Effect of cardiac surgery on respiratory muscle strength

Pulmonary complications, such as atelectasis, pulmonary oedema, pleural effusion, bronchospasm, and pneumonia, have been reported following cardiac surgery. Shallow breathing leading to impaired lung function is the major cause of respiratory complications. Decreases in respiratory muscle strength can be measured using the maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) produced in the oral cavity. This study aimed to determine the decrease in respiratory muscle strength 8 weeks following cardiac surgery. Moreover, the relationship between lung function and respiratory muscle strength was studied.

In this observational study, 42 adult cardiac surgery patients (10 women, 32 men; mean age 65 ± 7 years) were investigated. Lung function and respiratory muscle strength were measured preoperatively and at 2 months postoperatively.

The pre- and postoperative respiratory muscle strengths were in accordance with the predicted values. The MIP was 81.75 ± 22.04 cmH₂O preoperatively and 74.56 ± 18.86 cmH₂O at the 2-month follow-up (p = 0.146). The MEP was 98.55 ± 22.24 cmH₂O preoperatively and 88.86 ± 18.14 cmH₂O at the 2-month follow-up (p = 0.19). The preoperative lung function was in accordance with the predicted values; however, lung function significantly decreased postoperatively. At the 2-month follow-up, there was a moderate correlation between the MIP and forced expiratory volume (r = 0.59, p = 0 .0078).

The respiratory muscle strength was not impeded either before or 2 months after cardiac surgery. However, the exact mechanism for the alteration in lung function remains unclear. Measures to re-establish the ideal postoperative lung capacity should concentrate on different perioperative pulmonary exercises.