Effects of Inspiratory Muscle Training on Exertional Breathlessness in Patients With Unilateral Diaphragm Paralysis

1. RATIONALE AND BACKGROUND Diaphragmatic paralysis is an uncommon, yet underdiagnosed cause of dyspnea. Although the diaphragm performs most of the work, normal ventilation also requires the simultaneous contraction of other respiratory muscles (ie, scalene, parasternal portion of the internal and external intercostal muscles, sternocleidomastoid, trapezius). An increased effort in the struggle to breathe may fatigue the accessory muscles and lead to ventilatory failure. It is thus far not clear whether specific training of the respiratory muscle can improve or restore diaphragm function or accessory respiratory muscle function in these patients.

Depending on the etiology of the diaphragmatic paralysis, the prognosis of unilateral disease usually is good. Patients with phrenic injuries may recover fully or partially. At times, patients may also spontaneously recover from idiopathic disease. Patients who do not recover from unilateral diaphragmatic dysfunction generally lead relatively normal lives. Many patients however keep reporting symptoms of dyspnea that interfere with performance of daily activities. In this group, dyspnea typically develops with exertion, leading to increased ventilatory demands. Dyspnea can also be elicited by changes in posture (e.g. lying supine, bending forward). Depending on the activity profile of the subjects this might have an impact on quality of life. The investigators will therefore evaluate symptoms and recruitment of respiratory muscles of these patients during exertion (i.e. while performing an exercise test on a cycle ergometer).

The morbidity of the unilateral paralysis is mainly based on the underlying pulmonary functional status and the etiology of the paralysis. Most of the patients that are referred to the University Hospital Leuven report symptoms of dyspnea during exertion or with changes in posture. Diaphragmatic paralysis is more likely to affect the left hemidiaphragm. Unilateral diaphragmatic paralysis is characterized by abnormalities of pulmonary and respiratory muscle function. Patients develop restrictive ventilatory impairment, and the vital capacity and total lung capacity frequently are below 70% of the predicted normal values. Lung capacity is reduced further when the patient assumes the supine position.

In contrast to bilateral disease, physicians can usually diagnose unilateral paralysis with only radiographic studies. Because accessory muscle contraction may create the appearance of diaphragmatic movement, fluoroscopy studies may be misleading the physician when diagnosing bilateral diaphragmatic paralysis. In fluoroscopic sniff testing, paradoxical elevation of the paralyzed diaphragm is observed with inspiration and confirms diaphragmatic paralysis. However, the sniff test is not very specific; 6% of normal persons exhibit paradoxical motion on fluoroscopy. Computerized tomography may be indicated in certain patients to evaluate for potential causes of diaphragmatic paralysis that are due to mediastinal pathology and malignancy. 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.

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. 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. Ultrasonography can also be used to serially monitor patients with diaphragmatic paralysis for recovery.