Compensation of Respiratory-Related Postural Perturbation Is Achieved by Maintenance of Head-to-Pelvis Alignment in Healthy Humans.

Valérie Attali,Ségolène Rémy-Néris,Louis Clavel,Isabelle Rivals,Wafa Skalli,Baptiste Sandoz,Philippe Rouch,Thomas Similowski

doi:10.3389/fphys.2019.00441

Abstract

The maintenance of upright balance in healthy humans requires the preservation of a horizontal gaze, best achieved through dynamical adjustments of spinal curvatures and a pelvic tilt that keeps the head-to-pelvis alignment close to vertical. It is currently unknown whether the spinal and pelvic compensations of respiratory-related postural perturbations are associated with preservation of the head-to-pelvis vertical alignment. We tested this hypothesis by comparing postural alignment variables at extreme lung volume (total lung capacity, TLC; residual volume, RV) with their reference value at functional residual capacity (FRC). Forty-eight healthy subjects [22 women; median age of 34 (26; 48) years] were studied using low dose biplanar X-rays (BPXR; EOS®system). Personalized three-dimensional models of the spine and pelvis were reconstructed at the three lung volumes. Extreme lung volumes were associated with changes of thoracic curvature bringing it outside the normal range. Maximal inspiration reduced thoracic kyphosis [T1–T12 angle = 47° (37; 56), -4° variation (-9; 1), p = 0.0007] while maximal expiration induced hyperkyphosis [T1–T12 angle = 63° (55; 68); +10° variation (5; 12), p = 9 × 10-12]. Statistically significant (all p < 0.01) cervical and pelvic compensatory changes occurred [C3–C7 angle: +4° (-2; 11) and pelvic tilt +1° (0; 3) during maximal inspiration; C3–C7 angle: -7° (-18; -1) and pelvic tilt +5° (1; 8) during maximal expiration], resulting in preserved head-to-pelvis alignment (no change in the angle between the vertical plane and the line connecting the odontoid process and the midpoint of the line connecting the center of the two femoral heads ODHA). Lung volume related postural perturbations were more marked as a function of age, but age did not affect the head-to-pelvis alignment. These findings should help understand balance alterations in patients with chronic respiratory diseases that modify lung volume and rib cage geometry.

Highlights

The maintenance of upright balance in healthy humans largely depends on the preservation of an horizontal gaze (Hasegawa et al, 2017)
We describe postural alignment and its adjustments as a function of lung volume in upright healthy volunteers
This study shows that the changes in thoracic spinal curvature induced by maximal inspiration and maximal expiration in healthy humans, are fully compensated in terms of the head-topelvis alignment

Summary

Introduction

The maintenance of upright balance in healthy humans largely depends on the preservation of an horizontal gaze (Hasegawa et al, 2017). Breathing involves rotation of the costovertebral joints that modifies spinal curvature and, spinal postural alignment (Dally, 1908) It ensures that breathing induces a cyclic postural perturbation. This is reflected by respiratory-induced oscillations of the center of pressure, defined as the projection to the ground of the barycenter of vertical reaction forces, distributed over the entire surface of foot-ground contact. These oscillations disappear during breath-holding (Caron et al, 2004). They increase when ventilation increases (David et al, 2012)

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