Pulmonary embolism pathophysiology: Difference between revisions

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'''Editor(s)-In-Chief:''' [[C. Michael Gibson, M.S., M.D.]] [mailto:charlesmichaelgibson@gmail.com], {{ATI}}; {{AE}}
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==Overview==
==Overview==
Pulmonary embolism occurs when there is an acute obstruction of the pulmonary artery or one of its branches. It is commonly caused by a venous thrombus that has dislodged from its site of formation and embolized to the arterial blood supply of one of the lungs. The process of clot formation and embolization is termed [[thromboembolism]].
Pulmonary embolism (PE) occurs when there is an acute obstruction of the pulmonary artery or one of its branches. It is commonly caused by a venous thrombus that has dislodged from its site of formation and embolized to the arterial blood supply of one of the lungs. The process of clot formation and embolization is termed [[thromboembolism]]. PE results in the elevation of the pulmonary vessel resistance as a consequence of not only mechanical obstruction of the [[capillary]] by the [[embolism]], but also due to pulmonary vasoconstriction.  When pulmonary vascular resistance occurs following an acute PE, the rapid increase in the right ventricular [[afterload]] might lead to the dilatation of the right ventricular wall and subsequent [[right heart failure]].<ref name="pmid3916797">{{cite journal| author=Wiedemann HP, Matthay RA| title=Acute right heart failure. | journal=Crit Care Clin | year= 1985 | volume= 1 | issue= 3 | pages= 631-61 | pmid=3916797 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=3916797  }} </ref><ref name="pmid7484782">{{cite journal| author=Lualdi JC, Goldhaber SZ| title=Right ventricular dysfunction after acute pulmonary embolism: pathophysiologic factors, detection, and therapeutic implications. | journal=Am Heart J | year= 1995 | volume= 130 | issue= 6 | pages= 1276-82 | pmid=7484782 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=7484782  }} </ref>


== Pathophysiology ==
== Pathophysiology ==
=== Clot Formation ===
=== Clot Formation ===
* Most pulmonary emboli commonly originate in the [[iliofemoral vein]], deep within the vasculature of the lower extremity.
* Most PE commonly originate from a [[thrombus]] that has formed in the [[iliofemoral vein]], deep within the vasculature of the lower extremity.
* Less commonly, a pulmonary embolism may also arise in the upper extremity veins, renal veins, or pelvic veins.
* Less commonly, a PE may also arise from a [[thrombus]] in the upper extremity veins, renal veins, or pelvic veins.
* The development of thrombosis is classically due to a group of causes referred to as [[Virchow's triad]]. Virchow's triad includes alterations in [[blood flow]], factors in the vessel wall, and factors affecting the properties of the [[blood]]. It is common for more than one risk factor to be present.  Shown below is an image depicting [[Virchow's triad]].
* The development of thrombosis is classically due to a group of conditions referred to as [[Virchow's triad]]. Virchow's triad includes alterations in [[blood flow]], factors in the vessel wall, and factors affecting the properties of the [[blood]]. It is common for more than one risk factor to be present.  Shown below is an image depicting [[Virchow's triad]].


[[File:VTE Pathophysisology Virchow's triad.JPG|300x400px]]
[[File:VTE Pathophysisology Virchow's triad.JPG|300x400px]]


=== Embolization ===
=== Embolization ===
* After formation, a thrombus will travel from the site of origin and circulate through the [[inferior vena cava]] into the right ventricle and on into the pulmonary vasculature where it will lodge.<ref name="McGill">McGill University. (2004, June 24). Pulmonary Embolism. Retrieved May 7, 2012, from McGill Virtual Stethoscope Pathophysiology.</ref>
* After its formation, a thrombus might dislodge from the site of origin and circulate through the [[inferior vena cava]], into the right ventricle, and into the pulmonary vasculature.<ref name="McGill">McGill University. (2004, June 24). Pulmonary Embolism. Retrieved May 7, 2012, from McGill Virtual Stethoscope Pathophysiology.</ref>
* Depending upon the patient, there can be one or many pulmonary emboli present.  The size of the clot(s) and their physiologic impact will depend largely on the individual patient and subsequent anatomy of the vasculature. <ref name="McGill">McGill University. (2004, June 24). Pulmonary Embolism. Retrieved May 7, 2012, from McGill Virtual Stethoscope Pathophysiology.</ref>


=== Hemodynamic Consequences ===
=== Hemodynamic Consequences ===
*Hemodynamic complications arise as a result of the obstruction of flow within the pulmonary arteries.
*Hemodynamic complications and the nature of the clinical manifestations of a PE depend on a number of factors:<ref name="Hellas">Kostadima, E., & Zakynthinos, E. (2007). Pulmonary Embolism: Pathophysiology, Diagnosis, Treatment. Hellenic Journal of Cardiology, 94-107.</ref>
*In circumstances where more than two-thirds of the [[pulmonary artery]] is occluded, the right ventricle needs to find ways to preserve pulmonary perfusion. Some of the adaptative mechanism of the right ventricle are as follows:
** The size of the [[embolus]] and the degree to which it occludes the vascular tree and its subsequent branches 
**Generate a [[systolic blood pressure]] in excess of 50 mmHg.
** The presence of any preexisting cardiopulmonary conditions
**Maintain an average pulmonary artery pressure of approximately 40 mmHg.
** The role of chemical [[vasoconstriction]] as it is insinuated by [[platelets]] releasing [[serotonin]] and [[thromboxane]] in addition to other vasoconstrictors
*Without these adapations, a pulmonary embolism will lead to [[right heart failure]].<ref name="pmid6488744">{{cite journal| author=Benotti JR, Dalen JE| title=The natural history of pulmonary embolism. | journal=Clin Chest Med | year= 1984 | volume= 5 | issue= 3 | pages= 403-10 | pmid=6488744 | doi= | pmc= | url= }}</ref>
** The presence of pulmonary artery dilatation and subsequent [[vasoconstriction|reflex vasoconstriction]]
*Additional complications include the following:<ref name="McGill">McGill University. (2004, June 24). Pulmonary Embolism. Retrieved May 7, 2012, from McGill Virtual Stethoscope Pathophysiology.</ref>
 
**Increased resistence in the [[pulmonary vessels]].
* PE results in the elevation of the pulmonary vessel resistance as a consequence of not only mechanical obstruction of the [[capillary]] by the [[embolism]], but also due to pulmonary vasoconstriction.  Pulmonary vasoconstriction can be either biochemically mediated, hypoxia induced, or reflex-induced.<ref name="pmid1555481">{{cite journal| author=Elliott CG| title=Pulmonary physiology during pulmonary embolism. | journal=Chest | year= 1992 | volume= 101 | issue= 4 Suppl | pages= 163S-171S | pmid=1555481 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=1555481  }} </ref><ref name="pmid11033105">{{cite journal| author=Smulders YM| title=Pathophysiology and treatment of haemodynamic instability in acute pulmonary embolism: the pivotal role of pulmonary vasoconstriction. | journal=Cardiovasc Res | year= 2000 | volume= 48 | issue= 1 | pages= 23-33 | pmid=11033105 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11033105  }} </ref>
 
* Several mediators are involved the pulmonary [[vasoconstriction]] that occurs in the setting of acute PE, such as:
** [[Thromboxane A2]] (end product of [[arachidonic acid]] metabolism)<ref name="pmid11033105">{{cite journal| author=Smulders YM| title=Pathophysiology and treatment of haemodynamic instability in acute pulmonary embolism: the pivotal role of pulmonary vasoconstriction. | journal=Cardiovasc Res | year= 2000 | volume= 48 | issue= 1 | pages= 23-33 | pmid=11033105 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11033105  }} </ref>
** [[Serotonin]] (vasoconstrictor in the pulmonary circulation and vasodilator in the systemic circulation)<ref name="pmid11033105">{{cite journal| author=Smulders YM| title=Pathophysiology and treatment of haemodynamic instability in acute pulmonary embolism: the pivotal role of pulmonary vasoconstriction. | journal=Cardiovasc Res | year= 2000 | volume= 48 | issue= 1 | pages= 23-33 | pmid=11033105 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11033105  }} </ref>
** [[Endothelin 1]]<ref name="pmid11033105">{{cite journal| author=Smulders YM| title=Pathophysiology and treatment of haemodynamic instability in acute pulmonary embolism: the pivotal role of pulmonary vasoconstriction. | journal=Cardiovasc Res | year= 2000 | volume= 48 | issue= 1 | pages= 23-33 | pmid=11033105 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11033105  }} </ref>
** [[Prostaglandin F2α]]<ref name="pmid11033105">{{cite journal| author=Smulders YM| title=Pathophysiology and treatment of haemodynamic instability in acute pulmonary embolism: the pivotal role of pulmonary vasoconstriction. | journal=Cardiovasc Res | year= 2000 | volume= 48 | issue= 1 | pages= 23-33 | pmid=11033105 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11033105  }} </ref>
** [[Thrombin]]<ref name="pmid14656907">{{cite journal| author=Goldhaber SZ, Elliott CG| title=Acute pulmonary embolism: part I: epidemiology, pathophysiology, and diagnosis. | journal=Circulation | year= 2003 | volume= 108 | issue= 22 | pages= 2726-9 | pmid=14656907 | doi=10.1161/01.CIR.0000097829.89204.0C | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=14656907  }} </ref>
** [[Histamine]]<ref name="pmid14656907">{{cite journal| author=Goldhaber SZ, Elliott CG| title=Acute pulmonary embolism: part I: epidemiology, pathophysiology, and diagnosis. | journal=Circulation | year= 2003 | volume= 108 | issue= 22 | pages= 2726-9 | pmid=14656907 | doi=10.1161/01.CIR.0000097829.89204.0C | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=14656907  }} </ref>
 
* While [[serotonin]] and [[thromboxane A2]] are mainly produced by activated [[platelets]], the vascular wall and pulmonary neuroendocrine cells might also be the source of some [[vasoconstrictor]]s.<ref name="pmid11033105">{{cite journal| author=Smulders YM| title=Pathophysiology and treatment of haemodynamic instability in acute pulmonary embolism: the pivotal role of pulmonary vasoconstriction. | journal=Cardiovasc Res | year= 2000 | volume= 48 | issue= 1 | pages= 23-33 | pmid=11033105 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11033105  }} </ref>
 
* [[Prostacyclin]] is a vasodilator produced by the [[endothelial cells]] in response to the hemodynamic changes induced by the acute PE.<ref name="pmid11033105">{{cite journal| author=Smulders YM| title=Pathophysiology and treatment of haemodynamic instability in acute pulmonary embolism: the pivotal role of pulmonary vasoconstriction. | journal=Cardiovasc Res | year= 2000 | volume= 48 | issue= 1 | pages= 23-33 | pmid=11033105 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11033105  }} </ref>
 
* When pulmonary vascular resistance occurs following an acute PE, the rapid increase in the right ventricular [[afterload]] might lead to the dilatation of the right ventricular wall and subsequent [[right heart failure]]. In addition, the elevated pulmonary vascular resistance causes a decrease in the [[LV|left ventricular]] [[preload]] and consequently leads to systemic [[hypotension]].<ref name="pmid3916797">{{cite journal| author=Wiedemann HP, Matthay RA| title=Acute right heart failure. | journal=Crit Care Clin | year= 1985 | volume= 1 | issue= 3 | pages= 631-61 | pmid=3916797 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=3916797  }} </ref><ref name="pmid7484782">{{cite journal| author=Lualdi JC, Goldhaber SZ| title=Right ventricular dysfunction after acute pulmonary embolism: pathophysiologic factors, detection, and therapeutic implications. | journal=Am Heart J | year= 1995 | volume= 130 | issue= 6 | pages= 1276-82 | pmid=7484782 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=7484782  }} </ref> In patients with underlying cardiopulmonary disease, the [[cardiac output]] suffers substantial deterioration in overall output as compared to otherwise healthy individuals.
 
* [[Right heart failure]], as well as systemic [[hypotension]], can attenuate coronary perfusion and contribute to subsequent [[coronary ischemia]].<ref name="pmid3916797">{{cite journal| author=Wiedemann HP, Matthay RA| title=Acute right heart failure. | journal=Crit Care Clin | year= 1985 | volume= 1 | issue= 3 | pages= 631-61 | pmid=3916797 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=3916797  }} </ref><ref name="pmid7484782">{{cite journal| author=Lualdi JC, Goldhaber SZ| title=Right ventricular dysfunction after acute pulmonary embolism: pathophysiologic factors, detection, and therapeutic implications. | journal=Am Heart J | year= 1995 | volume= 130 | issue= 6 | pages= 1276-82 | pmid=7484782 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=7484782  }} </ref>
 
* In summary, the hemodynamic consequences of PE include:
**[[Pulmonary hypertension]]
**[[Pulmonary hypertension]]
**[[Right ventricular strain]]
**[[Right ventricular strain]]
**[[Congestive heart failure]]
**[[Right heart failure]]
**[[Vasoconstriction]]
**[[Systemic hypotension]]
*In patients with underlying cardiopulmonary disease, the [[cardiac output]] suffers substantial deterioration in overall output as compared to otherwise healthy individuals.
 
*In patients with coexisting [[coronary artery disease]], right ventricular failure is more common following a pulmonary embolism as compared to those without coexisting CAD.
===Abnormalities in Gas Exchange===
*In 10% of all pulmonary embolism cases, the pulmonary embolism develops into a [[pulmonary infarction]]. This is an exceedingly rare complication.<ref name="McGill">McGill University. (2004, June 24). Pulmonary Embolism. Retrieved May 7, 2012, from McGill Virtual Stethoscope Pathophysiology.</ref>
* In PE, [[hypoxemia]] occurs mainly due to the ventilation perfusion mismatch.<ref name="pmid14656907">{{cite journal| author=Goldhaber SZ, Elliott CG| title=Acute pulmonary embolism: part I: epidemiology, pathophysiology, and diagnosis. | journal=Circulation | year= 2003 | volume= 108 | issue= 22 | pages= 2726-9 | pmid=14656907 | doi=10.1161/01.CIR.0000097829.89204.0C | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=14656907  }} </ref> In fact, in the setting of an acute PE, the ventilation to perfusion ratio (V/Q) increases and the dead space enlarges.<ref name="pmid12468507">{{cite journal| author=Itti E, Nguyen S, Robin F, Desarnaud S, Rosso J, Harf A et al.| title=Distribution of ventilation/perfusion ratios in pulmonary embolism: an adjunct to the interpretation of ventilation/perfusion lung scans. | journal=J Nucl Med | year= 2002 | volume= 43 | issue= 12 | pages= 1596-602 | pmid=12468507 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12468507  }} </ref>
*Long term complications:<ref name="McGill">McGill University. (2004, June 24). Pulmonary Embolism. Retrieved May 7, 2012, from McGill Virtual Stethoscope Pathophysiology.</ref>
**[[Chronic obstructive pulmonary hypertension]]
**[[Ventilation/perfusion ratio]] (V/Q ratio)


=== Mechanism ===
* In addition, the occurrence of [[right to left shunt]] also contributes to the [[hypoxemia]] among patients with PE. When [[right to left shunt]] occurs, the administration of oxygen to the patient fails to correct the [[hypoxemia]].<ref name="pmid14656907">{{cite journal| author=Goldhaber SZ, Elliott CG| title=Acute pulmonary embolism: part I: epidemiology, pathophysiology, and diagnosis. | journal=Circulation | year= 2003 | volume= 108 | issue= 22 | pages= 2726-9 | pmid=14656907 | doi=10.1161/01.CIR.0000097829.89204.0C | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=14656907  }} </ref>
The diagram below summarizes the sequence of pathophysiologic events in pulmonary embolism:<ref name="pmid19041539">{{cite journal |author=Fengler BT, Brady WJ |title=Fibrinolytic therapy in pulmonary embolism: an evidence-based treatment algorithm |journal=Am J Emerg Med |volume=27 |issue=1 |pages=84–95 |year=2009 |month=January |pmid=19041539 |doi=10.1016/j.ajem.2007.10.021 |url=http://linkinghub.elsevier.com/retrieve/pii/S0735-6757(07)00699-7 |accessdate=2011-12-21}}</ref>


[[File:PE.png|650px|center]]
* [[Hypocapnia]] occurs among patients with PE secondary to a compensatory increase in the [[minute ventilation]].<ref name="pmid14656907">{{cite journal| author=Goldhaber SZ, Elliott CG| title=Acute pulmonary embolism: part I: epidemiology, pathophysiology, and diagnosis. | journal=Circulation | year= 2003 | volume= 108 | issue= 22 | pages= 2726-9 | pmid=14656907 | doi=10.1161/01.CIR.0000097829.89204.0C | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=14656907  }} </ref>


==References==
==References==

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] The APEX Trial Investigators; Associate Editor(s)-in-Chief: Rim Halaby, M.D. [2]

Overview

Pulmonary embolism (PE) occurs when there is an acute obstruction of the pulmonary artery or one of its branches. It is commonly caused by a venous thrombus that has dislodged from its site of formation and embolized to the arterial blood supply of one of the lungs. The process of clot formation and embolization is termed thromboembolism. PE results in the elevation of the pulmonary vessel resistance as a consequence of not only mechanical obstruction of the capillary by the embolism, but also due to pulmonary vasoconstriction. When pulmonary vascular resistance occurs following an acute PE, the rapid increase in the right ventricular afterload might lead to the dilatation of the right ventricular wall and subsequent right heart failure.[1][2]

Pathophysiology

Clot Formation

  • Most PE commonly originate from a thrombus that has formed in the iliofemoral vein, deep within the vasculature of the lower extremity.
  • Less commonly, a PE may also arise from a thrombus in the upper extremity veins, renal veins, or pelvic veins.
  • The development of thrombosis is classically due to a group of conditions referred to as Virchow's triad. Virchow's triad includes alterations in blood flow, factors in the vessel wall, and factors affecting the properties of the blood. It is common for more than one risk factor to be present. Shown below is an image depicting Virchow's triad.

Embolization

  • After its formation, a thrombus might dislodge from the site of origin and circulate through the inferior vena cava, into the right ventricle, and into the pulmonary vasculature.[3]

Hemodynamic Consequences

  • Hemodynamic complications and the nature of the clinical manifestations of a PE depend on a number of factors:[4]
    • The size of the embolus and the degree to which it occludes the vascular tree and its subsequent branches
    • The presence of any preexisting cardiopulmonary conditions
    • The role of chemical vasoconstriction as it is insinuated by platelets releasing serotonin and thromboxane in addition to other vasoconstrictors
    • The presence of pulmonary artery dilatation and subsequent reflex vasoconstriction
  • PE results in the elevation of the pulmonary vessel resistance as a consequence of not only mechanical obstruction of the capillary by the embolism, but also due to pulmonary vasoconstriction. Pulmonary vasoconstriction can be either biochemically mediated, hypoxia induced, or reflex-induced.[5][6]
  • When pulmonary vascular resistance occurs following an acute PE, the rapid increase in the right ventricular afterload might lead to the dilatation of the right ventricular wall and subsequent right heart failure. In addition, the elevated pulmonary vascular resistance causes a decrease in the left ventricular preload and consequently leads to systemic hypotension.[1][2] In patients with underlying cardiopulmonary disease, the cardiac output suffers substantial deterioration in overall output as compared to otherwise healthy individuals.

Abnormalities in Gas Exchange

  • In PE, hypoxemia occurs mainly due to the ventilation perfusion mismatch.[7] In fact, in the setting of an acute PE, the ventilation to perfusion ratio (V/Q) increases and the dead space enlarges.[8]

References

  1. ↑ 1.0 1.1 1.2 Wiedemann HP, Matthay RA (1985). "Acute right heart failure". Crit Care Clin. 1 (3): 631–61. PMID 3916797.
  2. ↑ 2.0 2.1 2.2 Lualdi JC, Goldhaber SZ (1995). "Right ventricular dysfunction after acute pulmonary embolism: pathophysiologic factors, detection, and therapeutic implications". Am Heart J. 130 (6): 1276–82. PMID 7484782.
  3. ↑ McGill University. (2004, June 24). Pulmonary Embolism. Retrieved May 7, 2012, from McGill Virtual Stethoscope Pathophysiology.
  4. ↑ Kostadima, E., & Zakynthinos, E. (2007). Pulmonary Embolism: Pathophysiology, Diagnosis, Treatment. Hellenic Journal of Cardiology, 94-107.
  5. ↑ Elliott CG (1992). "Pulmonary physiology during pulmonary embolism". Chest. 101 (4 Suppl): 163S–171S. PMID 1555481.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 Smulders YM (2000). "Pathophysiology and treatment of haemodynamic instability in acute pulmonary embolism: the pivotal role of pulmonary vasoconstriction". Cardiovasc Res. 48 (1): 23–33. PMID 11033105.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 Goldhaber SZ, Elliott CG (2003). "Acute pulmonary embolism: part I: epidemiology, pathophysiology, and diagnosis". Circulation. 108 (22): 2726–9. doi:10.1161/01.CIR.0000097829.89204.0C. PMID 14656907.
  8. ↑ Itti E, Nguyen S, Robin F, Desarnaud S, Rosso J, Harf A; et al. (2002). "Distribution of ventilation/perfusion ratios in pulmonary embolism: an adjunct to the interpretation of ventilation/perfusion lung scans". J Nucl Med. 43 (12): 1596–602. PMID 12468507.

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