A startup develops a continuous wearable ECG patch for detecting atrial fibrillation. The FDA tells them they must demonstrate substantial equivalence to an already-cleared predicate device. Which regulatory pathway are they following?

PMA (Premarket Approval) — required for all wearable devices 510(k) premarket notification — used for Class II devices De Novo request — used when no predicate device exists IDE (Investigational Device Exemption) — allows sale before approval

A company designs a new mechanical heart valve intended to permanently replace a diseased natural valve. Without intervention, patients with this condition die within months. Which FDA device class does this product fall into, and why?

Class I — because it is a mechanical rather than electronic device Class II — because it has a predicate device on the market Class III — because failure of a permanently implanted heart valve poses an immediate risk of serious injury or death Class I — because surgeons are trained to implant it correctly

A patient's pacemaker is programmed remotely by a cardiologist who adjusts the pacing rate and sensitivity thresholds from a clinic computer without the patient being present. Which engineering feature enables this?

Bluetooth Low Energy — the standard used for all consumer wearables Wireless telemetry — allowing bidirectional data exchange between the implanted device and an external programmer Wi-Fi — because hospitals have strong network infrastructure NFC — which is used only for payment terminals

An MRI scan of a patient's knee provides excellent contrast between cartilage, ligaments, and bone marrow without using ionising radiation. What physical phenomenon is MRI exploiting to generate this image?

X-ray attenuation differences between tissues of varying density Ultrasound reflection at tissue boundaries of differing acoustic impedance The alignment and relaxation of hydrogen proton magnetic moments in a strong external magnetic field Infrared emission differences between tissues at different temperatures

An emergency department needs to rapidly assess a patient for suspected rib fractures and internal bleeding after a car accident. The radiologist recommends CT rather than MRI. What is the most clinically relevant engineering reason for this choice?

MRI uses ionising radiation that is dangerous in emergencies CT is faster and provides superior bone and acute haemorrhage imaging, making it better suited to emergency trauma assessment CT has better soft-tissue contrast than MRI for all tissue types MRI cannot image the chest because it requires a breath hold

A pulse oximeter reads 96% SpO₂. The device uses two LEDs shining through the fingertip. Which wavelengths are used and why are two different wavelengths necessary?

Red (~660nm) and infrared (~940nm) — because oxygenated and deoxygenated haemoglobin absorb these wavelengths differently, allowing the ratio to indicate oxygen saturation Ultraviolet and visible blue — because haemoglobin fluoresces at these wavelengths Green and yellow — because these penetrate skin most effectively Infrared only — because a single wavelength gives a more stable reading

A study finds that pulse oximeters systematically overestimate SpO₂ in patients with darker skin pigmentation, leading to missed hypoxaemia. What engineering factor is responsible for this measurement bias?

Darker skin has lower blood vessel density, reducing pulsatile signal amplitude Melanin absorbs some of the same wavelengths used to measure haemoglobin, introducing a systematic error in the SpO₂ calculation Darker skin is thicker, increasing the path length for infrared light The devices malfunction at higher body temperatures common in these patients

A COVID-19 rapid antigen test produces a visible coloured line at the test zone within 20 minutes. The test uses nitrocellulose strips and antibodies. Which mechanism causes the coloured line to appear when the antigen is present?

The antigen changes colour when it denatures at the nitrocellulose membrane The antigen binds to labelled antibodies; this complex is captured by a second antibody at the test line, concentrating the label to produce a visible coloured band A PCR reaction amplifies the antigen's genetic material producing fluorescence The strip changes colour because the pH shifts when a virus is present

An ECG recording from a patient in an emergency room shows a strong 50Hz sinusoidal pattern superimposed on the cardiac signal, making the QRS complexes difficult to identify. What signal processing technique should the engineer apply first?

A low-pass filter cutting off above 40Hz — to remove all high-frequency content A high-pass filter above 100Hz — to emphasise fast cardiac transients A notch filter centred at 50Hz — to remove the mains electrical interference while preserving the cardiac signal Signal averaging of 100 consecutive beats — to reduce random noise only

A ventilator in an ICU is set to volume-controlled mode with a tidal volume of 500mL and a respiratory rate of 14 breaths per minute. The patient begins to breathe spontaneously between ventilator breaths. What clinical risk does this scenario pose if the ventilator is not adjusted?

The patient will receive too little oxygen because 500mL is below the normal tidal volume The circuit will disconnect because spontaneous breathing creates negative pressure Patient-ventilator dyssynchrony — the machine's fixed cycle can fight against the patient's own breathing effort, causing discomfort, increased work of breathing, and potential lung injury The ventilator will automatically switch to pressure-controlled mode

An ICD (Implantable Cardioverter-Defibrillator) successfully detects ventricular fibrillation and delivers a 35-joule internal shock that restores sinus rhythm. How does an ICD's function differ from a standard pacemaker?

A pacemaker only delivers low-energy pacing pulses; an ICD also detects life-threatening arrhythmias and can deliver a high-energy shock to restore normal rhythm An ICD operates wirelessly while pacemakers require a wired connection to the heart A pacemaker monitors SpO₂ while an ICD monitors ECG ICDs are only used externally during cardiac arrest; pacemakers are always implanted

A medical device approved under the EU's Medical Device Directive (MDD) must now comply with the newer Medical Device Regulation (MDR). A manufacturer discovers the MDR requires post-market clinical follow-up and more extensive technical documentation. What does this regulatory shift reflect?

The EU wanted to align its regulations with the US FDA's 510(k) process Regulators strengthened requirements after high-profile device failures revealed that pre-market evidence alone was insufficient to ensure ongoing safety The MDR removes clinical requirements to speed device approvals The change was driven entirely by Brexit, which excluded UK notified bodies