Background: Cough pressure, an expression of expiratory muscle strength, is usually measured with esophageal or gastric balloons, but these invasive catheters can be uncomfortable for the patient or their placement impractical. Because pressure in the thorax and abdomen are expected to be similar during a cough, we hypothesized that measurement at other thoracic or abdominal locations might also be similar as well as useful in clinical scenarios. This study aimed to compare cough pressures measured at thoracic and abdominal sites that could serve as alternatives to esophageal pressures (Pes).
Methods: Nine patients scheduled for laparotomy were asked to cough as forcefully as possible from total lung capacity in supine position. Three cough maneuvers were performed while Pes (the gold standard) as well as gastric, central venous, bladder and rectal pressures (Pga, Pcv, Pbl, and Prec, respectively) were measured simultaneously. The intraclass correlation coefficient (ICC) was used to evaluate the repeatability of the measurements in each patient at each site and evaluate agreement between alternative sites (Pga, Pcv, Pbl, and Prec) and Pes. Bland-Altman plots were used to compare Pes and the measurements at the other sites.
Results: Median (first quartile, third quartile) maximum pressures were as follows: Pes 112 (89,148), Pga 105 (92,156), Pcv 102 (91,149), Pbl 118 (93,157), and Prec 103 (88,150) cmH2O. The ICCs showed excellent within-site repeatability of the measurements (p < 0.001) and excellent agreement between alternative sites and Pes (p < 0.004). The Bland-Altman plots showed minimal differences between Pes, Pga, Pcv, and Prec. However, Pbl was higher than the other pressures in most patients, and the difference between Pes and Pbl was slightly larger.
Conclusions: Cough pressure can be measured in the esophagus, stomach, superior vena cava or rectum, since their values are similar. It can also be measured in the bladder, although the value will be slightly higher. These results potentially facilitate the assessment of dynamic expiratory muscle strength with fewer invasive catheter placements in most hospitalized patients, thus providing an option that will be particularly useful in those undergoing thoracic or abdominal surgery.
Trial registration: NCT02957045 registered at November 7, 2016. Retrospectively registered.
Keywords: Abdominal muscles [A02.633.567.050]; Cough [C23.888.852.293]; Laparotomy [E04.406]; Respiratory muscles [A02.633.567.900].