Cardiac Energy/control

Question 0

External cardiac work

Answer 0

• moving blood
• only about 10%
• stroke work
  SW = SV x MAP

Question 1

Energy Production

Answer 1

Ox-phos

• susceptible to injury if low O2 levels
• brief compensation via glycolysis (lactic acid screws with conduction and low pH screws with calcium release…so this is probably not optimum)

Question 2

Internal cardiac work

Answer 2

• external work is used an estimator
• roughly 5 x external
• mostly done during isovolumetric contraction

Question 3

Pressure vs volume work

Answer 3

• pressure is primary determinant
• volume has little effect
• determined by delta in O2 consumption

Question 4

Heart rate and work

Answer 4

• more costly because the heart spends more time in isovolumetric contraction which is where internal work takes place

Question 5

Contractility

Answer 5

• describes the relative ability of the heart to eject a stroke volume (SV) at a given prevailing afterload
• increases pressure work, but maintains CO at lower heart rate
• these effects tend to balance each other out

Question 6

Energy req estimate (and limitation)

Answer 6

• Double product = HR x MAP (KNOW)

- not a valid method when ventricles are dilated

Question 7

CO and SV Eq

Answer 7

CO=SVxHR

SV=EDV-ESV

Question 8

Autonomic control

Answer 8

• sympathetic (increase HR) NO beat to beat

- parasympathetic (decrease HR) SA node beats naturally at around 100 BPM

Question 9

Parasympathetic control of heart

Answer 9

• slows HR
• ACh opens Special K channels (increasing phase 4) and decreases Ca conductance
• predominantly the right vagus

Question 10

Sympathetic control of heart

Answer 10

• Right rate;left contractility
• stimulated by isoproterenol; inhibited by propranolol
• stimulates increase in K leak -> decreasing length (increasing steepness) of phase 4 and increases Ca conductance

Question 11

Epi vs norepi

Answer 11

• epi results in decreased resistance -> decreased afterload -> increased CO systolic pressure is increased while diastolic drops -> MAP remains the same
• Norepi increases contractility -> directly increasing CO. Increases both systolic and diastolic pressure

Question 12

Neural reg of cardiac function location

Answer 12

• frontal lobe
• orbital cortex
• motor/premotor
• solitary and rostral/caudal tract

Question 13

Baroreflex

Answer 13

• senses arterial pressure and responds by modulating HR
• decreased in chronic HTN
• can produce beat-beat variation (deficit-compensation) as seen in PVCs or in a block

Question 14

Bainbridge reflex and atrial receptors

Answer 14

• If HR is slow, the Bainbridge will jack up HR in response to infusion
• if HR is fast, the baroreceptor will slow down the rate upon infusion

Question 15

Resp cardiac arrhythmias

Answer 15

• cycle increases on expiration (and visa versa)

- vagus vs. phrenic activity

Question 16

Venous return during respiration

Answer 16

• increased intrathroacic pressure decreases venous return (passing out during vigorous valsalva)

Question 17

Chemoreceptors reflex

Answer 17

• respond to low O2 or high CO2 (much stronger drive)
• compensation is rapid
• can see this effect in quadriplegics

Question 18

Treppe phenomena

Answer 18

• Increase in contraction frequency -> increase in force

- produced by rise in intracellular Ca

Question 19

Molecular control

Answer 19

• Sympathetics: left greater control over vents
  > Gs stimulates cAMP production -> phosph of Ca channels shift ventricular function to left
• parasymps: inhibit SA node function. Muscarin ACh (M2) inhibit adenylate cyclase
  > vent shift to right function

Question 20

Hormonal control

Answer 20

• thyroid hormones and insulin both are positive inotropes (oddly so is glucagon)
• CO2 reduces contractit

Question 21

Premature ventricular contraction

Answer 21

Beat generated by PVC is early and sub maximal force due to inadequate filling
Following beat is greater than normal

Question 22

Ejection fraction formula

Answer 22

EF = SV/EDV = EDV - ESV/EDV

Question 23

Delta Pressure formula

Answer 23

( essentially V= IR)

Delta P = Q (flow)R

Question 24

MAP formula

Answer 24

MAP-RAP=(CO)(TPR)

MAP= Pdys + .33(Psys-Pdys) or diastolic + 1/3 pulse pressure

Question 25

Coronary arteries

Answer 25

• RPM: right; posterior IV, marginal

- Left coronary; LAD, circumflex (LLC)

Question 26

Starling curve

Answer 26

• force of contraction is proportional to EDV length of cardiac muscle fibers

Question 27

TPR calculation

Answer 27

TPR = MAP-RAP (80)*/CO

• 80 is the conversion factor for dyn*sys/cm^5

Question 28

A/P conduction velocity

Answer 28

• slowest: AV (as seen in PR interval)

- fastest: purkinje fibers

Question 29

CO, CO (based on O2), SW, DD, MAP, MAP looking at TPR

Answer 29

• CO=(HR)(SV)
• CO=q/(Pvo2-Pao2)
• SW=(SV)(MAP)
• DD=(HR)(MAP)
• MAP= Pdys + .33(Psys-Pdys)
• MAP-RAP=(CO)(TRP)