Broad individual immersion-scattering of respiratory compliance likely substantiates dissimilar breathing mechanics

Olivier Castagna,Bruno Schmid,Thibaut Prevautel,Thomas Similowski,Jacques Regnard,Guillaume Michoud,Antoine Delafargue

doi:10.1038/s41598-021-88925-x

Abstract

Head-out water immersion alters respiratory compliance which underpins defining pressure at a “Lung centroid” and the breathing “Static Lung Load”. In diving medicine as in designing dive-breathing devices a single value of lung centroid pressure is presumed as everyone’s standard. On the contrary, we considered that immersed respiratory compliance is disparate among a homogenous adult group (young, healthy, sporty). We wanted to substantiate this ample scattering for two reasons: (i) it may question the European standard used in designing dive-breathing devices; (ii) it may contribute to understand the diverse individual figures of immersed work of breathing. Resting spirometric measurements of lung volumes and the pressure–volume curve of the respiratory system were assessed for 18 subjects in two body positions (upright Up, and supine Sup). Measurements were taken in air (Air) and with subjects immersed up to the sternal notch (Imm). Compliance of the respiratory system (Crs) was calculated from pressure–volume curves for each condition. A median 60.45% reduction in Crs was recorded between Up-Air and Up-Imm (1.68 vs 0.66 L/kPa), with individual reductions ranging from 16.8 to 82.7%. We hypothesize that the previously disregarded scattering of immersion-reduced respiratory compliance might participate to substantial differences in immersed work of breathing.

Highlights

Head-out water immersion alters respiratory compliance which underpins defining pressure at a “Lung centroid” and the breathing “Static Lung Load”
Four subjects were unable to achieve satisfactory maneuvers during the immersion conditions, and their data were not included in the analysis presented here
The results presented in this article confirm the main known effects of immersion on breathing patterns and respiratory mechanics—leading to reduced functional residual capacity, expiratory reserve volume, and total respiratory compliance, with an increased tidal volume

Summary

Introduction

Head-out water immersion alters respiratory compliance which underpins defining pressure at a “Lung centroid” and the breathing “Static Lung Load”. We observed that after 30 min of controlled immersed exercising with identical dive-breathing devices, (i) the number of ultrasound lung comet tails was substantially higher in some subjects and (ii) the work of breathing was markedly different between the s ubjects[16]. The number of lung comet tails, an indicator of the amount of extravascular lung fluid, correlated with the amount of work of breathing (WOB) and with markers of right heart congestion and of right/left ventricular imbalance[16,17,18] These results raised the question of uncovering the mechanisms likely to underlie such differences in individual figures of WOB. Differences in individual respiratory compliance would result in different figures of WOB in similar conditions of immersed exercising amid roughly similar subjects. Later a standard SLL of 20 c mH2O was proposed as unique reference without alluding possible individual figure d eviation[22,27]

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Discussion

Conclusion