The relationship between respiratory system impedance and lung function in asthmatics: A prospective observational study

Changes in fractional exhaled nitric oxide, forced expiratory volume in one second, and forced oscillation technique parameters over three years in adults with bronchial asthma managed under Yokohama Seibu Hospital's coordinated care system

BACKGROUND

In western Yokohama, our hospital and primary care clinics manage adults with asthma via a coordinated care system. We investigated the changes in the fractional expired nitric oxide (FeNO), forced expiratory volume in 1 second (FEV1), and forced oscillation technique (FOT) parameters over 3 years in a cohort of patients in our collaborative system.

METHODS

From 288 adults with well controlled asthma managed under the Yokohama Seibu Hospital coordinated care system between January 2009 and May 2018, we selected 99 subjects to undergo spirometry, FeNO and FOT testing over 3 years and analyzed the changes in these parameters.

RESULTS

Of the 99 patients enrolled, 17 (17.2%) experienced at least one exacerbation (insufficiently controlled (IC)), whereas, 82 (82.8%) remained in well controlled during the 3-year study period. Of well-controlled patients, 54 patients (54.5%) met the criteria for clinical remission under treatment (CR); the remaining 28 patients did not meet the CR criteria (WC). There were no differences in FeNO, FEV1, or FOT parameters at baseline among the IC, WC, and CR groups. The levels of FEV1 decreased gradually, whereas the levels of FeNO decreased significantly over 3 years. The levels of percent predicted FEV1 (%FEV1) significantly increased. We also observed significant improvement in FOT parameters; reactance at 5 Hz (R5), resonant frequency (Fres), and integral of reactance up to the resonant frequency (AX). The CR group demonstrated significant relationships between the change in FeNO and the change in FEV1 and between the change in FEV1 and the change in FOT parameters. No significant correlations emerged in the IC or WC group.

CONCLUSION

The decrease in FeNO and increase in %FEV1, we observed in all study participants suggest that the coordinated care system model benefits patients with asthma. Although it is difficult to predict at baseline which patients will experience an exacerbation, monitoring changes in FeNO and FEV1 is useful in managing patients with asthma. Furthermore, monitoring changes in R5, Fres, and AX via forced oscillation technique testing is useful for detecting airflow limitation.

Longitudinal monitoring of asthma in the clinic using respiratory oscillometry

BACKGROUND AND OBJECTIVE

Asthma guidelines emphasize the importance of assessing lung function and symptoms. The forced oscillation technique (FOT) and its longitudinal relationship with spirometry and symptoms are unresolved. We examined concordance between longitudinal spirometry, FOT and symptom control, and determined FOT limits of agreement in stable asthma.

METHODS

Over a 3-year period, adults with asthma attending a tertiary clinic completed the asthma control test (ACT), fraction of exhaled nitric oxide (FeNO), FOT and spirometry. Analysis included between-visit concordance for significant change using Cohen's kappa (κ) and stable asthma FOT limits of agreement.

RESULTS

Data (n = 186) from 855 visits (mean ± SD 4.6 ± 3.0 visits), 114 ± 95 days apart, were analysed. Between-visit concordance was moderate between reactance at 5 Hz (X5) and forced expiratory volume in 1 s (FEV₁ ) (κ = 0.34, p = 0.001), and weak between ACT and FEV₁ (κ = 0.18, p = 0.001). Change in FeNO did not correlate with lung function or ACT (κ < 0.05, p > 0.1). Stable asthma between visits (n = 75; 132 visits) had reduced lung function variability, but comparable concordance to the entire cohort. Limits of agreement for FEV₁ (0.42 L), resistance at 5 Hz (2.06 cm H₂ O s L^-1 ) and X5 (2.75 cm H₂ O s L^-1 ) in stable asthma were at least twofold greater than published values in health.

CONCLUSION

In adults with asthma, there is moderate concordance between longitudinal change in FOT and spirometry. Both tests relate poorly to changes in asthma control, highlighting the need for multi-modal assessment in asthma rather than symptoms alone. The derivation of longitudinal FOT limits of agreement will assist in its clinical interpretation.

Longitudinal changes in pulmonary function and respiratory impedance of rheumatoid arthritis

The aim of this study was to examine long-term changes in pulmonary function and respiratory impedance (Zrs) as assessed by forced oscillation technique (FOT) of rheumatoid arthritis (RA)-related pulmonary disorders. Data of 42 RA patients who underwent pulmonary function tests and Zrs measurements at least twice at a >900-day interval were retrospectively reviewed. Zrs, respiratory resistance (Rrs) and reactance (Xrs), were measured as a function of oscillatory frequency from 4 to 36 Hz. The Rrs and difference between inspiratory and expiratory phases of Xrs were significantly decreased. Annual changes in Xrs parameters significantly correlated with those of spirometric parameters. Zrs parameters were significantly different between the low (the lower 75 percentile of incidence) and high (the top quartile) frequency of adverse respiratory event groups. The Zrs combined with spirometry may be beneficial to evaluate alterations in respiratory functions of RA.

Comparison of respiratory system impedance in asthma and COPD: A prospective observational study

BACKGROUND AND OBJECTIVE

A single assessment of within-breath variations of respiratory system reactance (Xrs) at 5 Hz (ΔX5) measured by the forced oscillation technique (FOT) has been reported to be useful for the detection of pathophysiological changes in chronic obstructive pulmonary disease (COPD) and asthma. We examined longitudinal changes in respiratory system resistance (Rrs) and Xrs during tidal breathing between stable asthma and COPD patients in order to clarify the features of changes of respiratory system impedance and airflow limitation for these conditions.

METHODS

Between April 2013 and September 2013, outpatients with a COPD or asthma diagnosis were recruited. We examined forced expiratory volume in 1 s (FEV₁ ) and FOT every 6 months until September 2015. Annual changes were estimated from the linear regression curve slope.

RESULTS

We included 57 and 93 subjects with COPD and asthma, respectively. The median follow-up period was 26 months (range: 24-29 months). Within-breath analysis showed that the difference between mean Rrs at 5 Hz and 20 Hz was significantly lower, and ΔX5 more negative, in COPD than in asthma patients. With regard to annual changes, only ΔX5 was significantly different, more negative, in COPD than in asthma patients. Comparing between COPD subjects of Global Initiative Chronic Obstructive Lung Disease (GOLD) stage I/II and those with asthma, there were no significant differences in respiratory system impedance at enrolment, while annual change in ΔX5 was significantly more negative in mild COPD than in asthma patients.

CONCLUSION

ΔX5 may be useful for long-term assessment of airflow limitation in COPD.