title: Ultrasound entropy may be a new non-invasive measure of pre-clinical vascular damage in young hypertensive patients.
abstract: 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.
  
  
  CONCLUSIONS
  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.
  
  
  BACKGROUND
  Clinical Trials.gov, NCT01047423.
authors.affiliation: Department of Cardiovascular Therapeutics & Pharmacology, Queen's University Belfast, Belfast, Northern Ireland. c.bleakley@yahoo.co.uk.|Department of Cardiology, Belfast City Hospital, Lisburn Road, Belfast BT9 7AB, Belfast, Northern Ireland. c.bleakley@yahoo.co.uk.
authors.forename: Caroline
authors.initials: C
authors.lastname: Bleakley
authors.affiliation: Department of Medical Physics, Queen's University Belfast, Belfast, Northern Ireland. aaron.mccann@belfasttrust.hscni.net.
authors.forename: Aaron
authors.initials: A
authors.lastname: McCann
authors.affiliation: Department of Cardiovascular Therapeutics & Pharmacology, Queen's University Belfast, Belfast, Northern Ireland. viv.c.r.n@hotmail.co.uk.
authors.forename: Vivienne
authors.initials: V
authors.lastname: McClenaghan
authors.affiliation: Department of Cardiovascular Therapeutics & Pharmacology, Queen's University Belfast, Belfast, Northern Ireland. pk_hamilton@yahoo.co.uk.
authors.forename: Paul Kevin
authors.initials: PK
authors.lastname: Hamilton
authors.affiliation: Department of Cardiovascular Therapeutics & Pharmacology, Queen's University Belfast, Belfast, Northern Ireland. auleenmillar@hotmail.com.
authors.forename: Auleen
authors.initials: A
authors.lastname: Millar
authors.affiliation: Department of Cardiovascular Therapeutics & Pharmacology, Queen's University Belfast, Belfast, Northern Ireland. r.plumb@qub.ac.uk.
authors.forename: Richard
authors.initials: R
authors.lastname: Pumb
authors.affiliation: Department of Cardiovascular Therapeutics & Pharmacology, Queen's University Belfast, Belfast, Northern Ireland. m.harbinson@qub.ac.uk.
authors.forename: Mark
authors.initials: M
authors.lastname: Harbinson
authors.affiliation: Department of Cardiovascular Therapeutics & Pharmacology, Queen's University Belfast, Belfast, Northern Ireland. g.mcveigh@qub.ac.uk.
authors.forename: Gary Eugene
authors.initials: GE
authors.lastname: McVeigh
mesh_terms: D000328:Adult; D000465:Algorithms; D002339:Carotid Arteries / Q000000981:diagnostic imaging*; D002340:Carotid Artery Diseases / Q000000981:diagnostic imaging* / Q000209:etiology*; D019277:Entropy; D005260:Female; D006801:Humans; D006973:Hypertension / Q000000981:diagnostic imaging* / Q000209:etiology*; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008297:Male; D008875:Middle Aged; D010363:Pattern Recognition, Automated / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014463:Ultrasonography / Q000379:methods*; D058067:Wavelet Analysis