This study confirms previous findings in much smaller groups of normal controls for quantitative ultrasound of the diaphragm and provides data that can be applied widely to the general population.

Objectives: To determine the sensitivity and specificity of B-mode ultrasound in the diagnosis of neuromuscular diaphragmatic dysfunction, including phrenic neuropathy.Methods: A prospective study of patients with dyspnea referred to the EMG laboratory over a 2-year time frame for evaluation of neuromuscular respiratory failure who were recruited consecutively and examined with ultrasound for possible diaphragm dysfunction. Sonographic outcome measures were absolute thickness of the diaphragm and degree of increased thickness with maximal inspiration. The comparison standard for diagnosis of diaphragm dysfunction was the final clinical diagnosis of clinicians blinded to the diaphragm ultrasound results, but taking into account other diagnostic workup, including chest radiographs, fluoroscopy, phrenic nerve conduction studies, diaphragm EMG, and/or pulmonary function tests.Results: Of 82 patients recruited over a 2-year period, 66 were enrolled in the study. Sixteen patients were excluded because of inconclusive or insufficient reference testing. One hemidiaphragm could not be adequately visualized; therefore, hemidiaphragm assessment was conducted in a total of 131 hemidiaphragms in 66 patients. Of the 82 abnormal hemidiaphragms, 76 had abnormal sonographic findings (atrophy or decreased contractility). Of the 49 normal hemidiaphragms, none had a false-positive ultrasound. Diaphragmatic ultrasound was 93% sensitive and 100% specific for the diagnosis of neuromuscular diaphragmatic dysfunction.Conclusion: B-mode ultrasound imaging of the diaphragm is a highly sensitive and specific tool for diagnosis of neuromuscular diaphragm dysfunction. Classification of evidence:This study provides Class II evidence that diaphragmatic ultrasound performed by well-trained individuals accurately identifies patients with neuromuscular diaphragmatic respiratory failure (sensitivity 93%; specificity 100%). Neurology ® 2014;83:1264-1270 GLOSSARY CMAP 5 compound muscle action potential; NCS 5 nerve conduction study; T MAX 5 thickness at maximal inspiration; T MAX /T MIN 5 diaphragm thickening ratio; T MIN 5 thickness at resting end-expiration.Diaphragm dysfunction can be difficult to diagnose, particularly when diaphragm paralysis is bilateral. The usual workup of patients presenting with unexplained dyspnea may include chest radiographs, fluoroscopy, phrenic nerve conduction studies (NCS), needle EMG of the diaphragm, pulmonary function testing, and transdiaphragmatic pressure measurements; all of these diagnostic tests can produce false-positive and false-negative findings, and some tests are invasive or uncomfortable for the patient.

BACKGROUND: Electromyographic evaluation of diaphragmatic neuromuscular disease in patients with COPD is technically diffi cult and potentially high risk. Defi ning standard values for diaphragm thickness and thickening ratio using B-mode ultrasound may provide a simpler, safer means of evaluating these patients.

STUDY DESIGN Clinical measurement, cross-sectional. OBJECTIVES To establish a set of normal values for diaphragm thickening with tidal breathing in healthy subjects. BACKGROUND Normal values for diaphragm contractility, as imaged sonographically, have not been described, despite the known role of the diaphragm in contributing to spinal stability. If the normal range of diaphragm contractility can be defined in a reliable manner, ultrasound has the potential to be used clinically and in research as a biofeedback tool to enhance diaphragm activation/contractility. METHODS B-mode ultrasound was performed on 150 healthy subjects to visualize and measure hemi-diaphragm thickness on each side at resting inspiration and expiration. Primary outcome measures were hemi-diaphragm thickness and thickening ratio, stratified for age, gender, and body mass index. Interrater and intrarater reliability were also measured. RESULTS Normal thickness of the diaphragm at rest ranged from 0.12 to 1.18 cm, with slightly greater thickness in men but no effect of age. Average ± SD change in thickness from resting expiration to resting inspiration was 20.0% ± 15.5% on the right and 23.5% ± 24.4% on the left; however, almost one third of healthy subjects had no to minimal diaphragm thickening with tidal breathing. CONCLUSION There is wide variability in the degree of diaphragm contractility during quiet breathing. B-mode ultrasound appears to be a reliable means of determining the contractility of the diaphragm, an important muscle in spinal stability. Further studies are needed to validate this imaging modality as a clinical tool in the neuromuscular re-education of the diaphragm to improve spinal stability in both healthy subjects and in patients with low back pain.

Diaphragm depth from the skin can vary by more than 4 cm. When image guidance is not available to enhance accuracy and safety of diaphragm EMG, it is possible to reliably predict the depth of the diaphragm based on BMI.