Three separate, but related, studies were performed on asthmatic subjects. In the first, respiratory rate was surreptitiously observed in acutely ill asthmatic subjects in the emergency room. In the second study, ventilatory pattern was monitored by respiratory inductance plethysmography in stable asthmatic subjects during methacholine-induced bronchoconstriction. In the third study, ventilatory pattern was monitored by RIP in stable asthmatic subjects during and following exercise.
Respiratory rate was noted in 47 acutely ill asthmatic and 42 nonasthmatic control subjects within a few minutes of their arrival in the emergency room while they were sitting on a standard emergency room stretcher. Patients with bronchitis, emphysema, or other known lung diseases were excluded. Where possible, in the asthmatic patients, flow-volume spirometry was measured before and one hour after therapy in the emergency room. The control subjects had been admitted to the emergency room with noncardiorespiratory symptoms and had respiratory rate monitored by an observer on admission and one hour later.
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A separate group of nine stable, asymptomatic asthmatic subjects and ten healthy nonasthmatic subjects underwent methacholine challenge testing. Respiratory rate and tidal volume were monitored using RIP. All subjects were asymptomatic prior to testing. All medications were withdrawn for at least 12 hours prior to testing.
The methacholine challenge test was administered by the method of Juniper and co-workers. Subjects were given saline solution, then doubling doses of methacholine, starting at 0.03 mgfail. Forced expiratory volume in one second (FEV,) was measured by a wedge spirometer with an automated one-second timer 30 and 90 seconds after each dose of methacholine. The test was stopped at 16 mg/ml of methacholine or when a 20 percent reduction of FEV, occurred.
Eight asthmatic patients whose asthma had been stable for over two weeks and eight healthy nonasthmatic subjects underwent six- minute treadmill exercise testing.
Respiratory rate and tidal volume
Respiratory Rate during Acute Asthma (Hasten et al) were monitored using RIP. All medications were withdrawn for at least 12 hours prior to testing.
The exercise test was performed in an air-conditioned laboratory under stable environmental conditions. The treadmill speed (Q to 8.5 km/h) and inclination (8 to 13 percent) were adjusted so that the subjects achieved at least 80 percent of their predicted maximal heart rates by the end of the challenge. Exercise was stopped early if the patient could no longer continue because of dyspnea or fatigue. The FEV, was measured by a wedge spirometer with an automated one-second timer before and serially upon termination of the exercise challenge.
Respiratory Inductance Plethysmography
In studies 2 and 3, each subject had a suitably sized transducer inductance coil placed around the rib cage just below the axilla, and a second coil positioned at the umbilicus above the iliac crest. The location of the coils was marked and checked regularly to ensure that their positions did not change. The least squares method of calibration for RIP was used. Following the technique specified by the manufacturer, calibration of RIP (DC mode) was performed with the subjects in both standing and supine postures. Rib cage and abdominal deflections from at least three representative breaths in each of the two postures were recorded on a multichannel recorder and separate compartmental amplification factors were calculated from simultaneous spirometric measures of tidal volume using simultaneous equations. Calibration was verified by comparing the sum of the deflections with tidal volume measured by spirometry. The calibration procedure was repeated if tidal volume measured by RIP and spirometry differed by more than ±10 percent. At the conclusion of the studies, tidal volume by RIP was measured against tidal volume by spirometry. The trial data were rejected if there was a mean tidal volume difference between the two methods of greater than 10 percent. tadacip 20