[Analysis of factors associated with chronic hypercapnia in patients with myotonic dystrophy]

Myotonic dystrophy (DM) is the most common dystrophy in adults. Several factors may explain the chronic CO2 retention. The selection of patients, different clinical stages and evaluation forms may explain the differing results obtained. Our objectives were to characterize respiratory function and to evaluate factors associated with chronic retention of CO2 in DM. We included 27 consecutive ambulatory and stable patients who were allocated into normocapnic and hypercapnic groups (PaCO2 ≥ 43 mmHg). Forced vital capacity (FVC), maximum static pressure, voluntary apnea time, Epworth scale and arterial blood gases were measured. The CO2 chemosensitivity was assessed using CO2 rebreathing (Read method). The slope ΔP0.1/ΔPCO2 expressed the CO2 chemosensitivity. A 59.3% (16/27) presented hypercapnia. FVC and respiratory muscle strength were normal or showed mild to moderate decrease. No significant differences in these variables were found in both groups. Inadequate response to CO2 (slope ΔP0.1/ΔPCO2 low (< 0.1 cm H2O/mmHg) or flat) was associated with hypercapnia (p < 0.005). Chronic retention of CO2 represented 11.56 times higher risk of inadequate response to CO2. The group with low-flat slope ΔP0.1/ΔPCO2 showed higher PaCO2 (p = 0.0017) and more prolonged voluntary apnea time (p = 0.002). We conclude that in our patients with DM, chronic CO2 retention was associated with the presence of abnormalities of the central control of breathing. Our results allow explaining previous reports describing the striking frequency of postoperative respiratory failure and difficulties in the process of weaning from mechanical ventilation.