Description
Blood Pressure is not a disease, everyone has a pressure, we need it to keep us upright and live. Your blood pressure varies depending on your level of physical and mental stress
In this easily accessible book Dr Dymond describes what high blood pressure is, the symptoms, various medications available, side effects and possible complications
The tests and investigations for high blood pressure are explained together with treatments and suggestions for changes to lifestyle and diet
High blood pressure - What is it? Mechanisms of high blood pressure How is high blood pressure diagnosed? Why is high blood pressure so dangerous? Tests and investigations Treating high blood pressure Treatment: What you need to know Hypertension in pregnancy, the menopause and in the elderly The truth about cholesterol and cholesterol lowering drugs Conclusions
`I've got blood pressure, doctor' is a common opening remark in the dialogue between patient and doctor. 'Blood Pressure' is not a heart disease. In fact it is not a disease at all, and we should be thankful that we have a blood pressure, for without it we could not be alive
When we talk about blood pressure we are referring to the pressure that keeps the blood circulating through our arteries to deliver blood to all our organs. If we slithered around like snakes, walked around on all fours like cats or if our brains were more or less on the same level as our hearts, then a low pressure would be needed to deliver the blood from the heart to the brain. Imagine what would happen if we suddenly stood upright: this low level of pressure would be insufficient to send the blood up to our heads and we would lose consciousness and fall over. With our heads so far above our hearts we need a higher level of pressure than a cat or a dog to send blood to the brain - giraffes require a pressure that is higher still
Blood pressure, or the pressure in the arteries, can be compared to the pressure required in a central heating system to send hot water from the boiler to the radiators in the upper floors of a house. Your heart is akin to the pump of the central heating system, the driving force that delivers blood around the body. The height of the blood pressure will depend both on the amount of blood that is pumped out by the heart with each beat, and also how vigorous or strong the heart muscle is.
However, the heart is far from being the ruling force in the control of blood pressure. As doctors have learned more about the causes of high blood pressure, it is now known that the heart is not nearly as important as the arterial system (sometimes known as the arterial tree) in the body
Let us imagine that the heart pumps 5 litres per minute around the body. If the arteries in the body are nicely relaxed and dilated (expanded), then the pressure in those arteries will be low, but if the arteries become narrowed or constricted, then the same 5 litres a minute will produce a much higher resistance, and hence a higher pressure
The concept of resistance to flow being related to the diameter of the blood vessels can easily be illustrated using the example of a garden hose. If you turn the hose full on and just let the water flow out through the end of the hose, then the stream may run for about a foot before falling to the ground. Now attach an adjustable nozzle that enables you to project the water for several feet in front of you onto distant flowerbeds. By adjusting the nozzle to achieve the maximum distance, you are in fact narrowing the orifice through which the water will flow so that it comes out at much higher pressure and will travel further
The open garden hose, therefore, represents your arteries when they are dilated or relaxed; the nozzle, at its tightest, represents the arteries when they are constricted. The tight hose nozzle is a high-resistance system that produces high pressure, and the open hose is a low-resistance system which equates to low pressure. In the body, it is the resistance produced by the arteries which dictates the blood pressure. Abnormally high resistance will make the blood pressure too high, causing high blood pressure (also known as hypertension)
The Arterioles It is not the largest arteries in the body which control resistance, but the smaller ones known as arterioles. These arterioles are controlled by many complex systems within the body, and it is quite normal for resistance in the arterioles to vary from organ to organ depending upon what we are doing. For example, after a meal the digestive system needs more blood, whereas the muscles need less. Resistance in the arterioles that deliver blood to the intestines will therefore be reduced, enabling blood flow to be diverted there, whilst arterioles in the muscles will constrict so blood is sent away from the muscles to where it is most needed. When we exercise, our hearts beat faster to increase the amount of blood travelling around the arterial system, but the arterioles supplying the muscles in the legs and arms will dilate, reducing resistance there, while blood flow to the intestines will be lowered
This regulatory mechanism of the arterioles helps us survive major trauma such as blood loss. If we have an accident and lose a substantial amount of blood, then blood flow must be preserved for the essential organs - namely the brain, the heart and the kidneys - to keep us alive. Arterioles to the skin and muscles will constrict so that what blood is left can be pumped at sufficient pressure to keep the brain, the heart and the kidneys working. This explains why someone who has lost a lot of blood has such cold skin
In patients who have abnormally high blood pressure, a persistently raised resistance in the arterioles is the major abnormality. The causes of this will be explained in Chapter ThreeBlood pressure is therefore not constant, and will change continuously depending upon the amount of blood pumped out by the heart and the resistance in the blood vessels. Blood pressure will fall while we are asleep and horizontal, and go up when we are active and upright. Figure 1.1 shows a print-out from a 24-hour blood pressure monitor showing the top and bottom readings and how they change when we are awake and when we are asleep (I will return to the definitions of the top and bottom readings below)
In patients with high blood pressure, the surges in pressure that occur on waking and in the morning hours may be responsible for the higher incidence of heart attacks and strokes at these times of the day (see Chapter Five)
About the author
Dr Duncan Dymond MD FRCP FACC FESC is a Consultant Cardiologist at St. Bartholomews Hospital, London and, despite his impressive medical and academic qualifications, is able to communicate very clearly in lay-person terms. Dr Dymond is the author of Jargon Busters Guide to Heart Attacks and also writes on a frequent basis in the Daily Mail
He has also appeared on various radio and TV programmes including Gloria Hunniford's Open House.
