Which statement is true regarding myocardial functioning in the normal heart, based upon the Frank Starling law?
An increase in afterload results in decreased systolic pressure, which creates a decreased cardiac output.
A decrease in afterload causes the cardiac muscles to hypertrophy, resulting in increased diastolic volume.
An increase in preload results in greater shortening of myocardial fibers, thereby increasing contractility.
A decrease in preload results in increasing diastolic muscle fiber length, which impedes contractility.
The Correct Answer is C
A) An increase in afterload results in decreased systolic pressure, which creates a decreased cardiac output:
This statement is not consistent with the Frank-Starling law. Afterload refers to the resistance against which the heart must pump blood during systole. An increase in afterload typically results in increased systolic pressure, not decreased, as the heart works harder to overcome the increased resistance. However, increased afterload can lead to decreased cardiac output due to the increased work of the heart.
B) A decrease in afterload causes the cardiac muscles to hypertrophy, resulting in increased diastolic volume:
This statement is not consistent with the Frank-Starling law. Afterload refers to the pressure or resistance against which the heart must pump blood during systole. A decrease in afterload typically reduces the workload on the heart, which may lead to reverse remodeling and a reduction in cardiac hypertrophy. Increased diastolic volume may occur due to reduced afterload, but it's not the direct result of hypertrophy.
C) An increase in preload results in greater shortening of myocardial fibers, thereby increasing contractility:
Correct. According to the Frank-Starling law, an increase in preload (end-diastolic volume or stretch of myocardial fibers) leads to greater overlap of actin and myosin filaments within myocardial fibers during systole. This increased overlap results in stronger myocardial contraction (increased contractility), leading to an increased stroke volume and cardiac output.
D) A decrease in preload results in increasing diastolic muscle fiber length, which impedes contractility:
This statement is not consistent with the Frank-Starling law. Preload refers to the degree of stretch of the myocardial fibers at the end of diastole. A decrease in preload would lead to decreased stretch of the myocardial fibers, not increasing diastolic muscle fiber length. Decreased preload typically results in decreased contractility rather than impediment to contractility due to reduced myocardial stretch.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is D
Explanation
A) Shivering:
Shivering is not a normal inflammatory response to wound healing. It may indicate systemic symptoms such as fever or chills, which could be indicative of infection or other complications.
B) Purulent drainage:
Purulent drainage (pus) is often a sign of infection rather than a normal inflammatory response to wound healing. While some serous or serosanguinous drainage may be expected initially, purulent drainage suggests an abnormal response.
C) Temperature of 102° F (37.8° C):
A temperature of 102° F (37.8° C) is indicative of fever, which can occur in response to infection or inflammation. While fever is part of the inflammatory response, it is not necessarily considered a normal finding in the context of wound healing and may indicate an abnormal response such as infection.
D) Redness and localized heat:
Correct. Redness (erythema) and localized heat are typical signs of the inflammatory phase of wound healing. Inflammation is a normal response to tissue injury and is characterized by increased blood flow to the area, resulting in redness and warmth. These signs indicate that the body's immune response is active and working to repair the injured tissue.
Correct Answer is C
Explanation
A) Increased preload that results in generalized peripheral edema:
This statement is incorrect. Decreased blood volume due to hemorrhage leads to decreased preload, not increased preload. Generalized peripheral edema is more commonly associated with conditions such as heart failure or kidney disease, where fluid retention leads to increased preload.
B) The lowered blood pressure results in a reduction of the heart rate:
While it's true that a decrease in blood pressure can trigger compensatory mechanisms such as an increase in heart rate (tachycardia), the specific response mentioned in this option is not entirely accurate. The primary compensatory response to hemorrhage-induced hypotension is typically an increase in heart rate, not a reduction.
C) Decreased preload that can lead to decreased cardiac output:
Correct. With decreased blood volume (preload), there is less blood returning to the heart during diastole. This leads to decreased ventricular filling and subsequently decreased stroke volume and cardiac output. Decreased cardiac output can contribute to hypotension and inadequate tissue perfusion.
D) Increased peripheral resistance resulting from poor renal perfusion:
While poor renal perfusion can trigger mechanisms to increase peripheral resistance (such as activation of the renin-angiotensin-aldosterone system), this option does not directly address the primary effect of decreased preload on cardiac output. Increased peripheral resistance alone does not adequately compensate for decreased preload to maintain cardiac output.
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