Early lung function and future asthma

Abstract

Asthmatic adults with lower lung function have been described as having had this worse condition early in life. Lung function is reduced in children with persistent asthma and continues low throughout adult life. The challenge is to know if impaired lung function is a risk factor of asthma, as a consequence of special congenital characteristics of the airways, or whether asthmatic patients suffer a loss in lung function as early as 9 years of age as a consequence of very precocious remodeling of the airways. The loss is so early in life that it is probably a congenital characteristic, however there is not a cut-off point with clinical interest to predict risk of asthma later in life. There are contradictory results regarding whether asthmatic children lose lung function as a consequence of the airway remodeling by the illness itself. This aspect seemed to be shown for children at risk-the offspring of asthmatic mothers. The early BHR seems to be very frequent even in healthy infants, but is probably not a risk factor for asthma years later; except in the offspring of asthmatic mothers in which it has been shown. There are still many uncertainties in this field; so, more research is needed in order to better understand the pathophysiology of asthma, the early risk factors and to design new therapeutic targets and early interventions to change the natural history of the disease. The Global Initiative for Asthma (GINA) (1) defines asthma as "a heterogeneous disease, generally characterized by chronic inflammation of the respiratory tract. It is defined by the history of symptoms such as wheezing, dyspnoea, chest tightness, and cough that vary with time and intensity, together with a variable limitation of the expiratory air flow." Therefore, from the point of view of lung function, the essential characteristic in asthma is the variable limitation of the expiratory flow. In children, and especially in infants, the assessment of this limitation is not easy and not only due to a lack of collaboration, but also due to the lack of consensus regarding the best technique for clinical use, as well as the fact that there are no good reference equations available (2). Despite these limitations, just 3 years ago, the official practical guides by the ATS on recurrent and persistent wheezing recommended lung function studies in infants by means of the raised volume rapid thoracoabdominal compression (RVRTC) technique in order to assess its usefulness for better patient management (3). It has been described that adult asthmatics who have a reduced lung function have had this condition since at least the age of 9 years (4). A recent metanalysis showed that serious infant asthma may be accompanied by a reduction in lung function that persists into adult life (5). The challenge is to know if the altered lung function is a risk factor for asthma, as a consequence of congenital characteristics in the airways, or if asthmatic patients suffer from a loss in lung function as early as 9 years of age, or even before, as a consequence of an early remodeling of the airways. Cohort studies offer the major advantage of enabling the factors that precede the development of asthma to be studied and, therefore, help us to establish risk criteria. With regard to the development of lung function and asthma throughout life what has been learnt from cohort studies can be approached from different points of view: (1) Is congenital reduced lung function a risk factor for the future development of asthma? (2) Does asthma itself cause a loss in lung function in an early stage of life? (3) Is the development of bronchial hyperresponsiveness (BHR) a risk factor for future asthma?