The results do not show any difference between the route of administration in terms of the ventilatory response produced by terbutaline. In other words, bronchodilator activity appeared independent of route of administration, in this group of patients with moderately severe airways obstruction. No difference could be seen in site of activity of the bronchodilator, with an equivalent response being seen for tests of large and small airways. These results suggest that a bronchodilator, whether delivered parenterally or by aerosol, can affect all parts of the tracheobronchial tree to produce equivalent bronchodilation, even in the presence of moderately severe airways obstruction. The distinction between large and small airways obstruction and the realization that asthma may preferentially affect different airways during the natural history of the disease have led to doubts that bronchodilators by inhalation can have as complete and comprehensive an effect as those delivered by mouth or parenterally. A number of studies argue that view, including the observations by Hensley et al, which showed isoprenaline by aerosol affecting small airways as opposed to a more central action of aerosol atropine. Studies of exercise-induced asthma treated by proventil have also shown that changes in residual volume that follow exercise can rapidly be reversed by inhaled bronchodilators, and this also suggests a peripheral action of the inhaled salbutamol used in that study. Further work by Wagner et al has shown that inhaled bronchodilators can rapidly affect ventilation—perfusion ratios and arterial blood gases, indicating a distal site of action. Studies carried out in Montreal by Antic and Macklem have shown that inhaled salbutamol can reverse the expiratory flow limitation, which appears to arise in small airways as judged by helium and air flow volume curves. All of these studies, therefore, have indicated that the inhaled route can effectively achieve peripheral as well as central bronchodilatation, and our results, which were designed specifically to examine this matter, support these conclusions. The study by Tashkin et al is difficult to interpret, since only single doses were used, and the nebulized dose was only 0.5 mg, which is very submaximal and not comparable with the subcutaneous dose of 0.5 mg, which is about maximal.
Basal values for the two days of the study were not significantly different for any of the indices measured. Both IV and inhaled routes of administration of terbutaline produced significant increases in FEVi, FVC, PEFR, MMFR, and MEF50. Both routes also produced a significant rise in VA and a fall in the slope of the alveolar plateau. These changes are shown graphically in Figures 3 and 4. The effect on the helium responsiveness of the MEF50 was variable, and although several patients showed increases, the mean responses of the whole group were not significantly different from the basal values. Both routes of administration also produced significant increases in effective pulmonary blood flow as measured by both single breath and rebreathing techniques. You may use ventolin, proventil, advair or flovent to treat asthma efficiently.
Flow volume loops were performed during maximal forced expiration, using a dry wedge spirometer (Floop 1 TM pulmonary function studies system, Oldelft). These were obtained with the subject breathing air and again after quiet breathing of a gas mixture of 80 percent helium and 20 percent oxygen for three minutes. The indices measured on the flow volume loops were forced expired volume in one second (FEVj), forced vital capacity (FVC), peak expiratory flow rate (PEFR), maximal midexpiratory flow rate (MMFR), and maximal expiratory flow at 50 percent of the vital capacity (MEF50). Helium responsiveness was assessed as the percentage increase in MEF50 of the helium-oxygen flow volume loop compared with that of the corresponding one breathing air.
The effects of terbutaline on pulmonary blood flow were measured by a rebreathing method introduced by Cander and Forster and used more recently by Petrini and Hyde, and also by the single-breath method originated by Krogh and Linhard and further developed by Denison and coworkers. One potential advantage of the single-breath method in asthma is that it produces less effect on airway caliber resulting from the maneuver itself than does vigorous rebreathing, which often induces bronchoconstriction. Buy asthma inhalers online to prevent asthma appearance.
Bronchodilators have been used to treat asthma for many years, but there is still controversy about the best route of administration and the indications for each route. There are many arguments in favor of inhalation therapy, which delivers the bronchodilator to the target organ, and thus keeps the plasma level to the minimum and reduces the likelihood of systemic side effects. Equal bronchodilata-tion with fewer side effects from salbutamol has been shown for the inhaled route by Bloomfield et al in severe acute asthma and by Spiro et al2 in moderately severe asthma.
There are, however, potential disadvantages to the inhaled route, the first being that its effectiveness might suffer with increasing airways obstruction as aerosol penetration and distribution become less efficient. This mechanism was invoked to explain the finding by Williams and Seaton of greater effect with salbutamol using the intravenous (IV) route in patients with severe acute asthma treated by proventil. Another possible objection to the inhaled route is that the aerosol is likely to be deposited preferentially in central and larger airways.