FREQUENCY-DEPENDENCE OF TOTAL RESPIRATORY RESISTANCE IN EARLY AIRWAY DISEASE

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Abstract
Patients who develop frequency dependence of lung compliance will theoretically have frequency dependence of pulmonary resistance. Ten healthy nonsmokers, 14 asymptomatic smokers and 6 patients with obstructive airway disease were studied. Frequency dependence of total respiratory resistance was determined by the superimposed oscillating airflow technique at 3-9 cycles/s, and frequency dependence of lung compliance was determined by measurements at 10-80 breaths/min. Spirometry, airway resistance, closing volume and closing capacity were also measured. Frequency dependence of lung compliance and total respiratory resistance were closely correlated (P < 0.001, r = 0.82), but closing volume, closing capacity, spirometry and airway resistance could not be used to identify subjects with abnormal frequency dependence of lung compliance. Measurements of frequency dependence of total respiratory resistance and lung compliance, total respiratory resistance at 3 cycles/s and closing volume minus expiratory reserve volume were able to distinguish significantly between the smokers and the nonsmokers, but spirometry, closing volume, closing capacity and airway resistance could not. In asymptomatic smokers and subjects with obstructive airway disease, frequency dependence of lung compliance probably can be predicted from measurements of frequency dependence of total respiratory resistance. These 2 tests appear to have equivalent sensitivity and selectivity in detecting the uneven time constants in the airways of asymptomatic smokers.

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