Change In Aortic Diameter Research Articles

Ascending aorta distensibility abnormalities in hypertensive patients and response to nifedipine administration

purpose: The purpose of the present investigation was to study the distensibility of the ascending aorta in patients with arterial hypertension and normal subjects before and after administration of a calcium antagonist, nifedipine.patients and methods: The distensibility of the ascending aorta was measured before and after nifedipine administration in 22 male hypertensive patients and 12 age-matched male normotensive subjects. Aortic distensibility was calculated as a function of changes in aortic diameter and pulse pressure, using the formula: 2 × (pulsatile change in aortic diameter)/[(diastolic aortic diameter) × (aortic pulse pressure)]. Aortic diameters were measured by echocardiography and aortic pressures were obtained by catheterization of the ascending aorta.results: In the basal state, the distensibility of the ascending aorta and aortic strain were lower in hypertensive patients than in normotensive subjects (p <0.001); the lower aortic distensibility, however, was associated with a greater distending pressure. A good inverse correlation (r = −0.81) was found between mean aortic pressure and aortic distensibility. The aortic distensibility was increased after nifedipine administration in both groups; this increase in aortic distensibility, however, was lower in the patients with hypertension compared with normotensive subjects (p <0.001).conclusions: Aortic distensibility is decreased in patients with arterial hypertension. Nifedipine administration increased the distensibility of the ascending aorta both in patients with arterial hypertension and in normotensive subjects. The increase of aortic distensibility after nifedipine administration was lower in hypertensive patients.

Correlates of aortic distensibility in chronic aortic regurgitation and relation to progression to surgery

Aortic distensibility decreases with increasing age. Patients with chronic aortic regurgitation eject a large stroke volume into the proximal aorta. A decrease in distensibility of the aorta may impose a higher afterload on the left ventricle and may contribute to deterioration of left ventricular function over time. Accordingly, aortic distensibility was measured in 33 patients aged 13 to 73 years who had chronic isolated aortic regurgitation with minimal or no symptoms.Ascending aortic diameter was measured 4 cm above the aortic valve by two-dimensional echocardiography and pulse pressure was measured simultaneously by sphygmomanometry. Aortic distensibility was calculated as (Change in aortic diameter between systole and diastole/End-diastolic diameter)/Pulse pressure. Left ventricular systolic wall stress and mass were derived from standard M-mode echocardiographic measurements. Left ventricular volumes and ejection fraction were measured by radionuclide ventriculography.Aortic distensibility decreased logarithmically with increasing age (r = − 0.62, p < 0.001) and also correlated inversely with systolic wall stress, left ventricular mass and end-diastolic volume. Patients who eventually underwent aortic valve replacement for symptoms of left ventricular dysfunction had significantly lower aortic distensibility than did those who did not yet require valve replacement: 0.09 ± 0.08 vs. 0.22 ± 0.19 × 100 (l/mm Hg) (p < 0.05).Thus, the reduced aortic distensibility that occurs with increasing age may contribute to the gradual left ventricular dilation and dysfunction seen in patients with chronic aortic regurgitation.

The marfan syndrome: Abnormal aortic elastic properties

Aortic distensibility and aortic stiffness index were measured at the ascending aorta (3 cm above the aortic valve) and the mid-portion of the abdominal aorta from the changes in echocardiographic diameters and pulse pressure in 14 patients with the Marfan syndrome and 15 age- and gender-matched normal control subjects. The following formulas were used: 1) Aortic distensibility = 2(Changes in aortic diameter)/(Diastolic aortic diameter) (Pulse pressure); and 2) Aortic stiffness index = ln(Systolic blood pressure)/(Diastolic blood pressure)(Changes in aortic diameter)/Diastolic aortic diameter. Pulse wave velocity was also measured. Compared with normal subjects, patients with the Marfan syndrome had decreased aortic distensibility in the ascending and the abdominal aorta (2.9 +/- 1.3 vs. 5.6 +/- 1.4 cm2 dynes-1, p less than 0.001 and 4.5 +/- 2.1, vs. 7.7 +/- 2.5, cm2 dynes-1, p less than 0.001, respectively) and had an increased aortic stiffness index in the ascending and the abdominal aorta (10.9 +/- 5.6 vs. 5.9 +/- 2.2, p less than 0.005 and 7.1 +/- 3.1 vs. 3.9 +/- 1.2, p less than 0.005, respectively). Aortic diameters in the ascending aorta were larger in these patients than in normal subjects, but those in the abdominal aorta were similar in the two groups. Linear correlations for both aortic distensibility and stiffness index were found between the ascending and the abdominal aorta (r = 0.85 and 0.71, respectively). Pulse wave velocity was more rapid in the patients than in the normal subjects (11.6 +/- 2.5 vs. 9.5 +/- 1.4 m/s, respectively, p less than 0.01). Thus, aortic elastic properties are abnormal in patients with the Marfan syndrome irrespective of the aortic diameter, which suggests an intrinsic abnormality of the aortic arterial wall.

Exogenous prostacyclin does not sensitize arterial baroreceptors

It has been shown that prostacyclin (PGI2) sensitizes cardiac receptors. However, the effects of PGI2 on arterial baroreceptors are not well understood. In rabbits anesthetized with alpha-chloralose (n = 12), we examined reflex changes in multiunit efferent renal sympathetic nerve activity (RSNA) during hypotension caused by intravenous PGI2 (0.1, 0.2, 0.5, 1.0, 2.0 micrograms/kg), nitroglycerin (NG; 5, 10, 20, 50, 100 micrograms/kg), and sodium nitroprusside (SNP; 5, 10, 20, 50, 100 micrograms/kg) before and after bilateral vagotomy. Before vagotomy, RSNA increased during hypotension caused by NG or SNP (P less than 0.01) but did not significantly change during comparable hypotension caused by PGI2. After vagotomy, PGI2 increased RSNA as much as NG or SNP. In another group (n = 6), we examined the changes in aortic pressure (AoP), multiunit afferent aortic nerve activity (ANA), and the aortic diameter (AoD) during hypotension caused by intravenous PGI2, NG, and SNP. The relationship between changes in AoP and those in ANA did not differ during hypotension caused by the three drugs. The relationship between changes in AoP and those in AoD and that between changes in AoD and those in ANA also did not differ. Finally, we examined changes in AoP, ANA, and AoD during ramp increases or decreases of AoP caused by intravenous angiotensin II or NG under background infusion of saline, PGI2, or SNP (n = 6). The relationship among these variables did not differ during infusion of PGI2 and SNP. These results suggest that PGI2 stimulates cardiac receptors with vagal afferents but does not sensitize arterial baroreceptors.

Distensibility of the ascending aorta: comparison of invasive and non-invasive techniques in healthy men and in men with coronary artery disease

Distensibility of the ascending aorta, measured non-invasively, was compared with values obtained by invasive techniques in 46 males (30 patients with coronary artery disease and 16 age-matched normal subjects). Aortic diameters were measured at a level 3 cm above the aortic valve using both echocardiographic and angiographic techniques. Aortic distensibility was calculated from the aortic diameters and aortic pressure or brachial artery pressure using the formula: 2 x (change in aortic diameter)/(diastolic aortic diameter) x (change in aortic pressure). Distensibility of the ascending aorta determined non-invasively was closely related to that obtained by direct measurements (r = 0.949, P less than 0.001). Patients with coronary artery disease had similar pressures, but markedly lower distensibility than normal subjects, as shown by both invasive and non-invasive techniques. The results indicate that aortic distensibility in patients with coronary artery disease can be obtained non-invasively with a high degree of accuracy.

Inconsistent Esophageal Doppler Cardiac Output During Acute Blood Loss

Application of the Doppler principle can provide relatively noninvasive and continuous measurement of cardiac output. However, it is based on certain assumptions that may introduce error. Esophageal Doppler cardiac output was compared with Fick cardiac output during acute blood loss (35-45% estimated blood volume) in eight anesthetized pigs. Mean Fick cardiac output decreased from 4.8 to 1.9 l/min, mean Doppler cardiac output from 4.9 to 2.9 l/min. This was accompanied by a decrease in mean arterial pressure from 119 to 55 mmHg and increase in heart rate from a mean of 115 to 156 beats/min. There was an inconsistent association between the two methods both within and between individual animals. Cubic polynomial regression equations of cardiac output with time indicated small measurement error in Fick (R2: mean 0.93, range 0.99-0.75) as opposed to Doppler (R2: mean 0.67, range 0.93-0.16) cardiac output. In one animal Doppler cardiac output showed an increase with time and in one the Doppler cardiac output measurements were unrelated to time. There was highly variable association comparing Fick versus Doppler cardiac output with correlations ranging from -0.76 to 0.98. A sign test for mean differences indicated that Doppler derived cardiac output was higher than Fick cardiac output, and the chance of this occurring if the true difference was zero was less than 1 in 1,000. A test for homogeneity of correlations was also rejected. Inaccuracies in individual assumptions in the computation of esophageal Doppler cardiac output, especially unaccounted changes in aortic diameter, are responsible for the inconsistent and unpredictable values of Doppler cardiac output obtained in this experimental model of hemorrhage.

Pulsatile diameter and elastic modulus of the aortic arch in essential hypertension: A noninvasive study

A noninvasive evaluation of the aortic arch diameter was performed in 16 subjects with sustained essential hypertension and in 15 normal subjects of similar age, gender and boyy surface area. In all subjects, measurements were obtained of brachial mean arterial pressure and pulse pressure, cardiac mass (judged on echocardiography) and carotid-femoral pulse wave velocity together with ultrasound determinations of aortic arch diastolic and systolic diameter (suprasternal window). For each subject, pulsatile change in aortic diameter, strain and aortic arch elastic modulus were calculated.Compared with normal subjects, the hypertensive subjects showed an increase in aortic arch diameter (diastolic diameter 29.6 ± 1.0 versus 25.4 ± 1.0 mm, p < 0.01), in elastic modulus (1.071 ± 0.131 versus 0.526 ± 0.045 105N·m−2, p < 0.001) and pulse wave velocity (11.8 ± 0.5 versus 8.90.3 m/s, p < 0.001). In the study group, a positive correlation was observed between diastolic aortic arch diameter and mean arterial pressure (r = 0.54, p < 0.01) and between elastic modulus and cardiac mass (r = 0.60, p < 0.01). Elastic modulus and age were positively correlated (r = 0.73, p < 0.01) in hypertensive but not in normal subjects (r = 0.08, NS).This study is the first to demonstrate noninvasively that both the aortic arch diameter and the elastic modulus are increased in patients with sustained uncomplicated essential hypertension. These findings suggest that the increase in elastic modulus could influence the development of cardiac hypertrophy, and that both age and blood pressure act independently as factors that alter the arterial wall of subjects with sustained essential hypertension.

Derivation of haemodynamic information from ultrasonic recordings of aortic diameter changes

An ultrasound phase-locked echo-tracking system was used for noninvasive measurements of diameter changes in the upper abdominal aorta of the anaesthetised cat. Comparisons were made between the noninvasively recorded diameter changes and central haemodynamic variables measured with inserted catheters and transducers. It was found that noninvasive observations of aortic diameter changes give reliable information on the direction and relative magnitude of the blood pressure change both in systole and in diastole. Indications of the direction of change of stroke volume, cardiac output, and aortic flow acceleration (a measure of cardiac inotropy) could also be gained. The information, taken together, comprises a pattern of response reflecting cardiovascular adjustments likely to have occurred. It is suggested that the technique is suitable for interpretation of (patho-) physiological changes in the foetus, as well as for determinations of great vessel compliance in man, i.e., in atherosclerosis research.

Accuracy of cardiac output measured by continuous wave doppler echocardiography during dynamic exercise testing in the supine position in patients with coronary artery disease

To estimate the accuracy of cardiac output measured by continuous wave Doppler echocardiography from the suprasternal notch and the utility of this method for evaluating left ventricular function during dynamic exercise, simultaneous thermodilution and Doppler cardiac output were measured in 34 patients with coronary artery disease during multistage ergometer exercise in the supine position. Cardiac output was measured at rest and during each stage of exercise. Twenty-five of the 34 patients whose thermodilution curves were adequate for analysis were studied during exercise. The correlation coefficient for the two methods was 0.85 at rest and 0.84 during exercise. Differences between the two methods were not significant at rest but were significant during exercise, with the thermodilution method giving the higher values. Underestimation by the Doppler method is probably due to technical problems and changes in aortic diameter during exercise.The 25 patients were classified into two groups according to pulmonary artery wedge pressure at peak exercise. There were 11 patients in Group 1 pressure (≥20 mm Hg at peak exercise) and 14 in Group 2 pressure (<20 mm Hg at peak exercise). There were significant differences in the change in cardiac index and in peak aortic velocity from rest to peak exercise between the two groups. A significant linear correlation between the percent change in peak aortic velocity and in pulmonary artery wedge pressure from rest to peak exercise was observed (r = −0.66, p < 0.001).These results indicate that : 1) continuous wave Doppler echocardiography can provide a noninvasive, reliable technique for measuring cardiac output during dynamic exercise testing in the supine position; and 2) the percent change in peak aortic velocity from rest to peak exercise may be a useful index for discriminating between patients with a normal versus an elevated pulmonary artery wedge pressure during exercise testing.

Seventy years of the Bainbridge reflex.

The discovery of the Bainbridge reflex 70 years ago, of a tachycardic response to a rise in central venous pressure, stimulated a lot of interest in this and other cardiovascular reflexes. The mechanoreceptors that elicit the reflex are located at the junction of the right atrium and caval veins or at the junctions of the pulmonary veins and the left atrium. The Bainbridge reflex is controversial, however, because its existence cannot always be demonstrated. Intravenous infusions, which usually elicit a reflex tachycardia, sometimes cause a bradycardic response. This paper reviews the history of the studies associated with the reflex. Results are reported, which demonstrate that the chronotropic response to i.v. infusions depends upon the resulting change in aortic diameter; bradycardia is evoked by infusions leading to a rise in aortic baroreceptor activity through increases in aortic diameter, volume or pressure; tachycardia follows whenever the infusion fails to trigger the baroreflex. The importance of the Bainbridge reflex as a counterbalance to the baroreceptor reflex is discussed.

Aortic stiffness in insulin-dependent diabetics: an echocardiographic study.

To assess the aortic stiffness (AS) in young (15-35 year old) insulin-dependent diabetics without manifestations of atherosclerotic disease or hypertension, M-mode echocardiography was used to measure relative changes in aortic diameter expressed as Aortic strain = Diameter change/Diastolic diameter-100% Aortic stiffness can be calculated from the formula AS = Pulse pressure/Aortic strain. Fifty-seven diabetics were investigated, 31 men (aged 23.6 +/- 5.6 years, mean +/- SD) and 26 women (aged 25.7 +/- 6.4 years). There were 26 healthy controls with similar blood pressure, 14 men (aged 25.0 +/- 5.5 years) and 12 women (aged 24.6 +/- 7.1). The AS in diabetic men was 14 +/- 8.0 (mean +/- SD) compared to 3.6 +/- 0.7 in controls (p less than 0.001). In diabetic women the AS was 5.8 +/- 3.1 compared to 4.3 +/- 1.3 in controls (p less than 0.05). Diabetic men also had much stiffer aortas than diabetic women (p less than 0.001). There was a linear correlation between AS and duration of diabetes in men (R = 0.70; (p less than 0.001). For females no such correlation was found, the AS frequently being within the range of the controls in spite of long duration of the disease. In males there was a significant correlation between AS and retinopathy (R = 0.49; p less than 0.01) and an inverse correlation with HDL-cholesterol/total cholesterol ratio (R = 0.51; p less than 0.01). In diabetic females AS was significantly greater in smokers (7.0 +/- 3.7) than in non-smokers (4.2 +/- 2.2; p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood flow in the ascending and descending aorta in term newborn infants

The combination of 2-dimensional real-time and pulsed Doppler echocardiography provides a noninvasive method of measuring blood flow and has been used to study blood flow at the lower thoracic level in the descending aorta of the human fetus. Using these techniques, we evaluated the proportion of cardiac output distributed through the descending aorta in 20 healthy term newborn infants at 1–6 days of age. Blood flow in the ascending aorta was 759 ±135 ml/min (mean ±S.D.) and in the descending aorta 482 ±92 ml/min indicating that 63.8% of the left ventricular output is distributed through the descending aorta. Peak systolic and mean blood flow velocities were comparable at the two sites, whereas the diameter of the descending aorta was 19% smaller than that of the ascending aorta. The changes in aortic blood flow were correlated with the changes in aortic diameter.

152 BLOOD FLOW IN THE ASCENDING AND THE DESCENDING AORTA IN TERM NEWBORN INFANTS

The combination of 2-dimensional real-time and pulsed Doppler echocardiography provides a noninvasive method of measuring blood flow and has been used to study blood flow at the lower thoracic level of the descending aorta (DA) in the human fetus. Using these techniques, we evaluated the proportion of cardiac output distributed through the DA in 13 term newborn infants (mean±SEM BW 3551±95 g, GA 40.1±0.3 w). Blood flow velocity was measured using a 3.5 MHz, range gated, pulsed Doppler velocity meter with the transducer positioned in the suprasternal notch. Blood flow in the ascending aorta (AA) was measured at the aortic root level and descending flow below the isthmus. The internal diameter of the AA was assessed at the level of the aortic valve using M-mode echocardiography and the diameter of the DA in the posterior atrioventricular groove with the use of the 2-D long axis view. Blood flow in the AA was 789±42 ml/min and in the DA 499±26 ml/min indicating that 63.5% of the left ventricular output is distributed through the DA. The mean blood flow velocity was comparable at both sites, whereas the mean diameter of the DA was 19% smaller than the diameter of the AA. In healthy term newborn infants approx. 2/3 of cardiac output is directed to the DA and 1/3 to brachial and carotid arteries. The changes in aortic blood flow are correlated with the changes in aortic diameter.

Validation of a third-generation Doppler system for studies of detailed aortic flow.

A multigated, third-generation Doppler velocity system has been developed and validated for detailed studies of aortic hemodynamics. The Doppler system employs a single 3-mm, 5-MHz crystal applied to the aorta at a fixed angle with respect to the flow axis and is capable of measuring velocity profile, blood vessel diameter, and integrated volume flow on a continuous, real-time basis. This represents a major developmental advance over existing first-generation, continuous-wave and second-generation, single-gated pulsed Doppler systems. Validation studies have been performed in vitro and in dogs. Aortic diameter was measured simultaneously with the volumetric Doppler system and with sonomicrometer probes. During changes in aortic diameter between 8 and 18 mm (n = 18), produced by temporary pulmonary artery occlusion or epinephrine infusion, quantitative agreement between the Doppler and sonomicrometer probes was found (r = 0.96). Velocity profile measurements and axial velocity values made with the Doppler system compared favorably with hot-film anemometry studies in vitro and in vivo. Although the current system is nondirectional, measurements of phasic aortic volume flow and absolute-time-averaged changes in flow rates showed an excellent correlation with chronically placed electromagnetic flow probes over a broad range of flow rates in vivo (1-5 l/min, n = 36, r = 0.95). This third-generation Doppler system should prove useful in clinical and research studies of detailed aortic hemodynamics.

Cross-sectional echocardiographic detection of aortic obstruction. 2. Coarctation of the Aorta.

Cross-sectional echocardiographic studies of the aortic arch and proximal descending aorta were performed in 18 patients with coarctation of the aorta and 20 normal subjects. In normals the aortic arch and proximal descending aorta appeared as an arcuate, echo-free structure curving across the plane of the scan. There were no localized changes in aortic diameter and the amplitude of aortic systolic pulsation was symmetrically maintained throughout the scan plane. Visualization of this region was possible in 16 of 18 patients with coarctation. In each of these cases there was a localized area of decrease in aortic diameter in the region of the left subclavian artery which corresponded to the angiographic appearance of the coarctation. In addition prominent systolic pulsation of the aortic arch proximal to the region of obstruction was evident. Cross-sectional echocardiography may offer a useful noninvasive method for direct visualization of aortic coarctation.

Dynamic aortic diameter measurements in vivo

A method has been described for measurement of the dynamic changes in internal aortic diameter following injection upstream of a radiopaque dye. The method makes use of information available in a video-angiocardiogram and requires special computer techniques to suppress total system noise. Tests to date have demonstrated the limits of accuracy and show it to be a useful technique that might be effectively applied in health and disease and to other structures as well.