Design of a Neonatal Monitor for Prevention of SIDS

1
Design of a Neonatal Monitor for Prevention of
SIDS

• Rishi Mathura,
• Nii-Okai Alcide, Momina Andrabi
• Divya Sharma, Joelson Guillaume

December 13, 2005
The City College of NY of The City University of
New York Department of Biomedical Engineering
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Introduction
Definition of SIDS

• Sudden infant death syndrome is the sudden death
  of an infant under one-year of age, which remains
  unexplained after performance of a complete
  postmortem investigation, including an autopsy
  and examination of the death scene.

Background of SIDS

• Healthy infants die suddenly and unexpectedly
  during their sleep
• Belief that infants suffocated, either by
  maternal overlaying or by being strangled in
  bedclothes- Now discarded
• A lack of physiological answers attribute to SIDS
  and makes sudden infant death syndrome
  complicated to understand.

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Statistics

• Most common cause of death in infants between the
  ages of 1 month to 1 year.
• Peak incident is between 2-4 months
• 95 of the deaths occur before the age of 6
  months
• Affects nearly 1 out of every 1,000 live births
• Accounts for nearly 3,000 SIDS deaths in the
  United States per year or approximately one baby
  every 3-hours
• Seasonal distribution- More deaths in winters
• More boys die of SIDS than girls
• African American and Native American children die
  more often than Caucasian neonates
• Frequency of death is more with children with
  abnormalities with brain functions arcuate
  nucleas involved with breathing and waking
  during sleep

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Potential Risk Factors

• Smoking, drinking, or drug use during pregnancy
• Poor prenatal care
• Premature birth or low birth-weight
• Mothers younger than 20
• Cigarette smoke exposure following birth
• Overheating from excessive sleepwear and bedding
• Stomach sleeping

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Physiology

• Sudden death is related to heart problems
• Studies show decreased beat-to-beat heart rate in
  infants at risk for SIDS
• SIDS is assumed to be related to an abnormal
  autonomic nervous system function that controls
  heart rate
• SIDS infants have a decreased ability to change
  heart rate in response to environmental
  challenges

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Preventive Methods/Home Remedies

• Place baby on his/her back on a firm
  tight-fitting mattress in a crib that meets
  current safety standards
• Remove pillows, quilts, comforters, sheepskins,
  stuffed toys, and other soft products from the
  crib, playpen, or portable crib
• Use a sleeper or other sleep clothing as an
  alternative to blankets
• If using a blanket, put baby with feet at the
  foot of the crib. Tuck a thin blanket around the
  crib mattress, reaching only as far as the baby's
  chest
• Make sure your baby's head remains uncovered
  during sleep.
• Do not let baby get too hot
• Follow healthy habits like no smoking during
  pregnancy and after pregnancy do not smoke around
  neonates

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Advantages a Neonatal Monitor

• Both normal infants and babies with increased
  risks can be monitored.
• Early detection of symptoms associated with SIDS.
• Parents peace of mind during neonates slumber.
• Continuous monitoring of infant for other
  childhood illnesses

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Required Specifications by Sponsor

• Efficient monitoring, storage, and analysis of
  the vital parameters of an infant less than 12
  months of age
• The vital parameters to be monitored are blood
  oxygen saturation, heart rate, and temperature.
• Connection to infant should be comfortable and
  non-irritating.
• An alarm system to warn of any critical changes
  in the parameters.

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Required Specifications by Sponsor

• The threshold for criticality is to be selectable
  and adjustable by the user
• Minimal size and weight
• Minimum developmental cost
• Observation of safety standards and regulations
  associated with medical devices

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Optional Specifications

• Monitoring of the infants sleeping position (on
  stomach or back)
• Monitoring the quality of air surrounding the
  baby
• Storage of the data acquired during the
  monitoring process in order to analyze trends and
  patterns of changes in the parameters

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Normal Physiological Ranges
Parameters

• Temperature 36.5-37.1C
• Heart rate 120-140 bpm
• Blood pressure 110/70 mm Hg
• Oxygen saturation (SpO2) 90-100

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Prior Art Analysis
Table 1. Comparison of neonatal monitors
currently used in clinical and home environment
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Prior Arts Analysis
Shortcomings of researched commercial devices

• False readings due to motion artifacts created by
  unstable sensors.
• Very few devices for the home setting measure all
  desired parameters
• Complicated and difficult user environment, with
  some advanced skills required.
• Cost commercial devices range from 200 USD to
  5500 USD depending on complexity and number of
  parameters monitored.

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Suggested Sensor to Measure Temperature
Thermistor

• Inexpensive
• Easily-obtainable
• Easy to use
• Reliable

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Suggested Sensor to measure Blood pressure -
Arterial Tonometer

• Noninvasive
• Measures systolic and diastolic blood pressure
• Utilizes forces transducers placed over a
  superficial artery

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Principles of Arterial Tonometer

• Force (F) is exerted on frictionless plate
• Transmits perpendicular Tensile force (T)
• F is equivalent to product of Pressure (P) and
  Area (A) of frictionless plate

Source Tonometry, arterial in J.G. Webster
(ed), Encyclopedia of Medical Devices and
Instrumentation. New York Wiley, 1988, pp.
2770-2776.
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Arterial Pulse Points


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Accuracy Interference

• Accuracy of measurement depends on specific
  placement of sensor
• Requires bone support
• Movement of tendons can generate interference

Source Tonometry, arterial in J.G. Webster
(ed), Encyclopedia of Medical Devices and
Instrumentation. New York Wiley, 1988, pp.
2770-2776.
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Description of Tonometer Sensor

• Silicon
• Etched silicon surface
• Pressure sensing diaphragms
• Piezoresistive strain gauges in diaphragms
• External circuit measures strain gauge

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Ability to Measure Blood Pressure and Heart Rate

• Periodicity of blood pressure waveform can be
  used to measure arterial pulse rate

Source Tonometry, arterial in J.G. Webster
(ed), Encyclopedia of Medical Devices and
Instrumentation. New York Wiley, 1988, pp.
2770-2776.
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Advantages of Oximetry

• Pulse oxygen saturation (SpO2) is now generally
  accepted as the fifth vital sign.
• Pulse oximetry is a simple non-invasive method of
  monitoring the percentage of haemoglobin (Hb)
  which is saturated with oxygen.
• Allows quick readings of SpO2 levels. This
  facilitates detection of malfunctioning of the
  circulatory system and the lungs.

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Principles of Oximetry

• Oxygen is carried in the bloodstream mainly bound
  to haemoglobin.
• The beams of light pass through the tissues to a
  photodetector.
• During passage through the tissues, some light is
  absorbed by blood and soft tissues depending on
  the concentration of haemoglobin.
• The sensor is placed on a peripheral part of the
  body such as a digit, ear lobe, big toe or the
  nose
• The amount of light absorption at each light
  frequency depends on the degree of oxygenation of
  haemoglobin within the tissues

www.nellcor.com/oximetryprinciples.
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Respiration Rate and CO2 Saturation

• Strain Gauge
• Measurement of respiration rate
• Strain gauges used with a Wheatstone bridge
• Patch or belt containing strain gauges placed
  around chest
• Strain gauges activated by strain due to
  respiratory movement of chest

• Capnography
• Detects hypoxia caused by excessive CO2
  inhalation
• Measures blood CO2 saturation level
• Sensor placed inside a nasal canula placed under
  nostrils

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Solutions Rejected on the Basis of Sensor
Placement

• Portable Hand Monitor (Glove)
• Advantages
• Allows mobility
• -transportation to different sleeping areas
  for infant
• Disadvantages
• Movement from digits and arm
• -motion artifacts i.e. incorrect readings
• Multiple sensors in one location
• - interference
• Infant may tamper with the glove and disrupt the
  readings

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Solutions Rejected on the Basis of Sensor
Placement

• Monitoring Respiration (Belt)
• Advantages- measurement of respiration,
  noninvasive
• Disadvantage additional sensor
• Monitoring CO2 saturation (nasal canula)
• Advantages will detect hypoxia
• Disadvantages- connected to the babys nasal
  passage (Capnography)
• -poses discomfort and morbidity in a home
  setting

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Proposed Sensing Device for a Pedal Neonatal
Monitor
RM

• Equipped with sensors to measure temperature,
  heart rate, blood pressure, and oxygen saturation

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Advantages of the Pedal Neonatal Monitor

• Noninvasive monitoring of parameters
• Minimum tendon movement on the dorsalis pedis
  limits interference
• Changes in temperature on the big toe provides
  early indication of critical shock
• Digits on the foot are well developed making it
  accessible to measure oxygen saturation on the
  infants big toe

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Basic Configuration of System
Sensors
Stand Alone
Semi-Stand Alone (Optional)
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Detailed Configuration of Stand Alone System
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Analog Conditioning

• Biological signals need amplification before
  processing
• Amplification and Filtering in analog phase
• Filtering necessary to ensure that only
  components of signal with frequencies more than
  half of sampling rate of ADC enter the ADC
• To prevent aliasing by the sampling process

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Digital Signal Analysis with Microcontroller

• Analog analysis involve several voltage
  comparators representing threshold settings
  bulky circuit
• Sampled signal affected less by noise than analog
  signal
• Convenient to represent threshold settings with
  algorithms
• Easier to allow threshold setting adjustments
  with algorithms

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Digital Signal Analysis with Microcontroller
(contd)

• Digital signals easily transferable
• Whereas, transfer of analog signals require
  modulation and demodulation
• Microcontroller is one computer chip with memory
  and I/O interfaces

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Analog to Digital Conversion

• A/D converter built on microcontroller chip
• Sampling frequency 1K Hz
• High sampling frequency needed for high
  resolution
• High resolution required for efficient data
  analysis

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Data Type

• SpO2 recording data every 15-20 sec
• HR/BP- recording data every 15-20 sec
• Temperature- recording data every 30 sec
• An alarm sounds- After a series of consecutive
  critical readings 45 sec to 1 min
• Readings taken are dependent on the neonates
  health condition
• Parents can choose different threshold settings
  on the box after consulting a physician
• These threshold settings have different
  algorithms which can possibly change the time
  period for each parameter depending on the
  neonates health condition

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Semi Stand Alone Device

• A Trendline (24 hours) for each of the
  parameters SpO2, HR/BP, and temperature can be
  stored
• Trendline- collection of data every minute at a
  sampling frequency of 1K Hz and averages that
  data at every five minutes
• Trendline can be used by physicians for further
  diagnosing and identifying parameters that cause
  SIDS
• Trendline can be relayed to a PC for storage by a
  bluetooth transmission

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Memory
Our device can have

• Short term memory on the microcontroller in the
  box
• Long term (optional) - part of the semi-stand
  alone feature of the device. Signal is relayed to
  the PC by bluetooth transmission for physician

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Wireless Data Transmission

• Data can be transferred by using bluetooth
  transmittor on the box
• Bluetooth is the name for a short-range radio
  frequency (RF) technology is capable of
  transmitting voice and data.
• The effective range of Bluetooth devices is 32
  feet (10 meters)
• Transfers data at the rate of 1 Mbps
• Baby can be carried around to other places when
  device is hooked on and data can be relayed to
  the PC

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Power Supply

• The monitor must pass all electrical safety
  standards.
• Battery
• -Battery powered to reduce complications
  associated with direct outlet connections
• -Rechargeable Battery which can be charged by
  connecting monitor to outlet

Battery Location
Recharging Outlet
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Power Supply (contd)

• Low Battery Indicator to alert operators on
  battery power levels
• Power indicators for on and off states

Battery Meter
Power button and light
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Proposed Solution Requirements

• A pedal neonatal monitor will satisfy the needs
  of proposal
• -Continuous monitoring of temperature, heart rate
  and blood oxygen saturation
• -Equipped with an alarm that can be activated in
  the event of critical changes in parameters

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Proposed Solution Optional

• Ability to measure blood pressure with multiple
  arterial tonometer sensors
• Transmission of data to computer for in depth
  analysis

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Future Considerations and Specifications

• Sensor Interface and Connection
• Properties of Sock material
• Waterproof fabric
• Wear and heat resistant
• Stretchable to accommodate foot growth
• Possibly disposable
• Strong enough to hold sensors
• Strong sensor fabric binding
• Sturdy Connection
• Detachable sock-box lead

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Future Considerations and Specifications (contd)

• Alarm Settings
• Custom built threshold settings
• Settings based on infant health, risk factors and
  time of day
• User adjustable parameter

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Future Considerations and Specifications (contd)

• Structure of box
• Child proof
• Light weight
• Made of tough material (break-proof)
• Dimensions 6 in. X 2.5 in. X 4 in.
• Power
• Monitor unusable when battery being charged

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Our Design
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Acknowledgement

• Sponsor
• Luis Cardoso
• Professors
• Luis Cardoso
• Marom Bikson
• Teaching Assistant
• Xiang Gu