20/21 - Pulmonary Vascular Disease & Cases Flashcards
What is an embolus?
A detached intravascular solid, liquid, or gaseous mass carried by the blood to a site distant from its point of origin.
Inevitably, emboli lodge in small blood vessels causing occlusion.
What are the different types of emboli?
- Thrombus
- Gas/air
- Fat
- Tumor
- Amniotic fluid
- Bone marrow
Where do pulmonary emboli originate?
Vast majority originate in the legs (deep veins); some in the pelvis or abdomen.
In-site pulmonary thrombosis are rare but can happen with pre-existing pulmonary HTN.
Where do thrombi in the deep veins of the legs go?
To the right side of the heart through the superior or inferior vena cava to the right atrium and right ventricle.
It then lodges in one of the branches of the pulmonary artery and obstructs blood flow which causes an infarction in the lung.
What is Virchow’s Triad?
The three factors that contribute to thrombosis:
Endothelial injury: ulcerated plaque, trauma, inflamm vascular injury (vasculitis), indwelling deviecs.
Hypercoagulability: Aneurysms, acute MI, atrial fibrillation, decreased mobility, surgery.
Stasis: Favtor V leiden, prothrombin gene mutation,
What does the clinical significance of PE depend on?
- Extent to which the pulmonary artery blood flow is obstructed.
- Size of occluded vessel
- Number of emboli
- Pre-existing cardiopulmonary status
- Release of vasoactive substances such as thromboxane A2 from activated platelets.
What are some ways that there is pulmonary compromise with a PE?
- Ventilation of non-perfused area
- Increased dead space
- Increased work of breathing
- Worsening ventilation-perfusion matching
- Hypoxemia, hypercapnia, resp. failure
What are some ways that there is cardiac compromise with a PE?
- Increased resistance to flow of blood from RV through to LA.
- Acute RV failure
- Remember that RV and LV are connected in series
- RV falis; LV gets progressively under-filled
- Shock/death
What are clinical sympatoms associated with PE? How is it diagnosed?
Chest pain, dyspnea, hypotension, low grade fever (from plately activation and cytokine release)., cough, hemoptysis, sudden cardiac death.
Usually diagnosed with CT scan of the chest.
How are PEs treated?
Usually treated with anticoagulation such as heparin and rarely throbolysis.
This is because heparin prevents more clots from forming and the current clot from getting bigger. It also allows time for the body to break fown the embolus itself.
How can pulmonary infarction occur?
Smaller emboli travel to the peripheral vessels and may cause hemorrhage.
Very rarely, the emboli cause infarction. Bronchial circulation comes from the aorta, and sustains the pulmonary parenchyma.
- This is not very common due to dual blood supply (bronchial and pulmonary)
Where are pulmonary infarcts more common and why?
Most affect the lower lobes because that’s where there’s more perfusion.
- typically wedge shaped extending out from the ischemic focus to the periphery
- usually hemorrhagic infarct
- Eventually heal and leave a small scar
What is the difficulty in diagnosing a PE?
The signs and symptoms are non-specific and therefore you need to have a high clinical suspicion of PE in order to rule out other potential causes of the symptoms.
What do pulmonary emboli cause mechanistically?
- Hypoxia, by worsening ventilation/perfusion mismatch
- Release of local inflamm mediators which cause bronchocontriction
- Strain on RV (has to pump across a clogged up circulation)
- Decreased venous return to left ventricle due to above
- Potential cardiac collapse and sudden death
Why might you not want to diagnose PE with a CT?
CT chest is may be contraindicated due to renal failure (note that diagnosing PE requires IV contrast)
**this was from the case in class and it may not always be the case**
What are four characteristics of pulmonary circulation?
- Low pressure
- Low resistance
- Distensible
- Recruitable (less perfused areas are able to be recruited)
How does Ohm’s Law apply to hemodynamics?
V = I x R
Voltage difference = flow or current x resistance of the circuit
Or in other words:
Pressure difference = flow of blood x resistance of the circuit
Using what we know about Ohm’s law and how it applies to blood hemodynamics, how do we calculate the mean pulmonary artery pressure?
Pressure difference = flow of blood x resistance of the circuit
Pressure difference is the mean pulmonary artery pressure minus the mean left atrial pressure.
Flow of blood is the CO
Resistance if the pulmonary vascular resistance.
This means that PA - LAP = CO x PVR and THUS:
Mean PA pressure = (CO x PVR) + Left atrial pressure
What is the calculation for mean pulmonary artery pressure?
Mean PA pressure = (CO x PVR) + left atrial pressure
What three things can cause pulmonary artery pressure to be high?
Well, we know that mean PA pressure = (CO x PVR) + Left atrial pressure
Therefore, PA pressure can be high with:
- Increased CO
- Increased PVR
- Increased left atrial pressure
The commonest (his words) cause of pulmonary HTN is, was, and ALWAYS will be…?
LEFT HEART DISEASE! Because left atrial pressure increases in left heart disease.
This is because Mean PA pressure = (CO x PVR) + left atrial pressure
Left heart disease can be caused by CAD, LV failure, hypertensive heart disease, valvular heart disease (mitral and/or aortic stenosis or regurg)
What can cause increased pulmonary vascular resistance?
- Presence of thrombi (recall that resistance varies inversely to the fourth power of the radius)
- Hypoxia (recall that hypoxia causes pulmonary vasoconstriction)
Thus chronic pulmonary emboli and chronic lung disease with chronic hypoxia may cause pulmonary HTN by increasing resistance.
What is pulmonary arterial HTN (PAH) and who is it seen in?
There’s a small subgroup of pts who have clinical evidence of pulmonary HTN with no left heart disease; no chronic lung disease, and no blood clots.
- This was formerly called “primary” pulmonary HTN and now is simply called pulmonary arterial HTN.
- Severe conditions are assocaited with this primary PH.
What clinical conditions are associated with primary pulmonary HTN (aka pulmonary arterial HTN)?
- Connective tissue diseases
- Vasculitis
- HIV
- Cirrhosis with portal HTN
- Congenital heart disease (tetralogy)
- Drug abuse
- Trily idiopathic
- Genetic/familial
