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

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.

Cervical Spine Hyperextension and Altered Posturo-Respiratory Coupling in Patients With Obstructive Sleep Apnea Syndrome

“…Indeed, we did not observed in our patients any pelvic compensation (29). Conversely we observed a compensatory thoracic hyperkyphosis (24,29). This compensation probably limits the disturbance of balance secondary to pathological spinal alignment (35), but may increase the risk of falls and others hyperkyphosisrelated comorbidities (46).…”

“…Anatomically, both rely on the integrity of the same musculoskeletal structures: the spine, thoracic cage, and trunk musculature. It has been shown that spinal curvatures are severely constrained by extreme variations in pulmonary volume (24). Additionally, normal ventilation cyclically perturbs balance.…”

“…This "postural disturbance" caused by ventilation is manifested in stabilometric recordings as minimal oscillations of the center of pressure whose ventilatory origin is suggested by their disappearance on breath-holding/apnea (26), and an increase in voluntary (27), or hypercapnic (28) ventilation. The end result is that the cyclical constraint imposed on the thoracic spine by normal breathing continually changes the head to pelvis vertical axis, requiring the body to compensate (29) at the neck and pelvis (24) to maintain normal postural balance. Each ventilatory cycle triggers spinal and pelvic contractions to compensate for this postural disturbance (30)(31)(32) and is evidence for the existence of a posturo-respiratory coupling that is in play across all joints from head to foot when standing.…”

“…We hypothesized that it may be the result of a pathological interaction between postural and ventilatory functions. Twelve patients with OSAS (4 women, age 53 years [51][52][53][54][55][56][57][58][59][60][61][62][63] (median [quartiles]), apnea hypopnea index 31/h [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41]) were compared with 12 healthy matched controls. Low dose biplanar X-rays (EOS ® system) were acquired and personalized three-dimensional models of the spine and pelvis were reconstructed.…”

Decreased respiratory-related postural perturbations at the cervical level under cognitive load

“…Postural and respiratory dynamics are intimately linked and exhibit strong temporal relationships in healthy humans (Dally 1908;Gurfinkel et al 1971;Perry and Carrier 2006). Ribcage movements during breathing disturb an individual's balance by modifying the costo-vertebral articulation position, thoracic spinal curvature and postural alignment (Dally 1908;Attali et al 2019) and by inducing ribcagerelated centre of mass (CoM) displacements. Breathingrelated postural perturbations during natural breathing are partially counteracted by phasic contractions of paravertebral (Kantor et al 2001) and pelvic floor muscles (Hodges et al 2007;Talasz et al 2011).…”