DISEASES OF THE PULMONARY VASCULATURE



Anatomy:  The lung has a dual vascular supply with blood flow from the pulmonary artery and 

from the bronchial arterial tree.  This is important in that the consequences of a blockage of 

the pulmonary vascular supply will depend somewhat on the state of the bronchial circulation.



EMBOLI

Definition:  An embolus is an intravascular mass which travels from its source to its point of 

impaction.  It can be of three types: solid, liquid, gas.  Solid emboli are the most common, 

and of these, the most common are thrombo-emboli, and the majority of the following relates 

specifically to thrombo-embolic disease.  However, it is worth remembering that emboli of 

foreign material and tumor occur in their appropriate circumstances.  The most common liquid 

emboli are fat or amniotic fluid.  Gas emboli are due to the injection or suction of gaseous 

substance into the vascular tree.



In pulmonary embolism, there are several physiological consequences:

A) reduction in the cross-sectional area of the pulmonary arterial bed.  This will increase the 

resistance to blood flow, and leads to increased stress on the right heart.  Tachycardia and 

decreased cardiac output can occur.  The extent of the embolic obstruction is the key; in 

normal states, more than 50% of the vascular bed must be obstructed before a significant 

increase in pulmonary arterial pressure will occur.  However, in subjects with additional 

disease (pulmonary or pulmonary vascular) relatively small additional changes due to the 

emboli may be sufficient to precipitate failure.



B) vascular spasm.  There are pharmacological consequences to acute emboli with release of 

vasoactive substances from the platelets in the embolus, or release of endothelin from the 

endothelium or vascular smooth muscle.



C) loss of surfactant in affected area:  This is not an acute event, occurring initially at 2-3 

hours, and most marked after 12 hours.  Frank atelectasis can occur within 24 to 48 hours.



D) infarction - see below



E) release of mediators:  This is particularly important in fat or amniotic fluid emboli which 

stimulate the release of mediators such as TNFà.  The most common complication of 

fat/amniotic fluid emboli is adult respiratory distress syndrome.  This is not a common 

complication of thrombo-embolic disease



Clinical manifestations:

1. sudden onset of unexplained dyspnea

This finding is related to the sudden addition of alveolar "dead space"



2. Pleuritis chest pain +/- hemoptysis

This is present only when infarction has occurred.



Physical Examination:

1. Is usually normal.

2. Atelectatic rales might be present if significant atelectasis has occurred.

3. Pleural rub or pleural effusion will not occur unless infarction has occurred.

4. Tachycardia: This is secondary to the increased resistance to flow

5. Murmur: These are present only in the case of massive emboli. A systolic ejection murmur 

can be found in the pulmonary area.  A systolic or continuous murmur can be heard over the 

lung fields.  These appear to be caused by turbulence of flow in the partially obstructed vessels 

(NOTE the key word here is partially)

6. Splitting of the second heart sound: This indicates severe embolic disease with pulmonary 

hypertension and failure of the right ventricle.

7. Fever: Really only occurs in conjunction with infarction.



Testing:

1. Blood gases:  Hypoxia is common, but is certainly not always present.  Potential 

mechanisms include:a) ventilation-perfusion disturbances; b) cardiac failure with a widened 

arterial-venous in O2; c) obligatory perfusion through hypoventilated lung zones

2. DLco: Depending on the extent of the emboli, DLco can be abnormal.   DLco is 

determined by the thickness of the alveolar wall, the area of lung available for gas exchange, 

and the reaction with hemoglobin (dependent upon the blood volume and the hemoglobin 

concentration).  Therefore, a normal DLco requires that ventilation be distributed evenly, that 

there is an appropriate alveolocapillary surface area, that there is capillary blood flow which 

matches ventilation, that there is appropriate amounts of hemoglobin, and that the alveolar 

interstitium not impede diffusion of oxygen (or carbon monoxide).  Alternatively, if ventilation 

is irregularly distributed (such as in small airway bronchiolitis), if there is decreased 

alveolocapillary surface area (such as post pulmonary resection or in emphysema), if there is 

abnormal capillary perfusion (such as in pulmonary emboli, or pulmonary hypertension), if the 

patient is anemic, or if the interstitium is altered by edema, increased cellularity or fibrosis 

(such as in pulmonary edema, interstitial inflammation, tumor cell infiltration, or interstitial 

fibrosis), the DLco will be abnormal.



3. ECG: Other than the tachycardia, the ECG is usually normal, unless emboli are extensive.  

In that case, there may be evidence of right ventricular strain with a right shift of the QRS axis 

and ST-T wave changes.



4. Hematologic / blood chemistry: These are usually normal.



5. Radiology: If an infarct is present, there are infiltrates in the area of infarct, corresponding 

to the extravasated blood.  With major emboli, there are some subtle findings.  There is 

redistribution of the blood supply to the unaffected part of the lung and this will be seen as 

increased density.  The nonaffected large pulmonary vessels may be dilated compared to the 

ones with the emboli which may suddenly "disappear" because of the absence of blood distal 

to the embolus. Remember that a normal chest radiograph does not preclude embolic disease.



6. Perfusion scans (scintiphotographs): Simply stated, these scans consist of the injection of 

gamma-emitting radionuclides either as microspheres or macroaggregated albumin.  A normal 

scan will show a homogeneous distribution of radioactivity in a configuration corresponding to 

the usual anatomy of the lung.  Any deviation represents an abnormality in blood flow.  If a 

scan is normal, it excludes significant pulmonary emboli.  If it is abnormal, the radiologist and 

clinician must pick from the variety of causes of abnormal blood flow, only one of which is 

embolic disease, the others being inflammation of any etiology, emphysema, carcinoma, 

fibrosis of any etiology.

When combined with a ventilation scan, mismatches between ventilation and perfusion can be 

determined.  A match between V and Q indicates parenchymal disease, while a mismatch is 

more characteristic of vascular obstruction (so long as it is the Q which is decreased). 

However, the latter is only to be considered if the abnormal scan is not in an area of 

parenchymal infiltrates, since V will usually be abnormal in an area of infiltration.



7. Angiography: Cardiac catheterization with injection of radio-opaque dye will image the 

pulmonary vessels (arterial and venous). This must be performed by experienced personnel to 

avoid artefacts of injection and interpretation.  Emboli will be visualized as filling defects or 

abrupt vessel cutoffs.



Complications and Sequalae:

1. sudden death: The patient dies in either an arrhythmia or in electro-mechanical dissociation.

2. infarct: The lung parenchyma obtains oxygenation from bronchial circulation and the 

pulmonary circulation.  The bronchial circulation supplies the airways up to the level of the 

distal conducting airways, but there are a large number of anastomoses to the alveolar 

capillary tree.  If there is appropriate cardiovascular function, the bronchial arterial supply can 

maintain the lung parenchyma in the absence of the pulmonary arterial circulation.  Emboli 

cause infarction only when the circulation is already inadequate (heart and lung disease are 

pre-existing).  Only approximately 10% of emboli actually cause infarcts.  Infarcts vary in size 

and characteristically extend to the pleural surface in a wedge shape distribution, with the 

broad base at the pleura.  An infarct is classically hemorrhagic, and there is an overlying 

pleural reaction.  Infarcts themselves can heal and condense to a relatively linear scar, or they 

can become superinfected and form septic infarcts with subsequent abscesses.

3. Pulmonary hypertension:  This is secondary to repeated showers of emboli.  As the emboli 

organize, the lumens of the pulmonary arteries become narrowed increasing resistance to 

blood flow. 



4. Sparse small or isolated emboli tend to organize forming webs (recannalization channels), 

or intimal plaques.  There would be no discernable consequences.



Therapeutic Goals::

1. immediate inhibition of the growth of thrombi at the source

2. promotion of embolic resolution

3. prevention of recurrence



PULMONARY HYPERTENSION

The pulmonary circulation is a low resistance and highly distensible vascular bed.  It is 

perfused by the entire cardiac output.  The normal pressure (in mm Hg) in the pulmonary 

artery is 20/12 (mean=15) at sea level, and 38/14 (mean=25) at approximately 15000 feet 

altitude. In general, a mean arterial pressure of 20 at sea level is considered abnormal, while 

at 15000 feet, a pressure of 25 is considered abnormal.  The left atrial pressure is 

approximately 5 regardless of altitude.  When one calculates pulmonary vascular resistance 

R=pressure difference across lungs/cardiac output per second.  It can be easily seen, 

therefore, that arterial resistance is increased at high altitude.  Another way to consider the 

relationship between pressure and flow is the simplistic formula P=Q X R, where Q 

represents flow and R represents the resistance to the flow.  

Pulmonary hypertension is a burden for the right ventricle, but it generally remains 

undetected until quite significant because of the tolerance of the right ventricle to afterload 

pressures.  Pulmonary venous pressures is considered abnormal when the left atrial pressure is 

greater than 12 mm Hg.  A pressure of 20 mm on an acute basis increases the risk of 

pulmonary edema.

Anatomy:  The large pulmonary arteries are elastic capacitance vessels, while the small 

muscular arteries and the partially muscularized arterioles are the resistance vessels.  Because 

of the large, distensible vascular bed in the normal individual, an increase in the cardiac output 

(such as during exercise) will increase the arterial pressure by only a few mm Hg.  In other 

words, at rest, the vascular bed maintains an intrinsic tone producing a baseline resistance.  

When cardiac output is increased, tone is decreased, and resistance to flow is decreased.

Etiologies of Pulmonary Hypertension:

There are many ways in which hypertension can be divided and sub-divided, and the 

classification below is not to be considered as other than a mechanism by which to understand 

how the pulmonary circulation can be altered. Remember the simple formula P=Q X R

1. Increases in flow:  These abnormalities include all of the congenital or acquired 

abnormalities which induce a left to right shunt of the blood flow into the right ventricle.



2. Increases in resistance

a) diseases of the main (elastic) pulmonary arteries: Obviously, a large saddle embolus sitting 

in the mainstem pulmonary arteries will cause an acute increase in resistance. Aneurysms of 

the pulmonary artery, congenital webs, vasculitis of the pulmonary artery, or tumors are all 

causes, but are very rare. The most common abnormality which would affect the large vessels 

is extrinsic compression because of tumor or inflammatory/fibrotic diseases.



b) lesions of the large muscular pulmonary arteries:  

1. embolic (of significant size) disease

2. pulmonary vasculitis



c) lesions of the medium to small muscular pulmonary arteries:

1. primary pulmonary hypertension:  This is a condition in which there is 

progressive alteration of the arteries of this size range with intimal fibrosis, 

muscular hyperplasia, muscular necrosis, intralumenal thrombi with plexogenic 

lesions.  The majority of the cases are idiopathic, but similar pathology is found 

after hypertension induced by anorexogenic drugs, and in patients with specific 

collagen vascular diseases (scleroderma), and in some patients with cirrhosis of 

the liver.

2. high altitude pulmonary hypertension

3. embolic disease (small sized/ particulates)



d) lesions of the arterioles/capillary bed:

1. emphysema

2. interstitial fibrosis

3. inflammatory diseases (bronchiectasis, sarcoid)

4. post lung resection

5. hypoventilation conditions

a) chest wall deformities

b) pleural restriction (fibrothorax)

c) neuromuscular conditions

d) marked obesity (Pickwickian syndrome)



e) lesions of the small veins

1. primary or secondary veno-occlusive disease



f) lesions of larger veins

1. external compression

2. congenital abnormalities

3. tumors



g) lesions of left side of heart

1. congenital abnormalities of left atrium

2. atrial myxoma 

3. mitral valve disease

4. left ventricular failure



Clinical Manifestations:

1. none

2. dyspnea, particularly with exercise:

This can be correlated with the knowledge of the resistance of the vascular bed.  When the 

vessels do not dilate with increasing cardiac output, resistance increases

3. chest discomfort:

This usually means that there is right ventricular strain.

4. syncope:

This may be related to vascular spasm or arrhythmia.  Patients with pulmonary hypertension 

appear prone to sudden death.

5. abdominal discomfort:

This is related to liver congestion 



Physical examination:

1. in early stages, no abnormalities can be found

2. evidence of right heart failure:

a) prominent jugular venous pulse

b) right ventricular heave

c) splitting of second heart sound

3. evidence of pulmonary edema:



Testing:

1. detection of hypertension:

2. exclusion of known causes:

a) chest radiograph

- evidence of right heart enlargement

- vascular pruning

b) cardiac echocardiograph

c) cardiac catheterization

d) angiography	



Therapeutic Goals:

1. if etiology apparent, try to alleviate

2. if no etiology apparent

a) reduce vascular resistance

- oxygen

- pharmacologic agents

- nitric oxide

b) support right ventricle



1

J.L. Wright