Clinical Studies: Heart failure
End-tidal CO2 pressure decreases during exercise in cardiac patients: Association with severity of heart failure and cardiac output reserve

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Abstract

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

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
V̇O2
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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