Which instrument is used to measure the blood pressure manually?

Correct — A, Sphygmomanometer. The name is built from the Greek sphygmos, meaning pulse, joined to manometer, an instrument for measuring pressure — literally a pulse-pressure meter. The manual version has three parts: an inflatable cuff wrapped round the upper arm, a bulb to pump it up, and a gauge that reads the pressure, either a column of mercury or an aneroid dial. It is used with a stethoscope. The cuff is inflated until it squeezes the brachial artery shut and blood stops flowing, then let down slowly. The moment blood first forces its way past the cuff, a tapping sound appears in the stethoscope — the first of the Korotkoff sounds — and the gauge reading at that instant is the systolic pressure, the peak pressure produced when the ventricles contract. As the cuff falls further the sounds fade and vanish, because the artery is no longer being constricted at all, and the reading where they disappear is the diastolic pressure, the pressure remaining while the ventricles relax and refill. That is the entire measurement, and it is why blood pressure is quoted as one number over another. The other three options are all laboratory separation or amplification instruments, and none of them touches a patient.

• (b)Centrifuge — Spins tubes at high speed so that denser components settle outward — how plasma is separated from blood cells in a laboratory. It separates a sample; it measures no pressure.
• (c)Electrophoresis — A technique, not really an instrument, in which DNA or protein fragments are driven through a gel by an electric field and sort themselves by size and charge. Used to read molecules, not to examine a patient.
• (d)Thermal cycler — The PCR machine, which repeatedly heats and cools a reaction mixture to copy a target stretch of DNA millions of times. Its subject is a nucleic acid sample, not a circulation.

Blood pressure is the force the circulating blood exerts on the walls of the arteries, and it rises and falls with every heartbeat. Systolic pressure is the peak, reached when the ventricles contract and eject blood into the aorta; diastolic pressure is the trough, when the ventricles relax and fill. Both are reported in millimetres of mercury, a unit inherited from the original mercury column, and a typical healthy adult reading is about 120 over 80 mm Hg. The manual measurement is indirect: rather than putting a sensor in an artery, it finds the cuff pressures at which blood flow through the brachial artery starts and stops being turbulent, using sound as the indicator.

This is an odd-category item, and spotting the category is faster than knowing every instrument. Three of the four options — centrifuge, electrophoresis, thermal cycler — belong to a laboratory bench and act on a sample in a tube. One belongs at a bedside and acts on a person. The word 'manually' in the stem is the second clue, distinguishing the cuff-and-stethoscope method from the digital oscillometric monitors now common at home, which read pressure from the oscillations of the cuff rather than from Korotkoff sounds. Two practical points are worth carrying. Mercury sphygmomanometers, long the reference standard, are being phased out in many countries because of mercury toxicity, so the aneroid dial and the digital monitor are what most students will actually see. And a single high reading does not establish hypertension, since pressure rises with anxiety, exertion and even the clinic itself — the reason repeat readings are taken.

• Sphygmomanometer comes from the Greek sphygmos, meaning pulse, plus manometer, a pressure-measuring instrument.
• The manual set consists of an inflatable arm cuff, an inflation bulb and a mercury column or aneroid dial, used together with a stethoscope.
• The first Korotkoff sound heard as the cuff deflates marks the systolic pressure; the point at which the sounds disappear marks the diastolic pressure.
• Systolic pressure corresponds to ventricular contraction and diastolic pressure to ventricular relaxation.
• Blood pressure is reported in millimetres of mercury, and a typical healthy adult reading is about 120 over 80 mm Hg.
• Digital oscillometric monitors read the oscillations of the cuff instead of listening for Korotkoff sounds, which is what the word 'manually' in the question rules out.
• A centrifuge separates by density, electrophoresis separates charged molecules by size and charge in an electric field, and a thermal cycler amplifies DNA by repeated heating and cooling.

• Reaching for a laboratory instrument because the question mentions blood; three of the four options work on samples in tubes, not on patients.
• Confusing the stethoscope with the sphygmomanometer. The stethoscope only carries the sound; the pressure is read off the gauge.
• Ignoring the word 'manually', which is there to separate the cuff-and-stethoscope method from a digital monitor.

As an instrument-to-use match, or in reverse — what does a sphygmomanometer measure. The 120 over 80 reading and what each number corresponds to are asked separately, as they are in Q75 of this same paper.

• practice — not a real PYQ

  While measuring blood pressure manually, the reading at which the first tapping sound is heard through the stethoscope corresponds to which one of the following?

  • (a)Diastolic pressure
  • (b)Systolic pressure
  • (c)Mean arterial pressure
  • (d)Pulse pressure

  Answer(b) Systolic pressure — blood first forces its way past the deflating cuff at the peak of ventricular contraction, and the sounds disappear at the diastolic reading.

• practice — not a real PYQ

  A thermal cycler is used chiefly for which one of the following?

  • (a)Separating plasma from blood cells
  • (b)Amplifying a target stretch of DNA
  • (c)Measuring lung capacity
  • (d)Sorting proteins by charge

  Answer(b) Amplifying a target stretch of DNA — it drives the polymerase chain reaction by cycling the reaction mixture through set temperatures.