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 <0.001) and a higher level of brain natriuretic peptide (637.2 ± 698.3 vs 228.3 ± 351.4 pg/ml, p = 0.002). The peak VO2 was lower (14.5 ± 5.6 vs 18.1 ± 6.3, p = 0.002), the slope of the increase in ventilation versus VCO2 was higher (39.8 ± 9.5 vs 33.6 ± 6.8, p <0.001), and end-tidal PCO2 both at rest and at peak exercise was lower in the patients with the spiral phenomenon than in those without it. In conclusion, the spiral phenomenon in the VCO2-versus-VO2 plot arising from the phase difference between VCO2 and VO2 oscillations reflects more advanced cardiopulmonary dysfunction in cardiac patients with oscillatory breathing.