Safely Light and Evaluate Extraordinary Physiology (SLEEP)

Safely Light and Evaluate Extraordinary Physiology

Joseph Hollmann

1 Introduction

Over 4 thousand infants die each year from sleep-related causes such as sudden infant death syndrome (SIDS). These sleep-deaths have been correlated to a variety of factors including sleep position, overheating, smoke inhalation, and the presence of soft objects which can induce suffocation. The lack of a single, clear cause is stressful for new parents and has given rise to a growing market segment devoted to infant sleep safety.

To help combat these deaths, we propose to use GE's LED technology to monitor a sleeping baby's heart rate, oxygen saturation, and body temperature during sleep time and alert parents to potential pathological states, and thus, creating the opportunity for intervention. The device will monitor the these vital signs by using non-contact sensing techniques, so it will be unnoticed by the baby and he or she is still able to get the sleep they need. In this proposal, I will discuss the techniques necessary for developing this system, named safely light and evaluate extraordinary physiology (SLEEP), with the goal of incorporating this into General Electric's new LED-based lighting fixtures.

I chose to focus on the infant safety market in part because I am expecting to be a dad this Fall. However, it is also important to note that there are 4 million babies born each year in the US and the market for infant safety-related products has exploded.

Devices such as baby monitors with cameras have flooded the space and are capturing a growing market share despite the limitation that devices require constant monitoring to be effective. Providing a non-contact and invisible monitoring system offers the potential for capturing a large portion of this market while also offering parents peace of mind.

I also note that even though my focus will be on infants, it should be clear this new lighting fixture can also be utilized for monitoring other at risk populations, such as the elderly and the infirm. Furthermore, the proposed device detects the presence of

Individuals and may also benefit security, and home safety applications.

2 SLEEP Design

The device will be designed to allow a baby to sleep in a crib without wires or attachments. Even the LED's will use light that is invisible, so the babies will not know it’s there. Despite being unnoticed, the SLEEP device will constantly monitor the baby's heart rate, oxygen saturation, and temperature using non-contact optical techniques, and will alert parents if something goes wrong. SLEEP will also incorporate sensors and intelligent algorithms that will minimize false alarms. Furthermore, the device will use established technologies like LED's and thermopiles to minimize the lighting fixture's

final cost. In the sections below I will discuss how the SLEEP device will operate.

2.1 Pulse Oximeter

A pulse oximter uses light to non-invasively measure the heart rate and oxygen saturation levels. It accomplishes this by using two different wavelengths of near infrared (NIR) light to illuminate the subject and then measures the diffusely reflected light. These wave-lengths are typically chosen to reside on either side of Hemoglobin's isobestic wavelength (approximately 810 nm) - for the sake of clarity we shall assume these wavelengths are 750 nm and 850 nm. The light from these LEDs travels through the tissue and is absorbed by hemoglobin in the blood, which is responsible for delivering oxygen to the body. The heart supplies this to the body by pumping new blood into our arteries about once a second for adults (or, up to 3 times a second for infants) and creates a pulsatile change in the concentration of hemoglobin. This, in turn, changes the amount of light absorbed. By measuring this change in light in time we can directly measure the heart rate. In addition, hemoglobin absorbs light in the NIR spectrum differently if it is carrying oxygen or not. We can figure out how much light is absorbed at each wavelength (remember, 780 nm and 850 nm) by turning the LEDs on and off (pulsed) at different times and making corresponding measurements. By comparing the measurements to each other and using well known equations in biomedical optics we can determine the ratio of oxygen carrying hemoglobin (or oxygen saturation) present. We can also take advantage of the fact that LEDs can detect light and use one as a photodetector for the pulse oximeter. This allows us to keep the component count down.

NIR light has the added advantage of being “invisible" to the human eye. This means the device means the device can monitor the baby without being seen, and may even be used while the subject is sleeping.

2.2 Thermal Measurements

Thermal radiation is light that is emitted from a heated surface. Its characteristics depend on the temperature of the surface. For instance, a healthy infant will have a temperature between 97 to 100 degrees Fahrenheit and emits infrared light with a peak around 10 microns. This light coming from the body can be measured using a low cost infrared sensor called a thermopile thus allowing for a non-contact measurement of body temperature. As shown in Figure 1, the thermopile will will allow SLEEP to determine when the infant is present and when it should start collecting measurements. Furthermore, it enables remote measurement of the infant's body temperature.

2.3 Sensor Geometry

Just as GE's current bulbs use multiple LEDs to illuminate a room, the SLEEP device will use multiple sensor clusters to ensure the entire crib is being monitored. An example, shown in Figure 2, demonstrates the concept where SLEEP acquires thermal measurements from several instrument clusters to find the baby. The baby is on one side of the crib so one cluster (shown in blue) measures a bare crib. However, another cluster (shown in red) registers the presence of the baby and begins measuring vital signals.

2.4 Other applications

Though the focus of this proposal has been infants, the SLEEP device can also be useful in monitoring the elderly and the infirm. Currently, blood oxygen levels, heart rate, and temperature are typically collected by devices in that require contact with patients thus limiting their use to critical care settings. However, SLEEP can easily be placed in a light fixture and provide non-contact, unobtrusive safety checks on our loved ones without inconveniencing them.

3 Conclusions

In this proposal we present a LED-based device that will help reduce infant sleep related deaths. This device will use near infrared and infrared light to provide non-contact blood-oxygen, pulse rate, and temperature measurements. We also discuss how we can combine these measurements to produce an accurate update of an infant's wellbeing.