| Pulmonary Function |
| All pulmonary-function tests were performed at various times of the day. |
| 1. Spirometry |
| Earlier studies (1958-1962) of vital capacity and pulmonary subdivisions were performed with subjects both standing and recumbent; they inspired maximally and then expired maximally into a 120-liter recording Tissot spirometer. Complete spirograms were also recorded for recumbent subjects with a ten-liter closed-circuit spirometer. A mouthpiece and nose-clip were used for these collections. Three trials were made for each effort (inspiratory reserve volume, expiratory reserve volume, and vital capacity). The largest value was recorded as the value for the day. The resting tidal volume was determined by dividing the total volume expired in a ten-minute air-collection period by the number of breaths during this period as counted from a kymograph tracing (Norris et al., 1956). Since 1963, spirometric studies have followed methods and calculations described by Kory et al. (1961), including forced expiratory volumes (FEV0.5 through FEV6.0). These tests are performed at each visit. |
| 2. Maximum Breathing Capacity |
| The maximum breathing capacity is determined in standing subjects who are asked to breathe as much air as possible into a spirometer through a low-resistance circuit for 15 seconds. Neither the rate nor the depth of breathing is specified, but the subject is urged to do his best throughout the test. The highest volume attained in three trials is taken as the value for the day (Norris et al., 1956). This test is administered on each visit. |
| 3. Pulmonary Gas Distribution |
| Total lung volume and functional residual volume were determined by the nitrogen wash-out method using an open-circuit technique (Edelman et al., 1968). The studies were performed at various times of the day with subjects in the seated position. The gas supply and collection bags were enclosed in an airtight box. Tidal volume was monitored by a model 350 Servo-spirometer (Med-Science Electronics, St. Louis) connected to the box. Nitrogen concentration of gas sampled at the mouthpiece was measured with a model 300 AR Nitralyzer (Med-Science Electronics). The instrument was calibrated with five standard gas mixtures within the 2% - 7% nitrogen range before each wash-out test. Continuous recordings of N2 concentration and tidal volume were made with a model 1508 Visicorder (Minneapolis Honeywell Regulator Co., Denver). Subjects were allowed to accommodate to the apparatus while breathing air. A vital-capacity maneuver consisting of a full inspiration followed by a full expiration was performed during this period. After the subjects had returned to a steady ventilatory pattern (usually within 0.5 - 1.0 min), and at the end of a normal expiration, a seven-minute period of oxygen breathing was begun. Functional residual capacity (FRC) was calculated from the collected expired air. Corrections were made for inspired nitrogen concentration and tissue nitrogen excretion (Darling et al., 1940). Tidal volume was taken as the mean for the seven-minute period; anatomic dead space was estimated from the height of each subject (Hart et al., 1963). |
| Uniformity of ventilation was initially assessed by the use of the lung-clearance index (LCI) (Becklake, 1952), which was later supplanted by a new index less dependent on tidal volume (Edelman et al., 1968). |
| This test was administered between 1962 and 1979 to randomly selected subjects. |
| 4. Lung and Chest-Wall Compliance |
| Since this test required the placement of an intra-esophageal balloon catheter to measure pressures, it was administered to only 42 subjects, aged 24 to 78 years, during 1962 and 1963 (Mittman et al., 1965). Although analysis of cross-sectional data showed a significant negative regression of chest-wall compliance on age, the regression of pulmonary compliance on age was not significant. In view of the discomfort to the subject, the large investment of time required to perform the test, and the lack of significant age regression for pulmonary compliance, the test was not repeated after 1963. |
| 5. Smoking History |
| A detailed smoking history is obtained on the first visit and is updated at each subsequent visit. |
| 6. Chest X-Ray |
| A standard roentgenogram is made for postero-anterior (P-A) and lateral views of the chest with the subject standing. The total equivalent radiation exposure received by the subject above the waist is 2 rads for the two tests. Gonadal exposure is minimized by standard techniques of collimation and shielding. The techniques and equipment used are monitored by the Maryland State Health Department and the Baltimore City Hospitals' Radiation Safety Officer. X-rays were initially repeated at each visit, but since 1979 have been routinely repeated no more frequently than every five years unless there is a specific clinical indication that more frequent examination is desirable. |
