This is also known as a Device for Indirect Non-Invasive Automatic Mean Arterial Pressure (DINAMAP).
Measurement of blood pressure was first attempted by Hales in 1733. He apparently inserted pipes into the arteries of animals. The blood pressure cuff was developed by Riva-Rocci in 1896. Cushing introduced the measurement of blood pressure into anaesthetic practice in 1901.
Stephen Hales (1677-1761). English naturalist.
Scipione Riva-Rocci (1863-1937). Italian physician.
Harvey Williams Cushing (1869-1939). American neurosurgeon. Pioneered diathermy, advocated record keeping and monitoring in Anaesthesia. Described Cushing’s disease, syndrome, reflex and ulcer.
Mechanism of action
A microprocessor controls the sequence of inflation and deflation of the cuff. The cuff is inflated to a pressure above the previous systolic pressure; it is then deflated incrementally. A transducer senses the pressure changes, which are processed by the microprocessor. This has an accuracy of +/- 2%. The mean arterial pressure (MAP) corresponds to the maximum oscillation at the lowest cuff pressure. The systolic pressure corresponds to the onset of rapidly increasing oscillations. Diastolic pressure corresponds to the onset of rapidly decreasing oscillations. It is also calculated from the systolic and MAP (MAP= diastolic + one-third pulse pressure)
The cuff should cover at least two-thirds of the upper arm. The width of the cuff’s bladder should be 40% of the mid-circumference of the limb. The middle of the cuff should overlay the brachial artery. The device has a fast rate of inflation and a slow cuff deflation. This avoids venous congestion and allows time to detect arterial pulsation.
Sources of error
If the cuff is too small, the blood pressure over-reads. Similarly, if too large then the blood pressure under-reads (greatest error is seen with an undersized cuff). Systolic pressure over-reads at low pressures (<60 mmHg) and under-reads at high systolic pressures. Arrhythmias such as atrial fibrillation affect accuracy. External pressure on the cuff (e.g. the surgeon!) can cause inaccuracies.
Frequent, repeated inflations can cause ulnar nerve palsy and petechial haemorrhage of the skin underlying the cuff.
[i] Blood pressure cuff compression injury of the radial nerve.
Lin CC, Jawan B, de Villa MV, Chen FC, Liu PP.
J Clin Anesth 2001; 13(4): 306-8.