Dynamic hyperinflation occurs in healthy subjects during maximal voluntary ventilation

Area of Science:

• Pulmonary Physiology
• Respiratory Mechanics
• Cardiopulmonary Exercise Testing

Background:

• Dynamic hyperinflation (DH) is typically observed in obstructive lung diseases during maximal voluntary ventilation (MVV), often attributed to expiratory flow limitation.
• In healthy individuals, maximal effort usually does not induce DH, challenging current physiological understanding.
• This study investigates DH occurrence in healthy subjects during MVV, questioning the necessity of expiratory flow limitation.

Purpose of the Study:

• To determine if dynamic hyperinflation (DH) can develop during maximal voluntary ventilation (MVV) in healthy individuals without expiratory flow limitation.
• To challenge the established concepts regarding the physiological conditions under which DH occurs.
• To explore potential predictors of DH onset in a healthy population.

Main Methods:

• Forty-three healthy subjects (40-68 years) performed MVV at increasing breathing frequencies (10-100 breaths/min) with maximal tidal volumes.
• Inspiratory capacity (IC) was measured at rest and periodically during MVV to detect DH.
• The breathing frequency at DH onset (BF_DH) was recorded and confirmed with a subsequent MVV.

Main Results:

• Dynamic hyperinflation (DH) occurred in 91% of healthy subjects at or below 100 breaths/min, with a mean onset frequency of 52 breaths/min.
• No significant correlation was found between DH onset and age, BMI, lung volumes, or flows.
• DH onset frequency (BF_DH) inversely correlated with resting IC/FVC, indicating lower resting ventilatory levels predict earlier DH onset.

Conclusions:

• Dynamic hyperinflation (DH) can manifest at variable, low breathing frequencies during MVV in healthy individuals.
• The onset of DH appears linked to the resting thoracopulmonary mechanical state.
• Baseline lung mechanics may influence susceptibility to DH during high-intensity ventilatory tasks.