Correlation between Peak Expiratory Flow Rate and Single Breath Count in Patients with Post-COVID Sequelae: An Observational Study

Abstract

Background: COVID-19 frequently impairs pulmonary function during the post-recovery phase. Assessing respiratory status using accessible, equipment-free methods such as Single Breath Count (SBC) and Peak Expiratory Flow Rate (PEFR) is valuable for monitoring long-term functional recovery. Objectives: To evaluate the correlation between PEFR and SBC, determine their test–retest reliability, and assess whether PEFR can predict SBC performance in individuals with post-COVID-19 sequelae. Materials and Methods: This observational study evaluated 60 patients with post-COVID-19 sequelae (aged 20–50 years) selected through convenience sampling. PEFR was recorded using a Mini-Wright peak flow meter, and SBC was evaluated using a standardised breath-counting protocol. Pearson’s correlation coefficient was used to determine the relationship between the measures. Intraclass correlation coefficients (ICCs) assessed test–retest reliability, while linear regression and k-fold cross-validation evaluated predictive validity and model stability. Results: A statistically significant weak-to-moderate positive correlation was observed between PEFR and SBC (r = 0.338, p = 0.008). Both measures demonstrated high test–retest reliability, with ICC values of 0.89 for PEFR and 0.86 for SBC. Linear regression showed that PEFR was a weak predictor of SBC (R² = 0.11, p = 0.037), a finding supported by k-fold cross-validation (mean r = 0.34 ± 0.30). Conclusion: SBC was significantly correlated with PEFR, indicating that the two measures reflect complementary dimensions of post-COVID respiratory impairment. Given their high test–retest reliability, integrating the equipment-free SBC into physiotherapy practice may provide a practical, low-cost option for remote monitoring and telerehabilitation.