In people with chronic obstructive pulmonary disease, or COPD, even mild cases of a blood condition known as hypoxemia (high-pok-SEE-mee-uh) can cause changes in the structure of the heart, a new study finds.1 But the researchers found that only a minority of patients had cardiac dysfunction as a result.
Low Blood O2
Hypoxemia is a condition in which oxygen in the blood is abnormally low. It is often found in people with pulmonary hypertension (PH), in which the blood pressure in the pulmonary artery leading from the heart to the lungs rises to abnormal levels.2
Severe forms of hypoxemia have been associated with abnormal changes in heart function in people with COPD.3,4 But whether mild hypoxemia can induce these cardiac changes isn't known, wrote Anton Vonk-Noordegraaf, MD, and his associates at Vrije Universiteit Medical Center in Amsterdam, The Netherlands.
Pulmonary hypertension is considered a common complication in people with COPD. This link is related primarily to hypoxemia.5
Hypoxemia's Effect on the Heart
To find out whether changes in the structure and/or function of the heart can be caused by mild hypoxemia in COPD patients, Vonk-Noordegraaf and his colleagues enrolled 25 people with the disease and compared them to a group of 26 people without COPD.
Using magnetic resonance imaging (MRI), the investigators measured the structure and function of each patient's right and left ventricles. Pulmonary artery pressures were also measured.
At the end of the study, the researchers found that the right ventricles of the patients with COPD were abnormally enlarged compared to those without the disease. The ventricular structure had been altered in the COPD group, as well. However, the function of both ventricles in the COPD patients and in those who were healthy were generally about the same, Vonk-Noordegraff's group discovered.
Five COPD patients had right ventricle systolic dysfunction, and four had left ventricular systolic dysfunction, meaning the ventricles weren't contracting and expelling blood as well as they should. None of the healthy patients had similar dysfunction.
Right heart failure is a classic outcome of pulmonary hypertension. This occurs when blood flow to and from the heart is hindered by narrowed blood vessels. This higher blood pressure increases the workload of the right ventricle, enlarging it, and eventually, causing it to fail.6
During rest in the COPD patients in this study, there was no evidence of pulmonary hypertension, the investigators wrote.
COPD's Link to PH
Vonk-Noordegraff and his team concluded that there is evidence of right-heart enlargement in people with COPD, even in cases of mild hypoxemia, "probably due to increases in pulmonary artery pressures that occur during exercise or sleep."
However, the changes in the structure of the heart seen in the tests conducted in the study apparently do not alter right or left ventricular systolic function in COPD patients, the study team concluded.
Disease Characteristics
COPD is a lung disease in which the lung becomes damaged, mostly because the tubes that carry air in and out are partially obstructed, making it harder to breathe. In people with the disease, the lungs' airways and air sacs lose their shape and elasticity, becoming more rigid. The walls of the airways also become thick and inflamed, and more mucous is produced. Cigarette smoking is the main cause of the disease, which is classified as the fourth leading cause of death in the United States.7
PH is a much more rare illness, affecting between 500 and 1,000 people each year. PH is characterized by abnormally high increases in pulmonary artery pressure for no apparent reason. This increase results in abnormal changes in the lung's blood vessels, which in turn, increases bloodflow resistance and puts a strain on the right ventricle.
It's estimated that most patients with PH are women between the ages of 20 and 40.8
1. Vonk-Noordegraaf A, Marcus JT, Holverda S, Roseboom B, Postmus PE. Early changes of cardiac structure and function in COPD patients with mild hypoxemia. Chest 2005 Jun;127(6):1898-903.
2. Girgis RE. Pulmonary hypertension due to respiratory disease: pathogenesis and diagnostic approach. Advances in Pulmonary Hypertension. Available at: http://www.phassociation.org/Medical/Advances_in_PH/Summer_2005/resp.asp. Accessed July 21, 2005.
3. Cargill RI, Keily DG, Lipworth BJ. Adverse effects of hypoxemia on diastolic filling in humans. Clin Sci (Lond) 1995 Aug;89(2):165-9.
4. Klinger JR, Hill NS. Right ventricular dysfunction in chronic obstructive pulmonary disease. Evaluation and management. Chest 1991 Mar;99(3):715-23.
5. Barbera JA, Peinado VI, Santos S. Pulmonary hypertension in COPD: old and new concepts. Monaldi Arch Chest Dis 2000 Dec;55(6):445-9.
6. Via G, Braschi A. Pathophysiology of severe pulmonary hypertension in the critically ill patient. Minerva Anestesiol 2004 Apr;70(4):233-7.
7. National Heart, Lung, and Blood Institute. National Institutes of Health. What is Chronic Obstructive Pulmonary Disease (COPD)? Available at: http://www.nhlbi.nih.gov/health/dci/Diseases/Copd/Copd_WhatIs.html. Accessed July 21, 2005.
8. American Heart Association. Primary or Unexplained Pulmonary Hypertension. Available at: http://www.americanheart.org/presenter.jhtml?identifier=4752. Accessed July 21, 2005.
John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include overseeing health news coverage for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
