Pulmonary Hypertension in Adults vs. Neonates
Adult Pulmonary Hypertension
Pulmonary Hypertension remains an elusive and difficult to treat disease, and the pathways involved in pulmonary vascular disease, to this day, are not well understood; significant research is an on going process. There are virtually no dedicated fellowships concerning pulmonary hypertension and cardiologists, pulmonologists or a combination of both typically treat the disease.
The primary obstacle to the treatment of pulmonary hypertension (PHTN, or PAH) is diagnosing this disease in the first place. It often takes more than a year to make the diagnosis in many patients. The primary symptoms, shortness of breath (SOB), chest pain, fatigue, arrhythmias and lower extremity edema, as any echo-tech or cardiologist knows, could be symptomatic of any number of possibilities e.g. congestive heart failure (CHF), valvular disease, pulmonary emboli’s, COPD, Emphysema, thrombus, or obesity and general ill-health, just to name a few.
There are currently five groups or classifications concerning pulmonary hypertension in adults:
Type I: Primary pulmonary hypertension (PAH). This is a disease of the vasculature of the pulmonary artery itself in which the pulmonary artery becomes enlarged or hypertrophied, there is vasoconstriction and a loss of arterial elasticity, and arterial pressure is significantly increased down-stream in the lungs.
Type II: Left heart related. If there is left heart failure, just remember the axiom “what goes in, must come out”. If the left heart fails to adequately pump out the incoming blood from the right side of the heart, blood backs up in the lungs (pulmonary edema). This causes the pulmonary vasculature to constrict in order to reduce blood flow going in to the lungs. As the backpressure increases, this will eventually lead to right heart failure.
Type III: Lung disease and hypoxia: Examples would be COPD, emphysema (obstructive airway diseases) lung damage due to injury and damage to the interstitial tissue (area around the air sacs and alveoli), occupational injuries or scarring of other membranous structures, capillary diseases, fibrosis (restrictive airway diseases). These diseases cause pulmonary vascular remodeling, increasing vascular resistance that may eventually lead to pulmonary hypertension.
Type IV: Thromboembolic. Thrombus would, of course, be a pulmonary embolism that would occlude a pulmonary artery; the severity would depend on the size and number of thrombi. An embolus would most likely be a vegetation, myxoma or other tumors affecting the right heart. If there is an obstruction or obstructions to blood flow in the pulmonary arteries, this increases vascular resistance.
Type V: Other. This includes unclear or idiopathic causes and other diseases such as sarcoidosis (addition of infiltrates or granulomas to the cardiac and vascular tissues), inflammatory diseases, metabolism disorders, fibrotic diseases and carcinomas.
Treatment for adult PHTN varies widely. Once the diagnosis is made, it is then incumbent upon the cardiologist or pulmonologist to decide what type of PHTN is present. Proper treatment for one type of PHTN may be deleterious for another type. A high level of expertise in the treatment of PHTN is not common. Incorrect identification of the type of PHTN can have devastating consequences. For example, once right heart failure sets in, mortality increases up to 50%
Medication is the preferred treatment for PHTN and primarily includes drugs that affect vasodilation, the receptor antagonist or receptor agonist process. Remember that primary PHTN involves an abnormal vasoconstrictive or abnormal thickening of the pulmonary vasculature.
In type IV patients, “clot busters” or thrombolytic therapy and/or surgery (pulmonary endarterectomy or balloon pulmonary angioplasty) may be advised. I am not going to delve too far into the treatment area for adult PHTN, as I am not a cardiologist.
What Goes in, Must Come Out
What does that mean? Most of the blood in the body resides in the veins (about 60%). Veins operate in a high volume, low-pressure, low velocity state and act as reservoirs or like lakes. Arteries contain 10% of blood volume and are like rivers, low volume, and high-pressure vehicles of blood flow. The heart contains about 8% of blood volume, and the lungs contain the rest, about 25%.
The right heart may appear to be about half the size of the left heart, and is measured that way (by echocardiography), but it is actually the same size and contains as much volume as the left heart. It pumps the same amount of blood.
Right side: Low pressure, high volume. Left side: high pressure, low volume. The right heart “wraps itself “ around the left ventricle horizontally, and the left heart is a more vertical structure. Normal values for the right heart are 2.6 cm; normal values for the left heart are up to 5.6 cm. Towards the end of systole, the right heart gives a little extra push to the left ventricle to aid in its’ ejection.
Pulmonary vasculature is very delicate compared to systemic vasculature, and is easily damaged by volume and/or pressure overload. Normal pressure in the right atrium (RA) is 5 mmHg. Normal pressure in the right ventricle is 25mmHg, as well as the pulmonary artery. The right side is easily damaged by volume and/or pressure problems. Pressure in the peripheral venous system (central venous pressure) is very low, about 5-10 mmHg. Pressure in the systemic arterial system is very high, about 120 mmHg.
As blood passes through the capillary system of the lung, pressure becomes very low. This allows oxygen transfer across the capillary bed of the lungs. Oxygen rich blood then travels through the pulmonary veins into the left atrium. Ideally, pressures remain low. Pressure in the left atrium should be about 5-10 mmHg.
Blood travels from a high-pressure environment (left side) to a low-pressure environment (right side). This is why blood flows in a continuous loop through the body. Fluid moves through a high-pressure environment to a low-pressure environment and then backs again.
Think of the right heart as just a low pressure, pumping vein. This brings us full circle to the pediatric heart.
Neonatal Pulmonary Hypertension
Pediatric cardiology in a nutshell, is concerned primarily with abnormal connections between the left-sided blood flow and right-sided blood flow. Under ordinary circumstances, the right side (venous) is completely separated from the left side (arterial) with the exception of the pulmonary capillary system and the systemic capillary system. This is where O2 saturated blood and CO2 saturated blood mix.
If there is an aberrant connection between the left and right sides, this will cause a pressure and/or volume overload to the right side of the heart or the right-sided vasculature. The right side of the heart will respond by becoming hypertrophied in order to accommodate the higher pressure, or the vasculature will respond by vasoconstriction in order to limit the amount and pressure of the incoming blood to the lungs.
If this goes on for a long period of time, the right-sided structures, being more delicate than left sided structures will become permanently damaged. Sometimes, this can be handled with medications in the event of PDA’s and ASD’s, (patent ductus arteriosis or atrial septal defect), but typically, it is dealt with surgically.
I will not go into the spectrum of congenital heart defects that will result in pulmonary hypertension. Please read my book “Heart Defects, Simplified” found on HeartDefectsSimplified.com for that information.
Every echo tech should pay attention to the right side of the heart in every echo, no matter what, especially if the patient is complaining of shortness of breath. Is the right ventricle hypertrophied? If it is, there is definitely pulmonary hypertension present. Does the right ventricle contact normally? How big is it? If it measures greater than 2.6 cm, then find out why. Measure the RVSP. Every echo tech knows how to do this, but make sure it is accurate! Is there an ASD or VSD? Many young people who have a stroke (CVA) often have an ASD (atrial septal defect or a VSD, ventricular septal defect). A TEE is appropriate in every person who has a stroke.
If you are a pediatric echo tech, then you know that any abnormal communication between the right and left side is abnormal. You should know what to do.
For much more information and access to over 60 blogs on Pediatric Heart disease, go to HeartDefectsSimplified.com
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