Abstract

ARUJ, Patricia K.; MONTEIRO, Sergio G.  and  DE VITO, Eduardo L.. Analysis of factors associated with chronic hypercapnia in patients with myotonic dystrophy. Medicina (B. Aires) [online]. 2013, vol.73, n.6, pp.529-534. ISSN 0025-7680.

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.

Keywords : Myotonic dystrophy; Hypercapnia; Alveolar hypoventilation; Respiratory underresponsiveness to hypoxia and hipercapnia.

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