Assessment of the long-duration effect of inhaled long-acting bronchodilator Salmeterol on cardiac autonomic control in adult asthma patients

The asthma patients usually received regular use of inhaled corticosteroid combined with long-acting beta agonist (LABA) for their asthma control. The inhaled LABA achieved the bronchodilation effect through sympathetic activation in airways of asthma patients. These LABAs might have the cardiovascular effects such as palpitation, tachycardia and QTc prolongation. There are studies investigating the short-duration effect of LABA on cardiac autonomic control in asthma patients. However, the long-duration effect of inhaled LABA on cardiac autonomic control in adult asthma patients remains lacking. In this study, we explored the longduration effect of inhaled bronchodilator Salmeterol (one kind of LABAs) on cardiac autonomic control with heart rate variability (HRV) analysis in adult asthma patients. Serial resting, surface ECGs were recorded at different time intervals (from baseline to 180^th min) after inhalation of Salmeterol in eligible adult asthma patients. Mean heart rate (mean RR), standard deviation of normal RR interval (SDNN), normalized low frequency band power (LFn), normalized high frequency band power (HFn) and the ratio LF/HF were obtained from analysis of heart rate variability (HRV) at these different time intervals.Significant increase of LF/HF after inhalation of Salmeterol as compared with baseline time interval was noted. Significantly increased LFn and decreased HFn without significant change of LF/HF were also noted as compared with baseline interval. Besides, significantly increased mean RR and SDNN were also noted. In this study, during the 3-hour duration after inhalation of Salmeterol in adult asthma patients, HRV analysis revealed that significant cardiac-sympathetic activation occurred at the 6^th min, which precedes the maximal effect of bronchodilation occurred 2 to 4 hours after inhalation of Salmeterol.