Nursing homes and welfare facilities for the elderly use wheelchairs to improve their level of activity and prevent them from becoming bedridden. Although wheelchairs are a useful aid, most elderly individuals who regularly use wheelchairs not only have walking problems but also have functional problems, such as muscle weakness due to age and paralysis due to cranial nerve disease. Because 80%–90% of the time that elderly people spend in wheelchairs is spent using the wheelchairs as chairs to sit in, this long usage time causes a problem.
The sitting posture also worsens over time, resulting in either “sacral sitting” with the pelvis tilted backwards or “slanted sitting” with the trunk inclined to the side. The loss of muscle strength leads to difficulties in maintaining a sitting posture in the wheelchair. These poor sitting postures can severely restrict movements of the upper limb and interfere with day-to-day activities. In addition to pressure ulcers, poor sitting postures can cause eating, swallowing, and digestive difficulties. Furthermore, respiratory movement and hemodynamics are also affected adversely.
Previously, studies have investigated the effects of different sitting postures qualitatively, assessing upright sitting, slouching, and forward tilting. Using radiographic imaging, Lin et al. (2006) compared the angles between individual sacral and lumbar vertebrae in different sitting postures in a portion of their subjects; however, they did not quantitatively show the pelvic inclination angle in other subjects.
In 2006, an international standard defining clinical guidelines for measuring sitting postures, the ISO16840-1:2006, was adopted. Following this, quantitative measurements of sitting postures in clinical settings gained momentum. ISO16840-1:2006 describes in detail, the method to measure a sitting posture by projecting two-dimensional planes of the sagittal, frontal, and horizontal planes. Measuring instruments that comply with ISO16840-1:2006 have been developed and are expected to come into use for various assessments and studies. Kemmoku et al. (2013) used sitting posture measurements to define bearing surface pressure and displacement force. Bearing surface pressure was divided into two phases: before and after, with the peak angle being a backward pelvic inclination angle of 15°. Displacement force increased gradually from 15° to 20°. However, from 20° onwards, displacement force increased appreciably. Few studies using sitting posture measurements, such as this one, have been published so far.
This study aims to elucidate and compare changes in autonomic nervous activity as a result of different wheelchair sitting postures in healthy individuals using postural measurement methods and to convert the results into normative data. The study also aims to assess assistive technology for wheelchair sitting postures for preventing secondary disorders in wheelchair-bound elderly individuals due to long periods of sitting and devise interventions for improving their functional activities.
Participants of the study comprised 13 healthy adults (without any spinal disorders) who could maintain a sitting posture throughout the duration of the measurements. All participants were female. The mean age was 23 ± 6 years.
Changes in autonomic nervous activity were measured for seven different wheelchair sitting postures. The postures changed in increments of 5° from an intermediate pelvic backward inclination in the sagittal plane from 0° to 30°.
Pelvic backward inclination angle was noninvasively measured using Horizon (Society for Research on Sitting Posture Measurement). This instrument measures sitting posture in accordance with ISO16840-1:2006. We adjusted the sitting position on the bearing surface by having subjects shift back and forth by small degrees. This was done to attain specific pelvic backward inclination angles as indicated by pointers on the anterior superior iliac spine (ASIS) and the posterior superior iliac spine (PSIS). Once the sitting posture was achieved, it was recorded using digital photographs in the sagittal plane (from the right side). Sitting posture measurement software, Rysis (Handa et al., 2010), was then used to analyze the participants’ posture and angles of body segment lines(Head line, Neck line, Sternum line, Trunk line, Abdominal line, Pelvic line) from the images taken.
Between sitting posture measurements, a 5-minute rest period was scheduled. During this time, electrocardiographic readings were recorded with a BioLog DL-2000 device and DL-320 ECG and respiration sensor (S&ME, Tokyo, Japan). Using these readings, autonomic nervous activity was analyzed at a low frequency (LF) of 0.04–0.15 Hz and a high frequency (HF) of 1.15–0.40 Hz using the frequency analysis program MemCalc (GMS, Tokyo, Japan). Measurement values for each pelvic backward inclination angle were comparatively analyzed using the statistical software SPSS 18.0 with the significance level set at 5%.
This study was approved by the research ethics committee of the Japanese Red Cross College of Nursing. On the test day, the subjects were provided with written and verbal explanations that it was their right to choose to collaborate in this study, they were free to refuse to participate, and their privacy would be protected. After they provided their consent, the test was initiated.
A significant difference was seen in the LF/HF ratio, a sympathetic nervous activity index, between the intermediate pelvic inclination angle of 0° and the angles of 15° and 30°. A significant difference was also seen between pelvic backward inclination angles of 5°and 25°.
At pelvic backward inclination angles of 30°, 25°, and 20°, the HF ratio, a parasympathetic nervous activity index, was significantly higher than that with 0°, 5°, and 10°. At a pelvic backward inclination angle of ≥20°, parasympathetic nervous activity increased compared with that from 0° to 10°. Significant differences were also seen between 30° and the angles of 15° and 20°, between 25° and the angles of 20°, 15°, and 0°, and between 5°, 10° and the angle of 0°.
It has been reported that parasympathetic nervous activity becomes dominant while resting in the supine position. In contrast, sympathetic nervous activity dominates when the head is lifted up. In this study, we found that sympathetic nervous activity was significant in an upright posture with a pelvic inclination angle of 0° or 5° and parasympathetic nervous activity became dominant during a “slanted sitting” posture with pelvic inclination angles of ≥20° when compared with those of 0°–10°.
We also found that displacement force in the sacral region increased more at a pelvic inclination angle of 20°. Parasympathetic nervous activity was dominant at 20°, and it appears that the “slanted sitting” posture along with dominant parasympathetic nervous activity led to subjects being in a prolonged relaxed state, which made it easy for sitting posture to collapse. This relaxed state was brought about by a predominant parasympathetic nervous activity while in a slanted position. Furthermore, because pelvic and trunk inclinations differed between participants, we hope to proceed with further basic research. This future research should elucidate the postural characteristics of wheelchair-bound elderly individuals and clarify the assessment viewpoints of elderly individuals requiring assistance for sitting posture.
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