Pulmonary Circulation Flashcards
What are some differences between pulmonary and systemic circulations?
There is minimal basal tone in pulmonary vessels making it a non-resistant system. Passive distension with increased pressure or flow without significant auto regulation.
What happens to vessels in the lung when exposed to hypoxic conditions?
The vessels vasoconstrict!! This is different than every other tissue in the body.
What are the two shunts talked about in the pulmonary system?
There is a pathological right to left shunt in which blood goes from the RV to the LV without being oxygenated in the lungs. There is a normal left to left shunt in which blood comes out of the base of the aorta and goes through the bronchial circulation and then back to the LV.
What is a physiological shunt?
It is the sum of normal anatomic shunt plus any pathological intrapulmonary right-to-left shunt that occurs when airways are blocked, resulting in hypoxemia.
What is mean pulmonary arterial systolic pressure (P_pa)? What pressure is classified as pulmonary hypertension? What pressure give pulmonary edema?
12 mmHg is normal. 20 mmHg is hypertension. 25 mmHg give edema, resulting in a diffusion problem.
What is the formula for Pulmonary vascular resistance (PVR)?
PVR = (Ppa - Pla) / CO
Ppa measured with Swan Ganz catheter give the pressure in the pulmonary artery.
Pla is the pressure in the left atrium given by wedge pressure.
CO is cardiac output
PVR is about 10 times less than TPR
Because of the lack of auto regulation what happens when flow or pressure increase?
PVR decreases. In contrast resistance in a systemic vascular bed increases as a compensation to increased perfusion pressure. The decrease of PVR during exercise is due to passive distension of perfused regions as well as by recruitment of additional capillaries.
How do alveolar vessels change during breathing?
Alveolar vessels open and close in response to changes in capillary pressure relative to alveolar pressure. These vessels are stretched closed during inflation.
How do extra-alveolar vessels respond to changes in intaluminal pressure?
The vessels expand during inflation due to decreased intrapleural pressure.
When is PVR minimum?
At FRC. The alveolar and extra-alveolar vessels are in series and have additive resistance. There is a U shaped relationship between lung volume and PVR. PVR is smallest near FRC and increases as transpulmonary pressure increases or decreases.
In a standing individual where is blood flow the greatest in the lung and why?
At the base due to gravity and passive distension. 6 times greater at the base than the apex.
What is zone 1 of the lung (in a standing individual)?
If pressure in the capillaries fall below that of Palv then the capillaries will collapse flow stops. Zone 1 is not present in healthy people but it could develop if pressure falls due to blood loss or low CO. Zone 1 is ventilated but not perfused.
What is zone 2 of the lung (in a standing individual)?
The middle of the lung where flow is determined by the pressure difference between Ppa and Palv. The flow is similar to the flow in a collapsible tube and gradually increases as you go down it. Pv has no effect on this zone
What is zone 3 of the lung (in a standing individual)?
This is the area where Pv exceeds Palv, resulting in the capillaries becoming wide open and flow is then determined by the difference in Ppa - Ppv. The driving pressure is constant, the resistance decreases and the row increases going down this zone.
What are the effects of a right-to-left shunt?
Unlike diffusion problems, breathing gas enriched in oxygen will not help patients with abnormal right to left shunts. The shunt results in more hypoxemia than hypercapnia.
