What are some possible causes of respiratory insufficiency if ventilation is adequate?
Lung interstitial defects, problems relating to blood (ie Anemia)
What are the factors that contribute to diffusion which can change in disease states?
Pressure (increases diffusion)
Distance (decreases diffusion)
Area (increases diffusion)
What is the typical surface area available for gas exchange in an adult human?
What is the usual path length (thickness of respiratory membrane)?
80 square meters
How is oxygen carried by blood? How much via each method?
Direct dissolution (follows Henry's law, 0.18ml/100ml)
Bound to hemoglobin (lecture says 5ml/100ml, should be closer to 19-20ml under normal conditions)
Compare the relative diffusion behaviors of CO2 and O2.
CO2 diffuses more easily, as it is more soluble in water/plasma. Carbon dioxide generally does not saturate under physiological conditions.
How can oxygen requirement be calculated?
Examine the extraction of oxygen (oxygen level at either end of a vascular circuit)
For total usage, look at arterial and venous oxygen, and cardiac output.
Why is carbon monoxide used to measure someone's oxygen DL?
Calculation of DL is nearly impossible since Pc cannot be measured. carbon monoxide almost completely binds hemoglobin, thus, its capillary gas pressure stays close to zero.
The DLCO can be converted back to DLO2 afterwards.
Distinguish between steady-state and single breath DL measurements.
Steady state involves breathing a low concentration CO gas mixture and then collecting exhalate. Single breath does this over a single full VC inspiration/expiration.
Steady state is preferable for those unable to complete single breath testing, and can be used during exercise studies.
How do DLCO and DLO2 correlate?
DLO2 is 1.23 times DLCO
How can lung volumes be measured without using a spirometer?
A pneumotachometer can measure volume by integrating a flow rate over time.
Why is methane a part of a diffusion test?
Methane is not absorbed at all, its relative dilution in the lungs is used to calculate total lung volume, which is needed for calculation of DLCO
What parameters can affect the measurement of DL values?
Age, height, gender. Also anemia, altitude, other blood problems, etc
How does DL change in exercise? How?
DL increases by a factor of 3, mostly by increasing the pressure gradient by increasing pulmonary perfusion (only modest changes in surface area, thickness etc)
How would the following conditions change DL?
Hemorrhage will decrease diffusion.
Anemia will also decrease diffusion.
Recall the equation: 1/DL = 1/DM + 1/(Qc * θ)
How do DL and DL/VA change in restrictive and obstructive lung diseases?
Restrictive: DL and VA both decrease, so DL/VA remains normal.
Obstructive: DL decreases more than VA, so DL/VA decreases.
How does V/Q mismatch affect diffusion capacity?
V/Q mismatch would reduce diffusion capacity. Recall that there will be no net diffusion in complete shunting (no ventilation) or dead space (no perfusion.
Describe how diseases like pneumonia or emphysema might affect diffusion capacity.
Pneumonia: Fluid in the alveoli impair diffusion, as does wall thickening.
Emphysema: Loss of surface area, decreases diffusion capacity.