Q11

Describe the distribution of blood flow in the lungs.

  • Linear increase from top to bottom
  • 3 zones explained by hydrostatic pressures

Explain how V/Q matching varies from apex to base in the normal lung.

  • Slow increase in ventilation from top to bottom but not as much as perfusion.
  • Highest V/Q at apex

What factors effect pulmonary vascular resistance?

  • Hypoxia – arteriolar smooth muscle to contract
  • One of low pH, autonomic or passive factors

Q12

What are the acute respiratory adaptations to altitude?

  • Hyperventilation. (Oxygen-haemoglobin curve shifts right or left.)

What are the longer term physiologic effects of altitude exposure?

  • Polycythaemia;
  • one of increased 02 carriage and viscosity;
  • RVH;
  • more capillaries;
  • increased oxidative enzymes.

Q13

Describe how blood flow is regulated at the level of the endothelium.

  • Vasodilators: prostacyclins, NO, kinins
  • Vasoconstrictors: endothelinthromboxane, serotonin

What other general effects do endothelins have on the cardiovascular system?

  • Positive inotrope and chronotrope
  • Rise in ANP/renin/aldosterone
  • Decreased GFR and renal blood flow

Q14

Describe how the renin-angiotensin system regulates blood pressure and flow.

  • Describes pathway
  • Fall in renal blood flow leads to renin
  • Renin, angiotensin I > II
  • Vasoconstrictor

What factors regulate renin secretion?

  • Stimulate:
    • sympathetic nervous system, catechols, prostaglandins
  • Inhibit:
    • Na and Cl reabsorp, inc BP, angio II, vasopressin

Q15

What changes in arterial blood pressure do baroreceptors respond to?

  • Carotid sinus (rise or fall)
  • Aortic arch (rise)

What happens when the baroreceptors detect a fall in arterial pressure?

  • Decreased firing rate of Hering’s nerve
  • CN IX transmits to vasomotor centre
  • Decreased parasympathetic outflow to heart
  • Increased sympathetic outflow to heart
  • Increased sympathetic outflow to vessels
  • Increased heart rate, contractility
  • Arteriolar and venous constriction

What is the Set Point?

  • Neutral MAP for vasomotor centre Around 100 mm Hg

Q16

Please explain the concept of compliance as it relates to the lung.

  • Volume change per unit pressure change (slope of pressure volume curve) =~200ml/cm H2O
  • Depends on lung volumes and demonstrates hysteresis , may draw compliance curve, point out that inc compliance at low volumes
  • Depends on structural proteins and surface tension

What factors affect compliance?

  • Decrease
    • Fibrosis, pulmonary oedema,  not ventilated, increased pulmonary venous pressure
  • Increase
    • Emphysema, asthma surfactant

Q17

What are the metabolic functions of the lung?
Prompt: What substances are metabolised in the lung?

Metabolism of vasoactive amines

  1. Activation of Angiotensin 1 à AT 2 (ACE in capillary endothelium)
  2. Inactivation of bradykinin (ACE); PGs E/F
  3. Uptake & storage of Serotonin
  4. Arachadonic acid metabolites à leukotrienes / SRS-A & Prostaglandins

Synthesis of

  1. Surfactant
  2. IgA
  3. Phospholipids
  4. Proteases (collagen/elastin breakdown)

Pass criteria:

  • 2 of each

Q18

What factors influence the rate of transfer of oxygen from the alveolus into a pulmonary capillary?

  • Process is passive diffusion ( ficks law of diffusion)
  • Affected by – surface area,  membrane thickness, gradient of p O2 ( o2 in alveolus and O2 binding capacity of Hb)
  • Also – constant –solubility and MW
  • (V = A/T x D x (P1-P2)
  • D = Sol/MW1/2

Could you give some clinical examples of when these may be affected?

  • Exercise alveolar hypoxia and thickening of blood gas barrier

Q19

What factors determine the work of breathing?

  • Elastic forces of the lungs and chest wall
  • Viscous resistance of the airways and tissues

Pass Criteria:

  • Bold to pass

What variables affect elastic workload?

  • Larger tidal volumes
  • Reduced compliance due to:
    • lung volume – a person with only one lung has halved compliance;
    • slightly less during inflation than during deflation;
    • increased by increased tissue mass – fibrosis or pulmonary congestion or chest wall restriction;
    • loss of surfactant

What variables affect viscous resistance?

  • Higher respiratory rates increasing flow rates
  • Decreased airway radius due to:
    • Lower lung volumes;
    • Bronchoconstriction;
  • Increased air density (eg SCUBA diving)
  • Increased air viscosity

Pass Criteria:

  • Bold to pass

Q20

What is the relationship between intrapleural pressure and lung volume?

  • Sigmoid curve of IP pressure vs volume, does not reach 0% lung volume
  • Shows lung volume is higher during deflation than inflation for any given pressure = Hysteresis
  • Shows that lung contains residual air, without any expanding pressure (due to airway closure)
  • Shows that compliance decreases at higher lung volumes – lung becomes stiffer due to reaching limits of elasticity

respiratory 3.jpg

Pass Criteria:

  • 3 out of 4 to pass

What variables affect pulmonary compliance?

  • Slightly greater during deflation than during inflation as noted above;
  • Lung volume – at very low and very high volumes compliance is reduced;
  • Increased when tissue elasticity is reduced, as in emphysema;
  • Decreased by increased tissue mass – fibrosis or pulmonary congestion;
  • Decreased by loss of surfactant

Describe how regional differences in intrapleural pressure affect the ventilation.

  • States that the intrapleural pressure is higher at the apex than at the base of the lung – to keep the lung expanded against its own weight
  • Increased compliance at base, hence better ability to ventilate base compared with apex

Pass Criteria:

  • Bonus if gives values 10cm H2O at apex, 2.5cm at base

GO ON TO
Questions 21 to 30