Project Proposal

P.O. Pro

WIRELESS REFLECTANCE PULSE OXIMETER

October 27, 2004

Team # 3

James Hart

Sofia Iddir

Rob Mahar

Naomi Thonakkaraparayil

I. Executive Summary

Blood oxygen content is now considered the 5th vital sign, joining: temperature, respiratory rate, heart rate and blood pressure [Briggs, 1999; Hill, 2000]. One of the main advantages of pulse oximetry is that measurements are taken non-invasively through optical measurements. The P.O. Pro is a wireless reflectance pulse oximeter device designed to monitor the blood oxygen content and pulse rate of newborn babies and small children. Parents will be able to rest easier knowing that if their child stops breathing or is having trouble breathing at any point, they will be notified by an alarm going off from a portable beeper device.

The P.O Pro will be available for a reasonable price at local retail stores without the need for prescription or any type of patient authorization, since it will not need Food and Drug Administration (FDA) approval. Of the other pulse oximeters on the market, none were implemented using a sensor on the ankle the way the P.O. Pro is designed, and only one other currently features a design for small children. The P.O Pro targets a niche in marketing that will allow it to be an affordable way for every parent to feel more comfortable when they put their children to bed.

Figure 1: Potential final product (P.O. Pro)

II. Statement of Need

A pulse oximeter measures and displays the pulse rate and the saturation of hemoglobin in arterial blood. This saturation of hemoglobin is a measure of the average amount of oxygen bound to each hemoglobin molecule.

The P.O Pro is to be feasible and straightforward enabling parents to operate the device on their child in the comfort of their homes. The final product should consist of a sensor module, a monitor and an alarm. The sensor is to be placed on a peripheral tissue bed on the child’s ankle. The monitor should be able to receive telemetric data through a signal from a sensor. The monitor along with an alarm could be placed in a different room, for instance, the parents’ room. The alarm must sound if an abnormal level of oxygen or pulse rate is detected.

In addition to infants and toddlers being the primary target, the product should be designed in such a way that it could be modified to further target a broader population such as athletes.

There is a large variety of Pulse Oximetry products available in the market, but none like the P.O Pro. Below are a few products that have certain similar aspects to that of the wireless reflectance pulse oximeter to be designed. One of the products currently available is the Avant® 4000 System with Bluetooth® Wireless Technology. The lightweight wrist-worn patient module wirelessly sends data to a small tabletop display, improving patient mobility and reducing bedside clutter. Another similar product is the SPO Medical Wireless PulseOx 6500 system which is compact, portable and operates in a wireless mode. The unit transmits data to a compact stand alone display and alarm unit. This product is ideal for clinical and ambulatory related applications.

The PedOMetrix which is currently under construction is similar to the design of the P.O. Pro. “The PedOMetrix is the trademark for SPO-USA'sWellness Baby Monitor (WBM), presently in development. The PedOMetrix trademark on a baby monitor will theoretically have the ability to detect changes in the baby's heart rate caused by a reduction in oxygen. The WBM is being designed to sound an alarm as soon as the baby's blood oxygen level begins to drop from a lack of breathing.This will occurwell before the baby's heart stops fromoxygen deprivation. This technique will allow for the caregiver to safely wake the baby. PedOMetrix baby monitors are presently in development and scheduled to be available in retail stores in 2005/6.” (Figure 2)


http://www.spo-usa.com/pages/2/index.htm

Figure 2: The PedOMetrix; a trademark for SPO-USA'sWellness Baby Monitor (WBM)

After conducting a patent research, it was determined that there are no patents that have currently been issued that would prohibit the construction of the P.O. Pro device. A patent that has been issued that is related to the P.O. Pro is an infant neonatal pulse oximeter sensor. This patent is for an improved infant pulse oximeter sensor substrate which conforms to the shape of the infant’s foot. In this design, the pad conforms to the heel while the detector is place on the top of the foot which is held in place with a stretchable sock. The rest of the issued patents are more generic patents that would not influence the design of P.O. Pro.

III. Project Description

Objective:

The P.O. Pro will monitor the blood oxygen content of infants and small children with the use of an LED and photodiode sensor. The information will then be sent using a wireless transmitter integrated circuit device to a bedside monitor. The wireless transmitter and receiver utilize Bluetooth Technologies. The monitor device will display the blood oxygen content on a digital display as well as the pulse rate of the child. This information is then sent to a portable beeper device that the parent can carry in their pocket or attach to their belt. If the child’s blood oxygen content or pulse rate drops below normal levels for any reason, an alarm will sound on the beeper device to alert the parents of a problem. The beeper will have a two figure digital display to show the oxygen content in the blood and an LED that flashes with the child’s pulse.

The sensor device will be attached to the ankle of the child using a flexible ankle band. Both the sensor device and the beeper device will be powered using rechargeable 3.6 Volt lithium batteries that are approximately the size of ½ of one AA battery. The bedside monitor device will be powered from a wall outlet. Below in table 1 are the preliminary technical specifications to be used in the design of the P.O Pro.

ELECTRICAL PARAMETERS / Sensor / Monitor / Alarm
Display / Minimum Number of Characters / 0 / 20 / 15
Minimum Height x Length x Width (Inches) / 0.5x2x1 / 2x6x3 / 1x3x1.5
Illumination / Visible under all lighting
Transmitter / Range (Feet) / Sensor → Monitor = 30 Monitor → Alarm=100
Physical Path / Transmitted data must pass through obstructions
Voltage Input / 5 Volts
Voltage Output / 18 Volts
Power Input / 10 Watts
Power Output / 1.8 Watts
Current Capabilities / 100 Milliamps - 2 Amps
Harmonic Distortion / Sample Rate of 50 Hertz per Channel
Stability / Drop Test
Accuracy / 3%
Precision / 95% Confidence Limit of Less than 3%
MECHANICAL PARAMETERS / Sensor / Monitor / Alarm
Weight / Maximum Weight / 3 Oz / 2-3 Ibs / 4 Oz
On/Off Switch / Minimum Size (Inches) / / / 0.25x0.125 / 0.25x0.125
MATERIAL PARAMETERS
Materials / Non-irritant / Polymer / Polymer
Color / Color of Body / Blue/Pink / Black / Black
SOFTWARE / Sensor / Monitor / Alarm
Machine Dependent / Wait Times (Seconds) / 20 / / / /
Maximum Execution Speed / 2 . / 2 / 2
Termination/Restart / / / 1 Button / 1 Button
Visibility Distance (Feet) / / / 10 to 15 / 10 to 15
HOUSE KEEPING / Recharge after use or every 12 hours

Table 1: Technical Specifications for the P.O. Pro

Methods:

Gases are not particularly soluble in blood, therefore for effective oxygen transport; a secondary method of transport is required. The compound hemoglobin provides a binding mechanism that allows oxygen to be transported through the blood. A lack of proper oxygen flow to cells can cause damage to the cells or even cell death if prolonged. When cells do not get enough oxygen the metabolic pathways in the cell that provide fuel slow down, creating a shortage of usable fuel for the cell. Hemoglobin therefore plays an important role in transporting the necessary amount of oxygen through the body. Hemoglobin changes color when oxygenated. An oxygenated hemoglobin molecule is bright red, while deoxygenated hemoglobin molecule is dark red (Figure 3).

Figure 3: Hemoglobin molecules are contained within red blood cells.

This color difference is used in the application of pulse oximetry. Pulse oximetry is a non-invasive process that measures oxygen saturation levels () by monitoring the percentage of hemoglobin (Hb), which is saturated with oxygen as well as measuring the heart rate.

The chemical binding of the different types of hemoglobin species changes the physical properties of the hemoglobin as well. Figure 4 shows the extinction coefficient of the oxyhemoglobin and deoxyhemoglobin at wavelengths in the range of interest in pulse oximetry. The absorbance of light in the red region of the spectrum is much higher for deoxyhemoglobin than for oxyhemoglobin. The deoxyhemoglobin is more transparent to light from the infrared region than the oxyhemoglobin.

Figure 4: Light absorption characteristics of two to types of hemoglobin

Pulse oximeters have been available for a little more than a decade, and have become a standard monitoring device in hospital critical care units, surgical theaters and at home. The P.O Pro will be able to identify changes in a baby's heart rate caused by a decrease in the oxygen level. As soon as the baby's blood oxygen level begins to drop from a lack of breathing, an alarm will sound, and the baby can be safely woken up. Premature infants, particularly those born more than seven weeks early, have apnea. Having apnea means there are times when the baby stops breathing (apnea spells). The condition of Apnea causes a sudden stop in breathing for more than ten seconds and a drop in heart rate below 90 beats per minute. Apnea may happen once or many times a day. The more immature the baby is, the more frequent the apnea spells are. The P.O. Pro would therefore be invaluable for any child since even healthy babies could face breathing problems for various reasons including improper sleeping position.

The basic schematic representation of how the P.O. Pro analyzes blood oxygen content can be seen in Figure 5 below. Data is collected at the sensor and sent to the patient module. The patient module or bedside monitor then performs the analysis of the data using the microprocessor. Data is subsequently displayed at the monitor and sent to the portable alarm or beeper device.

Figure 5: An illustration of a main block diagram of a pulse oximeter system.

The sensor contains two low-voltage, high-intensity LEDs as light sources and one photodiode as a light receiver. One LED emits red light (approximately 660 nm) and the other emits infrared light (approximately 940 nm). The absorbance is measured directly from the backscattered light in the blood (Figure 6). The LEDs are alternately illuminated using a four-state clock. The photodiode signal representing light from both LEDs in sequence is amplified and then separated by a two-channel demodulator, one channel sensitive to the infrared light waveform and the other sensitive to the red light waveform. These signals are filtered to remove the LED switching frequency as well as electrical and ambient noise, and then digitized by an analog-to-digital converter (ADC). The digital signal is processed by the microprocessor to identify individual pulses and compute the oxygen saturation from the ratio of the signal at the red wavelength compared to the signal at the infrared wavelength.

Figure 6: A reflectance pulse oximeter measuring the amount of light reflected back to the probe.

The most important component of a pulse oximeter system is the microprocessor. The microprocessor along with memory, input/output devices, communication circuits and additional peripheral devises constitutes the microprocessor based system (MBS). In this particular design project a microcontroller is to be utilized as it consists of a microprocessor, additional memory, ports and certain controls all built in the same chip. This replacement ensures minimal power consumption and size. The main power transformer for the microprocessor and data display is located in the monitor and isolated from the patient to prevent electric shock.

The microcontroller and data converters are programmed to allow the signal from the sensor to be digitized, analyzed, processed, and converted back to analog in order to illuminate the LEDs on the monitor and beeper device. Two sets of wireless transmitter/receiver pairs will be used to send the data collected by the sensor to the monitor then to the beeper device (Figure 7).

Figure 7: The Two Wireless Communication Pathways of the P.O. Pro

The design team is exploring two specific options for these devices. The first option is the RXM-900-HP3 Transmitter/Receiver pair which are high performance Rf modules. These devices send and receive analog or digital information in the 902-928 MHz range, and have a range of up to 1000feet. The HP3 pair will cost approximately $6.25 for the pair. The second option is produced by a company called Atmel Inc, is a monolithic transmitter/receiver pair that features Bluetooth™ wireless technology. This model, the T7024 features a current-saving standby mode and high efficiency with a 3 volt supply. The price of this pair is close to $10.00.

A schematic representation of how the information collected is sent from the sensor to the monitor and from the monitor to the beeper device can be seen in Figure 8 below.

Figure 8a: Schematic Diagram of the Wireless Data Transmitter Device

The above diagram (Figure 8a) shows how data from the sensor is sent to a modulator inside the unit on the subject’s leg which then sends the modulated signal to the Rf amplifier and eventually to the antenna which in turn sends the data as an Rf signal. This Rf signal is then received by the receiver device represented below (Figure 8b). Data is also sent by a transmitter within the monitor to the beeper device in the same manner.