Dynamic hyperinflation occurs in healthy subjects during maximal voluntary ventilation.

Audrey Herpeux¹Nathalie Yaël Pauwen^2*Roger Sergysels¹Vincent Ninane¹Anneleen Peeters¹Marie Bruyneel¹

• ¹Centre Hospitalier Universitaire Saint-Pierre, Brussels, Belgium
• ²Universite Libre de Bruxelles Faculte des Sciences de la Motricite, Brussels, Belgium

Background: Dynamic hyperinflation (DH) commonly occurs during maximum voluntary ventilation (MVV) in obstructive lung diseases and is usually attributed to expiratory flow limitation. However, in healthy individuals, maximal effort typically remains insufficient to induce DH. This study aims to determine whether DH can also develop during MVV in normal subjects, without expiratory flow limitation, challenging the current concepts of its occurrence in physiological conditions. Methods: Forty three healthy subjects (25 males/18 females; 40-68 yrs; FEV1: 3.4±0.8 L) performed MVV at increasing breathing frequencies (ranging from 10-100 breaths.min⁻¹) and maximal tidal volumes. Inspiratory capacity (IC) was measured at rest and every 12 seconds during MVV to detect DH. When DH occurred at a certain frequency (BFDH), a single additional MVV at a higher frequency was performed to confirm its occurrence. Results: DH occurred at or below 100 breaths.min⁻¹ in 39 of 43 healthy subjects (91%), with the mean onset at 52 breaths.min⁻¹. There was no significant correlation between the frequency of breathing at the onset of DH and age, body mass index, lung volumes or flows. However, BFDH was significantly and inversely correlated with resting [IC/FVC], meaning that individuals operating at lower resting ventilatory levels reached DH at lower BF. Conclusion: DH can occur at low and variable breathing frequencies during MVV in healthy subjects. The onset of DH may be related to the mechanical thoracopulmonary state at rest, suggesting that the baseline lung mechanics may determine the susceptibility to DH during high intensity ventilatory maneuvers.