Basic Sciences

Question 1

Plasma Osmolarity

Answer 1

=2 [Na + K] + [glucose] +[urea]

Normal: 280-290 mosmol/l

Question 2

Anion Gap

Answer 2

= [Na + K] - [Cl + HCO3]

Normal: 10-16mmol/l

Increased: renal failure, diabetic/alcohol ketoacidosis, lactic acidosis, salicylate poisoning, methanol, ethylene glycol, paraldehye

Decreased (increased unmeasured cation): potassium, magnesium, calcium, hypoalbuminaemia

Question 3

ECG

Answer 3

timing: small square: 0.04s (40ms), big square: 0.2s (200ms)

region: V1-2 right ventricle, V3-4 septum, V5-6 left ventricle

P axis: right to left -30 to +90 degrees

Right axis deviation: can be normal or associated RVH

Left axis deviation: usually abnormal conduction

PR interval: <0.16s in children, <0.18s adolescents

QRS interval: <0.12s children

QT interval: <0.44s QTc=QT/(square root RR)

P wave: amp <3mm, duration< 0.09s

QRS wave: voltage <0.03s

T wave: until 8yrs T wave inversion V1 is normal

J point: beggining S wave, early repolarisations, normal in kids if <3mm

Question 4

Cardiac depolarisation

Answer 4

4. Resting membrane potential

0. Depolarisation phase: Na+ in: positive feedback mechanism – more Na+ in causes more Na+ gates to open

1. Na+ gates close at -40mV. Slow influx Ca++ – > calcium induced calcium release peaks 0mV and causes binding to tropomyosin and muscle contraction.

2. Plateau phase: small trickle out of K+

3. Repolarisation : K+ out

4. Resting membrane potential

Question 5

Myocardial Contraction

Answer 5

cardiac muscle: thick (myosin) and thin (actin) filaments

contractile components: troponin (I/C/T), tropomyosin

• I: inhibits binding, C: binds Ca, T: binds tropomyosin

action:

• Ca enters and binds TnC changing the configuration and allowing actin/myosin to interact
• myosin binds ATPase
• powerstroke of myosin causes shortening
• relaxation with Ca release

Question 6

Cardiac Cycle

Answer 6

Question 7

Fetal Circulation

Answer 7

right ventricle:

• 10% output to lungs, 90% to aorta via ductus arteriosus
• twice the output LV

left ventricle:

• input from pulmonary vein and foramen ovale
• output (65% oxygen) to cerebral circ/coronaries

Question 10

Cardiac Pressures

Answer 10

Question 14

Cardiac Conduction System

Answer 14

Question 15

Liver metabolism of drugs

Answer 15

phase 1: CYP450 (1, 2, 3) enzymes oxidate, reduce or hydrolyse to make water sol.

phase 2: addition metabolite to water soluble group

phase 3: transport of conjugate drug into bile

Question 16

Ventricular Hypertrophy

Answer 16

RVH

• R in V1: 5<1 month, 4>1 month, 3>1 year
• S in V6: 3<1 month, 2>1 month, 1>1 year

LVH

• S in V1: 1<1 month, 2>1 month, 3>1 year
• R in V6: 3<1 month, 2>1 month, 1>1 year

Question 17

Pulmonary to Systemic Blood Flow Ratio

Answer 17

Qp:Qs = Sa(Aorta) – Sa(SVC) / Sa (Pulm vein) – Sa (Pulm artery)

= 90-70 / 95-90

=4/1 (4:1)

Question 19

Pulmonary Vascular Resistance

Answer 19

PVR= (pulmonary artery mean pressure- left atrial mean pressure)/pulmonary flow

Question 20

Thermodilution

Answer 20

definition: most accurate measure CO

method:

• catheter in PA
• inject known volume at set temperature into blood stream
• time take for temp to reach catheter indicates CO

Question 21

Systemic Vascular Resistance

Answer 21

SVR= (aortic mean pressure- right atrial mean pressure)/systemic flow