Abstract
Introduction: In slowly progressive myopathies, diaphragm weakness early manifests through sleep-related hypoventilation as reflected by nocturnal hypercapnia. This study investigated whether daytime tests of respiratory muscle function and diaphragm ultrasound predict hypercapnia during sleep.Methods: Twenty-seven patients with genetic myopathies (myotonic dystrophy type 1 and 2, late-onset Pompe disease, facioscapulohumeral dystrophy; 48 ± 11 years) underwent overnight transcutaneous capnometry, spirometry, measurement of mouth occlusion pressures, and diaphragm ultrasound.Results: Sixteen out of 27 patients showed nocturnal hypercapnia (peak ptcCO2 ≥ 50 mmHg for ≥ 30 min or increase in ptcCO2 by 10 mmHg or more from the baseline value). In these patients, forced vital capacity (FVC; % predicted) and maximum inspiratory pressure (MIP; % of lower limit or normal or LLN) were significantly reduced compared to normocapnic individuals. Nocturnal hypercapnia was predicted by reduction in FVC of <60% [sensitivity, 1.0; area under the curve (AUC), 0.82] and MIP (%LLN) <120% (sensitivity, 0.83; AUC, 0.84), the latter reflecting that in patients with neuromuscular disease, pretest likelihood of abnormality is per se higher than in healthy subjects. Diaphragm excursion velocity during a sniff maneuver excluded nocturnal hypercapnia with high sensitivity (0.90) using a cutoff of 8.0 cm/s.Conclusion: In slowly progressive myopathies, nocturnal hypercapnia is predicted by FVC <60% or MIP <120% (LLN). As a novelty, nocturnal hypercapnia can be excluded with acceptable sensitivity by diaphragm excursion velocity >8.0 cm/s on diaphragm ultrasound.
Highlights
In slowly progressive myopathies, diaphragm weakness early manifests through sleep-related hypoventilation as reflected by nocturnal hypercapnia
Thirteen patients were diagnosed with myotonic dystrophy type 1 (DM1), one with myotonic dystrophy type 2 (DM2), five with late-onset Pompe disease, and eight patients with facioscapulohumeral muscular dystrophy type 1 (FSHD1)
Nocturnal hypercapnia as defined by nocturnal peak transcutaneous carbon dioxide tension (ptcCO2) ≥50 mmHg for ≥30 min or an increase in ptcCO2 above the awake baseline by ≥10 mmHg was present in the 16 noninvasive ventilation (NIV) users only
Summary
Diaphragm weakness early manifests through sleep-related hypoventilation as reflected by nocturnal hypercapnia. This study investigated whether daytime tests of respiratory muscle function and diaphragm ultrasound predict hypercapnia during sleep. Since comparable evidence is still missing for patients with slowly progressive myopathies and muscular dystrophies the present study evaluated whether daytime tests of respiratory muscle strength and function predict nocturnal hypercapnia in this population. This study supplemented bedside diagnostic tests of respiratory muscle function by diaphragm ultrasound. The latter has been established as an assessment tool for inspiratory muscle strength and function that is both non-invasive and widely available [13]
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