Physiological Consequences of Increased Movement of Fluid Across Pulmonary Capillaries

Question 1

Partial pressure of O2 in air at sea level is

Answer 1

160mmHg

(atm: 760mmHg x O.21% O2 = 160mmHg)

Question 2

What is pulmonary artery pressure?

Answer 2

25/8 (mean = 15 mmHg)

Question 3

What is capilalry pressure?

Answer 3

12-8mmHg

Question 4

On exertion, CO increases to

Answer 4

from 5L/min to ~20L/min

Question 5

What are the hallmarks of the pulmonary circulation?

Answer 5

• low pressure
  
  • 1/10 systemic pressure
• pressure does not increase (much) with +CO
  
  • due to dilation & recruitment of pulmonary vessels (opening of vascular bed)

Question 6

On inspiration, the decrease in systolic pressure occurs along with

Answer 6

decreased pulmonary venous return to the LA

decreased CO

Question 7

What causes Kerley B lines?

Answer 7

dilated lymphatics

Question 8

What is metabolic acidosis?

Answer 8

• when PaCO2 is low
• low pH
• compensatory response to elevate pH back to normal
• primary abnormality is low HCO3- <22-28mmol/L (which -pH)
  
  • ​lost through diarrhea
  • being consumed by a buffer e.g. for lactic acid released in tissue hypoxia

Question 9

What is respiratory acidosis?

Answer 9

• when PaCO2 is high
• low pH
• CO2 is not being removed as quickly as it is being produced
  
  • tf issue is at level of respiratory system

Question 10

What factors determine fluid across the pulmonary capillaries?

Answer 10

• hydrostatic pressure inside and outside the capillary (n: Pc > Pi)
• oncotic pressure inside and outside the capillary (n: Oc > Oi)
• permeability of the capillary (σ)

**c = capillary; i = interstitial**

modelled by Starlings Law:

Net fluid out = K{(Pc-Pi) - σ(Oc-Oi)}

Question 11

What is respiratory alkalosis?

Answer 11

• high pH (driven by increased respiration) = alkalosis
• low PaCO2 (due to hyperventilation)
• high PaO2 (due to hyperventilation)

Question 12

What is metabolic alkalosis?

Answer 12

• high pH (>7.35-7.45)
• increased PaCO2 (due to hypoventilation)

Question 13

How much fluid normally leaks from the capillary to the interstitium?

Answer 13

5mL/hour

Question 14

What is normal lymphatic flow?

Answer 14

~20mL/hour

Question 15

What are the effects of pulmonary oedema on lung function?

Answer 15

• mechanical changes:
  
  • -compliance, - lung volumes (restrictive defect), +resistance, +WOB (elastic & resistive)
• gas exchange:
  
  • hypoxaemia due to shunt, low V/Q units, and diffusion impairment
• arterial blood gases:
  
  • -PaO2, - PaCO2, +pH (type I + metabolic alkalosis)
  • if severe, +PaCO2, -pH (metabolic & respiratory acidosis)
• pulmonary circulation:
  
  • +pulmonary vascular resistance

Question 16

compliance refers to

Answer 16

elasticity; the ability of the lungs to expand

Question 17

which lung volumes decrease in pulmonary oedema?

Answer 17

TLC, RV, FRC, VC

Question 18

What are the causes of pulmonary oedema?

Answer 18

• +capillary hydrostatic pressure
  
  • e.g. LV dysfunction, mitral stenosis, fluid overload, pulmonary veno-occlusive disease
• +capillary permeability
  
  • e.g. toxins, sepsis, multiple trauma, aspiration of gastric acid

exaggerated by:

• -colloid osmotic pressure (oncotic pressure)
• -lymphatic drainage