Use of an acoustic helium analyzer for measuring lung volumes.

We have evaluated the use of an acoustic gas analyzer (AGA) for the measurement of total lung capacity (TLC) by single-breath helium dilution. The AGA has a rapid response time (0-90% response = 160 ms for 10% He), is linear for helium concentration of 0.1-10%, is stable over a wide range of ambient temperatures, and is small and portable. We plotted the output of the AGA vs. expired lung volume after a vital capacity breath of 10% He. However, since the AGA is sensitive to changes in speed of sound relative to air, the AGA output signal also reports an artifact due to alveolar gases. We corrected for this artifact by replotting a single-breath expiration after a vital capacity breath of room air. Mean alveolar helium concentration (HeA) was then measured by planimetry, using this alveolar gas curve as the base line. TLC was calculated using the HeA from the corrected AGA output and compared with TLC calculated from HeA simultaneously measured using a mass spectrometer (MS). In 12 normal subjects and 9 patients with chronic obstructive pulmonary disease (COPD) TLC-AGA and TLC-MS were compared by linear regression analysis; correlation coefficient (r) was 0.973 for normals and 0.968 for COPD patients (P less than 0.001). This single-breath; estimation of TLC using the corrected signal of the AGA vs. Expired volume seems ideally suited for the measurement of subdivisions of lung volume in field studies.

Pseudo-internuclear oculomotor ophthalmoplegia secondary to Guillain-Barré polyneuronitis simulating myasthenia gravis in a air transport pilot.

A 32-year old experienced co-pilot was grounded because of handicapping and disabling doulbe vision and was off-flight from October, 1969, until January, 1972. He presented with a bilateral external ophthalmoplegia with alternate extreme divergent strabismus, and polyneuronitis. The clinical picture was confused by features resembling either a polyneuronitis of the Guillain-Barrè type, (confused by a false positive Tensilon test), myasthenia gravis, or a demyelinizing process. Because the prognosis for return to flight was so contradictory in these respective conditions, a long observative followup time was essential. The pilot recovered completely after 4 months. The long 2 year followup effectively ruled out the entity of myasthenia gravis as well as a progressive demyelinizing disease. The pilot was returned to full flight duties with no handicapping residuals. He has shown no evidence of recurrence to the date of this report (April, 1974). This case was reviewed and presented for its obvious aerospace implications.