WBR0990
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| Author | William J Gibson (Reviewed by Serge Korjian) |
|---|---|
| Exam Type | USMLE Step 1 |
| Main Category | Physiology |
| Sub Category | Pulmonology |
| Prompt | An attending in the cardiac intensive care unit at a major academic medical center is teaching a resident about the pulmonary vasculature. A patient with a history of hypertrophic cardiomyopathy is recovering from an anterior myocardial infarction and the following values below are measured. Which of the following corresponds to the pulmonary vascular resistance in this patient?
|
| Answer A | 0.72 mmHg·min/L |
| Answer A Explanation | See calculation in the explanation |
| Answer B | 1.39 mmHg·min/L |
| Answer B Explanation | See calculation in the explanation |
| Answer C | 11.25 mmHg·min/L |
| Answer C Explanation | See calculation in the explanation |
| Answer D | 13.9 mmHg·min/L |
| Answer D Explanation | This result can be achieved by dividing the difference in systolic and diastolic aortic pressures and dividing by the cardiac output (3.6L/min) |
| Answer E | 20.83 mmHg·min/L |
| Answer E Explanation | See calculation in the explanation |
| Right Answer | B |
| Explanation | [[Explanation::The pulmonary vascular resistance of a vessel can be calculated by the change in pressure across the segment divided by the flow (R=P/Q). Generally, the pulmonary capillary wedge pressure is a good estimate of the pressure in the left atrium. Therefore, pulmonary vascular resistance is given by the formula:
Plugging in values from the above case we get the following:
(15 mmHg - 10 mmHg)/(90 beats/minute*(.040 L/min))=5/3.60=1.39 mmHg·min/L.
Normal values for pulmonary vascular resistance range from 0.25–1.6 mmHg·min/L. |
| Approved | Yes |
| Keyword | Lung, Vasculature, Pulmonary hypertension, Hemodynamics, Hemodynamic |
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