WBR0990
| Author | PageAuthor::William J Gibson |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Physiology |
| Sub Category | SubCategory::Pulmonology |
| Prompt | [[Prompt::An attending in the cardiac intensive care unit at 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 are measured.
Pulmonary artery pressure (mean): 15 Pulmonary capillary wedge pressure (mean): 10 Aortic systolic pressure: 140 Aortic diastolic pressure: 90 Heart rate: 90 per minute Stroke Volume: 40 mL Which of the following corresponds to the pulmonary vascular resistance in this patient?]] |
| Answer A | AnswerA::0.72 mmHg·min/L |
| Answer A Explanation | AnswerAExp::Incorrect: See calculation in the explanation |
| Answer B | AnswerB::1.39 mmHg·min/L |
| Answer B Explanation | AnswerBExp::Correct: See calculation in the explanation |
| Answer C | AnswerC::11.25 mmHg·min/L |
| Answer C Explanation | AnswerCExp::Incorrect: See calculation in the explanation |
| Answer D | AnswerD::13.9 mmHg·min/L |
| Answer D Explanation | AnswerDExp::Incorrect: 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 | AnswerE::20.83 mmHg·min/L |
| Answer E Explanation | AnswerEExp::Incorrect: See calculation in the explanation |
| Right Answer | RightAnswer::B |
| Explanation | [[Explanation::In this question we are asked to calculate the pulmonary vascular resistance for this patient. Recall that the 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:
<math>PVR = (P_{pulmonary artery} - P_{capillary wedge})/Cardiac Output</math> α 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.
References: First Aid 2013 page 549 |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Lung, WBRKeyword::Vasculature, WBRKeyword::Pulmonary hypertension, WBRKeyword::Hemodynamics, WBRKeyword::Hemodynamic |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |