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