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A P Avolio

Publications and source records attributed to A P Avolio.

At least 19 recordsLinked to original sources
PubMed1995

Pressure wave propagation in a multibranched model of the human upper limb.

The influence of the large arteries and the peripheral load on pressure wave propagation in the human upper limb was investigated in an anatomically realistic multibranched model based on linear transmission theory. To mimic vascular changes seen in life, the viscoelastic properties of large arteries and the peripheral load properties (represented as modified windkessels) were altered as follows: Young's modulus (from 10.9 x 10(6) to 15.3 x 10(6) dyn/cm2) and phase (from 0 to 15 degrees) of the complex elastance, windkessel time constant (from 0 to 0.6 s), and peripheral reflection coefficient (from 0 to 0.95). The relationship between the central aortic and peripheral radial pressure waveforms was analyzed in the time and the frequency domain. Results indicate that the large arterial properties have less influence (peak systolic pressure changed by 3% and peak of transfer function changed by 29%) than the properties of the peripheral load (systolic pressure changed by 14% and peak of transfer function changed by 74%) on the pressure wave propagation in the upper limb.

Arm↗
PubMed1994

Functional origin of reflected pressure waves in a multibranched model of the human arterial system.

The effects of wave travel and wave reflection were simulated in a mathematical model of the whole arterial tree consisting of 142 uniform transmission line segments. The arterial model was partitioned into three separate segments: upper limbs, trunk, and lower limbs. Aging was simulated by increasing average pulse wave velocities of these segments (10.9-12.9, 8.0-11.7, and 9.0-11.3 m/s for upper limbs, trunk, and lower limbs, respectively). Reflection coefficients at the terminal elements were altered to simulate vasodilation (0.0) and vasoconstriction (0.95). The impedance patterns and spatial distribution of pressure waveforms generated by the model simulating aging and vasoconstriction were similar to in vivo measurements by other investigators. Reflected pressure waves from each segment reached the ascending aorta and contributed differently to the late systolic peak on the aortic pressure wave. Aging does not alter the origin of these reflected pressure waves in the trunk. Aortic impedance and pressure wave changes induced by simulation of dilation of splanchnic bed were similar to those observed experimentally with nitroglycerin.

Aorta↗
PubMed1991

Effect of aging on aortic morphology in populations with high and low prevalence of hypertension and atherosclerosis. Comparison between occidental and Chinese communities.

A comparative morphologic study of aortic changes with aging was conducted in different populations in an attempt to separate the effects of hypertension and atherosclerosis. Chinese and the occidental populations were chosen, as they are known to have a high prevalence of hypertension and atherosclerosis, respectively. Aortic tissue was collected from occidental (American and Australian) and Chinese populations from three geographic locations. Postmortem specimens were obtained from four fixed locations: ascending aorta (A), descending thoracic aorta (B), and abdominal aorta (suprarenal [C] and above the aortic bifurcation [D]). Histologic sections were used to measure aortic circumference, medial thickness, intimal thickness, and grade of atherosclerosis. Kidney sections were used to confirm the presence or absence of hypertension. A total of 302 cases (age range, 19 to 104 years; Male-to-female ration, 2:1) were studied: 112 Americans, 80 Australians, and 110 Chinese. Cases were divided into three age groups: 19 to 44; 45 to 64; and 65 years and older. The aortic circumference progressively decreased from sites A to D in all populations and age groups. The aortic circumference increased with age, and the increase was independent of the aortic location. When the populations were separated, however, the greater increase was at location A in the Chinese (P = .008) and locations D in the occidental (P = .13), a population contrast that was significant only in location A. Intimal thickness increased with advancing age and was maximal in the abdominal aorta. The population differences also were significant for intimal thickness and were significantly greater in the occidental population in B, C, and D locations, whereas for atherosclerosis significance was only seen in location D. Hypertension (as defined by the morphologic changes in the kidney) after adjusting for age, height, and weight resulted in no statistical significant effect on aortic circumference or on intimal thickness, but did show a significant increase in atherosclerosis score at locations B, C, and D. Also after adjusting for age, height, and weight, the Chinese had a significantly larger aortic circumference in location A compared with the occidental population, whereas in location D the occidentals with hypertension had a significantly larger circumference compared with Chinese, probably due to an interaction of atherosclerosis and hypertension. After similar adjustments, the medial thickness in locations A and C, the intimal thickness in B, C, and D, and atherosclerosis score in D were significantly greater in occidental than Chinese populations.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1990

Brachioradial delay.

Explore the source record for details and available documents.

Aortic Valve Stenosis↗
PubMed1990

Nitroglycerin has more favourable effects on left ventricular afterload than apparent from measurement of pressure in a peripheral artery.

Nitroglycerin (0.3 mg) was administered sublingually to 14 patients undergoing cardiac catheterization, and pressure waves compared in the ascending aorta and brachial artery. After nitroglycerin, ascending aortic systolic pressure fell in all cases (by 6-44, average 22 mmHg) whereas brachial systolic pressure remained unchanged (in three) or fell to a lesser degree (4-33, average 12 mmHg). Diastolic pressure did not change significantly. Alterations in pressure and in wave contour were explained on the basis of arterial dilation, with reduction in wave reflection. Nitroglycerin reduces left ventricular afterload through arterial dilation as well as preload through venous dilation. This effect on afterload is not apparent from measurement of pressure in the brachial artery.

Administration, Sublingual↗
PubMed1989

Effects of arterial dilator agents on central aortic systolic pressure and on left ventricular hydraulic load.

Recordings of pressure in the brachial or peripheral arteries fail to disclose the marked increase in systolic pressure that occurs in the proximal aorta and central arteries with increasing age and with hypertension. This systolic pressure boost is caused by wave reflection returning from the periphery of the body while the ventricle is still contracting. Such early wave reflection is caused in turn by increased pulse-wave velocity, attributable to stiffening of the aorta and major conduit arteries. Drugs have little effect on arterial stiffening, whereas wave reflection can be markedly reduced by agents that dilate peripheral arteries. Such reduction in wave reflection causes substantial decrease of systolic pressure in central arteries. Because of differential timing of wave reflection, however, such reduction is not apparent from pressure recordings taken in the brachial or other peripheral arteries. The sphygmomanometer, therefore, fails to show the favorable effects of reduced wave reflection in the proximal aorta and central arteries. Noninvasive tonometric pressure wave recordings can supplement the sphygmomanometer to assess the magnitude of beneficial effect.

Adult↗
PubMed1989

A comparison of brachial, femoral, and aortic intra-arterial pressures before and after cardiopulmonary bypass.

Following recent evidence that brachial and femoral artery pressures are more reliable than radial artery pressures after cardiopulmonary bypass, thirty-one adults had simultaneous pre- and post-bypass measurements of brachial, femoral, and ascending aortic pressures. Two minutes after cardiopulmonary bypass, brachial artery systolic pressure and mean arterial pressure fell significantly below corresponding pressures in the femoral artery and aorta. Five minutes after cardiopulmonary bypass, only brachial artery systolic pressure was still less than femoral and aortic systolic pressures. By ten minutes after bypass, all significant pressure differences had resolved except between brachial and femoral artery systolic pressures. Clinically significant (greater than or equal to 5 mmHg) aortic-to-brachial reductions in mean arterial pressures occurred in six (19%) patients at two minutes and in three (10%) patients at five and ten minutes after bypass. Equivalent aortic-to-femoral mean pressure diminution occurred in two (6%) patients at two minutes and one (3%) patient at five and ten minutes after bypass. Neither systemic vascular resistance nor body temperatures contributed significantly to post-bypass central-to-peripheral pressure reductions. Immediately following bypass, femoral artery pressures reproduce central aortic pressures more reliably than do radial or brachial artery pressures.

Aorta↗
PubMed1986

The kangaroo as a model for the study of hypertrophic cardiomyopathy in man.

In experiments in 14 anaesthetised kangaroos, 10 developed unexpected ventricular fibrillation and died. In seeking a cause for this, similarities were noted with hypertrophic cardiomyopathy (HC) in man. Like patients with this condition, kangaroos have unexplained left ventricular hypertrophy and are known to be susceptible to sudden death with excitement and exertion. Retrospective analysis of all data showed other features of hypertrophic cardiomyopathy: unusually rapid left ventricular pressure development in systole (peak dP/dt: kangaroo 3602 (SEM472); HC 1947(SEM172) mmHg X s-1), unusually slow left ventricular relaxation (exponential time constant: kangaroo 54(SEM7); HC 63 (SEM5) ms; relaxation time: kangaroo 128(SEM7); HC 112(SEM7) ms), and inappropriately long duration of mechanical systole in relation to ventricular depolarisation (393(SEM21) ms and 214(SEM15) ms respectively). A disparity between the duration of mechanical systole and electrical activation caused a type of incomplete tetanus to develop with ventricular extrasystoles, a phenomenon previously seen in patients with hypertrophic cardiomyopathy. These findings suggest that the kangaroo may be a useful experimental model for studying the fatal rhythm disturbances and abnormal ventricular dynamics in human hypertrophic cardiomyopathy.

Animals↗
PubMed1986

Ventricular/vascular interaction in patients with mild systemic hypertension and normal peripheral resistance.

Total left ventricular external power and aortic input impedance spectra were calculated from recordings of pulsatile pressure and flow in the ascending aorta of 22 human subjects undergoing cardiac catheterization. Eleven subjects had increased aortic pressure (systolic 153 +/- 3.8[SEM] mm Hg, p less than .001; diastolic 91 +/- 2.4 mm Hg, p less than .03; mean 118 +/- 2.4 mm Hg, p less than .001) and constituted the group with mild hypertension (average age 50 +/- 1.9 years). The other 11 (age-matched) subjects had normal arterial pressures and constituted the control group. Cardiac output in the hypertensive group was abnormally high (6.9 +/- 0.3 liters/min, p less than .04) compared with that in control subjects (6.1 +/- 0.2 liters/min), so that peripheral resistance was similar. Characteristic aortic impedance (index of aortic elastance) was increased in the hypertensive group (142 +/- 19 vs 72 +/- 4.5 dyne-sec-cm-5, p less than .002), as was the fluctuation of impedance moduli and phase. These elevated pulsatile components of arterial load were associated with a significant (p less than .002) increase in pulsatile left ventricular external power (89%), and the increased cardiac output was associated with a significant (p less than .001) increase in steady flow power (31%). The ratio of pulsatile to total power was also increased (38%) in the hypertensive group (p less than .001). Increased characteristic aortic impedance in the hypertensive group suggests that the human aorta is stiffer, and fluctuations in the impedance spectra suggest increased or less dispersed wave reflections.(ABSTRACT TRUNCATED AT 250 WORDS)

Aorta↗
PubMed1986

Ascending aortic impedance patterns in the kangaroo: their explanation and relation to pressure waveforms.

This study seeks to explain mechanisms responsible for the peculiar ascending aortic pressure waveform and impedance spectral pattern in kangaroos. Pulsatile pressure and blood flow velocity were measured and input impedance calculated in the ascending aorta, descending thoracic aorta, and brachiocephalic artery of 15 rock kangaroos. Pressure and velocity waveforms and impedance spectral patterns were interpreted with the aid of an asymmetric uniform T-tube model of the systemic arterial tree. The ascending aortic pressure waveform displayed a very large secondary wave that began in late systole or early diastole and continued throughout most of diastole. The peak of this secondary wave (which almost always occurred in diastole) was often greater than peak systolic pressure and results from apparently intense wave reflections from peripheral vascular beds. This contention is supported by the configuration of the impedance spectral pattern that is explained on the basis of a single (or dominant) functionally discrete reflecting site in the lower part of the body. These findings are explicable on the basis of body size and shape and the extreme eccentric location of the heart within the body. Wave reflections from the diminutive upper body are so small that they are totally dominated by intensive wave reflections from the large muscular lower body. These conclusions are supported by results obtained from the asymmetric T-tube model.

Animals↗
PubMed1985

Effects of age on ventricular-vascular coupling.

The effects of age on the interrelation between the physical properties of the arterial tree (aortic input impedance) and left ventricular performance (cardiac output) were studied in 45 subjects, aged 19 to 62 years, without apparent cardiovascular disease. Ascending aortic pulsatile pressure and blood flow velocity were measured with a multisensor catheter and cardiac output by green dye or the Fick method. Heart rate and end-diastolic aortic pressure remained unchanged with age, whereas aortic systolic, mean and pulse pressures and aortic radius increased. In subjects younger than 30 years, early systolic pressure usually exceeded late systolic pressure (type C beat); in subjects older than 50 years, late systolic pressure usually exceeded early systolic pressure (type A beat). In 55% of subjects aged 30 to 50 years, early and late systolic pressures were essentially equal (type B beat). The impedance spectra from all subjects showed fluctuations about the characteristic impedance (index of elastance) that were greater in the older subjects. Peripheral resistance increased 37% (r = 0.47, p less than 0.001) over the age range of 20 to 60 years, whereas characteristic impedance increased 137% (r = 0.66, p less than 0.001). The fundamental impedance modulus increased, and the impedance modulus minimum shifted to a higher frequency. These changes in the impedance spectral pattern indicate that the ascending aorta becomes stiffer and the cross section of the peripheral vascular bed decreases with age, causing increased pulse wave velocity and wave reflection.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Propagation of pressure pulse in kangaroo arterial system.

The pressure pulse contour in the ascending aorta of kangaroos is markedly different from that seen in other species, but the changes undergone by the pulse propagating along the aorta are quite similar. Alteration of wave contour and progressive amplification of the pulse in the distal aorta and peripheral arteries of other mammals have been attributed to elastic nonuniformity of the aorta and to peripheral wave reflection. In kangaroos the aorta approximates a uniform tube with essentially constant viscoelastic properties, whereas wave reflection from the lower body appears to be unusually intense and to emanate from a single functionally discrete reflecting site; this appears to be the result of arterial terminations in the muscular lower body. Intense wave reflection from the lower body is the dominant mechanism responsible for changes in the pressure pulse of kangaroos between the ascending aorta and peripheral arteries. Contour of the pulse in the ascending aorta is attributable to this and to close proximity of reflecting sites in the upper body.

Animals↗
PubMed1985

Effects of aging on arterial distensibility in populations with high and low prevalence of hypertension: comparison between urban and rural communities in China.

Arterial pulse wave velocity, an established index of arterial distensibility, was measured together with arterial pressure in a group of 524 normal subjects of both sexes 2 months to 94 years old (mean age 45.6 +/- 15.3 years [SD]) in rural Guangzhou, China, an area with known low prevalence of hypertension. Fasting serum lipid levels and overnight Na+ and K+ urinary excretion levels were determined in a subgroup of 104 subjects (ages 8 to 88 years). Comparisons were made with data obtained similarly from normal subjects in urban Beijing, an area with known high prevalence of hypertension. Serum cholesterol levels were similar and low in each group (Guangzhou, 4.34 +/- 0.12 mmol/liter [SE]; BEijing, 4.49 +/- 0.11 mmol/liter). Prevalence of hypertension (WHO criteria) was 4.9% (Guangzhou) and 15.6% (Beijing). In Guangzhou subjects pulse wave velocity was consistently lower in the aorta, arm, and leg, and increased to a lesser degree with age compared with Beijing subjects. Regression equations (x = pulse wave velocity [cm/sec], y = age [years]) were as follows: (1) aorta, Guangzhou: y = 5.1x + 533, r = .552, p less than .05; Beijing: y = 9.2x + 615, r = .673, p less than .001; (2) arm, Guangzhou: y = 0.61x + 817, r = .121, p less than .05; Beijing: y = 4.8x + 998, r = .453, p less than .001; (3) leg, Guangzhou: y = 4.43x + 718, r = .512, p less than .05; Beijing: y = 5.6x + 791, r = .630, p less than .001.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1984

Physiological and pathophysiological implications of ventricular/vascular coupling.

The purpose of this paper is to consider "ideal" ventricular/vascular coupling, and how this may be manifest in the time domain and in the frequency domain. The paper will also consider how such "ideal" coupling is achieved, and how it might be disturbed. The arterial system plays a crucial role in ventricular/vascular coupling since it separates the smallest vessels where flow is almost perfectly continuous from the ventricle, whose output is intermittent. Ventricular/vascular coupling can be assessed from measurements of pressure and flow in the ascending aorta (AA) (for left ventricle/systemic circulation), and in the main, pulmonary artery (MPA) (for right ventricle/pulmonary circulation). Ideal coupling is manifest as low pressure fluctuation in AA and MPA. Low pressure fluctuation results in pressure during systole being only slightly greater than pressure throughout the whole cardiac cycle, and pressure during diastole being only slightly less. This is desirable because pressure during systole determines ventricular output (when inotropic state and ventricular filling are constant), and ventricular metabolic requirement, while pressure during diastole in AA is a major determinant of coronary blood flow. In the frequency domain, "ideal" coupling is manifest as a correspondence between minimal values of impedance modulus in AA and MPA with maximal values of flow harmonics in AA and MPA, respectively. Factors responsible for "ideal" coupling have been identified as high distensibility of proximal arteries (with decreasing distensibility in peripheral arteries), wave reflection at arterial terminations, and a "match" between heart rate on the one hand and arterial length and wave velocity on the other. This favourable "match" results in the heart operating for both systemic and pulmonary circulations close to a node of pressure and antinode of flow; this match is improved under conditions which simulate flight and fight. While ventricular/vascular coupling appears to be close to ideal in most large mammals, it appears to be less than ideal in adult humans and some small mammals including guinea pigs, rats, and mice. The cause for mismatch in small mammals is unclear. In humans however, findings are attributable to progressive arterial degeneration which is known to commence in childhood and is apparent in the elderly as dilated tortuous arteries, high pulse pressure, and high likelihood of developing ventricular failure.

Aorta↗
PubMed1984

Exaggerated wave reflection in the kangaroo simulates arterial counterpulsation.

The ascending aortic pressure wave in kangaroos is quite different from that seen in other experimental animals and in humans, despite an ascending aortic flow wave that is virtually identical. The diastolic pressure surge in the ascending aortic pressure wave of kangaroos is very prominent--so much so that peak diastolic pressure is often greater than peak systolic pressure, with the pressure wave resembling that recorded in humans during intra-aortic balloon counterpulsation. Ascending aortic impedance patterns in kangaroos indicate the presence of a single functionally discrete reflecting site in the peripheral circulation, with high reflection coefficient. All findings--of pulse contour and impedance patterns--are explicable on the basis of arterial anatomy and body shape. Wave reflection from the distant, large, and vascular lower body appears to dominate the effects of wave reflection from the short, small, and less vascular head and forelimb system.

Animals↗
PubMed1983

Pulse-wave propagation in the arterial system of the diamond python Morelia spilotes.

Pulse-wave velocity (PWV) and pulse-wave amplification (PWA) were measured over a proximal [51 +/- 3 (SE) cm] and distal segment (60 +/- 6 cm) of the common descending aorta of 10 anesthetized diamond python snakes (Morelia spilotes). For proximal and distal segments, PWV values were 551 +/- 66 and 921 +/- 116 cm/s and PWA were 0.91 +/- 0.05 and 0.91 +/- 0.06, respectively. PWV for proximal and distal segments were significantly different (P less than 0.02), but PWA were not. PWA for separate harmonics of heart frequency showed no significant increase above unity. Increase of PWV between distal and proximal aorta indicates a reduction in arterial distensibility, a phenomenon that in other species is associated with amplification of the pressure pulse; this was not observed in snakes. Using a simple elastic tube model 56 cm in length and 3 mm in diameter it was found that the amplification produced by the measured PWV changes is offset by attenuation due to viscous damping. Thus similarity of pulse-wave contour throughout the snake's aorta is attributable to the opposing effects of elastic nonuniformity and viscous damping.

Animals↗
PubMed1983

Effects of aging on changing arterial compliance and left ventricular load in a northern Chinese urban community.

Pulse wave velocity (PWV) was measured by means of transcutaneous Doppler techniques in the aorta, right arm, and right leg of 480 normal subjects of both sexes in urban Beijing, China (age range 3 to 89 years, mean age 41 +/- 20.8 SD); supine blood pressure was recorded in the brachial artery of each subject with standard sphygmomanometric procedures. Serum cholesterol was determined in a subgroup of 79 subjects (age 17 to 85 years, mean 47 +/- 26 SD). PWV (y in cm/sec) was found to vary with age (x, years) at each of the three locations according to the following regression equations: aorta, y = 9.2x + 615, r = .673 (p less than .001); right arm, y = 4.8x + 998, r = .453 (p less than .001); right leg, y = 5.6x + 791, r = .630 (p less than .001). Systolic, diastolic, mean, and pulse pressures were found to increase with age. PWV also increased with mean supine blood pressure but was not related to serum cholesterol (average 4.49 +/- 0.11 [SEM], mmol/l). Compared with that of Western populations, serum cholesterol tended to be lower at all age groups, systolic pressure higher at ages over 35 years, and PWV higher at all ages. Because change in PWV is directly related to change in arterial compliance, these results indicate that aging and not concomitant atherosclerosis (known to be rare in Asian populations) is the dominant factor associated with reduced arterial compliance and increased left ventricular load in these subjects.

Adolescent↗