Lecture 1 - Respiratory Pathophysiology 1

Question 1

Respiratory failure definition?

Answer 1

when the lungs fail to adequately oxygenate the arterial blood and/or fail to prevent undue CO2 retention

Question 2

Hypoxia?

Answer 2

PaO2 < 8kPa (60mmHg) - type I respiratory failure

Question 3

Hypercapnia?

Answer 3

PaCO2 > 6.6kPa (50mmHg) - type II respiratory failure

Question 4

Causes of hypoxaemia?

Answer 4

reduced PiO2 (e.g. altitude), hypoventilation, V/Q mismatch, R-L shunt, diffusion

Question 5

Oxygen cascade?

Answer 5

atmospheric -> upper airway -> alveoli (influenced by pleural pressure and aCO2) -> capillaries (gas exchanged w influences) -> arteries -> tissues (big drop)

Question 6

Partial pressure of oxygen (PaO2)?

Answer 6

pressure that is exerted by oxygen when you have a mixture of gases

Question 7

Oxygen content (CaO2)

Answer 7

Amount of O2 bound to Hb + amount of O2 dissolved in blood (mL/dL)

Question 8

Oxygen saturation?

Answer 8

Fraction of oxygen saturated Hb relative to total Hb (saturated & unsaturated)

Question 9

Alveolar hypotension sign and causes?

Answer 9

PaCo2 rise; decreased brainstem respiratory drive (drugs), neuro-muscular incompetance (polio, mayasthenia gravis), abnormal load (related to work of respiratory muscles e.g. obesity, kyphosis

Question 10

Causes of hypercapnia?

Answer 10

alveolar hypotension or V/Q mismatch

Question 11

Alveolar ventilation?

Answer 11

inversely proportional to Pa CO2, minute ventilation = alveolar ventilation + dead space ventilation; pathology involves increase in minute but decrease in alveolar due to increase in ded space

Question 12

Influences on PAO2?

Answer 12

Patm, FiO2, PH2O, PACO2`

Question 13

Respiratory quotient?

Answer 13

R/RQ, ratio of CO2 produced by the body to oxygen consumed by the body, approx. 0.8

Question 14

A-a gradient calculation?

Answer 14

20 - (PaCO2/0/8) - PaO2 = 1-2kPa; young healthy can be less than 1, range widens through age due to V/Q mismatch

Question 15

Diffusion depends on?

Answer 15

area, thickness, driving pressure (capillary volume) and solubility and molecular weight of gas (Hb)

Question 16

Why use CO?

Answer 16

diffusion (and not perfusion limited), soluble, avidly binds Hb therefore no back pressure

Question 17

Diffusion equation?

Answer 17

Vgas = (solubility/sqrtMW) x (area/thickness) x (PA - Pc)

Question 18

Abnormal diffusion - alveolar capillary block?

Answer 18

interstitial/diffuse lung disease

Question 19

Abnormal diffusion - loss of diffusing surface area?

Answer 19

alveolar surface area issues e.g. emphysema

Question 20

Abnormal diffusion - capillary volume/Hb?

Answer 20

affected pulmonary vasculature e.g. pulmonary hypertenion, anaemia, pulmonary embolism