Basics HR & Myocardial Diffusion

• • as HR rises, diastole shortens and the time available for myocardial perfusion is reduced
  • but you need to factor in one more fact, as HR rises, myocardial workload is increased and so myocardial demand for O2 is increased, (i.e. as the heart works harder it needs more O2 in order to manufacture more ATP to power the contractions)
  • And this increased demand is occurring exactly at the same time that perfusion is decrease

  
• • However people without coronary artery disease are able to ensure that the myocardium gets the blood and O2 it requires irrespective of how hard it is working (at whatever HR or force of contraction)
  • So how does it do that? Well there are 2 main mechanisms, which ensure the myocardium is adequately perfused at all times in health
  • The myocardium is extremely efficient at extracting O2 from the coronary blood supply
  • To ensure the myocardium is appropriately perfused, in health the coronary arteries just vasodilate