A Dual Lung-Scanning Technic for Evaluation of Pulmonary Function

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The recent development of lung scanning with 5–50 μ, size aggregates of human serum albumin I31 has demonstrated the feasibility of scanning methods in evaluating pulmonary function (1–4). Injected intravenously, these particles are trapped temporarily in the pulmonary arteriolar-capillary bed with high efficiency on the first pass, and the subsequent scan image gives a semiquantitative estimate of pulmonary arterial blood flow distribution (5–7). Conceivably, information concerning airway patency could be obtained by scanning after inhalation of radioaerosols if a sufficient fraction were deposited uniformly throughout the lower respiratory tract and retained for a few hours. This preliminary report describes an inhalation technic which, combined with the intravenous method, provides a dual scanning procedure for the evaluation of regional pulmonary arterial blood flow and bronchial patency. Method Animal Studies: Mongrel dogs weighing from 7 to 19 kg are anesthetized with pentobarbital and intubated with a cuffed endotracheal tube. This tube is attached to a positive pressure respirator2 equipped with a nebulizer and exhalation manifold. The exhaust line is passed through a filter, and the inhalation procedure is carried out in a vented hood. Three to 4 ml of radioactive solution containing approximately 1 millicurie of isotope, 10 per cent glycerin, and 0.2 per cent tyloxypal3 are nebulized in a thirty-to-sixty-minute period. The animals are then scanned in the prone position. Normal animals in various positions and others with pulmonary arterial obstructions, complete and partial bronchial obstructions, and phrenic nerve section have been studied. Human Studies: Six normal subjects and 27 patients with various lung disorders have had inhalation scans. A commercial respirator-nebulizer with a mouthpiece and exhalation manifold is used. 4 The exhaust line runs to a filter in a vented hood. Three to 4 ml of the same radioactive solutions used for animals are nebulized and inhaled in ten to twenty minutes and the patient is scanned in the prone position. Immediately following this procedure, or the next day, the intravenous preparation is given and the scan is repeated. Results Numerous physiologic test materials labeled with Au 198 I131, I125, Hg197, or Tc99m were tested in dogs. Satisfactory inhalation scans are produced with aerosols of I131, I125 and Tc99m-Iabeled human serum albumin, Hg197 chlormerodrin and colloidal Au 198. The low energy I125, Hg197, and Tc99m labels are desirable because subsequent intravenous scanning with higher energy I131-albumin macroaggregates can be performed immediately with a scanner equipped with pulse-height discrimination.5 Sixty-two combined scan procedures were performed in 24 animals. Intravenous and inhalation scans in the prone or supine position have a similar appearance. After inhalation, little radioactivity is detectable in the trachea or major bronchi.