RESPIRATION PHYSIOLOGY |
Evaluation of Respiratory Pathophysiology from Pulmonary Function Tests and Blood Gas Analysis
| PROBLEM | DIAGNOSIS |
| Low Inspired Oxygen | PI-O2 (dry) << 160 mmHg or PI-O2 (wet) << 150 mmHg |
| Hypoventilation | PA-CO2 >> 40 mmHg; also PA-O2 << 100 mmHg |
| Restrictive | TLC << predicted |
| Obstructive | FEV1/VC << 80% or (if not Restrictive) PEF << predicted |
| Neurogenic | Maximum pressure << 100 cmH2O (neuromuscular problem) or V'E low even though no restrictive or obstructive disease (CNS problem) |
| Alveolar-Arterial Equilibration | AaDO2 (PA-O2 - Pa-O2) >> 5 mmHg (may need to use the alveolar air equation to calculate PA-O2) |
| Diffusion Limitation | DCO << predicted |
| Shunt | When inspiring pure oxygen, Pa-O2 << 570 mmHg or %Shunt >> 5% |
| V'A/Q mismatch | On nitrogen washout, N2% increase >> 1.5%; non-uniform distribution on radioactive tracer scan |
| Anemia | Hb << 150 gm/liter (15 gm/dl); Ca-O2<< expected from Pa-O2 or Sa-O2 (% saturation) |
| Low Cardiac Output | O2 extraction (Ca-O2 - Cv-O2) >> 50 ml-O2/liter (5 ml/dl) at rest |
predicted means predicted from patient's age, size, and sex
<< means significantly less than
>> means significantly greater than
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