CHEST-WALL MOTION BEFORE AND DURING MECHANICAL VENTILATION IN CHILDREN WITH NEUROMUSCULAR DISEASE

Patients with neuromuscular disease can display paradoxic motion of the rib cage (RC) and abdomen (AB), which increases the work of breathing and predisposes to respiratory muscle fatigue. Long-term mechanical ventilation can reverse chronic hypercapnea and decrease the work of breathing in these patients. Changes in chest wall motion (CWM) that occur during mechanical ventilation have not been studied. We have assessed CWM using a calibrated respiratory inductive plethysmograph before and during mechanical ventilation in 5 children and young adults with neuromuscular disease and paradoxic breathing at rest. Asynchrony of CWM was quantitated by measuring the phase shift, theta, between RC and AB motion (0-degrees = synchronous motion, 180-degrees = paradoxic motion). The volume contribution of the paradoxing compartment to tidal volume (PC/V(T)) was calculated. Before mechanical ventilation, mean +/- SEM V(T) was 122 +/- 17 mL, theta was 131 +/- 15-degrees-C, and PC/V(T) was -27 +/- 6%. During mechanical ventilation, V(T) increased to 274 +/- 47 mL (P < 0.05), theta decreased to 41 +/- 14-degrees (P < 0.05), and PC/V(T) increased to +39 +/- 9% (P < 0.02). We conclude that mechanical ventilation improves RC/AB asynchrony and reverses the negative contribution to tidal volume of the paradoxing compartment in children and young adults with neuromuscular disease. This implies that mechanical ventilation assumes most or all the role of the respiratory pump in these patients, which provides a rationale for the use of chronic or nighttime ventilation in the treatment of respiratory muscle fatigue. Assessment of CWM may be useful in the determination of optimal ventilator settings in this population. (C) 1993 Wiley-Liss, Inc.