Pulmonary Circulation Flashcards
Despite having the entire cardiac output flowing through the lung, the pressure is maintained relatively _____. Pulmonary vascular resistance is 10x ______ than TPR which contributes to the _______ in pressure.
Mean pulmonary pressure is ___mmHg. >____mmHg is hypertension & >____mmHg gives pulmonary edema & diffusion problems (increased filtration due to increased hydrostatic pressure).
Despite having the entire cardiac output flowing through the lung, the pressure is maintained relatively low. Pulmonary vascular resistance is 10x lower than TPR which contributes to the decrease in pressure.
Mean pulmonary pressure is 11mmHg. >20mmHg is hypertension & >25mmHg gives pulmonary edema & diffusion problems (increased filtration due to increased hydrostatic pressure).
Describe afterload
Afterload is the tension or stress developed in the wall of the left ventricle during ejection. In other words, it is the end load against which the heart contracts to eject blood.
Afterload is readily broken into components; aortic pressure and/or the pressure the ventricle must overcome to eject blood. The greater the aortic/pulmonary pressure, the greater the after load on the left/right ventricle, respectively.
The afterload of the right ventricle is less than the afterload of the left ventricle; hence, the right ventricle does less stroke work. This is why the walls of the right heart are thinner since they pump against a smaller afterload pressure.
Explain the abnormal right-left side anatomic shunt
If there is a portion of the lung suffering ischemia since the airways are blocked & venous blood goes through it, that means that this mixed venous blood was not oxygenated & bypassed the ventilation system. Normal anatomical shunts are left-left shunts (aorta to left atrium).
What is the physiological shunt?
The physiological shunt is the sum of the normal anatomical (left left) shunt and any pathological intrapulmonary shunt (right left)
Pathological right to left shunts can result in ______ without much ______ (there may or may not be though). Breathing gas enriched with Oxygen will ____ help patients with abnormal right to left shunts because ____.
Pathological right to left shunts can result in hypoxemia without much hypercapnea there may or may not be though). Breathing gas enriched with Oxygen will not help patients with abnormal right to left shunts because the blood is being bypassed in the shunt & will not be oxygenated anyway (this case is similar to patients with diffusion problems that have hypoxia without hypercapnea).
The increase in hypoxia over hypercapnia occurs because the oxygen dissociation curve has a steeper slope.
Pulmonary arteries & veins are both ______.
thin walled
Give the equation relating CO & pulmonary vascular resistance, PVR.
(PPA - PLA) = CO x PVR
PPA = pressure pulmonary artery
PLA = pressure left atrium
P = Q x R
If you increase the pressure in the passive pulmonary vessels (like by increasing CO), the radius _____, & the _____ decreases.
If you increase the pressure in the passive pulmonary vessels (like by increasing CO), the radius increases, & the resistance decreases (resistance is inversely proportional to the 4th power of the radius–since the pulmonary vessels are passive, resistance is determined by changes in volume).
Discuss the resistance of the pulmonary vessels & capillaries during inspiration & expiration
During inflation or inspiration, the intrapleural space (outside the lungs & in the chest wall) becomes negative & we inflate the alveoli & their volume increases. The extra-alveolar pulmonary vessels (arteries & veins) also get inflated, so their resistance goes down; however, the alveolar vessel capillaries get stretched & their luminal diameters decrease & their resistance increases. The opposite occurs during expiration. The resistances of the alveolar & the extra-alveolar vessels are in series, so you can add them.
For patients on ventilators, we want to not hyperinflate their lungs–we should inflate with the minimum volume to keep them @ FRC.
For the net effect or total resistance, resistance goes up when we inspire & goes down when we expire.
See figure pg. 224.
Note pulmonary vasoconstrictors & dilators on pg. 225
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Discuss the effect of gravity on the lung’s circulation
The blood falls down due to gravity & since the sympathetic system does not vasoconstrictor like the effect on when standing up from sitting down–we have more flow @ the base of the lung.
Gravity is a big effect.
The distribution of blood flow in the lungs is affected by gravitational effects on arterial hydrostatic pressure. Thus, blood flow is highest at the base, where arterial hydrostatic pressure is greatest and the difference between arterial and venous pressure is also greatest. This pressure difference drives the blood flow.
Mitral valve or aortic valve stenosis will cause pulmonary _______ and congestive heart failure. Oxygen _____ flow adequately in pulmonary edema.
Mitral valve or aortic valve stenosis will cause pulmonary edema and congestive heart failure. Oxygen cannot flow adequately in pulmonary edema.
Hypoventilation, right-to-left cardiac shunt, and ascent to high altitude all cause ______ by decreasing arterial _____. Of these, only ______ is associated with an increased A-a gradient, reflecting a lack of O2 equilibration between alveolar gas and systemic arterial blood.
Hypoventilation, right-to-left cardiac shunt, and ascent to high altitude all cause hypoxia by decreasing arterial Po2. Of these, only right-to-left cardiac shunt is associated with an increased A-a gradient, reflecting a lack of O2 equilibration between alveolar gas and systemic arterial blood. In right-to-left shunt, a portion of the right heart output, or pulmonary blood flow, is not oxygenated in the lungs and thereby “dilutes” the Po2 of the normally oxygenated blood. With hypoventilation and ascent to high altitude, both alveolar and arterial Po2 are decreased, but the A-a gradient is normal.
Hypoxia is defined as decreased O2 delivery to the tissues. It occurs as a result of decreased blood flow or decreased O2 content of the blood. Decreased O2 content of the blood is caused by decreased hemoglobin concentration (anemia), decreased O2-binding capacity of hemoglobin (carbon monoxide poisoning), or decreased arterial Po2 (hypoxemia).
**ANSWER WILL BE CORRECTED–Discuss chemicals that cause pulmonary arterioles & venules to constrict.
Histamine constricts bronchiolar smooth muscle around the airways but is a vasodilator. Increased blood flow does not elicit constriction. Two answers are correct: histamine and increased blood flow. I will edit the question on Monday.
The systemic and pulmonary circuits are connected in ______ and thus the flow must be ______ in the two circuits. Since the flows are the same, the flow ratio must be ____ (aorta/pulmonary artery). The pulmonary circuit is a ____ pressure, high flow circuit and consequently must be maintained as ______ pathway. Therefore, _____ pressures in the systemic circuit are due to the fact that it is a _____ resistance pathway. Most of our blood volume is in the _______ circuit.
The flow from the left ventricle approximately ______ the flow from the right ventricle. Also, right and left ventricular stroke volumes are approximately ______.
The systemic and pulmonary circuits are connected in series and thus the flow must be equal in the two circuits. Since the flows are the same, the flow ratio must be 1.0. The pulmonary circuit is a low pressure, high flow circuit and consequently must be maintained as low-resistance pathway. Therefore, higher pressures in the systemic circuit are due to the fact that it is a higher resistance pathway. Most of our blood volume is in the systemic circuit.
The flow from the left ventricle approximately equals the flow from the right ventricle. Also, right and left ventricular stroke volumes are approximately equal.
