Mechanical events and the pressure–volume relationships

Kirkman, Emrys

doi:10.1016/j.mpaic.2009.04.011

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Volume 10, Issue 8 , Pages 373-376, August 2009

Mechanical events and the pressure–volume relationships

Emrys Kirkman PhD is a Principal Scientist at Dstl, Porton Down, UK. He has a PhD from Manchester University and has worked at the MRC Trauma Group, Manchester, UK. He also holds honorary Senior Lectureships at the University of Durham and at the Academic Division of James Cook University Hospital, Cleveland, UK. Conflicts of interest: none declared

Abstract

Depolarization of cardiac muscle fibres spreads from fibre to fibre throughout the myocardium. In a single fibre, contraction starts just after depolarization and lasts until just after repolarization is complete. The atria contract, completing the filling of the ventricles and thus enhancing their action. In the absence of effective atrial contraction (e.g. atrial fibrillation) cardiac output is decreased on average by 15%. During diastole, when cardiac muscle is relaxed, blood returns to the heart and passes through the atrioventricular (AV) valves into the ventricles. The semilunar valves, between the ventricles and the arteries, are closed as arterial pressure exceeds ventricular pressure. Under normal circumstances, 70% of ventricular filling occurs by late diastole.

Keywords: extrinsic regulation, Frank–Starling mechanism, pressure–volume loops