Closing volume after inspiratory resistive loading to fatigue

Area of Science:

• Respiratory Physiology
• Pulmonary Function Testing
• Exercise Physiology

Background:

• Inspiratory resistive loading can lead to diaphragmatic fatigue.
• The physiological consequences of diaphragmatic fatigue, such as changes in breathing pattern and potential pulmonary edema, are not fully understood.

Purpose of the Study:

• To investigate the effect of inspiratory resistive loading to fatigue on closing volume in healthy subjects.
• To determine if the negative intrathoracic pressures generated during resistive loading induce pulmonary edema.
• To elucidate the cause of rapid shallow breathing following inspiratory resistive loading to fatigue.

Main Methods:

• Six healthy subjects underwent the single breath nitrogen washout test to measure closing volume.
• Subjects performed inspiratory resistive loading until diaphragmatic fatigue was evident (confirmed by electromyography).
• Closing volume was measured before and after the fatiguing loading period.

Main Results:

• Closing volume, expressed as a percentage of vital capacity, showed no significant difference before (10.5 +/- 1.7%) and after (10.1 +/- 1.9%) resistive loading to fatigue.
• Electromyographic evidence confirmed diaphragmatic fatigue in all subjects.

Conclusions:

• The findings suggest that inspiratory resistive loading to fatigue does not cause pulmonary edema, as evidenced by the unchanged closing volume.
• Rapid shallow breathing observed after inspiratory resistive loading to fatigue is likely a direct result of diaphragmatic fatigue, not pulmonary edema.