PEC EPE Biomedical flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Half-cell potential

The DC voltage developed at an electrode-electrolyte interface relative to a reference; Ag/AgCl is stable and low-noise, while polarizable metals drift, causing baseline artifacts in biopotential recordings.

Nernst equation

Relates equilibrium potential to ion concentration ratio: E = E0 - (RT/zF)ln(Q). At body temperature a tenfold monovalent gradient gives about 61 mV.

Goldman-Hodgkin-Katz equation

Computes resting membrane potential from all permeant ions weighted by permeability, explaining why the resting potential sits near but not exactly at the potassium equilibrium potential.

Hodgkin-Huxley model

Quantitative membrane model using voltage-gated sodium (m, h) and potassium (n) gating variables to reproduce action potential threshold, upstroke, repolarization, and refractory periods.

Instrumentation amplifier CMRR

Common-mode rejection ratio expresses differential gain divided by common-mode gain; high CMRR (80-100 dB) is essential to extract millivolt biopotentials from volt-level mains interference.

Driven-right-leg circuit

An active circuit that senses common-mode voltage and injects an inverted signal into the patient, reducing common-mode interference and improving biopotential amplifier performance.

Nyquist sampling theorem

Sampling must exceed twice the highest signal frequency to avoid aliasing; anti-aliasing filters precede the ADC, and diagnostic ECG needs at least 300 Hz sampling.

Microshock versus macroshock

Macroshock passes through intact skin and needs roughly 100 mA to fibrillate; microshock through intracardiac catheters can fibrillate at about 100 µA, driving type CF limits.

Pennes bioheat equation

Models tissue temperature as conduction plus blood perfusion cooling plus metabolic heat, used to plan RF ablation, hyperthermia, and thermal safety margins.

Stress and strain

Stress is force per area and strain is fractional length change; their slope in the linear region is Young's modulus, which characterizes tissue and implant stiffness.

Viscoelastic tissue behavior

Tissues show time-dependent response: creep under constant load and stress relaxation under constant strain, modeled with Maxwell or Kelvin-Voigt spring-dashpot combinations.

MRI SAR limit

Specific absorption rate quantifies RF heating; whole-body limits near 4 W/kg over six minutes constrain sequence design, alongside projectile and peripheral nerve stimulation hazards.

Ultrasound axial resolution

Axial resolution equals half the spatial pulse length; fewer cycles and higher frequency shorten the pulse, improving resolution at the cost of penetration depth.

CTDIvol and DLP

CTDIvol measures dose per rotation in mGy; DLP equals CTDIvol times scan length, and effective dose is estimated by multiplying DLP by a body-region conversion factor.

Half-value layer

The thickness of material that reduces beam intensity by half, equal to ln2 divided by the linear attenuation coefficient; it characterizes beam quality and filtration.

Photoelectric versus Compton

Photoelectric absorption dominates at low energies and high atomic number, giving contrast; Compton scatter dominates in soft tissue at diagnostic energies and degrades image contrast.

Pacemaker lower rate limit

The programmed minimum pacing rate; its escape interval equals 60 divided by the rate in seconds, and sensed intrinsic events reset the timing cycle in inhibit modes.

Biphasic defibrillation waveform

A two-phase shock, typically 120-200 J, that lowers defibrillation threshold versus monophasic shocks; impedance compensation adjusts duration to deliver consistent current.

Steam sterilization parameters

Autoclave cycles use saturated steam at 121 °C for 15 minutes or 134 °C for 3-4 minutes; heat-sensitive polymers instead require ethylene oxide or ionizing radiation.

510(k) premarket notification

The US pathway for Class II devices demonstrating substantial equivalence to a legally marketed predicate; Class III devices generally need the stricter PMA route.

EU MDR device classes

Devices are classified I, IIa, IIb, or III by risk and invasiveness; all but low-risk Class I require Notified Body conformity assessment and CE marking.

ISO 10993 biocompatibility testing

Test selection depends on contact nature (surface, external communicating, implant) and duration; cytotoxicity, irritation, and sensitization form the initial screening battery.

Type CF applied part

A cardiac-floating patient connection permitting the strictest leakage limit, about 10 µA, because intracardiac current paths carry microshock fibrillation risk.

Signal-to-noise ratio

Ratio of signal power to noise power; in biomedical measurement it improves with electrode contact quality, averaging, filtering, and amplifier input impedance matching.

Electrode-skin impedance

Contact impedance at the electrode interface; high impedance raises thermal noise and common-mode pickup, so skin preparation and conductive gel are used to lower it.

Wiener filtering

An optimal linear filter minimizing mean-squared error for known signal and noise spectra, used to suppress noise in ECG, EEG, and other biosignals.

Aliasing

The folding of frequencies above half the sampling rate into lower frequencies; prevented by analog anti-aliasing filters placed before the analog-to-digital converter.

Pulse oximetry principle

Uses differential light absorption of oxygenated and deoxygenated hemoglobin at red and infrared wavelengths, with the pulsatile AC component isolating arterial saturation.

Beer-Lambert law

Attenuation is exponential in absorber concentration, path length, and extinction coefficient; underpins pulse oximetry, spectrophotometry, and optical biosensors.

Biosensor transducer types

Amperometric, potentiometric, optical, and piezoelectric transducers convert biorecognition events into measurable signals; glucose oxidase amperometric sensors are a common example.

Fick principle

Cardiac output equals oxygen consumption divided by the arteriovenous oxygen content difference; it also underlies indicator-dilution and mass-balance measurements.

Windkessel model

A lumped-parameter model of arterial load using resistance and compliance elements to relate aortic pressure and flow, capturing pulsatile hemodynamics beyond simple resistance.