Ann Thorac Surg 1995;59:981-989
© 1995 The Society of Thoracic Surgeons
Effect of an Inelastic Aortic Synthetic Vascular Graft on Exercise Hemodynamics
Shin Y. Kim, PhD,
Thomas J. Hinkamp, MD,
William R. Jacobs, MD,
Robert C. Lichtenberg, MD,
Harold Posniak, MD,
Roque Pifarré, MD
Departments of Thoracic and Cardiovascular Surgery, Cardiology, and Radiology, Loyola University Medical Center, Maywood, Illinois
Accepted for publication January 10, 1995.
 |
Abstract
|
|---|
This study compared aortic input impedance characteristics between patients with aortic interposition Dacron grafts placed for traumatic aortic injury and normal age-matched control subjects. All subjects were examined at rest and after treadmill exercise. Magnetic resonance imaging was conducted to rule out anatomic (stenosis) effects. Exercise increased characteristic impedance (ie, reduced aortic distensibility) by 29% and decreased total systemic arterial compliance by 21% in the patient group, whereas the normal control group showed insignificant change in these variables after exercise. Peripheral pressure wave reflection was reduced substantially with exercise (27%) in the control group, with much less reduction observed in the patient group. These abnormal vascular hemodynamics were associated with significantly high cardiac energetic costs in the patient group. A plausible explanation for the observed differences lies in the exaggerated vascular impedance mismatch between compliant aorta and inelastic graft, when cardiac output increases dramatically.
|
Introduction
|
|---|
The aorta is a compliant vessel and acts as an elastic reservoir. It absorbs part of the hydraulic energy imparted to the blood during systole, which is released in diastole to maintain a constant distal flow. This function is known as a ``Windkessel'' property in the major conduit arteries including aorta. Operation on the diseased or the damaged aorta is performed mainly using synthetic grafts. The introduction of an inelastic graft in the highly distensible natural aorta may change the performance of the cardiovascular system due to the compliance mismatch between host artery and synthetic grafts [1], particularly when increased cardiac output is demanded [2]. Several studies have shown that the presence of a nondistensible vascular graft increases the left ventricular afterload primarily through the dramatic changes in the aortic vascular properties [2, 3]. Although the effects of an inelastic graft on the left ventricular and aortic hemodynamics have been recognized [1–6], there have been few reports to quantify these effects in humans. To this end, we compared the hemodynamic responses of two groups of subjects to upright treadmill exercise employing a noninvasively estimated aortic input impedance [7]. One group consisted of patients who had undergone a Dacron graft interposition in the thoracic aorta. The other group consisted of age-matched healthy volunteers.
|
Material and Methods
|
|---|
Study Subjects
Five male patients, aged 20 to 33 years (mean age, 27 years), who had undergone aortic interposition grafts for transected aorta due to blunt chest trauma participated in the study. They had an average of 5 postoperative years (standard deviation, 2 years) at the time of study. All the patients had the same type of surgical repair, end-to-end anastomosis of a woven Dacron graft interposition at the ligamentum arteriosum. Mean diameter and average length of the graft were 1.8 cm and 4.6 cm, respectively. Five volunteers, aged 26 to 34 years (mean age, 29 years), served as control subjects. All subjects appeared healthy and were taking no medication at the time of study. All gave informed consent to the protocol. The protocol was approved by the Human Subjects Committee of the Institutional Review Board.
Study Protocol
A 12-lead electrocardiogram was monitored in all subjects. The baseline supine study consisted of a two-dimensional echocardiogram, aortic Doppler echocardiography with time-corresponding right carotid pulse tracing. The right upper arm blood pressures were measured by a Dinamap 1846SX Vital Signs monitor (Critikon, Inc, Tampa, FL). After the baseline measurements, subjects assumed the upright position for at least 3 minutes before beginning the exercise. Subjects performed upright exercise tests to their target heart rate on an automated treadmill (Marquette CASE) following the Bruce protocol [8]. Exercise was initiated at the workload of 4 METS and was increased every 3 minutes by 3 METS. At the point of exhaustion, subjects immediately were placed in the supine position, and the same measurements previously described in the baseline study were repeated after cessation of exercise.
Aortic Doppler Measurements and Carotid Artery Pulse Tracings
Doppler echocardiography was performed from the suprasternal notch with a 1.9-MHz pencil-type continuous-wave Doppler transducer (Hewlett Packard, Andover, MA). Ascending aortic pressure was estimated by the calibrated carotid pressure pulse tracing. Calibration was performed with assignment of systolic pressure to the peak and diastolic blood pressure to the nadir of the pulse tracing [7]. Pulse tracings were performed using a pulse transducer (model SPT-301; Millar Instruments, Houston, TX) during a short period of apnea at mid- to end expiration. The real-time graphic display, with a rate of 100 mm/s, of the hemodynamic wave signals including aortic Doppler, carotid pressure pulse wave, and electrocardiogram, was viewed in a monitor and recorded in a built-in videocassette recorder (Sonos 1000; Hewlett Packard) for off-line computer-aided analysis.
Data Processing and Analysis
For estimating aortic annular cross-sectional area, the aortic diameter was measured from the leading edge of the anterior to the leading edge of the posterior echo at the annulus of the aortic root in a parasternal long-axis view. Aortic diameter was assumed to be circular and constant during exercise [9]. Cardiac output (CO) was calculated as the product of the Doppler mean velocity and aortic annular cross-sectional area. Hard copies were obtained from the selected video images for wave digitization. At least five consecutive pressure and flow recordings were digitized with a sampling interval of 5 ms using a digitizing pad (SummaSketch II; Summagraphics, Bristol, CT) interfaced with a personal computer (Everex 486/33).
Characterization of Vascular Properties and Impedance Spectrum
Digitized pressure and flow wave recordings were averaged for each period and Fourier analysis subsequently was performed for constructing the impedance spectrum (Fig 1
). The aortic input impedance spectrum was derived as the impedance modulus (Zn) and impedance phase (
n). The impedance modulus is the ratio of the respective pressure modulus to flow modulus (Qn) at a given frequency (n), and impedance phase is the difference between pressure and flow phase angle [7]. The zero-order term of the impedance spectrum is the total systemic vascular resistance. The modulus of the first harmonic impedance (Z1) was used as an index of ventriculoarterial impedance matching [7]. Characteristic impedance (Zc), an index of aortic stiffness, was the average impedance modulus from greater than 2 Hz at rest [10] or greater than 4 Hz after exercise to 12 Hz [11]. An index of pressure pulse wave reflection was obtained from the ratio of backward pressure amplitude to forward pressure amplitude [12]. The transmission time to and from the effective reflection site and total arterial compliance were calculated by the methods proposed previously [10, 13].
View larger version (24K):
[in this window]
[in a new window]
|
Fig 1. . Impedance moduli are at the top and phase angle at the bottom. The effect of exercise on the change in impedance spectra is qualitatively similar in both groups: significant reduction in systemic vascular resistance (the impedance at 0 Hz), right-sided shift of a pulsatile component of vascular impedance (Z1) due to the increase in heart rate, and less phase angle difference between pressure and flow indicating vasodilation. (A) Normal study. (B) Patient study.
|
|
Left Ventricular Function and Hydraulic Pumping Energy Cost
Mean systolic acceleration of the aortic flow, an index of contractility, was determined by dividing the peak velocity by the time from the onset of flow to peak velocity [9]. Myocardial oxygen consumption was estimated by the calculation of rate-pressure product (RPP) and tension-time index (TTI). The ratio of TTI over the diastolic pressure-time index (DPTI) was used to evaluate myocardial oxygen demand and supply [14]. The TTI and DPTI were obtained from the measurements of the area under the systolic and the diastolic portion of the aortic pressure curve, respectively. The RPP was calculated as systolic pressure multiplied by heart rate. The left ventricular external work was assessed by the calculation of hydraulic power. Pulsatile power (Wo) was calculated from the following formula [7]: Wo = 0.5 x 
Qn2 Zn cos(n). Mean power was calculated as the product of mean aortic pressure and flow, and total power (Wt) was the sum of mean and pulsatile power. The ratio of pulsatile to total power was used as an index of the efficiency of power transfer [7, 11]. The pumping energy cost was evaluated by the left ventricular energy expenditure for any given cardiac output or stroke volume [2]: Wt/CO, RPP/CO, and TTI/SV.
Magnetic Resonance Imaging Study
Four patients participated in magnetic resonance imaging study to rule out a potential stenosis at the place of graft anastomosis. Magnetic resonance images were acquired using Signa 1.5 Tesla scanner (General Electric Medical Systems, Milwaukee, WI). Several stenosis indices (SIs) were used for assessing the degree of stenosis. The first index, SI1, is the ratio of the diameter of the aortic arch to the diameter of descending aorta, and the second index, SI2, is the ratio of the graft diameter to the diameter of the descending aorta [15]. The third index, SI3, is the ratio of the diameter of the aortic arch to the diameter of the ascending aorta [16]. Measurements of diameter of aorta and graft were achieved by a built-in computer-aided electronic caliper of the magnetic resonance imaging system. The diameter of the ascending aorta just proximal to the innominate artery was measured on the sagittal image in a plane perpendicular to its long axis. The length and minimal diameter of the graft similarly were measured on the sagittal or parasagittal images. The diameter of the aortic arch between the left common carotid and the left subclavian artery was measured on coronal images. The descending aorta was measured on the axial images at least 2 cm distal to the graft.
Statistical Analysis
Wilcoxon signed-rank test (equivalent to Student's paired t test) was used to assess hemodynamic changes within individuals. Kruskal-Wallis (equivalent to Student's t test) one-way analysis of variance was used for group comparisons. A p value less than 0.05 was considered statistically significant. Data are presented as mean +/- standard deviation.
|
Results
|
|---|
Basic Hemodynamics at Rest and Immediately After Exercise
Normal subjects exercised for an average of 17 minutes with work load of 19 METS. Duration of exercise in patient group averaged 13 minutes with a work load of 15 METS. All subjects quit exercise due to dyspnea and fatigue. The basic hemodynamic data are listed in Table 1. No noticeable differences were found in resting and exercise hemodynamics between the groups. Diastolic pressures were not altered significantly by exercise in either group. However, the patient group demonstrated higher end-systolic pressures and lower SV than the normal subjects after exercise (both p = 0.03). Because of slight increase in SV after exercise in both groups, the increased CO was principally the result of an increase in heart rate (65 +/- 2 to 152 +/- 12 beats/min in normal group, p = 0.027; 69 +/- 4 to 153 +/- 12 beats/min in patient group, p = 0.005).
Vascular Properties and Impedance Data at Rest and Immediately After Exercise
The impedance data are summarized in Table 2. Representative examples of the input impedance spectra are shown in Figure 1A
for a normal study and Figure 1B for a patient. Exercise decreased systemic vascular resistance significantly by 57% and by 51% from their resting values in the normal and patient group, respectively. The reduction in systemic vascular resistance was associated with a substantial decrease in the impedance modulus of the first harmonic (Z1) in both groups, suggesting an improved vascular impedance coupling with ejecting ventricle. However, these variables remained significantly higher in the patient group even after exercise (both p = 0.035). A particularly interesting observation of the effect of exercise on impedance variables is found in the change of characteristic impedance (Zc), peripheral pressure pulse wave reflection, and total arterial compliance (C) (Fig 2). The Zc, an index of aortic stiffness, in the normal group remained unchanged by exercise (rest versus exercise: 85 +/- 11 versus 89 +/- 13 dynes • s/cm5; p = nonsignificant), whereas the patient group demonstrated increased Zc after exercise (rest versus exercise: 138 +/- 34 versus 177 +/- 45 dynes • s/cm5; p = 0.015). The patient group also showed significantly higher aortic stiffness value than that of normal group at both rest and after exercise (both p = 0.01). Exercise decreased peripheral pressure pulse wave reflection by 27% in normal subjects (rest versus exercise: 0.49 +/- 0.01 versus 0.36 +/- 0.09; p = 0.028). However, exercise decreased peripheral pressure pulse wave reflection slightly in the patient group (rest versus exercise: 0.68 +/- 0.04 versus 0.55 +/- 0.1; p = nonsignificant). Although total arterial compliance was not changed by exercise in the normal group (rest versus exercise: 1.95 +/- 0.11 versus 1.87 +/- 0.14 mL/mm Hg; p = nonsignificant), it was significantly reduced in the patient group (rest versus exercise: 1.67 +/- 0.28 versus 1.31 +/- 0.25 mL/mm Hg; p = 0.04). Resting pressure pulse transmission time to and from an effective reflection site is significantly shorter in the patient group than in the normal group (normal versus patient: 204 +/- 35 versus 124 +/- 24 ms; p = 0.001). Exercise decreased the transmission time by 66% (p = 0.028) and by 34% (p = 0.005) from the baseline at rest in the normal and patient groups, respectively. There was no statistically significant transmission time difference after exercise between the groups.
View larger version (20K):
[in this window]
[in a new window]
|
Fig 2. . Characteristics of vascular impedance properties between the groups at rest and after exercise. Significant changes in characteristic impedance (Zc) (A) and total arterial compliance (C) (B) were shown only in the patient group after exercise (29% increase in Zc and 22% reduction in compliance). Exercise lowered peripheral pressure pulse wave reflection (WRC) (C) and impedance modulus at the frequency of heart rate (Z1) (D) in both groups. However, the magnitudes of these variables were remarkably higher in the patient group compared with the normal group at rest (WRC, p = 0.001; Z1, p = 0.01) and after exercise (WRC, p = 0.024; Z1, p = 0.006).
|
|
Left Ventricular Function and Hydraulic Pumping Energy Cost
Cardiac contractile force represented by aortic blood flow acceleration [9] and left ventricular hydraulic external power, and myocardial oxygen demand/supply ratio (TTI/DPTI) were not different between the groups both at rest and after exercise (Table 3). In both instances, however, left ventricular hydraulic power transfer efficiency (Wo/Wt) and energetic costs to the heart for delivering a given cardiac output or stroke volume (Wt/CO, RPP/CO, or TTI/SV) were significantly higher in the patient group (Figs 3, 4). All of these variables show statistically significant difference between the groups with a p value of less than 0.03. Because all impedance variables resulted in significant difference between the groups, the relation between energetic costs and impedance variables was determined by a regressional analysis using group combined data. The results show that each energy cost index has exactly the same relationship with two impedance variables including characteristic impedance and total arterial compliance. Figure 5 shows that energetic cost is proportional to the value of characteristic impedance and inversely proportional to the value of total arterial compliance.
View larger version (26K):
[in this window]
[in a new window]
|
Fig 3. . Cardiac energetic cost between the groups at rest and after exercise. Error bar indicates one standard deviation. Exercise increased the ratio of tension-time index to stroke volume (TTI/SV) considerably in both groups (p = 0.034 in both groups). Although it was not statistically significant, the increase in cardiac energetic cost also was shown in the ratio of rate-pressure product to cardiac output (RPP/CO) in both groups after exercise. However, the patient group showed substantially higher cardiac energetic cost (in both TTI/SV and RPP/CO) than that of the normal group at rest and after exercise (both p < 0.03).
|
|
View larger version (21K):
[in this window]
[in a new window]
|
Fig 4. . Significantly higher cardiac external hydraulic work costs (Wt/CO) in the patient group than those in the normal subjects at rest (p = 0.03) and after exercise (p = 0.003) were associated with higher characteristic impedance (Zc) and lower arterial compliance values in the patient group than in the normal subjects.
|
|
View larger version (18K):
[in this window]
[in a new window]
|
Fig 5. . Relationship between a cardiac energetic cost and two vascular properties is illustrated by a linear regression analysis with 95% confidence intervals in group pooled data: where ``n' and ''p' indicate the data of normal and patient individuals, respectively: TTI/SV = -0.221 C + 0.853 (p = 0.001 with r = 0.767) and TTI/SV = 0.01 Zc + 0.365 (p = 0.006 with r = 0.59). (C = arterial compliance; n = normal data; p = patient data; SV = stroke volume; TTI = tension-time index; Zc = characteristic impedance.)
|
|
Magnetic Resonance Imaging Study
The measured and calculated data are outlined in Table 4. In these indices, the larger the value, the less the degree of stenosis of the aorta. These indices, the ratio of one portion the aorta to another portion of the aorta, have mean values ranging from 0.89 to 1.14.
|
Comment
|
|---|
Noninvasive Aortic Input Impedance Measurement
Validation of the noninvasive determination of aortic input impedance has been well elucidated by Kelly and Fitchett [7]. In the present study, exactly the same methods that they used were employed. However, the question remains as to whether this noninvasive method can determine reliably the aortic input impedance after maximal exercise. Figure 6 shows that the shape of the carotid pulse contours in our subjects at rest and immediately after maximal exercise looks very similar to that of the aortic pressure wave contours invasively obtained from 4 healthy college students at rest and during treadmill exercise [17]. It has been reported that brachial pressures measured by auscultation at rest and during exercise were in close agreement with the directly measured aortic pressures [18, 19]. Several studies using the methods that we employed in this study demonstrated that there was a close relationship between cardiac output measured by Doppler flow method and cardiac output measured by other conventional methods over a variety of clinical conditions [20]. In this approach, it was assumed that the carotid pulse pressure contours calibrated by upper arm blood pressures and Doppler flow can reflect accurately the central aortic hemodynamics after exercise. In addition, the magnitudes and the shapes of input impedance spectra found in our subjects are in agreement with those obtained invasively from subjects after supine exercise reported in the literature [10, 11]. Therefore we assumed this noninvasive method reliably measures the aortic input impedance after exercise.
View larger version (16K):
[in this window]
[in a new window]
|
Fig 6. . A representative calibrated carotid artery tonometric pressure pulse wave of the present study immediately after exercise is compared with the invasively obtained ascending aortic pressure of a normal subject (in Figure 3 of Reference 17 [Circulation 1968;37:954-64]) during maximal uptreadmill exercise. The aortic pressure was reconstructed from that figure with the authors' permission. All subjects in this study showed almost the same carotid pulse contours as that of the aortic pressure wave after exercise.
|
|
Magnetic Resonance Imaging Study
The mean values of the stenotic indices SI1, SI2, and SI3 in the control groups who had normal aorta are 0.75, 0.76 [15], and 0.9 [16], whereas the mean values of these indices in the present study are 1.14, 0.91, and 0.89, respectively. The values of SI1 and SI3 in the present study indicate no hypoplasia of the transverse aortic arch in our patient group, which is further supported by no difference in blood pressure levels between two groups in the present study. Because perioperative images were not available at the time of study, the exact degree of stenosis at the anastomosis, if any, in our patients could not be determined. However, compared with the values reported in other studies that employed the same indices for measuring the degree of stenosis in patients with coarctation repair and in normal control groups [15, 16], our data strongly suggest that our patients who participated in magnetic resonance imaging study appear to have no evidence of development of stenosis at the site of repair. Magnetic resonance imaging study was not performed in the 1 remaining patient. We assumed that this patient also had no evidence of stenosis at the repair site because his vascular property data, eg, characteristic impedance, peripheral pressure pulse wave reflection, and total arterial compliance, are in the similar range of other patients' data.
Vascular Properties and Impedance Data
The principal finding in the present study is that exercise did not change aortic characteristic impedance and total arterial compliance, but significantly reduced peripheral pressure wave reflection in the normal subjects, whereas exercise increased aortic characteristic impedance, decreased total arterial compliance significantly, and decreased peripheral pressure wave reflection, to a much lesser degree, in the patient group. Increases in the distending pressure [21] and age [22] are known to decrease the compliance of the vascular wall. In the present study, there was no significant difference in age and blood pressure levels between the groups, which eliminated these factors as possible causes of the observed impedance differences between the groups. It has been reported previously that the aortic characteristic impedance does not change in normal subjects and in patients with congestive heart failure during supine submaximal exercise [10, 11]. Characteristic impedance is related directly to the pulse wave velocity, but it is related inversely to the cross-sectional area of the vessel [10]. Pulse wave velocity in the normal and patient group appears to have increased on the order of 66% and 28%, respectively, based on the change in the calculated pulse wave transmission time after exercise. Because characteristic impedance remained constant, the change in aortic cross-sectional area must have been of the same order of magnitude, ie, equivalent to a change in the radius of approximately 28% in the normal group. However, only 5% to 7% change in the aortic radius was observed in the patient group, based on the change in characteristic impedance and pulse wave transmission. This indicates that the patient group has a significantly less distensible aorta than the normal group. The compliance of a woven Dacron graft is 0.16 and the compliance of a 20-year-old human thoracic aorta is 26.8 in relative units, which indicates that Dacron graft is approximately 168 times stiffer than aorta [1]. The compliance mismatch between Dacron graft and aorta may become more intensified when a high output flow condition is required. Under this circumstance the Dacron graft itself may behave as a functional stenosis [17], leading to a significant change in impedance at the interface of compliant artery with rigid segment. Therefore, significant decrease in compliance, less reduction in arterial pressure wave reflection, and less power transfer efficiency of arterial system (Wo/Wt) in the patient group after exercise may result from the increase in the local pressure pulse wave reflection [1, 6] and significant pulsatile energy loss [23] at the proximal segment of graft anastomosis. Furthermore, these hemodynamic disturbances at the graft anastomosis may explain the reduced ventriculoarterial coupling (Z1) in the patient group at rest and after exercise.
Ventricular Hydraulic Power and Energy Cost
Recently, Kelly and associates [2] investigated the effect of canine's entire aorta with a long Dacron graft on the acute change in cardiovascular function. When aortic blood flow was directed from the natural aorta to the synthetic graft, they observed a dramatic increase in myocardial oxygen consumption (32%) and characteristic impedance (52%), and a significant decrease in total arterial compliance (70%). As a result, cardiac mechanical efficiency defined by the ratio of stroke work/myocardial oxygen consumption decreased by 23%. However, it was associated with insignificant change in ventricular contractility and cardiac output. Similar results also were reported by Morita and associates [3] using an almost identical experimental model. Our patient data after exercise have a remarkable hemodynamic similarity to their experimental results. Time-tension index increased by 30%, characteristic impedance increased by 29%, total compliance decreased by 21%, and ventricular pumping efficiency decreased by 16% (SV/TTI), 15% (CO/RPP), and 17%. The changes in all of these variables are statistically significantly different (p < 0.05) between the groups. However, overall left ventricular mechanical function appeared the same in both groups at rest and after exercise, which was shown by mean aortic flow acceleration, left ventricular external hydraulic power, and myocardial oxygen demand/supply ratio. The increase in pressure pulse wave reflection resulting from the reduction in arterial compliance increases the left ventricular pressure (ie, increase in myocardial oxygen consumption) and decreases stroke volume [24], which may explain the higher cardiac energetic cost (ie, decreased cardiac mechanical efficiency) in the patient group.
Conclusion
In conclusion, with pulsatile blood flow, the compliant aorta acts as an elastic reservoir, absorbing energy during systole, which is released during diastole. The introduction of a rigid segment interferes with this function. At resting conditions, this compliance mismatch between host aorta and graft appears to be less important in the maintenance of distal blood flow during diastole. However, when high output is demanded, as during exercise, the compliance mismatch increases. Therefore, the exercise-induced intensified vascular and graft compliance mismatch could explain the characteristic hemodynamic difference between the two groups including higher cardiac energetic cost to maintain a given flow due to a less compliant proximal aorta and arterial system, and compromised decline in pressure pulse wave reflection in contrast to the significant drop in systemic vascular resistance. As reported in previous case reports on patients with extra-anatomic aortic bypass using long woven Dacron grafts [4, 5], left ventricular hypertrophy in this surgical patient group may result from insidious but significant pressure pulse wave reflection due to the loss of natural aortic ``Windkessel'' property.
|
Acknowledgments
|
|---|
This study was supported in part by the Bane Foundation.
|
Footnotes
|
|---|
Address reprint requests to Dr Pifarré, Department of Thoracic and Cardiovascular Surgery, Loyola University Medical Center, Maywood, IL 60153.
|
References
|
|---|
- Kinely CE, Marble AE. Compliance: a continuing problem with vascular grafts. J Cardiovasc Surg 1980;21:163–70.[Medline]
- Kelly RP, Tunin R, Kass DA. Effect of reduced aortic compliance on cardiac efficiency and contractile function of in situ canine left ventricle. Circ Res 1992;71:490–502.[Abstract/Free Full Text]
- Morita S, Kuboyama I, Asou T, et al. The effect of extraanatomic bypass on aortic input impedance studied in open chest dogs. Should the vascular prosthesis be compliant to unload the left ventricle? J Thorac Cardiovasc Surg 1991;102:774–83.[Abstract]
- Maeta H, Hori M. Effects of a lack of aortic ``Windkessel'' properties on the left ventricle. Jpn Circ J 1985;49:232–7.[Medline]
- Mitsui T, Maeta H, Fukuda I, et al. Left ventricular hypertrophy due to aortic bypass grafting with a long prosthesis. J Cardiovasc Surg 1986;27:201–6.[Medline]
- Appleyard R, Sauvage LR. Hemodynamic consequences of arterial replacement with a synthetic graft. Cardiovasc Res 1986;20:26–35.[Medline]
- Kelly R, Fitchett D. Noninvasive determination of aortic input impedance and external left ventricular power output: a validation and repeatability study of a new technique. J Am Coll Cardiol 1992;20:952–63.[Abstract]
- Bruce RA, Kusumi F, Hostner D. Maximal oxygen intake and nomographic assessment of functional aerobic impairment in cardiovascular disease. Am J Cardiol 1973;85:346–59.
- Daley PJ, Sagar KB, Wann LS. Doppler echocardiographic measurement of flow velocity in the ascending aorta during supine and upright exercise. Br Heart J 1985;54:562–7.[Abstract/Free Full Text]
- Murgo JP, Westerhof N, Giolma JP, Altobelli SA. Effects of exercise on aortic input impedance and pressure wave forms in normal humans. Circ Res 1981;48:334–43.[Abstract/Free Full Text]
- Laskey WK, Kussmaul WG, Martin JL, Kleaveland JP, Hirsheld JW, Shroff S. Characteristics of vascular hydraulic load in patients with heart failure. Circulation 1985;72:61–71.[Abstract/Free Full Text]
- Westerhof N, Spikema P, Van Den Bos GC, Elzinga G. Forward and backward waves in the arterial system. Cardiovasc Res 1972;6:648–56.[Medline]
- Liu Z, Brin KP, Yin FCP. Estimation of total arterial compliance: an improved method and evaluation of current methods. Am J Physiol 1986;251:H588–600.[Medline]
- Buckberg GD, Fixler DE, Archie JP, Hoffman JIE. Experimental subendocardial ischemia in dogs with normal coronary arteries. Circ Res 1972;30:67–81.[Abstract/Free Full Text]
- Kappetein PA, Guit GL, Bogers AJJC, et al. Noninvasive long-term follow-up after coarctation repair. Ann Thorac Surg 1993;55:1153–9.[Abstract]
- Leandro J, Smallhorn JF, Benson L, et al. Ambulatory blood pressure monitoring and left ventricular mass and function after successful surgical repair of coarctation of the aorta. J Am Coll Cardiol 1992;20:197–204.[Abstract]
- Rowell LB, Brengelmann GL, Blackmon JR, Bruce RA, Murphy JA. Disparities between aortic and peripheral pulse pressures induced by upright exercise and vasomotor changes in man. Circulation 1968;37:954–64.[Abstract/Free Full Text]
- Nagle FJ, Naughton J, Balke B. Comparisons of direct and indirect blood pressure with pressure-flow dynamics during exercise. J Appl Physiol 1966;21:317–20.[Free Full Text]
- Borrow KM, Newburger JW. Noninvasive estimation of central aortic pressure using the oscillometric method for analyzing systemic artery pulsatile blood flow: comparative study of indirect systolic, diastolic, and mean brachial artery pressure with simultaneous direct ascending aortic pressure measurements. Am Heart J 1982;103:879–86.[Medline]
- Ihlen H, Amile JP, Dale J, et al. Determination of cardiac output by Doppler echocardiography. Br Heart J 1984;51: 54–60.[Abstract/Free Full Text]
- Partel DJ, Jnicki JS, Carew TE. Static anisotropic properties of the aorta in living dogs. Circ Res 1969;25:765–72.[Abstract/Free Full Text]
- Learoyd BM, Taylor MG. Alterations with age in the viscoelastic properties of human arterial walls. Circ Res 1965;28:278–83.
- Strandness DE, Sumner DS. Hemodynamics for surgeons. New York, 1975.
- Elzinga G, Piene H, de Jong JP. Left and right ventricular pump function and consequences of having two pumps in one heart. A study on the isolated cat heart. Circ Res 1980;46:564–74.[Free Full Text]
This article has been cited by other articles:
|
|
|
|
 
H. H. Sievers
Reflections on reduction ascending aortoplasty's liveliness
J. Thorac. Cardiovasc. Surg.,
October 1, 2004;
128(4):
499 - 501.
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Morita, T. Asou, I. Kuboyama, Y. Harasawa, K. Sunagawa, and H. Yasui
Inelastic vascular prosthesis for proximal aorta increases pulsatile arterial load and causes left ventricular hypertrophy in dogs
J. Thorac. Cardiovasc. Surg.,
October 1, 2002;
124(4):
768 - 774.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. Bauernschmitt, S. Schulz, A. Schwarzhaupt, U. Kiencke, C.-F. Vahl, R. Lange, and S. Hagl
Simulation of arterial hemodynamics after partial prosthetic replacement of the aorta
Ann. Thorac. Surg.,
March 1, 1999;
67(3):
676 - 682.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Karamanoglu and M. P. Feneley
On-line Synthesis of the Human Ascending Aortic Pressure Pulse From the Finger Pulse
Hypertension,
December 1, 1997;
30(6):
1416 - 1424.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
S. Y. Kim, D. E. Euler, W. R. Jacobs, A. Montoya, H. J. Sullivan, V. A. Lonchyna, and R. Pifarre
Arterial Impedance in Patients During Intraaortic Balloon Counterpulsation
Ann. Thorac. Surg.,
March 1, 1996;
61(3):
888 - 894.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
L. L. Demer
A Skeleton in the Atherosclerosis Closet
Circulation,
October 15, 1995;
92(8):
2029 - 2032.
[Full Text]
|
|
|
Top
Abstract
Introduction
