Altered patterns of abdominal muscle activation during forced exhalation following elective laparotomy: An experimental research

Background: Post-operative pulmonary complications are common after exploratory laparotomy. Good abdominal muscle functioning is essential for forced exhalation and effective coughing. However, the impact of a laparotomy on abdominal muscle activity remains uncertain. The study aimed to assess abdominal muscle activity during forced exhalation following elective laparotomy. Materials and methods: A was carried out on those undergoing (n = 30) their first elective laparotomy. Abdominal muscle activity, as percentage maximal voluntary contraction (%MVC), was assessed during forced exhalation using surface electromyography (EMG) for transverse abdominis (TrAb), external oblique (EO), and rectus abdominis (RA) pre-operatively and up to seven days post-operatively. Peak expiratory flow rate (PEFR) was assessed during the forced exhalation maneuver. Median %MVC was used to represent the trends and Z-scores to report the change from the baseline activity. Spearman's correlation was used for the correlation between %MVC and PEFR. Results: Pre-operatively, we observed the %MVC of TrAb (75.58%) to be the highest followed by RA (66.28%) and EO (62.12%). Post-operatively, all the muscles demonstrated increased activity wherein EO (84.33%) was most active on post-op day1, and for the rest of the days TrAb was the most active. However, as observed from Z-scores of all the three muscles the activity of EO was raised significantly from the baseline. No correlation was observed between %MVC and PEFR. Conclusion: TrAb is the most active muscle that contributes to forced exhalation. Following an elective laparotomy, TrAb is no longer the most active muscle, rather it is the EO that primarily contributes to forced exhalation. This should be considered while providing post-operative respiratory care. However, more research is required in this area to better understand the role of expiratory muscle training for those undergoing elective laparotomies.