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The body can be regarded as a rather special internal combustion engine, insofar as its ability to perform mechanical work is concerned. Some of this work is expended to keep it alive, for instance by pumping the blood round and breathing, whilst the rest appears as external activity. Walking, running and lifting sacks of coal all involve the expenditure of energy which ultimately has to be derived from the fuel, i.e. the food supplied to the body. Just as in a car engine, not all the energy contained in food can be converted into mechanical work; at best only about 20% appears as work, the rest being converted into heat.
There are many occasions when one wants to measure how hard an individual is working or more correctly how much energy he is consuming. This is important in fields as diverse as the organisation of some industrial production processes in order to minimise the load on the worker, and the investigation of the factors causing obesity.
In a petrol engine we could measure the rate at which fuel is being consumed quite easily but in man it is impossible to measure fuel consumption directly, because our bodies contain large and variable energy stores on which we draw to supply our immediate needs.
However, we cannot store any substantial amounts of the oxygen which is required to 'burn' the fuel, and if therefore we were to measure the amount of oxygen removed from the inspired air this would provide an indirect but convenient method of measuring energy expenditure. This procedure is known as 'indirect calorimetry' and is performed these days by using interesting and complex physical methods of air flow measurement and gas analysis. We will endeavour to measure the efficiency of the human engine and compare it with that of a small petrol driven generator.
The heart was at one time thought to be the very seat of life and personality, and indeed we still speak of black hearted villains and soft hearted aunts. This was so presumably because the most obvious immediate sign of death was cessation of the heart beat. We now know that the heart is just a blood pump, or more correctly a pair of pumps, which are responsible for keeping the major transport system of the body in continuous motion. This knowledge has not decreased the importance of the heart because at normal body temperature we cannot survive a cardiac arrest of more than a few minutes.
The blood is the distribution system which supplies every cell in the body with nutrients and oxygen; the refuse collection agency which removes carbon dioxide and waste products from the cells; a branch of the post office which carries chemical messages from one organ or tissue to another, and the central heating or cooling system which ensures that heat is taken away from hard working parts of the body and supplied to other parts which only work correctly if kept at a constant temperature.
The demands of the body can vary considerably between say sleep and running as hard as you can. These can be met by increasing the speed and stroke volume of the pump, and also by adjusting the diameter of the blood vessels so that the blood can be directed to where it is needed most. Because one does not normally want to puncture the system one has to use indirect methods in order to find out what goes on inside it; for instance at what pressure is the heart delivering the blood, how fast is it flowing in different large arteries or veins, or even how much oxygen is being carried? One of the more difficult measurements is to find out how much blood the heart is actually pumping and how efficiently it does it. We shall try and find out all these things without spilling a drop!
It is one of the properties of muscle and nerve cells that their activity is accompanied by electrical events which can be detected outside the cells. An extreme manifestation of this effect is found in electric fish where special cells similar to muscle cells are connected in series like a multi-cell battery to produce external voltages sufficient to stun other fish.
This does not mean that muscles are in any sense electrically operated, or that nerves convey signals in the same way as copper wires, but only that chemical changes which take place at cell membranes when they are active also produce electrical signals. These sometimes may start further chemical changes in neighbouring cells thus stimulating them into activity or in the case of a nerve fibre will stimulate the next section of fibre thus causing the activity to travel along it.
Tissue in bulk is quite a good conductor of electricity because it consists mainly of salty water, and skin can be made reasonably conductive by appropriate treatment. In consequence electrodes applied to the skin can pick up signals from tissues deep inside the body. There are problems, however, just due to the fact that the whole of the inside of the body is conducting, because signals from many different sources can be mixed up with one another at the site of the electrodes. It is rather like fixing a microphone on to the outside wall of a large room in which there is a noisy party. Individual conversations, unless they happened to be very close to the microphone, would be impossible to distinguish, but you might be able to say that a lot of talking was going on. The band which produces a large and organised signal would come through quite clearly, and if a number of the party-goers all started to do the same thing like shouting 'fire', or encouraging the teams in a tug-of-war, then their collective signal would become apparent. If one wants to investigate the electrical activity of the body one faces exactly the same p
If one had to associate a particular instrument with doctors in general, it would certainly be the stethoscope. It enables him with convenience and decorum to listen to the noises inside his patient. Most of the interesting noises occur in the chest and in particular in or close to the heart, though bowel sounds have also received some attention. The interpretation of the sounds takes experience, but this can be supplemented by detecting the sounds electronically and displaying them as a picture, when it also becomes possible to measure the time relationship between them.
Man is really a tube about 10 metres long, if one considers the path between mouth and anus in which all our food is digested. It is not easy to explore the inside of this tube except close to the two ends. One way of measuring some of the physical conditions inside it such as pressure, temperature, movement, and even acidity is to swallow a very small radio-transmitter equipped with means to modultate the radio signal in accordance with the conditions it encounters. Such a transmitter can be allowed to pass right through the system, transmitting as it is moved along.
Another way of exploring the alimentary canal, which is also applicable to the tubes in the lung, is to use an endoscope. This is an optical system which can allow one to see round corners and also to examine in detail whatever is close to the tip of the device. When great flexibility is required endoscopes can be made out of bundles of special glass fibres, where each fibre carries one image point from the input end of the bundle to the viewing end. It is important therefore that the geometrical arrangement of the ends of the fibres at the two ends is identical in order to avoid scrambling the image, a requirement which makes them difficult and expensive to construct.
To be asked to diagnose a fault inside such a complex system as the human body without being able to look inside it would appear to make the task very difficult, yet this is a problem doctors had to face until the advent of X-rays at the turn of the century. Tissue and bone, except in very thin layers, are opaque to visible light; we cannot therefore look through or into the body in the ordinary sense at all. Other forms of electromagnetic radiation can penetrate tissue and bone to varying degrees, and with their aid avisible image can be reconstructed.
The most common form are X-rays which, until recently. Were only capable of producing a shadow picture in which fine detail could be obscured by denser shadows. Recent developments in X-ray scanning and subsequent construction of the image point by point, with the aid of a computer, have produced a spectacular improvement.
Gamma-rays, of even shorter wavelength than X-rays, are emitted by certain radioactive isotopes. Some of these isotopes are taken up preferentially by particular tissues or organs when introduced into the body. The gamma-rays can pass through tissue and with appropriate equipment a crude image can be obtained which shows where in the body the isotope has accumulated.
Then there is infra-red radiation, of rather longer wavelength than light, which can penetrate tissue to a small extent. However it is also emitted from the skin surface in relation to its temperature, and therefore an infra-red picture of a portion of the body will really be a temperature map of the surface and structures just beneath it. This is useful because inflammation or abnormal rate of growth will result in high temperature areas, and lack of blood supply in low temperature regions.
Lastly there is ultrasound, not an electromagnetic radiation, but just a mechanical vibration in a material at a much higher frequency than ordinary sound. A beam of ultrasound aimed into the body will be partially reflected whenever it
It is part of everyday social experience that we receive and send out signals indicative of our emotional or mental state. 'He looked happy' ... 'she sounded rather anxious' ... 'he parted with a confident handshake' ... 'there was the smell of fear about' ..., are all phrases which we use without really thinking about the nature of the signals involved. Most of the code, irrespective of the sense through which the message is received, almost certainly has to be learned. If we are faced with an individual whose social training has been entirely in another culture, such as a Japanese who has never been to Europe before, only very elementary signals get through in either direction. Perfume, make-up, and even hair styles may be used as signal flags which reinforce the impression we would like to create, probably by imitating and exaggerating the natural code. So far there is very little about this which we can measure, though there are people like caricaturists and actors who have obviously identified some of the important parts of the code and can produce the signals at will.
On the other hand emotion also affects many of the physiological factors mentioned in the previous lectures. This is a disadvantage to the doctor who may be misled by a temporary, emotion induced, abnormality, but also provides the basis for the work on 'lie detectors'. Some are obvious to the naked eye. a blush or a sudden pallor are no more than a change in the blood supply to the skin for instance.
During this course of lectures you, the audience, will get some impression of the personality and mood of the speaker, try to identify the clues on which you base your conclusions!
