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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)
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