Progressive Care Nursing Certification (PCCN) Practice Exam

When assessing a normal heart, a decrease in heart rate should cause the stroke volume to:

1. increase

2. decrease

3. remain the same

4. vary

The correct answer is: increase

When assessing a normal heart, a decrease in heart rate typically leads to an increase in stroke volume due to the relationship governed by the principles of cardiac physiology. Stroke volume is the amount of blood pumped by the heart with each beat. When the heart rate decreases, there is more time for the heart to fill with blood during diastole, which can enhance the stroke volume. This phenomenon is influenced by the Frank-Starling law of the heart. According to this principle, the more the cardiac muscle fibers are stretched (up to a physiological limit), the stronger the contraction will be. A slower heart rate allows for greater ventricular filling, which increases the preload (the initial stretching of the cardiac muscle) and leads to a greater force of contraction, thereby resulting in an increased stroke volume. In a normal physiological context, the body's compensatory mechanisms also come into play. If the heart rate drops, the body can adjust to maintain an adequate cardiac output, primarily by increasing stroke volume. Therefore, understanding the dynamic interplay between heart rate and stroke volume can help clarify why a decrease in heart rate results in an increase in stroke volume in a normal heart.