Cardiac Cycle
This heart sound is produced primarily by closure of the mitral and tricuspid valves.
What is S1?
This ECG wave represents ventricular depolarization.
What is the QRS complex?
This equation defines cardiac output.
What is heart rate multiplied by stroke volume?
This is the null value for a relative risk or odds ratio.
What is 1.0?
This study design is best for estimating the prevalence of dry eye disease at a single point in time.
What is a cross-sectional study?
During this phase, ventricular pressure rises while ventricular volume remains unchanged because all four valves are closed.
What is isovolumetric contraction?
This part of the cardiac conduction system normally serves as the primary pacemaker.
What is the sinoatrial node?
This mechanism explains why increased venous return normally increases stroke volume.
What is the Frank-Starling mechanism?
A study reports RR = 0.74 with a 95% confidence interval of 0.51–1.09. This is the correct statistical conclusion.
What is the result is not statistically significant?
This study design is generally preferred for evaluating the effectiveness of a new treatment.
What is a randomized controlled trial?
The aortic valve opens when left ventricular pressure becomes greater than this pressure.
What is aortic pressure?
The physiologic delay at this structure allows the ventricles additional time to fill before contracting.
What is the AV node?
After acute hemorrhage, decreased firing from these receptors initiates increased sympathetic activity.
What are arterial baroreceptors?
A treatment reduces progression from 25% in the control group to 10% in the treatment group. This is the absolute risk reduction.
What is 15%?
Explanation
ARR=0.25−0.10=0.15ARR = 0.25-0.10=0.15ARR=0.25−0.10=0.15
Investigators begin with patients who have a rare ocular disease, then examine previous exposures.
What is a case-control study?
This ventricular volume is present immediately before ventricular contraction and represents a major component of preload.
What is end-diastolic volume?
This ion is primarily responsible for the rapid phase 0 upstroke in ventricular contractile cells.
What is sodium?
This organ system provides the most important long-term regulation of arterial pressure.
What are the kidneys?
Using an absolute risk reduction of 15%, this is the number needed to treat after rounding appropriately.
What is 7?
Explanation
NNT=10.15=6.67NNT=\frac{1}{0.15}=6.67NNT=0.151=6.67
NNT is rounded upward to the next whole patient.
A study recruits patients exclusively from a specialty dry eye clinic and uses the results to estimate prevalence in the general population. This is the primary bias.
What is selection bias?
A sudden increase in afterload causes this initial change in end-systolic volume and stroke volume.
What is increased end-systolic volume and decreased stroke volume?
A medication that reduces the slope of phase 4 depolarization in SA-node cells will produce this effect on HR.
What is a decreased heart rate?
Because vascular resistance is inversely proportional to the fourth power of this variable, a small decrease in it greatly increases resistance.
What is vessel radius?
As disease prevalence increases, this diagnostic measure generally increases, while the negative predictive value generally decreases.
What is positive predictive value?
Participants who discontinue a study differ systematically from those who remain. This threat to validity is known as this type of bias.
What is attrition bias?