A paper on the pace of recovery from diaphragmatic fatigue and its unexpected dividends.

Abstract

Because the diaphragm is essential for survival, we wondered if it might be less vulnerable to the long-lasting effects of fatigue than limb muscles. Using a recently introduced magnetic probe to activate the phrenic nerves, we followed the evolution of twitch transdiaphragmatic pressure after inducing fatigue in healthy volunteers. Twenty-four hours after its induction, diaphragmatic fatigue had not fully recovered. Findings from this study later served as the foundation for incorporating a once-daily, T-tube-trial arm into a randomized controlled trial of techniques for ventilator weaning in intensive care unit patients and also influenced the design of a controlled trial of the weaning of tracheostomy patients who required prolonged ventilation. The research methodology was later employed to determine whether low-frequency fatigue is responsible for weaning failure. Employing a further modification of the technique--twitch airway pressure--it became evident that respiratory muscle weakness is a greater problem than fatigue in ventilated patients. Twitch airway pressure is now being used to document the prevalence and consequences of ventilator-induced respiratory muscle weakness. Our study--which began with a circumscribed, simple question--has yielded dividends in unforeseen directions, illustrating the fruitfulness of research into basic physiological mechanisms.