Ultrasound entropy may be a new non-invasive measure of pre-clinical vascular damage in young hypertensive patients

BACKGROUND: The identification of pre-clinical microvascular damage in hypertension by non-invasive techniques has proved frustrating for clinicians. This proof of concept study investigated whether entropy, a novel summary measure for characterizing blood velocity waveforms, is altered in participants with hypertension and may therefore be useful in risk stratification. METHODS: Doppler ultrasound waveforms were obtained from the carotid and retrobulbar circulation in 42 participants with uncomplicated grade 1 hypertension (mean systolic/diastolic blood pressure (BP) 142/92 mmHg), and 26 healthy controls (mean systolic/diastolic BP 116/69 mmHg). Mean wavelet entropy was derived from flow-velocity data and compared with traditional haemodynamic measures of microvascular function, namely the resistive and pulsatility indices. RESULTS: Entropy, was significantly higher in control participants in the central retinal artery (CRA) (differential mean 0.11 (standard error 0.05 cms(−1)), CI 0.009 to 0.219, p 0.017) and ophthalmic artery (0.12 (0.05), CI 0.004 to 0.215, p 0.04). In comparison, the resistive index (0.12 (0.05), CI 0.005 to 0.226, p 0.029) and pulsatility index (0.96 (0.38), CI 0.19 to 1.72, p 0.015) showed significant differences between groups in the CRA alone. Regression analysis indicated that entropy was significantly influenced by age and systolic blood pressure (r values 0.4-0.6). None of the measures were significantly altered in the larger conduit vessel. CONCLUSION: This is the first application of entropy to human blood velocity waveform analysis and shows that this new technique has the ability to discriminate health from early hypertensive disease, thereby promoting the early identification of cardiovascular disease in a young hypertensive population. CLINICAL TRIAL REGISTRATION: Clinical Trials.gov, NCT0104742

Statin therapy does not significantly alter microvascular function in uncomplicated hypertension

Objective Young patients with uncomplicated hypertension are frequently exempt from statin therapy as they generally fall below current treatment thresholds. This study examined whether there may be evidence of improved microvascular function in young patients with grade 1 hypertension after 12 weeks of statin therapy. Methods This was a randomized double-blind placebo-controlled crossover study in which 42 statin-naïve participants with grade 1 hypertension (mean systolic/diastolic blood pressure 142/92 mmHg) were randomized to receive either simvastatin 40 mg or a placebo for 12 weeks, followed by a 4-week washout period, after which the arms crossed for a further 12 weeks. Measures of vascular function were recorded at the beginning and end of each study period equating to four measures in total. The brachial artery was studied by flow-mediated dilatation (FMD) together with the resistive and pulsatility indices and mean velocity of flow. Results Statin therapy did not significantly alter the change in FMD seen in the brachial artery [standardized differential mean = 0.02 (0.23), confidence interval (CI) = −0.45 to 0.48, p = 0.932]. No significant changes were seen in the brachial artery mean velocity (CI = −9.68 to 11.51, p = 0.861), resistive index (CI = −0.11 to 0.12, p = 0.903), or pulsatility index (CI = −5.82 to 4.91, p = 0.864). Conclusion This study did not demonstrate any significant changes in established measures of microvascular function after treatment with a statin in a young hypertensive population with no antecedent cardiovascular disease. This may indicate that either the intervention was insufficiently vasoactive to produce a clinically detectable improvement in vascular function, or that the means used to assess the microvasculature were insufficiently sensitive to detect what may have been quite minor changes. </jats:sec

Impaired microvascular properties in uncomplicated type 1 diabetes identified by Doppler ultrasound of the ocular circulation

Objective: Quantification of Doppler flow velocity waveforms has been shown to predict adverse cardiovascular outcomes and identify altered downstream haemodynamics and vascular damage in a number of organ beds. We employed novel techniques to quantify Doppler flow velocity waveforms from the retro bulbar circulation.Methods and results: In total, 39 patients with uncomplicated Type 1 diabetes mellitus, and no other significant cardiovascular risk factors were compared with 30 control subjects. Flow velocity waveforms were captured from the ophthalmic artery (OA), central retinal artery (CRA) and the common carotid artery. The flow velocity profiles were analysed in the time domain to calculate the resistive index (RI), and time-frequency domain using novel discrete wavelet transform methods for comparison. Analysis of flow waveforms from the OA and CRA identified specific frequency band differences between groups, occurring independently of potential haemodynamic or metabolic confounding influences. No changes were identified in the calculated RI from any arterial site.Conclusion: Novel analysis of the arterial flow velocity waveforms recorded from the retro bulbar circulation identified quantifiable differences in Doppler flow velocity waveform morphology in patients with diabetes prior to the development of overt retinopathy. The technique may be useful as an additional marker of cardiovascular risk.<br/