A study on estimating blood pressure during body postural change based on pulse transit time

We are interested in healthcare for a bed ridden patient. Although a bed ridden patient in the hospital can be led to a circulatory disorder or a serious secondary disease, it is still difficult to give an adequate healthcare service for the patient due to side effects. Thus, we focus on the method of measuring the continuous and non-invasive bio signal in order to provide important insight into the patient's overall physical condition. In this paper, we estimate the blood pressure during the change of body posture based on the pulse transit time. Accordingly, we newly propose the measurement system and the equation for estimating the blood pressure, and then prove the effectiveness through the experiment of changing the body posture. Through all of results, we found that it is possible to estimate the blood pressure during the change (45 and 75 deg) of body posture with the continuous (5 min) and non-invasive method by monitoring the condition of patient.

I. Introduction

Fig. 1 shows a bed ridden patient by the brain injury or a long-stay (temporary bed ridden) patient by a surgery or any accident. The number of bed ridden patients diagnosed each year is increasing with population of the elderly people aged 65-year old [1]. A bed ridden patient has no choice but to live in the bed, because the patient cannot regulate the physical activity by himself. Generally, it is well known that the circulatory disorder is occurred when the same body posture lasts for a long time through the gravitational pressure of body weight. The risk factor of bedsore increases highly with the cause of the body weight and nutrition disorder. Thus, as one of healthcare services, the care giver or nurse should help the blood circulation by changing the body posture of patient regularly in order to prevent the secondary disease such as the bedsore. The change of body posture needs to perform one time per two hours at least [2]. Because the tissue damage begins when the body pressure of 70 ~100 mmHg puts pressure on the skin over two hours. However, the change of body posture without the consideration of patient's condition results in a lot of side effects such as the sickness, pyrexia, palpitation, an irregular pulse, and so on. It is necessary for the bio signal of a bed ridden patient to be checked because the direction of gravity has an influence on a human body [3]. The blood supplied to the heart is reduced when a person stand up because the blood pressure amount of 500 ~ 800 ml is moved to the abdomen and lower limb, and then the activity of blood pressure control organ decreases. Generally, it is well known that the normal value of blood pressure is maintained by the sympathetic nerve, the increase of pulse, and the cardiac contractile function when a person is health. However, symptoms including sickness, palpitation, and so on are occurred when the lowered value of blood pressure doesn't recover to the normal value as shown in Fig. 1 [4]. Accordingly, a bed ridden patient has a need to measure the blood pressure during the body postural change. Fig. 1.

An influence on the blood pressure of the body posture change in the case of a bed ridden patient.