Answer:
there is presently inadequate evidence to conclude that e-cigarettes, in general, increase smoking cessation.
Explanation:
because it is difficult to make generalizations about efficacy for cessation based on clinical trials involving a particular e-cigarette.
Answer: Refractory period of the cardiac action potential
Explanation:
Unlike the skeletal muscle which can be reactivated before it reaches a contraction, cardiac muscle must wait before it is almost completely relaxed to be activated again (because of its long refractory period), so one cannot make an increase in strength of contraction with a high frequency of stimulations.
