Pulm Physio Flashcards
What distiguishes V/Q mismatch from shunt?
Supplemental O2 correct the hypoxemia by raising the PO2 in blood coming from regions with a V/Q ratio
(supplemental O2 does not correct / improve conditions from a shunt)
What are the consequences of V/Q Mismatch?
- Low PaO2 (hypoxemia)
- Increased A-a Gradient
- Hypoxemia is corrected with supplemental O2,
- Also, any state of PaCO2:
- Normal PaCO2 (eucapnia)
- Increased PaCO2 (hypercapnia) or
- decreased PaCO2 (hypocapnia)
Explain Shunt and Dead Space Ventilation
- Blood Goes to Parts of the lung that do not have O2 to give it
- Blood does not go to parts of the lung that have oxygen
Explain Anatomical and Physiological Shunts
Physiological Shunt:
- Situation within lungs
- due to diffusion defect or obstruction to alveolus
- Seen in Acute Respiratory Distress Syndrome (ARDS)
- Pulm cap see no O2 and remain deoxygenated bc alveolus has diffusion defect
- No amount of O2 will correct shunting!
Anatomical Shunt:
- Shunt due to cadiac defects: cyanotic heart diseases
- Deoxygenated blood never saw the lungs
What is a shunt?
- desaturated blood bypasses oxygenation at the alveolar-capillary level
- increased PAO2 - PaO2 (A-a gradient)
- Refractory to supplemental O2
- Ex: intracardiac R–> shunt, ARDS
What are the consequences of a shunt?
- Low PaO2 (Hypoxemia)
- Increase A-a Gradient
- Low PaCO2 (Hypocapnia)
- Refractory to oxygen therapy
Dead Space Ventilation
Dead Space Ventilation (VD): Volume of air per minute that enters the conducting airways and does not participate in gas exchange
- VD: results in hypercapnia and hypoxia
Alveolar Ventilation (VA): Volume of air per minute that enters or exits the alveoli of the lung and participates in gas exchange
NB: if you don’t have perfusion CO2 cannot be perfused so you always have hypercapnia with Dead Space Ventiltation
Total Ventilation (VE): sum of alveolar and dead space ventilation
What are the changes in echocardiogram in RV overload
- Dilated RV
- Compressed D-shaped LV
- Flattended septum
- Increased pericardial constraint
What is the effect of Gravity on perfusion
- gravity is a passvie factor that affects relative perfusion of different regions of the lung
- pressures are greater in the more gravity dependent regions of the lung, and resistnace to blood flow is lower in lower regions owing to more recruitment and distention of vessels in these regions
- perfusion ceases when alveolar pressure is equal to pulmonary arterial pressure
- so when alveolar pressure > pulmonary arterial pressure, ther eis on blood in that region (zone 1)
- Zone 1 is ventilated but not perfused = ALVEOLAR DEAD SPACE
If Pa (pressure of alveoli) > PA (pressure of arteriole), what would happen?
Alveolar pressure would theoretically collapse the alveoli so you would no longer have efficient blood flow to that region
Zones of the Lung
Pressures in the pulm circulation relative to pressures in the surrounding alveoli
- Blood flow is greatest in the dependent regions of the lung
- Therefore the pressures in the dependent circulation relative to each other are greatest in the dependent regions: Zone 3
- Distension of the alveoli is greatest at the apicies
- Perfusion is least at that point –> zone 1
- Physiologic boundaries*
- *If you increase alveolar pressures in any region of the lung, that region would function as if it were in zone 1 (as if it has more alveolar perfusion than pulmonary distension)*
- With alveolar distension (where pressures are higher than pressures in capillaries) you will not have functional gas exchange, that is dead space.*
What is the effect of exercise on cardiac output and pulmonary artery pressure?
During exercise, cardiac output and pulmonary artery pressure increase anda ny exisiting zone 1 should be recruited to zone 3.
(true of situtations of incrase Cardiac output and increased pressures in zone 1)
Hypoxic Pulmonary Vasoconstriction
- alveolar hypoxia or atelectasis causes an active vasoconstriction inthe pulmonary circulation at that level
- occurs locally in the area of alveolar hypoxia
- diverts mixed venous blood flow away from poorly ventilated ares of the lung by locally increasing vascular resistance
- not a very strong response because ther eis so little smooth muscle in the pulmonary vasculature
What conditions may lead to pulmonary edema?
- increased capillary endothelium permeability (infections, toxins)
- increased capillary hydrostatic pressure (LV failure)
- Decreased interstituial hydrostatic pressure (negative pressure pulmonary edema)
- Increased reflection coefficient
- decrease in plasma colliod pressure (hypoproteinemia)
- increased interstitial colloid osmotic pressure
- lymphatic insufficiency
- any fluid that makes its way into the pulmonary interstitum must be removed by the lymphatic drainage of the lung
- volume of lymph flow is capable of increasing 10 fold under pathologic conditions –> if overhwlemed –> pulmonary edema
How is ventilation normally regulated?
- Vl is normally regulated by CO2 sensitive chemoreceptors in the central respiratory center to maintain PaCO2 within a normal range.
- Changes in Vl at constant metabolic rates affects PsCO2 per the alveolar ventilation equation: [PaCO2 - k* VCO2/V]
- An increase in PaCO2 normally increases ventilation.
Control Of Breathing During Exercise
- Phase I:
- abrupt increase may reflect anticipatory response
- Phase II:
- gradual increase invovles a variety of afferents
- Phase III:
- “steady-state”- reflects a precise matching of ventilation to metabolism below “anerobic threshold”
- ie: blood gases are unaltered
