Does the Severity of Central Sleep Apnea Correlate With Respiratory Gas Indexes During Cardiopulmonary Exercise Testing?

Exercise end-tidal CO2 predicts central sleep apnea in patients with heart failure

BACKGROUND

Increased CO2 chemosensitivity and augmented exercise ventilation are characteristic of patients with heart failure (HF) with central sleep apnea (CSA). The aim of this study was to test the hypothesis that decreased end-tidal CO2 by cardiopulmonary exercise testing predicts CSA in patients with HF.

METHODS

Consecutive ambulatory patients with New York Heart Association II to III HF were prospectively evaluated by CO2 chemosensitivity by rebreathe, cardiopulmonary exercise testing, and polysomnography (PSG). Subjects were classified as having either CSA (n = 20) or no sleep apnea (n = 13) by PSG; a central apnea-hypopnea index (AHI) ≥ 5 was used to define CSA. Subgroups were compared by t test or Mann-Whitney test and data summarized as mean ± SD. P < .05 was considered significant.

RESULTS

At rest, subjects with CSA had higher central CO2 chemosensitivity (Δminute ventilation [V.e]/Δpartial pressure of end-tidal CO2 [Petco2], 2.3 ± 1.0 L/min/mm Hg vs 1.6 ± 0.4 L/min/mm Hg, P = .02) and V.e (15 ± 7 L/min vs 10 ± 3 L/min, P = .02) and lower Petco2 (31 ± 4 mm Hg vs 35 ± 4 mm Hg, P < .01) than control subjects. At peak exercise, the ventilatory equivalents per expired CO2 (V.e/V.co2) was higher (43 ± 9 vs 33 ± 6, P < .01) and Petco2 lower (29 ± 6 mm Hg vs 36 ± 5 mm Hg, P < .01) in subjects with CSA. In addition, CO2 chemosensitivity, peak exercise V.e/V.co2, and Petco2 were independently correlated with CSA severity as quantified by the AHI (P < .05). Peak exercise Petco2 was most strongly associated with CSA (OR, 1.29; 95% CI, 1.08-1.54; P = .01; area under the curve, 0.88).

CONCLUSIONS

In patients with HF and CSA, ventilatory drive is increased while awake at rest and during exercise and associated with heightened CO2 chemosensitivity and decreased arterial CO2 set point.

Sleep-disordered breathing with nighttime hypocapnia relates to daytime enhanced ventilatory response to exercise in patients with heart disease

BACKGROUND

Sleep-disordered breathing (SDB) induces nighttime disturbance of arterial gases, such as carbon dioxide. However, it is still unclear whether nighttime SDB-related gas abnormality is related to respiratory dysregulation in daytime. Therefore, we examined the relationship between the arterial partial pressure of carbon dioxide (PaCO(2)) at nighttime and the respiratory response to exercise in daytime.

METHODS

Eighteen men (age, mean ± SD; 55 ± 11 years) with heart disease underwent multichannel respiratory monitoring through the night with transdermal measurement of PaCO(2) (PtcCO(2)) reflecting PaCO(2) and a cardiopulmonary exercise test in daytime. The ventilatory equivalent (VE)/carbon dioxide production (VCO(2)) slope as an index of ventilatory response to exercise and peak oxygen consumption (VO(2)) were obtained with a cardiopulmonary exercise test.

RESULTS

Of the 18 patients, 10 patients had obstructive SDB, 5 had central SDB, and 3 patients did not have SDB. The mean apnea-hypopnea index was 21 ± 17. Minimum nighttime saturation of O(2) was positively correlated with peak VO(2), but not with VE/VCO(2). Nighttime PtcCO(2) was not correlated with peak VO(2) but was negatively correlated with the VE/VCO(2) slope of the daytime cardiopulmonary exercise test (r=-0.53).

CONCLUSION

Nighttime lowering of PaCO(2) in SDB is related to an abnormal ventilatory response to exercise testing in the daytime. This finding suggests that nighttime hyperventilation in SDB alters both nighttime and daytime pathophysiological conditions in patients with heart disease.

Prognostic value of cardiopulmonary exercise testing in cardiac patients with atrial fibrillation

Parameters obtained from cardiopulmonary exercise testing (CPX) are recognized for their high prognostic value in predicting future cardiac events in cardiac patients. Our group compared the prognostic value of CPX parameters between patients with sinus rhythm (SR) and patients with atrial fibrillation (AF).Peak O2 uptake (VO2), the ratio of the increase in VO2 to the increase in work rate (ΔVO2/ΔWR), and the slope of the increase in ventilation to the increase in CO2 output (VE-VCO2 slope) were obtained from CPX in 72 AF patients and 478 SR patients. The prognostic values of these indices were compared between the two groups.Six cardiac deaths and 25 cardiac events were observed in the AF group and 9 cardiac deaths and 96 cardiac events were observed in the SR group, over a prospective follow-up period of 1,192 days. The percentages of cardiac deaths and cardiac events were higher in the AF group than in the SR group. In a multivariate Cox proportional hazards analysis, peak VO2 was identified as a sole significant predictor of cardiac death and cardiac events in SR patients and VE-VCO2 slope was identified as a sole significant predictor of cardiac death and cardiac events in AF patients.Our results suggest that the VE-VCO2 slope is strongly predictive of future cardiac events in patients with AF and that peak VO2 is strongly predictive of future cardiac events in SR patients.

Overshoot phenomena of respiratory gas variables during exercise recovery in cardiac patients

BACKGROUND

Transient increases (overshoot) in respiratory gas variables have been observed during exercise recovery, but their clinical significance is not clearly understood. Our group evaluated the relationship between the presence of overshoot of respiratory gas variables and the parameters obtained from cardiopulmonary exercise testing (CPX).

METHODS AND RESULTS

In total, 227 patients with various cardiac diseases underwent CPX. The overshoot phenomena of O₂ uptake (·VO₂), ·VO₂/heart rate (O₂-pulse), and CO₂ output (·VCO₂) were analyzed by respiratory gas analysis during recovery after maximal exercise. The overshoot of ·VO₂, O₂-pulse, and ·VCO₂ were recognized in 11 (5%), 43 (19%), and 12 (5%) patients, respectively. Compared with the patients without a ·VO₂ overshoot, those with a ·VO₂ overshoot had a significantly lower peak ·VO₂ (12.3±3.7 vs. 17.9±6.2ml·min⁻¹·kg⁻¹, P=0.003), lower anaerobic threshold (9.4±1.7 vs. 12.4±3.3 ml·min⁻¹·kg⁻¹, P=0.001), higher ·VE-·VCO₂ slope (38.0±5.2 vs. 33.2±9.6, P=0.013), and lower left ventricular ejection fraction (LVEF) (39.9±22.8 vs. 55.8±16.8%, P=0.003). Similar findings were obtained for the patients with an O₂-pulse overshoot and those with a ·VCO₂ overshoot.

CONCLUSIONS

The overshoot phenomena of respiratory gas variables during recovery after maximal exercise are correlated with impaired cardiopulmonary function 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) Collapse

Key Words

• end-tidal co₂ pressure
• peak \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{\rm{v}} $$\end{document}o₂
• exercise testing

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MESH Headings

• Aged
• Carbon Dioxide/metabolism
• Exercise/physiology
• Exercise Test/methods
• Female
• Follow-Up Studies
• Humans
• Kaplan-Meier Estimate
• Male
• Middle Aged
• Oxygen Consumption/physiology
• Predictive Value of Tests
• Prognosis
• Prospective Studies
• ROC Curve
• Respiratory Function Tests/methods
• Risk Factors
• Stroke Volume/physiology
• Ventricular Dysfunction, Left/diagnosis
• Ventricular Dysfunction, Left/mortality
• Ventricular Dysfunction, Left/physiopathology

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Affiliation(s)

Masayo Hoshimoto-Iwamoto The Cardiovascular Institute, 3-10 Roppongi 7-chome, Minato-ku, Tokyo, 106-0032 Japan School of Health and Sports Science, Juntendo University, Chiba, Japan
Akira Koike The Cardiovascular Institute, 3-10 Roppongi 7-chome, Minato-ku, Tokyo, 106-0032 Japan
Osamu Nagayama The Cardiovascular Institute, 3-10 Roppongi 7-chome, Minato-ku, Tokyo, 106-0032 Japan
Akihiko Tajima The Cardiovascular Institute, 3-10 Roppongi 7-chome, Minato-ku, Tokyo, 106-0032 Japan
Takeya Suzuki Department of Cardiovascular Medicine, Toho University Omori Medical Center, Tokyo, Japan
Tokuhisa Uejima The Cardiovascular Institute, 3-10 Roppongi 7-chome, Minato-ku, Tokyo, 106-0032 Japan
Hitoshi Sawada The Cardiovascular Institute, 3-10 Roppongi 7-chome, Minato-ku, Tokyo, 106-0032 Japan
Tadanori Aizawa The Cardiovascular Institute, 3-10 Roppongi 7-chome, Minato-ku, Tokyo, 106-0032 Japan

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