Pulmonary Vascular Disease

Pulmonary Embolism
 

A variety of materials can embolize pulmonary vasculature:

• Air (ex: due to an IV)
• Bone marrow (ex: due to fracture)
• Amniotic fluid
• Talc (ex: injection drug users)
• Thrombin clots à clots form in the deep veins of the legs, pelvic extremity vessels, or upper extremity vessels – clots can break loose & embolize pulmonary vasculature

Typical Case of Pulmonary Embolism:

36-year-old man developed acute onset of shortness of breath. He noted the breathlessness as his airplane was landing in Newark airport after a transcontinental air flight. Of note, 8 weeks prior to the onset of dyspnea the patient sustained a fracture of his right tibia. A cast was removed from the affected extremity 2 days prior to the flight to Newark. In addition to dyspnea, he also noted right-sided pleuritic chest pain. While leaving the plane the patient experienced a brief syncopal episode. He was brought to the UH emergency room.

On PE the patient complained of right-sided pleuritic chest pain. He appeared mildly anxious. The respiratory rate was 22 bpm, BP 138/85, P 102 regular. The rest of the patient’s physical examination was entirely within normal limits. CXR was WNL. ABGs on RA: pH 7.46, pCO₂ 33 (slightly decreased), pO₂ 72. V/Q scan of lungs showed several matched segmental defects (indicates intermediate probability for pulmonary embolism). Doppler examination of right leg was positive for deep vein thrombosis. 

Why is it important to diagnose Pulmonary Embolism?

• Incidence > 600,000 per year in the US
  • 11% of these individuals will die within 1 hour
  • 89% have a survival of > 1 hour
    • In 71% of these individuals a diagnosis is not made à 70% of these individuals will survive & 30% will die
    • In 29% of these individuals a diagnosis is made & therapy is instituted à 92% of these individuals will survive & 8% will die
• Untreated mortality ~ 30%
• Treated mortality ~ 2.1%
• Diagnosis frequently missed

Basically we want to try to prevent people from getting a pulmonary embolism if possible. We also want to think about a diagnosis of pulmonary embolism & make it rapidly so that treatment can be instituted.  

Factors which Predispose to Thromboembolism:

• Local trauma to the vessel wall
• Hypercoagulability
• Stasis

Risk Factors for Developing Pulmonary Embolism:

 Diagnosing Pulmonary Embolism:

·         Clinical suspicion

·         Ventilation-perfusion (V/Q) lung scan à indeterminate in 85% of cases (not a good test)

·         Spiral CT scan (with dye & rapid sequencing) à supplanting V/Q scan as the diagnostic test of choice

·         Doppler or impedance plethysmography of legs (ultrasound approach)

·         Quantitative d-dimer assay (performed by ELISA) à negative result excludes diagnosis – it’s a non-specific blood test

·         Pulmonary angiography à “gold standard” – patients are often considered too unstable to perform this test 
 

Pulmonary Hypertension

Pressure = Flow x Resistance (this is equivalent to Ohm’s Law)

Pulmonary artery pressure is increased (pulmonary hypertension) when:

·         The flow of blood through the pulmonary circulation is increased and/or

·         The resistance in the pulmonary circulation is increased

Pulmonary Artery vs. Systemic Artery Pressures

·         Pulmonary artery à systolic is 15 – 30mm, diastolic is 3 – 12 mm, & the mean is < 20 mm – high capacity & low pressure system

·         Systemic artery à systolic is 90 – 130mm, diastolic is 60 – 85 mm, & the mean is < 115 mmHg

Pulmonary hypertension à the mean pulmonary artery pressure is > 25 mmHg at rest or > 30 mmHg with exercise
 

Classification of Pulmonary Hypertension:

What are the diagnostic criteria for Primary Pulmonary Hypertension (PPH)?

·         Mean PAP > 25 mmHg at rest or

·         Mean PAP > 30 mmHg with exercise

·         Exclusions à left-sided cardiac valvular disease, myocardial disease, congenital heart disease, primary respiratory diseases, connective tissue diseases, chronic thromboembolic diseases

Pulmonary Vascular Diseases similar to Primary Pulmonary Hypertension:

·         Portal hypertension

·         Infection with HIV

·         Cocaine inhalation associated pulmonary hypertension

·         Appetite-suppressant drug associated pulmonary hypertension à fenfluramine and dexfenfluramine & amphetamines

Incidence of PPH à 1 – 2 cases per million per year – approx. 6% of these cases are familial (its an autosomal dominant trait) & the rest are spontaneous

Pathogenesis of PPH:

·         Altered function of pulmonary vascular epithelium à what are the potential factors, which have been proposed to explain the altered function?

o        Increased activity of thromboxane and/or diminished activity of prostacyclin (vasodilator)

o        Impaired synthesis of NO by the endothelium

o        Enhanced production of endothelium-derived endothelin (vasoconstrictor) 

Diagnosis of PPH:

·         Symptoms

o        Dyspnea (60%)

o        Fatigability

o        “Angina” (atypical chest pain)

o        Syncope

o        Raynaud’s phenomenon à constriction of blood vessels in the fingers

·         Evaluation

o        Echocardiography à rule out congenital, valvular, or myocardial disease and to estimate PAP

o        V/Q scan

o        Pulmonary function tests

o        Serological studies for connective tissue disease

o        Consider right sided heart catheter

Back to the Respiratory System Index