ACUTE EFFECTS OF BISOPROLOL ON RESPIRATORY SINUS ARRHYTHMIA

Respiratory sinus arrhythmia (RSA) is often quantified by computing th e spectra of heart period (HP) or of its reciprocal heart rate (HR) at the respiratory frequency. This study was undertaken to describe the effect of an acute beta-blockade achieved with bisoprolol on RSA, obta ined during a calibrated breathing (breathing frequency 0.25 Hz, tidal volume V-T 500 or 700 mL) in 15 normal volunteers, using a double-bli nd, placebo-controlled, cross-over method. The two heart signals were computed and the RSA values were compared to the individual estimates of vagal tone obtained using an additional atropine injection. The dif ference between the HP (or HR) value obtained after beta-blockade and the HP (or HR) value observed following the double blockade (bisoprolo l plus atropine) was taken as an index of cardiac vagal tone. Bisoprol ol administration resulted in a significant reduction in HR reaching 6 0.3 +/- 1.4 bpm at V-T of 500 mL (compared to 70.5 +/- 1.8 bpm with pl acebo, P < 0.001). Changes in HP were also significant with an increas e in HP reaching 1004.5 +/- 22.2 msec at this controlled V-T (compared to 860.3 +/- 21.5 msec with placebo, P < 0.001). Similar changes were observed at a V-T Of 700 mL. The relationship between RSA in bpm and vagal tone was not significant for HR while a significant positive rel ationship was observed between RSA in msec and vagal tone for the two respiratory patterns (r = 0.65 for a tidal volume of 500 mL, P < 0.01, and r = 0.62 for 700 mt, P < 0.05). This demonstrates that the detect ion of the variability effect highly depends upon the unit. The parall elism between vagal tone and RSA supports the view that the HF compone nt of HRV in msec quantifies the vagal tone. The increased RSA during beta-blockade could well reflect this vagotonic effect of this class o f drugs. (C) 1998 Elsevier, Paris.