Author: Hong, Tung Ho
Title: Biomechanical study of sleeping support and system optimization based on spine alignment
Advisors: Zhang, Ming (BME)
Degree: Ph.D.
Year: 2023
Subject: Spine
Hong Kong Polytechnic University -- Dissertations
Department: Department of Biomedical Engineering
Pages: xxiv, 190 pages : color illustrations
Language: English
Abstract: Sleep is a fundamental activity for maintaining health; people usually spend one-third of their time sleeping. The sleeping support system influences the spine alignment and impacts musculoskeletal health, sleep quality, and overall comfort. Previous studies suggest the sleeping support system should keep the spine in its neutral shape so that the intervertebral discs can be unloaded and rehydrated. However, limited studies have been conducted to measure spinal curvature in the position of lying supine because the back is in contact with the bed, making it challenging to observe. In addition, few studies have focused on disc loading in the supine position.
This study aims to understand the changes in spine alignment caused by sleeping support. The internal stress was revealed through computational simulation. The research results will help develop better sleeping support systems and improve sleep health.
A novel device was developed to measure the spine curvature in the supine position. This device contains a sensor tape and a tiny control box. The sensor tape was constructed based on a chain of inertial sensors, and it is thin and flexible with little influence on sleep posture. Sensors were assembled on self-developed flexible circuit boards using surface mount technology to achieve low thickness and high flexibility. Sensor data was read by the control box and sent to a computer by wireless connection. A special algorithm was developed to restore sensor inclinations to multiple arcs and connect them to curvature with high accuracy. The graphical user interface was programmed to display the shape of the sensor tape in real-time. The concept of axial tilt was introduced, the tilt angle can be displayed on the graphical user interface in real-time, and any abnormally twisted sensor will have a red cross warning on the graphical user interface. When measuring a circle with a diameter of 200 mm, the device's measurement accuracy is about 99%.
Experiments were conducted; volunteers lay supine on three mattresses with different stiffness. They are named as hard, medium, and soft mattress; the indentation load deflection of mattresses was 120, 42, and 20 lbs, respectively. A cervical pillow was used to support the craniocervical region. The curvature measurement device was used for the measurement of the spinal curvature. Compared to the medium mattress, experimental results show that the head was raised by 30.5 ± 15.9 mm, and the neck was raised by 26.7 ± 14.9 mm if lying on the soft mattress. The lumbar lordosis fell by 10.6 ± 6.8 mm if lying on the hard mattress.
Finite element models were developed for biomechanical investigation. The result of the computational simulation showed a 49% increase in the peak cervical disc loading with the head-raised posture while lying on the soft mattress. High disc loading is not conducive to disc rehydration, and this problem should be considered when selecting a soft mattress. High peak contact pressures were observed if lying on the hard mattress; high contact pressures may cause discomfort and skin ulcers. Therefore, the hard mattress can be considered unsuitable for use. The computational simulation discovered insufficient upper back support when using the cervical pillow. This finding establishes a direction for product improvement.
In conclusion, novel devices were developed to address the gaps in existing research, including a curvature measurement tape that can measure the covered back in the supine position and a human finite element model to predict biomechanical information. This study found that the torso sank deeper in the soft mattress, but the head and neck sank less, resulting in a forward head position in the bed. The elevated head and neck caused a 49% increment in cervical disc peak loading, while the same pillow was used on the softer mattress. In that case, the head and neck support becomes stronger and may negatively impact musculoskeletal health, so it is necessary to consider using a softer or lower pillow.
Rights: All rights reserved
Access: open access

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