Interaction of beta2-agonists and volume history in asthmatics and patients with chronic obstructive pulmonary disease

ABSTRACT

This cross sectional study is aimed [a] to dissect out the beta2-agonit response from volume history [VH] respons in asthmatics and chronic obstrutive pulmonary disease [COPD] patients, [b] to find out whether or not VH response of ariway resistance could be an indicator of the relationship between the airway and lung parenchymal hysteresis. The response of airway resistance' [Raw] as an indicator of airway tone was continously recorded to vairous degree of volume history before and 10 minutes after inhalation of 200 microgram salbutamol [beta2] in 25 asthmatics, 25 COPD patients and 25 healthy volunteers as controls. Important findings from this study are [a] in athmatics, VH alone decreased the average Raw by 28%. Beta2 decreased it by 39% while VH + beta2 decreased it by 50%. However, 6 asthmatics out of 25 shwoed a bronchoconstrictor response to VH. [b] In Patients with COPD, Raw response to VH, beta2 and VH + beta2 was evaluated to be 20, 12 and 12% respectively. However, 9 COPD patients out of 25 showed brochoconstrictor response to VH. [c] In controls, Raw response to VH, beta2 and VH + beta2 was found to be 45, 5 and 48% respectively. This study shows that both VH and beta2 responses of Raw are additive in controls as well asthmatics. However, such an effect is markedly reduced in patients with COPD. It may be proposed that VH response of Raw could be considered as an indicator of relative airway and lung parenchymal hysteresis determining the degree of airway tone