Your Answer : (Not Answered)

Correct Answer : B

The transducer in a blood pressure monitor is a strain gauge.

In invasive monitoring the arterial line is connected through a fluid-filled catheter to a transducer whose diaphragm flexes with pressure. Strain gauges on or in the diaphragm, wired as a Wheatstone bridge, change resistance and give a voltage proportional to pressure. Many automatic non-invasive monitors also use a piezoresistive (strain gauge type) sensor to read cuff pressure.

Piezoelectric sensors respond to changing pressure but not to a steady one, so they are not the standard choice. Thermistors measure temperature, and photodiodes are used in pulse oximetry.

Your Answer : (Not Answered)

Correct Answer : B

A ventilator's primary function is to supply oxygen and remove CO2.

A mechanical ventilator moves gas into and out of the lungs when the patient cannot breathe adequately. It delivers a set tidal volume or pressure, rate and oxygen fraction, often with PEEP, so that oxygen reaches the alveoli and carbon dioxide is washed out. In other words, it takes over the work of ventilation.

Circulating blood is the job of the heart or a heart-lung machine. Measuring heart rate is the job of a monitor, and delivering shocks is the job of a defibrillator.

Your Answer : (Not Answered)

Correct Answer : A

ECG electrodes are generally made of silver-silver chloride.

An Ag/AgCl electrode is nearly non-polarisable: charge crosses the interface freely through the reversible reaction between silver and silver chloride. This gives a low, stable half-cell potential, low noise and little motion artefact, which is why disposable ECG electrodes use an Ag/AgCl sensor with chloride gel.

Platinum is a polarisable metal whose half-cell potential drifts, so it is used more for stimulation and some implanted electrodes. Copper and nickel corrode, are noisy and can irritate the skin.

Your Answer : (Not Answered)

Correct Answer : B

The ECG is based on the electrical activity of the heart.

As the action potential spreads from the SA node through the atria, the AV node and the ventricles, the depolarising and repolarising heart muscle creates currents that spread through the body. Electrodes on the skin pick up the resulting potential differences, a few millivolts at most, and record them as the P wave, the QRS complex and the T wave.

Blood pressure changes are recorded by pressure transducers, mechanical contraction by methods such as echocardiography, and blood flow in arteries by Doppler ultrasound. The ECG records none of these.

Your Answer : (Not Answered)

Correct Answer : C

The main advantage is to provide electrical safety and noise reduction.

An isolation amplifier has no direct electrical connection between its input and output stages. The signal crosses a barrier by transformer, optical or capacitive coupling. This keeps the patient circuit floating, limits leakage current, protects the patient from mains faults and the equipment from defibrillator pulses, and breaks ground loops that cause interference.

Increasing gain, reducing distortion and widening bandwidth are jobs for ordinary amplifier design. An isolation amplifier is chosen for safety, not for these.

Your Answer : (Not Answered)

Correct Answer : C

The EOG records corneoretinal potentials.

The eye acts as a dipole: the cornea is positive relative to the retina by a steady potential of several millivolts. Electrodes placed beside and above or below the eyes detect how this dipole turns as the eye moves. The electro-oculogram is therefore used to record eye movements, for example in sleep studies and nystagmus testing.

Muscle potentials are recorded by the EMG, brain activity by the EEG, and cardiac rhythm by the ECG.

Your Answer : (Not Answered)

Correct Answer : B

The interface is modelled as a resistor-capacitor network.

At the electrode-electrolyte boundary a charge double layer forms, which behaves like a capacitor, in parallel with a charge-transfer resistance. A series resistance represents the electrolyte gel and the skin. The usual model, with a further parallel RC for the stratum corneum, therefore makes the interface impedance depend on frequency.

A pure resistor misses the capacitive, frequency-dependent behaviour. The interface has no significant inductance. A half-cell potential does appear in the full model as a small DC source, but on its own a voltage source does not describe the interface's impedance.

Your Answer : (Not Answered)

Correct Answer : C

The input impedance should be very high (in the MΩ range).

The electrode-skin interface has a source impedance from a few kilohms up to hundreds of kilohms, and it differs between electrodes. The amplifier's input impedance forms a voltage divider with it. Only when the input impedance is far larger, megohms or more, does almost all of the biopotential appear at the input, and do mismatches between electrodes stop turning common-mode noise into a differential error.

A very low or moderate (1-10 kΩ) input impedance would load the source and lose most of the signal. Matching the tissue impedance gives maximum power transfer, but a biopotential amplifier needs to measure voltage, not draw power.

Your Answer : (Not Answered)

Correct Answer : C

Alpha waves are most prominent during relaxed wakefulness with eyes closed.

Alpha rhythm (8-13 Hz) is recorded best over the occipital region when a person is awake, relaxed and has the eyes closed. Opening the eyes or concentrating blocks it, an effect called alpha block or desynchronisation, and it is replaced by beta activity.

An alert person with eyes open shows low-amplitude beta waves (above 13 Hz). Deep sleep shows slow, high-amplitude delta waves (below 4 Hz). Seizures show spikes and sharp waves, not a normal alpha rhythm.

Your Answer : (Not Answered)

Correct Answer : A

A defibrillator's function is to restore normal heart rhythm.

In ventricular fibrillation or pulseless ventricular tachycardia the heart muscle fires chaotically and pumps no blood. A defibrillator passes a brief high-energy shock (typically 120-200 J biphasic) through the chest. This depolarises a critical mass of the myocardium at once, ending the chaotic activity so that the SA node can take over again.

Defibrillators often include an ECG monitor to decide when to shock, but measuring the ECG is not their function. Recording EEG is a different instrument, and muscle stimulation is done with low-energy stimulators.

Your Answer : (Not Answered)

Correct Answer : B

Laser therapy is mainly used for tissue repair and pain reduction.

Low-level laser therapy (photobiomodulation) uses red or near-infrared light at low power, which causes no heating. It is thought to act on mitochondrial cytochrome c oxidase, and it is used in physiotherapy to speed wound and soft-tissue healing and to relieve pain and inflammation.

Lasers are not used for nerve blocking, which is done with local anaesthetics, or for blood purification, which is dialysis. They have no role in enhancing X-rays.

Your Answer : (Not Answered)

Correct Answer : D

Shortwave diathermy works at about 27.12 MHz.

Shortwave diathermy heats deep tissue with a high-frequency electromagnetic field. It uses the frequencies set aside for industrial, scientific and medical use, and 27.12 MHz (wavelength about 11 m) is by far the most common, with 13.56 and 40.68 MHz also allowed.

2.45 GHz is the microwave diathermy frequency. 50 Hz is mains frequency, which would stimulate nerves and muscle instead of heating. Around 100 kHz is far below the shortwave band.

Your Answer : (Not Answered)

Correct Answer : C

The modality is stereotactic radiosurgery.

Stereotactic radiosurgery delivers a single high dose to a small, sharply defined target. Many beams converge from different angles under stereotactic localisation, using a frame or image guidance, so the dose outside the target falls off steeply. The Gamma Knife and linac-based radiosurgery are examples.

Conventional external beam radiotherapy is normally given in many fractions over weeks. Brachytherapy places sources inside the tumour. Proton therapy is a particle type that can be used in several schedules, and the single-session multi-angle description defines radiosurgery.

Your Answer : (Not Answered)

Correct Answer : D

The Gamma Knife uses cobalt-60.

The Leksell Gamma Knife holds about 192 to 201 cobalt-60 sources arranged in a hemisphere. Their gamma beams (about 1.17 and 1.33 MeV) are collimated to meet at a single focal point, delivering a high dose to a small intracranial target while the dose to surrounding brain falls off steeply.

It uses no laser and no ultrasound. Machines that use X-rays from a linear accelerator for radiosurgery exist, such as the CyberKnife, but the Gamma Knife is defined by its cobalt-60 gamma sources.

Your Answer : (Not Answered)

Correct Answer : B

A home blood glucose sensor works on the electrochemical principle.

A drop of blood on the test strip reacts with an enzyme, usually glucose oxidase or glucose dehydrogenase, which oxidises glucose. The electrons released are transferred, through a mediator, to an electrode, and the meter measures the resulting current, which is proportional to the glucose concentration (amperometric detection). This is an electrochemical biosensor.

Electrophysiological measurements record the body's own electrical activity, as in ECG and EEG. 'Physio-chemical' and 'chemical' are too general; the meter specifically measures an electrical current produced by a chemical reaction, which is what electrochemical means.

Your Answer : (Not Answered)

Correct Answer : B

The respiratory system is a pneumatic system.

From an engineering point of view, the respiratory system moves air: the diaphragm and chest muscles change the volume of the lungs, creating pressure differences that drive air in and out through the airways. A system that works by gas pressure and gas flow is pneumatic, which is why lungs are modelled with pressure, flow, compliance and airway resistance, and why ventilators are pneumatic devices.

The circulatory system, which pumps a liquid (blood), is the hydraulic system of the body. The musculoskeletal system is the mechanical one, and the nervous system the electrical one.

Your Answer : (Not Answered)

Correct Answer : D

The key gives the Alpha rhythm.

Alpha waves, about 8 to 13 Hz, are the dominant rhythm of the EEG in an awake adult at rest with eyes closed, strongest over the back of the head. Biomedical instrumentation texts such as Khandpur's describe the alpha rhythm as the principal component of the EEG and an indicator of the state of alertness of the brain, because it is present in relaxed wakefulness and disappears (alpha blocking) when the eyes open or attention is engaged.

Beta activity, above about 13 Hz, accompanies active thinking but is low in amplitude and not the principal component. Theta (4-8 Hz) is seen in drowsiness and in children, and gamma is a high-frequency rhythm linked with sensory processing; neither is the principal component of the resting EEG.

Your Answer : (Not Answered)

Correct Answer : C

EEG is used to check the function of the brain.

An electro-encephalogram records the electrical activity of the brain through electrodes placed on the scalp. Its rhythms (alpha, beta, theta, delta waves) are used to diagnose epilepsy, sleep disorders and brain injury.

The retina's activity is recorded by an electroretinogram (ERG), muscle activity by an electromyogram (EMG), and kidney function is checked by blood and urine tests, not by EEG.

Your Answer : (Not Answered)

Correct Answer : B

An ECG is recorded with surface metal electrodes.

The electrocardiogram picks up the heart's electrical activity at the skin surface. Metal electrodes (commonly silver-silver chloride) are placed on the chest and limbs with a conducting gel to reduce skin contact impedance.

Penetrating (needle) electrodes are used for recordings such as EMG from muscle, not routine ECG. Non-contact probes and optical electrodes are not the standard way of recording the ECG.

Your Answer : (Not Answered)

Correct Answer : C

The key gives pulsed waveform of micro volt.

An ECG is the time-varying potential difference picked up by electrodes on the body as the heart beats. It is a repeating waveform (P wave, QRS complex, T wave), so it is not a steady dc level, which rules out option B, and its energy lies at low frequencies, roughly 0.05 to 100 Hz, which rules out the "high frequency signal" of option D. The quantity recorded is a voltage, not a current, so option A is out.

Option C is the only one describing a repeating waveform of a voltage. Its "micro volt" is loose: surface ECG amplitudes are about 0.1 to 2 mV, with the P wave near 100 to 250 µV. The item is a best-answer one, and C is the best of the four.