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Application of DSP for ECG Signal Analysis
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Q. 7.1 .1 Write short note on application of DSP for ECG signal analysis. $\text { (Ref. Secs. } 7.1,7.1 \text { and } 7.1 .2) \quad$ (8 Marks)

• Most of the biomedical signals are in audio range and DSP is widely used in many biomedical applications.

• The signals from the body, are captured using electrodes. But the major problem is addition of noise in such signals.

• To remove this noise signals; digital filters are used.

7.1.1 Fetal ECG Monitoring

• Electrical activity of a heart is called as electrocardiogram (ECG).
• Fetal ECG represents electrical activity of the baby's heart. It is similar to the adult ECG waveform.
• The Fetal ECG (FECG) contains five peaks namely PQRST. This waveform is shown in Fig.7.1 .1

• The Fetal Heart Rate (FHR) is obtained from R-to-R interval of the waveform shown in Fig. 7.1 .1 .

• $\mathrm{ECG}$ is having $\mathrm{P}$ -wave, QRS complex wave and T wave.
• Instantaneous heart rate is obtained by multiplying time interval between R-to-R (in miliseconds) by $60,000$ .
• A suitable DSP algorithm is used successive QRS complex waveform and from this, R-to-R interval is calculated. It gives value of corresponding FHR.
• The shape of QRS complex waveform changes from patient to patient.
• The obtained ECG signal is compared with a known standard ECG and then the locations of QRS complex in the obtained ECG can be determined on the basis of similarity.

7.1.2 DSP based Closed Loop Controlled Anaesthesia

• In case of surgery; anaesthesia is injected to the patient body.
• A proper amount of drug to induce anaesthesia is required to inject in the patient body.
• Extra amount of drug produces side effects, as well as less amount of drug can produce psychological consequences for a long term.
• So it is required to make necessary changes in the dose of anaesthetic drugs and to control the anaesthesia.
• Using DSP, a closed loop system can be designed to monitor the does of anaesthesia and it is an automatic system.
• But, this system requires an accurate measurement of the depth of anaesthesia and it requires a feedback signal to monitor the delivery of dose.
• We will discuss the closed loop system used for EEG (Electroencephalogram).
• EFG represents, electrical activity of the brain and it contains useful information for diagnostic of neurological disorders.
• From the EEG signals; the features like bispectral index Audiotory Evoked Response (AER) are extracted and then the depth of anaesthesia is determined.
• Basically AER signal gives information from consciousness to unconsciousness condition of the patient.
• But these AER signals are usually small and they are mixed up with EEG.
• So a proper system is required to extract these AER signals and then process it.
• A bispectral index is obtained by performing spectrum analysis of EEG.
• The signal I (k) operates infusion pump which controls the flow rate of drug.
• It gives information about the changes in frequency components of EEG at different consciousness levels.
• A block diagram of DSP based closed controlled anaesthesia system is shown in Fig. 7.1 .2 .
• EEG electrodes are placed on the scalp of the patient; which generates EEG signals.
• Using suitable signal processing method; noise contained in EEG is reduced.
• EEG monitor produces EEG index (bispectral index) and it gives the measurement of drug induced in patient body.
• This EEG index is used as a feedback signal and it is compared with the target EEG index.
• The target EEG index is a standard value which is determined by considering many biomedical factors.
• The difference between target EEG index and measured EEG produces an error signal, e (k).
• This signal is applied to PID (Proportional-Integral- Derivative) control; to generate the required control signal, C(k).
• The signal $C(k)$ is applied to pharmacokinetic $/$ pharamaco- dynamic model and this model generates a signal I (k) to determine the rate at which, drug is injected in to the patient body.