No abstract

During arm elevation, normal individuals predominantly recruit the diaphragm, whereas chronic obstructive pulmonary disease (COPD) patients use more the accessory inspiratory and abdominal expiratory muscles. To test that arm elevation is useful to study the ventilatory muscle response in COPD, and to define the factors that determine this response, we studied 34 patients (FEV1 0.95 +/- 0.08 L) during 2 min of arm elevation. Transnasal balloons were used to determine end-inspiratory and end-expiratory gastric (Pg), pleural (Ppl) and transdiaphragmatic (Pdi) pressures. The slope of delta Pg/delta Ppl (= Pgi - Pge/Ppli - Pple) was used to infer respiratory muscle recruitment. With linear regression, the delta Pg/delta Ppl during arm elevation significantly correlated with resting delta Pg/delta Ppl (r = 0.68), hyperinflation (FRC/TLC, r = 0.52), and diaphragmatic tension time index (TTIdi) (r = 0.47). With multiple regression, resting delta Pg/delta Ppl, percentage predicted FRC (FRC %pred) and TTIdi influenced delta Pg/delta Ppl during arm elevation (r = 0.84). Over the 2 min of arm elevation, the dependency upon resting breathing pattern decreased, while hyperinflation and TTIdi became increasingly important. Higher resting TTIdi values were associated with a faster and shallower breathing pattern (f/VT > or = 38) during arm elevation. We conclude that the pattern of respiratory muscle recruitment during arm elevation depends primarily on the resting breathing pattern. Over 2 min, the degree of hyperinflation and the force reserve of the diaphragm increasingly impact on the ability to recruit the diaphragm. Measurement of f/VT during arm elevation is useful to determine functional reserve of the diaphragm in severe COPD.

A routine chest radiograph in a 20 year old man revealed a giant air filled cavity of the left hemithorax under tension. At thoracotomy a large left lower lobe intraparenchymal cyst required lobectomy and the pathological findings were consistent with a bronchogenic cyst. Although tension bronchogenic cysts are common in infants, this case demonstrates their unusual presentation in an adult. (Thorax 1993;48:951-952) Large air filled cysts displacing the mediastinum and causing respiratory distress have been reported frequently in infants.1-3 In contrast, giant bronchogenic cysts containing air under pressure have rarely been described in older children and adults.3 6We present an adult with this unusual complication who underwent successful surgical resection.Case report A 20 year old Haitian man who had been living in the USA for one year came to -the tuberculosis clinic for evaluation of a positive tuberculin test. A chest radiograph showed a large cystic lesion occupying most of the left hemithorax, displacing the trachea and the mediastinum to the right (fig 1). He