What factors control cardiac output?

  • Cardiac Output = Heart Rate x Stroke Volume
  • Heart rate controlled by cardiac innervation – symp. / parasymp.
  • Stroke Volume:
  • Afterload
  • Preload – Starling Curve (Fibre length-tension) (2 out of 5):
    • Pericardial pressure
    • Ventricular compliance
    • Atrial filling
    • Blood volume
    • Intrathoracic pressure
    • Contractile state (3 out of 7):
      • Cardiac innervations
      • Hypoxia; hypercapnia; acidosis
      • Drugs +ve & -ve inotropes
      • Circulating catecholamines
      • Loss of myocardium
      • Intrinsic depression (Heart failure)
      • Force-frequency relationship

What are the major factors which determine myocardial oxygen consumption?

  • Intramyocardial tension
  • Contractile state of myocardium
  • Heart rate = Ventricular work/beat = SV x MAP


What factors determine cerebral blood flow?

  • Intracranial pressure
  • Local constriction/dilation of cerebral arterioles, autoregulation etc
  • MAP at brain level
  • Blood viscosity
  • Mean venous press at brain level

What substances are important for brain metabolism?

  • Oxygen ~49ml/min = 20% body O2 consumption
  • Glucose (major energy source) ~77mg/min
  • Glutamate (converted to glutamine as detox mech NH3) ~5.6mg/min


What is the normal value for venous return in the healthy human adult?

  • 5-5.5 l/min

What is the relationship between right atrial pressure and venous return?

  • Circulating blood volume
  • Sympathetic and parasympathetic tone.
  • Muscle pump
  • Right atrial pressure (intrathoracic and intracardiac pressures and factors that influence them like phases of respiration, tamponade, PEEP

What is the relationship between right atrial pressure and venous return?

  • Downslope – reduced driving pressure
  • Plateau – collapse of vein walls
  • Normal value for MSPF = 7 mmHg
  • Normal value for mean RAP = 0 mmHg


What are the major factors affecting the regulation of arterial pressure?

  • Seconds/minutes: baroreceptors, chemoreceptors, CNS ischaemic receptors
  • Minutes/hours: stress (stretch) relaxation, renin-angiotensin vasoconstriction, blood volume change and fluid shift through capillaries
  • Longer term: renal compensation via aldosterone, blood volume changes, salt intake


Describe the features of the action potential in cardiac pacemaker tissue.

  • Prepotential initially due to decrease in inward K+ movement then inward Ca2+ through T channels
  • Action potential due to inward Ca2+ through L channels
  • Repolarization due to inward K+ movement
  • No plateau

How do autonomic factors alter the slope of the prepotential?

  • Noradrenaline from sympathetic endings raises intracellular cAMP
  • Facilitates opening of L channels
  • Increased Ca2+ influx
  • Increased heart rate
  • ACh acts via muscarinic receptors and G protein to open K+ channels and decrease rate


What are the determinants of myocardial oxygen consumption?

  • Heart rate
  • Wall tension
  • Myocardial contractility

What are the changes in cardiac function with exercise and how these mediated?

  • Rate and stroke volume
  • Adrenaline and sympathetic discharge
  • Venous return

What are the physical laws involved?

  • Starling
  • 2 La Place P =2T/R


Describe or draw a cardiac pacemaker potential arising from the sino-atrial node.

cardio 12

  • RMP –60 mV
  • Prepotential to –40 mV
  • Leisurely upstroke to +ve value
  • Symmetrical downstroke to RMP

What are the ion fluxes that produce this pacemaker potential?

  • The decline in IK efflux permits the prepotential
  • ICaT (transient) influx completes the prepotential
  • ICaL (long) influx produces the upstroke
  • IK efflux produces the downstroke

Please describe how a pacemaker potential is conducted throughout the myocardium.

  • Specialised conduction tissue
  • SA node
  • atrial pathway
  • AV nod
  • Bundle of Hi
  • Purkinje system (bundles)


Please describe the arterial baroreceptors.

  • Located in the adventitia of the aorta at the apex of the aortic arch
  • Also in the adventitia of the internal carotid artery at the carotid sinus, immediately after the bifurcation from the common carotid.
  • The baroreceptors are stretch receptors, discharging at an increased rate in response to stretch of the arterial walls

What is the role of the arterial baroreceptors in regulation of systemic blood pressure?

  • There is a basal activity in the afferent nerves (glossopharyngeal and vagus) from the baroreceptors
  • Increased blood pressure stretches the baroreceptors
  • Stretch causes increased firing in the afferent nerves
  • The afferent nerves are inhibitory to the vasomotor centre
  • Inhibition of the vasomotor centre reduces central sympathetic outflow to the cardiovascular system
  • Decreased blood pressure has an opposite effect

What is the effect of chronic hypertension on the activity of the arterial baroreceptors?

They ‘reset’ to maintain normal basal activity at the elevated blood pressure.- reversible


Describe the cardiovascular compensations to acute blood loss.

  • Tachycardia;
  • Vasoconstriction;
  • Venoconstriction

Describe the other physiologic compensations to acute blood loss.

  • adrenaline/noradrenaline (sympathetic);
  • vasopressin;
  • glucocorticoids;
  • renin-angiotensin-aldosterone;
  • erythropoietin;
  • plasma protein synthesis.


What hormone systems are involved in the maintenance of Extracellular fluid volume?

  • Renin, angiotensin aldosterone/vasopressin

What are the effects of Atrial Naturetic Peptide in response to fluid overload?

  • Increase sodium secretion from the kidneys
  • Diuresis

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