3. Chest pain Flashcards
describe relationship of BP & SVR with parasympathetic nervous system
no parasympathetic innervation of blood vessels
describe relationship of SVR & BP with the sympathetic nervous system
sympathetic nerves decrease peripheral blood vessel diameter thereby increasing systemic vascular resistance and increasing blood pressure
occlusion of what is most likely to result in a fatal heart attack
left main coronary artery
which nerve innervates the pericardium?
Phrenic nerve
what is the stroke volume of the average person
70 mls
stroke volume equation
SV = end diastolic volume (EDV) - end-systolic volume (ESV)
what increases to signify left heart failure?
left ventricular end-diastolic pressure
what increases to indicate mitral valve stenosis
left atrial end-systolic pressure
what is the purpose of the Ductus Arteriosus in the foetal cardiovascular system?
allow blood to bypass the foetal lungs by shunting it from the pulmonary artery to the aorta
cardiac output equation
CO = HR x SV
pulmonary oedema in the presence of a normal central venous pressure is a sign of
left heart failure
severe pulmonary hypertension is a cause of
right heart failure
shortness of breath, severe peripheral oedema and ascites after a heart attack indicates
biventricular failure
which artery most frequently supplies the AVN?
right coronary artery
define cardiac output
volume of blood expelled by either ventricle of the heart
the amount of blood the heart pumps through the circulatory system in a minute
what is the normal cardiac output of an adult
4.7 litres of blood per minute
cardiac output equation
CO=SV x HR
define stroke volume
is the volume of blood pumped out of each ventricle each time the heart beats
Starling’s law of the heart
- ‘the strength of the heart’s systolic contraction is directly proportional to its diastolic expansion, with the result that under normal physiological conditions the heart pumps out of the right atrium all the blood returned to it without letting any back up in the veins’
- The Frank-Starling Law states that the stroke volume of the left ventricle will increase as the left ventricular volume increases due to the myocyte stretch causing a more forceful systolic contraction
when is myocardial perfusion
• myocardial perfusion occurs during heart relaxation when the subendocardial coronary vessels are open
perfused by the coronary arteries during the ventricular systole. The origins of the coronary arteries is behind the aortic semilunar valve which fills with blood during the ventricular diastole which then allows blood to be pumped into the coronary artery
cardiac cycle - systole
systole - • L ventricle contracts • pressure increases • mitral + AV valves closed 0.3 seconds pressure reaches 75mm Hg - just higher than pressure in aorta - AV valve opens
cardiac cycle - ejection phase
Ejection phase:
• 75mm Hg - at beginning - lowest BP in aorta - diastolic BP
• 0.25s
• blood ejected from LV to aorta - L ventricular volume decreases
• L ventricle continues to contract - pressure increases
• aortic pressure also increases (both equal)
• peak of 120 mm Hg reached - systolic BP - then decreases again
• difference in systolic and diastolic = pulse pressure (PP)
when aortic pressure increases pressure in L ventricle, AV valve closes - S2 (2nd heart sound) -
end systolic point reached - volume inside L ventricle = 50ml
ejection fraction = stroke volume / end diastolic volume
diastole
Ventricular relaxation and blood filling - 0.5 seconds:
• reduced ejectioon
• ventricles relax - aortic and pulmonary valves close - AV valves closed so no blood enters or leaves ventricles - isovolumetric relaxation (decrease in pressure, volume same)
• rapid ventricle filling and ventricle suction - blood in atria slightly pressurised due to
venous return from superior and inferior vena cava + pulmonary vein.
o pressure enough to open mitral and tricuspid valves
o lower pressure in ventricles than atria - mitral valve opens - pressure gradient -
blood moves down it - responsible for 80% of ventricular filling before atrial
contraction (other 20% from atrial contraction)
stroke volume equation
stroke volume = end diastolic volume - end systolic volume
ventricular tachycardia
not filling before it contracts
ventricular fibrillation
not enough blood pumped around the body
describe the coronary circulation of the heart
two coronary arteries arise from the aorta just beyond the semilunar valves; during diastole, the increased aortic pressure above the valves forces blood into the coronary arteries and thence into the musculature of the heart. Deoxygenated blood is returned to the chambers of the heart via coronary veins; most of these converge to form the coronary venous sinus, which drains into the right atrium
occlusion of the LAD
• Over time fatty deposits and calcium build up on inner artery walls and form plaque (atherosclerosis)
• It is the most commonly occluded of the coronary arteries Depending on where the occlusion is the left ventricle, right ventricle and IV septum can be affected.
symptoms: chest pain, sweating, difficulty breathing etc.
effects on the cardiac conduction pathway of occlusion of LAD
- Occlusion of the LAD artery leads to necrosis in the conducting system
- This can completely block impulse conduction between the atria and the ventricles
- Impulse conduction between the atria and ventricles can also be blocked (right/left bundle branch block)
- This can lead to Ventricular tachycardia (VT) and ventricular fibrillation (VF) which can lead to death
