Word: blood
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...myocardial oxygen demand (i.e., a greater need for oxygen in your heart) and decreased myocardial oxygen supply - or both. And unfortunately, some functions in the first hours of the day require more myocardial oxygen support: waking and commencing physical activities, the peak of the adrenal hormone cortisol [which boosts blood-pressure and blood-sugar levels] and a further increase in blood pressure and heart rate due to catecholamines (adrenaline and noradrenaline), which show a peak when you wake up. All those factors lead to an increase of oxygen consumption but at the same time contribute to the constriction of vessels...
...have to remember that blood coagulation is important in the genesis of what we call thrombi, the blood clots that can block the blood vessels and cut off supply to the heart. When we wake up, platelets, the particles in the blood that make thrombi, are particularly adhesive to the vessels. Usually we have an endogenous system - it's called fibrinolysis - to dissolve the thrombi. But in the morning, the activity of our fibrinolytic system is reduced. So we have a greater tendency to make thrombi that can occlude the coronary vessels. This contributes to further reduction of coronary blood...
...risk also higher during the last part of sleep? Usually, during the night, the cardiovascular system is "sleeping," which is characterized by low blood pressure and heart rate. But the last stage of sleep - REM, or rapid eye movement, sleep [when we believe most dreaming occurs] - is a risk period for cardiovascular emergencies because when you dream, you have a dramatic increase of activity of the autonomic nervous system - even more than when you are awake. Probably each of us can remember waking up in the morning sometimes feeling very tired. That's because during that stage of dreams...
...model, in which people were instructed to stay in bed for four hours after they woke up before rising. But the same pattern simply occurred four hours after waking, because the risk is linked to our activities. We can't be afraid of the catecholamines and the peak in blood pressure in the morning. It's part of our physiology. And for healthy people, it's not a problem...
...have to be sure that the pill we're prescribing is still active when patients need it most. It's not as easy as simply asking patients to take pills before bed instead of first thing in the morning, because during sleep we have a low heart rate and blood pressure. If you lower your blood pressure too much during the night, you risk reducing blood supply to the brain, and that can be harmful...