Origin of oscillatory kinetics of respiratory gas exchange in chronic heart failure

Background-Respiratory gas exchange measurements in patients with chronic heart failure (CHF) at rest and during exercise commonly reveal prominent slow oscillations in ventilation ((V) over dot (E)), measured oxygen uptake ((V) over dot O-2), and carbon dioxide production ((V) over dot CO2), whose origin is not clear. Voluntary simulation of periodic breathing (PB) in normals has been reported to generate a different pattern of oscillations in gas exchange from that seen in spontaneous PB. This necessitates hypothesizing that PB is caused by a primary oscillation in tissue metabolism or in cardiac output. Methods and Results-We developed an automated method by which normal controls could be guided to breathe according to a PB pattern. The resultant metabolic oscillations closely matched those seen in spontaneous PB and had several interesting properties. At low workloads (including rest), the oscillations in (V) over dot O-2 were as prominent as those in (V) over dot (E) in both spontaneous PB (alpha(VO2)/alpha(VE)=0.92+/-0.04) and voluntary PB (0.93+/-0.07). However, at increased workload, the oscillations in (V) over dot O-2 because less prominent than those in ii, in spontaneous PB (intermediate workload 0.63+/-0.05, high workload 0.57+/-0.04: P<0.001) and voluntary PB (intermediate 0.66+/-0.03, high 0.48+/-0.03; P<0.001), There was no difference in the relative size of metabolic oscillations between voluntary and spontaneous PB at matched workloads (P>0.05 at low, intermediate, and high workloads), Furthermore, (V) over dot O-2, peaked before (V) over dot (E), in both spontaneous and voluntary PB. This time delay varied from 6.4+/-0.4 s at low ventilation, to 11.3+/-0.9 s at high ventilation (P<0.0001). Conclusions-The magnitude and phase pattern of oscillations in gas exchange of spontaneous PB can be obtained by adequately matched voluntary PB, Therefore, the gas exchange features of PB an explicable by primary ventilatory oscillation.