ABSTRACT
The small airway, present since the origins of humanity and described barely a century ago, has recently been discovered as the anatomical site where inflammation begins in some obstructive lung diseases, such as asthma and Chronic Obstructive Pulmonary Disease (COPD), per se. Small airway dysfuction was identified in up to 91% of asthmatic patients and in a large proportion of COPD patients. In subjects without pathology, small airway represent 98.8% (approximately 4500 ml) of the total lung volume, contributing only between 10-25% of the total lung resistance; however, in subjects with obstruction, it can represent up to 90% of the total resistance. Despite this, its morphological and functional characteristics allow its dysfunction to remain undetected by conventional diagnostic methods, such as spirometry. Hence the importance of this review, which offers an overview of the tools available to assess small airway dysfunction and the possible therapies that act in this silent zone.
La vía aérea pequeña, presente desde los orígenes de la humanidad y descrita hace apenas un siglo, se ha descubierto recientemente como el sitio anatómico donde inicia la inflamación provocada por algunas enfermedades pulmonares obstructivas: asma y enfermedad pulmonar obstructiva crónica (EPOC), per se. Se ha identificado disfunción de la vía aérea pequeña en el 91% de los pacientes asmáticos y en una gran proporción de quienes padecen EPOC. En los pacientes sin enfermedad, la vía aérea pequeña representa el 98.8% (4500 mL) del volumen pulmonar total, y solo aporta del 10 al 25% de la resistencia pulmonar total; sin embargo, en sujetos con obstrucción puede suponer el 90% de la resistencia total. A pesar de esto, sus características morfológicas y funcionales permiten que la disfunción pase inadvertida por métodos diagnósticos convencionales, por ejemplo la espirometría. Con base en lo anterior, el objetivo de este estudio fue revisar el panorama general de los métodos disponibles para evaluar la vía aérea pequeña y los posibles tratamientos asociados con esta zona silente.
ABSTRACT
BACKGROUND: The main limitation of the six-minute walk test (6-MWT) is that not all pulmonary function testing facilities have an indoor flat, 30-m-long corridor. Therefore, this study aimed 1) to evaluate the correlation and agreement of the distances walked in 30-m- vs. 15-m-long corridors by subjects with chronic lung diseases (CLD group) and 2) to compare the levels of oxygen saturation (nSpO2), blood pressure (BP), heart rate recovery at minute one post-exercise (HRR1), and Borg scale scores for dyspnea and fatigue between the two distances walked. METHODS: A prospective, cross-sectional study was conducted at the National Institute of Respiratory Diseases in Mexico City. Subjects with chronic lung diseases and healthy adults were invited to participate. The distance of the 6-MWT was randomly assigned based on whether the first test was in the 15-m or 30-m corridor. RESULTS: Ninety individuals were included; the correlation in meters walked between the two corridors was r = 0.96 in CLD; the 95% limits of agreement for the 6-MWT ranged from -73 to +37 m. Most subjects walked further in the 30-m corridor (82%); however, the percent predicted values for the CLD group were 3.5% lower for the 15-m corridor than the 30-m corridor. Only 10.5% of the subjects with CLD would have been falsely classified as having a normal 6-MWT (false negative). No significant differences in the nSpO2, Borg scale, BP or HRR1 were found between the two 6-MWT corridor lengths. CONCLUSION: The 6-MWT can be performed using a 15-m corridor in subjects with CLD, and the results for the distance walked, HRR1, nSpO2, and Borg scale scores are similar to between the 15-m and 30-m corridors.
