A 43-year-old woman comes to the emergency department due to nausea and vomiting with left-sided chest pain. She states that the pain began 30 minutes ago while playing with her children. She has a history of dyslipidemia and hypertension. The patient's mother died from a myocardial infarction at age 51. Physical examination reveals mild tenderness to palpation over the left chest. An ECG and cardiac biomarkers are normal. She is scheduled for an exercise stress test. During the test, which of the following parameters is likely to be the most similar between the systemic and pulmonary circulation?

Question

A 43-year-old woman comes to the emergency department due to nausea and vomiting with left-sided chest pain.  She states that the pain began 30 minutes ago while playing with her children.  She has a history of dyslipidemia and hypertension.  The patient's mother died from a myocardial infarction at age 51.  Physical examination reveals mild tenderness to palpation over the left chest.  An ECG and cardiac biomarkers are normal.  She is scheduled for an exercise stress test.  During the test, which of the following parameters is likely to be the most similar between the systemic and pulmonary circulation?

Quizplus · Accepted Answer

In order to maintain blood flow through the body, the blood flow (mL/min) in the pulmonary circulation must closely match the blood flow in the systemic circulation. This is true for conditions of both exercise and rest as the circulatory system is a continuous circuit. If the flow of blood through the pulmonary circulation is less than the flow of blood through the systemic circulation, the left ventricle would soon empty completely. Alternately, if the flow of blood is significantly greater in the pulmonary circulation than it is in the systemic circulation, the left ventricle would soon be overloaded. The major exception to this is the bronchial circuit, which supplies oxygen and nutrients to the pulmonary parenchyma from the systemic circulation but drains mostly to the left atrium as opposed to the right atrium (creating a right to left shunt that acts as a partially independent circuit). However, this typically accounts for <5% of the systemic cardiac output. (Choice A) The arterial oxygen contents of the pulmonary and systemic circulations are dramatically different due to deoxygenated blood in the pulmonary arterial circulation and oxygenated blood in the systemic arterial circulation. (Choice B) Although the resistance of the pulmonary vasculature may be increased in some circumstances (eg, high altitudes, idiopathic pulmonary hypertension), the arterial resistance in the systemic circulation is considerably higher in all scenarios. (Choices D, E, and F) The mean arterial pressure, diastolic arterial pressure, and driving pressure for blood flow (difference between mean arterial and venous pressures) are considerably different in the pulmonary and systemic circulations both at rest and during exercise. The normal mean systemic arterial pressure ranges between 70-100 mm Hg and the normal mean pulmonary arterial pressure is approximately 14 mm Hg, whereas venous pressures in both circuits approach 0 mm Hg. Due to the low resistance of the pulmonary circuit, only a small difference between arterial and venous pressures is needed to maintain blood flow compared to the relatively large difference needed between systemic arterial and venous pressures. Educational objective: The circulatory system is a continuous circuit, and therefore the volume output of the left ventricle must closely match the output of the right ventricle. This balance is necessary to maintain continuous blood flow through the body and exists both at rest and during exercise. __________ References: Organ-specific physiological responses to acute physical exercise and long-term training in humans. (http://www.ncbi.nlm.nih.gov/pubmed/25362636)

A 43-Year-Old Woman Comes to the Emergency Department Due to Nausea