Use of the Electronic Nose for Diagnosing Respiratory Diseases Utilidad de la nariz electrónica para el diagnóstico de enfermedades de la vía respiratoria

The continuous search for non-invasive respiratory disease markers has led to the development of new techniques that can distinguish disease that affect the airway or pulmonary parenchyma. Thus, the analysis of exhaled air has gained importance in research, and in particular pathologies it has already been transferred to clinical practice. The evolution in new technologies has spurred the development of new devices, and with these the analysis of exhaled air has become an important non-invasive diagnostic method that may be used in the evaluation of pulmonary diseases. An example is the measurement of exhaled nitric oxide, now used in daily clinical practice for the diagnosis and follow-up of asthma. Since the age of classical medicine, the sense of smell has been used to classify certain diseases. Some examples are the putrid smell of infections due to anaerobes or the fruity scent of ketone in patients with diabetic ketoacidosis. In this new era of technological advances, devices are being developed that will be able to quantify and differentiate such smells in a more precise manner. One of these new devices is the electronic nose (E-nose), which could be described as a tool that is made up of a matrix of chemical sensors with overlapping sensitivities that, when exposed to volatile particles, experience specific changes in their electric resistance. An advanced system of pattern recognition that is able to recognize simple or complex aromas can, based on the integrated signal obtained from each of the sensors, create a smellprint.1 In order to understand how the E-nose works, it is necessary to clarify that the chemical sensors that make up the sensory matrix are not specific, meaning that they are not selective for a given compound, but instead for a groups of compounds. In fact, the E-nose technique in medicine is based on the detection of volatile organic compounds (VOC) that are present in the gaseous phase of human breathing.2 This response generates a signal whose pattern or smellprint can be recognized by comparing it with previously recorded patterns. In this context, the technology of the electronic nose is