Spectrum of autonomic cardiovascular neuropathy in diabetes

Diabetic patients with incapacitating orthostatic hypotension can have either a "hyperadrenergic" or "hypoadrenergic" presentation. Although the latter is related to overt autonomic neuropathy, the former is proposed to be explained by appropriate autonomic responses. We hypothesize, however, that both conditions are part of a spectrum of autonomic dysfunction.

We studied 16 consecutive diabetic patients with preserved renal function referred for incapacitating orthostatic hypotension and characterized their autonomic and neurohumoral cardiovascular regulation.

Six patients had a hyperadrenergic orthostatic response: systolic blood pressure fell 42 +/- 15 mmHg, heart rate increased 20 +/- 3 bpm, and plasma norepinephrine increased from 340 +/- 80 to 910 +/- 100 pg/ml. Ten patients had a hypoadrenergic response: systolic blood pressure fell 78 +/- 5 mmHg, heart rate increased only 7 +/- 3 bpm, and norepinephrine increased only from 130 +/- 28 to 230 +/- 40 pg/ml. Vagal (sinus arrhythmia, Valsalva ratio) and sympathetic (response to hyperventilation, postprandial hypotension) responses were impaired in both groups, but to a greater extent in the hypoadrenergic group. Notwithstanding severe orthostatic hypotension, the postural increase in plasma renin was blunted in both groups, more so in the hypoadrenergic group. Despite preserved renal function, patients had mild anemia due to impaired erythropoietin release, as seen in primary cases of autonomic failure.

Our results suggest that diabetic patients presenting with hyperadrenergic orthostatic hypotension have an initial stage of autonomic neuropathy, with overtly abnormal vagal function and early signs of sympathetic impairment. Furthermore, altered renin response can contribute to the patients' orthostatic hypotension.