36 - 40 Physics SBAs for the Primary FRCA

36 - 40 Physics SBAs for the Primary FRCA
Photo by Nguyen Dang Hoang Nhu / Unsplash

Question 36

You turn over the page of your FRCA Primary written examination and the first question asks you about the von Recklinghausen oscillotonometer.

Which of the following is true?

  • It requires the use of a stethoscope
  • It uses two overlapping cuffs
  • The systolic pressure is determined by the sensing cuff
  • The largest oscillations are detected as blood flow returns
  • The occluding cuff is larger than the sensing cuff


  • It uses two overlapping cuffs

The von Recklinghausen oscillotonometer has a small sensing cuff and a larger occluding cuff.

It also has a valve and a needle pressure gauge to allow deflation and measurement respectively.

A small lever allows the pressure gauge to measure the cuffs independently.

A stethoscope is not required.

  • Both cuffs are inflated until arterial flow is occluded
  • The sensing cuff is measured first, and slowly deflated until the needle starts to wobble (oscillate) denoting the systolic pressure
  • The sensing cuff is left at this pressure, and the lever flipped to the occluding cuff
  • The occluding cuff is then deflated until there are maximum oscillations, which are seen at mean arterial pressure
  • The oscillations then vanish at diastolic pressure