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