Cardiac Contractility - Assignment Example

Cardiac Contractility Increased Cardiac Contractility:Introduction of ionotropic agents such as digitalis increase contractility of the heart and, therefore, cause increase in the cardiac output. Due to this effect, the intersection point between cardiac output and venous return curve in ‘figure 5’ shift higher up. (Costanzo, 2010).Keeping this new change in mind, it can be presented on the graphical solver as shown below.Fig: 7. Effect of different variables on graphical solutionIncrease Heart Rate: Increasing the heart rate also increases the cardiac output.

This is because cardiac output is the total volume of blood ejected from the heart in systemic circulation in one minute i.e. CO = Stroke Volume x Heart Rate. As discussed earlier for increased contractility of ventricles, effect of increase heart rate can be plotted similarly on the graphical solution.Blood Loss or Transfusion: In a scenario, where there is excessive blood loss to an extent that compensatory mechanism cannot maintain sufficient venous return, a decrease in venous return results in decrease cardiac output.

As heart not able to meet the body requirement, condition is known as cardiac failure. Following graph (fig.8) represents interaction of Frank-Starling and venous return curves.Fig 8. Interaction of Frank-Starling and venous return curves (Source: Marini & Arthur, 2010, p.9) As the new curve intersects much lower, this new variable can be represented on graphical solver as shown in Fig 7.Assumptions seen in this Model: While plotting variables on this Model graph it is assumed that factors affecting other curve such as arteriolar or venous constriction are eliminated.

It will affect the predicted values by shifting or alternating the curves above or below normal. For example, while discussing the scenario of blood loss it was highlighted that compensatory mechanisms have failed to restore normal cardiac output. It is important because during initial blood loss, compensatory mechanisms such as sympathetic vasoconstriction can decrease venous compliance and restore adequate venous return. The effect of arteriolar and venous constriction of model curves is shown below in fig 9.

Figure 9 Alternate resistance and compliance curves (in red) showing higher resistance (arteriolarvasoconstriction), decreased arterial compliance (arterial vasoconstriction), and decreased venouscompliance (venoconstriction). The venous return curve is shown for the baseline relationships (blue)but not for vasoconstriction scenarios.Reference:Costanzo, Linda S. BRS Physiology. Lippincott Williams & Wilkins, 2010. Print.Marini, John J, and Arthur P. Wheeler. Critical Care Medicine: The Essentials.

Philadelphia: Wollters Kluwer/Lippincott Williams & Wilkins, 2010. Internet resource