Lecture 1 Overview

From Iusmphysiology

• started here on 01/19/11.

• today we start worrying about organ systems instead of facts.
• One of the most interactive is the cardiovascular system
  • Dead in 3-5 minutes when it stops.
• We'll look at healthy, then diseases.
• Bohlen
  • Been here a long time.
  • 24 turn around time for emails
  • Suggests rhoades and bell text
• Everything we need to know is in the lecture outlines
• Bring the next lecture outline each day because they will run over and together.
• Objectives will be tested.
  • He keeps his work, too, as can be seen from old tests.
  • Study the objectives; write them out.
  • All the non-objective stuff is to build a story around the cardiovascular system.
• Test items are from NBME, from other faculty, from students.
  • These should be studies because they are how we're going to get questioned.
  • He is going to teach us to do well on vignette questions.
• exam
  • 60% of the exam is vignettes
  • the rest are do you know the details questions

Contents 1 Cardiovascular physiology 1.1 Death 1.2 Blood vessels in situ 1.3 Clean healthy living 1.4 Two major functions of the CV system 1.5 Blood flow 1.6 Components of pressure 1.6.1 Cardaic output 1.6.2 Gravity 1.6.3 Veins 1.7 Resistance 1.8 Video 1.8.1 Viscosity of blood 1.9 Flow in the microvessels 1.10 Laminar flow 1.11 Poiseuille equation 1.12 Clinical vignette 1.13 clinical vignette

Cardiovascular physiology

Death

• many people die from the cardiovascular system going out.
• Young people are generally felled by congenital problems with the system.
• Statins are decreasing the cardiovascular deaths.
• Cubbiness is a big factor.
  • More obesity = more TAG, chol = more CV disease.
• Half the medical costs
  • Obesity, smoking, and ?

Blood vessels in situ

• Capillary with flow.
• RBCs aren't moving.
• RBCs are curled up like crepes.
  • they have to fold to get through caps.
  • This is good for exchange; oxygen to the tissues.
• Everything feeds back to feeding oxygen via caps.

Clean healthy living

• Goal is to be a healthy 80 yo.
• Exercise
• Diet and weight control
• Pick healthy grandparents

Two major functions of the CV system

• We have to maintain flow of blood.
  • Males in class pumping 5 liters / minute.
  • In shape can hit 35-45 liters / minute!
  • This is important because of all the things we have to get to the tissue:
    • Oxygen (dead in 3-5 minutes without it)
    • Water (dead in 3-7 days
    • Glucose (weeks worth of storage)
    • Lipids (months worth)
    • Proteins (months worth)
  • Get rid of:
    • CO2
    • GI food
    • Hormones
    • Glucose
    • Adipose
• So this is flow and exchange.
• How much is exchanged: flow in - flow out.
  • This can be played with.
  • Change flow to change the input to increase the exchange.
  • Flow X (Ca - Cv)
• Daily exchange:
  • 900 liters of oxygen
    • 1 acre of rainforest
    • 5 acres of open water air
  • CO2, glucose, lipids, protien, water

Blood flow

• Units will be liters / minute for cardiac output
• Organs we use ml / minute / 100 grams of tissue
  • Knowing this is pretty invasive, so they must be pretty sick
  • The only exception is the kidney where it is pretty easy to know the flow.
• Two key issues in determing blood flow
  • Must have energy to push blood through vessels.
    • Measured in mmHg; though this is toxic so we use spring measuring contraptions
    • Normally about 100 mmHg, this is about the force of four quarters stacked in our hand
    • Venous pressure is about 7 mmHg
    • so the difference for pushing blood all the way around is about 97 mmHg.
    • This works out to about 2 lbs / square inch when you take area into account.
    • Relatively, indianapolis' water supply is at about 50-70 lbs / square inch; so we are pretty low pressure
  • Forces opposing blood flow
    • Vascular resistance
      • Units: mmHg / ml / min / 100 grams (organs) or mmHg / liter / min / kg body mass (systemic)
      • We dissipate some energy for each unit of energy for each unit of blood that flows thorugh an organ.
      • We occasionally know a pt's resistance.
      • We often knwo which direction their resistance is heading.
      • Resistance = pressure / flow = 97 mmHg / 5 liters / minute / 70 kg = 0.28 mmHg / liter / min / kg
      • We'll rearrange this often.

Components of pressure

• There are two major sources of energy that generate pressure to move blood around: the heart (cardiac output) and gravity effects on columns of blood.
  • These two forces sum to generate all the force we have to move anything around in the body:
    • Move blood through capillaries
    • Push fluid through organs
    • Generate urine by pushing blood through glomerulus in kidney.
    • et cetera

Cardaic output

• The cardiac output generates arterial pressure against the total vascular resistance.
  • Arterial pressure = cardiac output * total vascular resistance.
• Total vascular resistance = "peripheral resistance" or just the resistance of the systemic blood system (not the pulmonary system).
• Cardiac output is measured in liters / minute.
• The heart uses about 10% the body's energy to do this.
  • 10 cal / hour
  • About half of a piece of white bread
  • pretty efficient

Gravity

• We're big, upright mammals so gravity affects our pressure.
• Standing pressures:
  • The pressure at the heart, when standing is about 100 mmHg; at the feet it is much higher.
  • This is because there is a gravity column from heart to the feet adding pressure.
  • In the veins of the ankles, the pressure would be about 88 mmHg.
  • The diff in the arterial and venous pressure \
  • In the skull the pressure is about 50 mmHg, but venous pressure is a little negative.
    • We have to careful with veins when people are sitting up because if you open it, it may suck air into it.
    • usually we don't see veins on people's heads because they are collapsed under very low pressure.
    • When we do, they are mad or sick.
• Lying down:
  • Little pressure is lost at the feet and heads.
  • Venous pressures are low, 2-5.
• When we're upright, we have all kinds of problems:
  • Veins are 3 times as wide in the feet as they are in the rest of the body.
• So what are the effects of gravity on the vasculature below the heart?
  • We can look at the pressure
  • Pressure = force / area
  • P = Pi x radius-squared x height x density / pi x radius squared
  • We usually measure this pressure with a device while the pt is standing.

Veins

• Over time, veins would hypertrophy and be distended and tortuous.
• We deal with this pressure via valves in the veins.
  • These collapse if the pressure pushes downward against it.
  • If you stand still, the veins get wider and the valves don't quite seal and in part the pressure can get back through the valve.
    • this occurs even when the valve seals as the seal bends backward.
  • As we walk, though, muscles squish the veins, even in the veins.
  • This helps push the blood up through the valves.
    • We call this a muscle pump.
    • Different than pumping up muscle when lifting weights.
  • Bend knees or where support stalkings (they even come in mmHg distinctions!).
  • Sitting at a desk, you're lower so the pressure isn't as high as when standing still, but you should move your legs a bit to force blood out and decrease pressure.

Resistance

• The resistance is the sum of all forces that resist the flow of blood
• There are two major factors: distortion of RBC membrane and friction in the moving blood and interaction with the vessel wall
• It's hard and complicated to get RBCs through caps
  • Membranes are torqued and stretched and twisted.
  • Accounts for 70% of resistance
• Friction in blood
  • Blood moves in parabolic flow: center moves faster than periphery
  • There is some friction among the RBCs flowing
  • There is interaction with the vessel wall, too.
  • These two account for 30% of resistance.
  • There is slowest velocity at the vessel wall.

Video

• "Blood is flowing in lamina".
• The blood cells are tumbling, more than turbulance.

Viscosity of blood

• More viscous = harder to flow.
• We can measure viscocity relative to water and at a certain temp.
• Water is the standard so it is "1".
• Plasma is about 1.6 - 1.8
  • Protein gives the plasma viscotiy.
• As you add RBCs, the viscosity goes up.
• for most of us, the viscocity is about 4.
• If you add more and more RBC, the heart has to work harder to push blood around.
• Shear force / shear rate = viscotiy
  • Energy discipated / velocity of flow
  • That is, the faster it goes, the more energy it dissipates.
  • Most of this is due to bending RBCs (75%)
• Hematocrit can tell you about viscocity because it is a measure of the ratio of RBCs in whole blood volume
• Polycythemia is when there are large RBCs so it will increase viscocity.
• Anemia will lower viscocity because it lowers the amount of RBCs in the blood
  • Sometimes this is good as an acute treatment for making things easier on the heart.

• these vessels are larger than bout 1 mm and the viscosity is mostly constant.
• Now we'll talk about microvessels and then everything about flow is different.

Flow in the microvessels

• Microvessels screw with all that we've said about flow.
• Viscocity drastically decreases as the vessel diamter is reduced below 1 mm.
  • We call this the apparent viscocity.
• How can this be?
• It is called the fahreaus lindqvist effect
• Depends on the ratio of the RBC size to the size of the vessel.
• In big vessels, cells flow as a liquid.
• In tiny vessels, cells flow as a little plug; different rules
  • Not as much bending and torquing
  • Flows more uniformly
  • Less energy dissipated
  • RBCs tend to migrate to the center of the vessel; this means they dissipate less energy as they flow.
  • this means plasma is on the outside; it has lower viscosity so it is good that it is in the area of the vessel that costs lots of energy to pass things along.
• We probably save 1/3 of the workload on the heart because of this effect. Whoa!

Laminar flow

• Parabolic flow is laminar flow where blood is flowing in lamina and there is no chaos
  • Flow is strickly dependent on the flow in - the flow out.
• If you try to push blood too fast, it goes over critical velocity.
  • it becomes chaotic and tumbles
• then flow is proportional to the square root of the difference between the pressure in and the pressure out.
• This occurs just a little at the peak of the ventricular contraction, right at the aortic valve.
  • We lose just a little energy here.
  • It is also a little chaotic when an atherosclerotic lesion is starting to close off a vessel.
    • this can be heard via stethoscope on corotids, femoral, etc once they are 50 - 60% occluded.

• started here on 01/20/11.

• chaotic conditions are rare unless you have sclerosis

Poiseuille equation

• when you put all this resistance and laminar flow and microvessel effects together, you get the resistance defined by the poiseuille equation
• Resistance = (pressure in - pressure out) / flow = (8 * viscosity * length) / pi * radius-to-the-fourth
• Flow = (pressure in - pressure out) / resistance = (pressure in - pressure out) * Pi * radius-to-the-fourth / 8 * viscosity * length
• Memorize this because we will be expected to know this on boards
• Note that changes in radius make a huge distance in flow and resistance.

• stopped here on 01/19/11.

• remember tha changes in blood flow are easily changed by radius.
  • gi can change dialation by 20%, skeletal muscle by 100%.

Clinical vignette

• J has chronic renal disease
• J is old
• J blood volume isn't regulated well; kidneys are increasing EPO
  • Probalby has blood problems
• She has cardiac overload; heart can't keep up with resting demands.
• Heart and kidneys work better after taking out RBCs from a liter of blood
• what's the problem?
• A is true
• B no reason to believe she's restricting
  • Her viscosity is too high.
• C she does have extra blood volume, but plasma probably isn't why it is high.
• D her RBCs may be crappy, could be true
  • This is pretty rare
• E could be that her heart is weakening because she's 87
  • But when RBCs are reduced she's better, so we're back to thinking viscosity is more important that heart strength

clinical vignette

• Soldier given large amounts of plasma.
  • Has nutrients, has clotting factors, increases blood volume.
• Despite 40% decrease of hematocrit, oxygen consumption has improved 25% as arterial pressure increased 20%.
  • RBCs are going through tract faster even though there are fewer.
  • Less oxygen in the flow but more flow.
• BP increases, brain gets perfused, she regains consciousness.
• A no, giving plasma didn't increase blood carriage
• B yes, if there is more to pump the heart will pump more
• C viscosity has decreased and thus flow has increased
• D down
• E up
• She can exchange because flow went up.

• continued on to Lecture 2 Heart Cycle on 01/20/11.