WBR0990

Author	PageAuthor::William J Gibson (Reviewed by Serge Korjian)
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 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? 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]]
Answer A	AnswerA::0.72 mmHg·min/L
Answer A Explanation	AnswerAExp::See calculation in the explanation
Answer B	AnswerB::1.39 mmHg·min/L
Answer B Explanation	AnswerBExp::See calculation in the explanation
Answer C	AnswerC::11.25 mmHg·min/L
Answer C Explanation	AnswerCExp::See calculation in the explanation
Answer D	AnswerD::13.9 mmHg·min/L
Answer D Explanation	AnswerDExp::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::See calculation in the explanation
Right Answer	RightAnswer::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. Educational Objective: Pulmonary vascular resistance is given by the change in pressure across the pulmonary vasculature divided by the cardiac output. References: First Aid 2014 page 599]]
Approved	Approved::Yes
Keyword	WBRKeyword::Lung, WBRKeyword::Vasculature, WBRKeyword::Pulmonary hypertension, WBRKeyword::Hemodynamics, WBRKeyword::Hemodynamic
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::