The average healthy human heart weighs about 300 g or approx 0.5% of the total body mass, yet the oxygen demand of the heart accounts for 7% of the resting body oxygen consumption and consequently 5% of the cardiac output. The normal myocardial oxygen consumption MVO2 per minute is approx 8 mL O2/100 g and varies widely between normal, diseased, and exercising states. The MVO2 is primarily dependent on the coronary blood flow (CBF) and the removal of oxygen from the coronary blood as follows: Arterial (CaO2) contents minus Venous (coronary sinus, CSO2) contents, such that
Secondary determinants that influence MVO2 include heart rate, myocardial stroke work, afterload, and/or the inotropic state of the heart.
During cardiac surgery, MVO2 can vary extensively, with the greatest MVO2 occurring immediately after bypass; replenishing energy stores requires a high oxygen demand (repaying oxygen debt). In contrast, cardiac arrest combined with myo-cardial hypothermia dramatically reduce MVO2 (Fig. 1). It should be noted that hypothermic and normothermic modes of c O
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.