Author(s): IUCHI, T., KIMURA, T., Institution: KOBE UNIVERSITY, Country: JAPAN, Abstract-ID: 1315

INTRODUCTION:
Human quiet standing, a fundamental posture, is mechanically unstable and accompanied by continuous postural sway. Traditionally, this spontaneous sway has been interpreted as a "control error" in postural control and therefore quantified as a measure of balance. Recently, however, it has been suggested that lower-leg muscle contractions associated with spontaneous postural sway function as a muscle pump that contributes to cardiovascular control under gravity, implying a collaborative link between postural and cardiovascular control systems (1–3). However, the control mechanisms underlying this link remain to be elucidated. Respiratory movement has also been shown to influence both standing posture and blood circulation. Therefore, it is essential to consider the involvement of the respiratory control system when examining the collaboration between postural and cardiovascular control. Accordingly, the purpose of this study was to experimentally investigate the response of respiratory movement to changes in venous return during quiet standing, thus aiming to clarify the role of the respiratory center in the collaborative mechanism of postural and cardiovascular regulation.
METHODS:
Fifteen healthy male participants (21-23 years) completed two sets of a quiet sitting task and a quiet standing task, each lasting 330 s. During one of the sets, cuff compression at 40 mmHg, with a duty cycle of 12 s ON and 48 s OFF, was applied to both lower legs to experimentally facilitate venous return. Respiratory flow, ECG RR interval (RRI), beat-to-beat blood pressure, and the foot center of pressure (CoP) were simultaneously recorded and analyzed during time intervals when cuff compression was off.
RESULTS:
A significant main effect of compression was observed in the respiratory rhythm during standing (P < 0.05); the mean power frequency was increased by cuff compression. In contrast, no significant changes in respiratory rhythm were observed during sitting. Additionally, a significant main effect of compression on mean RRI was observed in both the sitting and standing conditions (P < 0.05); mean RRI lengthened in the compression condition. No significant changes were found in mean systolic blood pressure.
CONCLUSION:
The results of RRI and SBP suggest that the blood circulation was effectively controlled in response to the changes in venous return. In this situation, the respiratory rhythm during quiet standing was increased. This may reflect the fact that the output of the respiratory center is modulated in response to changes in venous return.
REFERENCES:
1) Naruse et al. Eur J Appl Physiol 121:251-256, 2021.
2) Garg et al. Am J Physiol 307:H259-264, 2014.
3) Xu et al. Am J Physiol 313:H568–577, 2017.