Blood Flow; HPV; Shunts Flashcards
What volume of blood is found in the pulmonary circuit? This pulmonary volume represents what percent of the total circulating blood? How many ml of blood are in the pulmonary capillaries, pulmonary arteries and pulmonary veins?
Approximately 450 ml, or 9%, of the total blood volume is in the pulmonary circuit. 70 ml is in the capillaries and the remainder of the 450 ml (380 ml) is divided equally between arteries (190 ml) and veins (190 ml).
Compare pulmonary arterial blood pressure and intra- pulmonary pressure in Zone I of the lung. Is Zone I perfused? Why or why not?
Intrapulmonary pressure exceeds pulmonary arterial blood pressure in Zone 1. Zone I is not perfused because pulmonary artery pressure is less than alveolar pressure.
The alveolar capillaries are collapsed.
Compare pulmonary arterial blood pressure and
intrapulmonary pressure in Zone II of the lung. Is Zone II perfused? What is the perfusion pressure gradient in Zone II?
Pulmonary arterial blood pressure is higher than alveolar pressure in Zone II. Zone II is perfused. The perfusion pressure gradient in Zone II is pulmonary arterial blood pressure minus alveolar pressure.
How do pulmonary arterial and venous blood pressures compare to intrapulmonary pressure in Zone III of the lung? What is the perfusion pressure gradient in Zone III?
Pulmonary arterial and venous pressures exceed alveolar pressure in Zone III. The perfusion pressure gradient in Zone III is the difference between the pulmonary arterial blood pressure and the venous blood pressure.
What is a right-to-left shunt?
A right-to-left shunt occurs when some portion of the right heart’s output is shunted past the alveoli to the left ventricle.
What is an intrapulmonary shunt? Is an intrapulmonary shunt a right-to-left or left to-right shunt?
An intrapulmonary shunt is present when blood passes from the pulmonary artery to the pulmonary vein through capillaries of unventilated or poorly ventilated alveoli. This is a right-to-left shunt.
State the major consequence of a shunt.
A shunt causes a decrease in Pa02. Hypoxemia and tissue hypoxia result if a shunt develops and the patient is breathing room air and possibly also when breathing a high inspired oxygen concentrations.
What is the major consequence of deadspacing?
An increase in PaC02 is a consequence of mild deadspacing. With severe deadspacing, Pa02 will also decrease.
Describe the effect of alveolar hypoxia on the pulmonary circulation. What is this effect called?
In response to alveolar hypoxia, the pulmonary vessels constrict so that there is reduced blood flow to the unoxygenated alveoli. This is hypoxic pulmonary vasoconstriction (HPV).
What is the importance of hypoxic pulmonary’ vasoconstriction (HPV)?
Hypoxic pulmonary vasoconstriction (HPV) decreases shunt. HPV reduces perfusion to unventilated or poorly ventilated alveoli, and reduces the severity of the shunt.
What is the normal PA02-Pa02 gradient when breathing room air? When breathing 100% 02?
The PAO2-PaO2 gradient is normally about 5-15 mmHg (up to 25 mmHg is acceptable) when breathing room air. The PA02-Pa02 gradient is normally < 100 mmHg when breathing 100% 02.
The PA02-Pa02 gradient reflects what? The PaC02-PAC02 gradient reflects what?
The PA02-Pa02 gradient reflects the degree of right-to-left shunt. There normally is a small right-to-left shunt, which is reflected by a small PA02-Pa02 gradient of 5-15 mmHg. The PaC02-PAC02 gradient reflects deadspacing. Normally, there is a small PaC02-PAC02 gradient of 2-10 mmHg, when breathing room air.
When does the PA02-Pa02 gradient increase? PaC02-PAC02 gradient?
The PA02-Pa02 gradient increases any time shunting increases. The PaC02-PAC02 gradient also increases when deadspacing or shunting increases.
What is indicated by an abnormally large alveolar-arterial partial pressure difference (PA02-Pa02)?
A pathological right-to-left shunt (intrapulmonary or intracardiac).
What measurement is better than the PA02-Pa02 gradient for assessing right-to-left shunt when the patient is breathing a high Fi02?
The Pa02/PA02 ratio.
