The two blood pressure numbers obtained when a BP reading is taken, represent important life-sustaining events, which although minute in time, are intense in their effects. The systolic or top number of a reading is the systolic blood pressure in the bottom number is the diastolic pressure. In order to appreciate these numbers and the two critical events that they represent it is necessary to have a basic understanding of the cardiovascular system. The construction of a natural model can be helpful in achieving this understanding.

The cardiovascular system is a closed circuit within the body through which blood flows. It consist of the heart, blood vessels and nerve endings which modulate the actions of the heart and vessels. The left side of the heart pumps oxygen-rich and nutrient-rich blood to all the vital body tissues through arteries, and the delivery of oxygen and nutrients as well as the removal of waste products such as carbon dioxide from those tissues occurring via an exchange process in the smallest microscopic subdivided branches of the arteries, known as capillaries. The ends of those capillaries then join end-to-end with equally small vessels that merge in an identically opposite manner as the precedenting branching ones to form progressively larger vessels known as veins, which empty into the right side of the heart, as the blood flow through the circuit is from left to right in a counterclockwise direction. The blood is then pumped from the right side of the heart into the lungs where it is replenished with oxygen and cleansed of carbon dioxide, before then emptying into the left side of the heart for a repeat cycle of delivery to bodily tissues.

The cardiovascular system can be likened to Siamese rivers with parallel mainstreams traveling in opposite directions (one stream flowing out in the other flowing in). At various points from the outpoting stream branching tribunals flow out also, before joining together with merging tribories which feed into the inflowing river stream. The source of water for the outpeling river is a lake with a natural filter dividing it into two separate bodies of water. The water flowing in the inbound river empties into the right side of the lake and passes through the filter before entering the left side of the lake for recycling. The lake symbolizes the heart, and the filter which separates the lake symbolizes the lungs. The smallest subdivisions of the emerging tribories represent the capillaries which supply oxygen-rich and nutrient rich blood to the cells, and the communities through which the treaties flow represent tissues and cells of the body.

Blood pressure numbers obtained when a reading is taken represent conditions when the left side of the heart contracts to pump blood out and when it relaxes to refill with blood. The top number or systolic reading represents the force executed when the heart contracts, and the bottom number or diastolic reading is representative of the force executed when the heart is relaxed and filling with blood. Since according to the laws of physics, force = mass x acceleration, it is not surprising that the systolic blood pressure number is higher than the diastolic number because the amount of blood in the treaties, which equals the mass, and the speed of the blood flow through the arteries are both increased when the heart contracts to pump blood out and less when it relaxes to fill with blood.

Since the number of heartbeats or contractions followed by relaxations in a normal healthy state, range from between 60 to 90 per minute, one of these life-sustaining events only last for between 1 to 1 sec seconds. If that's not a marvel in and of itself what is even more amazing is that without these consecutive mini-events which generate the blood pressure numbers, life ceases to exist within just a few minutes of their absence. The top and bottom numbers of a blood pressure reading therefore, do not only represent cardiovascular events. They represent life. They also give meaning to the axiom – “even the largest avalanche is triggered by small things.” – Vernor Vinge