Abdominal Muscle Use during Breathing in Patients with Chronic Airflow Obstruction

Abstract

To assess the pattern of abdominal muscle contraction in stable patients with chronic obstructive pulmonary disease (COPD), we studied electromyograms of the rectus abdominis, external oblique, and transversus abdominis muscles in 40 patients with variable degrees of chronic airflow obstruction (FEV1 between 17 and 82% of predicted); 12 control subjects with normal pulmonary function tests were studied for comparison. The subjects were studied during resting breathing in the supine posture, and the electromyograms were recorded with concentric needle electrodes implanted with the aid of a high-resolution ultrasound. The rectus abdominis and external oblique were silent in virtually all patients. In contrast, 17 patients had invariable phasic expiratory activity in the transversus abdominis, and 11 additional patients had intermittent transversus expiratory activity. Expiratory contraction of the transversus was related to the degree of airflow obstruction (p less than 0.005), and when present, it persisted in the seated posture. We conclude that (1) when breathing at rest, many stable patients with severe chronic airflow obstruction contract the abdominal muscles during expiration, and (2) this expiratory contraction is usually confined to the transversus muscle. These observations also indicate that the physiology of dynamic hyperinflation and intrinsic positive end-expiratory pressure (PEEP) in such patients should be reevaluated.

Expiratory muscle pressure and breathing mechanics in chronic obstructive pulmonary disease

“…Critique of the method to quantify expiratory muscle contraction Previously, NINANE et al [1] evaluated abdominal muscle recruitment during quiet breathing in COPD patients by inserting needle electrodes into the abdominal muscles to record their electrical activities. In the current study, this approach to quantify expiratory muscle contraction was not used for the reasons that follow.…”

“…These results are consistent with our expectations. In fact, in spontaneously breathing COPD patients, the phasic electrical activity of transversus abdominis had already ceased when inspiratory muscle electrical activity started to appear at end expiration [1]. There was little overlap between these two events.…”

“…In a previous study by NINANE et al [1], it was clearly indicated that many patients with chronic obstructive pulmonary disease (COPD) have rhythmic electrical activity of the transversus abdominis muscle when breathing quietly at rest. This leads to a phasic rise in abdominal pressure during expiration in these patients [2±4].…”

“…This makes it unlikely for expiratory muscle recruitment in such COPD patients to be effective in lowering the end-expiratory lung volume. Based on this argument, NINANE et al [1] predicted that contraction of expiratory muscles, such as the transversus abdominis, would contribute little to improving the force generating ability of the diaphragm in COPD. On the other hand, DODD et al [9] proposed that even if expiratory muscle recruitment may not effectively reduce operating lung volume in COPD, it would still be able to decrease abdominal volume and thus still put the diaphragm at longer length or better mechanical geometry by which the force production of the diaphragm can be improved.…”

Balance recovery is compromised and trunk muscle activity is increased in chronic obstructive pulmonary disease

“…Pulmonary changes in COPD require greater activation of the abdominal muscles to assist in expiration [30][31][32]. Enhanced respiratory activity of the trunk muscles will have contributed to greater abdominal muscle EMG, and is reflected by greater baseline EMG.…”