Relationship between ventilatory pattern and peak VO₂ and area M regulates the respiratory system during exercise

Background: Exertional dyspnea is a major symptom of heart failure. We investigated the tidal volume (TV)-the respiratory rate (RR) regulation according to the peak O₂ uptake (VO₂) during cardiopulmonary exercise testing (CPET) for clarifying exercise ventilatory pattern.

Methods: We enrolled 1111 patients (66±13 years old, 68% men) who had undergone CPET at our hospital. We investigated the relationship between TV and RR and drew the TV/height-RR figure according to the %peak VO₂.

Results: During exercise, TV was greater, illustrated as higher %peak VO₂. However, RR was weakly correlated with %peak VO₂. Adjusted with age, height, sex, each point of RR, and %peak VO₂, TV during exercise highly correlated with age, height, each point of RR, and % peak VO₂ (R=0.726 to 0.821, p<0.01). In the figure, regardless of the %peak VO₂, TV/height and RR values were linearly related at rest, as well as at the point of anaerobic threshold, respiratory compensation, and peak exercise point, with each of these lines converging onto a single area (area M). The TV-RR slope values at early phase were also lower at lower %peak VO₂.

Conclusions: We identified three ventilatory regularities during exercise. First, TV increases as greater %peak VO₂. Second, the line relating TV/height and RR at each reference point during the incremental exercise test converged onto area M. Finally, the TV-RR slope at the early exercise phase was lower in patients with a lower %peak VO₂. These ventilatory regularities may assist in elucidating the excise ventilatory pattern and help the diagnosis of exertional dyspnea.