Chest
Volume 117, Issue 4, April 2000, Pages 1078-1084
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Clinical Investigations
CYSTIC FIBROSIS
Expiratory Airflow Patterns in Children and Adults With Cystic Fibrosis

https://doi.org/10.1378/chest.117.4.1078Get rights and content

Study objective

To determine whether tidal expiratory airflow patterns change with increasing airways obstruction in patients with cystic fibrosis.

Design

An observational study.

Setting

Lung function laboratory.

Patients

Sixty-four children and young adults with cystic fibrosis.

Measurements

After measuring FEV1 and airways resistance using body plethysmography, each subject was seated and asked to mouth breathe through a pneumotachograph for 2 min. The collected data were analyzed, and three expiratory airflow pattern-sensitive indexes were computed. The first index was derived from the ratio of the time to reach peak expiratory flow to the total expiratory time (tptef/te). The second index, Trs, was an estimate of the time constant of the passive portion of expiration. The third index,

, describes the slope of the whole post-peak expiratory flow pattern after scaling.

Results

Compared with FEV1, the index tptef/te was a poor indicator of airways obstruction (r2 = 0.15, p = 0.002). Trs showed a strong relationship with the severity of airways obstruction (r2 = 0.46, p < 0.001). Using

, the postexpiratory profile could be categorized into three shapes, and provided a good indicator of airways obstruction when linear and concave-shaped profiles occurred (r2 = 0.42, p < 0.001). Convex-shaped flow profiles had to be treated separately and were indicative of normal lung function.

Conclusions

In a cross-sectional study of patients with cystic fibrosis, increase in airways resistance above normal is reflected by quantifiable changes in the expiratory airflow pattern.

Section snippets

Patient Selection

Sixty-four cystic fibrosis patients (age range, 6 to 36 years, Table 1) attending for annual assessment of lung function were asked to perform an additional procedure of a 2-min collection of tidal breathing after completing their routine lung function tests. In two patients aged 12 and 8 years, measurements of static lung volumes and airways resistance (Raw) were not obtained because they were unwilling to have the door of the body box closed. All patients completed the additional 2-min tidal

tptef/te

There was a positive correlation of this index with both FEV1 percent predicted and Raw percent predicted and with respiratory rate but not with age (Table 3). Stepwise regression of tptef/te against these four predictors, age, respiratory rate, FEV1 percent predicted, and Raw percent predicted, showed that Raw percent predicted accounted for 18% of the variance, with respiratory rate contributing a further 6% and no other independent factor being identified.

Trs

There was a significant correlation

Discussion

This study shows that shape analysis of expiratory tidal flow vs time patterns gives similar information in young patients with cystic fibrosis as in other adults with disparate causes of airways obstruction (Fig 4).6, 7 There are significant correlations between the indexes of tidal expiratory flow, tptef/te, Trs, and

, and recognized measures of airways obstruction, but these relationships are not close enough to allow confident, accurate prediction of the severity of airways obstruction in

ACKNOWLEDGMENT

The authors thank Dr. D. Lane for allowing us to include his adult patients in this study. Preliminary data from this study were published as abstracts in Eur Respir J, 12, Supplement 28, 82s, P0584 and P0585, 1998; and Thorax, 53, Supplement 4, A61, P149, 1998. We also thank P. McShane for his help with the statistical analysis of the data.

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Cited by (16)

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    A comparison of all of the above indexes in subjects with healthy lungs and those with severe airway obstruction are shown in Table 2. Earlier studies678 have shown a relationship between the shape of the post-peak flow profile and severity of airway obstruction. Inspection of normalized post-peak flow expiratory profiles indicate that this relationship is best described by the change in flow at two common regions of the curve.

  • Predicting the outcome of respiratory disease in wheezing infants using tidal flow-volume loop shape

    2020, Allergologia et Immunopathologia
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    Some of the available studies that have assessed the response of wheezing disorders to inhaled corticosteroids14 are mainly based on thoraco-abdominal compression techniques on sedated children; however, this approach is not practical in daily medical practice. While the tPEF/tE ratio has been used to detect airway obstruction together with respiratory rate (RR),6,12,15 with a degree of success, the association of this parameter with a small airway caliber could not be demonstrated,16,17 possibly because parametric measurements exclude some valuable information expressed by the whole expiratory limb. As a result, the discriminating power of the TBFV loops has been underestimated in the past; the tPEF/tE ratio is the mathematical expression of the flow-volume loop during tidal breathing, but we feel that the shape of the loop includes a great deal more information, as the sequence of instant flows along the expiratory part of the loop may depend on the degree of obstruction of the airways, regardless of the value of the aforementioned ratio and thus may determine different loop morphologies.

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Supported by the Oxford-Radcliffe NHS Trust Charitable Fund.

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