Noninvasive method for determination of arterial compliance using Doppler echocardiography and subclavian pulse tracings. Validation and clinical application of a physiological model of the circulation

Characteristics of pulmonary artery strain assessed by cardiovascular magnetic resonance imaging and associations with metabolomic pathways in human ageing

Background

Pulmonary artery (PA) strain is associated with structural and functional alterations of the vessel and is an independent predictor of cardiovascular events. The relationship of PA strain to metabolomics in participants without cardiovascular disease is unknown.

Methods

In the current study, community-based older adults, without known cardiovascular disease, underwent simultaneous cine cardiovascular magnetic resonance (CMR) imaging, clinical examination, and serum sampling. PA global longitudinal strain (GLS) analysis was performed by tracking the change in distance from the PA bifurcation to the pulmonary annular centroid, using standard cine CMR images. Circulating metabolites were measured by cross-sectional targeted metabolomics analysis.

Results

Among n = 170 adults (mean age 71 ± 6.3 years old; 79 women), mean values of PA GLS were 16.2 ± 4.4%. PA GLS was significantly associated with age (β = -0.13, P = 0.017), heart rate (β = -0.08, P = 0.001), dyslipidemia (β = -2.37, P = 0.005), and cardiovascular risk factors (β = -2.49, P = 0.001). Alanine (β = -0.007, P = 0.01) and proline (β = -0.0009, P = 0.042) were significantly associated with PA GLS after adjustment for clinical risk factors. Medium and long-chain acylcarnitines were significantly associated with PA GLS (C12, P = 0.027; C12-OH/C10-DC, P = 0.018; C14:2, P = 0.036; C14:1, P = 0.006; C14, P = 0.006; C14-OH/C12-DC, P = 0.027; C16:3, P = 0.019; C16:2, P = 0.006; C16:1, P = 0.001; C16:2-OH, P = 0.016; C16:1-OH/C14:1-DC, P = 0.028; C18:1-OH/C16:1-DC, P = 0.032).

Conclusion

By conventional CMR, PA GLS was associated with aging and vascular risk factors among a contemporary cohort of older adults. Metabolic pathways involved in PA stiffness may include gluconeogenesis, collagen synthesis, and fatty acid oxidation.

A novel method for the noninvasive estimation of cardiac output with brachial oscillometric blood pressure measurements through an assessment of arterial compliance

OBJECTIVE

To propose and validate a new method for estimating cardiac output based on the total arterial compliance (Ct) formula that does not need an arterial waveform and to apply it to brachial oscillometric blood pressure measurements (OBPMs).

METHODS

One hundred subjects with normal heart anatomy and function were included. Reference values for cardiac output were measured with echocardiography, and Ct was calculated with a two-element Windkessel model. Then, a statistical model of arterial compliance (Ce) was used to estimate cardiac output. Finally, the measured and estimated cardiac output values were compared for accuracy and reproducibility.

RESULTS

The model was derived from the data of 70 subjects and prospectively tested with the data from the remaining 30 individuals. The mean age of the whole group was 43.4 ± 12.8 years, with 46% women. The average blood pressure (BP) was 107.1/65.0 ± 15.0/9.6 mmHg and the average heart rate was 67.7 ± 11.4 beats/min. The average Ct was 1.39 ± 0.27 mL/mmHg and the average cardiac output was 5.5 ± 1.0 L/min. The mean difference in the cardiac output estimated by the proposed methodology vs. that measured by Doppler echocardiography was 0.022 L/min with an SD of 0.626 L/min. The intraclass correlation coefficient was 0.93, and the percentage error was 19%.

CONCLUSION

Cardiac output could be reliably and noninvasively obtained with brachial OBPMs through a novel method for estimating Ct without the need for an arterial waveform. The new method could identify hemodynamic factors that explain BP values in an ambulatory care setting.

Three-dimensional regional bi-ventricular shape remodeling is associated with exercise capacity in endurance athletes

AIMS

Endurance athletes develop cardiac remodeling to cope with increased cardiac output during exercise. This remodeling is both anatomical and functional and shows large interindividual variability. In this study, we quantify local geometric ventricular remodeling related to long-standing endurance training and assess its relationship with cardiovascular performance during exercise.

METHODS

We extracted 3D models of the biventricular shape from end-diastolic cine magnetic resonance images acquired from a cohort of 89 triathlon athletes and 77 healthy sedentary subjects. Additionally, the athletes underwent cardio-pulmonary exercise testing, together with an echocardiographic study at baseline and few minutes after maximal exercise. We used statistical shape analysis to identify regional bi-ventricular shape differences between athletes and non-athletes.

RESULTS

The ventricular shape was significantly different between athletes and controls (p < 1e-6). The observed regional remodeling in the right heart was mainly a shift of the right ventricle (RV) volume distribution towards the right ventricular infundibulum, increasing the overall right ventricular volume. In the left heart, there was an increment of left ventricular mass and a dilation of the left ventricle. Within athletes, the amount of such remodeling was independently associated to higher peak oxygen pulse (p < 0.001) and weakly with greater post-exercise RV free wall longitudinal strain (p = 0.03).

CONCLUSIONS

We were able to identify specific bi-ventricular regional remodeling induced by long-lasting endurance training. The amount of remodeling was associated with better cardiopulmonary performance during an exercise test.

Doppler-Derived Arterial Load Indices Better Reflect Left Ventricular Afterload Than Systolic Blood Pressure in Coarctation of Aorta

BACKGROUND

Patients with vascular stiffening may display increased arterial afterload that is out of proportion to systolic blood pressure (SBP). Since vascular and endothelial dysfunction develop in patients with coarctation of aorta (COA), we hypothesized that for any SBP, patients with mild COA (COA peak velocity <2 m/s) will have a higher arterial afterload and increased left ventricular mass index (LVMI) compared with controls, and that Doppler-derived arterial load indices would be a better predictor of LVMI compared with SBP alone.

METHODS

We studied 204 COA patients (age 35±12 y) and 204 matched controls. Doppler-derived arterial afterload was assessed using effective arterial elastance index and total arterial compliance index.

RESULTS

Despite similar SBP, the mild COA group displayed higher arterial afterload as evidenced by a higher elastance index (3.3±0.9 versus 2.9±0.7 mm Hg/mL·m2; P<0.001) and lower total arterial compliance index (0.8±0.3 versus 1.2±0.5 mL/mm Hg·m2; P<0.001). This was associated with higher LVMI in COA (109±35 versus 93±32, g/m2; P<0.001). Compared with SBP (β=0.24 [95% CI, 0.02-0.45]), elastance index (β=20.2 [95% CI, 15.8-44.1]) and total arterial compliance index (β=-32.5 [95% CI, -43.8 to -123.6]) were better predictors of LVMI. Elastance index (but not SBP) was predictive of longitudinal increases in LVMI (r=0.43, P<0.001).

CONCLUSIONS

COA patients had higher arterial afterload compared with controls with similar SBP. In comparison to SBP, Doppler-derived arterial load indices correlate more strongly with LV hypertrophy. These data suggest that SBP may underestimate LV afterload in this population. This has important clinical implications since titration of antihypertensive therapy is currently based on SBP.

Beta-blockers in non-surgical patients with type A aortic dissection

Type A aortic dissection (TAAD) is a catastrophic condition with 24-48% mortality during the first day, if patients are not surgically treated. Due to old age and associated co-morbidities surgeons may be reluctant to operate and patients are administered medical therapy for the end of reducing systolic blood pressure and heart rate. Beta-blockers (BB) are the "medications of choice". Based on physical and physiological considerations, it was hypothesized that BB may actually exacerbate TAAD.

Arterial Compliance is an Independent Factor Predicting Acute Hemodynamic Performance of Intra-aortic Balloon Counterpulsation

Data concerning the effect of arterial compliance (AC) on hemodynamics during intra-aortic balloon counterpulsation (IABC) are lacking. This study examines the effect of AC on acute hemodynamics induced by IABC in 15 patients with post-infarction cardiogenic shock. AC was estimated by aortic pulse wave analysis using the reflection time index (RTI). Measurements were obtained once per day during IABC. The % reduction in systolic aortic pressure (ΔSAP), end-diastolic aortic pressure (ΔEDAP) and the peak aortic diastolic augmentation (PADA) were used as performance indices of IABC; 107 sets of measurements were obtained. Multivariate analysis indicated an independent association of each IABC performance index with AC (p<0.05). A high AC group (RTI≤20.6%, n=40) and a low AC group (RTI>20.6%, n=67) were obtained. ΔSAP, ΔEDAP and PADA were significantly higher in the low AC group by almost 75%, 54.6% and 11,3% (p<0.03), while arterial blood pressure did not significantly differ. Arterial compliance is an independent factor affecting hemodynamics during IABC. RTI values higher than 20.6% may predict a better acute hemodynamic response to IABC.

Do long-chain n-3 fatty acids reduce arterial stiffness? A meta-analysis of randomised controlled trials

Fish oils, rich in long-chain n-3 PUFA, are known to reduce various risk factors for CVD. However, conclusive evidence regarding the benefits of n-3 on arterial stiffness, a risk factor for CVD, has not yet been established. Consequently, we conducted the first study aimed to quantify the effects of n-3 supplementation on arterial stiffness through meta-analysis. Multiple databases and clinical trial registries were systematically searched up until September 2010 for randomised and controlled adult human clinical trials to investigate the effects of long-chain n-3 fatty acids on arterial stiffness. No limits were set on dosage sizes or sample characteristics. A total of ten n-3 trials met the final inclusion criteria; four using pulse wave velocity (PWV) and six using arterial compliance, measured as capacitive compliance or systemic arterial compliance, as respective outcome measures. Meta-analysis revealed that n-3 was statistically significant in effectively improving both PWV (g = 0·33; 95 % CI 0·12, 0·56; P < 0·01) and arterial compliance (g = 0·48; 95 % CI 0·24, 0·72; P < 0·001). There was no evidence of heterogeneity or publication bias. Results were not influenced by changes in blood pressure, heart rate or BMI. The findings of the present study reveal that supplementation with n-3 offers a scientifically supported means of reducing arterial stiffness. Reduction in arterial stiffness by n-3 may account for some of its purported cardioprotective effects.

Large artery biomechanics and diastolic dysfunctionin patients with Type 2 diabetes

AIMS

To comprehensively characterize large artery biomechanical properties and examine their relationship to cardiac function in patients with Type 2 diabetes mellitus (DM).

METHODS

Fifty-five individuals with Type 2 DM were compared with 66 age- and sex-matched healthy control subjects. Arterial biomechanical properties were assessed by systemic arterial compliance (SAC; two-element Windkessel model), carotid-femoral pulse wave velocity (PWVc-f), femoral-dorsalis pedis pulse wave velocity (PWVf-d) and carotid augmentation index. Cardiac structure and function were assessed by echocardiography.

RESULTS

Individuals with Type 2 DM had lower SAC and higher PWVc-f when compared with the healthy population. The PWVc-f was significantly lower than the PWVf-d in control individuals, but this difference was not evident in individuals with Type 2 DM due to higher PWVc-f. Augmentation index was similar in both groups, but the time to the first systolic inflection (time to reflection) was shorter in the individuals with Type 2 DM. The individuals with Type 2 DM had a greater prevalence of diastolic abnormalities when compared with the control group. Arterial stiffness indices, including SAC and pulse pressure, correlated with left ventricular filling pressure (defined as peak velocity during early diastolic filling divided by the velocity of movement of the mitral valve annulus in early diastole; r = -0.33 and 0.36 respectively.

CONCLUSIONS

Patients with Type 2 DM on standard medication showed preferential stiffening of the large central arteries. However, carotid augmentation index was not different between the two groups and is therefore not a reliable indicator of large artery stiffening in this patient group. Diastolic dysfunction, present in a significant proportion of this population with Type 2 DM, was closely associated with arterial stiffening, suggesting a common aetiology.

Estimation of the viscoelastic properties of vessel walls using a computational model and Doppler ultrasound

Human arteries affected by atherosclerosis are characterized by altered wall viscoelastic properties. The possibility of noninvasively assessing arterial viscoelasticity in vivo would significantly contribute to the early diagnosis and prevention of this disease. This paper presents a noniterative technique to estimate the viscoelastic parameters of a vascular wall Zener model. The approach requires the simultaneous measurement of flow variations and wall displacements, which can be provided by suitable ultrasound Doppler instruments. Viscoelastic parameters are estimated by fitting the theoretical constitutive equations to the experimental measurements using an ARMA parameter approach. The accuracy and sensitivity of the proposed method are tested using reference data generated by numerical simulations of arterial pulsation in which the physiological conditions and the viscoelastic parameters of the model can be suitably varied. The estimated values quantitatively agree with the reference values, showing that the only parameter affected by changing the physiological conditions is viscosity, whose relative error was about 27% even when a poor signal-to-noise ratio is simulated. Finally, the feasibility of the method is illustrated through three measurements made at different flow regimes on a cylindrical vessel phantom, yielding a parameter mean estimation error of 25%.

Arterial stiffness in the young: assessment, determinants, and implications

Arterial stiffness describes the rigidity of the arterial wall. Its significance owes to its relationship with the pulsatile afterload presented to the left ventricle and its implications on ventricular-arterial coupling. In adults, the contention that arterial stiffness as a marker and risk factor for cardiovascular morbidity and mortality is gaining support. Noninvasive methods have increasingly been adopted in both the research and clinical arena to determine local, segmental, and systemic arterial stiffness in the young. With adoption of these noninvasive techniques for use in children and adolescents, the phenomenon and significance of arterial stiffening in the young is beginning to be unveiled. The list of childhood factors and conditions found to be associated with arterial stiffening has expanded rapidly over the last decade; these include traditional cardiovascular risk factors, prenatal growth restriction, vasculitides, vasculopathies associated with various syndromes, congenital heart disease, and several systemic diseases. The findings of arterial stiffening have functional implications on energetic efficiency, structure, and function of the left ventricle. Early identification of arterial dysfunction in childhood may provide a window for early intervention, although longitudinal studies are required to determine whether improvement of arterial function in normal and at-risk paediatric populations will be translated into clinical benefits.

Relationship of maximum rate of pressure rise between aorta and left ventricle in pediatric patients. Implication for ventricular-vascular interaction with the potential for noninvasive determination of left ventricular contractility

BACKGROUND

The maximum rate of the ventricular pressure rise (dp/dt(max)) provides a reliable measure of ventricular contractility. However, its estimation requires invasive measurement of left ventricular (LV) pressure, limiting its bedside clinical applicability. In the present study, 2 hypotheses were tested: (1)that the ratio of dp/dt(max) between the aorta (Ao) and LV is consistent among patients despite marked differences in underlying cardiac disease, contractile state and heart rate when vascular mechanical and loading properties are taken into account, and (2)that using such a relationship, LV dp/dt(max) can be estimated from Ao dp/dt(max), potentially providing a method of noninvasive determination of LV contractility.

METHODS AND RESULTS

Data from 30 control children and 45 pediatric patients with various cardiovascular diseases revealed that the characteristic impedance (Zc) and mean arterial pressure were significant determinants of the Ao-LV dp/dt(max) relationship in both control and disease groups. LV dp/dt(max) estimated using the regression obtained in the control children (Ao dp/dt(max/)LV dp/dt(max) = 0.64+1.45*10(-4)*Zc-3.73*10(-3)*MAP, r=0.87) correlated well with the measured LV dp/dt(max) in the disease group, including measurements taken after dobutamine and atrial pacing (r=0.89).

CONCLUSIONS

Ao dp/dt(max) and LV dp/dt(max) are closely correlated through the vascular loading properties and LV dp/dt(max) can be derived from Ao dp/dt(max), which has potential as a noninvasive method of determining LV contractility.

The long-term effects of tibolone on aortic stiffness and endothelial function

OBJECTIVE

To investigate the effect of 10 years of treatment with tibolone on aortic stiffness and endothelial function.

DESIGN

Cross-sectional study of women currently participating in an open-label, non-randomized study of the long-term efficacy of tibolone. A total of 113 recently postmenopausal women were recruited in 1988. Fifty-eight agreed to take tibolone 2.5 mg daily and 55 were followed during the study as matched controls (who chose not to take any form of hormone replacement therapy (HRT) for the duration of the study). The groups were matched for age, weight and time since last menstrual period.

SETTING

A Central London Teaching Hospital.

SUBJECTS

After 10 years, 60 women remained in the study, 32 in the tibolone group and 28 in the control group. All of these women were invited to participate in this pilot study and attend the Menopause Research Unit. Fourteen women from each group agreed to attend. The main outcome measures were aortic stiffness, measured by pulse wave velocity, and endothelial function, as assessed by flow-mediated dilatation of the brachial artery.

RESULTS

Pulse wave velocity was significantly lower in the tibolone group (10.4 +/- 1.2) than in the control group (11.6 +/- 1.2), p = 0.042. The flow-mediated dilatations were similar in both groups.

CONCLUSION

In this study, long-term use of tibolone over 10 years has a beneficial effect on aortic stiffness. The differences seen in brachial artery vasoreactivity failed to reach statistical significance. Whether this is a true indication of the effects of long-term tibolone on brachial artery vasoreactivity will only be determined by performing a larger, placebo-controlled, randomized study.

Construction of an Artificial Heart Pump Performance Test System

A hydraulic loop, which simulates pressure/flow response of the human circulatory system, is needed to bench test the various versions of rotary left ventricular assist devices (LVADs). This article describes the design of such a loop and the simulated response of different physiological states, such as a healthy person in sleep, rest, and mild physical activity, and in different pathological states. The loop consists of: (1) pulsatile left and right cardiac simulators; (2) air/water tanks to model the venous and arterial compliances; (3) tygon tubes to model the venous, arterial, and other system flow resistances; and (4) a tuning clamp to model the variation in system resistance characteristics under different cardiac pressure/flow conditions. The simulated responses were compared to the data found in the literature to validate the loop performance prior to LVAD testing.

Characteristics of arterial stiffness in very low birth weight premature infants

Premature birth is a factor of increased blood pressure in adulthood. Little is known about the physiologic characteristics of the arterial bed in neonates. The aim of this study was to characterize in vivo the arterial compliance in neonates and its maturation profile in very low birth weight (VLBW) premature infants. A group of stable, VLBW premature infants was compared with a control group of near term neonates. The abdominal aortic wall distensibility coefficient (DC) and whole-body arterial compliance (WBAC) were determined using specifically designed noninvasive methods, based on ultrasonic measurements in combination with synchronous, beat-to-beat recording of aortic pulse pressure (PP). On the fifth day of life, WBAC and the CD were lower in VLBW premature infants than in controls. Furthermore, WBAC and the DC remained unchanged in VLBW premature infants 7 wk after birth. In conclusion, VLBW premature infants are characterized as early as the fifth day of life by high arterial stiffness, which persists when they reach their theoretical term. It can be speculated that early alteration of arterial elastic properties may pave the way for long-term elevation of arterial pressure in VLBW premature infants.

The arterial system in pre-eclampsia and chronic hypertension with superimposed pre-eclampsia

OBJECTIVES

To determine if the normal gestational changes in mechanical properties of the arterial system are altered in pre-eclampsia.

DESIGN

Prospective controlled observational study.

SETTING

University urban tertiary medical centre.

POPULATION

Eleven pre-eclamptics and 10 chronic hypertensives with superimposed pre-eclampsia were compared with 14 normotensive gravidas experiencing preterm labour, all receiving MgSO(4). Two additional control groups were studied as well: (A) nine normal pregnant women receiving neither magnesium nor epidural, for baseline comparisons; and (B) eight normotensive gravidas receiving epidural anaesthesia.

METHODS

Two-dimensional targeted M-mode echocardiograms and continuous wave Doppler velocity were used to obtain instantaneous pressure and flow data. Total vascular resistance (TVR) quantified the steady component of systemic arterial load; pulsatile arterial load was characterised by global arterial compliance (AC), aortic input impedance spectrum (Z(1)) and characteristic impedance (Z(0)).

MAIN OUTCOME MEASURES

TVR, AC, Z(1), Z(0).

RESULTS

Controls, pre-eclamptics and chronic hypertensives with superimposed pre-eclampsia, respectively: TVR index 1328 [299], 1973 [609]*, 2428 [562]*(,#) dyn second cm(-5) m(2); AC area index 1.69 [0.46], 1.19 [0.46]*, 0.93 [0.38]* mL mmHg(-1) m(-2); Z(0) index 253.2 [61.3], 327.0 [135.1], 307.5 [130.9] dyn second cm(-5) m(2); and Z(1) index 184.2 [56.5], 283.6 [81.6]*, 357.1 [119.5]* dyn second cm(-5) m(2) (*P < 0.05 vs control;(#)P < 0.05 vs pre-eclampsia). Normal gravidas (in secondary controls group A) had decreased mean systolic and diastolic blood pressures, and increased AC and cardiac indices, compared with women receiving magnesium tocolysis, verifying the need for these primary controls. No differences were noted between normotensive gravidas receiving epidural anaesthesia (secondary controls group B) and the non-anesthetised controls (group A), eliminating epidural as a confounder.

CONCLUSIONS

The normal gestational changes in systemic arterial mechanical properties are significantly altered in pre-eclampsia and these alterations are more marked with superimposed hypertensive disease.

Design and Initial Testing of a Mock Human Circulatory Loop for Left Ventricular Assist Device Performance Testing

A mock circulatory loop, which simulates the human circulatory system, is needed to bench test the various versions of continuous flow (CF) left ventricular assist devices (LVADs). This article describes the design and initial testing of such a loop. The loop consists of: (1) pulsatile left and right cardiac simulators; (2) air/water tanks to model the venous and arterial compliances; (3) tygon tubes to model the venous, arterial, and other system flow resistances; and (4) a tuning clamp to model the variation in system resistance characteristics under different cardiac pressure/flow conditions. Several loop measurements were carried out without an LVAD to verify the cardiovascular modeling of a healthy person in sleep, rest, and physical activity, and in different pathological states, and compared to the data found in the literature to validate the loop performance prior to LVAD testing.

Harvest of the radial artery for coronary artery surgery preserves maximal blood flow of the forearm

BACKGROUND

Use of the radial artery as a conduit for coronary artery surgery has increased dramatically. It has been assumed that blood flow to the forearm will not be compromised by its removal.

METHODS

Sixteen patients who had the left radial artery harvested for coronary surgery at least 3 months earlier were studied. The right radial artery was not harvested. The radial, ulnar, and brachial artery diameters and flows were measured using pulsed wave Doppler with a 15-MHz linear array transducer. Measurements were performed at rest, with the right radial artery compressed, and after ischemia with forearm exercise.

RESULTS

At rest, the (mean +/- SE) diameter of the left ulnar artery was consistently greater than the right (2.4 +/- 0.09 versus 2.1 +/- 0.09 mm, p = 0.001) as was flow (74 +/- 9.9 versus 48 +/- 8.5 mL/min, p = 0.005). There was no difference between diameters or flows in the brachial arteries. After compression of the radial artery, flow increased in the right ulnar artery from 39 +/- 8.0 to 72 +/- 17.6 mL/min (p = 0.019) without an increase in ulnar artery size and was not different from the left ulnar artery flow at rest (p = 0.440). After ischemic forearm exercise, flow increased in the two brachial arteries almost equally (left, 348 +/- 50; right, 371 +/- 63 mL/min).

CONCLUSIONS

Blood flow to the forearm and hand is not compromised by harvest of the radial artery.

Automatic determination of aortic compliance with cine-magnetic resonance imaging: an application of fuzzy logic theory

RATIONALE AND OBJECTIVES

Aortic compliance is defined as the relative change in aortic cross-sectional area divided by the change in arterial pressure. Magnetic resonance imaging (MRI) is a useful imaging modality for the noninvasive evaluation of aortic compliance. However, manual tracing of the aortic contour is subject to important interobserver variations. To estimate the aortic compliance from cine-MRI, a method based on fuzzy logic theory was elaborated.

MATERIALS AND METHODS

Seven healthy volunteers and eight patients with Marfan syndrome were examined using an ECG gated cine-MRI sequence. The aorta was imaged in the transverse plane at the level of the pulmonary trunk. A method based on fuzzy logic was developed to automatically detect the aortic contour.

RESULTS

Through our robust automatic contouring method, the calculation of aortic cross-sectional areas allows an estimation of the aortic compliance.

CONCLUSION

The aortic compliance can be obtained from a fuzzy logic based automatic contouring method, thereby avoiding the important interobserver variation often associated with manual tracing.

The n-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid increase systemic arterial compliance in humans

BACKGROUND

n-3 Fatty acids influence vascular function, but the effect of individual fatty acids on systemic arterial compliance (SAC) has not been reported. SAC, which reflects arterial elasticity, is emerging as a new cardiovascular risk factor and appears to predict future cardiovascular events.

OBJECTIVE

We tested whether the n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) improve SAC in dyslipidemic subjects.

DESIGN

Thirty-eight dyslipidemic subjects were randomly assigned to receive 3 g EPA/d (n = 12), 3 g DHA/d (n = 12), or a placebo (n = 14) in a 7-wk parallel, double-blind trial. Arterial functions were measured at the beginning and end of the interventions. Plasma lipids and plasma fatty acids were also measured.

RESULTS

Consumption of the n-3 fatty acids significantly increased SAC, whereas consumption of the placebo did not (P = 0.043; repeated-measures analysis of variance across the 3 groups); the increase was 36% with EPA and 27% with DHA. The major components contributing to the increase in SAC (systolic and pulse pressures and total vascular resistance) tended to decrease but not significantly. Plasma total and VLDL triacylglycerol were significantly lower in the n-3 fatty acid groups (P = 0.026 and 0.006, respectively; repeated-measures analysis of variance) than in the placebo group.

CONCLUSION

EPA and DHA increase SAC and tend to reduce pulse pressure and total vascular resistance, effects that may reduce the risk of adverse cardiovascular events.

Methods and devices for measuring arterial compliance in humans

This review analyses methods and devices used worldwide to evaluate the arterial stiffness. Three main methodologies are based upon analysis of pulse transit time, of wave contour of the arterial pulse, and of direct measurement of arterial geometry and pressure, corresponding to regional, systemic and local determination of stiffness. They are used in clinical laboratory and/or in clinical departments. Particular attention is given to the reproducibility data in literature for each device. This article summarizes the discussion of the dedicated Task Force during the first Conference of Consensus on Arterial Stiffness held in June 2000 (Paris, France).

Evaluation of arterial stiffness in children with Williams syndrome: Does it play a role in evolving hypertension?

BACKGROUND

Pathologic studies and surgical observations of thickened aortic walls have suggested an increase in aortic stiffness in patients with Williams syndrome. However, in vivo objective evaluation of aortic and arterial stiffness in Williams syndrome are lacking. Moreover, systemic hypertension, although prevalent in Williams syndrome, does not have a well-defined mechanism in this syndrome. Therefore, the purpose of this study was to quantitate aortic stiffness and arterial compliance in an objective manner, as well as to determine their roles in development of hypertension, in children with Williams syndrome.

METHODS

We studied 13 patients with Williams syndrome (aged 3-12 years) and 16 age-matched control subjects. Aortic stiffness was calculated from the beta index as follows: beta = (ln[P(s)/P(d)])/ ([D(s) - D(d)]/D(d)), where P(s) and P(d) are systolic and diastolic blood pressures and D(s) and D(d) are systolic and diastolic aortic dimensions, respectively. Arterial compliance (C) was calculated by the area method: C= (A(d) x CO x CL) / (A(t) x [P(es) - P(d)]), where A(t) is the total area and A(d) is the area under the diastolic portion of the arterial pulse tracing, CO is the cardiac output, CL is the cycle length, and P(es) is aortic end-systolic pressure.

RESULTS

In patients with Williams syndrome, the beta index was 2-fold higher than in control patients (9.02 +/- 3.15 vs 4.43 +/- 0.96, P <.005). Moreover, there was a strong positive correlation between the beta index and the systolic blood pressure (r = 0.8 and P <.0001). Compliance was decreased by 42% (0.41 +/- 0.11 vs 0.71 +/- 0.10 mL/mm Hg, P <.05), suggesting decreased arterial compliance.

CONCLUSIONS

Our study indicates that in vivo arterial stiffness is increased in patients with Williams syndrome. We speculate that increased arterial stiffness may be the predisposing cause of systemic hypertension in Williams syndrome.

Sublingual nitroglycerin delays arterial wave reflections despite increased aortic "stiffness" in patients with hypertension: a Doppler echocardiography study

Venodilatation with consequent reduction in left ventricular filling and end-diastolic wall stress is an important mechanism for the beneficial effects of nitroglycerin in ischemic heart disease and in left ventricular failure. The effects of sublingual nitroglycerin on arterial pulsatile hemodynamics are less well defined. Doppler echocardiography and the calibrated subclavian artery pulse tracing were used to assess hemodynamics in subjects with sustained arterial hypertension (n = 25) before and 5 to 10 minutes after sublingual deposition of 0.5 mg glyceryl trinitrate. Aortic characteristic impedance was calculated by averaging the modulus of the input impedance (ratio of pressure to flow) at high frequencies and by calculating the ratio of pressure and flow increments during upstroke. The pressure wave was split into forward and backward components, and the reflection coefficient (the ratio of backward to forward pressures) was calculated. Parameters of the arterial bed were estimated by using 2- and 3-element Windkessel models. Nitroglycerin delayed the return of arterial wave reflections by 17% (P =.02) and increased aortic characteristic impedance by 20% (P =. 01), but it did not influence total arterial compliance. Mean arterial pressure decreased 7% (P =.0001), but pulse pressure did not change. Stroke volume and the acceleration time of aortic root flow decreased by 13% (P =.0001) and 8% (P =.01), respectively. Cardiac output decreased 7% (P =.01), despite an increase in heart rate of 10% (P =.0001). Peripheral resistance tended to decrease (4%, P =.06). Thus, in subjects with sustained hypertension, sublingual nitroglycerin dilates peripheral, predominantly muscular arteries with a subsequent delayed return of reflected pressure waves. Reflex activation of the sympathetic nervous system with consequent increased acceleration of left ventricular ejection seems to counteract the effect of reduced mean arterial pressure (distending pressure) with respect to the "stiffness" of the aorta.

Individualizing the aorto-radial pressure transfer function: feasibility of a model-based approach

We fitted a three-segment transmission line model for the radial-carotid/aorta pressure transfer function (TFF) in 31 controls and 30 patients with coronary artery disease using noninvasively measured (tonometry) radial and carotid artery pressures (P(car)). Except for the distal reflection coefficient (0.85 +/- 0.21 in patients vs. 0.71 +/- 0.25 in controls; P < 0.05), model parameters were not different between patients or controls. Parameters were not related to blood pressure, age, or heart rate. We further assessed a point-to-point averaged TFF (TFF(avg)) as well as upper (TFF(max)) and lower (TFF(min)) enveloping TFF. Pulse pressure (PP) and augmentation index (AIx) were derived on original and reconstructed P(car) (P(car,r)). TFF(avg) yielded closest morphological agreement between P(car) and P(car,r) (root mean square = 4.3 +/- 2.3 mmHg), and TTF(avg) best predicted PP (41.5 +/- 11.8 vs. 41.1 +/- 10.0 mmHg measured) and AIx (-0.02 +/- 0.19 vs. 0.01 +/- 0.19). PP and AIx, calculated from P(car) or P(car,r), were higher in patients than in controls, irrespectively of the TFF used. We conclude that 1) averaged TFF yield significant discrepancies between reconstructed and measured pressure waveforms and subsequent derived AIx; and 2) different TFFs seem to preserve the information in the pressure wave that discriminates between controls and patients.

Vascular compliance as a measure of biological age

OBJECTIVES

To determine the measure of vascular compliance most closely related to age.

DESIGN

A review of 22 studies relating aortic compliance to age and a discussion of other factors related to vascular compliance.

MEASUREMENTS

Aortic compliance, elastic modulus, postmortem aortic changes, pulse wave velocity in the aorta, common carotid, lower limb and upper limb.

RESULTS

1. Aortic compliance and carotid artery compliance is closely related to age; 2. Compliance in the peripheral arteries, in 16 reports, appears less closely related to age; 3. There is evidence that aortic compliance is related to hypertension, cardiac function, and left ventricular hypertrophy and can be increased by exercise, hormonal therapy, antioxidant and antihypertensive treatment; and 4. Vascular compliance is more closely related to chronological age than other measures such as skin inelasticity, greying of hair, baldness etc.

CONCLUSIONS

Because of the close relationship between aortic and carotid compliance and chronological age, deviation from the age-predicted norm (biological age) may prove to be a good predictor of cardiovascular pathology.

Higher systemic arterial compliance is associated with greater exercise time and lower blood pressure in a young older population

OBJECTIVES

Arterial compliance is an important therapeutic target in older individuals in whom stiffening of the proximal arterial circulation is thought to underlie systolic hypertension and increased cardiac work. We have shown previously that arterial compliance is related to aerobic fitness and that it is increased in young (20 to 35 years old), previously sedentary individuals by a 4-week period of moderate aerobic training. The extent to which compliance relates to exercise performance in a random selection of young older patients has not been reported previously. Therefore, we examined the interrelationship between systemic arterial compliance (SAC) and time to cessation of exercise during a standard treadmill exercise test in an older population.

DESIGN

A cross-sectional survey.

METHODS

SAC was estimated at rest using simultaneous recordings of ascending aortic flow and carotid applanation tonometry in 43 subjects aged 67 +/- 7 years (mean +/- SD; 24 men and 19 women). Treadmill exercise testing was performed using a modified Bruce protocol. Aerobic capacity was assessed as Heart Rate-Blood Pressure product and exercise tolerance as total treadmill time.

RESULTS

SAC and exercise tolerance were related to gender, with men exhibiting greater exercise reserve and higher SAC than women. There was a significant positive correlation between SAC and time to cessation of exercise (r = .34; P = .03), with a negative correlation between SAC and resting heart rate-blood pressure product (r = -.66; P < .001). SAC was correlated with height and blood pressure. Exercise tolerance was related to height (P < .02).

CONCLUSIONS

These data indicate a positive association between SAC and fitness level in healthy older people and an inverse association between SAC and systolic blood pressure. Our findings are consistent with either (1) acquisition of a more compliant circulation and lower blood pressure through more physical activity or (2) that a more compliant arterial circulation and lower blood pressure permit greater athletic performance.

Estimation of arterial mechanics in clinical practice and as a research technique

1. Large conduit artery pathophysiology is associated with considerable morbidity with even normal ageing, irrespective of concurrent influences, associated with impaired arterial function. 2. Recent technical advances have enabled high-resolution non-invasive assessment of pulsatile arterial properties, but this has been largely confined to more muscular superficial arteries. There has been less study of arterial regions prone to disease that would, theoretically at least, benefit from pharmacological or other intervention to improve function. 3. Based on studies in animal models and, in particular, human arterial segments, specific pharmacological agents have been proposed as improving arterial behaviour. If this is to become a therapeutic target, it behoves increased effort to understand and measure meaningful indices of arterial function and to find ways of assessing response and outcome. 4. A number of different approaches to assessment and quantification of arterial mechanics are available in the literature. The present review compares and discusses some of these different techniques and looks at differences between arterial segments and evidence that appropriate intervention may beneficially modify arterial behaviour. 5. For clinical or research usefulness, assessment of arterial mechanics must provide more information than currently derived from simple numerical measurement of brachial blood pressure. This is particularly true because epidemiological risk evidence is based on brachial rather than central blood pressure recordings. There has been an explosion of work in this field in recent years and the present review does not pretend to reference all relevant material; rather, it tries to provide a broad coverage of the topic and hopes to support the need for continued endeavours in the field of arterial mechanics.

Total arterial compliance in ambulatory hypertension during selective beta1-adrenergic receptor blockade and angiotensin-converting enzyme inhibition

Aortic root flow and pressure estimates were obtained noninvasively with Doppler echocardiography and calibrated subclavian artery pulse tracing in 30 subjects with ambulatory hypertension in a randomized, crossover study with 4 weeks' treatment and washout periods. Total arterial compliance, assessed by use of a three-element Windkessel model of the arterial tree, increased 42% with atenolol (50-100 mg once daily), and 7% (p = NS) with captopril (25-50 mg twice daily). Atenolol reduced mean arterial pressure by 15%, heart rate by 22%, and cardiac output by 14%, and increased acceleration time of aortic root flow by 17% and stroke volume and ejection time each by 11%. Captopril reduced mean arterial pressure and total peripheral resistance each by 7%. Acceleration time of aortic root flow, ejection time, heart rate, stroke volume, and cardiac output were not significantly changed by captopril. We conclude that total arterial compliance, at the operational blood pressure, increases during selective beta1-adrenergic receptor blockade in subjects with ambulatory hypertension. Although the main mechanism may be a reduction in mean arterial pressure, it should be considered whether reduced heart rate may play an additional role. The nonsignificant increase in total arterial compliance during angiotensin-converting enzyme inhibition may primarily be a consequence of a modest reduction of the mean arterial pressure.

The compliance of the porcine pulmonary artery depends on pressure and heart rate

1. The influence of mean pulmonary arterial pressure (mean Ppa) on dynamic (Cd) and pseudo-static compliance (Cps) of the pulmonary artery was studied at a constant and a changing heart rate. Cd is the change in cross-sectional area (CSA) relative to the change in Ppa throughout a heart cycle. Cps is the change in mean CSA relative to the change in mean Ppa. If Cd is known, pulmonary blood flow can be computed from the Ppa using a windkessel model. We investigated whether Cps can be interchanged with Cd. 2. In nine anaesthetized pigs, we determined the mean CSA and Cd of the pulmonary artery at various Ppa levels, ranging from approximately 30 to 10 mmHg, established by bleeding. Two series of measurements were carried out, one series at a spontaneously changing heart rate (n = 9) and one series at a constant heart rate (n = 6). To determine CSA a conductance method was used. 3. Cps depended on pressure. The mean CSA versus mean Ppa curves were sigmoid and steepest in the series with the increasing heart rate (established by bleeding). The CSA versus Ppa loop during a heart cycle, giving Cd, was approximately linear and almost closed. The Cd versus mean Ppa relationship was bell shaped. Its width was smaller if the heart rate increased during the series of measurements. The pressure, where Cd was maximum, was higher at higher heart rates. Furthermore, the maximum Cd was not affected by the heart rate. 4. Because the pulmonary artery constricts with increasing heart rate, Cps will be overestimated during procedures where heart rate increases. Cd should be determined on a beat-to-beat basis to calculate flow because it changes with mean pulmonary arterial pressure and heart rate.

Use of radial artery applanation tonometry and a generalized transfer function to determine aortic pressure augmentation in subjects with treated hypertension

OBJECTIVES

The purposes of this study were to investigate the use of radial artery applanation tonometry and a generalized transfer function for the assessment of central aortic pressure augmentation in subjects taking commonly used antihypertensive agents (angiotensin-converting enzyme inhibitors, beta-adrenergic blockers, Ca2+ antagonists, diuretic therapy).

BACKGROUND

Applanation tonometry of the radial artery with a generalized transfer function has been proposed as a means of assessing central aortic blood pressure. Recently, a commercial apparatus based on this technique has become available; we therefore examined the effect of a generalized transfer function on derived central aortic pressure compared with measured brachial blood pressures and also investigated the potential of this technique to assess the influence of differing drug therapy.

METHODS

Two hundred and sixty-two hypertensive patients on stable medication were studied using the PWV Medical Blood Pressure Analysis System (version 2, DAT-1).

RESULTS

In univariate analysis, augmentation index showed association with age, sex, height and heart rate. In multivariate analysis, diastolic blood pressure and age (positively), height and heart rate (negatively) and sex were significantly associated. After adjustment for these variables, pressure augmentation was not associated with any antihypertensive treatment investigated. Linear relationships were demonstrated between brachial blood pressures and corresponding central pressures derived by transfer function methods.

CONCLUSIONS

Our findings suggest that if adjustment for central-peripheral pressure difference is necessary, simple linear relationships may be sufficient. Age, heart rate and height but not the class of antihypertensive medication affected the degree of pressure augmentation observed using this technique.

Complex and frequency-dependent compliance of viscoelastic windkessel resolves contradictions in elastic windkessels

Based on simulated data, recent studies by others showed that fitting measured pulse pressure with the pulse pressure predicted by the two-element windkessel (W2-based pulse pressure method, PPM) yielded estimates of total arterial compliance closer to simulated values than other estimation methods that use either the W2 model or the three-element windkessel (W3). A later experimental application of the PPM, made by us, however, yielded relatively non pressure dependent estimates of compliance that were in contradiction with pressure dependent estimates obtained from the W2 model by fitting to the full aortic pressure wave (full pressure method, FPM). To explain these contradictory findings, in the present study we interpreted the aortic input impedance in terms of a viscoelastic windkessel (VW), where total peripheral resistance is connected in parallel to a complex and frequency dependent compliance, Cc(j omega), described by the Voigt cell. Using ascending aortic pressure and flow taken from four dogs, under a variety of haemodynamic states, we compared the estimates of compliance obtained from the W3 and VW models and from different W2-based estimation methods: the FPM (Cw2), the PPM (Cpp), the decay time method, DTM (Cdt), and the area method, AM (C(am)). The VW-based estimates of complex compliance resolved contradictions in the W2-based estimates. Static compliance of VW-model, Cvw = Cc(0), showed a good correlation (p = 0.999) with Cw2. Correlation of static compliance with C(am) and Cdt estimates was affected by distortions in diastolic pressure decay. The modulus of VW model's dynamic compliance, ¿Cc(omega(h))¿, at the heart pulsation omega(h), was well correlated (p = 0.975) with Cpp. Analysis of data fit and compliance estimates indicated that the VW model yields an improvement over the W3 in the physical interpretation of the overall arterial properties.

Influence of body size and left ventricular ejection dynamics on total arterial compliance determined using Doppler echocardiography and subclavian artery pulse tracings in healthy humans

The aim was to investigate determinants of total arterial compliance in healthy humans. Estimates of aortic root pressures and flow were obtained non-invasively with the calibrated subclavian artery pulse tracing and Doppler echocardiography in 37 males (27-76 years) and 45 females (20-77 years). Total arterial compliance, estimated using a three-element vascular model, correlated positively with body height (r = 0.45, p < 0.01) and acceleration time of aortic root flow (r = 0.32, p < 0.01) and inversely with age (r = -0.34, p < 0.05), heart rate (r = -0.33, p < 0.01), and mean arterial pressure (r = -0.51, p < 0.01). Multivariate analysis indicated that height and heart rate contributed most to the prediction of total arterial compliance. The inclusion of mean arterial pressure within the model significantly reduced the contribution of age, but not that of body height and heart rate. After adjustment for height and heart rate, total arterial compliance did not differ significantly between gender. Thus, total arterial compliance, as assessed in this study, seems to reflect both arterial capacity and viscoelastic properties of the arterial wall. Differences in body size, heart rate and mean arterial pressure should be considered when comparing total arterial compliance in different groups.

Regression of radial artery wall hypertrophy and improvement of carotid artery compliance after long-term antihypertensive treatment in elderly patients

OBJECTIVES

The present study was designed to assess whether a diuretic- or an angiotensin-converting enzyme inhibitor-based treatment can reduce arterial wall hypertrophy of a distal muscular medium-sized artery--the radial artery--and the stiffness of a proximal large elastic artery--the common carotid artery.

BACKGROUND

Large-artery wall thickness and stiffness are increased during sustained essential hypertension and contribute to the increased risk of complications. Whether antihypertensive treatment can normalize the wall hypertrophy of conducting arteries has not yet been determined.

METHODS

Seventy-seven elderly hypertensive patients were randomized to receive 9 months of double-blind treatment with perindopril (2 to 8 mg/day) or the diuretic combination of hydrochlorothiazide (12.5 to 50 mg/day) plus amiloride (1.25 to 5 mg/day) after a 1-month placebo washout period. If systolic blood pressure remained at >160 mm Hg after 5 months, chlorthalidone or atenolol was added, respectively. Arterial variables, including radial artery mass and common carotid artery compliance, were calculated from noninvasive measurements of internal diameter and wall thickness with the use of high resolution echo-tracking systems at baseline and after 5 and 9 months.

RESULTS

During treatment, blood pressure and arterial variables changed to the same extent in both groups. After a 9-month treatment, systolic, diastolic and pulse pressures and radial artery wall thickness, mass and thickness/radius ratio decreased significantly (p < 0.01), whereas carotid compliance increased (p < 0.001). The decrease in radial artery thickness/radius ratio after a 9-month treatment was significantly related to the reduction in pulse pressure (p < 0.01), whereas the improvement in carotid compliance was related to the reduction in mean arterial pressure (p < 0.01). In healthy subjects and untreated hypertensive patients, radial artery diameter, wall thickness and thickness/radius ratio and carotid artery compliance did not change significantly during a 9-month observation period.

CONCLUSIONS

These results indicate that in elderly hypertensive patients, both angiotensin-converting enzyme inhibitor- and diuretic combination-based treatments can reduce radial artery wall hypertrophy and improve carotid artery compliance.

Total arterial compliance estimated by stroke volume-to-aortic pulse pressure ratio in humans

On the basis of the windkessel model, the stroke volume-to-aortic pulse pressure ratio (SV/PP) has been proposed as an estimate of total arterial compliance, but recent studies have questioned this approximation. Aortic pressure was obtained at rest in 31 adults undergoing cardiac catheterization (47 +/- 14 yr): controls (n = 7), patients with dilated cardiomyopathy (n = 10), and patients with other cardiac diseases (n = 14). We calculated PP, mean aortic pressure (MAoP), heart period (T), SV (thermodilution cardiac output/heart rate), total peripheral resistance (R), total arterial compliance estimated by area method (Carea), and the time constant of aortic pressure decay in diastole (RCarea). In the overall population (n = 31), there was no significant difference between SV/PP and Carea. SV/PP was linearly related to Carea (SV/PP = 0.99Carea + 0.05; r = 0.98; P < 0.001); the slope and intercept did not differ from unity and zero, respectively. Similar results were obtained in the three subgroups. These results implied that PP/MAoP and T/RCarea were proportionally related (T/RCarea = 1.18PP/MAoP - 0.07; r = 0.96; P < 0.001). We conclude that for humans at rest 1) SV/PP gave a reliable estimate of Carea, and 2) T normalized by the time constant of aortic pressure decay in diastole was proportionally related to PP/MAoP. This last relationship could be considered an aspect of the coupling between the left ventricle and its load.

Doppler echocardiographic reference values for healthy rhesus monkeys under ketamine hydrochloride sedation

Cardiac ultrasound is a noninvasive technique that is commonly used to serially evaluate cardiac structure and function. Recent advances in Doppler-Echocardiography enable the ultrasonographer to perform a sophisticated noninvasive assessment of cardiovascular physiology. The Rhesus monkey is a frequently used non-human primate animal model of human cardiovascular disease because this species closely models human anatomy and physiology. However, while this species is frequently used in cardiovascular research, standardized echocardiographic values generated from large numbers of normal Rhesus are not available. In the present study, we performed cardiac ultrasound imaging on 28 healthy Rhesus monkeys to obtain normal reference values of cardiovascular structure and function in this species. Nomograms were generated from these data by plotting parameters of cardiovascular geometry and function with body weight. These normal reference data were compared to previously reported values obtained from prior studies that used noninvasive, invasive, and morphometric techniques.

Non-invasive assessment of the changes in static and oscillatory components of peripheral pressure/flow relationships produced by moderate exercise in humans

OBJECTIVE

The generalized sympathetic activation induced by exercise is accompanied by an increase in heart rate, blood pressure and vascular resistance in non-exercising vascular beds. The aim of the present study was to test the feasibility of assessing, non-invasively, the static and oscillatory pressure/flow relationships of peripheral arteries and their continuous changes during dynamic exercise.

DESIGN

We studied 44 healthy humans at rest, during moderate exercise (recumbent bicycle exercise) and recovery using a totally non-invasive approach.

METHODS

Arterial pressure was measured using a plethysmographic device, and ipsilateral brachial artery flow and palmar skin microcirculation flow were assessed with continuous wave Doppler and laser Doppler, respectively. Continuous, long data segments (> 90 s) were acquired with a personal computer and used to determine the changes of pressure/flow relationships of peripheral arteries during dynamic exercise. A new simplified method utilizing a transfer function analysis extracted automatically unequivocal indexes of static and oscillatory properties of vascular system.

RESULTS

Moderate exercise induced significant increases of the static (Zo) and oscillatory (Zc) components of peripheral pressure/flow relationships in both brachial artery and skin microcirculation beds. Both indexes returned to control values during early recovery.

CONCLUSIONS

This simple, non-invasive approach was capable of assessing the changes of static and oscillatory vascular properties induced by dynamic exercise. This method could be applied for a better understanding of the vascular modifications that occur in other physiological or pathophysiological conditions also characterized by increases in sympathetic drive.

The use of multisite high resolution arterial imaging to assess arteriosclerosis

This article presents a model for the use of multisite, sonographic imaging to assess arteriosclerosis. The arteries of 100 randomly selected patients were scanned in three anatomical areas (carotid, femoral-popliteal, aorta-iliac) in conjunction with measurement of selected risk factors (smoking, cholesterol, triglycerides, high density lipoproteins, antioxidant levels). Arteries were interrogated for intimal wall hyperplasia, plaque, and ulceration. Multisite scanning (24 sites) detected the presence of pathology in all sites surveyed. The model was developed at the Cardiovascular Wellness Center in Westbury, NY.

Arterial compliance increases after moderate-intensity cycling

Exercise training elevates arterial compliance at rest, but the effects of acute exercise in this regard are unknown. This study investigated the effects of a single, 30-min bout of cycling exercise at 65% of maximal oxygen consumption on indexes of arterial compliance. Whole body arterial compliance determined noninvasively from simultaneous measurements of aortic flow and carotid pressure was elevated (66 +/- 26%) at 0.5 h postexercise (P = 0.04), followed by a decline to baseline 1 h after exercise. Aortic pulse-wave velocity, which is inversely related to compliance, was reduced (4 +/- 2%; P = 0.04) at 0.5 h postexercise. Pulse-wave velocity in the leg decreased by 10 +/- 4% at this time (P = 0.01). Mean arterial pressure was unchanged; however, central systolic blood pressure was reduced postexercise (P = 0.03). Cardiac output was elevated after exercise (P = 0.007) via heart rate elevation (P = 0.001), whereas stroke volume was unchanged. Total peripheral resistance was therefore reduced (P = 0.01) and would be expected to contribute to an elevation in arterial compliance. In conclusion, a single bout of cycling exercise increased whole body arterial compliance by mechanisms that may relate to vasodilation.

Left ventricular systolic and diastolic function assessed with two-dimensional and doppler echocardiography in "white coat" hypertension

OBJECTIVES

The aim of this study was to investigate left ventricular function in subjects with "white coat" hypertension, defined as office arterial diastolic pressure > or = 90 and ambulatory daytime pressures < 140/90 mm Hg.

BACKGROUND

The white coat arterial pressure response may, by influencing left ventricular function, have a confounding effect in studies of heart disease.

METHODS

Two-dimensional and Doppler echocardiography combined with the calibrated subclavian arterial pulse tracing, were used to assess variables of left ventricular function in 26 subjects with white coat hypertension (office arterial diastolic pressure > or = 90 and < 115 mm Hg and ambulatory daytime diastolic pressure > or = 90 mm Hg) and 32 normotensive subjects.

RESULTS

In subjects with white coat hypertension, systolic arterial pressure during the echocardiographic examination was significantly higher than ambulatory daytime systolic pressure. This pressure response was positively related to the ratio of the systolic to diastolic pulmonary venous flow peak velocities and to the peak velocity of flow reversion during atrial systole; it was inversely related to the ratio of early to late mitral flow peak velocities. Left ventricular stroke volume, ejection fraction and velocity of circumferential fiber shortening did not differ in the study groups, but left ventricular external work and end-systolic wall stress were increased in the white coat group.

CONCLUSIONS

The arterial pressure response in subjects with white coat hypertension is associated with increased left ventricular external work, increased end-systolic wall stress and alterations of left ventricular filling but normal ejection fraction and velocity of circumferential fiber shortening.

Determinants of arterial stiffness in Chinese migrants to Australia

The determinants of arterial properties in Chinese migrants to Australia were evaluated. Fifty-eight migrants had recently arrived while 25 were long term residents. All were apparently free of cardiovascular disease. In addition to ultrasound determination of the stiffness of the thoracic aorta, measurements were also made of pulse wave velocities in the trunk and limbs. Factors investigated as potential determinants of arterial properties included age, sex, blood pressure, plasma lipids, urinary electrolyte excretion and duration of residence in Australia. Aortic PWV (PWVAF), PWV from the femoral to dorsalis pedis artery (PWVFD) and the aortic elastic modulus Ep were all dependent on age and mean arterial pressure. Ep was additionally dependent on sodium excretion (negatively), PWVAF on LDL cholesterol (negatively) and migrant status and PWVFD on sex and potassium excretion (negatively). PWV in the arm (PWVBR) was only dependent on sex. Regional aortic stiffness Ep and PWVAF were significantly higher in the established compared with the recent migrants. Dietary differences were evident between the two migration groups, with recent migrants eating significantly more rice meals, but there were no differences in plasma total or HDL cholesterol or triglyceride concentrations. Determinants of the stiffness of the arterial circulation in disease free Chinese subjects change considerably from proximal to distal sites, with age, blood pressure and cholesterol effects being most pronounced proximally and sex and urinary potassium excretion distally. Increasing duration of Australian residence appears to be accompanied by an increase in proximal arterial stiffness.