Effects of nicorandil on kinetics of oxygen uptake at the onset of exercise in patients with coronary artery disease

Effect of acute blood pressure reduction on oxygen uptake kinetics at the onset of exercise in hypertensive patients

The aim of the present study was to investigate the adverse effects of hypertension on the cardiovascular system in daily activities and the effect of acute blood pressure reduction on oxygen (O(2)) uptake kinetics. Twenty hypertensive patients were included in the study group. Patients performed treadmill exercise tests (2.5 km/hour and 5 inclines) twice, before and after blood pressure reduction with sublingual captopril. In the control group, ten hypertensive patients underwent two tests one hour apart without blood pressure reduction brought about by drug therapy. The changes in O(2) kinetic values (O(2) deficit and mean response time [MRT]) between the two tests were investigated. In the study group, the O(2) deficit and MRT values measured during the first exercise testing were found to be 547 +/- 183 mL and 40 +/- 9 seconds, while those in the second exercise testing were 401 +/- 127 mL and 34 +/- 7 seconds, respectively. In the control group, the O(2) deficit and MRT values measured during the first exercise test were 491 +/- 217 mL and 42 +/- 16 seconds and 515 +/- 159 mL and 41 +/- 13 seconds in the second exercise test. The differences in O(2) deficit and MRT in the study group were considered to be statistically significant (P = 0.008 and P = 0.004, respectively). Based on our findings, there was a significant improvement in O(2) kinetic values with an acute reduction in blood pressure in hypertensive patients, most likely as a result of an improved response in cardiac output.

Comparison of oxygen uptake on-kinetic calculations in heart failure

PURPOSE

The analysis of oxygen (O(2)) uptake on-kinetics during steady-rate is gaining interest in the heart failure (HF) population. The rate change in O(2) at the initiation of exercise can be assessed via nonlinear regression time constant (TC) or an algebraic equation (mean response time [MRT]). These calculations are presumed to be interchangeable, but research supporting this claim is limited. This investigation compares and contrasts two of the more commonly used O(2) uptake on-kinetic calculations.

METHOD

Twenty-eight subjects diagnosed with compensated HF and 19 age, sex, and activity-matched controls underwent a symptom-limited exercise test and a steady-rate exercise session (6 min). Peak O(2) uptake, O(2) uptake at ventilatory threshold, the O(2) uptake TC (TC), and the O(2) uptake mean response time (MRT) were calculated for each subject.

RESULTS

O(2) uptake on-kinetics was significantly faster for the control group ( < 0.05) regardless of calculation method. There was a significant difference between the O(2) uptake TC and MRT for the HF group. All O(2) uptake on-kinetic calculations were significantly correlated with aerobic capacity.

CONCLUSIONS

O(2) uptake TC and MRT values may not be interchangeable in the HF population. All O(2) uptake on-kinetic calculations did produce a significant difference between experimental and control groups and correlated with indicators of aerobic capacity. The 10-s O(2) uptake on-kinetic calculations may be preferable secondary to expired gas fluctuations associated with breath-by-breath measures. Further work is, however, needed to determine which averaged O(2) uptake on-kinetic expression is optimal given the significant difference between TC and MRT. A mechanism for this difference may be the oscillatory ventilatory expired gas pattern demonstrated by some patients with HF.

Prognostic significance of cardiopulmonary exercise testing for 10-year survival in patients with mild to moderate heart failure

Although a number of studies have investigated the prognostic significance of exercise variables, they have focused only on short-term prognosis in relatively severe heart failure. This study was carried out to determine whether the indices obtained during cardiopulmonary exercise testing have prognostic significance during a 10-year follow-up in mild to moderate heart failure. Three hundred and sixty-four consecutive patients with cardiac disease performed 4 min of 20-W warm-up, followed by a symptom-limited incremental exercise test on a cycle ergometer. In addition to the measurements of peak oxygen uptake (VO2) and gas exchange (anaerobic) threshold, the time constant of VO2 kinetics during the onset of warm-up exercise was calculated using a single exponential equation. Data on mortality were available for follow-up in 260 patients. After 3,331+/-610 days of follow-up, 29 cardiovascular-related deaths occurred. The time constant of VO2 in the nonsurvivors was 76.7+/-43.3 s and was significantly prolonged compared with that of survivors (55.3+/-30.6 s, p=0.001). Peak VO2 and gas exchange threshold were both significantly lower in nonsurvivors than in survivors. Kaplan-Meier survival curves for 10 years of follow-up demonstrated a survival rate of 89.0% for patients with a normal VO2 time constant (< 80 s) and 71.7% for those with a longer time constant (> or = 80 s), showing a significant difference in survival (p=0.0028). Respiratory gas parameters obtained during exercise testing, particularly the time constant of VO2 kinetics, were found to be useful for predicting long-term prognosis in patients with chronic heart failure. These results suggest that cardiopulmonary exercise testing could be more applicable in ambulatory patients with minimal symptoms or minimal functional impairment.

Percutaneous transluminal coronary angioplasty improves oxygen uptake kinetics during the onset of exercise in patients with coronary artery disease

STUDY OBJECTIVES

Although percutaneous transluminal coronary angioplasty (PTCA) is known to have beneficial effects on exercise capacity, its effects on the cardiovascular response during the onset of exercise have not been clarified. The present study was undertaken to determine the effects of PTCA on the kinetics of oxygen uptake (VO(2)) during constant-work-rate exercise in patients with coronary artery disease, as well as on their indexes of maximal work capacity.

METHODS

Seventeen patients with coronary artery disease who received successful PTCAs performed a 50-W constant-work-rate exercise test for 6 min and a symptom-limited incremental exercise test both before and 4 months after the PTCA procedure. VO(2) was calculated from breath-by-breath analysis of respired gases. The time constant of VO(2) kinetics during the onset of 50-W exercise was determined by fitting a single exponential function to the VO(2) response.

RESULTS

In 14 patients without coronary restenosis, the time constant of VO(2) kinetics was significantly shortened from (mean +/- SD) 57.4 +/- 12.6 before PTCA to 48.2 +/- 9.5 s after PTCA (p = 0. 0035), indicating improved kinetics of the VO(2) response. In these subjects, the peak VO(2) obtained during maximal exercise testing also increased from 23.1 +/- 3.5 to 26.5 +/- 3.2 mL/min/kg, respectively (p = 0.0005). However, there was no improvement in these indexes in the patients who had restenosis after undergoing PTCA (n = 3).

CONCLUSION

Indexes of cardiopulmonary exercise testing, which reflect an efficiency of oxygen flow to the exercising muscle, can be used as an objective, noninvasive, and cost-effective guide for understanding which patients will not have coronary restenosis following PTCA.

Kinetics of pulmonary gas exchange during and while recovering from exercise in patients after anterior myocardial infarction

The effect of exercise intensity on gas exchange kinetics was investigated during exercise and recovery, as well as the relationship between the kinetics during exercise and recovery. Twenty-three patients with a history of anterior myocardial infarction performed low-intensity (38.7+/-8.3 W) and high-intensity (68.8+/-15.0 W) exercise for 6 min. The time constants of oxygen uptake (VO2), carbon dioxide output (VCO2) and minute ventilation (VE) were significantly prolonged during high intensity exercise compared with low-intensity exercise (61.2+/-8.6 vs 52.3+/-10.3 s, p<0.005 for the time constant of VO2). The time constant of VO2 was similar during exercise and during recovery from exercise of high (61.2+/-8.6 vs 66.2+/-12.2 s) as well as low intensity (52.3+/-10.3 vs 55.0+/-10.1 s). However, the time constants of VCO2 and heart rate were significantly shorter during recovery than during exercise. The time constants of VCO2 and VE were significantly longer than that of VO2 during both exercise and recovery. In the present study, it was found that (1) the gas exchange kinetics were influenced by the intensity of exercise; (2) the kinetics during recovery did not necessarily reflect the kinetics during exercise except for VO2; and (3) the kinetics of VCO2 and VE were delayed as compared with the VO2 kinetics. These characteristics should be taken into account when using gas exchange kinetics to estimate cardiopulmonary responses to exercise in patients with left ventricular dysfunction.

Kinetics of oxygen uptake at onset of exercise related to cardiac output, but not to arteriovenous oxygen difference in patients with chronic heart failure

Patients with chronic heart failure performed exercise tests to evaluate the relation of kinetics of oxygen uptake to cardiac output and arteriovenous oxygen difference at the onset of exercise. The kinetics of oxygen uptake are primarily determined by cardiac output; these kinetics are useful in evaluating exercise intolerance and cardiac output response during exercise.

Delayed VO2 kinetics during ramp exercise: a criterion for cardiopulmonary exercise capacity in chronic heart failure

PURPOSE

Kinetics of VO2 at onset of constant work rate exercise was previously shown to be slowed in patients with chronic heart failure (CHF) compared with that in healthy normals. Because bicycle ergometry with ramp protocol is usually used for exercise testing with CHF patients, it would be of practical importance if it can be shown that a delay in the time interval of linear increase of VO2 (TILIV) to work rate occurs after beginning ramp exercise. Data of central hemodynamics (CHF) and noninvasive cardiopulmonary parameters (CHF, normals) should also correlate with VO2 delay time if this parameter is related to cardiopulmonary exercise capacity.

METHODS

Fifteen males with CHF (mean +/- SEM: age 52 +/- 2 yr; ejection fraction 32 +/- 4%; peak cardiac index 3.9 +/- 0.3 L x m(-2) x min(-1)) and 28 healthy males (50 +/- 1 yr) were assessed. During ramp bicycle ergometry (3 min unloaded, work rate increments of 12.5 W x min(-1)), VO2 was measured breath by breath.

RESULTS

After the onset of ramp exercise, there was a difference in the TILIV between patients and normals (83.7 +/- 3.6 vs 66.8 +/- 2.9 s; P < 0.001). Significant differences between both groups were also found for VO2 at ventilatory threshold (VT) (10.1 +/- 0.1 vs 15.2 +/- 0.7 mL x kg(-1) x min(-1); P < 0.0001), VO2 at VT relative to predicted VT (58 +/- 4 vs 97 +/- 4%; P < 0.0001), peak VO2 (13.2 +/- 1.0 vs 34 +/- 1.4 mL x kg(-1) x min(-1), P < 0.001), and increase of systolic blood pressure (36 +/- 7 vs 71 +/- 5 mm Hg; P < 0.0001). In CHF, the TILIV correlated significantly with peak cardiac index and VO2 at VT (r = -0.71; P < 0.005 each), relative value of VO2/kg at VT (r = -0.61; P < 0.03), peak VO2/kg (r = -0.63; P < 0.01), and increase of systolic blood pressure (r = -0.52; P < 0.02). In the normals only VO2/kg at VT correlated significantly with TILIV (r = -0.41; P < 0.03). In patients, stepwise regression analysis identified three predictors which could explain 79% of the variance of TILIV: VO2/kg at VT (r2 = 0.51), peak cardiac index (r2 = 0.20), and peak VO2/kg (r2 = 0.08).

CONCLUSION

TILIV, determined at the onset of ramp exercise, is prolonged in CHF patients compared with that in normals and reflects severity of functional impairment because of reduced cardiac index and aerobic capacity. TILIV can provide information about changes in cardiopulmonary exercise capacity and thus can be used for follow-up and treatment studies in CHF.