Practice Questions: Problem


An elderly female patient became cyanotic and complained of dyspnea while being examined by a medical student in University Hospital. After she was treated in the emergency ward, respiratory and blood gas measurements were made, giving the following values:

  Predicted Measured After Brochodilator
Total Lung Capacity (TLC) 4.5 liters 5.5 liters 5.5 liters
Vital Capacity (VC) 3.5 liters 3.0 liters 3.1 liters
Functional Residual Capacity 2.5 liters 3.0 liters 3.0 liters
Residual Volume 1.0 liters 1.6 liters 1.5 liters
FEV-1 3.6 liters 1.5 liters 1.6 liters
FEV-1/FVC 80% 50% 53%

Arterial and venous blood gas samples were taken when the patient was breathing air and when she was breathing pure O2, in both cases with the patient at rest and without bronchodilator:

  Breathing Air Breathing 100% Oxygen
Pa-O2 60 mmHg 560 mmHg
Pa-CO2 48 mmHg 53 mmHg
Ca-O2 170 ml O2/liter blood 220 ml O2/liter blood
Pv-O2 25 mmHg 35 mmHg
Pv-CO2 60 mmHg 62 mmHg
Cv-O2 120 ml O2/liter blood 170 ml O2/liter blood

In addition, oxygen diffusing capacity (calculated from the measured carbon monoxide diffusion capacity) was found to be 4 ml/min/mmHg; the predicted value for this patient is 15 ml/min/mmHg.

For each of the following, indicate which are likely contributors to her respiratory difficulty, which can be ruled out, and which are uncertain. Be sure to state the reasons for each of your answers.

A. Restrictive lung disease (low compliance)
B. Obstructive lung disease (high airway resistance)
C. Anemia
D. Diffusion limitation
E. Shunt
F. Ventilation/perfusion non-uniformity
G. Heart failure (inadequate cardiac output)
H. Anxiety and depression associated with being treated by a medical student