HEART DISEASE: ORIGINS OF DISEASE – HIGH BLOOD PRESSURE
Abnormalities of blood pressure are so closely linked with most forms of heart disorder and distress that we had better set forth a few points in everyday language. During each pulse, the pressure is built up quickly by the heart's contraction, then falls — normally much more slowly — as the heart relaxes and the blood travels on through the network of vessels.
The highest pressure is often loosely referred to as "The Blood Pressure' and is correctly termed the systolic. The lowest may be called the 'resting' or diastolic pressure. The difference between the two is the 'pulse' or differential.
This last is in many respects the most significant of the three, since it is a measure of the work done by each beat of the heart, and, therefore, indicates the effort required to overcome resistance to the passage of blood throughout the system! On leaving the heart, the blood passes through repeatedly branching and diminishing vessels, the arteries; finally so numerous as to be uncountable and so fine as to allow the passage of corpuscles in single file only. These capillaries form the microscopic network which permeates every particle of active tissue in the body.
With this distribution complete, the smaller vessels run to join others and form ever-larger veins which bring the blood back towards the heart. The blood has now given up its oxygen and nutrients to the tissues, and in this spent state is darker than when it left the heart, freshly aerated. The veins are thinner-walled than the arteries, and those near the surface can be readily observed; the dark blood within gives them a bluish colour, and when warmed by exercise they can become much distended. The arteries are much tougher, and have in their walls strong, active muscle fibres which control their diameter.
Cardio & Blood