Michael F O'Rourke

University of New South Wales, Kensington, New South Wales, Australia

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Publications (81)544.69 Total impact

  • Michael F O'Rourke
    Internal Medicine Journal 04/2014; 44(4):325-30. · 1.82 Impact Factor
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    ABSTRACT: Objectives. Cerebral artery critical closing pressure (CCP) is an estimated parameter with no single accepted method of calculation. Variation between methods could be significant. This study investigates two models to estimate CCP using arterial blood pressure (BP) and middle cerebral artery flow velocity (FV) waveforms, quantifying the difference between radial and aortic BP as the BP input signal. Methods. Suspected and untreated hypertensive subjects (n=445, 203 female, 50±10 years, range 21 to 73 years old), referred to Ruijin Hospital in Shanghai, China, for 24-hours BP monitoring, were recruited. Radial BP and FV waveforms were acquired by applanation tonometry and transcranial Doppler respectively. Aortic BP waveforms were synthesised from the radial waveform using a validated transfer function (SphygmoCor®). CCP was estimated using the relationship between BP and FV waveforms by both linear regression (LR), and the first harmonic (H1) in Fourier decomposition. The difference between the two models was quantified if the BP waveform input signal was radial or aortic and compared by Student’s paired t-test. Results. Use of aortic instead of radial BP resulted in a 29% increase in estimated CCP using the LR model, and 25% increase using the H1 model (Figure, p<0.001). Radial BP resulted in variation between the models (4%, p<0.001). Aortic BP did not cause this variation (0.6%, p=0.49). Conclusions. Aortic, but not radial pressure gave a model independent estimate of CCP. However, estimated CCP within a model was significantly different depending on whether radial or aortic pressure was used.
    Artery Research 09/2013; 7(s 3–4):119.
  • Michael F O'Rourke, Michel E Safar
    Journal of the American College of Cardiology 04/2013; · 14.09 Impact Factor
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    ABSTRACT: Pulse wave velocity (PWV) is a measure of arterial stiffness and its increase with ageing has been associated with damage to cerebral microvessels and cognitive impairment. This study examined the relationship between carotid-femoral PWV and specific domains of cognitive function in a non-demented elderly sample. Data were drawn from the Sydney Memory and Ageing Study, a cohort study of non-demented community-dwelling individuals aged 70-90 years, assessed in successive waves two years apart. In Wave 2, PWV and cognitive function were measured in 319 participants. Linear regression was used to analyse the cross-sectional relationship between arterial stiffness and cognitive function in the whole sample, and separately for men and women. Analysis of covariance was used to assess potential differences in cognition between subjects with PWV measurements in the top and bottom tertiles of the cohort. Covariates were age, education, body mass index, pulse rate, systolic blood pressure, cholesterol, depression, alcohol, smoking, hormone replacement therapy, apolipoprotein E ε4 genotype, use of anti-hypertensive medications, history of stroke, transient ischemic attack, myocardial infarction, angina, diabetes, and also sex for the whole sample analyses. There was no association between PWV and cognition after Bonferroni correction for multiple testing. When examining this association for males and females separately, an association was found in males, with higher PWV being associated with lower global cognition and memory, however, a significant difference between PWV and cognition between males and females was not found. A higher level of PWV was not associated with lower cognitive function in the whole sample.
    PLoS ONE 01/2013; 8(4):e61855. · 3.73 Impact Factor
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    ABSTRACT: We examined whether the central aortic systolic blood pressure, a marker of the function of the systemic arterial tree, might be a more powerful predictor of the development of hypertension than the brachial-ankle pulse wave velocity, a marker of the stiffness of the large- to middle-sized arteries, independent of the conventional risk factors for the development of hypertension. In 1268 Japanese men without hypertension (43±8 years old), the relationships between three variables (the second peak of the radial pressure waveform (SP2), brachial-ankle pulse wave velocity and conventional risk factors measured at the first examination) with the presence of hypertension at the second examination (after 3 years' follow-up) were examined. Hypertension was detected at the second examination in 154 men. The best cutoff points of the brachial-ankle pulse wave velocity and SP2, for predicting the development of hypertension, were 12.7 m/s and 109 mm Hg, respectively. The results of a logistic regression analysis confirmed that an SP2 of 109 mm Hg (odds ratio=8.493, P<0.001) was a more powerful predictor of the development of hypertension than a brachial-ankle pulse wave velocity of 12.7 m/s, independent of the conventional risk factors. The net reclassification index of SP2 (at the best cutoff point) to brachial-ankle pulse wave velocity was 0.211 (P<0.001), indicating that SP2 is a better predictor of the development of hypertension than brachial-ankle pulse wave velocity. In middle-aged Japanese men without hypertension, SP2 may be a more powerful predictor of the development of hypertension than the assessment of stiffness in large to middle-sized arteries independent of the conventional risk factors.Hypertension Research advance online publication, 9 August 2012; doi:10.1038/hr.2012.123.
    Hypertension Research 08/2012; · 2.79 Impact Factor
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    ABSTRACT: Aortic stiffness is a major cause of age-related increase in arterial pulse pressure (PP) and associated increase in work load for the heart. A method to treat this condition is proposed: wrapping the ascending aortic wall with a highly compliant elastic material such that reducing the vessel diameter will shift the pulsatile load from the aortic wall to the wrap, thus increasing the functional compliance of the ascending aorta and decreasing the cardiac load. A multibranched mathematical model of the arterial system, in which every segment of the arterial tree is represented as a uniform elastic circular tube, has been used to simulate the effect of the wrapping procedure on PP and impedance changes, by varying the radius (R) and the stiffness (E) of the ascending aortic segment. The results of the simulation show that PP decreases with an increase in R and a decrease in E. A similar trend, but with a different sensitivity, is observed for the characteristic impedance (Z(c)) changes. The model shows that PP in the ascending aorta can be lowered by 8.8% by reducing R of 20% and decreasing the functional E by 80%, in good agreement with preliminary results obtained from an in vitro pilot study of elastic wrap in aortas. In conclusion, the modelling study demonstrates that the proposed aortic wrapping procedure is able to compensate for the increase in PP associated with R reduction by a decrease in PP determined by a reduction in functional E. Therefore, it supports the use of the aortic wrap as a potential non-pharmacological treatment of age-related increase in PP.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2012; 2012:657-60.
  • Michael F O'Rourke
    Journal of hypertension 07/2012; 30(7):1321-4. · 4.02 Impact Factor
  • Michael F O'Rourke, Michel E Safar
    Journal of hypertension 02/2012; 30(2):429. · 4.02 Impact Factor
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    Michael F O'Rourke, John Clubb
    Journal of the American College of Cardiology 04/2011; 57(14):1570-1; author reply 1571. · 14.09 Impact Factor
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    Journal of the American College of Cardiology 05/2010; 55(19):2183; author reply 2184. · 14.09 Impact Factor
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    ABSTRACT: Pulse waveform characteristics (Augmentation Index--AIx and pulse wave transit time) are measures of the timing and extent of arterial wave reflections. Although previous studies reported an independent association with cardiovascular morbidity, it remains to be established that waveform characteristics, derived from noninvasive pulse waveform analysis, predict cardiovascular outcomes independent of and additional to brachial blood pressure. We prospectively assessed AIx, heart-rate corrected AIx, and pulse wave transit time, using radial applanation tonometry and a validated transfer function to generate the aortic pressure curve, in 520 male patients undergoing coronary angiography. Primary endpoint was a composite of all-cause mortality, myocardial infarction, stroke, cardiac, cerebrovascular, and peripheral revascularization. During a follow-up of 49 months, 170 patients reached the primary endpoint. On the basis of Cox proportional hazards regression models, all pressure waveform characteristics predicted the primary endpoint. A 10% increase of AIx and heart-rate corrected AIx was associated with a 20.5% (95% confidence interval 6.5-36.4, P = 0.003) and 31.4% (95% confidence interval 13.2-52.6, P = 0.0004) increased risk of the primary endpoint, respectively. A 10-ms increase of pulse wave transit time was associated with a 20.8% (95% confidence interval 10.8-29.6, P = 0.0001) lower risk of the primary endpoint. In multiple adjusted models, AIx, heart-rate corrected AIx, and pulse wave transit time were independently associated with the combined endpoint even after adjustments for brachial blood pressure, age, extent of coronary artery disease, clinical characteristics, and medications. The study provides evidence that pulse waveform characteristics consistently and independently predict cardiovascular events in coronary patients.
    Journal of hypertension 02/2010; 28(4):797-805. · 4.02 Impact Factor
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    Michael F O'Rourke
    Journal of the American College of Cardiology 01/2010; 55(3):257. · 14.09 Impact Factor
  • Michel E Safar, Michael F O'Rourke
    Journal of hypertension 10/2009; 27(10):1960-1. · 4.02 Impact Factor
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    Michael F O'Rourke, Christopher S Hayward
    Journal of the American College of Cardiology 09/2009; 54(8):714-7. · 14.09 Impact Factor
  • Michael F O'Rourke, Thomas Weber
    Journal of hypertension 08/2009; 27(7):1505-6; author reply 1506-7. · 4.02 Impact Factor
  • Michael F O'Rourke, Michel E Safar
    Journal of hypertension 08/2009; 27(7):1504-5; author reply 1505. · 4.02 Impact Factor
  • Michael F O'Rourke
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    ABSTRACT: The arterial pulse at any site is created by an impulse generated by the left ventricle as it ejects blood into the aorta, together with multiple impulses travelling in the opposite direction from reflecting sites in the peripheral circulation. The compound wave at any site depends on the pattern of ventricular ejection, the properties of large arteries, particularly their stiffness (which determines rate of propagation) and the distance to and impedance mismatch at reflecting sites. Physicians are familiar with waveform analysis in the time domain, as in the electrocardiogram (ECG) where the principal features are explicable on the basis of atrial depolarisation followed by ventricular depolarisation, then repolarisation. Effects of cardiac functional and structural disease can be inferred from the ECG. It is more difficult to make similar interpretations from the pulse waveform and clinicians usually use this only to count heart rate, extremes of the pressure pulse to express systolic and diastolic pressure, and (sometimes) time from wave foot to incisural notch to measure time of systole and diastole. More information can be gleaned from the shape of the arterial pressure wave through consideration of the factors which create it--on stiffening of large arteries with age, effects of drugs on smallest arteries, and changes in such arterial properties on left ventricular load and function. Such is a major challenge to future physicians. It is aided by better and more accurate methods for measuring flow and diameter as well as pressure waveforms, and by appropriate use of other analytic techniques such as analysis of the pulse in the frequency domain.
    Medical & Biological Engineering 08/2008; 47(2):119-29. · 1.76 Impact Factor
  • Michael F O'Rourke
    Heart (British Cardiac Society) 07/2008; 94(6):690-1. · 5.01 Impact Factor
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    ABSTRACT: Premature cardiovascular disease (CDV) is highly prevalent in urban Indigenous Australians. We studied arterial structure and function in 144 volunteers aged 15-66 years to assess the role of dyslipidaemia and other traditional vascular risk factors on cardiovascular risk in young and older urban Indigenous Australians. We assessed carotid intima-media thickness (CIMT) by high-resolution B-mode ultrasound imaging of the common carotid artery and peripheral wave reflection using applanation tonometry to obtain the aortic augmentation index (AI) in Indigenous Australian participants of the Darwin Region Urban Indigenous Diabetes (DRUID) study. Participants aged 15-24 years demonstrated fewer cardiovascular risk factors than the older group (25-66 years) and predictors of CIMT and AI differed between younger and older groups. CIMT was higher in the older group (0.67mm vs. 0.61mm, p=0.004) and in those with diabetes (0.81mm vs. 0.67mm, p<0.001). AI was higher in the older group (24% vs. 0%, p<0.001), but was not affected by diabetes status. On multivariate regression analysis, low HDL-cholesterol was the only independent predictor of CIMT in the younger group; triglycerides, heart rate (inverse) and height (inverse) were independent predictors of AI in the same group. Dyslipidaemia (low HDL-cholesterol or elevated triglycerides) is independently associated with non-invasive measures of cardiovascular disease in a relatively healthy and young subgroup of this high-risk population. We propose that triglycerides and low HDL-cholesterol may represent the most useful commonly measured clinical indicators of cardiovascular risk in young, urban Indigenous Australians.
    Atherosclerosis 04/2008; 202(1):248-54. · 3.71 Impact Factor
  • Michael F O'Rourke, Michel E Safar
    Journal of Hypertension 03/2008; 26(2):377-8; author reply 378-9. · 3.81 Impact Factor

Publication Stats

3k Citations
544.69 Total Impact Points

Institutions

  • 1990–2013
    • University of New South Wales
      • • Graduate School of Biomedical Engineering
      • • Department of Medicine
      Kensington, New South Wales, Australia
  • 2007–2012
    • Victor Chang Cardiac Research Institute
      Darlinghurst, New South Wales, Australia
  • 1989–2012
    • St. Vincent's Hospital Sydney
      Sydney, New South Wales, Australia
    • Wake Forest University
      Winston-Salem, North Carolina, United States
  • 2008
    • Charles Darwin University
      • Institute of Advanced Studies
      Palmerston, Northern Territory, Australia
  • 2005–2007
    • Menzies School of Health Research
      Palmerston, Northern Territory, Australia
  • 1988–2004
    • Saint Vincent Hospital
      Worcester, Massachusetts, United States
  • 1991
    • Armed Forces Institute of Pathology
      Ralalpindi, Punjab, Pakistan
  • 1985
    • University of Florida
      • Department of Medicine
      Gainesville, Florida, United States