Respiratory Insufficiency in Myotonic Dystrophy: The Critical Influence of Hypoxia and Impedance to Breathing

Abstract

In patients with myotonic dystrophy without CO2 retention, we have previously documented that the chemosensitivity of the respiratory centers is well preserved but that weakness, excessive fatigability, and myotonia of the respiratory muscles com-promise the ventilatory output. Because hypoxemia is a frequent finding during the course of the disease, this study was designed to evaluate the influence of breathing 13% O2 on the performance of respiratory muscles. In 11 patients with the disease and 11 matched controls, we monitored minute ventilation (VE), tidal volume (VT), respi-ratory rate (f), occlusion pressure (P0.1), esophageal pressure (Pes), transdiaphrag-matic pressure (Pdi), timing of respiration (Ti/Ttot), thoracoabdominal coordination (Vrc/Vabd), and maximal mouth pressure against an occluded airway (Pmo), under hypoxic or normoxic conditions, and at rest, during rebreathing hypercapnia, and during resistive breathing. Hypoxia did not alter the transformation of P0.1 in Ve and did not acutely alter the strength of respiratory muscles, but it clearly altered the thoracoabdominal coordination (large oscillations in Vrc/Vabd), demonstrating en-hanced fatigability of the respiratory muscles in our patients under hypoxic con-ditions. Thus, hypoxia, via its influence on the performance of respiratory muscles, can contribute to the respiratory insufficiency of patients with myotonic dystrophy.