bmi 1

Department Information

The notes are derived from the Biomedical Instrumentation course offered at SR University, specifically under the Department of Electronics and Communication Engineering (ECE). The course objectives, topics, and information are structured as follows:

  • Course Code: 24EC201PE402
  • Course Title: Biomedical Instrumentation
  • Credits: 2 L, 0 R, 2 P, 3 C
  • Course Type: Program Elective
  • Instructor: Dr. V. Malathy

Unit Overview

Unit 1: Focuses on Biomedical Engineering and Instrumentation with emphasis on:

  1. Bioelectric signals and systems - specifically ECG, EEG, and EMG.
  2. Measurement techniques in medicine.
  3. Transducers and sensors in biomedical applications.
  4. Elements of medical devices.
  5. Ethical and regulatory aspects in biomedical engineering.
  6. Regulatory standards including FDA, ISO, and CE marking.

Lecture Topics

  • Lecture 1: Introduction to Bioelectric Signals and Systems (ECG, EEG, EMG).

Recap from Previous Lecture

The students are reminded of the basic signals and systems covered during the previous semester, providing continuity in learning.

ECG (Electrocardiogram)

Definition

An electrocardiogram (ECG) records the heart's electrical activity using electrodes placed on the skin. The resulting tracing on graph paper is crucial for assessing heart rate and rhythm, and diagnosing various cardiac conditions.

I. Basics of Electrophysiology

  • Pathway of Electrical Activity: The heart's electrical activity follows a specific path:
      - Starts at the Sinoatrial (SA) node
      - Spreads through the atria
      - Reaches the Atrioventricular (AV) node
      - Moves through the bundle of His, bundle branches, and Purkinje fibers.
  • Depolarization: The electrical activation that triggers muscle contraction.
  • Repolarization: The phase where the heart muscle recovers and resets.
  • ECG Deflections: An upward deflection indicates electrical activity towards a positive electrode, while a downward deflection indicates activity moving away.

II. ECG Waves, Intervals, and Segments

  • Components: A normal ECG has specific waves and flat lines indicating different stages of the cardiac cycle.

III. The ECG Grid and Heart Rate Calculation

  • Grid Representation:
      - Horizontal Axis:
        - 1 small box = 0.04 seconds
        - 1 large box (5 small boxes) = 0.20 seconds
      - Vertical Axis:
        - 1 small box = 0.1 mV
        - 1 large box = 0.5 mV
  • Heart Rate Calculation: To find heart rate from a regular rhythm ECG strip, count the number of large squares between two consecutive R waves and divide 300 by that number.

IV. Systematic ECG Interpretation

A structured approach for accurate ECG interpretation is essential, involving:

  1. Rate: Measure heart rate (normal range: 60-100 bpm).
  2. Rhythm: Check for regularity and presence of P waves before each QRS complex.
  3. Axis: Determine the heart's electrical axis with a normal range of approximately -30° to +90°.
  4. Intervals: Measure PR, QRS, and QT intervals to ensure normal bandwidth.
  5. Waves and Segments: Examine P waves, QRS complexes, ST segments, and T waves for abnormalities (e.g., ST elevation/depression).
  6. Clinical Correlation: Interpret findings in relation to the patient's symptoms and history.

V. Common Abnormalities

Deviations from the normal ECG pattern may indicate:

  • Arrhythmias: Irregular heart rhythms such as atrial fibrillation or ventricular tachycardia.
  • Ischemia/Infarction: Myocardial ischemia is indicated by ST depression or T wave inversion; myocardial infarction can produce significant ST elevation.
  • Electrolyte Imbalances: Conditions such as hyperkalemia can lead to prominent T waves, while hypokalemia may manifest as pronounced U waves.
  • Conduction Blocks: Indicated by prolonged PR intervals or wider QRS complexes.

EEG (Electroencephalography)

I. Introduction to EEG

  • Definition: EEG is a non-invasive method to record the spontaneous electrical activity of the brain using scalp electrodes.
  • Physiological Basis: EEG signals arise from summed excitatory and inhibitory post-synaptic potentials (PSPs) from pyramidal neurons in the cerebral cortex. Individual action potentials are generally too weak to detect with scalp EEG.
  • Signal Characteristics: Recorded voltages are in the microvolt (µV) range, depicted as waveforms over time.

II. Methodology and Equipment

  • Electrode Use: Small metal discs (e.g., silver/silver chloride) applied to the scalp with conductive paste for low impedance contact.
  • Electrode Placement: Utilizes the International 10–20 system for consistent results based on head measurements.
  • Recording and Amplification: Weak signals are processed through differential amplifiers which enhance signal clarity while eliminating noise.
  • Montages: Use different electrode pair combinations to help localize brain activity.
  • Digital Processing: Employs digital recording to filter artifacts and adjust display settings during analysis.

III. Normal Brain Wave Patterns

Brain activity is measured in rhythmic activity and transients categorized by frequency bands:

  • Delta (0.5-4 Hz)
  • Theta (4-8 Hz)
  • Alpha (8-12 Hz)
  • Beta (12-30 Hz)
  • Gamma (30 Hz and above)

IV. Clinical Applications and Interpretation

EEG is crucial for diagnosing brain function issues due to its high temporal resolution. Key applications include:

  1. Epilepsy and Seizures: Identification of abnormal discharges characteristic of seizures (e.g., spikes, sharp waves).
  2. Sleep Disorders: Used in polysomnography for delineating sleep stages.
  3. Other Conditions: Essential in evaluating coma, encephalopathies, and certain brain tumors.
  4. Activation Procedures: Including hyperventilation and strobe light stimulation to increase diagnostic yield.
  5. Artifacts: Filtering out non-brain signals such as muscle activity and environmental noise is critical for accuracy.

V. Advantages and Limitations

  • Advantages: Low cost, high temporal resolution, portability, and non-invasiveness.
  • Limitations: Poor spatial resolution, challenges in recording deep brain activities, and variance impacted by hair type and movement.

EMG (Electromyography)

I. Introduction & Physiological Basis

  • Definition: EMG is an electrodiagnostic technique assessing myoelectric activity produced by skeletal muscles.
  • Motor Unit (MU): The essential functional unit consists of a single motor neuron and all innervated muscle fibers.
  • Action Potential Generation: Impulses stimulate muscle fibers at the neuromuscular junction, generating electrical fields as fibers depolarize—culminating in Motor Unit Action Potential (MUAP).
  • Muscle Contraction: Can be augmented through the recruitment of more motor units and increased firing rates (rate coding).

II. Equipment and Techniques

  • Electrode Types:
      - Surface Electrodes: Non-invasive and used for general assessments, but may encounter crosstalk from multiple MUs.
      - Needle Electrodes: Invasive, allowing for precise localization of single MUs.
  • Instrumentation Setup: Includes electrodes, amplifiers (differential amplifiers with high common-mode rejection ratio), and filters for signal clarity.

III. Signal Processing

  • Filtering: Crucial for removing noise and artifacts such as those from power lines and motion.
  • Rectification & Smoothing: Converts raw signals into positive waveforms for amplitude analysis.
  • Analysis: Includes time-domain and frequency-domain analysis to assess parameters like muscle fatigue and recruitment.

IV. Applications & Clinical Uses

EMG serves vital roles in many fields:

  • Clinical Diagnosis: Pairs with Nerve Conduction Studies (NCS) to identify disorders like carpal tunnel syndrome, muscular dystrophies, and amyotrophic lateral sclerosis.
  • Rehabilitation & Prevention: Facilitates biofeedback and ergonomic assessments.
  • Research & Engineering: Extensively used in biomechanics and for controlling prosthetic devices.

Learning Outcomes

Upon completion of the lecture, students will have gained essential knowledge regarding bioelectric signals including ECG, EEG, and EMG.

Reference Materials

  • Primary Text: R.S. Khanpur, "Handbook on Biomedical Instrumentation", Third Edition, McGraw Hill Education (India) Private Limited, New Delhi, 2021.
  • Chapter Focus: Bioelectric signals and electrodes, pages 46-50.

Summary

In this lecture, the fundamental points concerning bioelectric signals such as ECG, EEG, and EMG were discussed.

Next Class

The upcoming lecture will cover techniques for measurement in medicine.