Introduction:
The study purpose was to investigate the pulmonary function test, respiratory muscle (RM) strength, functional capacity, and gait speed in Thai patients submitted to open heart surgery.

Methods:
A prospective observational cohort study was designed with 48 patients who underwent open heart surgery, aged 35–70 years, both males and females. The average duration of follow-up after cardiac surgery was 16.15 ± 4.97 days. Spirometry, RM strength, 6-minute walk test, and 5-meter walk test were performed. ANOVAs were used to compare whether these parameters significantly changed in the preoperative, prior to discharge, and follow-up periods.

Results:
Overall, 26 female and 22 male patients participated in the initial and follow-up study; the average age was 55.46 ± 10.35 years. There was a significant decrease in lung function (%predicted forced vital capacity [FVC] and %predicted forced expiratory volume in 1 second [FEV1]), RM strength (maximal inspiratory pressure [MIP] and maximal expiratory pressure [MEP]), functional capacity, and gait speed compared with preoperative values. Before discharge from hospital, the mean %predicted FVC was dramatically decreased to –22.87 ± 14.93 and %predicted FEV1 was –22.10 ± 15.59 compared with the preoperative period (p < 0.05). Furthermore, mean MIP dropped to –24.75 ± 17.08 cm H2O and MEP to –20.96 ± 15.79 cm H2O. These values did not fully recover after discharge from hospital (p < 0.001).

Conclusions:
Decreased lung function, RM, functional capacity, and gait speed were observed during hospitalization and follow-up time.