Cardiac Physiology 2

Question 1

3 main factors that change force of muscle fiber shortening

Answer 1

pre-load. afterload. contractility

Question 2

preload def

Answer 2

amount of filling or stretching of ventricles pre-contraction = volume of ventricle prior to systole

Question 3

afterload

Answer 3

resistance to emptying; the force against which the heart has to pump –> anything that opposes fiber shortening

Question 4

contractility

Answer 4

intrinsic vigor of fibre shortening

Question 5

preload: ventricle volume determines? which determines?

Answer 5

length of each muscle fiber –> determines amount of actin myosin overlap and vigor contraction

Question 6

preload: optimal sarcomere length? what if too long? too short?

Answer 6

2.2 um: too long = not enough overlap so less contraction speed and power. too short = strong not much room for fibers to contract

Question 7

what load for the preload force relationship? what vs. what

Answer 7

Frank Starling Law: ventricular filling vs. contractile force generated

Question 8

preload: normally resting sarcomere length is? so what? but what if too excessive?

Answer 8

short side of optimal so stretching = greater force. excessive stretch = less potential cross bridges so less effective contraction

Question 9

how to determine preload

Answer 9

how much blood fills the ventricle = end diastolic volume –> measured as end diastolic pressure “LVEDP”

Question 10

what factors help determine the Frank Starling curve

Answer 10

number of cross bridges v/w actin and myosin. titin (more stretch = more recoil). troponin C. stretch. intracellular Ca release from SR

Question 11

best measure of cardiac afterload is? which is determine by? which law?

Answer 11

wall tension needed to open aortic valve and get forward flow. pressure in chamber, radius (size of chamber), wall thickness –> La Place’s Law

Question 12

LaPlaces Law?

Answer 12

tension is proportional to pressure load aka arterial pressure and radius aka heart size. inversely proportional to thickness of heart wall

Question 13

contractility depends on? what are the independent changes called?

Answer 13

preload, afterload but also independent factors = inotropy

Question 14

inotropy def? measure directly by? indirectly by?

Answer 14

intrinsic vigor of fiber shorterning independent of pre/afterload. rate of fiber shortening (change in pressure/change in time). indirectly by % of ventricular volume ejected aka ejection fraction

Question 15

main factor that increases intotropy is? how?

Answer 15

Ca –> more Ca = more actin/myosin overlap = better force generation –> usually by increasing cAMP

Question 16

5 other inotropic factors

Answer 16

adrenaline/catecholamines. phosphodiesterase inhibitors (increase cAMP). digoxin (increase Ca influx). caffeine. angiotensin II.

Question 17

chronic factors that affect inotropy

Answer 17

type of myosin light chains –> heart failure you lose a, get more b which is slower. amount of ATP made by cell. release rate of Ca from troponin C. SR Ca reuptake, and release rate. cyotkines, hormones, paracrine factors

Question 18

lusitropy: aka? what is it? converse to?

Answer 18

relaxation inotropy = speed of myocardial relaxation; converse to speed of contraction aka inotropy

Question 19

lusitropy measured by?

Answer 19

rate of fiber relaxation –> negative change in ventricular pressure over change in time

Question 20

lusitropy increased by?

Answer 20

adrenaline: better and faster ventricular filling which increases preload (heart relaxing faster = more time for blood to flow into ventricles and get a good preload)