Hyperventilation in Postural Hypotension

In normal subjects hyperventilation causes a drop in arterial blood pressure, apparently because of the direct effect of hypocapnia on the peripheral vessels. In persons with disease of the auto-nomic nervous system, the drop in blood pressure is much greater because it is not effectively opposed by reflex vasoconstriction. Consequently, hyperventilation caused by anxiety may greatly intensify postural hypotension in such patients and contribute significantly to their disability. A pertinent case is reported. PATIENTS with postural hypotension from disease of the autonomic nervous system present an easy problem in diagnosis, but a difficult problem in therapy. The purpose of this paper is to point out the unusual response to overbreathing seen in these subjects and to call attention to the fact that prevention of the loss of carbon dioxide may be occasionally of therapeutic importance. Hyperventilation is a frequent cause of dis-turbances in consciousness in anxious patients when they are lying down. When these pa-tients stand, increased reflex action from standing, the usual postural fall in cerebral arterial pressure, and anxiety, caused by queer feelings from carbon dioxide loss, combine to produce marked overactivity of the auto-nomic nervous system and the common faint (reflex vasodyspnea syncope). Unless one faints, large and maintained falls in arterial pressure are not usually seen with emotional overbreathing. In our experience the disturbances in blood pressure and consciousness produced by stand-ing in patients with disease of the autonomic nervous system are not usually accompanied by hyperventilation. Our attention was called to the adverse effect of carbon dioxide los