Diaphragmatic Paralysis Workup
- Author: Nader Kamangar, MD, FACP, FCCP, FCCM; Chief Editor: Ryland P Byrd, Jr, MD more...
Arterial blood gas analysis may demonstrate hypoxemia in persons with bilateral diaphragmatic paralysis. Hypoxemia develops from atelectasis and ventilation-perfusion mismatching. Progressive hypercapnia also develops with disease progression.
This study reveals elevated hemidiaphragms, small lung volumes, and atelectasis.
In contrast to bilateral disease, physicians can usually diagnose unilateral paralysis with only radiographic studies. (see the image below).
Because accessory muscle contraction may create the appearance of diaphragmatic movement, this study may mislead the physician when diagnosing bilateral diaphragmatic paralysis (see the image below).
In fluoroscopic sniff testing, paradoxical elevation of the paralyzed diaphragm is observed with inspiration and confirms diaphragmatic paralysis (see the image below). However, the sniff test is not very specific; 6% of normal persons exhibit paradoxical motion on fluoroscopy. Due to compensatory respiratory strategies, apparently normal decent of diaphragms may also be seen with sniff test in bilateral diaphragmatic paralysis.
Computed tomography scanning of the chest
Computerized tomography may be indicated in certain patients to evaluate for potential causes of diaphragmatic paralysis that are due to mediastinal pathology and malignancy.
Magnetic resonance imaging of the neck
Magnetic resonance imaging may be indicated in certain patients to determine the presence of pathologic conditions involving the spinal column or nerve roots that are causing diaphragmatic paralysis.
M-mode ultrasonography is a relatively simple and accurate test for diagnosing paralysis of the diaphragm in the adult population and it can be performed at the bedside.
The paralyzed side shows no active caudal movement of the diaphragm with inspiration and abnormal paradoxical movement (ie, cranial movement on inspiration), particularly with the sniff test.
Patients can be scanned in the anterior axillary line with a curved linear transducer probe angled cranially at a 90° angle to the diaphragm. In this view, the liver is used as a window on the right, while the spleen is used on the left.
B-mode ultrasonography of diaphragm thickness in the zone of apposition of the diaphragm to the rib cage can also provide a sensitive and specific noninvasive assessment of diaphragmatic paralysis. Less than 20% thickening of the diaphragm muscle during inspiration is diagnostic of diaphragmatic paralysis.[3, 11]
Ultrasonography can also be used to serially monitor patients with diaphragmatic paralysis for recovery.
Pulmonary function testing and arterial blood gas analysis
Measuring the vital capacity in the upright and supine positions is the most important part of the pulmonary function test.
Diaphragmatic paralysis reduces the measured compliance of the lungs and a restrictive pattern can develop.
Normally, vital capacity in recumbency decreases by 10%. In contrast, patients with bilateral diaphragmatic paralysis show a 50% decrease in vital capacity when they are supine. This decrease is from cephalad displacement of abdominal contents.
Pulmonary function test results, however, are not always consistent and do not always correlate with the severity of dyspnea from diaphragmatic paralysis.
Maximal inspiratory pressures
Patients with diaphragmatic dysfunction and paralysis have a decrease in maximal inspiratory pressures (PI max). These patients cannot generate high negative inspiratory pressures. Therefore, the Pl max in these patients is less negative than -60 cm water.
Electromyography may reveal a neuropathic versus myopathic pattern, depending on the etiology. This can be accomplished by stimulation of the phrenic nerve at the neck.
Technical issues with electromyography include proper electrode placement to avoid “cross-talk” from adjacent muscles and variable results due to variable subcutaneous fat among individuals.
Measurement of transdiaphragmatic pressure
This is the criterion standard for diagnosis.
The transdiaphragmatic pressure is measured by placing a thin-walled balloon transnasally at the lower end of the esophagus, allowing reflection of the changes in pleural pressure. Then, a second balloon manometer is placed in the stomach to measure changes in intra-abdominal pressure. Gastric pressure should become more positive during inspiration. Esophageal pressure should become more negative during inspiration, demonstrating an increased in gradient during normal inspiration. In cases in which the sniff test is negative and clinical suspicion for diaphragmatic paralysis is still high, transdiaphragmatic pressure should be considered.
Consult with an expert to perform the test and interpret the results. This measurement can help differentiate diaphragmatic paralysis from other causes of respiratory failure.
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