Isometric growth of lungs and airways in asthma
Children and adolescents were treated with a bronchodilator drug (salbutamol) to which were added either a placebo drug or an inhaled corticosteroid. The two drugs, as in this study, because this leads to a high concentration in the airways - the target organ - with minimal systemic effects. In asthma we are dealing with a sterile inflammatory process that gives rise to increased bronchomotor tone. Bronchodilator drugs temporarily diminish or abolish the increased tone. They have no effect on the inflammatory process. Corticosteroids on the other hand suppress the inflammatory process with varying success varies from patient to patient and thus address the problem from a more fundamental perspective; in doing so they also prevent the occurrence of airway narrowing from increased bronchomotor tone, or diminish its extent. Intuitatively one would expect that in the case of an ongoing inflammatory process in the airways, airway growth might differ from that in which the inflammation is maximally suppressed.
In each patient k was assessed (k forms part of the equation in which MEF is proportional to Vk). In boys and girls the average for k was computed for each type of treatment. The illustration shows the upper and lower limit which delineates 50% of the observations at a high and at a lower lung volume. The average values are within the range of k that is compatible with isometric growth; there is no evidence that in patients who - one would think -were best treated (those who inhaled corticosteroids) lung and airway growth differed from that in the group with symptomatic treatment only.
- The hypothesis that growth of lungs and airways occurs isometrically cannot be rejected.
- We should add that whilst the development (that is the rate of change indicated by the power k) in these groups of asthma patients is the same, children who were treated with inhaled corticosteroid on average produced higher forced expiratory flows than those who were only treated with a bronchodilator drug. In other words, there is a difference in the level of flows, but granted that difference there is no difference in the rate of change during lung growth.
- Please take note of the fact that isometric growth does not seem to occur in each individual: in a significant proportion of subjects k falls outside the range compatible with the hypothesized growth pattern.
- Merkus PJFM, van Pelt W, van Houwelingen JC, van Essen-Zandvliet LEM, Duiverman EJ, Kerrebijn KF, Quanjer PH. Inhaled corticosteroids and growth of airway function in asthmatic children. Europ Respir J 2004; 23: 861-868.
- Weiss ST, Tosteson TD, Segal MR, Tager IB, Redline
S, Speizer FE. Effects of asthma on pulmonary function in children.
Am Rev Respir Dis 1992; 145: 58-64.
These authors come to comparable conclusions, although their findings suggest that asthma in girls is associated with a decreased rate of growth of FEV1.