The efficacy of bronchodilator therapy in patients with CF has been discussed previously by several authors. Zach et al showed that in a proportion of CF patients, increased bronchial smooth muscle tone mechanically compensated for structural damage; therefore, inhaled bronchodilators may induce airway compression during forced expiratory maneuvers. Our subjects were selected because they had a positive response to bronchodilators in the past, and during the protocol the individual improvement in FEVj from baseline was variable but at least 8 percent. Eggleston and coworkers studied the response to inhaled S in two groups of CF patients classified according to their response to inhaled methacholine. Among those who responded to methacholine, daily peak expiratory flow rate (PEFR) measurements improved significantly more with albuterol than with placebo.
However, it is known that CF patients may have excessively elevated transient expiratory airflows and PEFR measurements. Thus, an improvement in PEFR may only reflect increased central airway instability and not a decrease in peripheral airways obstruction. Hiatt et al studied a group of infants and young children with CF with a history of wheezing and acute respiratory symptoms, and found a significant increase in maximal expiratory flows after inhalation of metaproterenol. Thus, depending on the selection criteria, CF patients can respond significantly to adrenergic bronchodilator.
Several studies have assessed the effect of anticholinergic therapy in CF patients, and there are two studies in which the effect of the combination of drugs was tested. Weintraub and Eschenbacher studied adults with CF and found a 12.5 percent improvement in FEV! after metaproterenol treatment and a 17.1 percent increase after IB; when S and IB were used in combination, FEVi increased by 16.6 percent. In a group of young CF patients, we found on average a 7 percent increase in FEVi after S and 10 percent improvement after IB. After both drugs were inhaled, there was a 17 percent increase in FEVi from baseline. There are several factors that may explain the different results found in the present study compared with the two latter studies: age of patients studied, severity of the disease, interval between inhalations and pulmonary function measurements, the administration of combined sequential medication, and the use of inhaler solution vs metered dose inhaler.