In neurology, the most common respiratory problem is neuromuscular disease leading to hypoventilation. Respiratory muscles still functioning are called upon to work much harder, leading to muscle pains, anxiety, exhaustion and weight loss. Cough becomes weak and ineffective, secretions accumulate and are difficult to expel, hypoxia and hypercapnoea follow hypoventilation. Hypoventilation is associated with multiple discomforts, including dyspnoea, sleeplessness, daytime fatigue and sleepiness, morning headache, difficulty in phonation and the risk of aspiration pneumonia.

Unlike those who suffer from cardiac or respiratory disease, who experience major respiratory distress, a failing respiration may occur very quietly in neuromuscular disease, with no apparent resultant difficulty in breathing. If this is not recognized, persons suffering from myasthenia gravis or polyneuropathy may develop severe problems before observers realize they are not breathing effectively.

DYSPNOEA

Respiration is a finely balanced automatic process, controlled by multiple receptors sensing posture, lung and airway stretch, blood gases, muscle movement, even odours and airflow. Various kinds of imbalance are possible, and may coexist, upsetting the automatic adjustment of respiratory effort, and causing a feeling that respiratory muscles must work harder to maintain comfort.

Dyspnoea, an uncomfortable awareness of breathing, is a subjective discomfort, and its relationship with objective measures of respiratory function is complicated by the many other factors of circumstance and emotion. It will occur when there is a need for increased respiratory effort (as in lung disease) or an increased ventilatory requirement (as in hypoxaemia, anaemia or metabolic acidosis).