Blood Flow in the Brain, Lungs, and Heart (Nursing)

00:01 So now let's look at blood flow to special areas in the body.

00:05 Starting with the brain.

00:07 Blood flow to the brain must be constant because neurons are intolerant to ischemia, which causes a short of blood and therefore, oxygen coming to the brain.

00:20 Blood flow to the brain average is about 750 mL/min.

00:28 The way we control blood flow to the brain is through metabolic controls.

00:33 So when there is a decreased pH or an increase in the amount of carbon dioxide, we are going to have a marked vasodilation.

00:43 Very high carbon dioxide levels will depress autoregulatory mechanisms.

00:51 The brain is very vulnerable under extreme systemic pressure changes.

00:56 A main arterial pressure of less than 60 mm Hg can lead to syncope or fainting.

01:04 A mean arterial pressure of greater than 160 mm Hg can result in cerebral edema or swelling of the brain.

01:15 So now let's look at blood flow to the lungs.

01:18 To do this, we look at our pulmonary circuit, which is an unusual circuit as the pathway is very short.

01:25 The arterial resistance and pressure in our pulmonary circuit is actually much lower than what we find in our systemic circuit.

01:34 And this average is about 24/10 mm Hg versus the 120/80 mm Hg that we see in the rest of the body.

01:47 The autoregulatory mechanisms in the lungs are also opposite of what we see in the body.

01:53 In the lungs, low oxygen levels actually cause vasoconstriction and high levels promote phase o dilation.

02:02 This allows for blood to flow to areas that are oxygen-rich and away from areas that have inadequate oxygen supply.

02:13 When we look at blood flow to the heart, this is going to be influenced by aortic pressures and ventricular pumping.

02:21 During ventricular systole, our coronary vessels are going to be compressed.

02:27 Our myocardial blood flow is going to cease and stored myoglobin is going to supply sufficient oxygen.

02:35 During diastole, our high aortic pressure forces blood through the coronary circulation.

02:43 At rest, our coronary blood flows at about 250 mL/min.

02:49 And as controlled by way of myogenic mechanisms.

02:54 So during strenuous exercise, our coronary vessels are going to dilate in response to the local accumulation of vasodialators.

03:04 Blood flow is going to increase to about three to four times.

03:08 And this is going to be important because our cardiac cells use about 60% of the oxygen that are delivered to them.

03:17 Other cells in our body only use about 25% of the oxygen delivered to them.

03:22 So increasing our coronary blood flow as a way to provide more oxygen to those coronary cells, especially during strenuous exercise.