A reduction in lung function in people with heart failure (HF) after cardiac surgery is common and associated with morbidity. In this scenario, lung function is commonly assessed pre- and postoperatively with the slow vital capacity (SVC) measured with a ventilometer. However, new outcomes have been suggested to reflect the impact of surgery on lung function, such as the maximum phonation time (MPT). So far, the association between MPT and SVC has not been studied properly in HF.

To investigate the association between MPT and SVC in people with HF hospitalised for elective cardiac surgery.

This cross-sectional analysis included people with HF evaluated in the hospital before elective cardiac surgery. Sociodemographic data, anthropometric, and clinical characteristics were collected for sample characterisation. SVC was measured in mL with a ventilometer, by asking participants to inhale deeply and exhale slowly and completely into the device after a demonstration. MPT was measured as the maximum time in seconds, recorded with a stopwatch, to sustain the vocalisation of the vowel /i/ (in portuguese), in natural tone and intensity, after a demonstration. For both variables, the greatest result out of three repetitions was used for analysis. Jamovi 2.6.25 software was used to run the statistical tests: Spearman correlation coefficient and Mann-Whitney test. P-values < 0.05 was considered statistically significant.

74 individuals were included (57% women, 60 ± 11 years, New York Heart Association Functional Classification of 2 ± 1 points). The mean SVC was 2640 ± 874 mL, while the mean MPT was 12.2 ± 9.4 seconds. These two variables showed a weak and non-significant correlation (rs = 0.19; p = 0.10). After dividing the sample in two according to the mean SVC (< or = 2640 mL), no statistically significant difference was observed when comparing MPT between the two groups (10.3 ± 7.8 vs. 13.9 ± 10.5 seconds, respectively; p = 0.18).

In this study, MPT was not associated with SVC in individuals with HF before elective cardiac surgery. Future studies should investigate the same analyses investigated in our study, but in larger samples and at different time points, such as after surgery.

Despite the ease of measuring MPT, our findings suggest that MPT should not be used to reflect the impact of cardiac surgery on lung function in people with HF when SVC is not available.