Calculations

Question 1

how do you calculate alveolar ventilation? [1]
whats the unit?[1]

work out alveolar ventilation from information below

Tidal volume is 500ml, and anatomic dead space is 150ml. If fresh air entering the lungs is therefore 350 ml, and resp rate is 12 breaths per minute,

Answer 1

alveolar ventilation ml per min : (tidal volume - dead space) x resp rate (breaths per minute)

alveolar ventilation is 12 x 350 = 4200 ml per minute. This is the effective ventilation that brings abut the exchange of O2 and CO2.

Question 2

what is the equation to work out o2 or co2 exchange in lung? [1]

Answer 2

o2 or co2 exhancge = volume of alveolar ventilation X (room co2 / o2 - alveoli co2/ o2 / 100)

Question 3

calculate the o2 and co2 exchanges for the below values. assume alveolar ventilation is 4.2 l/min

Room o2 = 21%
alveolar o2 = 14%

Room Co2 = 0.04%
alveolar Co2 = 5.5%

Answer 3

Co2 output = 4.2 X (5.5 - 0.04 / 100) = 0.231 L/min

O2 input: 4.2 X (21 - 14 / 100) = 0.294 L/min

Question 4

how do you calculate compliance in respiratory physiology? [1]

Answer 4

compliance = change in volume / change in pressure

Question 5

whats the formula to calculate ejection fraction?

Answer 5

Ejection Fraction (%) = Stroke Volume (ml) / End-Diastolic Volume (ml)

Question 6

Mrs Rosanna Stewart has an end-diastolic volume (EDV) of 120ml and an end-systolic volume of (ESV) of 40ml.

Calculate her ejection fraction [1]

Answer 6

Ejection Fraction (EF) can be calculated using the following formula: Ejection Fraction (%) = Stroke Volume (ml) / End-Diastolic Volume (ml)

Stroke Volume (SV) can be calculated using the following formula: Stroke Volume (ml) = End-Diastolic Volume (ml) - End-Systolic Volume

Calculation:

EDV = 120 ml; ESV = 40ml;

Stroke Volume = 120 ml - 40 ml = 80 ml

Ejection Fraction = 80 ml / 120 ml = 66.7% (1 d.p.)