Apparatus for the Analysis of Heart Sounds

Team PacemakerLuke Philips, Ryan Laterza,

Min Dong Bian, Sarah Makhija

• Electronic Stethoscope/EKG Device• In collaboration with Mechanical and Software

Engineering students• Dr. Howard D. Weinberger

– Cardiologist and Co-Director of Cardiac Imaging at the University of Colorado at Denver and Health Sciences Center

– Apparatus and methods for analyzing heart sounds • Patent #5,687,738

Project Objectives

• Provide objective means of analyzing cardiac acoustics– Aid in diagnosis of heart murmurs

• Amplified signal from stethoscope, EKG• Handheld device, portable memory,

graphical display

Heart Physiology and Anatomy

Heart Murmur Pathology•Heart valve(s) fail to close/open properly, causing turbulent blood through the blood vessels

•Turbulent blood flow causes high and low pitch sounds known as heart murmurs

•Heart problems caused by the malfunction of heart valves

Estimates for 2003: 71,300,000 Americans have one or more forms of cardiovascular disease (CVD)

Use Case Diagram

Read ECG andAcoustic Data

Secure Card Memory Stick

Physician

Acoustic Analysis Utility for Cardiac Diagnoses

Display, Print, andSave Processed Data

Record ECG andAcoustic Data

Patient's Heart

ECK and Heart Acoustic Capture Device

Write ECG andAcoustic Data to Memory

Heart Rate and EKG Monitor

Using Bypass Capacitors and differential amplifier

What is an EKG?

• Graphic tracing of the voltage generated by the cardiac or heart muscle during a heartbeat

• EKG waveform:

Circuit Design Problem

• Electrical signal is very small: 1mv peak-peak

• The signal is noisy

• Solution:– Use differential amplifier and bypass

capacitors to design the circuits

Function

• In this case, differential amplifier will reduce the noise voltages

• Bypass capacitors help filter the electrical noise out of our circuit,the good default value for bypass capacitors is 0.1uF

The EKG Amplifier Circuit

Output of EKG

The output of EKG after modified circuit

How to store these data?

• Use Secure Digital Card (SD)• Two sizes: Regular, 32 × 24 × 2.1 mm

Mini, 20 x 21.5 x 1.4 mm• Capacity:

– Regular, 128, 256, and 512 MBs, 1, 2 and 4 GBs.

– Mini, 16MB to 2GB

Image of Mini SD Card

Mixed Signal Microcontroller Texas Instrument MSP430F427

Key Features• Supply Voltage Range 2.7 to 3.6 Volts

(Three 16-Bit ADCs Active) • Scalable Processor Frequency: 6Mhz (2.7

V) to 8Mhz (3.6 V)• Ultra low-Power Consumption:

– Active Mode: 400 µA at 1 MHz, 3.0 V – Standby Mode: 1.6 µA – Off Mode (RAM Retention): 0.1 µA

Key Features (cont.)• 6 µs Wake-Up From Standby Mode• 16-Bit RISC Architecture• 12 General Purpose 16-Bit Registers• 32 kB of FLASH Program Memory• 1 kB of Random Access Memory• Direct Memory Access Controller• Three Independent 16-Bit Sigma-Delta

A/D Converters

Key Features (cont.)• One 16-Bit Timer and Two 8-Bit Timers • Integrated LCD Driver for 128 Segments • Serial Communication Interface (USART),

Asynchronous UART or Synchronous SPI• Flash Memory can be Programmed by JTAG

Port, Bootstrap Loader, or In-System by the CPU

• Brownout Detector • Instruction Set Consists of Fifty-One Instructions

– Can Operate on Word and Byte– Seven Address Modes

TI MSP430F427 Pin Layout and Chip Dimensions

64 Pin Quad Flat Pack Chip

12.2 mm

12.2 mm

Analog To Digital Converters 16-Bit Sigma Delta ADC

• Sampling Frequencies– Low Power Mode Disabled

• 1Mhz– Low Power Mode Enabled

• 500Khz

• Analog Input Range with Gain = 1– ±500mV and 650 to 950 uA

• Gain = 1 has highest Signal to Noise Distortion Ratio

• Input Impedance = 200 kΩ

Power

• Li-Ion Battery Charger solution using the MSP430

Li-lon battery Features• Li-Ion ideal for portable

applications– High capacity-to-size

ratio– low self discharge

characteristic.

• Battery charging– power management

ICs– MCU controlled– logic devices

• MCU controlled– safe charging– time efficient– low cost

Battery Features (cont.)• Battery capacity, C, mA hours

• Battery current, C-Rate– 500 mA-h battery, C-Rate 500mA– 1C, 500 mA– 0.1C is 50 mA.

• Li-Ion battery charging, three stages:– Slow Charge: current of 0.1C– Fast Charge: current of 1C– Constant voltage

Current vs Voltage for Li-lon Battery Charging

• Risks of Li-Ion batteries– explosion due to

outgassing of electrolyte– Severe reduction in

battery life– sensitive to overcharging

• final voltage, ±50 mV of 4.1 or 4.2V.

• Fully charged– constant voltage, current

0.1C– Observe temperature– safe timing method

• charging time longer than a predetermined time

Typical Cell Phone Li-Ionbatteries rated at ~850 mAh

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• buck converter– constant current, constant

voltage– step down voltage converter– inductor as a current source– output load impedance, i.e.

the battery

• PNP and NPN transistors switch via PWM– switch closed

• current flows through inductor

• capacitor is charged– switch open

• inductor maintain current flow

– Inducing voltage• current flows through

diode• inductor charges capacitor

• LC network– low-pass filter– PWM frequency > cut-off

• capacitor voltage is constant• equal to the mean value of

input voltage to buck converter

• Inductor at 75 mH is sufficient• PWM 15 kHz• PWM resolution 8-bits• Capacitor is 220 mF, cutoff

frequency of LC network 1.2 kHz– helps capacitor reduce the output

voltage ripple– maintain DC voltage level

• Three channels on A/D converter on MSP430 to measure battery– battery voltage– battery temperature– battery current

Power

• Thermistor connected to negative pole of battery– resistance decreases

with temperature and thermistor voltage

• Risk of design– Complex– Fall back plan

• Alkaline batteries• Bench Power

Device UI - Keypad

• Ultralow-Power Keypad Interface With the MSP430

• draws 0.1 µA waiting• interrupt driven• no polling• Max 2 µA at 3 V if all

keys are pressed and held simultaneously

• No crystal required• Minimum external

components• Suitable for any

MSP430 device

Device UI - Keypad• Normal mode

– wait-for-press mode– rows driven high– column pins as inputs– interrupt on a rising edge

• 4.7 MΩ pull down resistors – inputs low– MSP430 low-power mode– MSP430 current consumption 100 nA.

• Maintained indefinitely until key is pressed

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Device UI - Keypad

• Risk of design– Moderate

Complexity

– Fall back plan• Individual hard-

wired buttons

Use Case Diagram Revisited

Read ECG andAcoustic Data

Secure Card Memory Stick

Physician

Acoustic Analysis Utility for Cardiac Diagnoses

Display, Print, andSave Processed Data

Record ECG andAcoustic Data

Patient's Heart

ECK and Heart Acoustic Capture Device

Write ECG andAcoustic Data to Memory

• Improvement upon current methods

– Range of human ear: 20 – 20kHz• May be important info beyond audible range

– Objective teaching tool– Time-saving– More accurate medical records and

diagnoses

• Possible extensions

– Diagnostic software– Analyze dependence on respiratory phase– Integrate EKG leads and stethoscope– Input patient data from computer rather than

keypad• Barcodes

Division of Labor

• Luke – Design power source, user-interface

• Ryan – Systems integration leader, implement microcontroller

• Min Dong – Design of memory stick, EKG amplifier

• Sarah – Team lead, assist team in technical undertakings

• All – Write user’s manual

Schedule

Thank you!

Questions?