## 2 A Brief Overview of the Related Concepts
### Respiratory Inductive Plethysmography (RIP)  
In addition to the conventional methods of measuring respiratory parameters, Respiratory Inductive Plethysmography (RIP) is a non-invasive method of measuring lung ventilation. Tidal volume measured with RIP shows a strong correlation with spirometry in healthy subjects [21; 22].  
It generally involves the movement of the chest during respiration to measure spontaneous tidal breathing, though labored breathing has also been studied with RIP. Two elastic belts are placed around the patient, one at the abdomen around the umbilicus and the other at the ribcage around the nipple line. Generally, RIP can be performed on subjects in around 5-10 min depending on the condition and calibration [23]. RIP devices usually use a transducer with coils connected to an analogue circuit that functions as a variable-frequency LC oscillator. The inductance may be calculated using the frequency and amplitude of the coils due to their inductive nature. The belts' length changes with each breath, causing the self-inductance of the coils to also vary. Changes in the ribcage's and the belly's circumference or cross-sectional area can be identified by observing alterations in the coils' self-inductance [24]. Figure 1 illustrates the basic operation of RIP.  
Although most current technologies show potential, the major advantage of RIP is that it allows for the examination of tidal breathing and breathing pattern changes in patients who are unable to cooperate due to their age or disease severity [25]. Moreover, the RIP system can also be implemented for individuals in an ambulatory environment [26; 27; 28]. The ease of use of this system, the device, and the method are coming to be of great interest to researchers and clinicians. This work intends to provide a complete account of the usability of RIP in a wide range of healthcare applications and to provide insight into its future research directions.  
The usage of RIP is not limited to adults only; its utility in pediatric care is underscored in [29], in which the authors provide age-related ranges of reference values for infants and children, emphasizing its non-invasive nature and utility in monitoring respiratory patterns in younger populations without requiring active cooperation. Technological advancements have led to the development of a low-cost, portable bio-impedance system capable of detecting both respiratory and heart activities, potentially improving patient care outside clinical settings [30]. The feasibility of RIP for long-distance medical consultations through a mobile application is particularly relevant in areas with limited access to medical facilities, offering a method for pre-diagnosing lung conditions remotely [31].  
Innovative applications, such as the automated detection of swallowing events using RIP, offer potential in remote monitoring of patients with swallowing disorders, providing a non-invasive method to assess and aid in managing these conditions [32]. Additionally, the authors of [33] introduced a method for detecting respiratory motions of the chest and abdomen without constraints using a flexible tactile sensor array, enhancing the  
Figure 1: Functional block diagram of RIP.  
comfort and feasibility of respiratory monitoring, especially in sleep studies. These studies illustrate the continuous evolution of RIP technology and its expanding applications across different fields, from pediatric care to remote health monitoring and sleep studies. The ongoing research and development in this area promise to further integrate RIP into diverse healthcare and research contexts, improving non-invasive respiratory assessment techniques and enhancing patient care.