Schematics Digital Blood Pressure Meter

Description: This digital circuit outlines a concept for a digital blood pressure meter that incorporates an integrated pressure sensor, analog signal conditioning circuitry, microcontroller hardware/software, and a liquid crystal display. The sensing system measures cuff pressure (CP) and extracts pulses for analysis to determine systolic and diastolic pressure. The design utilizes a 50 kPa integrated pressure sensor (Freescale Semiconductor, Inc. P/N: MPXV5050GP) with a pressure range from 0 mm Hg to 300 mm Hg. This technique is commonly used in automated non-invasive devices. A limb and its vasculature are compressed by an inflatable compression cuff. Blood pressure readings for systolic and diastolic values are taken at the parameter identification point. The oscillometric method simplifies measurement by assessing the amplitude of pressure changes in the cuff as it inflates beyond systolic pressure. The amplitude increases significantly as the pulse breaks through the occlusion, closely approximating systolic pressure. As cuff pressure decreases further, the pulsation amplitude rises to a maximum and then rapidly declines. The diastolic pressure index is identified at the onset of this rapid transition. Consequently, systolic blood pressure (SBP) and diastolic blood pressure (DBP) are determined by observing the regions of rapid increase and decrease in pulse amplitude, respectively. Mean arterial pressure (MAP) is located at the point of maximum oscillation. The cuff pressure is detected by Freescale's integrated pressure transducer. The sensor output is divided into two paths for different functions: one path measures cuff pressure, while the other undergoes further processing. Since the MPXV5050GP is signal-conditioned by its internal operational amplifier, cuff pressure can be directly interfaced with an analog-to-digital (A/D) converter for digitization. The second path filters and amplifies the raw CP signal to isolate an amplified version of the CP oscillations, which result from the expansion of the subject's arm during cardiac systole. The sensor output consists of two signals: the oscillation signal (approximately 1 Hz) superimposed on the CP signal (approximately 0.04 Hz). A 2-pole high-pass filter is designed to attenuate the CP signal before amplifying the oscillation signal. Proper attenuation of the CP signal is crucial; otherwise, the oscillation baseline may fluctuate, leading to inconsistent amplitude references for comparison.

The digital blood pressure meter circuit integrates several key components to ensure accurate readings of systolic and diastolic pressures. The integrated pressure sensor, MPXV5050GP, is the core element that detects cuff pressure. This sensor operates within the specified pressure range and is characterized by its high sensitivity and reliability, making it suitable for medical applications. The analog signal conditioning circuitry is essential for preparing the raw signal from the sensor for digital conversion. This involves filtering out noise and enhancing the signal quality.

The microcontroller serves as the brain of the device, executing the necessary algorithms to process the digitized signals. It analyzes the amplitude variations of the oscillation signal to determine the systolic and diastolic pressures based on the established criteria of rapid increases and decreases in pressure amplitude. The microcontroller also manages the display output on the liquid crystal display, presenting the user with clear and concise blood pressure readings.

The design includes a user interface for operating the device, allowing the user to initiate measurements and view results conveniently. Additionally, safety features are integrated to prevent excessive cuff inflation and ensure patient comfort. Overall, this digital blood pressure meter circuit represents a sophisticated approach to non-invasive blood pressure measurement, combining advanced sensor technology with intelligent processing capabilities.This Digital Circuit describes a Digital Blood Pressure Meter concept which uses an integrated pressure sensor, analog signal-conditioning circuitry, microcontroller hardware/software and a liquid crystal display. The sensing system reads the cuff pressure (CP) and extracts the pulses for analysis and determination of systolic and diastolic pressu

re. This design uses a 50 kPa integrated pressure sensors (Freescale Semiconductor, Inc. P/N: MPXV5050GP) yielding a pressure range of 0 mm Hg to 300 mm Hg. This method is employed by the majority of automated non-invasive devices. A limb and its vasculature are compressed by an encircling, inflatable compression cuff. The blood pressure reading for systolic and diastolic blood pressure values are read at the parameter identification point. The simplified measurement principle of the oscillometric method is a measurement of the amplitude of pressure change in the cuff as the cuff is inflated from above the systolic pressure.

The amplitude suddenly grows larger as the pulse breaks through the occlusion. This is very close to systolic pressure. As the cuff ressure is further reduced, the pulsation increase in amplitude, reaches a maximum and then diminishes rapidly. The index of diastolic pressure is taken where this rapid transition begins. Therefore, the systolic blood pressure (SBP) and diastolic blood pressure (DBP) are obtained by identifying the region where there is a rapid increase then decrease in the amplitude of the pulses respectively.

Mean arterial pressure (MAP) is located at the point of maximum oscillation. The cuff pressure is sensed by Freescale`s integrated pressure X-ducer °. The output of the sensors is split into two paths for two different purposes. One is used as the cuff pressure while the other is further processed by a circuit. Since MPXV5050GP is signal-conditioned by its internal op-amp, the cuff pressure can be directly interfaced with an analog-to-digital (A/D) converter for digitization. The other path will filter and amplify the raw CP signal to extract an amplified version of the CP oscillations, which are caused by the expansion of the subject`s arm each time pressure in the arm increases during cardiac systole.

The output of the sensors consists of two signals; the oscillation signal ( ‰ 1 Hz) riding on the CP signal ( ‰¤ 0. 04 Hz). Hence, a 2-pole high pass filter is designed to block the CP signal before the amplification of the oscillation signal.

If the CP signal is not properly attenuated, the baseline of the oscillation will not be constant and the amplitude of each oscillation will not have the same reference for comparison.