Understanding Blood Oxygen Saturation

Blood Oxygen Saturation

• SaO2 and SpO2 are different measurements of blood oxygen saturation.
• Oxygen is primarily carried in the bloodstream bound to hemoglobin in red blood cells.
• Pulse oximetry involves progressing from photoplethysmograms (PPGs) to a ratio of ratios that indicates blood oxygen saturation.
• Two wavelengths of light are needed because oxyhemoglobin and deoxyhemoglobin absorb light differently at different wavelengths.
• In PPG, tissues contribute differently to the AC versus DC portions.
• Equations and coefficients model light transmission through tissue to calculate the oxygen saturation.
• Blood oxygen saturation is typically ascertained at different body locations for adults and infants.
• Transmission-mode and reflectance mode sensors have inherent tradeoffs.
• Research laboratories might want to design their own PPG acquisition equipment for specialized research purposes.
• Major considerations exist when trying to make pulse oximetry available in resource-limited settings, including cost, power requirements, and ease of use.
• Physical conditions and realities can affect the ability of pulse oximeters to work properly, including motion, skin pigmentation, and ambient light.

Electrode-Based Techniques: Passive vs. Active

• Passive electrode techniques record electrical activity generated by the body.
• Active electrode techniques deliver electrical stimulation to the body.

Passive Techniques

• Variations on passive electrode-based techniques include electrocardiography (ECG), electromyography (EMG), electroencephalography (EEG), electrogastrography (EGG), and electrooculography (EOG).
• ECG signals measure the electrical activity of the heart.
• EMG signals measure the electrical activity of muscles.
• EEG signals measure the electrical activity of the brain.
• EGG signals measure the electrical activity of the stomach.
• EOG signals measure eye movement by measuring the corneo-retinal standing potential.
• Benefits of wearable electrode systems include continuous monitoring and convenience.
• Challenges of wearable electrode systems include signal quality, comfort, and battery life.

Active Techniques

• Active electrode systems are useful in applications such as functional electrical stimulation (FES) and transcutaneous electrical nerve stimulation (TENS).
• An EDA (GSR) system measures skin conductivity, which changes with sweat gland activity.
• Traditional polygraphs include components that measure EDA, heart rate, respiration rate, and blood pressure.
• Neurostimulation has uses in treating chronic pain, depression, and movement disorders.
• Tasers affect the human body by disrupting the nervous system, causing muscle contractions and incapacitation.
• Defibrillators affect the human body by delivering an electrical shock to the heart to restore a normal rhythm.

Wearable/Implantable Devices: Emergence Timeframes

• Implantable cardiac pacemakers emerged in the 1950s to regulate heart rhythms.
• Cochlear implants emerged in the 1970s to restore hearing in individuals with severe hearing loss.
• Holter monitors emerged in the 1960s to continuously record heart activity over an extended period.
• Wearable continuous glucose monitoring systems emerged in the early 2000s for real-time glucose level tracking.
• Health/fitness trackers emerged in the 2010s to monitor activity levels, sleep patterns, and other health metrics.

'Autonomy' in Wearable Medical Devices

• 'Autonomy' for wearable medical devices refers to the device's ability to function independently without constant user intervention or external control.

Wearable System in Chronic Disease Management

• Wearable systems can play a role in chronic disease management by providing continuous monitoring, personalized feedback, and remote data transmission to healthcare providers.

SensoScan Clip and AliveCor Kardia Band

• The SensoScan clip is novel for its ability to detect skin cancer.
• The AliveCor Kardia band enables users to record and monitor their heart rhythm via a smartphone.
• These devices promote a change in care paradigm by enabling proactive and personalized health monitoring.

Wearable Device Design Considerations

• Data handling involves collecting, storing, and processing data generated by the wearable device (e.g., accelerometer).
• Signal processing involves filtering, amplifying, and analyzing the sensor signals to extract meaningful information (e.g., ECG signal processing).
• Feedback involves providing real-time information or alerts to the user through visual, auditory, or tactile cues (e.g., a notification when activity levels are low).
• Telecommunications involves transmitting data wirelessly to a smartphone, computer, or cloud-based platform for remote monitoring and analysis (e.g., Bluetooth connectivity).
• Physical design involves selecting materials, form factors, and ergonomic considerations to enhance user comfort, wearability, and aesthetics (e.g., flexible sensors).

Principal Component Analysis

• Principal component analysis aims to reduce the dimensionality of complex datasets by identifying the most important underlying patterns or components.

Feature Extraction and Classification

• Feature extraction involves identifying and quantifying relevant characteristics or attributes from a sensor signal.
• Classification involves assigning the sensor signal to a category based on the extracted features.

Flexible Polymers for Biomedical Sensing

• Three physiochemical properties that make new flexible polymers useful for biomedical sensing applications are biocompatibility, conductivity, and sensitivity.

Benefit of Flexible Materials

• Flexible materials enable the creation of wearable sensors that conform to the body's contours, enhancing comfort and adherence.

'Smart Tattoos'

• Smart tattoos will respond to changes in parameters, the tattoos are expected to change color or display a visual signal to indicate changes in pH, glucose, or electrolyte levels.

Smart Contact Lenses

• Smart contact lenses can be practically applied in continuous glucose monitoring for diabetes management and intraocular pressure monitoring for glaucoma detection.

Microneedles for Transdermal Drug Delivery

• Microneedles offer advantages, including painless drug delivery and improved drug absorption.
• Disadvantages of microneedles include limited drug delivery volume and potential skin irritation.

Cochlear Implant Mechanism

• A cochlear implant helps to restore hearing by directly stimulating the auditory nerve with electrical signals, bypassing damaged parts of the inner ear.

Sound Frequency Mapping in Cochlear Implant

• In a cochlear implant, sound frequency is mapped to position in the spiral-shaped cochlea, with high frequencies mapped to the base and low frequencies mapped to the apex.

Cause of Hearing Loss

• According to the Advanced Bionics video, the primary cause for severe-to-profound hearing loss that motivates the use of a cochlear implant is damage to the hair cells in the cochlea.

Types of Pacemakers

• Three types of pacemakers are single-chamber pacemakers (stimulating one heart chamber), dual-chamber pacemakers (stimulating two heart chambers), and biventricular pacemakers (stimulating both ventricles).

Modern Pacemaker Pathway

• For a modern pacemaker, leads are threaded into the heart through a vein (e.g., subclavian vein), and the pulse-generator module is implanted under the skin near the collarbone.

'Closed-Loop' Artificial Pancreas

• A 'closed-loop' artificial pancreas monitors blood glucose levels continuously and automatically delivers insulin to maintain glucose levels within a target range.

Medical Imaging Approaches

• Transmission imaging involves sending energy through the body and detecting what passes through (e.g., X-ray).
• Reflection imaging involves sending energy into the body and detecting what bounces back (e.g., ultrasound).
• Emission imaging involves detecting energy emitted by the body itself (e.g., PET scan).

Discovery of X-Rays

• X-rays were discovered in 1895 by Wilhelm Conrad Roentgen.

Descriptor “X-Ray”

• An “X” was used because the nature and properties of the rays were unknown at the time of discovery.

Tissue Differentiation

• X-rays best differentiate between tissues with different densities, such as bone and soft tissue.

CT Image vs. X-Ray Radiograph

• A CT image displays a cross-sectional view of the body, while an X-ray radiograph displays a projected view of the body.

Projection and Radon Transform

• A projection is a way of representing a 3D object as a 2D image by integrating the object's density along a set of parallel lines.
• The Radon transform is a mathematical operation that computes the projections of an object from all possible angles.

Purpose of Rotation in CT

• Rotation serves to acquire multiple projections of the object from different angles, which are then used to reconstruct a cross-sectional image.

Re-Creation of Cross-Sectional Image

• Words used to describe the re-creation of a cross-sectional image include reconstruction, back-projection, and filtered back-projection.

Advantage of CT

• An X-ray CT image offers the main advantage over an X-ray radiograph by displaying a cross-sectional view of the body, which provides more detailed information about the internal structures.

Creating 3D Image

• A 3D image can be created from CT scan data by stacking multiple cross-sectional images together and rendering them into a 3D volume.

Visible Human Project

• Three types of images were created for the Visible Human Project: transverse anatomical images, CT images, and MRI images.
• The thickness of the respective image slices varies depending on the imaging modality: 1 mm, 1 mm, and 3 mm.

Cryosection Image

• The general process used to create a cryosection image involves freezing a cadaver, sectioning it into thin slices, and photographing each slice.

Definition Ultrasound

• Ultrasound frequencies lie above the range of human hearing, typically above 20 kHz.

Medical Imaging

• The ultrasonic frequency range typically employed for medical imaging is 2-18 MHz.

Echolocation

• Two types of animals that utilize ultrasonic sonar for echolocation are bats and dolphins.

Ultrasound-Related Terms

• A piezoelectric crystal converts electrical energy into mechanical energy (sound waves) and vice versa.
• A bidirectional transducer can both emit and receive sound waves.
• Demodulation extracts the information from the returning signal.
• Time gain compensation compensates for the attenuation of sound waves as they travel through tissue.
• An ultrasonic burst is a short pulse of high-frequency sound waves.
• Tissue acoustic impedance is the resistance of tissue to the propagation of sound waves.
• Ultrasonic reflection is the phenomenon of sound waves bouncing off interfaces between tissues with different acoustic impedances.

Tissue Depths

• Given the speed of sound in tissue, you should be prepared to convert burst reflection times into tissue depths using the formula: depth = (speed of sound * time) / 2.

A-Mode Ultrasound

• For A-mode ultrasound, signal voltages versus time can be converted into pixel grayscale values versus image position (tissue depth) by mapping the amplitude of the signal to the brightness of the pixel.

Piezoelectric Crystal

• (a) A single piezoelectric crystal can produce an M-mode image by repeatedly emitting sound waves along a single line and displaying the resulting reflections over time.
• (b) Multiple crystals can produce a B-mode image by arranging them side-by-side to create a linear array that scans across the tissue.

Imaging Frequency Relationship

• An increase in imaging frequency increases image resolution but reduces imaging depth and vice versa.

Butterfly iQ Probe

• The Butterfly iQ ultrasonic imaging probe is unique because it is a single-probe, whole-body ultrasound system that connects to a smartphone or tablet.

Fundamental Tissue Information

• MRI depicts the density of protons in different tissues as a function of 3D position.

MRI Functions

• The main magnetic coil in an MRI unit creates a strong magnetic field that aligns the protons in the body.
• The orthogonal radiofrequency pulser emits radio waves that excite the protons and cause them to emit signals that can be detected.

Radioactive Tracers

• Radioactive tracers bind to specific types of tissue depending on their chemical properties.
• A PET imaging system displays information about the metabolic activity of tissues, not anatomy.
• This information is displayed in cross-section.

PET System

• In a PET system, the radioactive tracer emits positrons, which collide with electrons and produce gamma photons. These photons are detected by the PET scanner.

Gamma Photon Conversion

• A gamma photon is converted into an electrical voltage (count) through a series of steps: scintillation, photomultiplication, and electronic processing.

SPECT vs PET

• The main difference between SPECT and PET systems is the type of radioactive tracer used.
• SPECT tracers emit gamma rays directly, while PET tracers emit positrons that produce gamma rays.

Thermographic Image

• A thermographic image depicts the temperature distribution on the surface of the body.
• Medical applications where thermographic imaging has proved useful include detecting breast cancer and identifying areas of inflammation.