Blood Flow, Blood Pressure, and Resistance (Nursing)

00:00 So let's take a look at some of the factors that affect our blood circulation.

00:06 First, blood flow refers to the volume of blood flowing through to our vessels, organs, or our entire circulation in a given period.

00:16 Blood flow is measured in milliliters per minute, and is equivalent to our cardiac output for the entire vascular system.

00:25 Blood flow overall is relatively constant when at rest, but in any given moment can vary at individual organ levels based on the needs of those organs.

00:37 Blood Pressure is the force per unit area that is exerted on the wall of a blood vessel by the blood.

00:45 This is expressed in units of mm Hg.

00:49 We measure the systemic arterial blood pressure in the large arteries near the heart such as the aorta.

00:57 And a pressure gradient provides the driving force that keeps our blood moving from higher to lower pressure areas.

01:07 Resistance is going to be the opposite of blood flow.

01:11 This is going to be a measurement of the amount of friction that the blood is going to encounter within our vessel walls.

01:19 This is generally found in our peripheral or systemic circulation.

01:24 There are three important sources of resistance to blood flow, blood viscosity, or the thickness of our blood, our total blood vessel length, and the blood vessel diameter.

01:36 Starting with blood viscosity, the thickness or stickiness of our blood is due to the formed elements and plasma proteins within our blood.

01:47 The greater the viscosity, the less easily molecule are able to slide past each other inside of the blood vessel.

01:55 So increase viscosity is going to equal an increase in the resistance.

02:02 Another factor contributing to resistance is the total blood vessel length.

02:07 Generally, the longer a blood vessel, the greater the resistance encountered by the blood inside of that vessel.

02:16 The third contributor to resistance is blood vessel diameter.

02:20 This has the greatest influence on resistance.

02:24 And frequent changes alter the peripheral resistance.

02:28 While viscosity and blood vessel length are going to be relatively constant.

02:34 Fluid close to the walls it's going to move more slowly than the fluid in the middle of the tube.

02:41 This is referred to as laminar flow.

02:45 Resistance varies inversely with the fourth power of our vessel radius.

02:51 So if the radius increases, the resistance is going to decrease and vice versa.

02:57 For example, if the radius is doubled, then the resistance is going to drop by 1/16, or one to two raise to the four as much.

03:08 The small diameter arterials are going to be our major determinants of our peripheral resistance, because they're going to actually change their radius frequently.

03:18 This is in contrast to our larger arteries that do not change their radius very often.

03:25 abrupt changes in our vessel diameter or obstacles such as fatty plex in arthrosclerosis, can also dramatically increase resistance.

03:36 This is because laminar flow is disrupted, and instead the blood flow becomes turbulent.

03:42 And this irregular flow is going to cause an even more increase in the resistance in the blood vessel.

03:51 So blood flow is directly proportional to our blood pressure gradient.

03:57 Therefore, if our blood pressure increases our blood flow is going to speed up.

04:02 Think about it this way.

04:04 Think about what happens when you put your finger in a water hose to partially blocked the water.

04:10 The water is going to spray out faster and at a higher pressure.

04:15 Blood flow is also inversely proportional to our peripheral resistance.

04:20 So if the resistance increases, then our blood flow will decrease.

04:27 Resistance is going to be more important and influencing our local blood flow because it is easily changed by altering the diameter of our blood vessels using the smooth muscles of the blood vessel.