The Management of Chronic Hypoventilation: Diagnostic Evaluation (3)
Pulmonary function testing, including spirometry, measurement of lung volumes, and determination of maximal inspiratory and expiratory pressures should also be routine. These measurements allow identification of patients with severe obstructive or restrictive lung diseases as well as those with muscle weakness. If bilateral diaphragmatic paralysis is suspected, vital capacity should also be measured in the supine position. In the presence of paralyzed diaphragms, supine vital capacity should be markedly diminished compared with the upright. Pulmonary function may also help in identifying those patients with an additional contributing factor to their chronic hypoventilation aside from lung disease alone. If the FEV! exceeds 1 L in a patient with chronic hypoventilation, lung disease is probably not the sole cause of the chronic hypoventilation and other factors should be sought. ventolin inhalers
Disordered breathing during sleep is very common in patients with chronic hypoventilation. Therefore, polysomnography occupies a central role in the examination of such patients. Ideally, polysomnography should consist of an overnight sleep study with monitoring of the electroencephalogram, electromyogram, and electro-oculogram, air flow at the mouth and nose, chest wall motion, and oximetry. Monitoring of carbon dioxide levels by end-tidal or transcutaneous techniques is desirable, but reliable measurements may be difficult. Afternoon nap studies or overnight monitoring of oximetry alone are useful if they yield positive results, but they should not be used to exclude sleep apnea in patients with chronic hypoventilation. Polysomnography is indicated for any patient with chronic hypoventilation and an FEV! of greater than 1L, anyone being considered for ventilatory assistance using a negative pressure device, and anyone with symptoms to suggest obstructive sleep apnea, such as snoring or excessive daytime sleepiness.