Effects of blood pressure reduction on central arterial pressure waves in severe pre-eclampsia
BACKGROUND Hypertensive disorders of pregnancy are the second commonest cause of morbidity and mortality in pregnancy. Severe pre-eclampsia is a hypertensive emergency with a high mortality rate. Even in survivors of pre-eclampsia, the lifelong risk of cardiac events is increasedUntreated hypertension results in target organ damage in organs which are supplied by a pulsatile blood flow, such as the kidneys and the brain. AIM Although blood pressure (BP) reduction in severe pre-eclampsia is well recognised as preventing the complications thereof, the impact of BP reduction on central arterial pulsatile load mediated by wave reflection, which is not detected at the brachial pulse, is unknown. METHODS Using non-invasive tonometric approaches and wave separation analysis (SphygmoCor software) the impact of BP reduction using standard pharmacological approaches on central arterial pressure waves was determined in 19 women with a de novo diagnosis of severe pre-eclampsia.RESULTS Whilst brachial BP was markedly reduced (p<0.0001), brachial pulse pressure (PP) failed to show significant decreases (p=0.10) with therapy. In contrast, even after adjustments for steady component pressures (mean arterial pressure) central arterial PP (PPc) decreased (p<0.01) and this change was attributed to an attenuation of reflected (backward wave, Pb) (p<0.05), but not forward (p=0.64) wave pressures. Although pharmacological reduction in BP was strongly associated with decreases in arteriolar tone (as indexed by mean arterial pressure, MAP), the strong relations between decreases in Pb and PPc (p<0.0001) were unaffected by adjustments for MAP. CONCLUSION This study is the first to assess the effect of antihypertensive therapy on central aortic pressures in a hypertensive emergency. Central arterial pulsatile load is decreased by standard pharmacological approaches to managing hypertensive emergencies in pre-eclampsia. Importantly, this effect is through an impact of therapy on wave reflection independent of arteriolar function and no peripheral BP measure adequately indexes this beneficial effect.
A research report submitted in partial fulfilment of the requirements for the degree of Master of Medicine in Anaesthesia to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, 2020