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| What is an EKG and how does it work |
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Definition
1. Because the heart depolarizes as 2 separate syncytial masses of cells, there is a comparatively large electrical current generated during the sequential depolarization/repolarization cycle. The potential current generated spreads throughout the body and a small amount of electrical potential (millivolts) can actually be recorded on the surface of the body. A recording of this electrical potential obtained from discrete points on the surface of the body is referred to as an EKG. Thus an EKG is a recording (or picture) of the electrical activity of the heart obtained on the surface of the body. |
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| Depolarized myocardium as a ____ surface |
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Draw how the EKG looks
- at rest
- beginning of atrial depolarization and after SA node fires
- atrial depol half completed
- atrial synctium completely depol
- delay between depol and repol
- beginning of atrial repolarization
Show charge distribution, location of arrow (+ on right, - on left) and graph (positive on +y axis, negative on -y axis, and time on x axis) |
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. The standard lead system for recording the EKG is the 3 limb bipolar lead system (frontal system), which is based upon Einthoven's triangle. We will concentrate on this lead system, particularly lead II. What are the most commonly used lead systems in small animal cardiology. |
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Definition
A. Lead I. Positive terminal on the left foreleg. Negative terminal to the right foreleg.
B. Lead II. Positive terminal on the left hindleg. Negative terminal to the right foreleg
C. Lead III. Positive terminal to the left hindleg. Negative terminal to the left foreleg.
[image] |
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Show the waveforms of the electrocardiogram using a diagram depicting the relationship between the action potential of representative myocardial cells and the EKG waveforms that occur as a result of their action potentials.
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| Draw a sample EKG and include all the components. |
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| What are the components of the EKG? |
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Baseline
P wave
QRS complex
T wave
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Definition
= isoelectric point when there is no electrical potential between areas of the myocardium. This occurs, for example, when all cells of each syncytia are either polarized or depolarized.
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electrical potential generated from atrial depolarization
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potential generated from ventricular depolarization
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potential generated from ventricular repolarization
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E. Because of AV nodal delay, ____ depolarization (P wave) occurs ___ to ____ depolarization (QRS complex)
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| True or false: atrial repolarization is organized. |
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| F. Atrial repolarization is disorganized (small potential differences) and usually occurs during ventricular depolarization. Thus the atrial equivalent of the T wave (the atrial T wave) is usually not visible because it is small and masked by the larger QRS complex. |
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1.Na enters HCN channel of excitatory cells
2.An SA nodal cell reaches threshold
3.Every cardiac cell has an action potential (transmited cell to cell in < 200 msec)
4.Ca enters cells
5.Ca binds to troponin
6.Troponin-Tropomyosin conformational change
7.Actin-Myosin cross bridge formation
8.Shortening of myocardial contractile cells
9.Since all cells contract at ~ same time we have a heart beat!!! |
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What produces the sounds heard by a stethoscope? |
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Turbulent blood flow caused by changes in velocity or direction of blood flow
-For example, when a valve opens or closes |
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Heart Sounds (turubulent blood flow produces sounds)
S1= |
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Definition
| first heart sound ("lub"), occurring at the onset of systole, due to AV valve closure and semilunar valve opening |
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Definition
| second heart sound ("dub"), occurring at the onset of diastole, due to semilunar valve closure and AV valve opening |
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| Which heart songs are normal/abnormal? |
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Definition
S1 and S2 are normal and are heard in all mammals.
There are third and fourth heart sounds (S3 and S4) which are not normally heard, except in very large animals, such as horses. |
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Definition
| are abnormal heart sounds that occur whenever there is turbulent flow of blood. This commonly occurs when heart valves fail to function properly. |
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| There are 2 main types of valvular abnormalities. In each of them, a murmur may be heard. What are they? |
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Definition
Valvular insufficiency
Valvular stenosis |
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| a valve that does not close adequately, thru which retrograde flow occurs (in dogs, usually involves the mitral valve) |
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| a valve which does not open adequately, and consequently restricts flow |
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sounds produced by turbulent flow in the vascular system (outside of heart)
- partial obstruction of a vessel
- abnormal connection between an artery and a vein (“AV fistula”). |
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| Left AV valve (mitral ) insufficiency |
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Definition
During ventricular systole (contraction) pressure in ventricle (up to 120 mmHg) exceeds that in left atrium (<5mmHg)
Blood flows backwards thru incompletely closed valve, causing turbulence of blood which produces a sound or murmur
Normal heart sounds: http://www.youtube.com/watch?v=dDg7GDpR1RE
Left AV valve insuficiency: http://www.youtube.com/watch?v=vL0s_nEkC8Q&feature=player_embedded
http://www.youtube.com/watch?v=vL0s_nEkC8Q&feature=player_detailpage |
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| Systemic Arterial Blood Pressure |
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Definition
Pressure measured in mmHg
Similar throughout arterial tree
Often referred to as “blood pressure”
Blood pressure is the key variable in the cardiovascular system |
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| Blood flow to tissues requires: |
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| 1) Blood pressure that is at the proper level (“set point”) Too low (systemic hypotension) causes body organs and tissues to have inadequate blood flow (ischemia) Too high (systemic hypertension) damages organs and tissues 2) Blood pressure that is constant (variable pressure prevents organ and tissue blood flow from matching needs) |
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| What 3 variables describe blood flowing through a vessel? |
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Definition
[image]
P = hydrostatic blood pressure (mmHg) – created by force of left ventricular ejection of blood
Q = blood flow (mL/min)
R = resistance or the opposition to blood flow offered by a vessel.
The relationship between resistance to blood flow (R), diameter (D), and length (L) of a single blood vessel is referred to as the Poiseuille's Law:
R= k (L/D4), where k is Poiseuille's constant. What does this mean?
If you double the length, you double a vessel’s resistance to flow.
If you halve the diameter of a vessel, you increase R by 16 times!!!!
If I were planning to control R, I would alter diameter of a vessel:
Increase diameter = vasodilation (reduces R)
Decrease diameter = vasoconstriction (increases R) |
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| hydrostatic blood pressure (mmHg) – created by force of left ventricular ejection of blood |
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| resistance or the opposition to blood flow offered by a vessel. |
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Ohm’s Law of electrical circuitry |
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Definition
(V = I x R)
the driving force difference between two points (V or voltage)
rate of flow of electrons (I or current)
Opposition to flow or resistance (R)
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Ohm's Law of the Cardiovascular System (P = Q x R)
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the driving force difference between two points (P or pressure)
rate of flow (Q or flow)
Opposition to flow or resistance (R or resistance) |
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| Ohm's law of cv system applied |
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Definition
Pressure (P) = Q X R
•But what are P and Q?
–P = Blood pressure
•average = mean arterial pressure (MAP)
–Q = CO = cardiac output = stroke volume x heart rate;
–R=total peripheral vascular resistance (TPR)
•Pressure (P) = Q x R becomes
MAP = CO x TPR = (HR x SV) x TPR
SV, HR, and TPR = 3 DETERMINANTS OF BLOOD PRESSURE
Any change in blood pressure occurs from a change in one of these 3
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•Any factor which alters heart rate is called a chronotrope.
•A positive chronotrope increase HR
•A negative chronotrope reduces HR.
•Autonomic nervous system.
–Parasympathetic (vagus nerve; post-ganglionic fiber; muscarininc receptors; acetylcholine as neurotransmitter) stimulation of the SA node leads to a slowing of phase 4 depolarization and hence a slowing of the heart rate (negative chronotrope)
–Sympathetic stimulation (cardiac nerves; post-ganglionic fiber; ß1 receptor in heart, norepinephrine as neurotransmitter) of the SA node exerts a positive chronotropic effect. |
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Definition
stretch before contraction = end-diastolic volume
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Starling Law of Heart (this diagram):
[image] |
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Definition
Normally, the more blood that is presented
to a chamber of the heart (venous return), the more it ejects. |
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| What are + and - ionotropes? What effects do they have on contractility? |
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Definition
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Definition
–Preload (pre-stretch of myocardium)
–Contractility of myocardium |
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| What vessels control TPR (total peripheral resistance) |
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Definition
•Recall Poiseuille's Law:
R= k [length/(diameter)4].
The vessels that control total peripheral resistance are the arterioles.
Why?
-They are small (hence by the above Law, they have lots of R).
-They are innervated, hence their diameter can be adjusted to control TPR.
Arteries: Lots of smooth muscle but it is not innervated and their diameter is so
big they have offer almost no resistance to flow. |
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Definition
•All tissues have some ability to control resistance (that is, they can control the diameter of their own arterioles).
–Called Intrinsic Control of Resistance
–Vital tissues (Brain, Kidney, Heart) have very effective Intrinsic Control (This make sense!)
•Since MAP = SV x HR x TPR, the control of MAP would be served by a general way to adjust the diamtere of many body arterioles
–Called Extrinsic Control of Resistance
–Nonvital tissues (Skin, Abdominal viscera) are affected more by this mechanism than vital tissues
•Skeletal muscle is unique – Nonvital tissue at rest, Vital tissue at times of exercise (e.g., running from predator)
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Definition
•HR controlled by
–(+/- chronotropic effect of autonomic nervous system)
•SV controlled by
–pre-stretch of myocardium (preload=EDV)
–contractility of myocardium (+/- inotropic effect of sympathetic division of autonomic nervous system)
•TPR controlled by
–interplay between intrinsic control in each tissue vs. autonomic nervous system control (sympathetic extrinsic control) |
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| What are the 2 MAP control systems |
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Definition
•Neurologic
–Arterial Baroreceptor System (uses Autonomic Nervous System)
•Hormonal
–ReninAngiotensinAldosterone System |
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| Renin Angiotensin Aldosterone System |
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Definition
(Hormonal system which assists arterial
baroreceptor system to maintain MAP at
proper level). There are 2 hormonal
agents involved (2 soluble agents that
circulate in plasma) |
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| Angiotensin II (instantaneous effect): |
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Definition
-Polypeptide hormone (8 amino acids)
-Vasoconstriction of nonvital tissues
-Increase TPR which increases MAP |
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| Aldosterone (takes 3-5 days) |
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Definition
-Steroid hormone from adrenal cortex
-Retention of salt and water by kidney
-Increases blood volume which
increases venous return.
-Increased venous return increases
end-diastolic volume (EDV=preload)
and this increases stroke volume (SV)
and thus MAP |
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You are a veterinarian presented with a 500 kg horse that has been hit by a car. The animal has lost a lot of blood
How much is a lot in a horse (i.e., what is its expected blood volume?)
What effect would this have on the following parameters (up, down, stay the same) and what is the mechanism of each change?
Stroke volume
Systemic arterial blood pressure (MAP)
HR
TPR
Blood flow to the horse’s intestinal tract
Blood flow to the horse’s brain |
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You are a physician assistant working in a hospital. You note that a previously normal 70 kg male has accidentally received 5 liters of fluids intravenously.
How much is a lot in this man (i.e., what is its expected blood volume?)
What effect would this have on the following parameters (up, down, stay the same) and what is the mechanism of each change?
Stroke volume
Systemic arterial blood pressure (MAP)
HR
TPR
Blood flow to his intestinal tract
Blood flow to his brain |
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You are an Olympic runner. Starting from rest, you run a mile at top speed.
What effect would this have on the following parameters (up, down, stay the same) and what is the mechanism of each change?
Blood flow to your leg muscles
Stroke volume
HR
TPR
Systemic arterial blood pressure (MAP)
Blood flow to your intestinal tract
Blood flow to your brain |
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Definition
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| 3 components of respiration |
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Definition
All 3 together = Respiration
In physiology, we will focus on the first 2
Ventilation
-Mechanical movement of air in and out of lungs
Gas Exchange
-Lungs: Between air and blood
-Tissues: Between blood and cells
Oxygen utilization
-Biochemical processes in cell |
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