What is the inherent rate of the AV (atrioventricular) node area?
40 to 60.
20 to 40.
60 to 80.
80 to 100.
The Correct Answer is A
The atrioventricular (AV) node is an essential component of the cardiac conduction system responsible for transmitting electrical impulses from the atria to the ventricles. The inherent rate of the AV node refers to its intrinsic ability to generate electrical impulses in the absence of external influences.
Here's a breakdown of each option:
A) 40 to 60:
Correct. The inherent rate of the AV node is typically 40 to 60 beats per minute (bpm). This rate is slower than that of the sinoatrial (SA) node, which has an inherent rate of 60 to 100 bpm. The AV node acts as a backup pacemaker, ensuring that the ventricles receive electrical impulses even if the SA node fails to function properly.
B) 20 to 40:
This range is not consistent with the typical inherent rate of the AV node. A rate of 20 to 40 bpm would be unusually slow and could indicate significant conduction system abnormalities rather than the normal functioning of the AV node.
C) 60 to 80:
This range is more characteristic of the inherent rate of the SA node rather than the AV node. The SA node is the primary pacemaker of the heart, and its inherent rate is typically 60 to 100 bpm.
D) 80 to 100:
Similar to option C, this range is more consistent with the inherent rate of the SA node rather than the AV node. The SA node typically has a faster intrinsic rate compared to the AV node.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
A) An increase in afterload results in decreased systolic pressure, which creates a decreased cardiac output:
This statement is incorrect. According to 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 incorrect. 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. The Frank-Starling law states that 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 incorrect. 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 an impediment to contractility due to reduced myocardial stretch.
Correct Answer is C
Explanation
DKA is a serious complication of diabetes mellitus characterized by hyperglycemia, ketosis, and metabolic acidosis. The laboratory results consistent with DKA include:
Elevated blood glucose level: A blood glucose level of 525 mg/dL (28 mmol/L) is significantly elevated and consistent with DKA.
Low arterial blood pH: A decreased arterial blood pH indicates acidosis, which is characteristic of DKA. Normal arterial blood pH ranges from 7.35 to 7.45.
Low bicarbonate (HCO3-) level: A low bicarbonate level indicates metabolic acidosis, which is also characteristic of DKA. Normal bicarbonate levels range from 21 to 28 mEq/L (21 to 28 mmol/L).
Among the options provided:
A) Arterial blood pH 7.5 and bicarbonate level 32 mEq/L (32 mmol/L):
This pH and bicarbonate level are indicative of alkalosis, which is not consistent with DKA.
B) Arterial blood pH 7.42 and bicarbonate level 18 mEq/L (18 mmol/L):
This pH is within the normal range, and the bicarbonate level is slightly decreased but not indicative of metabolic acidosis consistent with DKA.
C) Arterial blood pH 7.25 and bicarbonate level 10 mEq/L (10 mmol/L):
Correct. This pH is decreased, indicating acidosis, and the bicarbonate level is significantly below the normal range, consistent with metabolic acidosis characteristic of DKA.
D) Arterial blood pH 7.38 and bicarbonate level 29 mEq/L (29 mmol/L):
While the pH is within the normal range, the bicarbonate level is elevated, which is not consistent with metabolic acidosis seen in DKA.
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