Basic Physiology To Know

Question 1

How is heart rate controlled?

Answer 1

HR is set by SAN pacemaker activity - this is modulated by the autonomic nervous system (+ adrenals to a degree)
- denervated heart has rate 100-120

Question 2

How is cardiac output regulated?

Answer 2

Complex interplay of the main factors effecting it (HR/preload/contractility/afterload)

Note HR can increase 3x (60 to 180bpm) whereas SV can only increase 0.5x (70 to 105ml)

Question 3

Factors affecting contractility

Answer 3

Sympathetic nervous system via B1 adrenoreceptor action
Tachycardia “The Bowditch effect” intrinsic contractility is increased with HR is high
Drugs..
Disease..

Question 4

What is afterload and what does it depend on

Answer 4

The work done to oppose forces preventing the shortening of myocytes

Depends on: SVR (And transmural pressures???)

Note: increased AL leads to decreased SV but also increased LVEDV which would in turn lead to a greater SV
Overall after a sudden increase in AL there is a reduction in SV before it gradually returns to normal
- Note this is not true of the failing heart

ANREP effect - an increase in afterload cause an increase in intrinsic inotropy so the drop in SV is smaller than the frank starling mechanism would predict

Question 5

Bowditch effect?

Answer 5

Increased heart rate leads to increased inherent contractility

Question 6

Cerebral blood flow in adults?

Cerebral perfusion pressure formula and value

Answer 6

CBF = 50ml/100g/min (of brain tissue)

CPP = MAP - (ICP + CVP)

Question 7

Autoregulation of cerebral blood flow: MAP

Answer 7

Auto regulates between MAP of 50 & 150 mmHg

This shifts up in chronic hypertensives

Question 8

Autoregulation of cerebral blood flow: PCO2

Answer 8

CBF increases as PCO2 increases up to approximately a PCO2 of 10 kPa

Shifted up in chronic CO2 retention

Question 9

Autoregulation of cerebral blood flow: PO2

Answer 9

CBF static if PO2 >8 but if less than CBF increases dramatically

CBF at max around PO2 5 kPa

Question 10

Alveolar gas equation

Answer 10

Equation that describes the partial pressure of oxygen at the alveolar level

PAO2 = FiO2(PiO2) - PACO2/RQ

PAO2 = FiO2(Patm - PH2O) - PACO2/RQ

Note that PACO2 assumed to be in equilibrium with PaCO2 so used interchangeably

Question 11

Shunt equation

Answer 11

QS/QT = (Cco2 - CaO2)/(Cco2 - CvO2)

Gives a ratio of shunt blood flow to total blood flow

Normal is less than 0.3

Question 12

Pulmonary vascular resistance equation

Answer 12

PVR = (mPAP - LAP)/CO x 80

If x80 units are dyne/S/cm5 or if not in woods units

Question 13

Factors increasing PVR

Answer 13

Increased PaCO2
Decreased pH
Decreased PO2
Adrenaline
Noradrenaline
Thromboxane A2
Angiotensin II
Serotonin
Histamine
High or low lung volume

Question 14

Factors decreasing PVR

Answer 14

Decreased PaCO2
Increased pH
Increased PaO2
Isoprenaline
Acetylcholine
Prostacyclin
NO
Increased peak airway pressures
Increased pulmonary venous return
Volatile anaesthetic agents

Question 15

Lung volume at which PVR is lowest

Answer 15

FRC

Question 16

Ventilation perfusion of lung by region graph

Answer 16

Question 17

Different deadspaces..

Answer 17

Physiological - sum of anatomical and alveolar

Anatomical - conducting airways (Fowlers method)

Alveolar - airways ventilated but not perfused (Bohr eq.)