**2. Chest displacement due to breathing and heart beating**

Using microwave Doppler radar, several techniques were established in order to sense the cardiopulmonary activity. When a microwave signal is transmitted to a person's chest, the power of the reflected signal when it occurs at the air/skin interface is higher than the power of the signal reflected from internal organs. Then, the signal reflected off the person's chest contains information about the chest displacement due to cardiopulmonary activity including breathing and heartbeat. Based on these displacements, the heartbeat rate and the respiration rate can be extracted. However, these motions are not the same for all people. This section describes the mechanism of the chest displacement due to both heartbeat and respiration, as well as some experiments measuring the displacement amount.

#### **2.1. Surface motion due to the cardiac cycle**

When the heart beats, it pushes blood through the lungs and to tissues throughout the whole body. A pressure is generated when the heart contracts in order to drive the flow of the blood. While contracting, the heart hits the cavity of the chest creating a significant displacement at the surface of the skin. As the left ventricle carries out blood to all parts of the body, the contraction and relaxation of the left ventricle cause a larger chest motion than other heart actions in healthy subjects. During isovolumetric contraction, the heart normally undergoes a partial rotation in a counterclockwise direction, causing the lower front part of the left ventricle to strike the front of the chest wall [1]. Also, the left ventricle shortens while contracting, shaping the heart to be more spherical, increasing its diameter, and further adding to the impulse on the chest wall [2]. The peak outward motion of the left ventricular impulse occurs either simultaneously with or just after the opening of the aortic valve. Then the left ventricular apex moves inward [1]. The left ventricular motion causes the chest to pulse outward briefly and the adjacent chest retracts during ventricular ejection [3]. This impulse occurs at the lowest point on the chest where the cardiac beat can be seen, and it is normally above the anatomical apex [4]. Some studies found a second outward movement at the apex: the pre-ejection beat [5]. Many techniques for quantitatively measuring the gross displacement of the chest wall have been applied, including the impulse cardiogram [1], a single-point laser displacement system [6], structured lights and the Moiré effect [7], laser speckle interferometry [8], a capacitance transducer [9], a magnetic displacement sensor [10], and a phonocardiographic microphone [11]. The values of the skin motion due to heartbeat vary between individuals due to physiological difference, age differences, and body shape differences. Since the amount and the speed of the motion of the heart within the chest changes with age, it is expected that the amount of the chest motion due to the heartbeat changes with age. Recent studies found that the expected movement of the mitral valve ahead the heart's long axis is about 1.49 cm at age of 20 with an expected velocity of 7.48 cm/s, and 1.22 cm at age of 84 with an expected velocity of 7.48 cm/s [12]. Another study showed that the displacement of the septum decreases with age, but the displacement of the left lateral wall and the posterior wall of the heart remains constant between ages 49 and 73 [13]. The absolute diastolic displacement of annular sites among children increases significantly with increasing body weight (which is expected since the size of the heart and thorax is increasing), but the percent displacement was inversely proportional to body weight [14]. Although there is no significant change in left ventricular ejection volume with age, the arterial pressure wave varies greatly with age: arterial wall thickness increases, arterial diameter increases, and arterial distensibility decreases [15]. The arterial wall rigidity is expressed as [16]

$$
\alpha = 0.421 + 0.0602 \times \text{age} \tag{1}
$$

This indicates that pulses will be smaller and more difficult to measure in older subjects. At a pulse, subjects aged between 60 and 70 years have 50% lower variation in the cross-sectional area of the artery than subjects aged between 20 and 30 years [16]. When the variation in the arteries' diameter decreases, the amplitude of the surface skin displacement will decrease. This results in decreasing the signal-to-noise ratio when measuring the pulse using a Doppler radar. In average, the peak-to-peak chest motion in adults due to the heartbeat is about 0.5 mm.

#### **2.2. Surface motion due to respiration**

creased. Hence, a touchless cardiopulmonary monitoring is needed for such applications and

When a radio wave is transmitted toward a person, it will be reflected off his/her body. If the reflection occurs off the chest of a motionless person, the reflected signal has a phase modu‐ lation due to the Doppler effect due to the movement of the chest, which is caused mainly by heartbeats and breathing. On the other hand, when the breath is held, the reflected signal will

The aim of this chapter is to present a tunable system in terms of power and frequency that shows the capability to detect chest displacement due to heart beat at different operational frequencies and for different transmitted powers. This allows specifying the appropriate operational frequency for the minimum transmitted power. In addition, simultaneously with a PC-based ECG, measurements are performed at the four different sides (front, back, left, and right) of the person under test (PUT). Wavelet transforms are used in order to separate the heartbeat signal from the cardiopulmonary signal and to extract the heartbeat rate (HR).

The rest of this chapter is organized as follows: Section 2 provides background information about chest-wall displacement. Section 3 describes related work for the system design and the signal processing technique. Section 4 presents the proposed system and some preliminary results obtained at different operational frequencies. Section 5 shows the cardiopulmonary signals obtained at different sides from the subject and presents the results upon applying the

Using microwave Doppler radar, several techniques were established in order to sense the cardiopulmonary activity. When a microwave signal is transmitted to a person's chest, the power of the reflected signal when it occurs at the air/skin interface is higher than the power of the signal reflected from internal organs. Then, the signal reflected off the person's chest contains information about the chest displacement due to cardiopulmonary activity including breathing and heartbeat. Based on these displacements, the heartbeat rate and the respiration rate can be extracted. However, these motions are not the same for all people. This section describes the mechanism of the chest displacement due to both heartbeat and respiration, as

When the heart beats, it pushes blood through the lungs and to tissues throughout the whole body. A pressure is generated when the heart contracts in order to drive the flow of the blood. While contracting, the heart hits the cavity of the chest creating a significant displacement at the surface of the skin. As the left ventricle carries out blood to all parts of the body, the contraction and relaxation of the left ventricle cause a larger chest motion than other heart actions in healthy subjects. During isovolumetric contraction, the heart normally undergoes a

could be a prominent tool in home health care applications.

32 Advanced Biosignal Processing and Diagnostic Methods

depend on the chest displacement due to heartbeat alone.

proposed signal processing technique. Section 6 concludes the work.

**2. Chest displacement due to breathing and heart beating**

well as some experiments measuring the displacement amount.

**2.1. Surface motion due to the cardiac cycle**

The chest surface motion due to breathing is the combination of the abdominal and rib cage movements. A linear correlation exists between cross-sectional area of the thorax, displace‐ ment of the diaphragm, displacement of the rib cage, and lung volume [17]. At the third rib, the angle of the pump handle changes between 20° and 30°, and the rib radius changes between 10.6 and 10.8 cm. At the seventh rib, the angle of the pump handle changes between 30° and 37°, and the rib radius changes between 1.37 and 1.42 cm [18]. Comparing the chest motion in the front/back, left/right, and up/down directions shows that the largest motions correspond to the sternum and the navel. Sternum moves forward 4.3 mm with inspiration, and the navel which moves forward 4.03 mm with inspiration [19]. The relation between tidal volume and abdominal wall linear displacement is measured using a laser displacement measuring device [20]. An expansion of the abdomen is observed: 4 mm for 400 ml inspiration and 11 mm for 1100 ml inspiration. Also, during spontaneous breathing, an abdominal displacement of 12 mm is observed.
