Post on 06-Jan-2016
description
transcript
Vital Signs MonitorVital Signs MonitorUConn BME 4900UConn BME 4900
Vital Signs MonitorVital Signs Monitor Purpose
As the population ages, many people are required by their doctors to take vital signs on a daily basis.
Developed for the average person to use at home.
Vital signs transmitted to a computer and ultimately to a doctor.
MeasurementsMeasurements
What can it measure? Electrocardiogram
(ECG) Three leads (Right
arm, left arm, right leg)
What is an ECG?What is an ECG?
Records a time waveform of heart electrical activity.
Used to diagnose heart problems Arrhythmia Myocardial infarction Conduction blocks (bundle branch block)
ECG TraceECG Trace
Cardiac Electrical ActivityCardiac Electrical Activity
The ECG WaveformThe ECG Waveform
Measuring Electrical ActivityMeasuring Electrical Activity 3 leads
2 arm 1 leg
As cardiac muscle depolarizes it creates a potential on the skin
Potential measured as a vector Difference between right and left
electrode measured with a differential amplifier.
Measuring Electrical ActivityMeasuring Electrical Activity
Circuit consists of: 3 op amp differential amplifier Low pass filter (Cutoff: 0.05 Hz) High pass filter (Cutoff: 160 Hz) Gain Amplifier
Differential AmplifierDifferential Amplifier
What does the buffer do? Provides a high input impedance which means low current flow
What is the purpose of C2 and C3? Remove DC offset Offset would be amplified by 1000x
10 mV at 1000x gain = ~10V
Feedback Amplifier
Buffer
Differential Amplifier
Differential AmplifierDifferential Amplifier
V1 & V2 are in the microvolt range
We need it to be in the milivolt range so Rf/R1 is set to ~1,000
11stst Order LPF Order LPF
The ECG is known to be a low frequency signal
Usually less than 100Hz
A LPF can be used to remove the high frequency noise in the signal
High Pass FilterHigh Pass Filter ECG frequency range ~0.05 Hz – 150 Hz Why do we need to eliminate frequencies <0.05
Hz? Avoid distortion of the ST wave
MicroprocessorMicroprocessor Provides Analog to Digital (A/D) conversion
Waveform y(t) sampled at a fixed rate Δt Voltage read every Δt and converted to a number If resolution is 8 bits
Gives us 28 = 256 counts over 5V range ~19.5 mV per count
Patient IsolationPatient Isolation
Bluetooth is wireless technology Bluetooth provides separation of the patient from
the equipment and line source Very important to protect patient from electrical
shock
Labview SoftwareLabview Software
Labview RequirementsLabview Requirements
Receive serial data from bluetooth Display raw and filtered EKG Calculate heart rate