Factors affecting cardiac performance and S&S of CVD Flashcards
What is pericardium
Forms a fibrous covering around the heart holding it in a fixed position in thorax
A tri-layer sac consisting of a tough, outer fibrous layer and a thin, inner serous layer
Inner serous layer consists of a visceral layer and parietal layer
Visceral layer (also known as epicardium) covers entire heart and great vessels
What does pericardium do
Provides physical protection and barrier to infection
What is myocardium
Muscular portion of heart, forms the wall of atria and ventricles
Dense structures, intercalated discs (unique to cardiac muscle), separate the cardia muscle fibres from neighbouring cardiac muscle cells
What is endocardium
- Thin, three-layered membrane that lines the heart
- Innermost layer consists of smooth endothelial cells supported by a thin layer of connective laye
What blood flows in right side of heart
- Receives deoxygenated blood from body
- pumps deoxygenated blood to lungs
What blood flows in left side of heart
- receives oxygenated blood from lungs
- pumps oxygenated blood to body
what is systemic circulation
carries oxygenated blood away from heart to body tissues, and oxygen-depleted blood back to heart
what is pulmonary circulation
carries oxygen-depleted blood away from heart to lungs, and oxygenated blood back to heart
What is diastole
ventricles relax for filling
What is systole
ventricles contract to rapidly eject blood from ventricle
What is HR
no of times heart beats per min
what is Sv
volume of blood pumped from ventricles in 1 heart beat
what is CO
total volume of blood pumped by heart.min
what is ejection fraction
% of EDV (end-diastolic volume) pumped in one heart beat
Explain normal electrophysiology of heart
SA node generates impulse atrial contraction begins
Impulse displayed at atrioventricular node (AV node)
Impulse passes to heart apex and ventricular excitation begins
Ventricular excitation complete
What are functions of CV system
Transport transporting oxygen, nutrients, meds, waste products for elimination
Control system:distribution of Hormones
Temperature regulation important to deliver heat to surface
What are the determinants of CO
- HR
- Preload
- Contractility
- Afterload
What are normal CO values at rest
5L/min
What are normal CO values with strenouse activity
15L/min
-in atheletes= 35L/min
What is the CO with severe heart failure
less than 4L/min
what is normal SV
60-130mL
what is the effect of PNS and SNS on HR
PNS–>decreases HR
SNS–.> increases HR
What are effects of increased HR on EDV and preload
end-diastolic volume falls and preload decreases
what is the effect of chronotropes on HR
+ve chronotropes= increased HR
-ve chronotropes= decreased HR
What is tachycardia
HR that exceeds the normal resting HR, hence a resting HR of >100 beats/min
What is bradycardia
slower than normal HR, hence usually between 60-100 beats/min
What is BP
pressure exerted by blood on arterial walls
whats is BP regulated by
- Arterial pressure
- Effect of Cardiac Output (Q)
- Effects of Total Peripheral Resistance (TPR)
- Effect of hormones
what is systolic and diastolic BP
- Systolic BP: pressure during ventricular contraction (systole)
- Diastolic BP: pressure during ventricular filling (diastole)
what are the effects of CO on BP
- If CO increases, arterial blood volume increases and therefore arterial pressure
- If CO decreases, arterial blood pressure will decrease
What is TPR
- total peripheral resistance
- Determined by changes in diameter of the arterioles
what are the effects of TPR on BP
- Vasoconstriction: increases arterial pressure (AP)
- Vasodilation: decreases AP
Effects of hormones on BP
- ADH–> antidiuretic hormone
- causes reabsorption of water in kidneys= decreased blood volume
What is Frank-Starling law
- Within physiological limits, the force of contraction (of the heart) is directly proportional to the initial length of the muscle fibres
- The ability of the heart to change its force of contraction and therefore stroke volume in response to changes in venous return
define preload
- Tension or stretch of myocardial fibres before contraction begins
- Workload imposed upon the ventricle prior to contraction
- Represents the amount of blood the heart must pump each beat
- Largely determined by venous return to heart and accompanying stretch of the cardia muscle fibres
Define afterload
- The force required to eject blood from the heart–> force against which heart must pump
- It is the work presented to the heart after contraction–>i.e. the ‘left over’ blood
- The systemic arterial blood pressure is the main source of afterload work on the left heart and pulmonary arterial pressure is the main source of afterload work on the right heart
Factors affecting preload
- changes in circulating blood volume
- changes in distribution of blood volume
- atrial contraction
- intrapericardial pressure,
- pumping action of skeletal muscle
How does circulating blood volume affect preload
- decreased total blood volume= decrease preload
- increased total blood volume= increase preload
How does distribution of blood volume affect preload
- gravity causes blood to pool in LL, hence not much in thorax
- if head-down tilt= increase in blood volume in thorax= increase preload
How does atrial contraction affect preload
increased atrial contraction= increased preload
READ NOTES
ON PRELOAD
What factors affect afterload
- Peripheral resistance
- Tension in ventricular wall
How does peripheral resistance affect afterload
- Compliance and radius of BV’s
- Blood viscosity–>start to produce more haemoglobin to pick up oxygen= increases blood viscosity, making blood thicker= more work for heart
-Changes in pressure within vessels–>biggest determinant of right ventricular afterload will be constriction
what is inotropic state of myocardia contractility
-Change in force and speed of shortening of heart muscles that in independent of changes in preload/afterload
What are positive and negative inotropes
- Positive inotropes–> digitalis, calcium, adrenaline/noradrenaline, caffeine
- Negative inotropes–>beta blockers
What are some factors related to contractility
- SNS stimulation (fight and flight)
- inotropes
- phhysiological depresents
- damage to myocardium, valves, conducting system
What are the variables used to assess contractility
- SV–> good indicator of ventricular performance; directly related to myocardial fibre shortening
- Ejection Factor (EF)
- Rate-pressure product (RPP)
READ NOTES
ON RESPONSE TO INCREASED PRE/AFTERLOAD
Define orthostatic intolerance
- The inability of the cardiopulmonary system to maintain BP and adequate cerebral perfusion pressure against gravity
- Development of S&S during upright standing that are relieved by recumbency
how does bed rest for 24hrs or longer effect orthostatic intolerance
- negative fluid balance occurs
- Peripheral vasodilation occurs and cardiac filling pressure are reduced
- decrease in SV below the excepted normal for individual in supine
- Blood becomes more viscous–> increased risk of venous stasis, thromboembolism and DVT
- diuresis (urine output)–> loss of blood volume
effect of lying-standing on Blood distribution
- 700ml blood loss from thorax
- Decreased SV and CO
- Compensatory increase in HR and peripheral vasoconstriction to increase peripheral vasoconstriction
effect of standing-lying on Blood distribution
- Acute increase in thoracic blood volume which results in an increased preload (venous return)
- Hence increase in SV and CO
- In order to maintain constant BP, compensatory decrease in HR, peripheral vascular resistance and diastolic BP occurs
effect of standing inactively for 20mins on Blood distribution
- increased hydrostatic pressure in feet
- Leads to transudation of fluid from vasculature into interstitial tissues
- Results in increase in plasma volume interstitial tissues
- Net effect within body is a reduced absolute blood volume
- Called Relative Hypovolaemia–>systemic BP is reduced as a result
Orthostatic intolerance S&S
- Decreased BP
- Increased HR–>in an attempt to compensate the low stroke volume
- Weak pulse–>it is a result of the reduction in SV and BP (this reflects the low pulse volume)
- SNS–> dizziness, fainting (syncope), pallor, sweating, tremor, nausea
Orthostatic intolerance management
- Acute–>activate muscle pump, elevate legs
- Prevention
- Avoid/correct hypovolaemia–> decreased volume of circulating blood in body
- Gravitational stimulus
- Early mobilisation–> dangling, sit out of bed
