Understanding Common Biomedical Signals
Biomedical signals are electrical or mechanical phenomena generated by the body that can be measured and analyzed. These signals are fundamental to understanding physiological processes, diagnosing diseases, and developing effective medical devices. This module will introduce you to some of the most common biomedical signals encountered in medical device research and clinical practice.
Electrocardiogram (ECG/EKG)
The electrocardiogram (ECG or EKG) records the electrical activity of the heart. It's crucial for diagnosing various cardiac conditions, such as arrhythmias, myocardial infarction, and conduction abnormalities. The ECG waveform consists of distinct waves (P, QRS complex, T) representing different phases of the cardiac cycle.
ECG reflects the heart's electrical rhythm.
The ECG measures the electrical impulses that cause the heart to beat. These impulses originate in the sinoatrial (SA) node and spread through the heart, causing muscle contraction. The pattern of these electrical events is displayed as a waveform.
The electrical activity of the heart is generated by the depolarization and repolarization of cardiac muscle cells. The SA node acts as the natural pacemaker, initiating an electrical impulse that spreads through the atria, causing them to contract. This impulse then travels to the atrioventricular (AV) node, where it is briefly delayed, and then down the Bundle of His and Purkinje fibers to the ventricles, causing them to contract. The ECG captures these electrical events as voltage changes over time, typically measured using electrodes placed on the skin. The P wave represents atrial depolarization, the QRS complex represents ventricular depolarization, and the T wave represents ventricular repolarization.
Electroencephalogram (EEG)
An electroencephalogram (EEG) measures and records the electrical activity of the brain. It is widely used to diagnose epilepsy, sleep disorders, brain tumors, and other neurological conditions. EEG signals are characterized by different frequency bands (delta, theta, alpha, beta, gamma) associated with various states of consciousness and cognitive activity.
The electrical activity of the brain.
Electromyogram (EMG)
An electromyogram (EMG) measures the electrical activity produced by skeletal muscles. It is used to detect abnormalities in muscle function, nerve damage, and neuromuscular disorders like muscular dystrophy or carpal tunnel syndrome. EMG signals are typically recorded using needle electrodes inserted into the muscle or surface electrodes placed on the skin.
EMG signals represent the electrical potential generated by muscle fiber depolarization during voluntary or involuntary muscle contractions. When a motor neuron stimulates a muscle fiber, it causes a wave of depolarization that propagates along the sarcolemma. This electrical activity creates a measurable voltage difference that can be detected by electrodes. The amplitude and frequency of these signals are related to the force and speed of muscle contraction.
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Electrooculogram (EOG)
The electrooculogram (EOG) measures the resting electrical potential between the cornea and the retina of the eye. It is used to assess eye movements, diagnose certain eye diseases, and is often used in sleep studies to track rapid eye movement (REM) sleep. The EOG signal changes as the eye moves within its electrical field.
Blood Pressure
Blood pressure is the force of blood pushing against the walls of arteries. It is a vital sign indicating cardiovascular health. Measured as systolic (pressure during heart contraction) and diastolic (pressure when heart rests between beats), it's commonly monitored using sphygmomanometers, which can be manual or automated, often incorporating oscillometric or auscultatory methods.
Accurate blood pressure measurement is critical for managing hypertension and preventing cardiovascular events.
Pulse Oximetry
Pulse oximetry is a non-invasive method used to measure the oxygen saturation level of the blood (SpO2) and pulse rate. It works by passing red and infrared light through a translucent part of the body, such as a fingertip or earlobe, and measuring the difference in absorption between oxygenated and deoxygenated hemoglobin.
Other Important Signals
Beyond these core signals, other important physiological measurements include:
- Heart Rate Variability (HRV): The variation in time between heartbeats, reflecting autonomic nervous system activity.
- Body Temperature: A fundamental indicator of metabolic state and health.
- Respiratory Rate: The number of breaths per minute, indicating pulmonary function.
- Blood Glucose Levels: Crucial for managing diabetes, often measured invasively or non-invasively.
| Signal | Primary Measurement | Key Applications |
|---|---|---|
| ECG | Heart's electrical activity | Cardiac arrhythmias, heart attacks |
| EEG | Brain's electrical activity | Epilepsy, sleep disorders, neurological conditions |
| EMG | Muscle electrical activity | Muscle disorders, nerve damage |
| EOG | Eye's electrical potential | Eye movements, sleep studies |
| Blood Pressure | Force of blood against artery walls | Hypertension, cardiovascular health |
| Pulse Oximetry | Blood oxygen saturation | Respiratory function, anesthesia monitoring |
Learning Resources
Provides a foundational overview of biomedical signal processing concepts and their importance in medical devices.
A comprehensive, in-depth explanation of ECG interpretation, waveforms, and clinical applications.
Explains what an EEG is, how it's performed, and what it's used to diagnose, from a reputable medical institution.
Details the EMG procedure, its purpose in diagnosing nerve and muscle disorders, and what to expect.
A clear explanation of how pulse oximetry works and its significance in monitoring oxygen levels.
An academic overview of the field, covering various signal types and processing techniques.
A video introducing the broad field of biomedical engineering, touching upon signal acquisition and analysis.
A review article discussing various physiological signals and the technologies used for their measurement.
An in-depth look at Heart Rate Variability, its physiological basis, and clinical relevance.
A general overview of biomedical signals, their classification, and common examples.