18 Diffusion capacity Flashcards
Factors that affect diffusion in lungs
Surface area - 80 meters ^2
Thickness- 0.6u (hair is 25u)
Pressure gradient- PO2 usually 40-100mmHG with hemoglobin 5ml/100ml blood (W/o 0.18/100)
Diffusion is proportional to
^ Pressure
^ Solubility
^ Area
V distance V sqrt(molecular weight)
Solubility of O2 and CO2
SO2 = 0.03mL/L/mmHg
SCO2 =0.6 mL/L/mmHg
Oxygen uptake per 100 mls in systemic capillaries
5mls
Stroke volume
about 70ml/ beat
Average CO
about 5000 ml/min
Average O2 requirement in periphery at rest
250mL/min
DL
diffusion rate/ (alveolar pressure - capillary pressure)
Steady state measure of DL
Breathe 0.1-0.2% CO for 5-6 mins, collect expired gas over last 2 minutes.
easier for lung disease patient, can be used during exercise
Single breath DL
Full inspiration with trace CO and reference gas- hold for 10 secs, maximal exhale.
- Rapid results
- more difficult to perform
- higher DL values than steady state measurements.
Refence is diluted into residual volume. ( so ratio of exp/insp =vc/TLC)
Diffusion capacity is then proportional to area, pressure, and time * ratio of expired reference gas/expired CO
Male and female average Dl
Males upper 20slow30s
Females- middle 20s
Exercise effect on DL
Increases by a factor of 3
Why is CO2 less succeptible to diffusion impairment
More soluble
More control
CO2 doesnt saturate
DL in lung disease
Restrictive- Decreased DL and VA
Obstructive– Decreased DL , increased or normal VA
VQ mismatch
Low ventilation - shunt
Low perfusion- dead space
