12.6 D Flashcards
What is the Fick Method?
the gold standard for measuring cardiac output
What does the Fick Method essentially say?
the amount of blood flowing through the systemic circulation (cardiac output) is equal to the rate of oxygen consumption by the systemic organs divided by the difference in oxygen concentration in arterial and venous blood
Under normal conditions, how much oxygen is in arterial blood?
20 mL oxygen per 100 mL blood
Under normal conditions, how much oxygen is in venous blood?
15 mL oxygen per 100 mL blood
According to Fick’s law, if blood flow to the organs is increased but oxygen consumption remains constant, what must be true?
less oxygen will be removed form each 100 mL of blood
According to Fick’s law, if blood flow to the organs remains constant but oxygen consumption increases, what must be true?
more oxygen will be removed from each 100 mL of blood
What is the Fick Equation?
CO = (consumption)/(arterial O2 content - venous O2 content)
Because of clinical challenges, what is the modified Fick Equation?
CO = (oxygen uptake)/(arterial O2 content - venous O2 content)
What is the thermal dilution technique?
an indirect Fick method used to measure cardiac output by injecting cold saline and measuring temperature downstream with a thermocouple
The magnitude of a shunt is equal to what?
the difference between pulmonary blood flow and cardiac output
What happens to the blood O2 content in the area where a shunt originates?
it isn’t altered
What is the role of renin?
to increase circulating levels of angiotensin II
What is angiotensin II?
a potent vasoconstrictor
In addition to being a vasoconstrictor, angiotensin II triggers release of what substance?
aldosterone
What is aldosterone?
a molecule that promotes resorption of sodium and water from the kidney
What happens to total blood volume in an individual with a ventricular septal defect?
it increases because low LV SV triggers release of aldosterone
How does blood volume in the left ventricle change with a interventricular shunt?
it is initially decreased but the resulting decrease in MAP and release of aldosterone restores and even raises it
Why does the left ventricle hypertrophy when there is an interventricular shunt?
because aldosterone raises the overall blood volume to compensate
Describe the MEA of a newborn compared to a healthy adult?
newborns have experience right ventricular hypertrophy and a right axis deviation at birth because of the high resistance to flow in their lungs
What happens to end diastolic volume of the left ventricle in someone with patent ductus arteriosus?
it is increased
Shunts always result in what compensation? How does this affect the heart?
- increase in blood volume
- hypertrophy of the left atrium and ventricle, and often the right ventricle
