![Hemoglobin extinction curves. Pulse oximetry uses the wavelengths of 660 nm and 940 nm because these wavelengths are available in semiconductors. The oximeters measure red and infrared light transmitted through and reflected by a tissue bed. There are several technical problems to accurate estimation of SaO 2 by this method. For example, many light absorbers other than arterial Hb are in the transmitted light path (e.g., skin, soft tissue, venous). A group of absorbers in a typical sample of living tissue is shown in Figure 4 [18].](https://www.researchgate.net/profile/Ali-Buelbuel-2/publication/312279299/figure/fig1/AS:450817628086272@1484494706256/Hemoglobin-extinction-curves-Pulse-oximetry-uses-the-wavelengths-of-660-nm-and-940-nm_Q320.jpg)
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International Journal of
Applied Mathematics,
Electronics and Computers
Advanced Technology and Science
ISSN: 2147-82282147-6799 http://ijamec.atscience.org
Original Research Paper
This journal is © Advanced Technology & Science 2013 IJAMEC, 2016, 4(Special Issue), 211–215 | 211
Pulse Oximeter Manufacturing & Wireless Telemetry for Ventilation
Oxygen Support
Ali İhsan Bülbül *1, Serdar Küçük 2
Accepted 3rd September 2016
Abstract: Pulse Oximeter devices are widely used as a non-invasive method for instant monitoring of blood oxygen saturation and heart
rate. In this paper, a wireless microcontroller based pulse oximeter is proposed to measure the oxygen delivered to the patient via the
oxygen flowmeter. In the first step, the signals received from reusable SpO2 sensor (finger probe) are processed by a microcontroller to
determine the blood oxygen saturation and heart rate. Depending on the current blood oxygen saturation value, wireless signals are sent
to the non-invasive ventilation flow meter vacuum regulator to deliver the necessary oxygen into the patient. Oxygen supplied to the
patient is automatically controlled according to the oxygen saturation change.
Keywords: Pulse Oximeter, Oxygen saturation, Ventilation, Oxygen flow meter, Oxygen regulator, Circuit design, Wireless control.
1. Introduction
Oxygen is the common drug to be used in the care of patients
who present with medical emergencies. Currently, ambulance and
emergency department teams are likely to give oxygen to all
breathless a large number of patients [1].
The amount of oxygen saturated hemoglobin in arterial blood is
expressed with oxygen saturation [2]. Formerly, the most
common method of assessing oxygenation was the use of arterial
blood gases [3]. This is painful for patients and has the serious
complications of vascular injury or occlusion and infection. The
methods of applying also pose the risk of needle stick injury to
staff [4].
Today, pulse oximetry is a safe and simple method of assessing
oxygenation [2]. At the same time, they are cheap and easy to
carry devices. Pulse oximeter is a measuring device as peripheral
arterial oxygen saturation in the blood non-invasively. Pulse
oximeter shown in Figure 1, can be monitored from bedside
monitors as used alone. Pulse oximeter is required
intraoperatively monitors. During patient monitoring using pulse
oximeters the early detection of untoward events is the most
important, especially as it may contribute to the prevention of
hypoxic insults [5].
Figure 1. Pulse oximeter.
Pulse oximetry is a routine device used in surgery, intensive care
units and operating rooms, due to its cheapness. It is a non-
invasive device and easy to be used. [6].
Oxygen flowmeter illustrated in Figure 2 is used to give the
oxygen to the patient through the humidifier, nose nozzle and
mask. Vacuum regulator allows patients to adjust the vacuum
level. It has the manometer to see visually the pressure. Vacuum
regulator is set manually as shown in figure 2.
Figure 2. Oxygen Flowmeter, Vacuum regulator.
The patient may need to be supported by mechanical ventilation
when the respiratory system fails [7]. Mechanical ventilation is
common form of life support in the intensive care unit (ICU) [8].
Although mechanical ventilation is one of the ultimate life-
supporting technologies, in recent years, there has been renewed
interest in the injury that it can cause. The concept that high
airway pressures during positive pressure ventilation can cause
gross injury manifest has been well known and investigated for a
long time [9]. It was found that an average of 40% of the patients
died in the process of finalizing mechanical ventilation. It was
found that also a high overall mortality in the intensive care unit
[10].
In the literature, there have been several studies on pulse
oximetry. Although the small number of wireless applications,
studies involving with oxygen flow meter have not been a part of
literature. Some of the studies in the literature on pulse oximetry
and wireless communications are as follows: Watthanawisuth and
_______________________________________________________________________________________________________________________________________________________________
1 Biomedical Engineering, Technology Faculty, Kocaeli University,
Kocaeli /Turkey
* Corresponding Author: Email: aliihsanbulbul@yahoo.com
Note: This paper has been presented at the 3rd International Conference
on Advanced Technology & Sciences (ICAT'16) held in Konya (Turkey),
September 01-03, 2016.
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his team (2010) worked on the monitoring of pulse oximetry with
wireless wearable system [11]. Qing Cai, Jinming Sun, Ling Xia
and Xingqun Zhao (2011), have created a wireless pulse oximeter
sensor using a wrist strap [12]. Turban and Niwayama (2011)
have worked on reducing the power consumption of wireless
pulse oximeter [13]. Rekha Chandra, Safer and Srividya (2015)
worked on the development and miniaturization of wireless pulse
oximeter [14]. Render, Ayaz and Dalkılıç (2014) worked based
on the Arduino Healthduino wireless Mobile Health Monitoring
System, cloud-based database, doctors and patients mobile
applications [15]. In the study by using RF technology. Adochie
and colleagues wireless pulse oximeter is designed. Also it has
been monitored with WiFi or GSM / GPRS technology [16].
The studies mentioned above do not both measure oxygen
saturation and supply oxygen automatically to the patients. The
aim of this study is to design a system that measure first the
oxygen saturation and provide the required oxygen to the patients
via a wireless and oxygen flowmeter system. For this purpose, a
microcontroller is used to measure the blood oxygen saturation. A
wireless signal including the measured blood oxygen saturation
data is sent to the non-invasive ventilation flow meter vacuum
regulator to deliver the required oxygen into the patient. This
process is repeated as the doctor's recommendation continues.
Thus, according to symptomatic status of the patient, mechanical
ventilation causing pre-intervention to acute respiratory failure is
no mere required. By using proposed device in this study, O2
saturation can be precisely arranged and delivered to the patients.
Microcontroller programming with proper protocols based on the
different patient stories and different diseases can prevent the
problems caused by human influences.
2. Pulse Oximetry
Respiratory system are specialized to allow gas exchange
between ambient air and blood. The 97% part of oxygen
composes of chemical compounds with the hemoglobin in the red
blood cell and rest of 3% composes of dissolved in the fluid
plasma and cells. Oxygen saturation is defined as the ratio of
hemoglobin to total hemoglobin bound to oxygen in the blood.
The O2 saturation is close to 100% under normal conditions. The
O2 saturation between 97% and 100% represents good gas
exchange within the person. Hypoxia is mentioned above when
SpO2 level falls below 90% and may require respiratory support.
Identifying hypoxia conditions in an early stage is important.
Thus an early intervention becomes possible and therapy starts
immediately.
According to the blood gas analysis method, 'arterial oxygen
saturation' is represented by the symbol SaO2 in the literature.
This parameter corresponds to the oximetry method 'arterial
oxyhemoglobin concentration' (represented by the measured
SpO2 symbol). The main difference between SaO2 and SpO2
parameters is that SpO2 presents the amount of oxygen bound to
the hemoglobin molecule found while SaO2 denotes the total
amount of oxygen in the arteries [17].
Oximeters are devices that determine the oxygen concentration of
various species of Hb [18].
2.1. Principles of Pulse Oximeter
Light is transmitted, absorbed, or reflected when it passes through
matter. The relative absorption or reflection of light at different
wavelengths is used in several monitoring devices to estimate the
concentrations of dissolved substances. This type of measurement
is called as spectrophotometry and is based on the Beer-Lambert
Law. According to the Beer-Lambert Law, if a known intensity of
light illuminates a chamber of known dimensions, then the
concentration of a dissolved substance can be determined if the
incident and transmitted light intensity is measured [18].
The pulse oximetry is based on two physical principles. The first
one is the light absorbance of oxygenated hemoglobin and the
second one is the absorbance at different wavelengths with
pulsatile (AC) component [19]. Pulse oximeter is based on the
principles to absorb light different level by oxygenated
hemoglobin with reduced hemoglobin [14].
The form of Hb is important issue. In the adult blood usually
contains four species of Hb: HbO2, reduced Hb, methemoglobin
(metHb), and carboxyhemoglobin (COHb). Each of Hb species
has a different light absorption profile. The different absorption
constants for each Hb species over a range of light from red to
infrared are shown in Figure 3 [18].
Figure 3: Hemoglobin extinction curves.
Pulse oximetry uses the wavelengths of 660 nm and 940 nm
because these wavelengths are available in semiconductors.
The oximeters measure red and infrared light transmitted through
and reflected by a tissue bed. There are several technical
problems to accurate estimation of SaO2 by this method. For
example, many light absorbers other than arterial Hb are in the
transmitted light path (e.g., skin, soft tissue, venous). A group of
absorbers in a typical sample of living tissue is shown in Figure 4
[18].
Figure 4: Pulse oximetry signals.
The AC component represents absorption of light by the
pulsating arterial blood at the top of the figure. The DC (baseline)
component represents absorption of light by the tissue layer. The
pulse oximeters mostly use only two wavelengths of light,
typically 660 nm (red light) and 940 nm (infrared light). The
pulse oximeter first determines the fluctuating or AC component
of absorbance at two wavelengths. Secondly it divides this value
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by the DC component to obtain the pulse-added absorbance
which is independent of the incident light intensity. Thus, the
oximeter then calculates the ratio (R) of the two pulse-added
absorbance (one for each wavelength) [19]:
(1)
Pulse oximetry is calibrated using the calculated value of R. An
example of a pulse oximeter calibration curve is shown in Figure
5 [22].
Figure 5: Typical pulse oximeter calibration curve.
The curve used in all commercial pulse oximeters are based on
experimental studies in healthy human volunteers. Although each
manufacturer is different, these curves are similar [18].
2.2. SpO2 Probe
Biosensors are important tools in food safety, diagnostics,
medical monitoring and biological warfare agent’s detection
systems. Pulse oximeter probe is a sensor that detects oxygen.
The pulse oximeter probes are used for the purpose of evaluation
of the patient's oxygen saturation; it is the best perfused on
fingers, toes, nose area, ear lobes.
In adult and pediatric size probes are manufactured in accordance
with multiple and disposable use (Fig. 6).
Figure 6: Reusable and disposable SpO2 probes.
The attenuation characteristics of light passing through the
fingertip consist of three components: tissue loss, and (vein) the
weakening of the artery (artery) attenuation. Tissue attenuation
and veins attenuation have a constant characteristic. Arteries
(arterial) blood flow in fingertip causes light attenuation
variation. The reason is the change in the oxygen saturation of the
blood pumped to the body blow to the heart of each pulse. Heart
rate (pulse) signal is superimposed on the fixed component which
is weakening. Thus, arterial oxygen saturation can be calculated
by subtracting from the total attenuation of the attenuation
constant and vein tissue attenuation components [17].
The SpO2 value can be read incorrectly in some situations,
environmental effects, and technical. These conditions are:
Very bright light in the operating room (such as more
lighting).
Abnormalities in value of carboxyhemoglobin and
methemoglobin.
Electrocautery device can be prevented by
transportation of signal to diode when it running.
It may be affected by light emitted from the surgical
light in the hall.
SpO2 value can be measured or read incorrectly when
the patient's fingernails very long, fingernails with
diamonds, henna, dyed and so on.
3. Pulse Oximeter Manufacturing And Wireless
Telemetry For Ventilation Oxygen Support
In this study, a telemetry control system is proposed to support
oxygen to the patients based to the data measured by pulse
oximeter. The schematic diagram of proposed wireless telemetry
system for ventilation oxygen support with pulse oximeter is
shown in Figure 7.
Figure 7: Wireless telemetry for ventilation oxygen support with pulse
oximeter.
3.1. Pulse Oximeter Manufacturing
The pulse oximeter block diagram in Figure 7 is illustrated in
Figure 8 in detail. Pulse oximeter is proposed to design using
microcontroller.
Figure 8: Block diagram of pulse oximeter.
The probe consists of a photodiode and two LEDs including red
and infrared LEDs. The SpO2 sensor LEDs are connected as
shown in Figure 9.
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Figure 9: SpO2 sensor leds.
The LEDs are controlled by the microcontroller PWM signal.
However, the microcontroller PWM output cannot provide
enough power to drive properly led. LEDs are forced to give
enough energy by the led driver circuit. A finger probe measures
the oxygen saturation via pulse oximeter probe as analog signal.
Since the only one photodetector for the two LED signals, the
signals cannot be received at the receiver at the same time, thus
requiring switching of signals. Double the switching drive
integrated, red and infrared LEDs with two signals from the
microcontroller does turn on and off. The timing diagram to drive
the LEDs is shown in Figure 10.
Figure 10: Timing diagram.
Photodiode generates an analog current depending on the light
absorption. This current must turn into voltage. That
transformation is performed in analog signal conditioning circuit.
The analog signal conditioning circuit is illustrated as in Figure
11.
Figure 11: Analog signal conditioning circuit.
The SpO2 is calculated when the signal is applied to Analog-
Digital Converter (ADC) module in microcontrollers. Signal
conditioning circuit consists of three stages. First stage is
amplifier (transimpedance amplifier), which takes a few micro-
amps current by photodiode and turning into a few millivolts.
Transimpedance amplifier is an amplifier as well as current-
voltage converter. The signal passes by High Pass Filter (HPF).
Therefore background light interference is reduced. High Pass
Filter output is upgraded with second stage gain amplifier.
There are two filter applications. The first one is a passive RC
filter illustrated within a circle in Figure 11. The second one is in
the microcontroller as software. The digital filter is called FIR.
Microcontroller include Digital Signal Processing (DSP) unit.
DSP performs digital Finite Impulse Response (FIR) that is the
filtered data. FIR is a software filter. The filtered data is used to
calculate the pulse amplitude. The pulse amplitude is used to
calculate SpO2 and heart rate.
Finally microcontroller sends the computed data about blood
oxygen saturation to the second microcontroller via wireless unit.
3.2. Wireless Oxygen Flowmeter Control
Flowmeter manually operate in general. In this study it is
operated automatic control with a motor and motor driver circuit.
It uses pulse oximeter wireless data for automatic control.
3.2.1. Oxygen Supply And Equipment
Oxygen is supplied for patients from two sources, including
central system and O2 tubing. Flowmeter (oxygen flow measuring
equipment) and humidifier (humidification oxygen canister) is
located in the patients unit. It is shown in Figure 2.
The pressure in the oxygen tube is very high to provide oxygen to
the patient. The pressure to be used medically appropriate level
(40-70 psi-pounds) must be reduced. Therefore, regulator is used
in order to regulate the pressure. Regulator is an arranger by
display.
Flowmeter adjusts the flow rate per minute of oxygen delivered
to the patient. Humidifier is a chamber used depending
flowmeter. It allows the moisture of the oxygen from the oxygen
source.
In patients with respiratory; nasal cannula, simple face mask,
partial mask recycled, recyclable mask, venturi mask, nebulizer
mask and oxygen header methods are used. In patients without
respiratory mask balloon system (Baggins valve- mask) is used
[14].
3.2.2. Motor Control Circuit
In this application, a motor is mounted on the flowmeter. The
data is taken from a pulse oximeter with wireless communication
module.
The motor control system is shown in figure 12. This system
provides motor control with wireless data from pulse oximeter. It
is controlled motor speed and left-right rotation by
implementation of the appropriate voltage values.
Figure 12: Motor control system block diagram.
The data from the pulse oximeter is named as A0 and A1.
Equation 2 is used for to determine motor speed.
(2)
K0 and K1 expressions in the equation 2 are coefficients used to
determine the applied voltage to the motor according to the
received value.
If the pulse oximeter measurement SpO2 value falls under 95%,
then the motor works. If it falls under 90% then the oxygen
transferred to the patient is increased. If the measurement value
rise above 95%, then rotation reversed valve is closed.
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Motor situation and SpO2 values can be changed easily in the
microcontroller. Thus working system can be programmable
according to doctor’s protocol.
4. Conclusion
Developments in electronics and sensor technology yields several
advantages for biomedical applications. For example, analog and
digital devices for bio-signal treatment can easily be employed by
microcontrollers.
Biosensors and pulse oximeter probes can be the candidate
subject for different researches. The conventional analogue
probes are required to be updated. Instead of these instruments, it
is possible to develop better digital probes.
This study has not been finalized yet. The pulse oximeter
telemetry system presented in this study is cheap, fast, easy to use
& setup and medical risks low example. The mechanical
ventilation risks for using hypoxia control were explained.
Furthermore mechanical ventilation devices are very expensive.
The manual flowmeter using simple oxygen support is not
enough for hypoxia control. This application eliminates both
drawbacks of applications.
This study leads to some other studies such a new design of pulse
oximeter that decrease the heat and other pigments effect, a new
device that adjusts blood pressure, bilirubin, cholesterol, glucose
levels and hemoglobin counter.
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