Pulmonary Hypertension

· Pulmonary hypertension is a disorder of the pulmonary vasculature that is diagnosed when the PAS > 30 mmHg

· Or: Pulmonary hypertension is present when the mean PA pressure exceeds 20 mmHg.

· Primary pulmonary hypertension is rare.

· Postoperative pulmonary hypertension usually occurs in patients who have had preoperative elevations of PA pressures secondary to pulmonary disease or who have acquired , congenital cardiac valvular disease. Classically, mitral stenosis is associated with high PA pressures when it is severe or of long duration

1) Chemical & Humoral substances

Vasoconstrictors:	Vasodilators:
i) Adrenaline ii) NorAdrenaline iii) Angiotensin iv) Histamine v) Hypoxemia vi) Hypercapnia vii) Acidosis viii) Prostaglandins?	i) Bradykinin ii) Acetylcholine iii) Aminophylline iv) Isoproterenol

2) Cardiopulmonary disorders

Secondary PHT:

1) Increased resistance to pulmonary venous drainage

a) increased left ventricular diastolic pressure

i) LVF [eg secondary to systemic hypertension]

ii) reduced LV compliance

iii) constrictive pericarditis

b) Left atrial hypertension

i) mitral valve dx

ii) left atrial myxoma

c) Pulmonary venous obstruction

i) congenital stenosis of pulmonary vein

2) Increased resistance to flow via pulmonary capillary bed

Reduction of pulmonary vascular bed: Pulmonary fibrosis & wide spread interstitial diseases —diffuse increase in fibrous tissue in lung, obliterates and compresses pulmonary capillaries

a) Decreased cross-sectional area of pulmonary vascular bed secondary to parenchymal dx

i) COAD

ii) Restrictive lung dx

b) Other conditions associated with decreased cross-sectional area of pulmonary vascular bed

i) Primary pulmonary hypertension

c) Decreased cross-sectional area of the pulmonary vascular bed secondary to Eisenmenger syndrome

i) Right to left shunts —> severe obliterative changes in pulmonary bed —> left to right shunt

3) Increased resistance to flow through large pulmonary arteries

a) Pulmonary thromboembolism

[Emboli directly obstruct pulmonary arteries and arterioles and may produce secondary vasoconstriction via release of vasoactive substances]

b) Pulmonary stenosis

4) Hypoventilation

a) Obesity

b) Neuromuscular disorders

i) polio

ii) damage to brain stem

iii)myasthenia gravis

c) Disorders of chest wall

5) Miscellaneous causes of hypertension

a) Tetralogy of Fallot

b) High altitude

Primary PHT:

Primary pulmonary hypertension

Presumably due to pulmonary arteriolar sclerosis, which thickens the walls and decreases the calibre of vessels, medial hypertrophy + intimal fibrosis

Causes of Pulmonary Hypertension
Primary pulmonary hypertension
Disorders of ventilation
	High altitude
	Primary central hypoventilation
	Obstructive sleep apnea
	Cystic fibrosis
	Chronic obstructive pulmonary disease
	Kyphoscoliosis
Congenital heart disease
	Intracardiac shunting with left to right shunt
Valvular heart disease, commonly mitral valve disease
Left ventricular failure
Pulmonary embolism

Long term consequences of PHT

• A reduction in the size of the vascular bed or intense pulmonary vasoconstriction secondary to alveolar hypoxia causes the small pulmonary arteries to develop medial muscle wall layer hypertrophy and thickening of the intimal lining of the vessels, sometimes with fibrosis, which results in the non compliance of the pulmonary vascular bed. This in tern creates a pressure buildup in the right heart secondary to the impedance to right ventricular outflow.

Eisenmenger syndrome

§ “decreased cross-sectional area of the pulmonary artery bed with irreversible pulmonary hypertension”

§ refers to patients with congenital cardiac lesions (rarely acquired eg VSD post MI) and severe pulmonary hypertension in whom the reversal of the left-to-right shunt has occurred

§ Reversible conditions are those, which the decreased pulmonary arteriolar cross-sectional area is the result of medial hypertrophy and vasoconstriction

§ Irreversibility is associated with the presence of necrotising arteritis and plexiform (twisted bundle) lesions in these small vessels

Timing of Cardiac Repairs

§ Intracardiac lesions should be repaired while there is still a left-to-right shunt. Surgical repair is indicated before an inoperable right-to-left shunt ensues

§ When the PVR ≥ SVR, and the anatomical changes of the pulmonary vessels are predominantly by presence of necrotising arteritis and plexiform (twisted bundle) lesions, surgical closure of the intracardiac lesion will fail to relieve pulmonary hypertension and will be associated with a prohibitive immediate risk

§ An operation at this time, will hasten death in most survivors who had either balanced shunts or predominantly right-to-left shunts as closure of the right-to-left shunt merely increases the load on the already overburdened right ventricle