Piezo film sensor for capture of arterial wave pulse

Module by: Akhila Tadinada

Summary: We propose to develop a blood pressure (BP) monitoring system which can be used for continuous ambulatory blood pressure measurement. The system will be used to measure blood pressure cycles for a person by recording a person’s blood pressure 24 hours a day for 7 days. Blood pressure cycles give an idea of a person’s chronobiological cycle. It has proved that if treatment is administered to a person at appropriate times based on the chronobiological cycle the treatment is more effective. A lot of diseases such as heart attack, stroke, kidney disease, retinopathy, and other major handicapping and fatal diseases can be cured effectively using this method. Presently available BP monitors are bulky, sensitive to motion and cannot be used for continuous monitoring. The proposed system is based on Chen et.al, US Patent No. 6,599,251 which measures blood pressure non invasively using arterial pulse delay. The questions we plan to raised in this project are - what kind of sensors can be used to compute pulse delay, how can we get rid of the motion artifacts and how to make the sensors independent of position sensitivity. To answer these questions we conducted experiments on different sensor configurations and characterized the sensor using the data received. The experimental setup used two piezoelectric sensors that are placed on the wrist and mid arm. The signals from both the sensors are then compared to compute the arterial pulse delay. The sensor characterization results thus achieved are presented in this paper.

I) Introduction

The IEEE phoenix and Franz Halberg Chronobiology institute [1] have pioneered a project for the development of an ambulatory blood pressure monitoring system.

Blood pressure cycles give an idea of a person’s chronobiological cycle. A blood pressure cycle is a record of the blood pressure values of person over a period of one day. Dr. Franz Halberg has shown that if a person is treated by studying these blood pressure cycles in his body then a lot of diseases such as heart attack, stroke, kidney disease, retinopathy, and other major handicapping and fatal diseases can be cured [2]. Every person has an individual blood pressure cycle depending on what time of the day his blood pressure increases and falls. If treatment is administered to a patient keeping in mind his blood pressure cycle, the treatment will be more effective. For example- In case of cancer treatment, chemotherapy is less toxic if administered at certain times in the blood pressure cycle as compared to other. This can make a huge difference in healing the patient.

To measure the blood pressure cycles of a person we need to measure blood pressure for a period of 7 days at an interval of 30 minutes. To implement this we need a cheap, ambulatory blood pressure monitoring system that can be used by subjects to record their blood pressure. There are certain problems facing such a wide spread implementation of the device.

On the basis of the problems discussed above we propose to develop an ambulatory blood pressure monitor take with the following features -

Keeping the above mentioned pointers in mind we developed a device that is based on non-invasive technology. Experiments were conducted to test the device and the results are presented here in this paper. In this paper we will study II) Noninvasive blood pressure measurement III) Implementation IV) Experimental Setup V) Results VI) Discussion VII) Future work VIII) Conclusion

II) Non – invasive blood pressure measurement

We propose to implement a device based on Chen et. al, US Patent No. 6,599,251 which states that arterial pulse delay is proportional to blood pressure. The relation is expressed as

P = a + b ln(T)

where T – Time delay(milliseconds)

a,b – constants depending on the nature of the subject and the signal detecting

device.

Arterial pulse is the rhythmic expansion of the artery [9]. Arterial pressure also known as aortic pressure changes with the changes with the stroke volume. The figure shown here shows the arterial pulse. In the present method we measure the time difference between the peaks of an arterial wave pulse. This delay is proportional to systolic blood pressure. Similarly if we compute the delay between the valleys of the arterial pulse wave, we can compute the diastolic blood pressure. Averaging over the wave gives us the mean arterial pressure.

Figure 1

Fig 1: Arterial wave pulse [9]

To measure the delay, two sensors are placed at different locations on the human body.For example – one sensor is placed at the wrist and the other sensor is placed at mid arm. Arterial pressure signals are measured at both the locations and the delay between corresponding peaks is measured; this gives us the value of T. The constant a and b can be calibrated for each patient using a single pair of reference blood pressure from a standard instrument and corresponding elapse time.

Our main focus in this project is to record arterial wave pulses and compute the delay between corresponding peaks. The constants a and b will be computed at a later stage.

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This work is licensed by Akhila Tadinada under a Creative Commons Attribution License (CC-BY 2.0).

Last edited by Akhila Tadinada on Dec 19, 2007 1:41 pm US/Central.