Can We Use the Maximum Phonation Time as a Screening of Pulmonary Forced Vital Capacity in Post-COVID-19 Syndrome Patients?

To verify the accuracy of the maximum phonation time of the vowel /a/ (MPT/a/), fricative /s/ (MPT/s/), number counting (MPTC), and number reached in this count (CN) to estimate forced vital capacity (FVC) in patients with post-COVID-19 syndrome. Cross-sectional study involving adult patients, who were admitted to the intensive care unit and referred to the Post-COVID-19 Rehabilitation Outpatient Clinic. Voice function was assessed using a Vocal Handicap Index (VHI) self-assessment questionnaire and MPT tests. To perform the phonatory tests, the patients remained in a standing posture and were instructed to inhale as much air as possible and, during a single exhalation, at usual pitch and loudness, sustain the emission of /a/ and /s/; and in another breath, to perform the ascending numerical count, starting from the number one up to the highest number they could reach. Pulmonary function was assessed by spirometry. The receiver operating characteristic (ROC) curve was plotted, and FVC values lower than the normal limit by Z-score (fifth percentile) were classified as impaired lung function. The predictive values and likelihood ratios were calculated. A total of 70 patients participated, with 20–30% having a high VHI. Approximately 24% had an FVC impairment and significantly low values of MPT/a/, MPT/s/, MPTC, and CN. The test results showed overall accuracy of 70% and the cutoff points of 8.83, 7.50, 8.80, and 13, respectively, with high sensitivity, predictive negative value and low specificity, predictive positive value, and positive likelihood ratio. Our results suggest that the MPT has moderate discriminatory power for FVC impairment, indicating that it is not a reliable indicator of pulmonary function in the population studied. Therefore, in patients with an MPT of less than 8.83 seconds, or a CN lower than 13, other criteria should be added to improve the diagnostic accuracy and support the decision to perform more complex investigations.