Inspiratory effort and respiratory muscle activation during different breathing conditions in patients with weaning difficulties: An exploratory study

Abstract

Background: Recent studies suggest that fast and deep inspirations against either low or high external loads may provide patients with weaning difficulties with a training stimulus during inspiratory muscle training (IMT). However, the relationship between external IMT load, reflected by changes in airway pressure swings (Delta Paw), and total inspiratory effort, measured by oesophageal pressure swings (Delta Pes), remains unexplored. Additionally, the association between Delta Pes, Delta Paw, and inspiratory muscle activations remains unclear. Objectives: The ai of this study was to compare Delta Pes and Delta Paw and their relationship with inspiratory muscle activation in patients with weaning difficulties during different breathing conditions. Methods: Delta Pes and scalene, sternocleidomastoid, and parasternal intercostal muscles activation were recorded during the following conditions: 1) (proportional) pressure support ventilation; 2) unsupported spontaneous breathing; 3) low-load IMT (load: <10% maximal inspiratory pressure, PImax = 3 cmH(2)O) executed with slow and deep inspirations (low-load slow) and 4) low-load IMT (load: <10% maximal inspiratory pressure, PImax = 3 cmH(2)O) executed with fast deep inspirations (low-load fast); and 5) high-load IMT (load similar to 30% PImax) executed with fast and deep inspirations. Delta Paw, end-inspiratory lung volume, and peak inspiratory flow were recorded during conditions 2-5. Variables were compared across conditions using mixed-model analysis. Spearman's rank correlations were calculated between inspiratory muscle activations and both Delta Pes and Delta Paw. Results: Five patients (age: 68 +/- 1 y; 20% male; PImax: 37 +/- 7 cmH(2)O [59 +/- 23% predicted]; forced vital capacity: 0.66 +/- 0.16 L [21 +/- 6% predicted]) were included in the study. Delta Pes values were 3-4 times larger than DPaw values during unsupported spontaneous breathing and IMT conditions. Delta Pes, sternocleidomastoid activation, end-inspiratory lung volume, and peak inspiratory flow were larger during low-load fast IMT than during low-load slow IMT and unsupported spontaneous breathing but were similar between low-load fast and high-load IMTs. Inspiratory muscle activations correlated weakly to moderately with Delta Paw and moderately with Delta Pes. Conclusions: In five patients with weaning difficulties, low-load fast IMT provided a training stimulus similar to high-load IMT. Both yielded significantly higher training stimulus than low-load slow IMT and unsupported spontaneous breathing. These results should be considered in future trials comparing IMT with sham conditions. (c) 2024 Australian College of Critical Care Nurses Ltd. Published by Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.