Tidal expired airflow patterns in adults with airway obstruction

Abstract

Earlier studies have shown that time and flow indices derived from tidal expiratory flow patterns can be used to distinguish the severity of airway obstruction. This study was designed to address two aspects of tidal expiratory flow patterns: 1) how do expiratory flow patterns differ between subjects with normal and obstructed airways; and 2) can a sensitive index of airway obstruction be derived from these pattern differences? Tidal expiratory flow patterns from 66 adult subjects with varying degrees of airway obstructive disease with a forced expiratory volume in one second (FEV1) of 20-121% predicted were examined. In each subject, the expired flow pattern from each consecutive breath was scaled and then averaged together to create a single expired pattern. A detailed examination of the scaled flow patterns in 12 subjects (six with normal airways and six with airway obstruction) showed that the shape of the post-peak expiratory flow portion was different in the subjects with airway obstruction. A slope index, S, was derived from the scaled patterns and found to be sensitive to the severity of airway obstruction, correlating with FEV1 (% pred) with r2=0.74 (p<0.05, n=57). The S index also correlated (r2=0.36, p<0.05, n=47) with the functional residual capacity (FRC) (% pred) which was >100% in subjects with severe airway obstruction and lung overinflation. In subjects with normal airways, three further airflow patterns could be distinguished, which were different from the patterns seen in subjects with the severest airway obstruction. Scaled flow patterns from tidal expiration collected from uncoached subjects, can be used to derive an index of airway obstruction.

Relationship Between Spontaneous Expiratory Flow-Volume Curve Pattern and Air-Flow Obstruction in Elderly COPD Patients

“…On the other hand, assessment of the spontaneous expiratory flow-volume (SEFV) curve has been reported as a method to evaluate the severity of airway obstruction, which has the advantage that it is easily measured via spirometry during quiet breathing. [3][4][5][6][7][8][9][10] Shortening of the time to reach the peak expiratory flow 3 and the slope of the late SEFV curve, 4 which can be obtained from the SEFV curve, has been reported to be related to airway obstruction. Moreover, a method to assess the pattern of the SEFV curve has been reported, and concavity of the SEFV curve has been found to be related to expiratory flow limitation.…”

Detecting airways obstruction from the tidal flow profile

“…MORRIS et al [1] examined the latter part of the tidal expiratory flow pattern in patients with varying degrees of airflow obstruction and found that the expiratory time constant correlated positively with standard measures of airflow obstruction. WILLIAMS et al [2] also showed that a shape index related to the rate of decay of post-maximal expiratory flow correlated strongly with airflow obstruction, as determined by conventional methods. These studies suggest that a simple, noninvasive procedure may be used to derive an important physiological parameter that is not normally so easily obtained.…”

“…The results of MORRIS et al [1] and WILLIAMS et al [2] are, therefore, interesting from a clinical perspective be-cause they suggest that the severity of airflow obstruction, a parameter of key concern to the respiratory specialist, may be derived easily and noninvasively, namely from airflow measurements at the mouth. The physiological basis of this approach is not difficult to appreciate.…”

“…The two papers in this issue from the Osler Chest Unit at Oxford University [1,2] exploit the fact that the breathing pattern in humans is affected in characteristic ways when the pulmonary airways are obstructed. MORRIS et al [1] examined the latter part of the tidal expiratory flow pattern in patients with varying degrees of airflow obstruction and found that the expiratory time constant correlated positively with standard measures of airflow obstruction.…”

“…Consequently, it is not surprising that airflow obstruction tends to lead to characteristic changes in the pattern of spontaneous breathing. MORRIS et al [1] and WILLIAMS et al [2] have tried to identify particular features of the expiratory airflow pattern that capture these characteristic changes.…”