O P Tungland MD - Consultant Audiological Physician

 

The postural system refers to what we usually call balance. Keeping our balance is something we learn, just as we learn to speak, by practise, until we speak and move unconsciously. We’ve all seen small children first of all lifting themselves to crawl, until by the age of about 12 months they can stand up, then gradually taking their first faltering steps holding on to objects and people around them.

The crucial difference between a child that can do this and one that can not, is that the child who has stood up has lifted the eyes from the floor and started to form a perception of the horizon and thereby the vertical. At this stage the child will regularly fall, while the brain tries to maintain it in a desired position in relation to the perceptual horizontal and vertical. This learning process goes on, building up a ‘postural memory’ so that by the age of about four and a half it can walk without thinking about it.

The postural ‘memory’ is built up by the simultaneous sensory input from these three systems: The musculo-skeletal (proprioseptive) system plus the sensation of touch and pressure, the vision and the balance organs in the inner ears.

Sensors in the muscles, the bones and the joint capsules, inform the brain when the muscles contract or relax, thereby registering movement or angulations of the joints, in particularly the ankles, hips and neck. The ankles because they regulate small sway, the hips because they regulate larger sway and the neck and shoulders because they control the position of the head where the two other organs plus the brain are situated! The combination of touch and pressure informs the brain about, for example, our clothing - whether shoes are comfortable or not and what surface we are walking on.

The two balance organs, one on each side in the inner ears, work together to tell our brain about acceleration and stoppage in a linear or angular manner and how gravity is affecting us. Simplistically one could say that one side gets excited while the other inhibits as we move, in order to have a stable net information, seen from the brain. So, when one of them stops working properly, which may be for a variety of reasons, there is a loss of inhibition of the normal activity of the healthy side, giving a sensation of spinning in the direction on the normal side. This is what we call vertigo.

Keeping our balance also requires information from our eyes as to where we are in space and what is happening in that space. The balance organs are involved in keeping our eyes fixed on an object while we move our head, and to maintain a steady image of the horizon through the vestibular ocular reflex, which prevents our eyes from bobbing up and down as we walk. This is well illustrated by the fact that when we shake our heads and look at something, such as the page of a book, we can still read it, but if we shake the book and keep our heads still, we can’t, because the words become blurred.  When we follow an object with our eyes it actually passes from one side of the retina to the other at a greater speed then the eye movement giving an impression of movement. However, if you manage to keep your eyes on the moving object at the same speed as the object, it gives you a feeling that the background moves. In other words, it is the peripheral vision that registers movement.

As we learn to move and register visual impressions, the brain learns to predict what may happen next and the information from our eyes is also conveyed unconsciously and we merely ‘scan’ our surroundings to avoid, for example, bumping into lamp-posts and other people in crowded places. As long as these three systems simultaneously generate matching information between them, and that information matches the stored information in the postural memory, you maintain your balance. If one of the sensors does not match the other two or does not match the postural memory, you will feel dizzy. However, you can also feel dizzy when there is nothing wrong with any of these systems, but you start registering sensations of conflicting information, such as travel sickness or when you learn ‘new tricks’, like spinning around and trying to walk in a straight line immediately after spinning. Any sudden change, such as when we miss a step, or trip over something, will trigger reflex actions of the arms or legs to compensate, to try to prevent a fall.

There are a number of medical conditions that can create problems in the balance organs, but simplistically they fall into three categories. In the first category there is a loss of function on one side. To understand what symptoms this will create we have to revert to the model of activity and inhibition. With a loss of function, you actually lose the normal inhibition of the continuous activity on the healthy side, which creates a spinning sensation to the healthy side. This spinning lasts until the brain has compensated for the loss, which is usually in the order of 24 to 48 hours. During this time the spinning is continuous and most people are violently sick, cannot move, and are bedridden. When they do get out of bed they will feel very unsteady with short lived spinning sensations in relation to positional changes. They will have a tendency to veer off line while walking, while the brain adjusts and compensates for the loss. However, if they keep on provoking these sensations they rapidly get better and are usually without symptoms within two to eight weeks, depending on age and fitness.

The second category is when there is a fluctuation in the functioning of the balance organ and the hearing organ, leading to a gradual permanent loss of hearing and balance function on one side. Using the same model, these patients would have sudden drops in hearing and balance function giving a hearing loss on one side and a spinning to the opposite healthy side lasting for a minimum of one hour and a maximum of 24 hours, creating nausea and vomiting and usually needing bed rest. However, the function of hearing and balance then starts coming back, and therefore the brain needs to readjust. But in this phase it spins to the sick side in relation to positional changes and general activity, but only for seconds or may be a couple of minutes dependent on the level and speed of improvement in hearing and balance. Unfortunately, most people with this kind of problem think they are going to have a serious attack and therefore go to bed, and may stay in bed until the process has stabilised, which can take from hours to days and even weeks. Provocative activity would shorten this phase considerably.

The third category is related to certain movements, like turning in bed to one side, but not the other, or bending the head back, provoking a spinning sensation that can last from a couple of seconds up to half a minute. It rarely provokes nausea nor vomiting and in most cases stops by itself within three months. These symptoms are generated by ’misplaced’ crystals or debris in one balance organ and can be cured by repositional movements if they do not stop by themselves.

The usual reaction to a feeling of dizziness is fear, we tense our muscles and keep our head still, and we change the way we use our eyes, either by fixing our gaze straight ahead or looking down at the floor to prevent tripping and falling. This change in behaviour, however, changes the simultaneous input from the three sensory organs, which may no longer match each other or the postural memory, thereby producing a sensation of dizziness. The natural reaction is to avoid the position or situation that provokes the dizziness, but unfortunately this usually makes things worse, as the brain is deprived of stimulation. If there is a loss, the brain and the other organs need to compensate for it, and that can only take place by provocation. The same is the case if there are no loss, but a mismatch of information between the sensors.

Most people would lose their confidence, if the sensation dizziness were recurrent. To compensate, we tense up and try to control our balance by using our eyes. At this stage the three systems no longer work together and generate a sensory mismatch that often leads to a visual overload in the conscious part of the brain. This, in turn, triggers autonomic reactions such as hot flushes, cold sweats and clamminess, pallor, nausea and/or hyperventilation, sometimes even leading to loss of consciousness.

As with tinnitus habituation, many patients recover spontaneously when they are given reassurance and information on how the balance system works. Tailor made vestibular rehabilitation exercises will help, as does exercise such as Tai Chi. Tai Chi has proved particularly suitable for older people and anyone whose balance problem may be worsened by complications such as stiffening of the joints and cardiovascular problems.

In older people there are often problems with balance. This may be because of the general ageing process as they begin to lose their strength and vision and not least their confidence. Continued activity is therefore of utmost importance. Simple provocative exercises to increase or maintain activity in order to maintain confidence is essential. Keep the eyes on ‘random activity’ unrelated to balance perception by looking around while walking and only randomly look at the floor.