Breathing movements are directed both reflexly by neurons in the medulla and pons and behaviorally through cortical and limbic neurons. The two modes of control have afferent and efferent interconnections and interact continuously but their relative influences shift considerably through the sleep-waking cycle. In an awaked state behavioral control prevents apnea and by itself is able to maintain normal blood gas tensions except during exercise above the anerobic threshold. During sleep the maintenance of breathing depends on input from chemoreceptors. If apnea should occur during sleep, this is regularly followed by arousal so as to return the control of breathing to the behavioral system. In certain pathological states breathing is persistently regulated either automatically as in the "locked in" syndrome or voluntarily in the congenital central hypoventilation syndrome. Respiratory movements and forces produce sensations that can be accurately perceived and when sufficiently intense result in symptoms of shortness of breath or dyspnea. This in turn can initiate volitional adjustments in the level and pattern of breathing. Dyspnea can have both beneficial and adverse effects. In asthmatics, dyspnea serves as an early warning signal of airway narrowing; but in patients with chronic airways obstruction or in patients with normal lungs and panic disorder dyspnea may be an incapacitating symptom. Recent investigations using techniques such as functional brain imaging and electrical and magnetic brain stimulation as well as increasingly sophisticated psychophysical approaches have provided important insights into the workings of the suprapontine regulation of breathing and its role in health and disease.
Keywords: thoracoabdominal pump, respiratory centers, pulmonary interstitial, vagal afferents, Dyspnea, (PET), brainstem, RESPIRATORY SENSATION
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