Periodic Changes in Tidal Volume and Respiratory Rate in Heart Failure During Exercise

Abstract

Periodic breathing (PB) is commonly seen in patients with severe heart failure at rest, and exercise augments these breathing oscillations. The mechanism leading to PB in heart failure is not well understood. It is also unknown if the ventilatory oscillations are induced by fluctuations in tidal volume (VT) Respiratory rate (RR), or both. We analyzed the amplitude of ventilation (VE), VT, RR, and partial pressure of endtidal CO2 (PetCO2) oscillations, during 48 PB cycles, from 14 patients with heart failure, during incremental exercise. Phase relationship were compared by visually fitting a sine wave to the oscillation of each variable. The mean period of the oscillations was 0.95 ± 0.16 min/cycle. The mean fluctuation (Δ) of a variable, relative to the mean value of V,/I>E, VT, RR, and PetCO2 [Δ = (peak – nadir)/mean], was 45 ± 16, 44 ± 20, 18 ± 10, and 13 ± 11%, respectively. Phase relationship analysis revealed that VE and VT oscillate in phase (VE lags VT by only 6 ± 9°, p = NS). In contrast, RR was out of phase with VE (RR lages VE by 143 ± 63°, P < 0.01). As expected from this pattern, PetCO2 oscillates in a direction opposite to VE and VT oscillations. Due to the large phase shift, the RR contribution to the amplitude of VE Oscillations was not significant. It is concluded that in heart failure during exercise. VT oscillations are larger and are out of phase relative to RR oscillations. Therefore, VT is the predominant determinant of PB. Any hypothesis on the mechanism of the ventilatory oscillations should also account for the dissociation between tidal volume and respiratory rate.