Overall action of caffeine on hea rate is ?
Ans. is'b' i.e., Decreases (Ref: KDT Vh/e P. 4881)CaffeineCaffeine out of the three naturally occurring methylxanthines, only caffeine is used as a CNS stimulant.Methylxanthines directly stimulate the hea and increase force of myocardial contractions.They tend to increase hea rate by cardiac action, but decrease it by causing vagal stimulation- net effect is variable.Tachycardia is more common with theophylline, but caffeine generally lowers hea rate.
Increases
Decreases
No effect
First increases then decreases