BY : Prof (Dr) Brig Ashok K Rajput (Retd), MD(Medicine), MD(Chest), DTCD, DNB (Pulmonary Medicine), FNCCP(I), Senior Consultant, Pulmonology, Venkateshwar Hospital
When you are awake, your body needs more oxygen, glucose and other nutrients than when you are sleeping. Hence in the waking hours, your breathing is quicker, takes in more oxygen from the atmosphere. Medical research has shown that your respiratory intake is about 7.6 liters of air per minute during waking which drops to about 6.4 liters per minute in sleep. Also your heart has to work harder to transport those substances to the farthest reaches of your body. Hence your blood pressure is also a bit higher during this time than during sleep.
Now if someone keeps waking up in the night, perhaps on account of what the doctors describe as Sleep Disordered Breathing (SDB), this cycle of sleep and wakefulness gets disturbed. The heart and lungs are not able to slow down for some part of the day, as in steady sleep, because of which the blood pressure remains on the higher side. Over a period of several years, the other harmful effects of chronic high blood pressure also begin showing up and one of them is heart disease.
The causes of sleep disturbances could be many, among the most common being Obstructive Sleep Apnea (OSA). What this means is that when you are asleep, your upper airways (mouth and throat) could have some obstruction to the smooth flow of air. Maybe your tongue is disproportionately large or your lower jaw is too small. In severe OSA, the obstruction causes your breathing to stop for as long as 60 seconds, and this could happen 15-30 times per hour! Consequently, the brain is starved of oxygen, and it pushes you to wake up immediately.
There is also an intimate connection between the heart and lung function, which is not difficult to understand. Given that the different body organs require a certain amount of oxygen and glucose (the main source of biological energy) throughout the 24 hours, the lungs have to supply a specific quantity of oxygen and the heart has to provide a certain amount of blood to all the body tissues. Obviously, if one of these, say the lungs and airway system, performs below par, the other, namely the heart and circulatory system has to work harder! The result: high blood pressure and chronic heart disease.
To examine whether these apparently logical conclusions actually bear out in reality, the world’s largest study (The Sleep Heart Study) was conducted from 1997 to 2008, and it clearly showed that “OSA is associated with an increased risk of cardiovascular disease in middle aged and older men”. A 2010 article in Circulation, published by the American Heart Association reports that men with an AHI (Apnea-Hyperpnea Index) of 30 or more had a 68% increased risk of developing heart disease.
An article in the online journal Cardiosmart, published by the American College of Cardiology describes OSA and high blood pressure as “a dangerous pair”! Both the conditions have been separately linked with significantly higher risk of heart attack and paralytic stroke. It doesn’t help that the one of the commonest predictors of OSA, namely obesity, is also an important risk factor in diabetes, hypertension and heart disease. A double whammy, one might say.
Other studies have shown that OSA in India occurs in about 2.4 to 3.4% of men of all ages, but this percentage increases rapidly as the men approach middle age. Further, 34% of middle aged American men and 17% of women can be expected to suffer from OSA.
So can nothing be done to bring relief for those who suffer from OSA? Fortunately, that is not the case. Most patients of OSA show a positive response to CPAP (Continuous Positive Air Pressure). Here a mask-like device to be worn on the face while sleeping is utilized to push a suitable amount of air into the mouth, so that the upper airway can be kept open. But whether patients under treatment with CPAP actually show a normalization of blood pressure or a lower frequency of serious heart disease has not been clearly established.