Left ventricular ejection time: a potential determinant of pulse wave velocity in young, healthy males

Blood Haemoglobin Concentration Is Directly and Independently Related with Pulse Wave Velocity, a Measure of Large Artery Stiffness

High haemoglobin level has been associated with metabolic syndrome, elevated blood pressure (BP), and increased mortality risk. In this cross-sectional study, we investigated the association of blood haemoglobin with haemodynamics in 743 subjects, using whole-body impedance cardiography and pulse wave analysis. The participants were allocated to sex-stratified haemoglobin tertiles with mean values 135, 144, and 154 g/L, respectively. The mean age was similar in all tertiles, while body mass index was higher in the highest versus the lowest haemoglobin tertile. The highest haemoglobin tertile had the highest erythrocyte and leukocyte counts, plasma C-reactive protein, uric acid, renin activity, and aldosterone. The lipid profile was less favourable and insulin sensitivity lower in the highest versus the lowest haemoglobin tertile. Aortic BP, cardiac output, and systemic vascular resistance were similar in all tertiles, while the pulse wave velocity (PWV) was higher in the highest versus the lowest haemoglobin tertile. In linear regression analysis, age (Beta 0.478), mean aortic BP (Beta 0.178), uric acid (Beta 0.150), heart rate (Beta 0.148), and aldosterone-to-renin ratio (Beta 0.123) had the strongest associations with PWV (p < 0.001 for all). Additionally, haemoglobin concentration was an explanatory factory for PWV (Beta 0.070, p = 0.028). To conclude, blood haemoglobin concentration had a small direct and independent association with a measure of large artery stiffness.

Influence of training status on cardiac and vascular functioning in young recreational and competitive male rowers

Introduction

The aim of the study was to investigate the influence of training status on cardiovascular function in young male recreational and competitive rowers.

Methods

Ejection duration in percentage to the heart rate period (ED%), subendocardial viability ratio (SEVR), augmentation index at 75 bpm (AIx75) and carotid to femoral pulse wave velocity (cf-PWV) of competitive rowers (CR) (age 17.6 ± 4.1 years), recreational rowers (RR) (age 16.7 ± 2.70 years) and athletes practicing other recreational sports (ORS) (age 15.3 ± 1.4 years) were assessed.

Results

ED% was lower in CR compared to ORS (31.9 ± 3.9% vs. 38.4 ± 4.8%; p = 0.026) and cf-PWV was higher in CR compared to ORS (5.5 ± 1.0 m/s vs. 4.7 ± 0.5 m/s; p = 0.032). SEVR was higher in CR compared to RR and ORS (165.8 ± 33.7% vs. 127.4 ± 30.4% and 128.3 ± 27.8%; p = 0.022) and AIx75 was lower in CR compared to RR and ORS (-15.7 ± 8.6% vs. 1.2 ± 9.9% and 1.5 ± 9.1; p = 0.001).

Discussion

Healthy, young competitive male rowers reported higher myocardial performance and better cardiovascular health than recreational athletes. Interpretations of cf-PWV in competitive rowers should be performed alongside other cardiovascular indicators.

Difference between ejection times measured at two different peripheral locations as a novel marker of vascular stiffness

Pulse wave velocity (PWV) has been recommended as an arterial damage assessment tool and a surrogate of arterial stiffness. However, the current technology does not allow to measure PWV both continuously and in real-time. We reported previously that peripherally measured ejection time (ET) overestimates ET measured centrally. This difference in ET is associated with the inherent vascular properties of the vessel. In the current study we examined ETs derived from plethysmography simultaneously at different peripheral locations and examined the influence of the underlying arterial properties on ET prolongation by changing the subject’s position. We calculated the ET difference between two peripheral locations (ΔET) and its corresponding PWV for the same heartbeat. The ΔET increased with a corresponding decrease in PWV. The difference between ΔET in the supine and standing (which we call ET index) was higher in young subjects with low mean arterial pressure and low PWV. These results suggest that the difference in ET between two peripheral locations in the supine vs standing positions represents the underlying vascular properties. We propose ΔET in the supine position as a potential novel real-time continuous and non-invasive parameter of vascular properties, and the ET index as a potential non-invasive parameter of vascular reactivity.

Arterial viscoelasticity: role in the dependency of pulse wave velocity on heart rate in conduit arteries

Experimental investigations have established that the stiffness of large arteries has a dependency on acute heart rate (HR) changes. However, the possible underlying mechanisms inherent in this HR dependency have not been well established. This study aimed to explore a plausible viscoelastic mechanism by which HR exerts an influence on arterial stiffness. A multisegment transmission line model of the human arterial tree incorporating fractional viscoelastic components in each segment was used to investigate the effect of varying fractional order parameter (α) of viscoelasticity on the dependence of aortic arch to femoral artery pulse wave velocity (afPWV) on HR. HR was varied from 60 to 100 beats/min at a fixed mean flow of 100 ml/s. PWV was calculated by intersecting tangent method (afPWVTan) and by phase velocity from the transfer function (afPWVTF) in the time and frequency domain, respectively. PWV was significantly and positively associated with HR for α ≥ 0.6; for α = 0.6, 0.8, and 1, HR-dependent changes in afPWVTan were 0.01 ± 0.02, 0.07 ± 0.04, and 0.22 ± 0.09 m/s per 5 beats/min; HR-dependent changes in afPWVTF were 0.02 ± 0.01, 0.12 ± 0.00, and 0.34 ± 0.01 m/s per 5 beats/min, respectively. This crosses the range of previous physiological studies where the dependence of PWV on HR was found to be between 0.08 and 0.10 m/s per 5 beats/min. Therefore, viscoelasticity of the arterial wall could contribute to mechanisms through which large artery stiffness changes with changing HR. Physiological studies are required to confirm this mechanism.

NEW & NOTEWORTHY This study used a transmission line model to elucidate the role of arterial viscoelasticity in the dependency of pulse wave velocity on heart rate. The model uses fractional viscoelasticity concepts, which provided novel insights into arterial hemodynamics. This study also provides a means of assessing the clinical manifestation of the association of pulse wave velocity and heart rate.

Psychophysiological correlates of systemic inflammation in black and white men

Inflammation plays a critical role in the pathophysiology of cardiovascular disease (CVD) and levels of circulating inflammatory markers are associated with future CVD risk. However, the physiological mechanisms that control systemic levels of circulating inflammatory markers are not well understood. Here, we explore possible autonomic nervous system mechanisms by testing whether resting and stressor-evoked cardiovascular responses are associated with two markers of systemic inflammation: interleukin (IL)-6 and C-reactive protein (CRP). Subjects were 159 black and 129 white men (M=33.0years) who completed a laboratory protocol including an anger recall speech task. Electrocardiography and impedance cardiography data were collected during a resting baseline, the speech task, and a final recovery period. Hierarchical regressions tested whether resting or stressor-evoked levels of heart rate (HR), high-frequency heart rate variability (HF-HRV), pre-ejection period (PEP), and pulse transit time (PTT) were associated with CRP or IL-6. Higher resting HR was associated with higher CRP (β=0.19, p=0.003) and IL-6 (β=0.13, p<0.05). Similarly, shorter resting PTT was associated with higher CRP (β=-0.21, p<0.001) and IL-6 (β=-0.14, p=0.02). In addition, greater stressor-evoked decreases in HF-HRV were associated with higher CRP (β=-0.14, p=0.01). Associations were independent of age, race, body mass index (BMI), smoking behavior, and socioeconomic status. Resting HF-HRV and PEP were also associated with CRP and IL-6, but associations were not significant after controlling for BMI and smoking behavior. These findings indicate that resting HR and PTT, as well stressor-evoked HF-HRV reactivity, are associated with systemic inflammation. Our results suggest that both tonic and stressor-evoked sympathetic and parasympathetic nervous system activity may contribute to regulation of systemic inflammation.

Improved Blood Pressure Prediction Using Systolic Flow Correction of Pulse Wave Velocity

Hypertension is a significant worldwide health issue. Continuous blood pressure monitoring is important for early detection of hypertension, and for improving treatment efficacy and compliance. Pulse wave velocity (PWV) has the potential to allow for a continuous blood pressure monitoring device; however published studies demonstrate significant variability in this correlation. In a recently presented physics-based mathematical model of PWV, flow velocity is additive to the classic pressure wave as estimated by arterial material properties, suggesting flow velocity correction may be important for cuff-less non-invasive blood pressure measures. The present study examined the impact of systolic flow correction of a measured PWV on blood pressure prediction accuracy using data from two published in vivo studies. Both studies examined the relationship between PWV and blood pressure under pharmacological manipulation, one in mongrel dogs and the other in healthy adult males. Systolic flow correction of the measured PWV improves the R² correlation to blood pressure from 0.51 to 0.75 for the mongrel dog study, and 0.05 to 0.70 for the human subjects study. The results support the hypothesis that systolic flow correction is an essential element of non-invasive, cuff-less blood pressure estimation based on PWV measures.

Pulse Wave Velocity Prediction and Compliance Assessment in Elastic Arterial Segments

Pressure wave velocity (PWV) is commonly used as a clinical marker of vascular elasticity. Recent studies have increased clinical interest in also analyzing the impact of heart rate, blood pressure, and left ventricular ejection time on PWV. In this article we focus on the development of a theoretical one-dimensional model and validation via direct measurement of the impact of ejection time and peak pressure on PWV using an in vitro hemodynamic simulator. A simple nonlinear traveling wave model was developed for a compliant thin-walled elastic tube filled with an incompressible fluid. This model accounts for the convective fluid phenomena, elastic vessel deformation, radial motion, and inertia of the wall. An exact analytical solution for PWV is presented which incorporates peak pressure, ejection time, ejection volume, and modulus of elasticity. To assess arterial compliance, the solution is introduced in an alternative form, explicitly determining compliance of the wall as a function of the other variables. The model predicts PWV in good agreement with the measured values with a maximum difference of 3.0%. The results indicate an inverse quadratic relationship ([Formula: see text]) between ejection time and PWV, with ejection time dominating the PWV shifts (12%) over those observed with changes in peak pressure (2%). Our modeling and validation results both explain and support the emerging evidence that, both in clinical practice and clinical research, cardiac systolic function related variables should be regularly taken into account when interpreting arterial function indices, namely PWV.

Association of resting heart rate with cardiovascular function: a cross-sectional study in 522 Finnish subjects

Background

High resting heart rate (HR) is associated with increased cardiovascular risk in general populations, possibly due to elevated blood pressure (BP) or sympathetic over-activity. We studied the association of resting HR with cardiovascular function, and examined whether the hemodynamics remained similar during passive head-up tilt.

Methods

Hemodynamics were recorded using whole-body impedance cardiography and continuous radial pulse wave analysis in 522 subjects (age 20–72 years, 261 males) without medication influencing HR or BP, or diagnosed diabetes, coronary artery, renal, peripheral arterial, or cerebrovascular disease. Correlations were calculated, and results analysed according to resting HR tertiles.

Results

Higher resting HR was associated with elevated systolic and diastolic BP, lower stroke volume but higher cardiac output and work, and lower systemic vascular resistance, both supine and upright (p < 0.05 for all). Subjects with higher HR also showed lower supine and upright aortic pulse pressure and augmentation index, and increased resting pulse wave velocity (p < 0.001). Upright stroke volume decreased less in subjects with highest resting HR (p < 0.05), and cardiac output decreased less in subjects with lowest resting HR (p < 0.009), but clear hemodynamic differences between the tertiles persisted both supine and upright.

Conclusions

Supine and upright hemodynamic profile associated with higher resting HR is characterized by higher cardiac output and lower systemic vascular resistance. Higher resting HR was associated with reduced central wave reflection, in spite of elevated BP and arterial stiffness. The increased cardiac workload, higher BP and arterial stiffness, may explain why higher HR is associated with less favourable prognosis in populations.

Trial registration

ClinicalTrials.gov, NCT01742702

Left ventricular ejection time, not heart rate, is an independent correlate of aortic pulse wave velocity

Several studies showed a positive association between heart rate and pulse wave velocity, a sensitive marker of arterial stiffness. However, no study involving a large population has specifically addressed the dependence of pulse wave velocity on different components of the cardiac cycle. The aim of this study was to explore in subjects of different age the link between pulse wave velocity with heart period (the reciprocal of heart rate) and the temporal components of the cardiac cycle such as left ventricular ejection time and diastolic time. Carotid-femoral pulse wave velocity was assessed in 3,020 untreated subjects (1,107 men). Heart period, left ventricular ejection time, diastolic time, and early-systolic dP/dt were determined by carotid pulse wave analysis with high-fidelity applanation tonometry. An inverse association was found between pulse wave velocity and left ventricular ejection time at all ages (<25 years, r(2) = 0.043; 25-44 years, r(2) = 0.103; 45-64 years, r(2) = 0.079; 65-84 years, r(2) = 0.044; ≥ 85 years, r(2) = 0.022; P < 0.0001 for all). A significant (P < 0.0001) negative but always weaker correlation between pulse wave velocity and heart period was also found, with the exception of the youngest subjects (P = 0.20). A significant positive correlation was also found between pulse wave velocity and dP/dt (P < 0.0001). With multiple stepwise regression analysis, left ventricular ejection time and dP/dt remained the only determinant of pulse wave velocity at all ages, whereas the contribution of heart period no longer became significant. Our data demonstrate that pulse wave velocity is more closely related to left ventricular systolic function than to heart period. This may have methodological and pathophysiological implications.

Association of longer QT interval with arterial waveform and lower pulse pressure amplification: the Nagahama Study

BACKGROUND

Central systolic blood pressure (cSBP) has been postulated to correlate closely with cardiovascular risk. Identifying factors associated with cSBP is therefore important. Prolonged QT interval is known to be associated with cardiovascular outcomes and might also be associated with the arterial waveform and cSBP. We investigated the possible associations between electrocardiogram wave interval and cSBP in general population samples.

METHODS

Brachial blood pressure and radial arterial waveform were measured simultaneously. Augmentation index (AIx) was calculated from the radial waveform as the ratio of the height of the late systolic peak to that of the first peak. cSBP was defined as the absolute pressure of the late systolic peak.

RESULTS

In the first panel (n = 8,085), QT interval was strongly association with AIx (r = 0.330; P < 0.001). This association remained significant even in the heart rate-adjusted analysis (r = 0.184; P < 0.001). Although subjects with a longer QT interval were older and had higher blood pressure, heart rate, and pulse wave velocity, multivariable analysis with adjustment for these covariables nevertheless identified longer corrected QT interval as an independent determinant of increased AIx and smaller pulse pressure amplification (PPa; brachial SBP minus cSBP) (β = -0.066; P < 0.001). This association was replicated in the independent second panel (n = 1,412) (β = -0.105; P < 0.001). In contrast, QRS interval was positively associated with PPa (β = 0.056; P < 0.001).

CONCLUSIONS

Longer QT interval and short QRS duration were significantly associated with arterial waveform and PPa. Our results provide a clue to the elucidation of unidentified mechanisms of the increased cardiovascular outcome and mortality risks in subjects with longer QT interval.

Sex-specific programming of cardiovascular physiology in children

AIMS

Increasing evidence suggests that adverse prenatal environments, as indicated by low birth weight, cause long-term changes in cardiovascular physiology that predispose to circulatory disease. The mechanisms are poorly understood, most human studies have been carried out in adults and little is known about early pathophysiological changes. Therefore, we have assessed the relationship between birth weight and cardiovascular physiology in children.

METHODS AND RESULTS

In 140 healthy boys and girls (aged 7-9 years), born at term and followed prospectively, we continuously recorded blood pressure, electrocardiograms and cardiac impedance before, during, and after 10 min of psychosocial stress (Trier Social Stress Test for Children). In boys, an association of lower birth weight with higher resting systemic arterial pressure (β = -6.8 mmHg/kg, P= 0.03) and a trend towards higher vascular resistance (β = -87 dyne s/cm(5)/kg, ns) were substantially strengthened following stress (β = -9.5 mmHg/kg, P= 0.003 and β = -139 dyne s/cm(5)/kg, P = 0.02, respectively). In girls, lower birth weight was associated with a shorter pre-ejection period (β = 8.0 ms/kg, P = 0.005) and corrected QT interval (β = 11.9 ms/kg, P = 0.003) at rest and little changed by stress.

CONCLUSION

Smaller size at birth is associated with sex-specific alterations in cardiac physiology; boys had higher systemic vascular resistance and girls had increased cardiac sympathetic activation.

The relationship between effective arterial capacitance and pulse wave velocity is dependent on left ventricular stroke volume

BACKGROUND

increased arterial stiffness is a predictor of cardiovascular events. The stroke volume (SV) to pulse pressure (PP) ratio is an estimate of arterial capacitance. Pulse wave velocity (PWV) is a measure of arterial stiffness. This study evaluated the effect of left ventricular (LV) SV on the SV/PP-PWV relationship.

METHODS

97 patients had applanation tonometry and echocardiography to measure arterial capacitance (SV/PP), PWV, and central aortic pressure.

RESULTS

50 patients had normal SV and 47 had low SV. For all patients, PWV inversely correlated with SV/PP. PWV and SV/PP correlated more strongly in the normal SV group than in the low SV group. Aortic PP was significantly correlated with PWV in all patients, in the normal SV group, and in the low SV group.

CONCLUSION

effective arterial capacitance correlates with PWV. The presence of decreased SV weakens the relationship.

Change in pulse transit time and pre-ejection period during head-up tilt-induced progressive central hypovolaemia

OBJECTIVE

Traditional vital signs such as heart rate (HR) and blood pressure (BP) are often regarded as insensitive markers of mild to moderate blood loss. The present study investigated the feasibility of using pulse transit time (PTT) to track variations in pre-ejection period (PEP) during progressive central hypovolaemia induced by head-up tilt and evaluated the potential of PTT as an early non-invasive indicator of blood loss.

METHODS

About 11 healthy subjects underwent graded head-up tilt from 0 to 80 degrees . PTT and PEP were computed from the simultaneous measurement of electrocardiogram (ECG), finger photoplethysmographic pulse oximetry waveform (PPG-POW) and thoracic impedance plethysmogram (IPG). The response of PTT and PEP to tilt was compared with that of interbeat heart interval (RR) and BP. Least-squares linear regression analysis was carried out on an intra-subject basis between PTT and PEP and between various physiological variables and sine of the tilt angle (which is associated with the decrease in central blood volume) and the correlation coefficients (r) were computed.

RESULTS

During graded tilt, PEP and PTT were strongly correlated in 10 out of 11 subjects (median r = 0.964) and had strong positive linear correlations with sine of the tilt angle (median r = 0.966 and 0.938 respectively). At a mild hypovolaemic state (20-30 degrees ), there was a significant increase in PTT and PEP compared with baseline (0 degrees ) but without a significant change in RR and BP. Gradient analysis showed that PTT was more responsive to central volume loss than RR during mild hypovolaemia (0-20 degrees ) but not moderate hypovolaemia (50-80 degrees ).

CONCLUSION

PTT may reflect variation in PEP and central blood volume, and is potentially useful for early detection of non-hypotensive progressive central hypovolaemia. Joint interpretation of PTT and RR trends or responses may help to characterize the extent of blood volume loss in critical care patients.

Age-specific relationship of aortic pulse wave velocity with left ventricular geometry and function in hypertension

Aortic pulse wave velocity (PWV), generally considered an intrinsic marker of arterial stiffness, might depend in part on the velocity of myocardial fiber shortening, but the relation between PWV and myocardial function in humans has been understudied. A total of 237 untreated hypertensive subjects over a wide age range (18 to 88 years) underwent aortic PWV determination and echocardiography, from which the mean velocity of circumferential fiber shortening was calculated as a measure of the velocity of myocardial shortening, and relative wall thickness was taken as a measure of left ventricular concentric remodeling. Patients were divided in 3 age groups (<40 years, 40 to 59 years, and >or=60 years). In the young, aortic PWV was directly associated with heart rate-corrected velocity of circumferential fiber shortening (r=0.39; P=0.002) but not to relative wall thickness (r=-0.01; P=0.95). The opposite was found in the older group, in which aortic PWV was accompanied by a concentric left ventricular geometric pattern (r=0.44 with relative wall thickness; P=0.009) and a reduced velocity of circumferential fiber shortening (r=-0.54; P<0.001) and stress-corrected midwall fractional shortening (r=-0.56; P<0.001). Intermediate values were found in the middle-aged group (r=0.23; P<0.01 with relative wall thickness; r=-0.07, P value not significant with velocity of circumferential fiber shortening). In conclusion, the relation between aortic PVW and the left ventricle is strongly age dependent. These data suggest that, in young people, aortic PWV is partly determined by an increased velocity of myocardial shortening. With increasing age, a relationship between aortic PWV (as a measure of arterial stiffness) and left ventricular concentric geometry emerges, which ultimately leads to a depressed ventricular systolic function.

Interaction between pulse wave velocity, augmentation index, pulse pressure and left ventricular function in chronic heart failure

Pulse wave velocity (PWV), the carotid augmentation index (AIx), and pulse pressure (PP) may be prognostic factors in heart failure, but the possible influence of the ejection fraction (EF) and other simple haemodynamic variables on them has not been investigated in this setting. Noninvasive methods were used to measure carotid-radial (CR), carotid-femoral (CF) PWV and AIx, and brachial PP, in 135 consecutive patients with stable symptomatic chronic heart failure. The patients were divided into two groups, with preserved (>or=40%) or reduced (<40%) EF. CF-PWV, AIx and PP were lower in the decreased EF group (8.85+/-2.77 versus 10.60+/-2.75 m/s, P<0.001; 121+/-21 versus 132+/-24, P=0.009 and 41+/-19 versus 67+/-17 mmHg, P<0.001), but CR-PWV values were similar regardless of the EF status. These results were not modified after adjustment for age and sex. Multiple regression analysis showed that AIx and PP were systematically related to time domain parameters (heart rate or ejection duration) and EF, whatever the group. CF-PWV was weakly related to time domain values and unrelated to mean blood pressure (BP) or EF in the preserved EF group, whereas it was related to both mean BP and EF in the low EF group. In conclusion, whatever the EF level, PP and AIx were strongly modulated in the time domain, by pressure and by the EF level. The same relationships were found with CF-PWV, but only in the reduced EF group. Whether CF-PWV is the best prognostic factor in patients with 'diastolic' heart failure must be confirmed in a prospective study.

Clonidine Lowers Blood Pressure by Reducing Vascular Resistance and Cardiac Output in Young, Healthy Males

PURPOSE

Clonidine is a classical sympatholytic drug that is widely used for the treatment of hypertension. Experimental and clinical studies suggest that Clonidine may activate baroreflex. The aim of this study was to determine the hemodynamic response to Clonidine under physiological conditions and to test the hypothesis that Clonidine would reduce cardiac output and blood pressure resulting in an increase in total peripheral resistance.

METHODS

Clonidine's hemodynamic effect was evaluated in 28 young, healthy subjects after a single i.v. dose of 1 microg x kg(- 1). Impedance cardiography, systolic time intervals and pulse wave analysis were used to characterize myocardial and vascular function.

RESULTS

Clonidine lowered blood pressure, heart rate, left ventricular ejection time, and pulse wave velocity and increased pre-ejection period. Stroke volume and cardiac output decreased gradually over the investigation time of 240 min. Central systolic blood pressure (SBP) was lowered to a larger extent than peripheral SBP. Total peripheral resistance was characterized by an immediate fall of short duration followed by a continuous rise above baseline after 120 min. Placebo did not have any significant effect on hemodynamic parameters.

CONCLUSIONS

Clonidine's blood pressure lowering effect is mediated by both an immediate decrease in vascular resistance and a prolonged decrease in cardiac output, and Clonidine lowers central SBP more than peripheral SBP.