ILA 3 - Chest Pain Flashcards
What is cardiac output, what variables contribute to it?
Cardiac output is the volume of blood expelled from the heart per minute
CO = HR x SV
ave HR = 70, (60-100)
What factors affect cardiac output
Increasing HR will increase CO
- para/sym
- adrenaline (will increase HR) - acts on B-adrenergic receptors in SAN
- body temp
- hormones other than adrenaline eg, noradrenaline, adenosine
Increasing SV will increase CO
- changes in end-diastolic volume (total volume of blood just before contraction) - can change due to myotrophy/obesity/exercise
- symp
- changes in afterload (arterial pressures against which the ventricles pump)
- contractility
What risk factors increase a person’s chance of high blood pressure?
- High dietary sodium levels
- Obesity
- Alcohol intake
- Lack of physical acitvity
- Hypertension
- Chronic stress
- Older age
- Genetics
- Elasticity of blood vessels
- Volume depletion - eg loss of salts due to excess sweating or burns, diarrhea, vomiting
- depression of cardiac pumping ability (eg during a heart attack)
-other causes
damage to kidneys = renal hypertension due to excessive RAAS renin and aldosterone
medication
Describe starling’s law of the heart
Stroke volume of the heart increases in response to an increase in the volume of blood filling the heart (the end diastolic volume) when all other factors remain constant.
more stretch = longer muscle fibres = greater stretch
-The greater the end-diastolic volume the greater the force of contraction and greater the volume of blood that can be pumped by the blood
- in a healthy individual an overloading of blood in the ventricle triggers an increase in muscle contraction to raise CO
- in heart failure the cardiac muscle is too weak to pump an adequate amount of blood
Describe the cardiac cycle
- Blood flows from IVC and SVC to RA
- Through tricuspid to RV
- Through pulmonary valve to pulmonary arteries
- Blood from lungs flows to LA via 4 pulmonary veins
- Blood flows through the bicuspid/mitral valve to LV
- Blood flows through aortic valve to aorta and body
When is myocardium perfusion highest in a normal person
Myocardial perfusion is the flow of blood to the CORONARY ARTERIES the flow is greatest at the highest gradient (highest when the aortic valve is closed during diastole)
flows into coronary sinuses from the root of the aorta
Describe pressure changes in the heart
- LV pressure rises as blood trickles from LA to LV
- LA contracts and mitral valve snaps shut - atrial kick
- Pressure in LV increases dramatically opening aortic valve
- Ventricular ejection occurs and aortic pressure increases
- Aortic valve closes. backflow causes the dicrotic notch (this is peak perfusion)
- Pressure decreases as V relaxes and A fills
- Mitral valve opens as blood flows from A to V
(pressure of LV rises)
What are the consequences of an occlusion of the LAD?
MI/ANGINA/HEART FAILURE
What are the consequences of an occlusion of the RCA?
MI/ANGINA/ARTHYMIA
What is a pulmonary edema? What can cause this?
Pulmonary edema is an accumulation of fluid in the lungs.
This can occur due to L ventricle heart failure, this is because the LV pumps less blood out of the heart than it receives from the lungs via the pulmonary vessels (and right side of heart)
This means that there is an increase in pressure in the pulmonary vessels, increased capillary pressure increases the filtration rate to a speed that is faster than the rate that lymphatics can drain the fluid
-This means that fluid accumulates
(often in the legs in the day when the patient is standing and slowly absorbed back into lungs during the night when the patient is supine)
What is peripheral edema? What can cause this?
Peripheral edema is when there is fluid accumulation in the tissues of the body, often the lower limb
This could be due to R sided heart failure because this side of the heart cannot pump the blood to the lungs efficiently, so it backs up in the veins and leaks out of the capillaries accumulating in the tissues. “backward failure” this causes “venous congestion”
What is stroke volume?
Stroke volume is the volume of blood expelled by L ventricle per heart beat
end diastolic volume(total volume of blood at end of filling) - end systolic volume(blood left after contraction) = SV
What is afterload?
Afterload is the pressure in the wall of the left ventricle during ejection
Afterload is increased when aortic pressure and systemic vascular resistance are increased, by aortic valve stenosis, and by ventricular dilation. When afterload increases, there is an increase in end-systolic volume and a decrease in stroke volume.
What is blood pressure?
the pressure of the blood in the circulatory system,
measured as systole (120-140) / (80-90) over diastole
BP = CO x total peripheral resistance
- peripheral resistance - (blood vessel diameter, blood viscosity, total vessel length)
- vessel elasticity
- blood volume
- cardiac output
What is heart failure
When the heart fails to pump an adequate cardiac output
-this triggers baroreceptors (decreased triggering)
1) increased HR
2) increased peripheral pressure
3) also triggers fluid retention in kidneys
(can cause odema)
- the ventricles may become stiff and not fill properly (reduced diastolic volume)
- ventricles can’t pump blood efficiently throughout the body
-often L sided heart failure
