The sensor produces an output voltage that varies with the pressure measured in the cuff. It includes special circuitry to minimize errors caused by changes in temperature. We also provide a filtering circuit that conditions the signal from the pressure transducer. The output voltage from the Blood Pressure Sensor is linear with respect to pressure. The software used with the sensor calculates the blood pressure parameters.
Calculating Blood Pressure (Oscillometric Method)
The software used with the sensor determines the blood pressure of the subject by using the oscillometric method, a non-invasive means of measuring blood pressure. It is based on the principle that blood pumped through the arteries by the heart causes the arterial walls to flex. When a cuff (placed around the upper arm to occlude the brachial artery) is inflated and then slowly deflated at a constant rate, an arterial pressure pulse forms. These pressure pulses pass from the arteries, through the arm, and into the pressure cuff itself.
When the artery is fully compressed, blood flow stops along with the pulsations. As the pressure in the cuff is slowly decreased, the arterial blood pressure increases to the point that blood is forced through the artery in short pulses. As the pressure in the cuff continues to decrease, more blood flows through the occluded artery and the pulses become increasingly significant until maximum amplitude is reached. Further decrease of the cuff pressure minimizes the occlusion of the artery and the pulses continue to decrease until the occlusion is removed.
Cuff pressure measured by sensor
These pressure pulses, when separated from the decaying mean pressure of the cuff, form an oscillating waveform. The peak-to-peak amplitudes of this waveform create a bell shaped “envelope”. Within the envelope, the amplitudes of the waveform increase through the systolic blood pressure and continue increasing until the mean arterial pressure (MAP) is reached. Physiologically, the cuff pressure corresponding to the maximum amplitude approximates the mean arterial pressure. Generally, the systolic blood pressure is calculated by determining the point along the envelope prior to the MAP using a known percentage of the maximum amplitude. Diastolic blood pressure is calculated using the same method and the portion of the envelope following the MAP.
Oscillatory waveform used to create “envelope”