Physiology

Question 1

What is the max allowable variability with spirometry?

Answer 1

5%

Question 2

Equation for working out alveolar pressure in flight/atmospheric changes

Answer 2

Pi02 = 0.21 x Patm - p (water vapour)
At sea level: Patm = 760, p = 47
Plane/mt Patm = 650

Question 3

Pulse oximetry reading 90% corresponds to what Pa02 approximately (under norms metabolic conditions)

Answer 3

60mmHg = 90%
40mmHg = 75% 
(P50 = Pa02 50% = 27mmHg)

Question 4

What is the composition of dry air?

Answer 4

21%oxygen
78%nitrogen
0.04%c02
0.92%inert substances

Question 5

Formula for Pa02

Answer 5

Partial pressure 02 = 760mmHg x 0.21 = 160

Question 6

What is the O2 pressure cascade from alveoli?

Answer 6

Pi02 influenced by Fi02 and atm pressure 150
PA02 info by alv vent and 02consumpt 100
Pa02 infl by venous admixture, gas diffusion, mixed CvO2 = 95
Tissue cap p02 infl by 02 delivery, consumption 60mmHg
Intracellular = 15mmHg

Pa02 is perfusion limited (reaches alv pressure by 1/3 through capillary), in Abn conditions becomes diffusion ltd

Question 7

What is the alveolar gas equation? Normal value?

Answer 7

PA02 = (pB - Ph20) FI02 - PAC02/R
R = resp quotient normally 0.8
A-a = efficacy of gaseous exchange (usually 1-3kPa). Increased in intrinsic lung disease.

Question 8

How long does blood normally take to traverse pulm capillaries?

Answer 8

0.75s
O2 takes 0.3sec
In severe exercise takes up to 0.2 sec for blood in capillary

Question 9

Are N20 and Co2 perfusion or diffusion ltd?

Answer 9

Perfusion
(N20 takes 0.1s to reach equilibrium)
C02 diffuses 20x faster so elimination of co2 is much less of a problem than 02 delivery