The influence of angiotensin II-induced vasoconstriction on common carotid artery blood flow and velocity-time profiles in normal women.
Non-invasive methods of measuring blood velocity, especially Doppler velocimetry, are being increasingly used in obstetrics to provide observational information. We report a preliminary study of their usefulness in experimental studies. Doppler velocimetry was used to assess blood flow and velocity-time profiles in the common carotid artery of seven women of reproductive age before and during the incremental administration of angiotensin II. Angiotensin II infusion evoked the expected increments in systolic and diastolic arterial pressure and fall in heart rate. Angiotensin II was associated with a dose-dependent fall in maximum blood velocity, which, at an average rise in systolic blood pressure of 23 mmHg, had fallen from 91 +/- 16 to 52 +/- 4 (mean +/- SD, p < 0.01). Absolute maximum blood velocity was strongly correlated with systolic and diastolic blood pressures (p < 0.001 for both). The minimum velocity was unaltered throughout, and the calculated flow did not change significantly (490 +/- 100 cf. 380 +/- 50 ml/min). Overall, these findings are in agreement with those previously reported using invasive methods of monitoring flow during angiotensin II infusion, and further support the usefulness of Doppler velocimetry as an investigative tool in human physiology and pharmacology.However, the pulsatility index, resistance index and systolic/diastolic velocity ratio all fell significantly during angiotensin II infusion (p < 0.01 for all). The conventional interpretation of a fall in these indices, i.e. reduced downstream resistance, is clearly erroneous under these circumstances, since angiotensin II induces arteriolar vasoconstriction. This illustrates the importance of interpretation of Doppler velocity envelopes in the light of pharmacological mechanisms likely to be evoked by the experimental procedure.
Loquet
P
P
Department of Therapeutics, University Hospital, Nottingham, UK.
Broughton  Pipkin
F
F
Symonds
E M
EM
Rubin
P C
PC