A 60-year-old man comes to the physician for follow-up 8 weeks after coronary artery bypass graft surgery. Although his exertional chest pain is improved since surgery, he is short of breath when walking briskly. He also complains of orthopnea that has worsened since the surgery. The patient has no fever, chills, cough, weight loss, or chest pain. His medications include aspirin, atorvastatin, metoprolol, amlodipine, and albuterol/ipratropium as needed. He is an ex-smoker with 20-pack-year history.
His blood pressure is 134/87 mm Hg, pulse is 57/min, and respirations are 14/min. His oxygen saturation on room air is 96% while sitting and 90% while supine. His body mass index is 31 kg/m². Physical examination shows a middle-aged man in no acute distress. Jugular venous pressure is estimated at 6 cm H₂O. Lung examination is notable for decreased breath sounds at the left base with dullness to percussion. Cardiac examination shows a 2/6 mid-systolic murmur at the right sternal base and normal second heart sound. The surgical wound is well apposed and clean.
Chest x-ray reveals a raised left hemidiaphragm and mild scarring of the right lung base.
Spirometry in the upright position shows forced expiratory volume in 1 second of 69% of predicted, forced vital capacity of 70% predicted, and FEV₁/FVC ratio of 0.98. Spirometry performed in the supine position shows forced vital capacity of 59% of predicted.
Which of the following is the best test to diagnose the cause of this patient's dyspnea on exertion?

Question

Quizplus · Accepted Answer

This patient's presentation suggests unilateral diaphragmatic paralysis likely due to phrenic nerve injury during cardiac surgery. The phrenic nerves originate from C3-C5 to innervate the diaphragm on each side. Unilateral diaphragmatic paralysis is more common than bilateral paralysis and is usually due to the following: Phrenic nerve injury during cardiac surgeryViral infections (eg, herpes zoster, poliomyelitis)Other (eg, trauma, tumor, cervical spondylosis, neck surgery)Idiopathic Phrenic nerve injury during cardiac surgery Viral infections (eg, herpes zoster, poliomyelitis) Other (eg, trauma, tumor, cervical spondylosis, neck surgery) Idiopathic Patients with unilateral diaphragmatic paralysis and no underlying lung disease are usually asymptomatic at rest but can develop dyspnea with exertion. Patients with underlying lung disease may report dyspnea at rest, orthopnea, or sleep-disordered breathing. Chest x-ray usually reveals elevated hemidiaphragm. However, this can be missed in some postoperative patients due to other changes (eg, pleural effusions, infiltrates, atelectasis). Diagnosis is confirmed by asking patients to sniff forcefully under fluoroscopy (sniff test). The normal diaphragm moves downward during inspiration and the paralyzed side has paradoxical upward movement. Spirometry shows a restrictive defect (low forced vital capacity), but the normal decrease of <10% in the supine position is exacerbated and may fall > 50%. This results from the cephalad displacement of the abdominal viscera. Patients may also have supine hypoxemia, but hypercarbia is rare in the absence of lung disease. Asymptomatic patients with unilateral diaphragmatic paralysis do not require treatment. Many patients with mild-to-moderate dyspnea may improve spontaneously within 1-2 years. However, those with significant impairment may benefit from ipsilateral surgical diaphragmatic plication. (Choices A, D, and E) Exercise echocardiography is not needed at this time as the patient has no exertional chest pain. He has no risk factors or signs of endocarditis and no symptoms of heart failure as well. Transesophageal echocardiography and serum pro-brain natriuretic peptide levels are therefore not required. (Choice C) This patient's spirometry results showed mild obstruction with low vital capacity. If this patient had not had surgery, computed tomography scan of the chest would be indicated to exclude tumor compressing the phrenic nerve. Educational objective: Unilateral diaphragmatic paralysis occurs rarely due to phrenic nerve injury after cardiac surgery. Patients may present with dyspnea at rest or with exertion and supine hypoxemia. Spirometry shows a drop in forced vital capacity in the supine position, and chest x-ray reveals elevated hemidiaphragm. Diagnosis is confirmed via the "sniff test" using fluoroscopy. __________ References: Acquired paralysis of the diaphragm. (http://www.ncbi.nlm.nih.gov/pubmed/20112633) Phrenic nerve injury and diaphragmatic paralysis following pacemaker pulse generator replacement. (http://www.ncbi.nlm.nih.gov/pubmed/23083538)

A 60-Year-Old Man Comes to the Physician for Follow-Up 8