The grey area of effort syndrome and hyperventilation: from Thomas Lewis to today.

Lewis used the diagnosis 'effort syndrome' for subjects whose ability to make and sustain effort had been reduced by homeostatic failure. A major element was depletion of the body's capacity for buffering the acids produced by exercise. In his view this systems disorder was not to be regarded as a specific organ disease, and losing sight of the metabolic element would foster the invention of fanciful, unphysiological diagnoses. His views were dismissed because normal resting plasma bicarbonate levels were considered by others in that era to exclude serious depletion of the body's total capacity for buffering the effects of exertion. Today, effort syndrome is still a useful diagnosis for a condition of exhaustion and failure of performance associated with depletion of the body's buffering systems. Other elements associated with homeostatic failure are now recognised, principally emotional hyperarousal and hyperventilation. Their physiological interrelationships are described. Effort syndrome is amenable to recovery through rehabilitation, and it may be a mistake to treat chronic fatigue syndrome and unspecific illness without including it in the differential diagnosis.