# A Real-Time Remote Respiration Measurement Method with Improved Robustness Based on a CNN Model
## 1 Introduction  
Respiration is a basic vital sign that can be used to intuitively evaluate human health along with heart rate, blood pressure, and body temperature. It is widely used as a standard indicator in medical, human-computer interaction, forensic investigation, and sports research [1; 2; 3; 4; 5; 6]. In addition, changes in respiration are important to understand changes in the vital state of the body because levels of oxygen and carbon dioxide in the blood suitable for life activities are maintained by controlling the rate of respiration [7]. Respiration can be used as a good indicator to monitor vital signs, and monitoring respiration rates can also help identify high-risk patients and prevent dangerous situations because physical changes due to respiration exhibit greater variability compared to those caused by heart rate and blood pressure [8; 9]. Even in medical environments, increased rates of respiration are effective in predicting various abnormal conditions, such as respiratory failure due to muscle weakness, readmission to intensive care units, and cardiopulmonary arrest, and 21% of patients with 25-29 breaths per minute die in the hospital [10; 11]. Therefore, research and development on vital sign monitoring systems that include respiratory rate measurementcan be usefully utilized to prevent physical health risks by detecting deterioration in patients' heart conditions in advance [12; 13]. Respiration is influenced not only by physical health, but also by psychological conditions, including anxiety, depression, anger, and stress, and is closely related to changes in levels of consciousness caused by drugs and sleep [14; 15; 16]. Therefore, respiration is a very important indicator that can be applied to observe changes in human physical and psychological health and other conditions, and can be widely used in medicine, as well as various other fields. During human metabolism, all cells in the body use the oxygen in the blood to metabolize energy and release carbon dioxide through cellular respiration. As a result of cellular respiration, blood oxygen concentration decreases and carbon dioxide concentration increases, and ventilation occurs; that is, gas is exchanged in the alveoli of the lungs owing to the difference in partial pressure of the gas with air introduced from the outside. To maintain an appropriate level of oxygen concentration, the human body reduces the pressure in the chest cavity by contracting the diaphragm to bring in external air (inhalation) or increases the pressure in the chest cavity by relaxing the diaphragm to expel internal air from the body (exhalation). This process is known as respiration. Thus, respiration can be defined as a complex interaction between the central nervous system, respiratory-related motor neurons, and respiratory muscles [17]. Contact-based methods to measure respiration can be classified into four approaches, including manual measurements [18; 19], measuring changes in impedance using electrodes [20; 21; 22; 23], measuring pressure using belt-type sensors [24; 25; 26], and measuring airflow from the nose and mouth [27; 28; 29]. First, a conventional method of manually counting the rate of respiration by eye is widely used. Table 1 summarizes the advantages and disadvantages of each method. These approaches share several limitations in common. Separate sets of special equipment are necessary for each, which are not usually available. In addition, for accurate measurement, the equipment must be in close contact with the patient; the process of preparing to perform the measurement is long and complex, and tends to be inconvenient for the subject, such as by imposing strong pressure or limiting their freedom of movement. Discomfort felt by users may cause inaccurate measurement results owing to changes in on respiration rate occurring for that reason. Although this limitation can be used to understand various human conditions, it limits the application of measuring respiration in various fields.