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What does contractility refer to?
The health of the cardiac muscle. The more the muscle is stretched, the greater the snap will be, like a rubber band . . . until it breaks.
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Define preload
The amount of blood coming into the right side of the heart.
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Define afterload
- Think of the B/P . . . for now.
- The higher it is, the harder it is for the left ventricle to push the aortic "door" open and deliver the blood to the rest of of the body.
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What is the formula of Cardiac Output?
- Heart Rate x Stroke Volume = Cardiac Output.
- HR x SV = CO
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What is the Cardiac Index (CI)?
Individualized CO divided by the Body Surface Area (BSA), which is weight x height.
CO / BSA = CI
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What is the best way to determine whether a person has good perfusion?
- Mean Arterial Pressure (MAP)
- You must have a MAP of 60 - 70 to adequately perfuse your organs.
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What two criteria need to exist, to say someone is in shock?
Systolic B/P of <90 AND the person is symptomatic.
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What determines Cardiac Output?
Heart Rate and Stroke Volume
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If the heart rate is increased, what does it do to the cardiac output?
Increased heart rate, means increased cardiac output.
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What systems or illnesses can increase your heart rate?
- a. Autonomic Nervous System (ANS) Sympathetic natural and synthetic (medications such as Albuterol which give you a sympathetic response)
- b. Temperature
- c. Emotions
- d. Medications
- e. Excess thyroid hormone (either natural or sympathetic)
- f. Dehydration
- g. Sepsis
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What is the direct relationship between HR and O2 consumption?
Increased HR requires more O2.
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If all of your vital signs (HR, temp., RR, and B/P) are high, what organ disorder should you suspect?
If all vital sins are high, think thyroid.
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What determines the amount of stroke volume?
- a. The contractility of the heart
- b. Afterload
- c. Preload
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How is contractility measured?
Through the Ejection Fraction (EF), which measures the volume ejected from the ventricle wit each contraction. A normal value is 55-75%.
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How is the Ejection Fraction (EF) tested or measured?
- NON-INVASIVE: Echo Cardio Gram (ECG), this takes a picture of the ventricle when it is full and again when it is empty. What % moves forward with each contraction?
- INVASIVE: Cath Lab (using dye), taking a picture of the ventricle when it is full and empty.
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What is the normal range for the Ejection Fraction (EF)?
- 55-75%
- 10% = Cardiac Cripple
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What parts of the arterial system influence afterload?
- SVR: Systemic vascular resistance which is a calculated value
- PVR: Pulmonary vascular resistance which is a much lower pressure than the systemic (20/5-10)
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What influences afterload?
HINT: Think B/P
- a. Vascular resistance against the ventricular action
- b. Influenced by the arterial system (SVR and PVR)
- c. Pulmonic and Aortic valves
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How is afterload assessed?
Through the B/P (systolic)
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