Constant Work Rate Exercise Test Research Articles

Reliability of submaximal exercise tests in patients with COPD. Chronic obstructive pulmonary disease.

Submaximal constant work rate exercise tests are often used to measure the efficacy of an exercise intervention, but the reliability of these tests in patients with chronic obstructive pulmonary disease (COPD) has not been established. To examine the reproducibility of submaximal exercise responses of COPD patients compared with those of healthy elderly subjects. Sixteen COPD patients and 15 healthy subjects performed four weekly submaximal exercise tests against two different constant work rates: 20 W and 50% of the peak work rate (PWR). Spirometry was performed before each exercise test. COPD patients and healthy subjects were: age 69 +/- 5 and 65 +/- 5 yr, body mass index 26.4 +/- 3.9 and 26.7 +/- 3.0 kg x m(-2), respectively. Both groups had no change in minute ventilation (V(E)), oxygen uptake (VO2), breathlessness (RPB), and leg fatigue (RPLF) for either work rate over repeated measures (P > 0.05). At 50% PWR test-retest reliability coefficients for V(E) and VO2 ranged from r = 0.88 to r = 0.96 for COPD patients and from r = 0.72 to r = 0.97 for healthy subjects; for RPB and RPLF test-retest reliability ranged from r = 0.76 to r = 0.89 for COPD patients and from r = 0.70 to r = 0.91 for healthy subjects. Intrasubject mean absolute differences for repeated measures of V(E), VO2, RPB, or RPLF were low and there were no group differences (P > 0.05). Percent error for V(E) and VO2 ranged from 6 +/- 3 to 9 +/- 7%, and for RPB and RPLF ranged from 19 +/- 18 to 68 +/- 65% for both groups at each work rate. Submaximal exercise responses were reliable over a 1-month period, and measures of the physiological and psychophysical responses of COPD patients were as reliable as those of healthy subjects.

A Four-Minute Submaximal Constant Work Rate Exercise Test to Assess Cardiovascular Functional Class in Chronic Heart Failure

To develop a submaximal constant work rate exercise test able to grade cardiovascular dysfunction in patients with chronic heart failure, 80 patients and 59 control subjects performed a symptom-limited incremental exercise test and a constant work rate exercise test at a fixed work rate (50 W for 4 minutes). The time constant of VO2 at the start of constant work rate exercise and time for gas exchange ratio (respiratory exchange ratio) to equal 1 were independent predictors of cardiovascular functional class and correctly classified the functional class in 89 +/- 9% and 83 +/- 11% of patients, respectively.

Skeletal Muscle Oxygenation and Oxygen Uptake Kinetics Following Constant Work Rate Exercise in Chronic Congestive Heart Failure

The aim of the present study was to determine the kinetics of recovery of muscle oxygenation (MO) from comparable levels of exercise in patients with chronic congestive heart failure (CHF) and in normal subjects, and to relate MO kinetics to the level of exercise intolerance. Ten patients with stable CHF secondary to ischemic cardiomyopathy (ejection fraction 34 ± 6%) (mean age 47 ± 10 years) and 8 healthy matched control subjects underwent an upright incremental cycle ergometer exercise test with gas exchange analysis and a 6-minute constant work rate protocol at 60% of peak oxygen consumption (V̇O2). Oxygenation of the vastus lateralis muscle was continuously monitored during exercise and recovery using near infrared spectroscopy. Recovery V̇O2 and MO mean response times for the constant work rate exercise test were longer in patients with CHF than in control subjects (p <0.05). Both V̇O2 and MO mean response times were inversely related to peak VO2 (r = −0.73 and −0.52, respectively; p <0.05 for both). Thus recovery of muscle and total body oxygenation from submaximal exercise is more delayed the greater the cardiac dysfunction, as assessed by peak V̇O2. This suggests that regeneration of phosphocreatine and/or resaturation of venous oxyhemoglobin take place more slowly the worse the cardiac function.

Effect of exercise training and detraining on gas exchange kinetics in patients with chronic obstructive pulmonary disease.

Symptom-limited incremental exercise tests are used to estimate the training effect on patients with chronic obstructive pulmonary disease (COPD). However, there is a need for objective parameters for measurement on submaximal exercise testing. The purpose of this study was to assess the usefulness of measurement of oxygen uptake (VO2) kinetics during a constant work rate exercise test of patients with COPD after exercise training. Eleven patients with COPD performed exercise tests before and after cycle ergometer training on 3 days per week for 8 weeks; they then went without training for 5 months and performed the same tests. They performed an incremental exercise test to symptom-limited maximum and a constant work rate exercise test for 6 min on a cycle ergometer. The time constant of VO2 during the onset of constant work rate exercise was significantly decreased (from 63.5 +/- 7.8 s to 53.2 +/- 8.0 s) after exercise training (P = 0.021), but was significantly increased (to 73.4 +/- 14.9 s) after 5 months without training (P = 0.001). The oxygen pulse at steady state during constant work rate exercise testing was significantly increased after exercise training but decreased 5 months later. The change in blood lactate from rest to steady state during constant work rate exercise was significantly decreased after exercise training, but increased 5 months later. Measurement of the time constant of VO2 and oxygen pulse during constant work rate exercise are useful for the objective evaluation of the training effect of patients with COPD.

Evidence that circulatory oscillations accompany ventilatory oscillations during exercise in patients with heart failure.

Periodic breathing (PB) during exercise in patients with congestive heart failure (CHF) is associated with prominent oscillations (OSC) of O2 uptake (VO2). We hypothesized that the VO2 OSC represent OSC in true O2 exchange, resulting from concomitant cardiac output fluctuations and are not merely due to OSC of lung O2 stores. We compared the amplitude of the OSC of VO2, ventilation (VE), and end-expiratory lung volume (EELV) in 17 patients with CHF and PB and in seven healthy control subjects who volitionally simulated PB. Subjects underwent an incremental and/or a constant work-rate exercise test. VE and VO2 were measured breath by breath. EELV change was estimated by summing the difference between inspiratory and expiratory tidal volumes for each breath. The amplitude of the OSC, delta, is expressed as the ratio of the difference between the peak and nadir of the oscillating variable divided by its mean [delta = (peak - nadir)/mean]. In CHF, during incremental testing, the amplitude of the VE OSC was smaller than that of the VO2 OSC (delta VE = 49 +/- 15% [SD], delta VO2 = 63 +/- 25%, p less than 0.01). In contrast, during volitional PB in the control subjects, VE OSC were larger than VO2 OSC (delta VE = 48 +/- 12%, delta VO2 = 25 +/- 11%, p less than 0.01). This suggests that changing VE itself cannot account for the marked VO2 OSC seen in CHF. In the patients, EELV showed no systematic OSC, did not correlate with delta VO2, and was not significantly different from zero.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucose turnover in response to exercise during high- and low-FIO2 breathing in man.

The purpose of this study was to assess whether breathing high or low concentrations of O2 could affect glucose turnover during exercise in man. Ten healthy subjects performed two constant work-rate exercise tests, one when the fraction of inspired O2 (FIO2) was 0.15 and the other at the same work rate but when the FIO2 was 0.80. The work rate for each subject was chosen so that blood lactate would be elevated during hypoxia, but would be lower during hyperoxia. Glucose appearance (Ra) and disappearance (Rd) were measured using the primed, constant infusion of [3-3H]glucose. Although the work rate was the same during hypoxia and hyperoxia in each subject, hypoxic exercise was accompanied by a significantly larger rest to exercise increase in Rd (delta Rd) compared with hyperoxia by 265%. Similarly, delta Ra was greater during hypoxia than during hyperoxia by 188%. Lactate to pyruvate ratios were significantly higher during hypoxic exercise suggesting a shift in the cell redox to a more reduced state. Insulin and glucagon were not affected by the FIO2, but both epinephrine and norepinephrine were increased during hypoxic exercise, which may explain the increase in Ra. The regulation of blood glucose during exercise in vivo appears to be dependent on the availability of oxygen to the working muscle cells.

Cardiac function during exercise: a study of systolic time intervals during increasing and constant work rate exercise tests.

Cardiac function during exercise: a study of systolic time intervals during increasing and constant work rate exercise tests.