Question

Obstructive shock results from an obstruction of either the great vessels of the heart, or the heart itself. One cause of this is called tamponade (not to be confused with tapenade, an olive spread perfect for picnics or light entrées). Tamponade is caused by a pericardial effusion, build up of fluid in the sack which encloses the heart, or bleeding into the pericardium, either of which compress the heart.

Describe how this would impact stroke volume and ventricular contractility. Explain your reasoning.

Answer 1

The outer layer covering of heart is made up of fibrous tissue which is not so elastic in nature and hence accumulation of fluid in the pericardial space leads to increase in pressure.

Continuous accumulation of fluid results in decrease blood entry into ventricles due to successive diastolic period. However, the pressure increasing on the heart compels the septum to bend towards the left ventricle which causes an decrease in stroke volume. This leads to development of obstructive shock and if left untreated can result in cardiac arrest as well.

Increase in ventricular diastolic pressure decreases coronary effusion pressure resulting in closure of mitral and tricuspid valves earlier than regular that results in reduced ventricular volume and diastolic flow ( decrease in cardiac output). Endogenous catecholamines increase in order to compensate for the decreased cardiac output which consequently increases the heart rate and contractility for the maintenance of cardiac output in the situation of decreased stroke volume. Increased contractility leads to an increase in ejection fraction promoting more of ventricular emptying. This leads to right artrial/ventricular collapse, the hallmark of cardiac tamponade.