Vital Capacity Impairment due to Neuromuscular Disease and its Correlation with Diaphragmatic Ultrasound: A Preliminary Study

The purpose of this pilot study was to evaluate the correlation between diaphragmatic excursion measured by a right sub-costal ultrasound approach and forced vital capacity in patients with amyotrophic lateral sclerosis (ALS) or myotonic dystrophy (MD). All patients referred for pulmonary function testing underwent ultrasonic measurement of diaphragmatic excursion during quiet breathing, voluntary sniffing (Esniff) and forced breathing (EDEmax). Forty-five patients were included, mainly for amyotrophic lateral sclerosis or myotonic dystrophy. There was a significant correlation between EDEmax values and forced vital capacity (FVC) values (r = 0.68 [0.46–0.90], p < 0.0001) and between EDEmax values and percentage of predicted FVC values (r = 0.75 [0.55–0.95], p < 0.0001). At a threshold of EDEmax < 5.5 cm, the sensitivity and specificity of ultrasonic diaphragmatic excursion in predicting FVC ≤ 50% of theoretical values were 100% [66%–100%] and 69% [52%–84%] respectively, without any significant difference between males and females. There was no statistical correlation between maximal inspiratory pressure and Esniff.