The abnormal heart rate response to a deep breath in borderline labile hypertension: a sign of autonomic nervous system dysfunction.

A group of patients with borderline or labile hypertension were prospectively recruited and asked to take a deep breath while lying supine and being monitored by electrocardiography. Their attenuated heart rate responses were sharply abnormal, demonstrating an excessively rapid rate throughout but without quickening on inspiration nor slowing with expiration. It is suggested that this further demonstrates inadequate autonomic control, sympathetic and parasympathetic, of the heart in labile hypertension and even at a moment when the patient's blood pressure is normal.