Cardiovascular Disease and Sleep Apnoea

Cardiovascular disease refers to diseases of the heart and/or blood vessels.  It includes conditions like hypertension (high blood pressure), angina (chest pain), coronary artery disease, cardiac arrhythmia (abnormal heartbeat causing the heart to pump less effectively) and congestive heart failure. 

 

These diseases develop over time and can interrupt the flow of blood to the heart and brain, causing life-threatening conditions such as heart attack and stroke.  Cardiovascular disease is the main cause of death in the UK.1

Well known risk factors for cardiovascular disease include smoking, diabetes, obesity and high cholesterol. We also know that sleep apnoea can lead to CVD.2 The more severe the sleep apnoea, the greater the risk for developing hypertension and subsequently other forms of CVD. 

The good news is that in patients with severe obstructive sleep apnoea, treatment with CPAP reduces the risk of a cardiovascular event to the same as in those without sleep apnoea and in simple snorers.3

The cardiovascular system is responsible for providing the tissues in the body with oxygen and nutrients and removing wastes like carbon dioxide.  In order to do this, the heart pumps blood containing oxygen, nutrients and wastes through the blood vessels (arteries, veins and capillaries).

Blood pressure is a measure of the force exerted on the vessels and the volume of blood flowing through them so is a good indicator of cardiovascular health.  Sustained hypertension may be the first indication of a disorder or disease of the blood vessels or heart.  Between 35% and 80% of patients with hypertension have sleep apnoea. 4,8

The coronary arteries supply the heart with oxygen rich blood, essential to keep the heart muscle alive. Atherosclerosis is a common coronary artery disease and occurs when deposits of fat, cholesterol and plaque build up inside the coronary artery walls.  These deposits reduce the size of the coronary artery so reduce the supply of oxygen rich blood to the heart muscle.  When blood cells get stuck to the plaque build up inside the coronary artery walls, blood clots can occur.  Blood clots block the coronary artery and prevent oxygen reaching the heart muscle.  If the heart does not receive the oxygen it needs to function, the result is damage or death of the heart tissue and can lead to a heart attack, heart failure or arrhythmias.  Angina is a symptom of coronary artery disease.  Many patients with coronary artery disease are on medication and some have had coronary artery bypass surgery.

If atherosclerosis occurs in blood vessels leading to the brain, there is increased risk of a stroke.

30% of patients with coronary artery disease also have sleep apnoea. 9

The effects of coronary artery disease are made worse during an apnoea or hypopnoea during which time when there is little or no oxygen being added to the blood.  In someone with coronary artery disease where the blood flow to the heart muscle is limited, this decrease in oxygen in the circulating blood may not be enough to properly supply the heart muscle.  Also, immediately following an apnoea or hypopnoea, the blood vessels in the body narrow as a result of sympathetic nervous system activity.  This further reduces the blood flow and reduces the likelihood of oxygenated blood reaching the heart.  There are other mechanisms linking sleep apnoea to cardiovascular disease, such as oxidative stress, increased coagulation and inflammation.

Treatment with CPAP minimises apnoeas and hypopnoeas therefore minimises sympathetic nervous system activity.  While on CPAP, oxygen is constantly supplied and the blood vessels are not narrowed as a result of sleep apnoea.

Patients with untreated obstructive sleep apnoea have a fivefold increase in developing coronary artery disease within 7 years.  The risk decreases by two thirds when obstructive sleep apnoea is treated.11

Congestive heart failure is one of the most devastating forms of cardiovascular disease.  It occurs when the heart is not able to pump enough blood for the body’s needs.  It is caused by many conditions, including hypertension, coronary artery disease, heart attack and diabetes.  38% of patients in the EU with congestive heart failure die within a year of diagnosis19 and there is a low survival rate beyond 5yrs.

75% of patients with congestive heart failure also have sleep apnoea.  In patients with heart failure, untreated OSA (AHI>15) is associated with an increased risk of death independently of confounding factors.13

During an apnoea or hypopnoea the heart rate slows but as soon as breathing resumes, the heart rate drastically increases.  The increased heart rate combined with the constriction of the blood vessels make an already inefficient pump even worse and places unnecessary strain on the heart.  CPAP treatment reduces the apnoeas and hypopnoeas that cause this scenario. 

CPAP treatment is known to improve the prognosis of heart failure14 and improve cardiac health15.

 

References:

1. Taken from HeartStats.org

2. Sahar E, Whitney CW, Redine S, et al. Sleep–disordered breathing and cardiovascular disease. Cross sectional results of the Sleep Heart Health Study. Am J Resp Care Med 2001; 163: 19-25

3. Marin, et al, 2005 Lancet

4. Logan et al. J Hypertension, 2001

5. Oldenburg et al. The European Journal of Heart Failure, 2007

6. Garrigue et al. Circulation 2007

7. Somers et al. Circulation 2004

8. Sjostrom et al. Thorax 2002

9. Schafer et al.  Cardiology 1999

10. Sanner et al. Clin Cardiol 2001

11. Peker.   Eur Respir J 2006; 28: 596-602

12. McMurray. JJ Heart 2000

13. Wang. JACC Vol 49, no 15 April 2007

14. Kasai et al Chest 2008

15. Shivalkar, et al.  JACC 2006

16. Sin DD, et al. Risk factors for central and obstructive sleep apnoea in 450 men and women with congestive heart failure. Am J Respir Crit Care Med 1999; 160: 1101.

17. Javaheri S, et al. Sleep apnoea in 81 ambulatory male patients with stable heart failure: types and their prevalences, consequences, and presentations. Circulation 1998; 97: 2154.

18. Bradley TD and Floras JS. Sleep apnoea and heart failure Part I: Obstructive sleep apnoea. Circulation 2003; 107: 1671.