Observational Study to Collect an Image Dataset of Healthy Population With a Characterization of the Potential Factors, Both Intrinsic (Age, BMI, Sex, Fitzpatrick Phototype, Risk Factors) and Extrinsic to the Subject (Distance and Illuminance), That May Influence the Methodologies Used to Obtain Vital Signs. The Aim is to Develop Algorithms and AI Models That Can Obtain a Set of Vital Signs Image-based. The Dataset Has Been Recorded Synchronized With the Main Vital Signs by Means Gold Standard Technologies.

5.2.1. SCIENTIFIC JUSTIFICATION OF THE PROJECT Vital signs monitoring is essential in modern clinical patient care both in hospital and at home. Some examples are heart rate (HR), respiratory rate (RR), oxygen saturation (SpO2) or blood pressure (BP), which provide crucial information on the state of a human biological system (2). The recording of these signals is usually performed with traditional devices that require contact with the patient through elements such as surface electrodes, pulse oximeter, or piezoelectric transducers. These devices are unsuitable for long-term vital signs monitoring as they can cause discomfort, irritation and a cumulative risk of fungal and bacterial infections. Moreover, they can cause skin infections, wounds and harmful reactions on patients with fragile skin, such as premature babies, older people or burned patients (3). On the other hand, many of the materials used to monitor patients are only intended for a single use (such as electrodes and leads), and then must be disposed, which entails important costs (2).

The idea of recording of these signals without the need for direct skin contact is rising as an alternative able to eliminate potential medical complications and to solve usability issues related to the need for contact devices. New technologies aim to monitor multiple vital signs with a single device, at any time and in any place (4), which would allow the prevention of certain pathologies while improving patients' health. In addition, the costs associated with the acquisition of single-use sensors, as well as patients' hospitalisation, would be reduced.

Recently, there has been a notable development in the techniques for obtaining vital signs from non-contact technologies. These focus on the observation of physical and physiological variations of the human body due to the activity of the respiratory and cardiovascular systems. Notably, these variations include skin colour, temperature, impedance changes, head motion, arterial pulse motion, and thoracic and abdominal motion (2,5).

One of the most used technologies in the development of portable devices to monitor physiological signals is video camera imaging. This passive contactless method exploits two main principles (2). First, the colour of blood varies due to the exchange of gases through cardiorespiratory action, altering the optical properties of the skin. This can be described as photoplethysmography (PPG) (5). These variations in skin colour can be appreciated in sequences of images obtained with a video camera and be exploited to obtain a signal of remote PPG (rPPG), from which several vital signs can be measured. The second principle is based on the measurement of the ballistocardiogram (BCG), which depends on subtle cyclic head motions generated as a result of pressure changes from the influx of blood at each pulse (2,5).

Since video cameras do not need any kind of interaction with the patient, they represent a promising approach for contactless monitoring. Their main advantages are their robustness, reliability, safety, cost-effectiveness, and suitability for long distance and long-term monitoring.