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Cardiac Cycle Exam 2
Exam 2 Lecture 5
20
Pharmacology
01/30/2012

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Term
What is cardiac output?
Definition
The quantity of blood pumped out of the ventricles each minute.
Term
How do you calculate cardiac output?
Definition
Heart rate * Stroke Volume or Heart Rate * (EDV - ESV)
Term
What can change cardiac output?
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
Term
What is cardiac index?
Definition
Cardiac output normalized for weight. The higher the weight, the higher the CO. Normal CI is 3.
Term
What are the parameters that effect cardiac output?
Definition
- Preload/Increased fiber length
- Afterload
- Inotropy - increased calcium in the cytoplasm
- HR
- ANS
- Hormones
- Drugs - Epi, Dig, Ca-channel blockers.
Term
How does heart rate affect cardiac output?
Definition
As heart rate increases, cardiac output increases to a point where heart cannot get adequate oxygen, then decreases
Term
How does preload affect cardiac output?
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.
Term
What is the Frank-Starling mechanism?
Definition
The greater the stretch (increased preload), the greater force of contraction and quantity of blood.
Term
If a person has chronic heart failure and reduced cardiac output, how does the heart compensate?
Definition
Increase the fiber length to get the same return of blood, returning the cardiac output to normal. This is negative inotropy.
Term
What is afterload? What changes are seen?
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.
Term
What is inotropy and how does it affect cardiac output?
Definition
Force of contraction seen by increasing calcium. Independent of fiber length -- decreases ESV --> increased SV and CO.
Term
What are factors influencing CO independent of preload, afterload, and HR?
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
Term
How does the ANS affect HR?
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
Term
What effect does increasing heart rate have on cardiac output?
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.
Term
What intrinsic and extrinsic mechanisms control heart rate?
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.
Term
What are baroreceptors? How do they react to BP increase?
Definition
When BP increases, Baroreceptors send inhibitory impulses --> Vagus nerve is turned on and vasodilation occurs. Overall decrease in resistance, HR, CO --> Decreased BP.
Term
How do baroreceptors respond to decreased BP?
Definition
Decreased number of inhibitory messages. Constriction occurs and the heart accelerates --> increased resistance, HR, CO --> increased BP.
Term
What are the 2 most common reasons for a hypereffective heart/increased CO?
Definition
- SNS stimulation
- Cardiac hypertrophy from chronic increased workload
Term
What are some pathologies that increase CO?
Definition
-Beriberi - B1 deficiency
- AV shunts - results in increased venous return
- Hyperthyroidism - increased metabolism
- Anemia - decreased resistance
- Drugs - Vasodilators, positive inotropes.
Term
What are some pathologies that decrease CO?
Definition
- Coronary blockage
- Nerve inhibition
- Abnormal rhythm
- Valvular heart disease
- CHF
- Tamponade
- Drugs
- Hemorrhage