Which of the following is a TRUE statement regarding determinants of myocardial oxygen demand?
Myocardial oxygen demand has constant relationship to the cardiac work. Cardiac work is composed of external and internal cardiac work. External cardiac work refers to work done during the ejection phase of the cardiac cycle. Internal work refers to the work done during isovolemetric contraction. Even though the external cardiac work is less than half of the total cardiac work it has a constant relationship with the oxygen demand. The Oxygen demand increases with increase in external work done. The three major determinants of myocardial oxygen demand are: ventricular wall stress, hea rate and contractility. If the hea rate increases the number of contractions and the amount of ATP consumed per minute increases and the oxygen requirement rises.
Inversely related to hea rate
Has constant relation to external cardiac work
Directly propoional to duration of systole
Is negligible at rest