Physiological and clinical insights from reservoir-excess pressure analysis

Aortic reservoir-excess pressure parameters are associated with worse cognitive function in people with untreated stage II/III hypertension

OBJECTIVE

Hypertension is a recognized risk factor for the development of cognitive impairment and dementia in older adults. Aortic stiffness and altered haemodynamics could promote the transmission of detrimental high pressure pulsatility into the cerebral circulation, potentially damaging brain microvasculature and leading to cognitive impairment. We determined whether reservoir-excess pressure parameters were associated with cognitive function in people with hypertension (HT) and normotension (NT).

METHODS

We studied 35 middle-aged and older treatment-naïve stage II/III HT (office systolic BP 176 ± 17 mmHg) and 35 age-, sex- and body mass index-matched NT (office systolic BP 127 ± 8 mmHg). Parameters derived from reservoir-excess pressure analysis including reservoir pressure integral (INTPR), excess pressure integral (INTXSP), systolic rate constant (SRC), diastolic rate constant (DRC) and pulse wave velocity (PWV) were calculated from an ensemble-averaged aortic pressure waveform derived from radial artery tonometry. Cognitive function was assessed using the Addenbrooke's Cognitive Examination Revised (ACE-R), Trail Making Test Part A (TMT-A) and Part B (TMT-B).

RESULTS

All reservoir-excess pressure parameters were greater in HT than NT (all P < 0.05). Greater INTXSP was associated with lower ACE-R score (rs = -0.31), longer TMT-A (r = 0.31) and TMT-B (r = 0.38). Likewise, greater DRC and PWV were also associated with lower ACE-R score (rs = -0.27 and rs = -0.33), longer TMT-A (r = 0.51 and r = 0.40) and TMT-B (r = 0.38 and r = 0.32). Greater INTXSP, DRC and PWV are consistently associated with worse cognitive function in this study.

CONCLUSIONS

These observations support a potential mechanistic link between adverse haemodynamics and a heightened risk of cognitive impairment in older adults with hypertension.

Estimation of central blood pressure waveform from femoral blood pressure waveform by blind sources separation

Background

Central blood pressure (cBP) is a better indicator of cardiovascular morbidity and mortality than peripheral BP (pBP). However, direct cBP measurement requires invasive techniques and indirect cBP measurement is based on rigid and empirical transfer functions applied to pBP. Thus, development of a personalized and well-validated method for non-invasive derivation of cBP from pBP is necessary to facilitate the clinical routine. The purpose of the present study was to develop a novel blind source separation tool to separate a single recording of pBP into their pressure waveforms composing its dynamics, to identify the compounds that lead to pressure waveform distortion at the periphery, and to estimate the cBP. The approach is patient-specific and extracts the underlying blind pressure waveforms in pBP without additional brachial cuff calibration or any a priori assumption on the arterial model.

Methods

The intra-arterial femoral BPfe and intra-aortic pressure BPao were anonymized digital recordings from previous routine cardiac catheterizations of eight patients at the German Heart Centre Berlin. The underlying pressure waveforms in BPfe were extracted by the single-channel independent component analysis (SCICA). The accuracy of the SCICA model to estimate the whole cBP waveform was evaluated by the mean absolute error (MAE), the root mean square error (RMSE), the relative RMSE (RRMSE), and the intraclass correlation coefficient (ICC). The agreement between the intra-aortic and estimated parameters including systolic (SBP), diastolic (DBP), mean arterial pressure (MAP), and pulse pressure (PP) was evaluated by the regression and Bland-Altman analyses.

Results

The SCICA tool estimated the cBP waveform non-invasively from the intra-arterial BPfe with an MAE of 0.159 ± 1.629, an RMSE of 5.153 ± 0.957 mmHg, an RRMSE of 5.424 ± 1.304%, and an ICC of 0.94, as well as two waveforms contributing to morphological distortion at the femoral artery. The regression analysis showed a strong linear trend between the estimated and intra-aortic SBP, DBP, MAP, and PP with high coefficient of determination R2 of 0.98, 0.99, 0.99, and 0.97 respectively. The Bland-Altman plots demonstrated good agreement between estimated and intra-aortic parameters with a mean error and a standard deviation of difference of -0.54 ± 2.42 mmHg [95% confidence interval (CI): -5.28 to 4.20] for SBP, -1.97 ± 1.62 mmHg (95% CI: -5.14 to 1.20) for DBP, -1.49 ± 1.40 mmHg (95% CI: -4.25 to 1.26) for MAP, and 1.43 ± 2.79 mmHg (95% CI: -4.03 to 6.90) for PP.

Conclusions

The SCICA approach is a powerful tool that identifies sources contributing to morphological distortion at peripheral arteries and estimates cBP.

Arterial Blood Pressure Features of Hypertensive Patients with Typical and Atypical 460 nm Skin Fluorescence Response to Transient Ischaemia

Flow-mediated skin fluorescence (FMSF) at 460 nm is a non-invasive method for assessing dynamic changes in the reduced form of nicotinamide adenine dinucleotide (NADH) and microcirculation in forearm skin under varying conditions of tissue perfusion. Typically, fluorescence increases during ischaemia, but atypical cases show a temporary signal decrease instead of a constant increase. This study aimed to explore the clinical implications of atypical FMSF patterns in patients with newly diagnosed untreated hypertension. NADH fluorescence and pulse wave analysis were performed on 65 patients. Differences in peripheral and arterial pulse pressure profiles were examined based on FMSF curve courses. Patients with atypical curve courses had significantly (p < 0.05 or lower for all) higher heart rate, peripheral and central diastolic pressure, tension time index, central rate pressure product, shorter diastole duration, and reservoir pressure-time integral. Hypertensive patients with atypical FMSF signals had less advantageous blood pressure profiles. Although the underlying factors causing these symptoms are unknown, the atypical FMSF pattern may reflect increased sympathetic stimulation and vascular resistance. The visual assessment of the FMSF curve may have important clinical implications that deserve further investigation.

Sex differences in pressure and flow waveform physiology across the life course

Cardiovascular disease (CVD) has long been deemed a disease of old men. However, in 2019 CVD accounted for 35% of all deaths in women and, therefore, remains the leading cause of death in both men and women. There is increasing evidence to show that risk factors, pathophysiology and health outcomes related to CVD differ in women compared with men, yet CVD in women remains understudied, underdiagnosed and undertreated. Differences exist between the sexes in relation to the structure of the heart and vasculature, which translate into differences in blood pressure and flow waveform physiology. These physiological differences between women and men may represent an important explanatory factor contributing to the sex disparity in CVD presentation and outcomes but remain understudied. In this review we aim to describe sex differences in arterial pressure and flow waveform physiology and explore how they may contribute to differences in CVD in women compared to men. Given that unfavourable alterations in the cardiovascular structure and function can start as early as in utero, we report sex differences in waveform physiology across the entire life course.

Excess pressure but not pulse wave velocity is associated with cognitive function impairment: a community-based study

BACKGROUND

Carotid-femoral pulse wave velocity (cf-PWV), an index of mainly distal aortic stiffness, has been inconsistently associated with cognitive function. Excess pressure, derived from the arterial reservoir-excess pressure analysis, may integrate the pulsatile load of the proximal aorta. The present study examined whether increased excess pressure is associated with cognitive function impairment in community adults.

METHODS

A total of 992 community participants (69.5% females; mean age: 67.3 years; education 13.6 years) without cerebrovascular disease or dementia received the Montreal Cognitive Assessment (MoCA) to evaluate global cognition. Arterial reservoir and excess pressure, arterial stiffness, and wave reflections were assessed, using carotid tonometry and aortic Doppler flowmetry.

RESULTS

Excess pressure integral (XSPI), percentage XSPI, cf-PWV, characteristic impedance (Zc), and forward and backward pressure amplitude (Pf, Pb, respectively) were significantly higher in 197 participants (19.9%) with a low MoCA score (<26 or <25, depending on level of education). In multivariable analyses, XSPI (standardized odds ratio, 95% confidence interval, 1.30, 1.06-1.59), and percentage XSPI (1.27, 1.06-1.52) but not cf-PWV (1.04, 0.85-1.26) were significantly associated with a low MoCA. Further analysis revealed that Pf and Zc were the major determinants of XSPI (partial R2: Pf = 0.656, Zc = 0.467) and percentage XSPI (Pf = 0.459, Zc = 0.371). In contrast, age, instead of Pf and Zc, was the major determinant of cf-PWV (partial R2: age = 0.187).

CONCLUSIONS

Excess pressure (XSPI/percentage XSPI), mainly determined by the pulsatile hemodynamics of the proximal aorta, was significantly associated with cognitive function impairment in middle-aged and elderly community adults.

Carotid Reservoir Pressure Decrease After Prolonged Head Down Tilt Bed Rest in Young Healthy Subjects Is Associated With Reduction in Left Ventricular Ejection Time and Diastolic Length

Background

The arterial pressure waveform reflects the interaction between the heart and the arterial system and carries potentially relevant information about circulatory status. According to the commonly accepted 'wave transmission model', the net BP waveform results from the super-position of discrete forward and backward pressure waves, with the forward wave in systole determined mainly by the left ventricular (LV) ejection function and the backward by the wave reflection from the periphery, the timing and amplitude of which depend on arterial stiffness, the wave propagation speed and the extent of downstream admittance mismatching. However, this approach obscures the 'Windkessel function' of the elastic arteries. Recently, a 'reservoir-excess pressure' model has been proposed, which interprets the arterial BP waveform as a composite of a volume-related 'reservoir' pressure and a wave-related 'excess' pressure.

Methods

In this study we applied the reservoir-excess pressure approach to the analysis of carotid arterial pressure waveforms (applanation tonometry) in 10 young healthy volunteers before and after a 5-week head down tilt bed rest which induced a significant reduction in stroke volume (SV), end-diastolic LV volume and LV longitudinal function without significant changes in central blood pressure, cardiac output, total peripheral resistance and aortic stiffness. Forward and backward pressure components were also determined by wave separation analysis.

Results

Compared to the baseline state, bed rest induced a significant reduction in LV ejection time (LVET), diastolic time (DT), backward pressure amplitude (bP) and pressure reservoir integral (INTPR). INTPR correlated directly with LVET, DT, time to the peak of backward wave (bT) and stroke volume, while excess pressure integral (INTXSP) correlated directly with central pressure. Furthermore, Δ.INTPR correlated directly with Δ.LVET, and Δ.DT, and in multivariate analysis INTPR was independently related to LVET and DT and INTXSP to central systolic BP.

Conclusion

This is an hypothesis generating paper which adds support to the idea that the reservoir-wave hypothesis applied to non-invasively obtained carotid pressure waveforms is of potential clinical usefulness.

Accuracy and applicability of non-invasive evaluation of aortic wave intensity using only pressure waveforms in humans

Background.Wave intensity (WI) analysis is a well-established method for quantifying the energy carried in arterial waves, providing valuable clinical information about cardiovascular function. The primary drawback of this method is the need for concurrent measurements of both pressure and flow waveforms.Objective. We have for the first time investigated the accuracy of a novel methodology for estimating wave intensity employing only single pressure waveform measurements; we studied both carotid- and radial-based estimations in a large heterogeneous cohort.Approach.Tonometry was performed alongside Doppler ultrasound to acquire measurements of both carotid and radial pressure waveforms as well as aortic flow waveforms in 2640 healthy and diseased participants (1439 female) in the Framingham Heart Study. Patterns consisting of two forward waves (Wf1, Wf2) and one backward wave (Wb1) along with reflection metrics were compared with those obtained from exact WI analysis.Main Results. Carotid-based estimates correlated well for forward peak amplitudes (Wf1,r = 0.85,p < 0.05; Wf2,r = 0.72,p < 0.05) and peak time (Wf1,r = 0.94,p < 0.05; Wf2,r = 0.98,p < 0.05), and radial-based estimates correlated fairly to poorly for amplitudes (Wf1,r = 0.62,p < 0.05; Wf2,r = 0.42,p < 0.05) and peak time (Wf1,r = 0.04,p = 0.10; Wf2,r = 0.75,p < 0.05). In all cases, estimated Wb1 measures were not correlated. Reflection metrics were well correlated for healthy patients (r = 0.67,p < 0.05), moderately correlated for valvular disease (r = 0.59,p < 0.05) and fairly correlated for CVD (r = 0.46,p < 0.05) and heart failure (r = 0.49,p < 0.05).Significance. These findings indicate that pressure-only WI produces accurate results only when forward contributions are of primary interest and only for carotid pressure waveforms. The pressure-only WI estimations of this work provide an important opportunity to further the goal of uncovering clinical insights through wave analysis affordably and non-invasively.