dizziness

dizziness The term ‘dizziness’ is used to describe both ‘lightheadedness’ and vertigo. Lightheadedness may consist of a clouding of consciousness, a difficulty in focusing rational thought, or a difficulty in concentrating. Vertigo is the illusion of movement either of oneself or of the surroundings.

The illusion of movement, when the neighbouring train departs the station, or the feeling of being drawn toward the ground or the sea when standing on a high point, are recognized by many. The feeling of falling is a part of our dreams. We enjoy the illusion of movement in 3-D and circular surround cinemas. Children enjoy the vertigo they can trigger by spinning on the spot. All these are perceptions we have in the absence of illness, but many people experience dizziness as part of an illness, which can ruin their quality of life and lead to a loss of independence. Lightheadedness and vertigo can lead to a final common pathway of anxiety and hyperventilation, resulting in a spiral of deteriorating lightheadedness. This overlap of symptoms and the final common pathway justify the acceptance of the term ‘dizziness’.

Balance information is processed within the vestibular nuclei of the brain stem. Inputs include the sensory organs of the ears and eyes, proprioceptive and tactile sense, and higher centres in the brain. There is no single area of the cerebral cortex involved with balance information alone. On the contrary, PET scanning (positron emission tomography, which ‘maps’ relative activity in the different regions of the brain) reveals that balance-related inputs influence many large areas of the cerebral cortex. Therefore, dizziness can lead to a myriad of symptoms, depending on which areas of the brain are involved. The extent of these complex connections is highlighted by the effect of stimulating the balance organs of the left ear, by running cold water into the left ear canal, in patients with left-sided sensory ‘hemi-neglect’ due to a right cerebral hemisphere stroke. For several minutes after the irrigation of the water into the left ear, during the dizziness which this causes, function may be improved in the previously numb and poorly-used left side of the body. This complex neuronal networking is also crucial to our ability to suppress dizziness with training or rehabilitation, as pilots, gymnasts, and dancers demonstrate.

Any factors that can alter the function of the many parts of the brain dealing with balance function can lead to dizziness and a variable cluster of symptoms. These include any cause of inadequate blood flow (and therefore of oxygen and glucose supply) to the brain — as for example at the onset of fainting, or in illnesses causing heart failure or obstruction of the blood vessels — or impaired nutrient supply due to decrease in blood sugar (hypoglycaemia). Inadequate brain blood flow may result from overbreathing (hyperventilation) — from whatever cause, including pain. Dizziness may also be the result of environmental agents, such as carbon monoxide poisoning from faulty domestic appliances or car exhaust fumes, which again impair the brain's oxygen supply. Likewise with other causes of oxygen shortage (hypoxia) such as high altitude or lung disease.

Damage to the balance organs themselves, as a result of trauma, infection, or other disease affecting the inner ears, may result in dizziness, though the brain has a remarkable capacity to compensate fully for such pathology. For reasons that are currently being investigated, some patients become over-reliant on visual clues for stability, and they become dizzy when they are exposed to excessive visual clues, such as in shopping malls, even when there is no definable structural pathology.

Dizziness can therefore be a manifestation of illness anywhere in the body; to determine the cause, a careful evaluation of the patient and their circumstances is essential.

Peter Savundra

See also balance; fainting; proprioception; vestibular system.