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Author: Y.-W. Liu, Y.-L. Hsu, W.-Y. Chang (2014-01-14); recommendation: Yeh-Liang Hsu (2014-01-14).
Note: This paper was presented in The 9th World Conference of the International Society for Gerontechnology (ISG 2014), Taipei, Taiwan, 2014/06. Gerontechnology 2014; 13(2):254

Development of a soft motion sensing mattress for tele-monitoring applications

Purpose  The bed is an integral part of our daily lives. Tele-monitoring of bed-related events provides valuable information of the status of an older adult. Many care systems have been developed based on events detected in bed, for example, detection of bed-exit and fall events1, recognition of sleep pattern and quality2, prediction of early signs of illness3, and the monitoring of obstructive sleep apnea syndrome (OSAS)4. In such systems, motion sensing in bed, or “bed actigraphy”, is the core technique. This paper presents the development of a commercialized soft motion-sensing mattress, WhizPAD, for unobtrusive sensing of body motion in bed (Figure 1).  Method  WhizPAD is a thin mattress pad made of memory foam and conductive textile materials. Instead of adding sensing components into the bed, WhizPAD is designed into a mattress with motion sensing capability using the same material and fabrication process of the bedding manufacturer, so that the mattress is comfortable, flexible in use, easy to install, and low cost. The average resistance of the textile-based piezoresistive sensor decreases monotonically with applied pressure in the range of 1,800-4,300Pa, which is equivalent to pressure caused by the presence of an adult. Given the event algorithms implemented in a bedside data processor, the pressure signals collected by WhizPAD can be used to detect on/off bed, sleep posture, movement counts, and respiration rate. Integrated with information and communication systems, caregivers can maintain awareness of older adults’ daily activities and needs by using their mobile devices to access the WhizPAD for real-time monitoring and historical data record of bed-related activities, as well as receiving service reminders and alerts for abnormal events.  Results & Discussion  With the body-shaped memory foam atop the sensing layer, WhizPAD also helps to decrease the stress applied on the skin. The average body pressure is 17.2% lower when the WhizPAD is put on top of a standard mattress of a nursing bed. In a series of functional tests, sensitivity and positive predictive value (PPV) of recognizing the basic bed-related events ranges from 0.79 to 1.00 (Table 1). WhizPAD outputs the respiration rate every 20 second. The average difference of respiration per minute output by WhizPAD is 0.63/min higher than the integer number of complete respiration cycle detected by Polysomnography (PSG). WhizPAD is being sold in department stores and has been implemented in nursing homes in Taiwan. Additional sensors for activity of daily living (ADL) monitoring, such as infrared sensor for human movements and electric current sensor for electrical appliance usage, are being integrated with the bedside device of the WhizPAD, so that it can be extended into a bed-centered telehealth system.

References

1.     Bruyneel, M., Libert, W., Ninane, V., “Detection of bed-exit events using a new wireless bed monitoring assistance”, Int J Med Inform. 2011, 80(2): 127–132.

2.     Cheng, C. M., Hsu, Y. L., Young, C. M. “Development of a portable device for tele-monitoring of physical activities during sleep”, Telemedicine and e-Health. 2008, 14(10): 1044-1056.

3.     Mahnot, A., Popescu, M. “FUMIL-Fuzzy Multiple Instance Learning for early illness recognition in older adults”, Fuzzy Systems (FUZZ-IEEE), 2012 IEEE International Conference. 2012, 1-5.

4.     Bruyneel, M., Van den Broecke, S., Libert, W., Ninane, V., “Real-time attended home-polysomnography with telematic data transmission”, Int J Med Inform. 2013, 13: 57-59.

Keywords: Bed actigraphy, textile-based sensor, motion sensing, sleep monitoring

Table 1. Sensitivity and PPV of recognizing basic bed-related events

Functions

On/off bed

Sleep posture

Movement count

Types

Lying flat

Lying side

Sensitivity

1.0

0.79

0.92

1.00

PPV

1.0

0.86

0.84

0.94

Figure 1. The soft motion-sensing mattress WhizPAD

Figure 1. The soft motion-sensing mattress, WhizPAD