Recovery of Gas Exchange Variables and Heart Rate: MATERIALS AND METHODS
Patients with COPD (n = 16) were recruited from the outpatient department of the Albuquerque VA Medical Center for participation in this study. All were clinically stable and had not had an exacerbation of their disease for at least six weeks prior to study. In all patients, arterial blood gas analysis at rest revealed oxygen tensions greater than 55 mm Hg (range, 57 to 66 mm Hg) and normal carbon dioxide tensions (range, 32 to 37 mm Hg). Electrocardiograms revealed normal sinus rhythm in all patients; right axis deviation was present in six, right ventricular hypertrophy in one, and right atrial enlargement in two patients.
The control group (n = 9) consisted of normal aged subjects who volunteered to participate in a study of blood donation in the elderly. The present study was performed before blood donation. Subjects were accepted for inclusion in the study on the basis of absence of clinical evidence of cardiopulmonary disease and normal findings on electrocardiography and echocardiography. canadian pharmacy viagra
All participants gave informed consent, and the study was approved by the Human Research and Review Committee of the University of New Mexico and the Research Committee of the Albuquerque VA Medical Center.
Spirometry was performed using a heated pneumotachograph (Pneumotest Erich Jaeger, Rockford, IL). Predicted values were those of Morris et al.
Graded ergometry was performed on an electrically braked cycle (Erich Jaeger, Rockford, IL). All subjects selected pedal frequencies of 40 to 60 cycles per minute. This cycle maintains a constant workload for pedal frequencies of 40 to 100 cycles per min. All patients and control subjects maintained a constant pedal frequency within this range throughout the exercise and recovery phases. Respiratory gas exchange variables, Ve, Vo2, Vco2, RER, and excess Vco2 were determined as previously described® using 15-s timed collections of expired air (Incarepulmobil). Excess Vcos is defined as the Vco2 attributable to nonmetabolic sources (buffering of lactic acid) and is calculated by the following equation:
Excess Vco2 = (RER, – RERb^JVo* where RER, is the RER at any time during exercise or recovery, RERwitae »s the RER value obtained in the third minute of warm- up pedaling (discussed subsequently), and Voa is the Vo2 at any time during exercise or recovery. The RER, was 0.86 ±0.07 (mean ± SD) for the group with COPD and 0.84 ±0.06 for the control group (NS).
After a three-minute warm-up period of 0-W pedaling, the workload was increased 10 W/min for the patients with moderate to severe COPD and 15 W/min for the patients with mild COPD. In the control subjects the workload increments were 15 W/min for subjects weighing less than 68.1 kg (150 lb) and 20 W/min for subjects weighing more than 68.1 kg. Using standard encouragement, exercise was continued to the point of volitional fatique. All of the patients with COPD stopped exercise due to breathlessness, whereas the control subjects stopped because of leg fatigue. At the termination of exercise, the cycle workload was returned to 0 W, and the subject continued pedaling for ten minutes of active recovery.
Recovery half-times are reported as the minutes required for return of a variable to 50 percent of the difference between the maximal value attained during exercise and the value during the unloaded pedaling warm-up period before exercise. The percentage of recovery of Ve, for example, is calculated by the following equation where Ve, is the maximal Ve during exercise, Ve, is the Ve at any time during recovery, and Vei is the mean Ve during the third minute of the warm-up period. In the event of incomplete recovery within 10 min, the recovery half-time was recorded as 10 min.
Data were entered into a microcomputer data base and analyzed with a commercial statistical package (Systat). Croup differences in continuous variables were analyzed by the unpaired Students t- test. Linear regression was used to examine the relationship between gas exchange and HR recovery times and FEV,. Values for p<0.05 were considered significant.