Effects of acute and chronic angiotensin converting enzyme inhibition by spirapril on cardiovascular regulation in essential hypertensive patients. Assessment by spectral analysis and haemodynamic measurements.

1. The effects of a first dose and of chronic treatment with spirapril, a novel angiotensin converting enzyme (ACE) inhibitor, on short-term blood pressure and heart rate fluctuations were assessed by fast Fourier spectral analysis. The effects on systemic haemodynamics in supine and standing position were also studied. We treated 11 patients with 3 mg and 13 patients with 12 mg spirapril for 8 weeks. 2. Overall blood pressure variability was not changed by spirapril. By spectral analysis the changes in blood pressure and heart rate variability in various frequency bands can be assessed, which may be related to changes in activity of the autonomic nervous system. The relative power in the mid-frequency band (0.08-0.12 Hz) of supine systolic pressure was 23 +/- 10% during placebo and decreased during treatment with 12 mg to 11 +/- 4% (P < 0.01 vs placebo, first dose) and to 13 +/- 6% (P < 0.01, chronic treatment). Standing systolic mid-frequency power was 38 +/- 12% during placebo and decreased to 27 +/- 9% (P < 0.01 vs placebo) after the first dose of 12 mg, but it did not decrease after chronic treatment (29 +/- 13%). Treatment with 3 mg induced no changes in mid-frequency blood pressure variability. A decrease in power of the mid-frequency band may point to a decrease in sympathetic vascular drive. The power in the high-frequency band (0.15-0.40 Hz) of heart rate did not change after treatment, suggesting that there is no change in the vagal cardiac drive. 3. Supine blood pressure decreased by a decrease in vascular resistance by 16 +/- 23% (3 mg) and 14 +/- 19% (12 mg) after 8 weeks treatment. Heart rate, stroke volume and cardiac output did not change. No orthostatic hypotension occurred after the first dose. In the 12 mg group the orthostatic induced rise in heart rate (compared with supine) increased from + 9 +/- 5 beats min-1 (placebo) to + 14 +/- 4 beats min-1 (P < 0.05) after the first dose. No changes in the orthostatic heart rate increase occurred in the 3 mg group. The orthostatic changes in stroke volume, cardiac output and vascular resistance were not influenced by spirapril. 4. In conclusion, the decrease in mid-frequency blood pressure variability may suggest an inhibitory effect of acute and chronic ACE inhibition upon sympathetic vasomotor control. Vagal activity was not influenced as high-frequency heart rate variability did not change. Acute and chronic ACE inhibition did not blunt important cardiovascular reflexes, as the haemodynamic response to orthostasis remained intact.