Invivo Magnitude 3150M, Operation Manual

Page: 43 / 80

4-5
Figure 4-5. Oscillometric Measurement Method
NOTE
The point of maximum oscillations is coincident with mean arterial pressure regardless
of arterial elasticity so long as the ratio of air volume in the cuff to the volume of the
artery under compression does not greatly exceed ten (10) to one (1). For this reason
it is advisable to keep the cuff air volume to a minimum by using the smallest cuff size
possible for each patient.
b. As cuff pressure is reduced to just below the systolic pressure, the force of the height
of the systolic pressure wave forces the occluded artery open, blood spurts through
the artery and the amplitude of the oscillations increase sharply. This is the systolic
pressure.
c. With further reduction in cuff pressure the artery opens for a longer time during each
cardiac cycle, which causes increasingly larger oscillations in the cuff pressure until
they reach a point of maximum oscillation amplitude. This point of maximum
oscillations has been well-demonstrated to be Mean Arterial Pressure.
d. With continued cuff-pressure reduction, the underlying artery is open throughout the
cardiac cycle, and the arterial-wall movement is less. The cuff pressure oscillations
begin to decrease in amplitude until they become uniform. The point at which the
amplitudes become uniform is diastolic pressure.
4.2.2 Patient and Cuff Preparation. The patient should remain calm and motionless while the
monitor is being used. If the patient is overactive, prolonged or inaccurate readings may result.
Perform the following to prepare the patient and cuff for monitoring:
a. Cuff Selection. The cuff is selected and positioned as it would be for an auscultatory
blood pressure determination, and the current guidelines of the American Heart
Association should be followed. The bladder width of the cuff should be 40% of the
circumference of the limb. For a correct fit on adult and pediatric cuffs, the Index
line on the end of the cuff must fall between the two Range lines printed on the inside
of the cuff. For correct fit on neonatal cuffs, choose the size with the stated
circumference range that fits the circumference of the limb of the neonate.