Do You Know All Heart Disease?

When the return of blood to the heart increases, it stretches the heart muscle. This stretching activates the vagus nerve, which in turn increases the stroke volume. Stroke volume refers to the amount of blood pumped out of the heart with each heartbeat. Therefore, as the heart muscle stretches, it is able to contract more forcefully, resulting in an increased volume of blood being pumped out of the heart.

The correct answer is that cardiac output is determined by heart rate and stroke volume. Cardiac output is the amount of blood pumped by the heart per minute, and it is calculated by multiplying the heart rate (the number of times the heart beats per minute) by the stroke volume (the amount of blood pumped by the heart with each beat). Therefore, both heart rate and stroke volume play a role in determining the cardiac output.

The vagus nerve is primarily responsible for the parasympathetic control of various organs in the body. It helps regulate heart rate by slowing it down, which is the opposite of a positive inotropic effect. A positive inotropic effect refers to an increase in the force of contraction of the heart muscle, which is not directly related to the vagus nerve. Therefore, the (+) inotropic effect is least related to the vagus nerve.

Sympathetic nerve stimulation typically increases heart rate, stroke volume, and cardiac output. However, it does not have a direct inotropic effect, which means it does not directly affect the force of contraction of the heart. This is because sympathetic stimulation primarily affects the rate and rhythm of the heart, rather than the strength of the contractions.

Starling's law states that the force of myocardial contraction is directly proportional to the preload, which is the amount of blood that fills the heart during diastole. When the heart is filled with a greater volume of blood, the myocardial fibers are stretched, leading to a more forceful contraction. Therefore, preload plays a crucial role in determining the force of myocardial contraction. Heart rate, end systolic volume, and blood pressure do not directly relate to Starling's law.

Starling's law of the heart states that an increase in preload, which is the stretching of the cardiac muscle fibers before contraction, leads to an increase in myocardial contractile force. This means that when the amount of blood entering the heart increases, the heart muscle fibers stretch more, resulting in a more forceful contraction and a greater volume of blood being pumped out of the heart. Therefore, the correct answer is Starling's law of the heart.

Stroke volume refers to the amount of blood pumped out of the heart with each contraction (beat). It is measured in milliliters (ml) per beat. This measurement is important in assessing cardiac function and determining the efficiency of the heart's pumping action. By knowing the stroke volume, healthcare professionals can evaluate the heart's ability to supply oxygen and nutrients to the body's tissues.

During ventricular diastole, the atrioventricular valves are closed, preventing blood from flowing back into the atria. At the same time, the semilunar valves are open, allowing blood to be ejected from the ventricles into the pulmonary artery and aorta. This allows the ventricles to fill with blood, preparing them for the next contraction (systole). Therefore, the correct answer is that blood fills the ventricles during ventricular diastole.

Vagal discharge is least likely to increase cardiac output because it refers to the activation of the vagus nerve, which has a parasympathetic effect on the heart. The vagus nerve slows down the heart rate and decreases the force of contraction, resulting in a decrease in cardiac output. On the other hand, increased heart rate, increased stroke volume, and increased venous return all have a positive effect on cardiac output by increasing the amount of blood pumped by the heart per minute.

Vagal discharge is most likely to cause bradycardia. The vagus nerve, which is part of the parasympathetic nervous system, slows down the heart rate by releasing acetylcholine. This inhibitory effect on the heart's pacemaker cells leads to a decrease in heart rate, resulting in bradycardia. The other options, such as beta1 adrenergic receptor activation, parasympatholytic effect, and muscarinic blockade, would have the opposite effect and increase heart rate, making them less likely to cause bradycardia.

Milliliters per minute is a unit of measurement that describes the volume of blood pumped by the heart in one minute, which is known as cardiac output. Cardiac output is the product of stroke volume (the amount of blood pumped by the heart with each beat) and heart rate (the number of times the heart beats per minute). Therefore, the correct answer is cardiac output.

Atropine, a muscarinic blocker, increases heart rate by blocking the action of acetylcholine on the muscarinic receptors in the heart. Acetylcholine normally slows down the heart rate by binding to these receptors and causing a decrease in the firing rate of the sinoatrial node, which is responsible for initiating the electrical impulses that regulate heart rhythm. By blocking the effects of acetylcholine, atropine allows the heart to beat faster, resulting in an increase in heart rate.

Preload refers to the amount of blood in the ventricle at the end of its resting phase, just before it contracts. It represents the volume of blood that fills the ventricle during diastole and stretches the myocardial fibers. Preload is an important determinant of stroke volume, which is the amount of blood ejected from the ventricle with each contraction. Therefore, the correct answer is preload.

Vagal discharge is least related to tachydysrhythmias because it refers to the activation of the parasympathetic nervous system, which generally has a slowing effect on the heart rate. Tachydysrhythmias, on the other hand, are characterized by abnormally fast heart rhythms. Therefore, vagal discharge is not directly associated with the occurrence or exacerbation of tachydysrhythmias.

Sympathetic nerve stimulation is least related to bradycardia because it increases heart rate, while bradycardia is characterized by a heart rate less than 60 beats per minute. Bradycardia can be caused by factors such as vagal discharge, which slows down the heart rate, and negative chronotropic effect, which decreases the heart rate. However, sympathetic nerve stimulation activates the sympathetic nervous system, which typically increases heart rate and is therefore not directly related to bradycardia.

Venodilation refers to the relaxation and widening of the veins, which results in increased venous capacity and decreased venous return to the heart. This decrease in venous return reduces the preload, which is the amount of blood filling the ventricles during diastole. Therefore, the correct answer is that venodilation decreases preload.

The correct answer is that the drug activates the beta1 adrenergic receptors and causes a (+) inotropic effect. This means that the drug binds to and stimulates the beta1 adrenergic receptors in the heart, leading to an increase in the strength of the heart's contractions. This can be beneficial for a patient in heart failure, as it helps improve the heart's pumping ability and cardiac output.

If a drug causes a (+) inotropic effect, it means that it increases the force of contraction of the heart. A (-) dromotropic effect refers to a decrease in the conduction velocity of electrical impulses in the heart, while a (-) chronotropic effect means a decrease in heart rate. Therefore, when a drug has these effects, it would lead to a slow heart rate.

Ventricular systole refers to the contraction of the ventricular myocardium. During this phase of the cardiac cycle, the ventricles contract, pumping blood out of the heart and into the arteries. This contraction is essential for maintaining blood flow and ensuring that oxygenated blood is distributed to the body's tissues and organs. Ventricular depolarization, the opening of the valves of the ventricles, and ventricular filling are all part of different phases of the cardiac cycle but do not specifically refer to the contraction of the ventricular myocardium.

In heart failure, the heart is unable to pump blood effectively, leading to a decrease in ejection fraction. End-diastolic volume (EDV) is the amount of blood in the ventricles at the end of diastole, and it is most likely to increase in heart failure due to the heart's inability to fully empty during systole. As a result, the ventricles become more filled with blood, causing an increase in EDV while ejection fraction decreases.