Pressure Flashcards
Sesion 3 (26 cards)
What is the greatest pressure drop in the cardiovascular system?
Arterioles and capillaries
The tension in the vessel walls is related to which factors?
- Radius of the vessel
- Pressure inside the vessel (law of Laplace)
What is the typical systolic and diastolic reproducibility error for a sphygmomanometer?
- Systolic: ±2 mm
- Diastolic: ±5 mm
What factors affect the accuracy of a sphygmomanometer?
- Obesity of patient
- Patient orientation
- Experience of clinician
What happens when the pressure cuff of a sphygmomanometer is inflated?
It stops blood flow
What indicates the systolic pressure in a sphygmomanometer reading?
First Korotkoff sound
What indicates the diastolic pressure in a sphygmomanometer reading?
No sound
What are some causes of error in direct measurement of blood pressure?
- Blood clotting
- Air bubbles
What is the equation for power in the context of cardiac power?
Power = pressure X (Volume pumped per unit time)
By what factor does blood pressure increase during exercise?
50%
How does cardiac work relate to stroke volume and heart rate?
Cardiac circulation = Stroke volume (80 ml) * Heart rate (75 bpm) = approximately 6 l/minute
What is the flow velocity equation?
V = flow rate / cross-sectional area
What does Poiseuille’s law apply to?
Rigid tubes of constant radius
What is the effect of a restriction on flow?
Larger pressure necessary for the same flow
What type of flow occurs in the aorta during a part of systole?
Turbulent flow
What is laminar flow characterized by?
Blood in contact with the wall is essentially stationary
What principle states that pressure is equivalent to potential energy?
Bernoulli principle
What happens to kinetic energy as velocity of flow increases through a restriction?
Kinetic energy increases, potential energy decreases
What is the pressure in the cardiovascular system during different phases?
- 5-6 mmHg
- 25 mmHg
- 125 mmHg
What is the difference between relative and absolute pressure?
- Relative pressure: expressed relative to atmospheric pressure
- Absolute pressure: true pressure = atmospheric pressure + gauge pressure
What is a manometer used for?
Measuring both positive and negative pressure
What is the atmospheric pressure equivalent in mmHg?
760 mmHg
What is the SI unit for pressure?
Pa (Pascal)
In what situation is negative pressure observed in the lungs?
During inhalation
