Treatment Complications
H.5 Cor Pulmonale

Cor pulmonale literally means “the heart of the lungs.” Its formal pathological definition is “right ventricular enlargement, hypertrophy, or dilation, secondary to lung disease.” To understand cor pulmonale, one must appreciate the physiology of the normal pulmonary circulatory system and its response to disease.

Pathophysiology

As described elsewhere in this monograph, COPD is, in most patients, a mixture of two or three related pulmonary diseases. These include asthmatic bronchitis and chronic bronchitis, which involve inflammation of the airways, bronchi, and bronchioles; and pulmonary emphysema, which affects the lung parenchyma through destruction of alveolar walls and their associated capillary circulatory framework.

In emphysema, the capillary bed is progressively and irreversibly destroyed, which eventually raises pulmonary vascular resistance and pulmonary artery pressure. Persistent and worsening pulmonary hypertension, in turn, finally results in cor pulmonale. Cor pulmonale usually appears only in the very advanced stages of emphysema.

In both chronic bronchitis and asthmatic bronchitis, however, pulmonary hypertension may occur much earlier in the course of disease than in emphysema. When hypoxemia, hypercarbia, and acidosis develop in chronic bronchitis, they cause pulmonary artery vasoconstriction, which increases pulmonary vascular resistance and, again, results in pulmonary hypertension that leads to irreversible vascular changes. Chronic severe hypoxemia is invariably present, often associated with secondary erythrocytosis.

If untreated, the increased pulmonary artery pressure will eventually “overload” the right ventricle. The normal heart's first response is to expand the size of the right ventricular muscle. This hypertrophy can compensate for mild pressure overloads for months or even years. Eventually, however, the heart dilates, and symptoms of right-sided heart failure or decompensated cor pulmonale (elevated neck veins, congested liver, and peripheral edema) appear.

At this stage, pulmonary artery pressures are usually elevated above 25/15 mm Hg, and they may reach as high as 60/30 mm Hg, although this is rare. (Normal pulmonary artery pressure in a young person at rest averages 15/8 mm Hg; the upper limit of normal is 25/15 mm Hg.) The right ventricle fails and further pulmonary artery pressure elevation to systemic levels does not occur as it does in primary pulmonary hypertension. The reason for a relatively modest increase in pulmonary hypertension in COPD and the heart's failure to increase its right ventricular mass to deal with rising pulmonary vascular resistance is not known.

Clinical Diagnosis

If a patient presents with peripheral edema, elevation of the neck veins, and a congested liver, one can make a clinical diagnosis of right-sided heart failure. If such a patient has a significant degree of COPD and an elevated hematocrit with hypoxemia as outlined above, the diagnosis of cor pulmonale as a complication of COPD can be made with a high degree of confidence without further expensive tests other than a standard electro-cardiogram. More extensive and expensive tests such as echocardiography or right ventricular catheterization should be done only if the patient does not respond to standard therapy as outlined below and/or if there is clinical evidence of additional left-sided heart disease.

Standard Therapy

As discussed throughout this monograph, the basic treatment for all complications of COPD, including cor pulmonale, is to treat the underlying airflow obstruction to improve the patient's oxygenation. Patients with mild heart failure can be managed by restricting their salt intake to 2 g per day and prescribing a good 24-hour diuretic such as hydrochlorothiazide (25 to 50 mg once a day), bumetanide (1 to 2 mg once a day), or furo-semide (20 to 40 mg given twice daily). Many clinicians mistakenly prescribe furosemide once in the morning only, which causes patients to excrete salt early in the day but then retain it again after the evening meal.

Oxygen Therapy

If edema cannot be controlled by salt restriction and diuretics, and/or if the patient presents with severe edema and obvious decompensated cor pulmonale, the most essential treatment is supplemental oxygen. Oxygen must be given at whatever flow rate (dosage) and with whatever delivery system required to achieve arterial oxygen saturations in the 90% to 95% range, 24 hours per day.

It is a good practice for the clinician to check follow-up hematocrit or hemoglobin levels at 4 to 8 week intervals. If the patient is being adequately oxygenated, secondary erythrocytosis will resolve within 4 to 8 weeks in almost all patients. Persistent erythrocytosis indicates that the patient is either not using his or her oxygen as much as required, or that desaturation is present during sleep despite the fact that supplementary oxygen is being breathed. In these situations, a sleep study (Discussed in Section H.3) should be performed to see if additional therapy for obstructive sleep disorder is needed and if therapy such as cpap is required.

Digitalis

Time and experience have shown that digitalis is not effective in the treatment of cor pulmonale when it is used without first controlling the patient's underlying hypoxemia and pulmonary hypertension. Once this is done, digitalis is rarely needed. Digitalis is a poor inotropic agent in cor pulmonale, but it still has a role as a chronotropic drug since it helps control ventricular rates in patients with atrial fibrillation or flutter and a fast ventricular response. When left-sided heart failure accompanies right-sided heart failure (see below), digitalis is helpful as an inotropic agent for the left ventricle.

Refractory Cor Pulmonale

If treatment for cor pulmonale as outlined above does not relieve right-sided heart failure, chronic thromboembolic disease or coexisting left-sided heart failure may be present. Diagnosis of these diseases requires additional invasive tests and referral to a specialist is recommended.

References

Dunn MI, Galiber DP. When chronic lung disease leads to cor pulmonale. J Respir Dis 1993;14:957-971. This is a review of the pathogenesis and treatment of cor pulmonale associated with COPD.

Galiber DP, Dunn MI. When left heart failure complicates COPD. J Respir Dis 1994;15:475-486. A succinct discussion of the effects of left heart failure on the manifestations and prognosis of COPD.

MacNee W. Pathophysiology of cor pulmonale in chronic obstructive pulmonary disease, part one. Am J Respir Crit Care Med 1994;150:833-852. This is the first part of a detailed state-of-the-art review of the pathogenesis of cor pulmonale.

MacNee W. Pathophysiology of cor pulmonale in chronic obstructive pulmonary disease, part two. Am J Respir Crit Care Med 1994;150:1158-1168. This second part reviews associated left heart failure and the treatment of cor pulmonale. The two articles together contain 519 references!

Neff TA, Petty TL. Long-term continuous oxygen therapy in chronic airway obstruction (cao). Ann Int Med 1970;72:621-626. This study gives data on the early clinical experiences in Denver using long-term oxygen therapy to treat COPD.

Petty TL (Chairman), Nocturnal Oxygen Therapy Trial Group, (nott). Continuous or nocturnal oxygen therapy in hypoxemic chronic obstructive lung disease: A clinical trial. Ann Int Med 1980;93:391-398. This multicenter trial showed better survival with nearly continuous oxygen therapy (average 19.4 hrs/day) compared with nocturnal oxygen therapy (average
11.8 hrs/day).