Download Heart_Rate_(HR)

Heart Rate Monitor (HRM)
Measurement of HR
• Plethysmograph or ECG techniques
• ECG superior as distinguishable R peak
• HR derived by
– Sensors: Limb or chest electrodes
– amplification of ECG
– Measuring either the average or instantaneous
time interval between two R peaks
• Range 0-250 beats/min
Methods
• Average Calculation
• Beat-to-Beat Calculation
• Combination of Beat to Beat and averaging
Average Calculation
• Used in patient monitoring systems
• No. of pulses in a given time  Average
beat/min
• R-Wave  pulse of fixed amplitude and
duration  average current from these pulses
• Averaging or F – V circuit: to display avg., HR in
beats/min
• Diode pump circuit for F-V
R
wave
Diff.,
Rect.
Sharp
pulse
pulses
Voltage across C2 : e= C V f R
• Does not show changes in the time between
pulses
• Does not represent true picture of the heart
Instantaneous (Beat-to-beat)
monitoring
• Facilitates detection of arrhythmias
• Permits timely observation of cardiac
emergencies
• Time between two consecutive pulses
measured  formula  converted to beats
/min
• Formula = 60/T, Where T R-R time interval
Instantaneous HR monitors
• Detection based on QRS complex
• Sensitive to movement artifacts  noise often
triggers false alarm
• Artifact removal filters
• False rate alarm reduction by QRS matched
filters
QRS matched filters
• 15 sample finite-impulse-response-filter
• Filter gives max. O/P when similarly shaped
waveforms are i/p
• T waves produce suppressed O/P
Modern HRM
• Two elements
– chest strap transmitter
– wrist receiver or mobile phone
• In early plastic straps
– water or liquid was required to get good
performance.
• Later units
– conductive smart fabric with built-in
microprocessors for ECG analysis and HR
determination
Modern HRM
• Radio pulse or a Unique Coded Signal (UCS)
transmitted to receiver for every detected
beat
– UCS prevents cross-talk interference from nearby
transmitters
• New versions include Micro controller unit
– ECG continuous monitoring and calculating the
heart rate, and other parameters
– may include accelerometers which can detect
speed and distance
Modern HRM
Wrist strap/
wearable
sensors
Receiver
Amplifier
& Filter
Demodulator
Modulator
Amplifier
& Filter
Transmitter
MCU
HR
Advanced models
• Advanced models measure
– Heart rate variability & breathing rate
– Wearable fabric HRM
• Sensor fusion algorithms
– allow these monitors to detect core temperature
and dehydration
Receiver
• Various features
– Average HR
– time in a specific heart rate zone
– calories burned, breathing rate
– built-in speed and distance
• Detailed logging can be downloaded to a
computer.