Cardiac Output & Reserve Flashcards
Mention factors affecting cardiac output
- Posture: inc in standing
- Temp inc by heat
- Drugs & hormones: epinephrine, norepinephrine, glucagon & thyroxine.
- Physical & mental activity
- Pregnancy (inc by 10%)
- Meals esp heavy
- Pathological conditions, dec heart failure & rapid dysrhythmias & valve disease. Inc in anemia, thyrotoxicosis & fever.
Mention methods of measurement of CO in experimental animals
- In anesthesied animals, electromagnetic or ultrasonic flowmeter in placed on ascending aorta or pulmonary trunk.
- Heart-lung preparation, bell cardiogram is placed on ventricles & records volume changes throughout cardiac cycle
Mention equation for calculation CO by Fick’s law
CO = O2 consumption/A-V difference of O2
Describe the disadvantage of dye dilution method
Recirculation of the dye, and so the time of the curve is determined by extrapolation leading to error.
Mention parameters measures by echocardiography used to assess cardiac function
EDV, ESV, SV & EF
Mention factors controlling stroke volume
Preload, afterload, contractility.
Mention factors maintaining heart contractility & pathological conditions affecting it.
Normal blood flow Normal metabolism Healthy myocardium Patho: 1. Hypoxia, hypercapnia & acidosis 2. MI 3. Diseased or intoxicated myocardium 4. Intrinsic depression
Continuous inc in afterload leads to …..
Myocardium hypertrophy causing it to weaken or fail.
Describe the effect of afterload during exercise
The negative afterload may operate during exercise as the skeletal muscle bv are dilated leading to in SV & CO with low costs of energy & O2 consumption.
Mention the effect of marked inc or dec of HR on SV & why?
Both cause dec SV
Inc, due to reduction if ventricular filling
Dec, as in AV block because the inc in ventricular filling with marked prolongation of filling period is minimal and cannot compensate for the decrease in heart rate.
Heterometric stimulation depends on …, stimulated by …., a ….phenomenon. Its time is ….
Homeometric stimulation deoends on ….. at constant …. stimulated by …., a …. phenomenon. Its time is ….
EDV, inc VR, preload, seconds (2 to 5 min)
Contractility (inotropism), EVD, high maximum ventricular systole, afterload, unlimited.
Mention conditions in which homeotropic & heterotropic are esp important.
Homeo: conditions of inc afterload as aortic stenosis/atherosclerosis, or after hetero in exercise.
Hetero: postural changes, transplanted/denervated heart, in failing heart.
Mention factors affecting EVD
- Venous return
- Atrial contraction
- Compliance of the heart
Mention factors affecting venous return
Venous tone Muscular exercise Circulating blood volume Body position Intrathiracic pressure negativity
Compliance of heart depends on
- Increased intrapericardial pressure
2. Decreased ventricular compliance
Mention physiologically & humorally mediated extrinsic regulation mechanisms
Phys: 1. Sympathetic 2. Parasympathetic 3. Neurohormones Humoral 1. Drugs affecting cAMP 2. Glucagon 3. Direct myocardial depression 4. Drugs affecting IC, digitalis
Shift of starling curves represents effects of …..
Homeometric regulation
Mention the factor causing shift to the left of CO-RAP curve
Adrenergic support by symp stimulation or circulating catecholamines
The point in which the two starling curves meet is called …..
Equilibrium point
Describe the effect of heart failure on combined ventricular function-venous return curve & treatment
The ventricular function curve is shifted to the right and intersects venous return curve at a lower point at higher RAP (CVP) & LOW CO&VR.
Digitalis has +ve inotropic effect shift the equilibrium point back towards normal & corrects the low CO & hight CVP.
Describe the mechanism of raising CO to 12 L/min
- HR is increased to max sinus rhythm by removal of inhibitory vagal effect. (Bainbridge reflex)
- SV is increased by inc VR & EDV first by heterometric then by homeometric mechansim.
Cardiac reserve is the difference between …&….
Maximum & basal cardiac output
Describe mechanism of raising CO beyond permissive limit
By sympathetic adrenergic stimulation & ciculating catecholamines
- Increased HR by +ve chronotropic effect upto 180 bpm
- Increased SV by +ve inotropic effect by dec ESV up to 30 mL or less.
Mention long kasting mechanisms of inc cardiac reserve
Diltation & hypertrophy
Describe causes of diltation in long-lasting mechanisms
Volume overload
In aortic valve incompetence, ventricular septal defect & advanced CHF. To increase SV, EDV is increased
Describe causes of hypertrophy in long-lasting mechanisms
Pressure overload
Hypertension, aortic valve stenosis. To overcome excess resistance the LV has to increase its wall thickness
Mention limitations of permissive limit increase & extrinsic mechansim
Permissive has no limit
Ex: amount if stored norepinepherine & epinephrine & responsiveness to beta-adrenergic stimulation.
Mention limitations of ESV & EDV changes in inc cardiac output
ESV: incraesed contractility dec ESV, when marked can lead to hear injury (athelete heart lesion)
EDV: Inc can lead overtretch beyond starling limit with diastolic dysfunction & extra needs of oxygen.
GR: HR increase is limited
As marked increase leads to dec ven filling, dec SV, increased work load & oxygen consumption & dec blood supply to ventricles.
GR: Hypertrophy may limit heart blood supply
Because when marked, the increase in blood supply of myocardium does not increase to same extent as muscular element.
Explain determinants of of O2 consumption
- Inotropic state (directly proportional)
- Heart rate (the frequency of activation is more imp than the force of activation)
- Tension (directly proportional, inc in dilatation and dec in hypertrophy but O2 requirements are inc due to inc inotropic state).
Define mechanical efficiency of the heart & mention effect of ANS
Its is the percentage of work done to total energy expenditure
Para inc ME and Symp dec ME
Carduac work is …., max is …., reserve is ….
6-8 Kg/min
80 Kg/min
73 Kg/min
Define potential and kinetic work
P, work required to move a certain amount of blood against a given pressure
K, work needed to give velocity to blood
Mention reflexes of the coronary arteries and explain
Anrep’s reflex: increase in VR causes coronary VD reflexly
Bezold Jarisch reflex: lead to a fall in ABO & HR
Gastrocoronary reflex: gastric fullness, esp eith fatty meal reflexly causes coronary VC
