Lecture 4 Arterial Blood Pressure

From Iusmphysiology

• continued here from Lecture 3 Cardiac Mechanics on 01/21/11 at 9:32AM

Contents 1 Objectives 2 Slide 2 3 Diastolic arterial pressure 4 Flow chart 5 Translation of the mechanical properties of large arteriels to cyclic systolic and diastolic arterial pressure 6 Long term changes in vascular distensibility and capacitance... 7 Measuring blood pressure 7.1 Oddities of peripheral arterial blood pressure 8 Case: 56yo w

[edit] Objectives

• Not many objectives but they are important.

[edit] Slide 2

[edit] Diastolic arterial pressure

• All the arteries get stretched, not just the aorta.

[edit] Flow chart

• When elasticity goes down, the diastolic pressure drops dramatically.
• Pulse pressure is the difference in the two pressurs. Usually about 40 mmHb.
  • Be suspicious if it gets higher.
  • There is usually something wrong with disensibility.

[edit] Translation of the mechanical properties of large arteriels to cyclic systolic and diastolic arterial pressure

• Capacitance is the volumne held in the vessel under a certain pressure.
  • One point in the curve.
• Compliance is the slope of the curve at a given point.
• Diastolic pressure depends on the relationship of distensibility and capacitance.
• Systolic pressure depends on the relationship between distensibility and capacity of the volume caused by cardiac pumping.

What's the difference here?

[edit] Long term changes in vascular distensibility and capacitance...

• When distensibility goes down, then when the heart stops pumping the pressure goes down so diastolic pressure goes down becauase there is no energy in the distenstion to keep the pressure up.
  • This is why there can be a widening of systolic and diasstolic pressure.
  • this is also why left ventricles get larger.
• If atherosclerosis is appartent in large arteries, it is considered to be plentiful in the smaller arteries.
  • This gets bad when coronary arteries are clogged but heart wants to use more and more oxygen for more and more vent tissue.

[edit] Measuring blood pressure

• Oliver Whendel Holmes brought BP measurement to the US, then became a supreme court judge.
• Recall the laploss relationship.
• Pinside (pressure inside the pressure) - poutside (pressure outside the vessel) = wall tention / radius.
• Once the vessel is closed with the balloon you can release the pressure.
• At some point the pinside will be higher than the poutside (the balloon pressure).
  • Blood will squirt through the artery and we can hear it with the stethoscope.
  • As the poutside is continued to lower, the sound will get louder and will last longer.
• Then the sound becomes muffled
  • This depends on the equipment and the hearing of the measurer.
• Then the pressure is lowered and the sound goes away because there is no turbulance.
  • When it disappears you're at the diastolic pressure.

• stopped here at 10AM on 01/21/11.
• started here at 11AM on 01/21/11.

• One problem is that people come in different sizes.
  • We can measure on arm, leg, or finger.
    • Finger measurement isn't very accurate.
  • If you don't fully surround the limb; if you dont' you don't get a good reading.
  • The width of the cuff (along the longitudinal length of the arm) should be about the diameter of the limb.
  • When too large, you collapse too much muscle and pressure is underestimated because you don't get turbulant flow of blood.
  • Too msall and you over estimate the pressure.
  • The hospital effect is that many people in hospitals are larger so you have to use leg cuffs on the

arm.

[edit] Oddities of peripheral arterial blood pressure

• Recall that pressure waves go quickly and bounce back.
• When wave bounce they do odd things.
• The wave forms of the bp in different arteries look different.
  • This is because of how the wave bounces back.

[edit] Case: 56yo w

• Brachial artery best represents the aortic pressure because there isn't much reflection there.
• The pt's diastolic pressure falls distally, which is what should happen.
• Systolic pressure shouldn't fall that much though, in distal parts.
• So she is probably feeling turbulant flow from a partial occlusion.
  • And this will decrease pressure in areas distal to the occlusion.
• A is the correct answer.
• C: not right because it doesn't hurt and inflammation hurts
• D: occlusion of common iliac: no because upper thigh has a proper pressure but an occlusion in common iliac artery would cause decreased bp distal to it.
• E: massive occlusion: no because she has a relatively moderate problem that can be watched and maybe fixed.

• continued on to Lecture 5 Microcirculation on 01/21/11 at 11:15AM