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Biomedical subjects

Michael F O'Rourke

Publications and source records attributed to Michael F O'Rourke.

At least 19 recordsLinked to original sources
PubMed2006

Relation of arterial stiffness to left ventricular diastolic function and cardiovascular risk prediction in patients > or =65 years of age.

There is a paucity of data regarding the relation between the various noninvasive indexes of arterial stiffness and left ventricular diastolic function. In 188 subjects aged > or =65 years (mean 75 +/- 5; 71% men), the concordance and strength of the association between measures of arterial stiffness and left ventricular diastolic function were evaluated. Indexes of arterial stiffness (brachial and aortic pulse pressure [PP], carotid-femoral pulse-wave velocity [PWV], and augmentation pressure [AP]) were measured using applanation tonometry. Diastolic function was classified in terms of instantaneous diastolic function grade and quantitated as left atrial volume, a measure of chronic diastolic burden. Risk for new cardiovascular events was estimated using a validated clinical echocardiographic risk algorithm. Aortic and brachial PP, PWV, and AP were correlated positively with left atrial volume and diastolic function grade. After adjusting for age, gender, and clinical and echocardiographic covariates, 1-SD increases in aortic PP, brachial PP, PWV, and AP were associated with 6%, 6%, 4%, and 4% increases in indexed left atrial volume, respectively. Similarly, 1-SD increases in aortic PP, brachial PP, and AP were associated with 84%, 81%, and 83% increased risk for diastolic dysfunction, respectively (all p <0.04). PWV and aortic and brachial PP were superior to AP in discriminating subjects with the highest risk of having new cardiovascular events (5-year risk >50%; area under receiver-operating characteristic curve 0.67, 0.67, 0.70, and 0.56, respectively; p <0.05). In conclusion, increased arterial stiffness was associated with more severe left ventricular diastolic dysfunction, although the strength of the association varied according to the specific measure used. Aortic PP, brachial PP, and PWV appeared superior to AP in risk discrimination in this elderly cohort.

Aged↗
PubMed2006

Age-related changes in carotid artery flow and pressure pulses: possible implications for cerebral microvascular disease.

BACKGROUND AND PURPOSE: We sought to establish the relation between the pulsatile components of pressure and flow waveforms in the carotid artery and their change with age. METHODS: Distention (pressure) and axial flow velocity waveforms were recorded noninvasively and simultaneously from the common carotid artery of 56 healthy subjects aged 20 to 72 years. RESULTS: There was a close relation between the time intervals of pressure and flow waves: from foot to first shoulder or peak, to second shoulder or peak, and to incisura (r=0.97, P<0.0001 for each), which approximated the line of identity. The peak and nadir of flow velocity decreased with age, but late systolic flow augmentation increased substantially (1.6 times in the older group); this can be attributed to earlier wave reflection from the lower body. Pressure augmentation index (PAI) and flow augmentation index (FAI) increased similarly with age (PAI (%) = 0.84 x age - 26.6; FAI (%) = 0.75 x age + 11.9; both P<0.0001). CONCLUSIONS: Arterial stiffening with aging increases carotid flow augmentation and can explain the increasing flow fluctuations in cerebral blood vessels. Measurement of carotid FAI may provide a gauge for risk of cerebral microvascular damage, just as PAI provides a gauge for risk of left ventricular hypertrophy and failure.

Adult↗
PubMed2006

Clinical use of indices determined non-invasively from the radial and carotid pressure waveforms.

OBJECTIVE: To evaluate the clinical use of radial and carotid artery applanation tonometry as an independent supplement to cuff sphygmomanometry. METHODS: In 44 patients, radial and carotid tonometric pressure recordings were taken at short intervals apart by two persons who had prolonged experience with both. Comparisons were made between directly recorded radial and carotid waveforms and between aortic waves synthesized from both, using SphygmoCor. Focus was on waveform features: time intervals between wavefoot and incisura, denoting ejection duration, between wavefoot and first systolic peak or shoulder T1, and augmentation index - the rise in pressure from this point to systolic peak divided by pulse pressure. RESULTS: No patient had discomfort with radial tonometry, whereas many found carotid tonometry uncomfortable. Beat-to-beat variability was lower for the radial than carotid site. The device's operator "quality index" was achieved for 78% of radial waveforms but just 20% of carotid waveforms (P<0.05). Interobserver variability was lower for all indices derived from radial, cf. carotid, waveforms. For the two observers combined, there was no difference between aortic indices determined from carotid and radial sites except for T1 (radial-derived 117+ or -17 ms, cf. carotid-derived 103+ or -17 ms, P<0.05), but this did not influence the value of augmentation index (radial-derived 26+ or -13%, cf. carotid-derived 28+ or -14%, P=NS). CONCLUSION: The present study conforms with most published results, and indicates superiority of radial to carotid tonometry in clinical practice.

Adult↗
PubMed2006

Pulse wave analysis and pulse wave velocity: a review of blood pressure interpretation 100 years after Korotkov.

The pulsatile component of blood pressure (ie, pulse pressure) has received considerable attention as an important risk factor for cardiovascular disease. In particular, central blood pressure measurements in the ascending aorta or in the carotid artery are expected to be more useful than conventional brachial pressure measurements for predicting cardiovascular events because central pressure, not the brachial pressure, is the pressure that target organs encounter. Due to wave reflection, the blood pressure in the upper limb does not represent the central blood pressure; therefore, leading researchers have enthusiastically promoted a noninvasive method of measuring central blood pressure and the resulting aortic stiffness. Until now, there has been an increasing body of evidence to support the accuracy and superiority of central blood pressure measurements as well as the assessment of aortic properties over classical brachial pressure measurements. In this review, the information regarding these "central" indices derived from 2 main methods, namely "pulse wave analysis" and "pulse wave velocity", for the application of central blood pressure measurements and arterial stiffness to clinical study and practice, has been summarized.

Aorta↗
PubMed2006

Effects of nifedipine on systemic and pulmonary vascular impedance in subjects undergoing cardiac catheterization.

Nifedipine 10 mg, administered sublingually to 12 patients following diagnostic cardiac catheterization, caused reduction in systemic resistance, and change of impedance together with alteration in contour of the ascending aortic and left ventricular pressure waves. The substantial reduction in ascending aortic and left ventricular systolic pressure with nifedipine occurred despite an increase in stroke volume and cardiac output, and was associated with similar reductions in mean pressure and indices of wave reflection. In the same patients, there were no significant changes in pulmonary vascular resistance or impedance, nor in pulmonary artery or right ventricular pressure pulse contour. For the systemic circulation, as with nitroglycerin and nitroprusside, reduction in wave reflection appears to be an important factor in the drug's action and for its beneficial effects on cardiac load in the treatment of angina pectoris, systemic hypertension and left ventricular failure. Thus the observed effects of nifedipine were attributed to vasodilatation of the systemic arteries and arterioles.

Administration, Sublingual↗
PubMed2006

Central arterial pressure and arterial pressure pulse: new views entering the second century after Korotkov.

The ubiquitous brachial cuff method gained widespread clinical acceptance for blood pressure recording after confirmation of its prognostic value in 1917. This method displaced radial pulse waveform analysis by sphygmography, which also gave prognostic Information but was difficult to use. Since that time, brachial cuff sphygmomanometry has migrated from the physician's office to 24-hour monitoring and home use, with electronic methods replacing the Korotkov sound technique for determining systolic and diastolic pressure. Detailed instrumental studies, required by regulatory bodies, revealed inaccuracies of all cuff methods for recording true intra-arterial pressure. A major source of inaccuracy in assessing left ventricular load is the amplification of the pressure wave in its transit from the central aorta to upper limb arteries, as extensively studied by Earl H. Wood at the Mayo Clinic in Rochester, Minn, in the 1950s. This limitation can be overcome by combining newer methods using radial artery waveform analysis in conjunction with conventional cuff sphygmomanometry to noninvasively measure the central aortic pressure waveforms. Recent studies using radial tonometry have proved that this is more effective than conventional manometry in predicting cardiovascular events and gauging response to therapy. Measurement of central as well as peripheral arterial pressure and physiology is becoming increasingly used as an office practice and a laboratory procedure.

Aging↗
PubMed2005

Effect of sildenafil on cardiac performance in patients with heart failure.

Sildenafil is rarely used in patients with heart failure despite a high prevalence of erectile dysfunction, and the theoretic possibility that by increasing nitric oxide availability, it may improve left ventricular (LV) load and performance. This study aimed to determine the peak effects of sildenafil on LV load and performance in patients with heart failure caused by systolic LV dysfunction. Twenty patients with controlled LV failure and ejection fractions <35% received sildenafil 50 mg or a matching placebo when not receiving regular medication for > or =12 hours, in a randomized, placebo-controlled, double-blind, 2-way crossover fashion. Cardiac output was measured by Doppler echocardiography. The aortic pressure waveform was determined using generalized transfer function from radial artery applanation tonometry. Aortic and femoral arterial stiffness was determined as carotid-femoral and femoral-pedal pulse-wave velocity (PWV); wave reflection was measured as an augmentation index (AIx). Cardiac index increased significantly (by 0.37 L/min.m(2), p <0.0001), with the peak effect 60 minutes after sildenafil administration. Compared with the baseline value, total systemic resistance showed a reduction of 479 dynes.s.cm(-5) (p <0.0001). Aortic and lower limb PWV decreased significantly (by 0.89 and 1.14 m/s, respectively, p <0.0001 for both), as did AIx (by 3.6% absolute, p <0.0001); these remained significant after adjustment for mean pressure and heart rate changes. In conclusion, sildenafil improves cardiac performance because of a decrease in LV load, which is caused by decreases in peripheral resistance, in aortic and large artery stiffness, and in wave reflection from peripheral sites. This can explain the increase in cardiac output and in exercise capacity with sildenafil in patients with heart failure.

Aged↗