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HKIE Professional Assessment - Biomedical Discipline study materials
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HKIE Professional Assessment - Biomedical Discipline practice questions

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Question 1Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

Which mechanical property best describes a material's resistance to elastic deformation under a tensile load, expressed as the slope of the initial linear portion of the stress-strain curve?

  1. Creep resistance
  2. Young's modulus Correct answer.
  3. Toughness
  4. Ductility

Explanation

Young's modulus is defined as the ratio of stress to strain in the linear elastic region, so it is literally the slope of that initial straight segment. It quantifies stiffness, meaning resistance to elastic (recoverable) deformation. The other properties describe energy absorption, plastic extension, or time-dependent strain instead.

Question 2Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

A bone specimen is loaded in tension to 0.2% strain and returns to its original length when unloaded. This behaviour indicates the loading remained within which region?

  1. The ultimate strength point
  2. The fracture point
  3. The elastic region Correct answer.
  4. The plastic region

Explanation

Full recovery of original length on unloading is the defining feature of elastic deformation. Plastic deformation would leave a permanent residual strain. Ultimate strength and fracture are points on the curve beyond yielding where irreversible damage has occurred.

Question 3Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

In a long bone such as the femur, which anatomical region is primarily responsible for longitudinal growth during childhood and adolescence?

  1. The articular cartilage
  2. The medullary cavity
  3. The epiphyseal plate Correct answer.
  4. The periosteum

Explanation

The epiphyseal plate is the cartilaginous growth plate where endochondral ossification lengthens the bone. Once it closes in adulthood, longitudinal growth ceases. The periosteum contributes mainly to appositional (width) growth, and the medullary cavity is a marrow space.

Question 4Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

Which class of biomaterial is most commonly selected for a permanent hip stem because it combines high strength with the ability to form a passive oxide layer?

  1. Polyethylene
  2. Titanium alloy Correct answer.
  3. Calcium phosphate ceramic
  4. Silicone elastomer

Explanation

Titanium alloys offer high specific strength and spontaneously form a stable passive titanium oxide surface layer that provides corrosion resistance in the body. This combination suits load-bearing permanent implants. The other options lack the strength or durability required for a femoral stem.

Question 5Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

According to the Hagen-Poiseuille relationship for laminar flow in a rigid tube, how does volumetric flow rate change if the vessel radius is halved while pressure gradient and viscosity are held constant?

  1. It remains unchanged
  2. It falls to one-half of the original value
  3. It falls to one-sixteenth of the original value Correct answer.
  4. It falls to one-quarter of the original value

Explanation

Hagen-Poiseuille flow is proportional to the fourth power of radius. Halving the radius gives a factor of (1/2)^4, which equals 1/16. This strong fourth-power dependence explains why small changes in vessel calibre cause large changes in resistance and flow.

Question 6Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

A cylindrical ligament replacement must carry a tensile load of 500 N with a peak allowable stress of 25 MPa. What minimum cross-sectional area is required?

  1. 200 mm²
  2. 20 mm² Correct answer.
  3. 0.05 mm²
  4. 2 mm²

Explanation

Stress equals force divided by area, so area equals force divided by stress. Dividing 500 N by 25 MPa (25 N/mm²) gives 20 mm². Keeping units consistent in newtons and square millimetres avoids conversion errors.

Question 7Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

Which statement correctly describes the role of the sarcoplasmic reticulum in skeletal muscle contraction?

  1. It generates ATP through oxidative phosphorylation
  2. It synthesizes collagen for the tendon insertion
  3. It stores calcium ions and releases them to trigger cross-bridge cycling Correct answer.
  4. It transmits action potentials from the motor neuron to the myofibril

Explanation

The sarcoplasmic reticulum is a specialised calcium store in muscle. Depolarisation triggers calcium release, which binds troponin and permits actin-myosin cross-bridge formation. Reuptake of calcium into the same store initiates relaxation.

Question 8Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

A polymeric component of a prosthetic valve is required to flex repeatedly without accumulating permanent deformation. Which property should be maximised for this requirement?

  1. Density
  2. Water absorption
  3. Surface roughness
  4. Elastic resilience Correct answer.

Explanation

Elastic resilience is the capacity to absorb and return strain energy during cyclic deformation, which is exactly what a repeatedly flexing leaflet needs. High resilience limits residual strain and hysteresis. Roughness, water uptake and density do not govern recovery from flexure.

Question 9Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

Which mechanism most accurately explains the anticoagulant action of heparin in an extracorporeal circuit?

  1. It enhances the activity of antithrombin, accelerating inactivation of thrombin and factor Xa Correct answer.
  2. It directly lyses formed fibrin strands
  3. It chelates calcium ions and blocks the coagulation cascade
  4. It inhibits platelet adhesion to the tubing surface

Explanation

Heparin binds antithrombin and increases its affinity for thrombin and factor Xa, dramatically accelerating their inactivation. This is the basis of its use in dialysis and bypass circuits. Calcium chelation and fibrinolysis are separate mechanisms belonging to other agents.

Question 10Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

In a three-electrode electrochemical cell used to assess implant corrosion, which electrode is maintained at a known, stable potential to allow accurate measurement of the working electrode?

  1. The sensing electrode
  2. The working electrode
  3. The reference electrode Correct answer.
  4. The counter electrode

Explanation

The reference electrode provides a stable, known potential against which the working electrode potential is controlled and measured. The counter electrode merely completes the current path. The working electrode is the specimen under investigation.

Question 11Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

A balloon catheter must be inflated inside a stenosed artery without exceeding a vessel wall pressure of 1.2 MPa. If the balloon is modelled as a thin-walled cylinder with radius 4 mm and wall thickness 0.1 mm, what hoop stress arises at that internal pressure?

  1. 96 MPa
  2. 24 MPa
  3. 48 MPa Correct answer.
  4. 4.8 MPa

Explanation

For a thin-walled cylinder, hoop stress equals pressure times radius divided by wall thickness. Using 1.2 MPa, 4 mm and 0.1 mm gives 1.2 times 4 divided by 0.1, which is 48 MPa. The radius-to-thickness ratio of 40 also confirms the thin-wall assumption is reasonable.

Question 12Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

Why is a material with a modulus close to that of cortical bone often preferred for a cementless femoral stem?

  1. It reduces stress shielding of the surrounding bone Correct answer.
  2. It prevents all bacterial colonisation
  3. It eliminates wear debris generation
  4. It guarantees complete osseointegration

Explanation

A large mismatch between implant and bone stiffness causes the implant to carry most of the load, shielding bone from stress and leading to resorption. Matching modulus more closely distributes load to bone and limits stress shielding. Osseointegration, wear and infection depend on surface and other factors, not modulus alone.

Question 13Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

During the cardiac cycle, which event produces the first heart sound heard on auscultation?

  1. Opening of the atrioventricular valves during ventricular filling
  2. Closure of the atrioventricular valves at the onset of ventricular systole Correct answer.
  3. Closure of the semilunar valves at the end of ventricular systole
  4. Contraction of the atria during late diastole

Explanation

The first heart sound arises when the mitral and tricuspid valves snap shut as ventricular pressure rises above atrial pressure at the start of systole. Semilunar valve closure generates the second sound. Valve opening and atrial contraction are normally silent.

Question 14Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

Which unit expresses the compliance of a blood vessel in a way consistent with its definition as change in volume per unit change in pressure?

  1. kg per m³
  2. N per m
  3. m³ per Pa Correct answer.
  4. Pa per m³

Explanation

Vascular compliance is defined as the change in contained volume divided by the change in transmural pressure. Its unit is therefore volume per pressure, for example cubic metres per pascal. The reciprocal, elastance, would carry pressure per volume.

Question 15Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

A candidate biomaterial for a degradable suture is required to lose strength predictably over four weeks in vivo. Which degradation mechanism is most directly appropriate?

  1. Passive dissolution of a platinum wire
  2. Hydrolytic scission of ester bonds in a poly(lactic-co-glycolic acid) backbone Correct answer.
  3. Oxidative wear of an alumina ceramic
  4. Creep of a crosslinked silicone under load

Explanation

Poly(lactic-co-glycolic acid) degrades by hydrolysis of its ester backbone, and the ratio of lactide to glycolide tunes the strength-loss timeline. This makes it a standard choice for absorbable sutures. The other options describe mechanisms that are not predictable bulk resorption.

Question 16Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

Which factor most strongly determines whether blood flow in a large artery is laminar or turbulent?

  1. The Reynolds number Correct answer.
  2. The oxygen saturation
  3. The haematocrit
  4. The plasma oncotic pressure

Explanation

The Reynolds number, a dimensionless ratio of inertial to viscous forces, predicts the transition from laminar to turbulent flow. Above a critical value, disturbances amplify and turbulence develops. Haematocrit affects viscosity and thus the number, but the number itself is the deciding criterion.

Question 17Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

A prosthetic foot is designed so that energy stored during heel strike is returned during push-off. Which property of the spring element should be maximised to achieve this?

  1. Coefficient of friction
  2. Plastic yield strength
  3. Elastic resilience Correct answer.
  4. Viscous damping

Explanation

Elastic resilience is the strain energy recoverable per unit volume during elastic deformation, so maximising it allows more energy to be stored and returned each step. Damping dissipates energy as heat and reduces return. Plastic yielding would cause permanent deformation.

Question 18Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

Which statement correctly distinguishes the function of osteoblasts from that of osteoclasts in bone remodelling?

  1. Osteoclasts form the periosteum, while osteoblasts form the marrow
  2. Osteoblasts resorb mineralised bone, while osteoclasts deposit new matrix
  3. Osteoblasts deposit new bone matrix, while osteoclasts resorb mineralised bone Correct answer.
  4. Both cell types deposit bone matrix but differ in their location

Explanation

Osteoblasts are the bone-forming cells that secrete osteoid and promote its mineralisation. Osteoclasts are multinucleated cells that resorb bone by acidification and enzymatic digestion. Their coupled activity maintains bone mass during remodelling.

Question 19Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

A hydrogel contact lens must remain hydrated and soft while transmitting oxygen. Which property is most relevant to its oxygen transport performance?

  1. Refractive index
  2. Tear strength
  3. Oxygen permeability Correct answer.
  4. Compressive modulus

Explanation

Oxygen permeability quantifies the rate at which oxygen diffuses through the lens material and is the key metric for corneal health. Modulus, refractive index and tear strength govern comfort, optics and durability respectively, not oxygen flux.

Question 20Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

In a strain-gauge plethysmograph, the measured change in limb volume is used to infer blood flow. Which assumption underlies this inference?

  1. Volume change over a short interval reflects the arterial inflow that has not yet drained Correct answer.
  2. The limb behaves as a rigid body
  3. Venous outflow is always greater than arterial inflow
  4. Blood viscosity remains zero during measurement

Explanation

Plethysmography briefly occludes venous return, and the initial rate of limb swelling reflects arterial inflow before venous drainage equilibrates. The method assumes the volume change tracks blood entering the segment. Rigid-body and zero-viscosity assumptions are physically impossible.

Question 21Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

Which mechanism best explains the improved wear resistance of a cobalt-chromium femoral head articulating against crosslinked ultra-high-molecular-weight polyethylene?

  1. The cobalt-chromium surface dissolves preferentially in synovial fluid
  2. Crosslinking lowers the melting point of polyethylene
  3. Crosslinking reduces the molecular mobility that permits plastic drawing and wear particle formation Correct answer.
  4. The polyethylene becomes hydrophilic and dissolves in the joint fluid

Explanation

Crosslinking creates covalent bonds between polymer chains, restricting the chain sliding and drawing that generates wear debris under articulation. This reduces abrasive and adhesive wear. It does not lower melting point or cause dissolution of either component.

Question 22Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

Which statement correctly describes the relationship between muscle force and sarcomere length described by the length-tension curve?

  1. Force is independent of sarcomere length
  2. Force increases monotonically as sarcomeres are stretched beyond overlap
  3. Force is maximal when sarcomeres are shortest and filaments overlap completely
  4. Force is maximal at an intermediate length where actin-myosin overlap is optimal Correct answer.

Explanation

The length-tension curve peaks at an intermediate sarcomere length where the number of available actin-myosin cross-bridges is greatest. Overstretching reduces overlap and force, while extreme shortening compresses filaments and also reduces force. The relationship is therefore bell-shaped rather than monotonic.

Question 23Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

A biomaterial surface is modified to resist protein adsorption in blood. Which surface characteristic is generally most effective for this purpose?

  1. High positive charge density
  2. High hydrophilicity combined with neutral charge Correct answer.
  3. High surface roughness
  4. High hydrophobic character

Explanation

Hydrophilic, electrically neutral surfaces bind a tightly held water layer that thermodynamically resists protein adsorption. This is the principle behind PEGylated and zwitterionic coatings. Charged or hydrophobic surfaces tend to attract proteins through electrostatic or hydrophobic interactions.

Question 24Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

Which statement correctly describes the origin of the resting membrane potential of a neuron?

  1. It arises from equal permeability to all ions across the membrane
  2. It arises mainly from selective potassium permeability and the resulting ion gradients Correct answer.
  3. It is maintained entirely by chloride influx through open channels
  4. It is generated by active transport of glucose across the membrane

Explanation

At rest the membrane is far more permeable to potassium than to other ions, so potassium efflux down its gradient leaves the interior negative. The sodium-potassium pump maintains the gradients that sustain this potential. Equal permeability or chloride influx alone would not produce the observed resting value.

Question 25Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

A tissue-engineered cartilage construct must support compressive load while allowing nutrient diffusion. Which scaffold design best balances these requirements?

  1. A rigid metal mesh with closed cells
  2. A highly porous hydrogel with interconnected pores and adequate compressive modulus Correct answer.
  3. A fully dense non-porous polymer block
  4. A scaffold with sealed surface pores and low water content

Explanation

Interconnected porosity permits nutrient and waste diffusion, while the hydrogel matrix provides a hydrated load-bearing phase with a compressive modulus suited to cartilage. Sealing pores or using dense or closed-cell structures blocks transport. A metal mesh with closed cells also fails the diffusion requirement.

Question 26Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

A tendon graft is loaded in uniaxial tension and its stress-strain curve is recorded. Which point on that curve defines the yield point used to characterise the onset of permanent deformation?

  1. The point of maximum stress reached before rupture
  2. The point where the tangent modulus becomes zero at failure
  3. The point where the curve deviates from linearity by a defined offset strain Correct answer.
  4. The point where the curve first becomes non-zero after loading begins

Explanation

The yield point marks the transition from elastic to plastic behaviour, and for materials without a sharp knee it is defined by a specified offset strain (commonly 0.2%) from the linear region. Beyond this point, unloading leaves residual (permanent) deformation in the tissue. The maximum stress and the failure point describe ultimate strength, not yield.

Question 27Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

A titanium hip stem is to be fixed without bone cement. Which combination of bulk material properties best supports long-term fixation by load transfer to the surrounding femur?

  1. Low elastic modulus relative to bone, combined with a rough or porous surface for bone ingrowth Correct answer.
  2. High elastic modulus relative to bone, combined with a smooth surface to reduce bacterial adhesion
  3. High elastic modulus relative to bone, combined with a polished surface to minimise friction
  4. Low elastic modulus relative to bone, combined with a fully smooth surface to prevent tissue attachment

Explanation

Cementless fixation relies on stable mechanical interlock and biological anchorage, so a lower-modulus stem reduces stress shielding while a rough or porous surface permits bone ingrowth. Together these promote durable load transfer to the femur. Surface finish for ingrowth and bulk stiffness act together, not independently.

Question 28Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

In a skeletal muscle, the force generated at a given activation level depends strongly on sarcomere length. Which explanation accounts for the descending limb of the length-tension curve at long sarcomere lengths?

  1. The series elastic element stores more energy, reducing force transmitted to the tendon
  2. Calcium release from the sarcoplasmic reticulum falls sharply as the sarcomere is stretched
  3. Fewer actin-myosin cross-bridges can form because the thick and thin filament overlap is reduced Correct answer.
  4. Thin filaments are pulled past the thick filament centre, causing active tension to rise

Explanation

Active tension depends on the number of cross-bridges that can form, which is set by the overlap between actin and myosin filaments. As the sarcomere is stretched beyond optimal length, overlap decreases and fewer cross-bridges generate force. This produces the descending limb of the length-tension relationship.

Question 29Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

A poly(lactic-co-glycolic acid) suture is intended to lose strength predictably after implantation. Which mechanism most directly governs its loss of mechanical strength in vivo?

  1. Enzymatic cleavage of peptide bonds by circulating proteases
  2. Hydrolytic scission of ester bonds in the polymer backbone, accelerated by the aqueous environment Correct answer.
  3. Dissolution of the polymer without any covalent bond breaking
  4. Oxidative attack on carbon-carbon bonds by reactive oxygen species

Explanation

PLGA degrades mainly by hydrolysis of its ester linkages, and the rate is sensitive to water uptake, local pH, copolymer ratio and device geometry. Chain scission reduces molecular weight and, once a critical value is reached, mechanical strength falls. This is a chemical degradation process, not simple dissolution.

Question 30Biomedical engineering fundamentals (biomechanics, biomaterials, physiology for engineers)

A rigid spherical particle of density 1050 kg/m3 and diameter 20 micrometres settles in a Newtonian fluid of density 1000 kg/m3 and dynamic viscosity 1.0 mPa·s. Using Stokes' law, which value best approximates its terminal settling velocity?

  1. About 1.1 x 10^-2 m/s
  2. About 1.1 x 10^-4 m/s Correct answer.
  3. About 1.1 x 10^-8 m/s
  4. About 1.1 x 10^-6 m/s

Explanation

Stokes' law gives v = (density difference x g x d^2) / (18 x viscosity). Substituting 50 kg/m3, 9.81 m/s2, (20 x 10^-6)^2 m2 and 18 x 10^-3 Pa·s yields approximately 1.1 x 10^-4 m/s. The strong dependence on diameter squared means small changes in particle size shift the velocity greatly.

Question 31Medical devices and instrumentation (design, sensors, signal acquisition, safety)

A pressure sensor for an invasive blood-pressure catheter must measure 0 to 300 mmHg with a resolution of 1 mmHg. Which specification most directly determines whether this resolution is achievable?

  1. The sensor's operating temperature range
  2. The sensor's sensitivity in µV/V/mmHg combined with the readout noise floor Correct answer.
  3. The sensor's full-scale output voltage
  4. The sensor's overpressure tolerance

Explanation

Resolution is set by how much signal each mmHg produces (sensitivity) relative to the electronic noise floor of the readout chain. A high sensitivity with a low-noise amplifier gives fine resolution; large full-scale output alone does not. Overpressure and temperature range affect safety and drift, not the smallest resolvable increment.

Question 32Medical devices and instrumentation (design, sensors, signal acquisition, safety)

In a single-ended ECG acquisition front end, a 50 Hz mains interference appears strongly on the trace. Which design change most directly improves common-mode rejection?

  1. Reducing the gain of the first amplifier stage
  2. Adding a low-pass filter with a 40 Hz cutoff
  3. Increasing the ADC sampling rate
  4. Replacing the single-ended input with a differential instrumentation amplifier with matched electrode impedances Correct answer.

Explanation

Mains interference couples as a common-mode signal; a differential amplifier rejects it only when the electrode source impedances are matched. Sampling rate and post-filtering do not address common-mode conversion. Reducing first-stage gain worsens the noise budget without improving rejection.

Question 33Medical devices and instrumentation (design, sensors, signal acquisition, safety)

A medical device is classified as Class IIb under the EU MDR. Which conformity assessment route is generally required for a device in this class?

  1. Approval by a national competent authority before each shipment
  2. Certification solely by the testing laboratory that performed EMC testing
  3. Involvement of a notified body in the conformity assessment Correct answer.
  4. Self-declaration by the manufacturer with no notified body involvement

Explanation

Under the EU MDR, Class IIb devices generally require a notified body to assess the quality management system and technical documentation. Self-declaration is reserved for lower-risk Class I devices. National authority pre-approval per shipment and laboratory-only certification are not the MDR routes.

Question 34Medical devices and instrumentation (design, sensors, signal acquisition, safety)

A pulse oximeter uses the ratio-of-ratios method. Which pair of wavelengths is conventionally used and why?

  1. Blue and yellow, because melanin absorbs both identically
  2. Red and infrared, because oxygenated and deoxygenated haemoglobin differ in absorption between these bands Correct answer.
  3. Ultraviolet and green, because skin transmits both equally
  4. Microwave and red, because water absorption dominates

Explanation

Pulse oximetry exploits the different absorption spectra of oxyhaemoglobin and deoxyhaemoglobin, typically around 660 nm red and 940 nm infrared. The ratio of pulsatile to non-pulsatile absorption at both wavelengths yields the oxygen saturation estimate. Other wavelength pairs lack this differential absorption behaviour.

Question 35Medical devices and instrumentation (design, sensors, signal acquisition, safety)

A defibrillator delivers a 200 J biphasic shock. Which patient-safety feature is most important to prevent accidental discharge into a rescuer?

  1. A rechargeable battery pack
  2. A high-resolution LCD display
  3. A discharge control requiring deliberate operator action with a clearly indicated charged state Correct answer.
  4. An impedance-compensated energy delivery circuit

Explanation

Accidental shock prevention relies on deliberate, guarded discharge controls and clear charged-state indication so the operator intends to deliver energy. Impedance compensation improves dose accuracy but does not prevent inadvertent discharge. Displays and batteries are unrelated to this hazard control.

Question 36Medical devices and instrumentation (design, sensors, signal acquisition, safety)

An infusion pump uses a stepper motor driving a syringe plunger. Occlusion is detected by monitoring motor current. Which limitation of current-based occlusion detection should the designer account for?

  1. It is sensitive to mechanical friction and temperature, which can cause false alarms or missed occlusions Correct answer.
  2. It only works with peristaltic pumps
  3. It cannot detect occlusion at low flow rates because current is always zero
  4. It requires an optical sensor to function

Explanation

Motor current reflects total load, including friction, viscosity and temperature effects, not only occlusion back-pressure. These confounders can trigger false alarms or mask a genuine occlusion. The method does not depend on optical sensing and is not limited to peristaltic designs.

Question 37Medical devices and instrumentation (design, sensors, signal acquisition, safety)

An ECG signal is sampled at 500 Hz with a 12-bit ADC. What is the approximate quantisation step size if the input range is ±5 mV?

  1. About 24 µV
  2. About 240 µV
  3. About 0.24 µV
  4. About 2.4 µV Correct answer.

Explanation

A 12-bit converter over a 10 mV total span gives 10 mV / 4096 ≈ 2.4 µV per least significant bit. The sampling rate does not affect the quantisation step. This is well below typical ECG signal amplitudes, so quantisation noise is not the limiting factor.

Question 38Medical devices and instrumentation (design, sensors, signal acquisition, safety)

A wearable heart-rate monitor uses a photoplethysmographic sensor. Which factor most strongly degrades signal quality during vigorous exercise?

  1. Increased ambient room lighting
  2. Reduced battery voltage
  3. Motion artefact and changes in tissue blood volume Correct answer.
  4. Longer Bluetooth packet intervals

Explanation

Motion artefact and exercise-induced changes in perfusion and venous pooling distort the pulsatile optical signal. Ambient light is a concern but is usually managed by optical shielding and modulation. Battery voltage and radio packet timing do not directly corrupt the optical waveform.

Question 39Medical devices and instrumentation (design, sensors, signal acquisition, safety)

A device labelled as meeting IEC 60601-1 is being integrated into a system with a second mains-powered device via a USB cable. Which safety consideration is most relevant?

  1. The USB data rate must match between devices
  2. The combination must be assessed as a medical electrical system, including protective earthing and leakage current Correct answer.
  3. The USB cable must be shorter than 0.5 m
  4. Both devices must use the same firmware version

Explanation

Combining devices can create new earth paths and alter leakage currents, so the assembly must be evaluated as a medical electrical system under the collateral standard. Data rate, firmware and cable length are not the governing safety issue. Earthing and leakage current limits are the central concerns.

Question 40Medical devices and instrumentation (design, sensors, signal acquisition, safety)

A thermistor-based temperature probe for a patient monitor uses a negative temperature coefficient (NTC) thermistor. How does its resistance change as temperature rises?

  1. Resistance oscillates
  2. Resistance increases
  3. Resistance decreases Correct answer.
  4. Resistance stays constant

Explanation

An NTC thermistor has a negative temperature coefficient, so its resistance falls as temperature increases. This is the defining behaviour that distinguishes it from a positive temperature coefficient device. The change is monotonic and predictable over the rated range.

Question 41Medical devices and instrumentation (design, sensors, signal acquisition, safety)

An electrocardiograph must meet a maximum input circuit leakage current limit. Which design measure most directly limits patient leakage current from the isolated patient circuit?

  1. Using a high-impedance isolation barrier with adequate creepage and a patient auxiliary current design limit Correct answer.
  2. Reducing the sampling rate
  3. Increasing the ADC resolution
  4. Adding a larger display

Explanation

Patient leakage current is controlled by the isolation barrier and by limiting patient auxiliary current through the applied parts. Creepage and clearance in the isolation design are central. ADC resolution, display size and sampling rate do not limit leakage current.

Question 42Medical devices and instrumentation (design, sensors, signal acquisition, safety)

A blood glucose meter uses an amperometric enzyme electrode. Which relationship underlies its measurement principle?

  1. The capacitance of the electrode is proportional to glucose concentration
  2. The resistance of the electrode is proportional to glucose concentration
  3. The current is proportional to the rate of the enzymatic reaction, which depends on glucose concentration Correct answer.
  4. The voltage across the electrode is proportional to glucose concentration

Explanation

In amperometric biosensors, a fixed potential drives oxidation of a mediator or peroxide, and the resulting current is proportional to the reaction rate and hence to glucose concentration. Voltage is held constant, and resistance or capacitance are not the primary measurands. The enzyme provides selectivity for glucose.

Question 43Medical devices and instrumentation (design, sensors, signal acquisition, safety)

A clinician reports that a monitor shows a flat line although the patient is conscious. Which fault is most consistent with this presentation?

  1. A drift in the display backlight brightness
  2. A slow battery discharge
  3. An increase in ambient temperature
  4. A disconnected patient lead combined with loss-of-signal detection failure Correct answer.

Explanation

A flat trace in a conscious patient suggests the signal path is broken, for example a detached lead, while the monitor fails to flag the loss of signal. Backlight, battery and ambient temperature do not produce a false asystole trace. The design lesson is that lead-off detection must be reliable and annunciated.

Question 44Medical devices and instrumentation (design, sensors, signal acquisition, safety)

Which statement best describes the purpose of a high-pass filter in an ECG front end?

  1. It removes high-frequency muscle artefact
  2. It removes baseline wander caused by respiration and electrode motion Correct answer.
  3. It removes 50/60 Hz mains interference
  4. It increases the common-mode rejection ratio

Explanation

Baseline wander is a low-frequency artefact, so a high-pass filter with a low cutoff (typically around 0.05 Hz for diagnostic ECG) removes it while preserving the ST segment. Mains interference is handled by a notch or by common-mode rejection, and muscle artefact is high frequency. The filter does not itself change common-mode rejection.

Question 45Medical devices and instrumentation (design, sensors, signal acquisition, safety)

A pacemaker's sensing amplifier must distinguish cardiac depolarisation from noise. Which combination of characteristics is most appropriate for the sensing channel?

  1. Band-pass filtering matched to the intracardiac electrogram spectrum with adaptive sensitivity Correct answer.
  2. Wide bandwidth with high gain and no filtering
  3. Low-pass filtering at 1 Hz with fixed threshold
  4. High-pass filtering at 100 Hz with fixed threshold

Explanation

Pacemaker sensing uses band-pass filtering tuned to the frequency content of intracardiac signals and adaptive sensitivity to avoid oversensing of noise and undersensing of small signals. Wideband unfiltered sensing invites oversensing. A 1 Hz low-pass or 100 Hz high-pass would reject the wanted signal.

Question 46Medical devices and instrumentation (design, sensors, signal acquisition, safety)

A medical device uses a rechargeable lithium-ion battery and is intended for home use. Which safety measure is most important for the battery subsystem?

  1. A higher capacity cell to reduce charging frequency
  2. A protection circuit limiting overcharge, over-discharge and short-circuit current Correct answer.
  3. A larger display to show charge percentage
  4. A faster charging algorithm without temperature monitoring

Explanation

Lithium-ion cells can fail dangerously under overcharge, over-discharge or short circuit, so a protection circuit with cell monitoring is essential. Display information does not mitigate the hazard. Higher capacity and faster charging without temperature monitoring increase risk rather than reduce it.

Question 47Medical devices and instrumentation (design, sensors, signal acquisition, safety)

An ultrasound transducer array is designed for a 5 MHz centre frequency. Which parameter primarily determines the axial resolution?

  1. The spatial pulse length, which depends on the number of cycles per pulse Correct answer.
  2. The number of elements in the array
  3. The width of the transducer footprint
  4. The acoustic impedance of the matching layer

Explanation

Axial resolution is approximately half the spatial pulse length, so fewer cycles per pulse and higher frequency improve it. Element count and footprint mainly affect lateral resolution and field of view. Matching layer impedance governs transmission efficiency, not axial resolution.

Question 48Medical devices and instrumentation (design, sensors, signal acquisition, safety)

A device transmits real-time waveform data over a wireless link to a central station. Which design choice best ensures timely alarm delivery when the link degrades?

  1. Rely on best-effort transmission and let the display show the last value
  2. Implement a bounded latency protocol with loss detection and a local alarm at the bedside Correct answer.
  3. Compress the waveform more aggressively without error checking
  4. Increase the display resolution at the central station

Explanation

Alarm delivery must be time-bounded, so the design needs latency guarantees, loss detection and an independent local alarm at the bedside. Best-effort transmission with stale values risks missed alarms. Display resolution and unchecked compression do not ensure timeliness or integrity.

Question 49Medical devices and instrumentation (design, sensors, signal acquisition, safety)

Which quantity does a Hall-effect sensor in a medical device most directly measure?

  1. Magnetic flux density Correct answer.
  2. Relative humidity
  3. Capacitance
  4. Optical absorbance

Explanation

A Hall-effect sensor produces a voltage proportional to magnetic flux density, enabling non-contact position, current and speed sensing. Capacitance, absorbance and humidity require different transduction principles. Hall sensors are common in device mechanisms and current monitoring.

Question 50Medical devices and instrumentation (design, sensors, signal acquisition, safety)

A ventilator's pressure sensor is calibrated at sea level but used at high altitude. Which error is most likely if no compensation is applied?

  1. A systematic offset in delivered pressure due to changed ambient reference pressure Correct answer.
  2. A random error with zero mean and no bias
  3. An increase in battery consumption
  4. A loss of electrical isolation

Explanation

Gauge pressure sensors use ambient pressure as their reference, so a change in altitude shifts the reference and introduces a systematic offset in delivered pressure. This is a bias, not zero-mean random noise. Isolation and battery consumption are unrelated to barometric reference changes.