Nursing 2005: Cardiovascular Disorders: (part 1) Disorders of Blood Flow and Oxygenation Flashcards
Systolic phase (S1)
- one contraction
- ventricle contraction
- mitral and tricuspid valves close
Stroke volume
.- amount of blood pumped out during systole
- 70 cc average
Ejection fraction
- ejects 66% of blood
- Estimated by echocardiography
- stroke vol/end- diastolic vol
Diastole (S2)
- ventricles fill = relax
- aortic and pulmonary valves close
- end of diastole
- atrial contract
- most supply goes to the heart because its relaxed
Frank-Starling Law
- length tension of preload to myocardial contractility
- contraction of heart increases if muscle fibers are stretched
- increase contractility if ventricles fill
- generated by vol
- over stretched = fatigue of muscles overtime
- inc contractility if inc in ventricle filling
Laplace law
- dilation = ?
- amount of tension in the wall that the ventricle produces depends on its size
- dilation = decreases ability to eject blood and to contract
Cardiac output
- amount of blood pumped out of the heart in 1 minute
- CO = HR x Stroke volume
- normal heart rate 70-80 beats/min
- 5-6 liters/min
What are the factors affecting cardiac output?
- Preload
- After load
- Heart rate
- Contractility
- Preload
- determined by
- inc preload
- pressure generated in left ventricle at the end of diastole = end diastole pressure
- more blood in ventricles = higher the preload
- increase preload =
- increase force of contraction = increase cardiac output
- inc force of contraction = inc cardiac output
- High preload is good for a healthy heart, but not for people with heart disease d/t weak heart
- determined by:
- amount of venous return entering ventricle after diastole
- blood left in ventricle after systole
- Afterload
- inc
- dec
- resistance that the left ventricle has to pump blood to eject it
- after contraction
- decrease after load = heart pumps easily
- inc in after load= harder for heart to pump because it has to work harder
- Heart rate
- autonomic nervous sys
- average 70 beats/min
- slight increase in HR = increase cardiac output
- as HR increases = stroke vol decreases –> decreases cardiac output
- Contractility
- heart changes force of contraction
Inotropic agents
- affects force of contraction
+ = inc contractility
Ex: epinephrine
Anatropic agents
- = dec force of contraction
Ex: meds that the heart has to work hard , use of alcohol
Arteriole blood Pressure
- measure of pressure exerted by blood against arterial system
- SBP (systolic blood pressure) = ventricles contract
- DBP (diastolic blood pressure) = ventricles relax
How do you calculate blood pressure?
SBP/DBP
What is normal bp?
120/70
Pulse pressure
- difference between SBP and DBP
- normal 1/3 of SBP
Ex: what is the pulse pressure of 120/80
120/1/3= 40
- high = arteriosclerosis
- low = heart failure
Mean Arteriole Pressure (MAP)
Average pressure in arteries throughout cardiac cycle
- MAP = DBP + 1/3 Pulse Pressure
What are the main factors that influence BP?
- Cardiac output
- Systemic vascular resistance (SVR)
- force opposing the movement of blood in small arteries and arterioles
What are the mechanisms that regulate BP?
- Nervous system
- Baroreceptors
- hormones
- Renal system
- Endocrine system
- Nervous system
A. Baroreceptors
B. hormones
A. Baroreceptors
- stim NS
- specialized nerve ells in arch of aorta and arteries
- sensitive to pressure and stretching
- shut down sympathetic = enhance
- parasympathetic = dec BP
B. hormones
- stimulate NS
- dec in BP = parasympathetic = inc BP
- Renal system
- no Na excretion and ECF
- renin -> angiotensinogen -> angiotensin 1 -> angiotensin 2 -> aldosterone inc
- water and sodium tension is cause by aldosterone
- Endocrine
- ADH is released
- inc ECF vol -> inc BP
Hypertension
- Incidence
- d/t
- failure of a system = high BP
- sustained elevation of arterial BP
- SBP= > 140
- DBP = >90
- repeated readings when monitored = HTN
- inc afterload d/t pressure and constriction
- strains heart and blood vessels
- cardiovasc problems and organ failure
- no symptoms
- Incidence
- depends on ethnicity = blacks more susceptible
- men >60
- people with diabetes
What is the significance of HTN?
- heart works harder
- more strain on the heart and blood vessels
Primary HTN
- cause = unknown
- genetic of environmental factors
- 95% of cases
- ages 30-50
- diet:
- high in sodium
- low mag, low cal
- smoking
- stress
- alcohol
Secondary HTN
- caused by systemic disease process that inc systemic vascular resistance or cardiac output
ex: renal disease = d/t kidney failure, hormone problem, meds that inc bp
- can be treated and eliminated
Isolated Systolic HTN
- sustained in elevation SBP= >160 DBP= < 90 - diastolic pressure would be low or normal -seen in elderly d/t weakened vessels
What are the pathophysiology of HTN
- high pressure stim thickening and strengthening to handle stress
- smooth muscles grow larger = lumens narrow
- injury = imflam = inc permeability
- which substances can enter vessel walls
- causes more thickening, vasoconstriction, inc resistance
- changes lining of vessels to let calcium in d/t thickening
What are the long term clinical manifestations?
- heart
- failure d/t afterload
- CAD, angina, MI - brain
- aneurysm, stroke - kidneys
- renal faulure - retina
- lack of o2 = blind
- sclerosis