Respiratory muscle dysfunction in facioscapulohumeral muscular dystrophy.

Respiratory insufficiency in facioscapulohumeral muscular dystrophy has rarely been studied. We compared two age- and sex-matched groups of 29 patients, with and without respiratory dysfunction. Tests in the 29 patients with respiratory dysfunction suggested predominant expiratory muscle dysfunction, leading to ineffective cough in 17 patients. Supine and upright vital capacities were not different (P = 0.76), suggesting absence of diaphragmatic dysfunction. By stepwise regression, only expiratory reserve volume correlated with the Walton and Gardner-Medwin score (R(2) = 0.503; P = 0.001). Compared to controls, patients with respiratory dysfunction had higher values for the Walton and Gardner-Medwin score (6.1 ± 1.9 vs. 3.2 ± 1.2; P <0.0001) and body mass index (26.9 ± 6.0 vs. 22.9 ± 4.0 kg/m(2); P = 0.003) and a smaller number of D4Z4 allele repeats (4.8 ± 1.6 vs. 5.7 ± 1.8; P = 0.05). Mechanical ventilation was required eventually in 20 patients, including 14 who were wheelchair bound. Three patients had acute respiratory failure requiring mechanical ventilation; 16 patients had poor airway clearance, including 10 with sleep apnea syndrome, responsible in 7 for chronic hypercapnia. Two patients presented isolated severe sleep apnea syndrome. Respiratory dysfunction in facioscapulohumeral muscular dystrophy is predominantly related to expiratory muscle weakness. Respiratory function and cough effectiveness should especially be monitored in patients with severe motor impairment and high body mass index.

Optoelectronic vital capacity measurement for restrictive diseases.

OBJECTIVE: To determine whether optoelectronic plethysmography accurately evaluated vital capacity (VC) in patients with respiratory muscle dysfunction of variable severity, including those with paradoxical abdominal movements. METHODS: In 20 subjects, VC was measured in the supine position using both spirometry and optoelectronic plethysmography (6 optoelectronic cameras and 52 reflective markers on the anterior chest wall). RESULTS: Spirometry VC (VC-Spiro) correlated positively with optoelectronic VC (VC-Opto) (r(2) = 0.99, P < .001), and the regression line was very close to the identity line (VC-Opto [mL] = -1.202 + 1.007 × VC-Spiro [mL]). A Bland-Altman plot showed that the mean difference was -20 mL (95% CI -63 mL to 24 mL) and the limits of agreement were 163 mL (95% CI 106 mL to 231 mL) and -203 mL (95% CI -271 mL to -146 mL). The difference between the 2 values expressed as the percentage of the mean value was < 15% in all 20 subjects, < 10% in 17 (85%) subjects, and < 5% in 11 (55%) subjects. The difference, expressed as the percentage of the mean value, was unrelated to the contribution of abdominal motion to VC (r = 0.02 and P = .94), but was significantly related to body mass index (r = 0.53, P = .02). CONCLUSIONS: Optoelectronic plethysmography is accurate and suitable for VC measurement in patients with various degrees of respiratory failure, including those with paradoxical abdominal movements. This noninvasive method may be an attractive alternative for accurately measuring VC in the event of air leakage (through the mouth or tracheostomy) or when patients are unable to breathe with the dead space added by the spirometer.

Vital capacity versus maximal inspiratory pressure in patients with Guillain-Barré syndrome and myasthenia gravis.

BACKGROUND: The objective is to determine whether maximal inspiratory pressure (P(imax)) measurement is more sensitive than vital capacity (VC) measurement to detect acute respiratory muscle failure considering a theoretical curvilinear relationship between volume and pressure. METHODS: Review of VC and P(imax) of all patients hospitalized in ICU for Guillain-Barré syndrome (GBS) and myasthenia gravis (MG) exacerbation. RESULTS: 84 consecutive caucasian patients between 19- and 70-years-old hospitalized in intensive care unit from April 2008 to December 2010, for MG exacerbation (44 patients) and GBS (40 patients). The regression curve between VC and P(imax) was linear rather than exponential (r = 0.599, P > 0.0001). The contingency table demonstrated agreement between VC and P(imax) (χ(2)= 26.7, P = 0.0001), with similar number of patients having abnormal P(imax) associated to normal VC and normal P(imax) associated to abnormal VC (9 (10.7%) vs. 8 (9.5%) respectively). Six of the patients developed an important decrease of VC from normal value to less than 60% of the predicted value and did not present evident curvilinear relationship between VC and P(imax) during this follow-up. CONCLUSIONS: Because the regression between VC and P(imax) was linear rather than curvilinear, P(imax) was not more sensitive than VC for early detection of respiratory muscle failure in patients hospitalized in ICU for GBS and MG exacerbation. Therefore, VC remains well suited to assess acute respiratory muscle failure and P(imax) gives poor additional information.