Atrial Pressure Changes During Cardiac Cycle
Atrial contraction → increase in atrial pressure ('a' wave).
As the atria begin to relax → there is small fall in pressure ('x' wave).
[1. (As the atrioventricular valves close → there is a small backflow of blood.) + 2. (Ventricles contract as close chambers → rise in ventricular pressure → some bulging of atrioventricular valve into the atria)] → Rise in atrial pressure ('c' wave).
Contraction of ventricular musculature along with contraction of papillary muscles of atrioventricular valve → pulls atrioventricular valve towards ventricles → fall in atrial pressure ('x1' wave).
Ongoing filling of atria during diastole → rise in pressure ('v' wave).
Opening of atrioventricular valve → rushing of blood from atria to ventricles → fall in pressure ('y' wave).
Next cycle begins with atrial contraction → increase in pressure ('a' wave) .