NEUMOLOGÍA PEDIÁTRICA

Neumol Pediatr 2021; 16 (1): 5 - 10 C o n t e n i d o d i s p o n i b l e e n h t t p : / / www. n e umo l o g i a - p e d i a t r i c a . c l 12 Técnica de oscilações forçadas na avaliação e manejo de crianças asmáticas: uma revisão narrativa RESULTS From the search in the database 101 articles were found, after reading the abstracts and doing an integral review, 18 articles that contemplate the methodological characteristics specified for this study (Table 1). The researches of Dubois et al. (3), 1956, and Heijkenskjöld Rentzhog et al. (8), 2013, present mixed samples (children and adults), however, the first study is considered to be the precursor on evaluation through FOT and the second is a study of great relevance to the analysis of bron- chial reversibility markers, therefore, even if there are also data from adults in those studies, the results obtained from children’s evaluations still justify their addition in the table. Based on the presented results, (13) (72%) studies created multi frequencies evaluations, with an amplitude be- tween 5 and 35 Hz. From these, 9 (69%) added complementary exams being spirometry, the most frequent one (1-4,6,10,13,14, 8). As to the clinical outcomes, five articles (28%) approached bronchial alterations, five (28%) investigated possi- ble discrepancies between the sensibilities of the measurements among different equipments, as well as its association in the establishment of a diagnosis and, eight articles (44%) produced evaluations regarding pulmonary impedance. Eleven studies were case-control type studies (61%), in which the FOT presented enough sensitivity to observe pul- monary alterations and witness asthma’s physio pathological aspects, in which healthy children, regarding a respiratory pers- pective, presented significantly higher average R rs and X rs com- ponents. The observed alterations in the R rs values demonstrate that the technique is effective to evidence bronchial reversibility post BD use (7,9,15,15). DISCUSSION FORCED OSCILLATION TECHNIQUE The FOT was proposed in 1956 from the elabora- tion of a method that allowed to evaluate mechanical proper- ties of the respiratory system. The characterization of respi- ratory impedance is based on the analysis of its components: resistance (R rs ) and reactance (X rs ). These values are obtained by overlapping pressure fluctuations on ventilation during the evaluation period (8). One of the main advantages of this me- thod is the ease with which the maneuvers can be performed, in such a way that the subject being analyzed only has to breath at a normal rate for the impedance data to be collec- ted (9). PULMONARY IMPEDANCE The Z rs demonstrate the total mechanical charge offered by the respiratory system, as well as its resistive, elastic and interactive properties. The impedance is compo- sed by the R rs and the X rs , being determined in multi frequency oscillations (1,17). The R rs describes the total energy disper- sion, encompassing the sum of the product of the Newtonian resistances related to the airways, the pulmonary tissue and the thoracic wall, as well as the resistance that results from the redistribution of the gas (8). The X rs describes the accu- mulation of energy in the respiratory system, the potential energy is associated with the respiratory complacency (C rs ), while the kinetic energy is described by the respiratory iner- tance (I rs ) (9). The I rs is related to the energy involved in the acceleration and deceleration of the fluid (air) in the airways as well as in the pulmonary tissue (1). The measurement of impedance by the FOT is ba- sed on the response to oscillations of pressure applied in the airways. These impulses are generated by a speaker and induce a oscillatory flow in which the amplitude of the wave is inverse- ly proportional to the mechanical impedance of the respiratory system (Z rs ) (15). Higher frequencies represent the impedance of central regions, while the lower frequencies describe peripheral and central areas of the respiratory system (17). This tool’s different evaluation methods present specific benefits. The analysis by monofrequencied waves are tuned for the immediate evaluation of the breathing process, since it allows to observe the alterations presented in the airways during a respiratory cycle. This method of evaluation contemplates resistive and elastic properties of the respira- tory system (5,7,13,15,17). The studies in which a multi frequency evaluation was used represent the majority of the analyzed studies (71%), this type of analysis can be characterized as a slow one, since it represents the average behaviour of the res- piratory system through various ventilatory cycles, genera- ting even more detailed results. The indexes obtained from this analysis contemplate R rs and X rs in various frequencies, allowing the evaluation of indexes associated to the total re- sistance, the non-homogeneity and the respiratory system’s dynamic complacency (1-4,6,8,9,12,15,16,18). APPLACABILITY IN ASTHMA SUFFERER Although it was created in the 1950’s, the FOT’s first studies regarding asthma in children were only available in the year 1970. The initial studies showed that children with asthma presented an increase of the total respiratory sys- tem’s resistance because of the reduction of the airway gau- ge. This characteristic is best described by measurements that use low frequency, which include central and peripheral airways (1,3,7). The respiratory system’s total complacency is also altered in asthma patients, a factor that is associated with the increase of peripheral airway resistance as pointed out before. However, this modification is also accompanied by the group of anatomopathological alterations caused by the bronchial remodeling, a factor that hinders the elasticity of the airways and causes excessive bronchial lean muscle constriction (14). The heterogeneity of the ventilation, commonly al- tered in obstructive pulmonary diseases, also reduces the respiratory complacency by aerial imprisonment, affecting the respiratory reactance observed by the FOT (1,10,19). The R rs and the X rs are indirect markers of bron- chial obstruction and have a good sensitivity for a peripheral airway evaluation (12,17). The resistance reduction after the inhalation of a bronchodilator has a good sensitivity and ex- cellent specificity for asthma in children (11,21). Forced oscillation technique in the ssessment and management of asthm tic child n Neumol Pediatr 2021; 16 (1): 11 6