Application of the Forced Oscillation Technique in Patients With Preserved Ratio Impaired Spirometry

Background Preserved ratio impaired spirometry (PRISm) identifies patients who exhibit a reduced forced expiratory volume in one second (FEV1) without qualifying for obstruction on spirometry. Although patients with PRISm may present with symptomatic or radiological similarities to those with chronic obstructive pulmonary disease, they represent a distinct entity with a propensity to develop obstruction over time. The forced oscillation technique (FOT) serves as a noninvasive method to assess pulmonary mechanics. This study aims to elucidate the FOT findings in selected patients diagnosed with PRISm. Methodology A prospective descriptive analysis was conducted among adult patients with PRISm. Patients with a reduced FEV1 (<80%) and preserved ratio were enrolled. These patients underwent FOT testing. Data collection included the patients' characteristics along with pulmonary function test and FOT parameters. Results A total of 20 patients diagnosed with PRISm were included in the study. The cohort predominantly consisted of females (75%) and individuals of Caucasian descent (80%). The median age of the patients was 54.25 years, and the average body mass index (BMI) was calculated to be 34.16 kg/m². Of the 20 patients, four (20%) were current smokers, 35% were former smokers, and the remaining 45% had never smoked. Only descriptive analysis was performed due to the limited sample size. The majority of the study population (55%) exhibited abnormal FOT findings, characterized by elevated reactance and/or resistance. Normal FOT parameters were observed in 45% of the patients. Normal FOT was observed in patients with elevated BMI, while abnormal FOT parameters were identified in patients with normal total lung capacity and in those with normal forced vital capacity. These abnormalities were also observed in patients with a normal BMI and in individuals who never smoked. Conclusions Our findings indicate that patients with PRISm exhibit increased airway resistance and/or reactance. This study is unique in its emphasis on the potential application of FOT in this specific patient subgroup. Additionally, we highlight the presence of FOT abnormalities in patients with a normal body habitus and no smoking history, suggesting that patients with PRISm warrant further investigation.