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

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 (ΔPaw), and total inspiratory effort, measured by oesophageal pressure swings (ΔPes), remains unexplored. Additionally, the association between ΔPes, ΔPaw, and inspiratory muscle activations remains unclear.

Objectives: The ai of this study was to compare ΔPes and ΔPaw and their relationship with inspiratory muscle activation in patients with weaning difficulties during different breathing conditions.

Methods: ΔPes 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 cmH₂O) executed with slow and deep inspirations (low-load slow) and 4) low-load IMT (load: <10% maximal inspiratory pressure, PImax = 3 cmH₂O) executed with fast deep inspirations (low-load fast); and 5) high-load IMT (load ∼ 30% PImax) executed with fast and deep inspirations. ΔPaw, 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 ΔPes and ΔPaw.

Results: Five patients (age: 68 ± 1 y; 20% male; PImax: 37 ± 7 cmH₂O [59 ± 23% predicted]; forced vital capacity: 0.66 ± 0.16 L [21 ± 6% predicted]) were included in the study. ΔPes values were 3-4 times larger than ΔPaw values during unsupported spontaneous breathing and IMT conditions. ΔPes, 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 ΔPaw and moderately with ΔPes.

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.

Clinical trial registration numbers: NCT03240263 and NCT04658498.