The 3 major determinants of myocardial oxygen demand are Heart Rate, Contractility and wall stress HEART RATE::- If a relatively fixed amount of oxygen is consumed per heartbeat, one would expect the oxygen demand per minute to increase linearly with heart rate. Thus a doubling Heart rate would yield a doubling of oxygen demand. In fact, demand more than doubles with a two-fold increase in heart rate. The source this additional oxygen demand is the staircase phenomenon, in which increased heart rate causes a small increase in contractility, and increases in contractility mean more oxygen consumed.
CONTRACTILITY::= More oxygen is used by a highly contractile heart compared to more relaxed heart. Contractility is extremely difficult to measure. Quantitative Assessment:- Strictly defined, the contractile state of the heart is a dynamic intrinsic characteristic that is not influenced by…
