6.0 Theory of Operation for Press-Mate, Genius and Filac
6.1
Theory of Oscillometry: Press-Mate
Oscillometry, or the oscillometric method, is a technique that may be used to automatically, non-invasively m
easure blood pressure. The basic oscillometric method is relatively simple and can lead to a quick, comfortable,
and reliable measurement of blood pressure. The fundamentals of the technique are easily explained.
In applying oscillometry, an inflatable cuff is placed around a limb, usually the upper arm. When the cuff is
inflated and the pressure in the cuff exceeds systolic blood pressure, blood ceases to flow through the brachial
artery. When the inflated cuff stops blood flow, each time the heart contracts, a very small pulse may be
observed superimposed upon the cuff pressure signal. These small pulses are called oscillometric pulses.
Slowly relieving the pressure in the cuff will allow the cuff pressure to eventually become equal to the systolic
blood pressure. With cuff pressure equal to the systolic blood pressure, blood can once again start to flow
through the brachial artery, causing the oscillometric pulses to suddenly increase in amplitude.
If the pressure in the cuff is allowed to continue to decrease, the amplitude of the oscillometric pulses will
continually increase. When cuff pressure reaches mean arterial blood pressure, the amplitude of the
oscillometric pulses are at a maximum. As the pressure of the cuff is relieved, the oscillometric pulses slowly
decrease in amplitude. When the cuff pressure reaches the diastolic blood pressure, the amplitude of the
oscillometric pulses suddenly drops.
COLIN MEDICAL INSTRUMENTS CORP. has pioneered the development of an oscillometric technique that
uses continuous linear deflation, which is similar to, but better controlled than, the manual auscultatory technique.
The continuous cuff deflation technique is very comfortable for the patient, because the pressure in the cuff is
being constantly relieved after the initial cuff inflation. Furthermore, COLIN has implemented algorithms in its
oscillometric blood pressure monitors, which adjust the cuff deflation rate according to the patients heart rate.
These special algorithms allow determination of a blood pressure measurement with maximum accuracy obtained
in minimum time. This adds to the comfort of the patient.
Some measurement artifacts, such as exaggerated patient motion, arrhythmia, and hypovolemia, make any blood
pressure measurement impossible. However, COLIN has developed proprietary algorithms that will reject
several types of artifacts and still obtain an accurate measurement. In some instances, the artifact may become
quite severe and the monitor will not be able to obtain an accurate blood pressure measurement. In this situation
an alarm, when properly set, will notify the clinician of a change.
6-1