Flashcards in Week 5 RM Deck (24)
Is V/Q ratio higher at the apex or the base?
What is the normal hydrostatic pressure of pulmonary capillaries?
What is the net filtration pressure of movement of fluid out of capillaries? (Capillary pressure + hydrostatic pressure of interstitium)
15mmHg (+7mmHg push out and -8mmHg suck out)
What happens on a pulmonary embolism to the ventilation and perfusion?
There will be ventilation of air but not perfusion of blood. V/Q will equal infinity. Alveolar air will equal that of the atmosphere because there is not any gas exchange . Co2 levels will equal 0
Explain the venous admixture or shunt
Mixing of oxygenated arterial blood with poorly oxygenated or venous blood. (Explain further!!!!!!!)
What is the normal time in seconds for the cardiac cycle!
How far beyond the right ventricle does the pulmonary artery run before it divides into its left and right branches?
How does the thickness and diameter of the pulmonary arteries compare to the aorta and systemic counterparts?
Walls are 1/3 the thickness of the aorta. Thinner walls and wider diameter
In comparison to the systemic circuit, describe the pressure and resistance of the pulmonary circulation.
Pulmonary vascular pressure and resistance is much lower than the system circuit
What is the pressure in the pulmonary artery?
What is the pressure in the pulmonary veins?
What is the average volume of blood in the lungs at any time and how much of it is involved in gas exchange at one time?
Approx 450ML. ~80mL is involved with gas exchange at one time.
True or false, blood flow to the lungs is essentially equal to cardiac output
How does the lung ensure that adequate aeration of the blood occurs?
By blood being directed to areas of the lung where the alveoli are best oxygenated
Describe hypoxia pulmonary vasoconstriction
• PAO2 (pulmonary artery oxygen levels) decreases below normal
• Causes adjacent blood vessels to constrict for 3-10 minutes vascular resistance may increase more than 5 fold with extremely low oxygen levels
• Changes in vascular resistance promotes blood flow to areas of lung that are better ventilated this is an automatic mechanism for matching blood flow and ventilation
What's two factors determine oxygen and carbon dioxide levels?
rate of alveolar ventilation and rate of alveolar gas exchange
What happens to the V'A/Q ratio when there is adequate ventilation but little/no perfusion?
Ratio is infinity
Where anatomically is the ideal VA/Q ratio?
In line with the heart. Above is too high oxygen and below is too poor oxygen
Describe the 3 Zones of the lungs
Zone 1: no blood flow during any part of cardiac cycle. Alveolar capillary pressure never exceeds alveolar air pressure.
Zone 2: intermittent blood flow when pulmonary arterial pressure peaks. Diastolic lower than alveolar pressure so flow is intermittent.
Zone 3: continuous blood flow , alveolar capillary pressure always exceeds the alveolar air pressure
Normal lungs have zones 2 & 3; zone 1 blood flow only occurs under abnormal conditions
During heavy exercise, blood flow to the lungs can be increased 4-7 fold. State the 3 ways this extra flow is accommodated for
Extra flow is accommodated in three ways:
1. Increasing number of open capillaries (up to 3x increase)
2. Distending all capillaries (more than 2fold increase)
3. Increasing pulmonary arterial pressure
The ability of the lungs to accommodate increased flow helps to prevent a significant rise in pulmonary pressure
What keeps the alveoli dry?
• The negative pulmonary interstitial pressure helps to keep the alveoli dry
• There are pores between the alveolar epithelial cells though which proteins as well as fluid and electrolytes can pass
•when excess fluid appears in the alveoli, is sucked mechanically into the interstitial space and then into the lymphatic vessels
What are some causes of pulmonary edema and when does it occur?
• Will occur when pulmonary interstitial fluid pressure rises from the negative to positive range
• May be caused by left sided heart failure, infections , myocardial infarctions , trauma etc
• Rapid leakage of plasma proteins and fluid out of the pulmonary capillaries into the interstitial spaces and alveoli
What is the edema safety factor and what's happens if it is surpassed?
• For a significant edema to occur, pulmonary capillary pressure must normally rise above the colloid osmotic pressure - therefore there is a safety factor of around 21mmHg
• When pulmonary capillary pressure remains elevated chronically, lymph vessels expand and increase their capacity to carry fluid away
• When pulmonary capillary pressure does rise, even slightly above the safety factor level, lethal pulmonary edema can occur within hours (20-30 minutes if pressure is greater than 25mmHg above the safety factor)