Term
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Definition
| The quantity of blood pumped out of the ventricles each minute. |
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Term
| How do you calculate cardiac output? |
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Definition
| Heart rate * Stroke Volume or Heart Rate * (EDV - ESV) |
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Term
| What can change cardiac output? |
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Definition
- Size/body weight.
- Age - decreases due to decreasing metabolic activity and muscle mass
- Level of metabolism
- Degree of activity - increase in exercise requires more oxygen -- increase in CO |
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Term
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Definition
| Cardiac output normalized for weight. The higher the weight, the higher the CO. Normal CI is 3. |
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Term
| What are the parameters that effect cardiac output? |
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Definition
- Preload/Increased fiber length
- Afterload
- Inotropy - increased calcium in the cytoplasm
- HR
- ANS
- Hormones
- Drugs - Epi, Dig, Ca-channel blockers. |
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Term
| How does heart rate affect cardiac output? |
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Definition
| As heart rate increases, cardiac output increases to a point where heart cannot get adequate oxygen, then decreases |
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Term
| How does preload affect cardiac output? |
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Definition
| Preload is the degree of tension in the muscle when it contracts, or fiber length/LVEDV/LVEDP. Increased preload leads to increased CO. See the EDV shift right and increased contractility. No change in ESV. |
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Term
| What is the Frank-Starling mechanism? |
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Definition
| The greater the stretch (increased preload), the greater force of contraction and quantity of blood. |
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Term
| If a person has chronic heart failure and reduced cardiac output, how does the heart compensate? |
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Definition
| Increase the fiber length to get the same return of blood, returning the cardiac output to normal. This is negative inotropy. |
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Term
| What is afterload? What changes are seen? |
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Definition
| The back pressure exerted on the pulmonary valves by arterial blood, important in HTN and stenosis. If there is greater resistance to output --> decreased SV --> decreased CO. Increases ESV --> decr SV. |
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Term
| What is inotropy and how does it affect cardiac output? |
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Definition
| Force of contraction seen by increasing calcium. Independent of fiber length -- decreases ESV --> increased SV and CO. |
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Term
| What are factors influencing CO independent of preload, afterload, and HR? |
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Definition
- Increase in Extracellular calcium levels - increase in conctractile force
- Decrease in Extracellular potassium -- greater K efflux, RMP more negative
** note - potassium stabilized the membrane, preventing influx of ANYTHING.
- increase in body temp -- increase HR |
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Term
| How does the ANS affect HR? |
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Definition
- Vagus nerve decreases HR (PNS). Normal input at rest. A PNS F-S curve looks like CHF.
-SNS increases HR and force of contraction. See a decrease in right atrial pressure.
- In SNS stimulation, CO can go as high as 25L/min |
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Term
| What effect does increasing heart rate have on cardiac output? |
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Definition
Increases rate of ventricular emptying which increases cardiac output.
-- More APs = more phase 2's = more entry of Calcium. Increase in Na/Ca exchange. Calcium more readily available in the SR. |
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Term
| What intrinsic and extrinsic mechanisms control heart rate? |
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Definition
- Intrinsic mechanisms - the Bainbridge reflex - An increase in volume produces a reflex stimulation of the SNS to the SA node, increases HR.
- Extrinsic - Baroreceptors. |
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Term
| What are baroreceptors? How do they react to BP increase? |
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Definition
| When BP increases, Baroreceptors send inhibitory impulses --> Vagus nerve is turned on and vasodilation occurs. Overall decrease in resistance, HR, CO --> Decreased BP. |
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Term
| How do baroreceptors respond to decreased BP? |
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Definition
| Decreased number of inhibitory messages. Constriction occurs and the heart accelerates --> increased resistance, HR, CO --> increased BP. |
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Term
| What are the 2 most common reasons for a hypereffective heart/increased CO? |
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Definition
- SNS stimulation
- Cardiac hypertrophy from chronic increased workload |
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Term
| What are some pathologies that increase CO? |
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Definition
-Beriberi - B1 deficiency
- AV shunts - results in increased venous return
- Hyperthyroidism - increased metabolism
- Anemia - decreased resistance
- Drugs - Vasodilators, positive inotropes. |
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Term
| What are some pathologies that decrease CO? |
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Definition
- Coronary blockage
- Nerve inhibition
- Abnormal rhythm
- Valvular heart disease
- CHF
- Tamponade
- Drugs
- Hemorrhage |
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