Peripheral Vascular System

Arterial Circulation
The factors that affect arterial circulation are blood flow, peripheral vascular resistance and blood pressure.

Blood Flow - volume transported in a vessel, in an organ, or throughout the entire circulation over a given period of time, mL/min.

Peripheral Vascular Resistance (PVR) - opposing forces or impedance to blood flow as the arterial channels become more and more distant from the heart.

3 Factors of PVR:

•  the greater the viscosity or thickness of the blood the greater the resistance to moving and flowing
• the longer the vessel, the greater the resistance to blood flow.
• the smaller the diameter of a vessel, the greater the friction against the walls of the vessel thus the greater the impedance to blood flow.

Blood Pressure - force exerted against the walls of the arteries by the blood as it is pumped from the heart. Most accurately referred to as mean arterial pressure (MAP).

MAP = CO x PVR

Blood flow, PVR and BP, which influence arterial circulation, are in turn influenced by various factors:

SNS: vasoconstriction thereby increasing BP

PNS: vasodilation of the arterioles, lowering BP

Baroreceptors in the aortic arch, carotid sinus, and other large vessels can cause reflex SNS stimulation, resulting in vasoconstriction, increased HR and increased BP.

Kidneys: when BP decreases, the kidneys initiate RAAS which stimulates vasoconstriction, resulting in the release of Aldosterone, increasing sodium and water retention. In addition, pituitary release ADH to promote renal reabsorption of water. Net result is an increase in blood volume and consequent increase in CO and BP

Temperature: Cold causes vasoconstriction, whereas warmth produces vasodilation.

Chemicals, hormones and drugs influence BP by affecting CO and/or PVR i.e Epinephrine causes vasoconstriction and increased HR; Prostaglandins dilate blood vessels; Endothelin is a potent vasocontrictor; Nicotine causes vasoconstriction; alcohol and histamine causes vasodilation.

Salt, saturated fats and cholesterol elevate BP by affecting blood volume and vessel diameter.

Other factors that may also affect BP:

• Race
• Gender
• Age
• Weight
• Time of day
• Position
• Exercise
• Emotional state

LeMone/Burke/Bauldoff

p 876-879