Clinical Significance of a Spiral Phenomenon in the Plot of CO2 Output Versus O2 Uptake During Exercise in Cardiac Patients

A spiral phenomenon is sometimes noted in the plots of CO2 output (VCO2) against O2 uptake (VO2) measured during cardiopulmonary exercise testing (CPX) in patients with heart failure with oscillatory breathing. However, few data are available that elucidate the clinical significance of this phenomenon. Our group studied the prevalence of this phenomenon and its relation to cardiac and cardiopulmonary function. Of 2,263 cardiac patients who underwent CPX, 126 patients with a clear pattern of oscillatory breathing were identified. Cardiopulmonary indexes were compared between patients who showed the spiral phenomenon (n = 49) and those who did not (n = 77). The amplitudes of VO2 and VCO2 oscillations were greater and the phase difference between VO2 and VCO2 oscillations was longer in the patients with the spiral phenomenon than in those without it. Patients with the spiral phenomenon also had a lower left ventricular ejection fraction (43.4 ± 21.4% vs 57.1 ± 16.8%, p 1.0 because lactic acid is buffered by bicarbonate, resulting in the formation of carbonic acid, which dissociates to water and CO2.2 A peculiar spiral (vortex) phenomenon progressing in a counterclockwise direction is sometimes recognized in the plot of VCO2 against VO2 during CPX in patients with heart failure with oscillatory breathing.3 In the present study, we determined how frequently the spiral phenomenon can be observed during CPX in cardiac patients with oscillatory breathing and evaluated whether this phenomenon is related to impaired cardiopulmonary function.