured at the beginning and end of exercise.ResultsNeural respiratory drive at rest decreased significantly(26.6±11.3% vs 21.6±10.8% P<0.05) in patients with COPD after treatment with tiotropine, whereas neural respiratory drive before and after one month treatment as usual was almost the same. Exercise duration was improved ( from 320.0±98.9s to 469.2±159.2s, p<0.05) in patients with COPD after treatment with Tiotropium. Mean effciency of neural respiratory drive in patients with COPD after treatment with Tiotropium was higher than that after treatment with placebo (0.3±0.1 in Visit-2 vs 0.4±0.1 in Visit-3,P<0.01).ConclusionsNeural respiratory drive at rest in patients with COPD was higher than that in healthy subjects. Efficiency of neural drive decreases in patients with COPD during treadmill exercise. Neural respiratory drive reached a submaximal plateau during constant load exercise in both healthy subjects and patients with COPD. Tiptropine can significantly reduce neural respiratory drive at rest and improve efficiency of neural respiratory drive in patients with COPD during exercise, which may be a mechanism responsible for an improvement in exercise tolerance and a reduction of dyspnea.
|
PDF Full Text Request