Postural control and ventilatory drive during voluntary hyperventilation and carbon dioxide rebreathing

Coupling Between Posture and Respiration Among the Postural Chain: Toward a Screening Tool for Respiratory-Related Balance Disorders

Alteration of posturo-respiratory coupling (PRC) may precede postural imbalance in patients with chronic respiratory disease. PRC assessment would be appropriate for early detection of respiratory-related postural dysfunction. PRC may be evaluated by respiratory emergence (REm), the proportion of postural oscillations attributed to breathing activity; assessed by motion analysis) as measured from the displacement of the center of pressure (CoP) (measured with a force platform). To propose a simplified method of PRC assessment (using motion capture only), we hypothesized that the REm can appropriately be measured derived from single body segment the postural oscillations of a single body segment rather than whole body postural oscillations. An optoelectronic system recorded the breathing pattern and the postural oscillations of six body segments in 50 healthy participants (22 women), 34 years [26; 48]. The CoP displacements were assessed using a force platform. One-minute recordings were made in standing position in four conditions by varying vision (eyes opened/closed) and jaw position (rest position/dental contact). The Sway Path and Mean Velocity of the CoP and of the representative point of each body segment were recorded. The REm was measured along the major and the minor axis of the 95% confidence ellipse of the CoP position (REm_MajorAxisCoP; REm_MinorAxisCoP) and of that of each body segment. SwayPathCoP and MVCoP varied widely across the four conditions (par< 0.000001). These changes were related to the visual condition ( [Formula: see text]) while the jaw position had no effect. The REm_MajorAxisCoP and the REm_MinorAxisCoP changed across conditions ( [Formula: see text]); this was related to vision while jaw induced changes only for the REm_MinorAxisCoP. The SwayPath, the Mean Velocity and the REm of all body segments were significantly correlated to the CoP, but the highest correlations were observed for the thorax, the pelvis and the shoulder. PRC may be assessed from the postural oscillations of thorax, pelvis and shoulder. This should simplify the evaluation of respiratory-related postural interactions in the clinical environment, by using a single device to simultaneously assess postural oscillations on body segments, and breathing pattern. In addition, this study provides reference data for PRC and its sensory-related modulations on body segments along the postural chain.

Relationship between disturbances of CO2 homeostasis and force output characteristics during isometric knee extension

To determine whether disturbances of CO₂ homeostasis alter force output characteristics of lower limb muscles, participants performed four isometric knee extension trials (MVC_30%, 10s each with 20-s rest intervals) in three CO₂ conditions (normocapnia [NORM], hypercapnia [HYPER], and hypocapnia [HYPO]). Respiratory frequency and tidal volume were matched between CO₂ conditions. In each MVC_30%, the participants exerted a constant force (30% of maximum voluntary contraction [MVC]). The force coefficient of variation (Fcv) during each MVC_30% and MVC before and after the four MVC_30% trials were measured. For the means of the four trials, Fcv was significantly lower in HYPER than in HYPO. However, within HYPER, a significant positive correlation was found between the increase in end-tidal CO₂ partial pressure and the increase in Fcv. MVCs in NORM and HYPO decreased significantly over the four trials, while no such reduction was observed in HYPER. These results suggest that perturbed CO₂ homeostasis influences the force output characteristics independently of breathing pattern variables.

Inspiratory muscles contributions to postural control in healthy older women

It was hypothesized that induced inspiratory muscles effort, by an acute inspiratory resistance load (IRL) use, increases the postural sway and the neuromuscular activity of postural muscles in older adults. Fifteen older women breathed spontaneously, controlled (15 cycles/minute), and with acute IRL (15 cycles/minute and target load of 30 % of maximal inspiratory pressure) in random order. The breathing tasks were performed in an orthostatic position (eyes closed) during one minute on a baropodometer plate to acquire center-of-pressure (COP) oscillations and with electromyography (EMG) recording. The root mean square (RMS) of EMG was calculated. COP oscillations were higher with IRL use than spontaneous and controlled breathing tasks, but not between spontaneous and controlled conditions. EMG activity of Tibialis anterior and Soleus muscles were higher with IRL use in comparison to spontaneous and controlled breathing conditions. In conclusion, IRL use influenced the postural control through increased postural sway and neuromuscular compensation of the lower limbs in older women.

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

PURPOSE

In healthy humans, postural and respiratory dynamics are intimately linked and a breathing-related postural perturbation is evident in joint kinematics. A cognitive dual-task paradigm that is known to induce both postural and ventilatory disturbances can be used to modulate this multijoint posturo-ventilatory (PV) interaction, particularly in the cervical spine, which supports the head. The objective of this study was to assess this modulation.

METHODS

With the use of optoelectronic sensors, the breathing profile, articular joint motions of the cervical spine, hip, knees and ankles, and centre of pressure (CoP) displacement were measured in 20 healthy subjects (37 years old [29; 49], 10 females) during natural breathing (NB), a cognitive dual task (COG), and eyes-closed and increased-tidal-volume conditions. The PV interaction in the CoP and joint motions were evaluated by calculating the respiratory emergence (REm).

RESULTS

Only the COG condition induced a decrease in the cervical REm (NB: 17.2% [7.8; 37.2]; COG: 4.2% [1.8; 10.0] p = 0.0020) concurrent with no changes in the cervical motion. The CoP REm (NB: 6.2% [3.8; 10.3]; COG: 12.9% [5.8; 20.7] p = 0.0696) and breathing frequency (NB: 16.6 min-1 [13.3; 18.7]; COG: 18.6 min-1 [16.3; 19.4] p = 0.0731) tended to increase, while the CoP (p = 0.0072) and lower joint motion displacements (p < 0.05) increased.

CONCLUSION

This study shows stable cervical spine motion during a cognitive dual task, as well as increased postural perturbations globally and in other joints. The concurrent reduction in the PV interaction at the cervical spine suggests that this "stabilization strategy" is centrally controlled and is achieved by a reduction in the breathing-related postural perturbations at this level. Whether this strategy is a goal for maintaining balance remains to be studied.

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

Obstructive sleep apnea syndrome (OSAS) is associated with postural dysfunction characterized by abnormal spinal curvature and disturbance of balance and walking, whose pathophysiology is poorly understood. 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 [51–63] (median [quartiles]), apnea hypopnea index 31/h [24–41]) 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. We also estimated posturo-respiratory coupling by measurement of respiratory emergence, obtaining synchronized center of pressure data from a stabilometric platform and ventilation data recorded by an optico-electronic system of movement analysis. Compared with controls, OSAS patients, had cervical hyperextension with anterior projection of the head (angle OD-C7 12° [8; 14] vs. 5° [4; 8]; p = 0.002), and thoracic hyperkyphosis (angle T1–T12 65° [51; 71] vs. 49° [42; 59]; p = 0.039). Along the mediolateral axis: (1) center of pressure displacement was greater in OSAS patients, whose balance was poorer (19.2 mm [14.2; 31.5] vs. 8.5 [1.4; 17.8]; p = 0.008); (2) respiratory emergence was greater in OSAS patients, who showed increased postural disturbance of respiratory origin (19.2% [9.9; 24.0] vs. 8.1% [6.4; 10.4]; p = 0.028). These results are evidence for the centrally-mediated and primarily respiratory origin of the postural dysfunction in OSAS. It is characterized by an hyperextension of the cervical spine with a compensatory hyperkyphosis, and an alteration in posturo-respiratory coupling, apparently secondary to upper airway instability.

Improvements of Shooting Performance in Adolescent Air Rifle Athletes After 6-Week Balance and Respiration Training Programs

CONTEXT

Several factors, such as balance and respiration training programs, have been identified as contributing to a shooting performance. However, little is known about the benefits of these programs on the shooting records of adolescent air rifle athletes.

OBJECTIVE

The purpose of this study was to investigate whether balance and respiration training can contribute to the shooting performance required for adolescent air rifle shooting athletes.

DESIGN

Case-control study.

SETTING

Shooting range.

PARTICIPANTS

A total of 21 adolescent air rifle athletes were recruited from the local school community and assigned to an experimental (n = 11; EG) or control (n = 10; CG) group.

INTERVENTION

The EG performed respiration and balance training for 30 minutes 3 times a week for 6 weeks, and the CG performed balance training only.

MAIN OUTCOME MEASURES

Data were collected on the respiratory function, muscle activity, and shooting record before and after the 6-week intervention.

RESULTS

The forced vital capacity (FVC), forced expired volume in 1 second (FEV1), FEV1 as a percentage of FVC, peak expiratory flow, and maximum voluntary ventilation were significantly increased in the EG, and FEV1 as a percentage of FVC was significantly increased in the CG (P < .05). The FVC and peak expiratory flow postintervention were significantly different between the groups (P < .05). The activity of the right internal oblique (IO) and left IO muscles of the FVC were significantly different in the EG (P < .05). Within-group changes in right external oblique, right IO, and left IO of the maximum voluntary ventilation were significantly increased in the EG (P < .05). The right IO and left IO activity improved more significantly in the EG than CG (P < .05). There was no difference between the groups with respect to the shooting records.

CONCLUSIONS

The clinical significance of this study is the balance and respiration training affected the respiration function capacity and muscle activity, but did not affect the shooting record. Nevertheless, these training are a potential approach method to improve athletes' shooting record.

Acute reduction in cerebral blood velocity on supine-to-stand transition increases postural instability in young adults

We tested the hypothesis that transient deficits in cerebral blood flow are associated with postural sway. In 19 young, healthy adults, we examined the association between the drop in cerebral blood flow during supine-to-stand transitions, indexed by transcranial Doppler ultrasound [middle cerebral artery blood velocity at diastole (MCAdv)] and near-infrared spectroscopy [tissue saturation index (TSI)] and the center of pressure displacement while standing. Participants performed transitions under three conditions aimed at progressively increasing the drop in MCAdv, in a randomized order: 1) a control transition (Con); 2) a transition that coincided with deflation of bilateral thigh cuffs; and 3) a transition that coincided with both thigh-cuff deflation and 90 s of prior hyperventilation (HTC). The deficit in diastolic blood velocity (MCAdv deficit) was quantified as the difference between MCAdv and its preceding baseline value, summed over 10 s, beginning at the MCAdv nadir. Compared with Con, HTC led to greater drops in MCAdv (P = 0.003) and TSI (P < 0.001) at nadir. The MCAdv deficit was positively associated with the center of pressure displacement vector-average using repeated-measures correlation (repeated-measures correlation coefficient = 0.56, P < 0.001). An a posteriori analysis identified a sub-group of participants that showed an exaggerated increase in MCAdv deficit and greater postural instability in both the anterior-posterior (P = 0.002) and medial-lateral (P = 0.021) directions in response to the interventions. These findings support the theory that individuals who experience greater initial cerebral hypoperfusion on standing may be at a greater risk for falls.NEW & NOTEWORTHY Dizziness and risk for falls after standing might link directly to reduced delivery of oxygen to the brain. By introducing challenges that increased the drop in brain blood flow in healthy young adults, we have shown for the first time a direct link to greater postural instability. These results point to a need to measure cerebral blood flow and/or oxygenation after postural transitions in populations, such as older adults, to assist in fall risk assessment.

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

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.

Voluntary control of breathing affects center of pressure complexity during static standing in healthy older adults

Background Physiological/biomechanical systems display high degrees of complexity in their corresponding physiological and/or biomechanical outputs, indicative of normal healthy physiological functioning, though little attention has been paid to potential mechanisms which may affect complexity. Center of pressure (CoP) dynamics also display high degrees of complexity and may be affected via altered respiratory-motor interactions such as during voluntary control of breathing. Purpose The purpose of this study was to investigate the differences in the complexity of CoP dynamics during autonomous vs. voluntary control of breathing and between different voluntarily controlled breathing conditions. Methods Center of pressure recordings were taken from 18 older adults during static standing under three different breathing conditions: 1) neutral breathing, 2) abdominal breathing, and 3) thoracic breathing, the first constituting the autonomous breathing condition and the latter two constituting voluntarily controlled breathing conditions. CoP dynamics were quantified using sample entropy, standard deviation, 95% sway area, and average radial velocity. Repeated measure MANOVAs were used to assess the effect of breathing on CoP dynamics, with top-down application of ANOVAs and pairwise comparison as needed. Results Voluntary control of breathing during both conditions resulted in significantly higher CoP variability and lower sample entropy than during autonomous control of breathing in the mediolateral direction, indicating less complex dynamics and loss of system control. No significant differences between voluntary breathing conditions were observed. Conclusion Voluntary control of breathing significantly affected on CoP dynamics during static standing. The complexity of the postural control system may be affected via alterations in respiratory-motor interactions.

Postural- and respiratory-related activities of abdominal muscles during post-exercise hyperventilation

The present study focuses on the role of superficial abdominal muscles revealed by electromyographic recordings during the maintenance of a bipedal stance perturbed by post-exercise hyperventilation. Twelve healthy subjects performed six 30-s postural tests: one pre-exercise test while breathing quietly, then one test every minute for the 5 min immediately following a maximum-intensity, incremental cycling exercise test. Displacement of the centre of pressure in the sagittal plane was monitored over time. Myoelectric activities of the obliquus externus (OE), obliquus internus (OI) and rectus abdominis (RA) muscles were recorded by surface electromyography (EMG). Metabolic parameters were measured with a portable telemetric device. The change in ventilatory drive induced by exercise was accompanied by a significant increase in both postural sway parameters and EMG activities. For OE and OI, the increased EMG activities were prominent during expiration, whereas OI was silent during inspiration. OE and RA were activated during both expiration and inspiration. It is concluded that the compensation of respiratory disturbances of the erect posture appears to be less effective when minute ventilation increases. The patterns of muscle activity suggest that abdominal muscles are controlled differentially and that their functional coordination is dependent on the respiratory demand.

Postural strategy and back muscle oxygenation during inspiratory muscle loading

PURPOSE

Most healthy individuals show a multisegmental control strategy during challenging standing conditions, whereas others show a rigid ankle-steered strategy, which is assumed as suboptimal. Respiratory-demanding tasks exert a perturbing effect on balance, although the underlying mechanisms remain poorly understood. The purpose of this study was to investigate whether inspiratory resistive loading (IRL) affects postural strategy, back muscle oxygenation, and blood volume during postural control.

METHODS

We assessed the acute effects of increased respiratory effort by measuring the center of pressure displacement in 12 healthy individuals during upright standing on an unstable support surface while breathing against an IRL. Simultaneous ankle and back muscle vibration was used to evaluate the proprioceptive strategy (multisegmental vs ankle-steered) during postural control. Back muscles oxygenation and blood volume were assessed using near-infrared spectroscopy (tissue oxygenation index, deoxyhemoglobin, oxyhemoglobin, and combined hemoglobin).

RESULTS

An increased proprioceptive gain at the ankles and an decreased gain at the back were observed after approximately 7 min of IRL. Retrospectively, the group was subdivided on the basis of the participants' dominant proprioceptive use during a baseline postural control. During IRL, the ankle-steered group showed an increased reliance on ankle proprioception compared with a multisegmental group (-5.9 ± 3.1 and 1.0 ± 1.9 cm, respectively, P < 0.05). Tissue oxygenation index, deoxyhemoglobin, oxyhemoglobin, and combined hemoglobin declined progressively in the ankle-steered group during the IRL (from baseline (100%) to -1%, -1%, -45%, and -18%, respectively, P < 0.05), whereas no decline was found in the multisegmental group (from baseline (100%) to 134%, 82%, 129%, and 153%, respectively, P > 0.05).

CONCLUSION

Individuals who adopted an ankle-steered strategy during IRL showed a progressive decline in back muscle oxygenation and blood volume. In contrast, IRL did not affect back muscle oxygenation and blood volume in individuals who showed a multisegmental strategy in upright standing.

Higher ventilatory responses during and after passive walking-like leg movement in older individuals

Background

Minute ventilation (V·E) during walking has been shown to be higher in older individuals than in young individuals, but the mechanisms underlying the higher ventilatory response is unclear. Central command and peripheral neural reflex are important neural control mechanisms underlying ventilatory response during exercise. Passive leg movement has been used to exclude the influence of central command due to the lack of voluntary activation of muscles. The aim of the present study was to compare the ventilatory response during and after passive walking-like leg movement (PWM) in young and older individuals.

Methods

Eight young subjects (20 ± 2 years) and seven older subjects (70 ± 1 years) participated in this study. Subjects spent 7 minutes in a quiet standing (QS) position. Thereafter, they performed 14-minute rhythmic PWM at 1 Hz and this was followed by 7 minutes of QS.

Results

V·E values during pre-PWM QS were calculated as 1-minute averages using data obtained between 5 and 6 minutes. V·E values at pre-PWM QS in the young and older groups were 8.4 ± 2.1 and 7.5 ± 1.2 l/minute, respectively. V·E values increased significantly at the first minute of PWM to 11.4 ± 2.2 and 10.4 ± 2.5 l/minute in the young and older groups, respectively (P <0.001). In the young group, V·E at the last minute of PWM (9.2 ± 2.0 l/minute) was not significantly different from that at pre-PWM QS due to a decline in V·E, whereas V·E at the last minute of PWM in the older group (9.4 ± 2.2 l/minute) was still significantly higher (P <0.01). On the other hand, V·E at the first minute of post-PWM QS (7.2 ± 1.8 l/minute) was significantly lower than that during pre-PWM QS in the young group (P <0.05) but not in the older group.

Conclusions

Ventilatory response during and after PWM is higher in older individuals than in young individuals. This may be associated with a mechanism(s) other than central command. Our findings may explain part of the higher V·E response while walking in older individuals.

Proprioceptive changes impair balance control in individuals with chronic obstructive pulmonary disease

Introduction

Balance deficits are identified as important risk factors for falling in individuals with chronic obstructive pulmonary disease (COPD). However, the specific use of proprioception, which is of primary importance during balance control, has not been studied in individuals with COPD. The objective was to determine the specific proprioceptive control strategy during postural balance in individuals with COPD and healthy controls, and to assess whether this was related to inspiratory muscle weakness.

Methods

Center of pressure displacement was determined in 20 individuals with COPD and 20 age/gender-matched controls during upright stance on an unstable support surface without vision. Ankle and back muscle vibration were applied to evaluate the relative contribution of different proprioceptive signals used in postural control.

Results

Individuals with COPD showed an increased anterior-posterior body sway during upright stance (p = 0.037). Compared to controls, individuals with COPD showed an increased posterior body sway during ankle muscle vibration (p = 0.047), decreased anterior body sway during back muscle vibration (p = 0.025), and increased posterior body sway during simultaneous ankle-muscle vibration (p = 0.002). Individuals with COPD with the weakest inspiratory muscles showed the greatest reliance on ankle muscle input when compared to the stronger individuals with COPD (p = 0.037).

Conclusions

Individuals with COPD, especially those with inspiratory muscle weakness, increased their reliance on ankle muscle proprioceptive signals and decreased their reliance on back muscle proprioceptive signals during balance control, resulting in a decreased postural stability compared to healthy controls. These proprioceptive changes may be due to an impaired postural contribution of the inspiratory muscles to trunk stability. Further research is required to determine whether interventions such as proprioceptive training and inspiratory muscle training improve postural balance and reduce the fall risk in individuals with COPD.

Effects of breathing on multijoint control of center of mass position during upright stance

Breathing exerts destabilizing effects on postural stability during quiet stance. The authors conducted an experiment to evaluate the role of motor abundance in the organization of the postural synergy compensating for the effects of breathing. They measured the kinematic pattern of covariation among the major joints of the postural chain (ankle, knee, hip, trunk, and neck) as a function of different breathing modes (spontaneous, paced, and increased volume) and different stance instructions (still vs. relaxed) using the uncontrolled manifold approach. Joint variability was structured to preserve the stable position of the center of mass. This result supports the hypothesis that motor abundance of the postural chain plays an important role in the flexible compensation for breathing during quiet stance.