Relation between oscillatory breathing and cardiopulmonary function during exercise in cardiac patients.

BACKGROUND: Oscillatory breathing, alternating between hyperpnea and hypopnea, has been recognized in cardiac patients, especially in those with heart failure. We evaluated whether the cycle length and amplitude of oscillatory breathing correlate with impaired cardiopulmonary function during exercise. METHODS AND RESULTS: We analyzed respiratory gas data during cardiopulmonary exercise testing (CPX) in 17 cardiac patients (68 ± 12 years) who showed clear oscillatory ventilation during CPX. The cycle length (time from peak to peak) and the amplitude (difference between peak and nadir) for both oscillating ventilation (VE) and oscillating O(2) uptake (VO(2)) were calculated from several consecutive oscillations noted at rest, and compared with indices of CPX. Oscillating VO(2) preceded oscillating VE in 16 of the 17 patients. Peak VO(2) (10.3 ± 3.1 ml min(-1)kg(-1)) correlated significantly negatively with the cycle length of the VE oscillation (r=-0.60, P=0.010), and of the VO(2) oscillation (r=-0.61, P=0.008), and the difference in time between the peak of oscillating VE and the corresponding peak of VO(2) (r=-0.58, P=0.012). Similarly, the slope of the increase in VE to the increase in CO(2) output (45.6 ± 11.5) correlated significantly positively with the cycle length of the VE and VO(2) oscillations (r=0.68, P=0.002; r=0.67, P=0.003, respectively). CONCLUSIONS: The cycle length of oscillatory breathing is closely related to impaired cardiac reserve during exercise in cardiac patients.

Abnormal end-tidal PO(2) and PCO(2) at the anaerobic threshold correlate well with impaired exercise gas exchange in patients with left ventricular dysfunction.

BACKGROUND: The aim of the present study was to compare the end-tidal O(2) pressure (PETO(2)) to end-tidal CO(2) pressure (PETCO(2)) in cardiac patients during rest and during 2 states of exercise: at anaerobic threshold (AT) and at peak. The purpose was to see which metabolic state, PETO(2) or PETCO(2), best correlated with exercise limitation. METHODS AND RESULTS: Thirty-eight patients with left ventricular (LV) ejection fraction <40% underwent cardiopulmonary exercise testing (CPX). PETO(2) and PETCO(2) were measured during CPX, along with peak O(2) uptake (VO(2)), AT, slope of the increase in ventilation (VE) relative to the increase in CO(2) output (VCO(2)) (VE vs. VCO(2) slope), and the ratio of the increase in VO(2) to the increase in work rate (ΔVO(2)/ΔWR). Both PETO(2) and PETCO(2) measured at AT were best correlated with peakVO(2), AT, ΔVO(2)/ΔWR and VE vs. VCO(2) slope. PETO(2) at AT correlated with reduced peak VO(2) (r=-0.60), reduced AT (r=-0.52), reduced ΔVO(2)/ΔWR (r=-0.55) and increased VE vs. VCO(2) slope (r=0.74). PETCO(2) at AT correlated with reduced peak VO(2) (r=0.67), reduced AT (r=0.61), reduced ΔVO(2)/ΔWR (r=0.58) and increased VE vs. VCO(2) slope (r=-0.80). CONCLUSIONS: PETCO(2) and PETO(2) at AT correlated with peak VO(2), AT and ΔVO(2)/ΔWR, but best correlated with increased VE vs. VCO(2) slope. PETO(2) and PETCO(2) at AT can be used as a prime index of impaired cardiopulmonary function during exercise in patients with LV failure.

Overshoot phenomenon of oxygen uptake during recovery from maximal exercise in patients with previous myocardial infarction.

The overshoot in oxygen uptake (VO2 overshoot) during recovery from maximal exercise is thought to reflect an overshoot in cardiac output. We investigated whether this phenomenon is related to cardiopulmonary function during exercise in cardiac patients. A total of 201 consecutive patients with previous myocardial infarction underwent cardiopulmonary exercise testing (CPX). An apparent VO2 overshoot during the recovery from CPX (6.5+/-8.1% increase relative to the peak VO2) was observed in ten patients. A comparison of patients with the VO2 overshoot to those without the VO2 overshoot revealed that the former had a significantly lower left ventricular ejection fraction (40.1+/-19.1 vs. 55. 2+/-14.9%, respectively, p = 0.002) and larger left ventricular diastolic and systolic dimensions. Patients with the VO2 overshoot also had a significantly lower peak VO2 (13.1+/-6.1 vs. 18.1+/-4.5 ml/min/kg, p < 0.001), lower DeltaVO2/DeltaWR (work rate) (6.6+/-3.8 vs. 9.5+/-1.7 mL/min/W, p < 0.0001), and a higher E (minute ventilation)/VCO2 (carbon dioxide output) slope (45.0+/-18.6 vs. 32.6+/-6.6, p < 0.0001) than those without the overshoot. A VO2 overshoot during recovery from maximal exercise was found in 5% of patients with previous myocardial infarction. This condition, which suggests a transient mismatch between cardiac contractility and afterload reduction, was found to be related to impaired cardiopulmonary function during exercise.

Prognostic value of end-tidal CO2 pressure during exercise in patients with left ventricular dysfunction.

We compared the prognostic power of end-tidal CO(2) pressure (PETCO(2)) during exercise, an index of arterial CO(2) pressure, with those of established respiratory gas indexes during exercise testing in patients with left ventricular dysfunction. Seventy-eight consecutive patients with a left ventricular ejection fraction (LVEF)

Determination of the V.E/V.CO2 slope from a constant work-rate exercise test in cardiac patients.

Incremental exercise testing to a symptom-limited maximum has been used to measure the ratio of the increase in ventilation (V.E) to the increase in CO(2) output (V.CO(2)) during exercise (V.E/V.CO(2) slope), a valuable index reflecting the severity of the ventilation-perfusion mismatch in heart failure. Here we studied whether this same value for the slope of V.E/V.CO(2) could be determined from a short constant work-rate exercise test of moderate intensity. Twenty-three patients with a previous myocardial infarction underwent moderate-intensity (69+/-15 W) constant work-rate exercise for 6 min and an incremental work-rate exercise test to the max. The V.E/V.CO(2) slope was calculated from the incremental exercise test from the start of increasing the work-rate to the ventilatory compensation point. The V.E/V.CO(2) slope was similarly calculated from the start of constant work-rate exercise until the 4th minute, when V.E and V.CO(2) changed minimally. The V.E/V.CO(2) slope determined from incremental exercise was 33.8+/-5.9, ranging from 20.9 to 42.8. The slope obtained from constant work-rate exercise was 32.9+/-5.7. The V.E/V.CO(2) slopes obtained from the two exercise tests did not differ significantly. The slope obtained from constant work-rate exercise was significantly positively correlated with the slope obtained from the incremental exercise (r=0.84, p<0.0001). The V.E/V.CO(2) slope can be determined from constant work-rate exercise at a moderate intensity. This indicates that the relationship between ventilation and CO(2) output is consistent and independent of the mode of exercise testing.

Clinical significance of cerebral oxygenation during exercise in patients with coronary artery disease.

BACKGROUND: Recent investigations have demonstrated that cerebral oxyhemoglobin (O(2)Hb) decreases during exercise in patients with left ventricular dysfunction, reflecting a cerebral hypoxia. We sought to establish a prognostic value of decreased cerebral O(2)Hb during exercise in cardiac patients, and to compare it with those of indexes obtained from cardiopulmonary exercise testing (CPX). METHODS AND RESULTS: A total of 344 consecutive patients with coronary artery disease were enrolled in the study. All the patients performed CPX, during which cerebral O(2)Hb was continuously monitored using near-infrared spectroscopy. There were 13 cardiac deaths and 78 cardiovascular events during the prospective follow-up period of 1,231+/-538 days. The change of O(2)Hb measured at the forehead from rest to peak exercise (DeltaO(2)Hb) was significantly lower in non-survivors than in survivors (-1.5+/-3.3 vs 1.7+/-3.2 micromol/L, p=0.0004). By multivariate Cox proportional hazards analysis, DeltaO(2)Hb and left ventricular ejection fraction (LVEF) were found to be independent prognostic markers for cardiac deaths. The DeltaO(2)Hb, LVEF and peak oxygen uptake were found to be significant prognostic markers for cardiovascular events, mainly for heart failure worsening and sudden cardiac death. CONCLUSION: The present findings suggest that a decrease in cerebral O(2)Hb during exercise predicts future cardiovascular events in patients with coronary artery disease.