Abdominal weight and inspiratory resistance: their immediate effects on inspiratory muscle functions during maximal voluntary breathing in chronic tetraplegic patients

Objective: To study the immediate effects of maximal voluntary (MV) breathing, with and without abdominal weight (AW) or inspiratory resistance (IR), on inspiratory muscle functions in chronic tetraplegic patients. Design: A crossover trial design. Setting: Rehabilitation department of a university hospital. Participants: Nine tetraplegic men injured at the C4 to T1 levels, with a mean duration of injury of 72.8 months. Interventions: Each subject performed MV breathing without and with AW load (AWMV breathing) and IR load (IRMV breathing) separately. Main Outcome Measures: Electromyographic (EMG) activity of the inspiratory muscles, mouth pressure, inspiratory flow, and inspiratory volume. Results: AWMV breathing evoked greater diaphragmatic EMG activity, inspiratory flow, and inspiratory volume than did IRMV breathing, although the increase of diaphragmatic EMG activity was not statistically significant. Conversely, IRMV breathing produced greater sternocleidomastoid EMG activity and negative mouth pressure than did AWMV breathing. Both AWMV and IRMV breathing evoked greater inspiratory muscle EMG activity than did MV breathing. Conclusion: AW and IR loads have differential immediate effects on the inspiratory muscle functions during MV breathing in patients with chronic tetraplegia, suggesting that these two breathing maneuvers may have dissimilar mechanisms of training in such patients. The muscle EMG activity evoked during MV breathing with AW or IR is greater than that without a mechanical load, implying that mechanically loaded training in tetraplegic patients results in load compensatory adjustments via their respiratory motor output to improve respiratory function.