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CLINICAL STUDIES: HEART FAILURE

End-tidal CO₂ pressure decreases during exercise in cardiac patients

Association with severity of heart failure and cardiac output reserve

^a Second Department of Internal Medicine, Faculty of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan
^* Internal Medicine, the Cardiovascular Institute, Tokyo, Japan

Manuscript received December 17, 1998; revised manuscript received December 30, 1999, accepted March 1, 2000.

Reprint requests and correspondence: Dr. Akihiro Matsumoto, The Second Department of Internal Medicine, Faculty of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan, 113
amatsu-tky{at}umin.u-tokyo.ac.jp

OBJECTIVES

We measured end-tidal CO₂ pressure (PETCO₂) during exercise and investigated the relationship between PETCO₂ and exercise capacity, ventilatory parameters and cardiac output to determine the mechanism(s) of changes in this parameter.

BACKGROUND

It is unclear whether PETCO₂ is abnormal at rest and during exercise in cardiac patients.

METHODS

Cardiac patients (n = 112) and normal individuals (n = 29) performed exercise tests with breath-by-breath gas analysis, and measurement of cardiac output and arterial blood gases.

RESULTS

PETCO₂ was lower in patients than in normal subjects at rest and decreased as the New York Heart Association class increased, whereas the partial pressure of arterial CO₂ did not differ among groups. Although PETCO₂ increased during exercise in patients, it remained lower than in normal subjects. PETCO₂ in relation to cardiac output was similar in patients and normal subjects. PETCO₂ at the respiratory compensation point was positively correlated with the O₂ uptake (r = 0.583, p < 0.0001) and the cardiac index at peak exercise (r = 0.582, p < 0.0001), and was negatively correlated with the ratio of physiological dead space to the tidal volume. The sensitivity and specificity of PETCO₂ to predict an inadequate cardiac output were 76.6% and 75%, respectively, when PETCO₂ at respiratory compensation point and a cardiac index at peak exercise that were less than the respective control mean–2 SD values were considered to be abnormal.

CONCLUSIONS

PETCO₂ was below normal in cardiac patients at rest and during exercise. PETCO₂ was correlated with exercise capacity and cardiac output during exercise, and the sensitivity and specificity of PETCO₂ regarding decreased cardiac output were good. PETCO₂ may be a new ventilatory abnormality marker that reflects impaired cardiac output response to exercise in cardiac patients diagnosed with heart failure.

Abbreviations and Acronyms   PETCO2 = end-tidal CO2 pressure   PaCO2 = partial pressure of arterial CO2   P[a-ET]CO2 = arterial–end-tidal CO2 difference   NYHA = New York Heart Association   O2 = O2 uptake   VD/VT = the physiologic dead space to tidal volume ratio   %FVC = forced vital capacity expressed as percent of predicted   %FEV1 = forced expiratory volume in 1 s expressed as percent of predicted   VA/Q = ventilation/perfusion

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