ALTERED CARDIOVASCULAR AUTONOMIC REGULATION AFTER 2-WEEK INHALED SALBUTAMOL TREATMENT IN ASTHMATIC-CHILDREN

We studied the effects of therapeutic 2-week inhaled salbutamol treatm ent on the cardiovascular and respiratory autonomic nervous regulation in eight children with asthma. In this randomized: double-blind, plac ebo-controlled crossover study our test subjects inhaled 200 mu g salb utamol or placebo thrice daily for 14 days. After the 14-day treatment we continuously measured electrocardiogram, finger systolic arterial pressure (SAP) and flow-volume spirometry at baseline and the response to a single 600 mu g salbutamol inhalation. The periodic variability components of R-R intervals (the time between successive heart beats) and SAP in relation to respiration were assessed using spectral analys is. Two-week salbutamol treatment increased baseline low frequency (LF ) variability (P < 0.05) and low frequency/high frequency (LF/HF) vari ability ratio of R-R intervals (P < 0.05) when compared to the placebo treatment. As a response to the single salbutamol inhalation the incr ease in LF/HF ratio of R-R intervals was smaller after the 2-week salb utamol treatment (P < 0.01). No significant differences were found in the bronchodilatory response after the treatment period. Conclusion Tw o-week salbutamol treatment shifts the cardiovascular autonomic regula tion to a new level characterized by greater sympathetic responsivenes s and slight beta(2)-receptor tolerance. Because these effects were ev ident 18 h after cessation of the therapy they are likely to reflect t he adaptation of organ responses to regular therapy or altered central autonomic regulation rather than direct drug effect. A slight toleran ce developed in the sympathovagal cardiac response but not in the bron chodilatory response.