**2. Anatomy and physiology: mechanics of respiration**

When one thinks of breathing, the airways and the airflow come to mind. Therefore, an understanding starting with the structures involved in this process is very important.

#### **2.1 Respiratory system**

The respiratory system consists of the following structures [12, 13] (**Figure 1**):

• Nose: nasal fossae; nasal cavity; pharynx (muscle tube); larynx (cartilage tube); trachea—bifurcates into two primary bronchi, which enter the pulmonary lobes, then subdivided into progressively smaller structures: bronchioles, ducts, and alveoli (where gas exchange occurs).

**53**

**Figure 1.**

*Breathing Monitoring and Pattern Recognition with Wearable Sensors*

fluid, which contributes to respiratory mechanics.

withdraw CO2 from the body to maintain homeostasis [13].

in more severe cases, it may lead to respiratory insufficiency.

expressed as Eq. (1).

to [14].

• Airways: space from the nose to the bronchioles (where no gas exchange

occurs). The structures up to the trachea are responsible for conducting, filter-

• Lungs: the principal organs of the respiratory system, surrounded by a membrane of connective-elastic tissue called visceral pleura. There are also the parietal pleura, which cover the thoracic cavity. Between them, there is pleural

Not only structures play an important role in respiration. Airflow direction delimits the breathing phases. Breathing comprises two steps. The first is the transport of oxygen (O2) through inhalation, from the environment to the cells. The second is the transport of carbon dioxide (CO2) from the intracellular to the environment. Breathing aims to supply the cells with adequate amounts of O2 and

The lungs are positioned in an airtight space, and the oscillation of their pressure volume is the basis for respiratory control. The intrathoracic pressure is negative compared to the lung pressure. The lung functions as an elastic structure that resists deformation. The ability of the lung to expand is called compliance [14] and is

C = dV/dP (1)

Compliance requires a respiratory effort under conditions of normality. When compliance is reduced, more effort is demanded from the respiratory system, and,

Thorax compliance (CT), lung compliance (CL), and lung-thorax system compliance (CLT) may be expressed by Eqs. (2), (3) and (4), respectively, according

*Breathing process: (a) structures involved in the breathing process; (b) inhalation event; and (c) exhalation event.*

*DOI: http://dx.doi.org/10.5772/intechopen.85460*

ing, heating, and humidifying the air.

*Breathing Monitoring and Pattern Recognition with Wearable Sensors DOI: http://dx.doi.org/10.5772/intechopen.85460*

*Wearable Devices - The Big Wave of Innovation*

ing and pattern detection are discussed in this chapter.

The main topics for the development of wearable devices for breathing monitor-

The development of wearable devices to monitor breathing activity allows giving rise to various medical care services. For example, considering people with asthma or chronic obstructive pulmonary disease, the environmental conditions directly affect their breathing, and a wearable device is able to continually measure air quality and pulmonary function [7]. The device could trigger alarm functions for drug uptake, contact a general practitioner for an appointment, or call emergency services [8]. The measurement of air quality is important, as pollutant exposure can lead to acute asthma attacks [7]. This happens usually after days under exposure. If a system detects pollutant exposure, it can warn the person and help to prevent attacks [7, 9]. Other applications of wearable devices include sleep monitoring for apnea detection [3], speaking detection as an indicator of social interaction [10], respiratory impedance [8], etc. The detection and tracking of respiratory movement for imageguided chest and abdomen radiotherapy, for compensation of movement during treatment, are additional uses of wearable devices [11]. Moreover, researchers have studied ways to develop smart fabrics, which are comfortable and nonintrusive, for

**1.1 Why is it important to monitor breathing activity with wearable devices?**

different applications such as healthcare, sports, and military scenarios [5].

**breathing monitoring and pattern detection?**

**2. Anatomy and physiology: mechanics of respiration**

ducts, and alveoli (where gas exchange occurs).

processing and machine learning methods.

**1.2 What is important to know for the development of a wearable device for** 

The creation of these wearable devices requires understanding the anatomy and physiology of the respiratory system. The knowledge about its structure and function leads to the development of devices that do not interfere with respiratory mechanics or daily life activities. It also allows selecting the best sensors in each case. Therefore, it is important to have an overview of the main types of electronic sensors used in recent years and how they have been applied, as well as signal

This chapter covers these topics concisely as a guide for people interested in developing wearable devices for respiratory monitoring. The next section introduces the anatomy and physiology of the respiratory system. The sections 3, 4, and 5 discuss, respectively, the electronic sensors, signal processing methods, and machine learning techniques applied to respiratory signals for pattern recognition.

When one thinks of breathing, the airways and the airflow come to mind. Therefore, an understanding starting with the structures involved in this process is

The respiratory system consists of the following structures [12, 13] (**Figure 1**):

• Nose: nasal fossae; nasal cavity; pharynx (muscle tube); larynx (cartilage tube); trachea—bifurcates into two primary bronchi, which enter the pulmonary lobes, then subdivided into progressively smaller structures: bronchioles,

**52**

very important.

**2.1 Respiratory system**


Not only structures play an important role in respiration. Airflow direction delimits the breathing phases. Breathing comprises two steps. The first is the transport of oxygen (O2) through inhalation, from the environment to the cells. The second is the transport of carbon dioxide (CO2) from the intracellular to the environment. Breathing aims to supply the cells with adequate amounts of O2 and withdraw CO2 from the body to maintain homeostasis [13].

The lungs are positioned in an airtight space, and the oscillation of their pressure volume is the basis for respiratory control. The intrathoracic pressure is negative compared to the lung pressure. The lung functions as an elastic structure that resists deformation. The ability of the lung to expand is called compliance [14] and is expressed as Eq. (1).

$$\mathbf{C} = \mathbf{d} \mathbf{V} / \mathbf{d} \mathbf{P} \tag{1}$$

Compliance requires a respiratory effort under conditions of normality. When compliance is reduced, more effort is demanded from the respiratory system, and, in more severe cases, it may lead to respiratory insufficiency.

Thorax compliance (CT), lung compliance (CL), and lung-thorax system compliance (CLT) may be expressed by Eqs. (2), (3) and (4), respectively, according to [14].

**Figure 1.** *Breathing process: (a) structures involved in the breathing process; (b) inhalation event; and (c) exhalation event.*

$$\mathbf{C}\_{T} = \frac{\mathbf{d} \mathbf{V}}{\mathbf{d} \, P\_{T}} \tag{2}$$

$$\mathbf{C}\_{L} = \frac{\mathbf{d} \mathbf{V}}{\mathbf{d} \, P\_{L}} \tag{3}$$

$$\mathbf{C}\_{LT} = \frac{\mathbf{d} \mathbf{V}}{\mathbf{d} \mathbf{P}\_{LT}} \tag{4}$$

Breathing also involves air diffusion, exchange from a more concentrated to a less concentrated medium. Poiseuille's law governs the flow resistance as expressed by Eq. (5).

$$\mathcal{R} = \frac{8\eta \mathcal{L}}{\pi r^4} \tag{5}$$

Where *R* is the flow resistance, L is the length, η is the viscosity of air, and *r* is the radius of the tubes.

**Figure 1** shows the main structures and processes involved in breathing.

#### **2.2 Muscles involved in breathing and their functions**

The diaphragm is the most important muscle of inspiration. When it contracts, there is a decrease in intrapleural pressure and an increase in lung volume [13]. Simultaneously, an increase in abdominal pressure is transmitted to the chest through the apposition zone to expand the lower thoracic cavity. When the diaphragm contracts, the lower rib cage expands. One may observe the bucket handle movement that causes an increase in thorax transverse diameter due to the elevation of the ribs during inspiration [15]. Elevation and sternum forward movement during inspiration causes the increase of thorax anteroposterior diameter. Diaphragm contraction also contributes to increasing the longitudinal thorax diameter [12].

Scalene muscle, sternocleidomastoid muscle, and intercostal muscle are inspiration auxiliary muscles. During forced expiration, the abdominal muscles contract, and the diaphragm is pushed upward, thus causing a decrease in chest diameters. Abdominal muscle is also important for coughing [16].
