Laboratory Studies
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.
The hallmark of patients with diaphragmatic paralysis is hypercapnia and a respiratory acidosis. The hypoxemia is a consequence of the hypoventilation. This is a key distinction and P(A-a) O2 gradients may be normal if there is no underlying parenchymal lung disease.
Imaging Studies
Chest radiography
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. [13] (see the image below).
Acute unilateral left diaphragmatic paralysis in a patient with moderately severe chronic obstructive pulmonary disease. The patient previously was asymptomatic but developed class III dyspnea following the new event.
Bilateral diaphragmatic paralysis can be subtler to recognize with radiographic studies alone. See image below.
Radiograph of a patient with bilateral diaphragmatic paralysis displaying low lung volumes.
Fluoroscopy
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).
Fluoroscopy of elevated left hemidiaphragm in a patient with unilateral diaphragmatic paralysis. The diaphragm moves paradoxically upward during inspiration.
In fluoroscopic sniff testing, paradoxical elevation of the paralyzed diaphragm is observed with inspiration and confirms diaphragmatic paralysis (see the image below). [14] However, the sniff test is not very specific; 6% of normal persons exhibit paradoxical motion on fluoroscopy. [9] Due to compensatory respiratory strategies, apparently normal decent of diaphragms may also be seen with sniff test in bilateral diaphragmatic paralysis. [3]
Fluoroscopy of elevated left hemidiaphragm in a patient with unilateral diaphragmatic paralysis. The diaphragm does not move during expiration. For confirmation, a sniff test is required.
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
MRI 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.
Dynamic MRI has been used by some institutions to evaluate diaphragmatic disorders.
Ultrasonography
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. [15]
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, 16]
Ultrasonography can also be used to serially monitor patients with diaphragmatic paralysis for recovery. [3]
Other Tests
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. [9]
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.
Important to note is that decreased maximal pressures are the hallmark of bilateral diaphragmatic paralysis. The decrease may not be as easy to detect in those with unilateral diaphragm paralysis.
Electromyography
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. Phrenic nerve stimulation can be done with electrical (surface or needle electrodes) and magnet stimulation. Operator expertise is an important factor in testing.
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. [3]
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 increase 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.
Normal transdiaphragmatic pressure is approximately 148 cm water in men and 122 cm water in women. [17] Unilateral diaphragmatic paralysis is associated with a maximal transdiaphragmatic pressure of greater than 70 cm water, and thus does not significantly effect transdiaphragmatic pressure generation during normal ventilatory behaviors, but can compromise higher-force, nonventilatory, behaviors like coughing or sneezing. Bilateral diaphragmatic paralysis, however, can impair normal ventilatory behaviors as it is associated with a maximal transdiaphragmatic pressure of less than 40 cm water. [18, 19, 20]
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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Acute unilateral left diaphragmatic paralysis in a patient with moderately severe chronic obstructive pulmonary disease. The patient previously was asymptomatic but developed class III dyspnea following the new event.
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Fluoroscopy of elevated left hemidiaphragm in a patient with unilateral diaphragmatic paralysis. The diaphragm moves paradoxically upward during inspiration.
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Fluoroscopy of elevated left hemidiaphragm in a patient with unilateral diaphragmatic paralysis. The diaphragm does not move during expiration. For confirmation, a sniff test is required.
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Radiograph of a patient with bilateral diaphragmatic paralysis displaying low lung volumes.
