Peripheral resistance depends on?

AIIMS Bhuvneshwar NO- 2018

Applied Physiology

Easy

Appeared in: AIIMS Bhuvneshwar NO- 2018

Explanation

Peripheral resistance is the opposition to blood flow, primarily determined by the diameter of blood vessels.
Arterioles, known as 'resistance vessels', have muscular walls that can constrict or dilate, making them the main site for regulating systemic vascular resistance.
According to Poiseuille's Law, resistance is inversely proportional to the fourth power of the vessel's radius. This means even minor changes in arteriole diameter have a massive impact on resistance and blood pressure.

Option A: Stroke volume is the amount of blood pumped by the heart per beat. It is a key component of cardiac output (Cardiac Output = Stroke Volume × Heart Rate), not peripheral resistance.
Option B: Veins are 'capacitance vessels' that hold blood. Their contraction increases the return of blood to the heart (preload) but they contribute very little to the total peripheral resistance.
Option D: Blood volume is the total amount of fluid in the circulatory system. It influences the overall blood pressure and cardiac output, but it is not the direct determinant of the resistance to flow itself.

Visual 1: Diagram - Illustrating Poiseuille's Law, showing how a small decrease in vessel radius dramatically increases resistance to flow.
Visual 2: Infographic - Comparing the cross-sections of arteries, arterioles, capillaries, and veins, highlighting the thick muscular wall of arterioles relative to their lumen size.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Determinants of peripheral vascular resistance as background academic context rather than a clinical decision trigger.
Understanding peripheral resistance is crucial for managing hypertension. Many antihypertensive medications, such as vasodilators (e.g., hydralazine) and calcium channel blockers (e.g., amlodipine), work by relaxing the smooth muscle of arterioles, increasing their diameter and thus reducing resistance.
In critical care settings, nurses frequently administer vasopressor medications (e.g., norepinephrine) that constrict arterioles to increase peripheral resistance and raise blood pressure in hypotensive patients.
What if? If a patient is given a potent vasodilator drug, the diameter of their arterioles will increase significantly. This will cause a sharp decrease in peripheral resistance, leading to a potentially dangerous drop in blood pressure (hypotension).

How to Approach the Question

First, identify the core physiological concept in the question, which is 'peripheral resistance'.
Recall the fundamental equation for blood pressure: Blood Pressure (BP) = Cardiac Output (CO) × Peripheral Resistance (PR).
Analyze the given options to determine which one is a direct component of Peripheral Resistance, as opposed to Cardiac Output.
Stroke volume and blood volume primarily influence Cardiac Output. Contraction of veins affects preload, which also influences Cardiac Output.
The diameter of arterioles is the primary factor that the body adjusts to change resistance on a moment-to-moment basis.
Therefore, select the option that directly relates to the constriction or dilation of the body's main resistance vessels.

Concept Tested & Keywords

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