Patients with asthma who had combined impairment of both forced vital capacity and area under the reactance curve had notably worse asthma control.
Standard care for severe asthma aims to preserve forced vital capacity (FVC) unless other issues such as airway remodeling or air trapping are detected. An additional assessment of area under the reactance curve (AX) can also be applied to determine small airway dysfunction attributed to lung stiffness. AX includes the total area dominated by the capacitance and reflects the elastic properties of the lung.
For a study published in Lung, Rory Chan, PhD, and colleagues aimed to determine the prognostic value of using FVC in conjunction with AX assessment. “Here we explore if there may be potential synergistic interaction between FVC and AX in terms of impaired asthma control as Asthma Control Questionnaire (ACS) and exacerbations requiring oral corticosteroids (OCS), whilst also looking at the relationship to type 2 (T2) biomarkers as peripheral blood eosinophils, fractional exhaled nitric oxide (FeNO) and total immunoglobin E (IgE),” the study authors state.
Number of Asthma Exacerbations Requiring Oral Corticosteroids Noted
The study team retrospectively collected data from the National Health Service Tayside health informatics database. They identified 181 patients with moderate-to-severe asthma who had spirometry and oscillometry measurements on file. Impairment was denoted based on cut points of less than 100% and 1.0 kPa/L or greater. FeNO was assessed using NIOX VERO and peripheral blood eosinophils and total immunoglobulin E (IgE) were measured using blood testing.
The ACQ was used to determine the participating patients’ asthma control. This questionnaire is based on international guidelines to measure the adequacy of asthma control and uses a seven-point scale ranging from 0, meaning no impairment, to 6 meaning extremely poorly controlled asthma. The number of asthma exacerbations requiring OCS was also noted.
SPSS Statistics 27 was used to perform the statistical analysis and Shapiro-Wilks was applied to assess outliers for normality in the data pool prior to analysis. Significant differences in spirometry (mean 95% CI) were evaluated by performing an overall analysis of variance.
Patients With Combined Impairment of FVC and AX Had Worse Asthma Control
Results showed that the study participants who had combined impairment of FVC and AX had significantly worse asthma control as demonstrated in their higher ACQ scores. These participants also had more severe exacerbations requiring OCS and worse spirometry (FEV1 and forced expiratory flow [FEF] rate between 25% and 75%) than those subjects with impaired FVC but preserved AX (Table). There were no significant differences in T2 biomarkers noted.
Furthermore, the researchers observed a similar pattern in patients with preserved FVC and impaired AX as opposed to patients with the preservation of both FVC and AX with the exception that there were no differences in exacerbations.
Clinicians might conceivably be lulled into a false sense of security in an individual with preserved FVC by using spirometry alone, Dr. Chan noted. “From a practical point of view, oscillometry is much easier to perform during normal tidal breathing and is more physiological than the artificial expiratory maneuver with spirometry,” the study authors wrote. They concluded that in patients with moderate-to-severe asthma, using both spirometry and oscillometry provides a more comprehensive characterization of airway physiology.