Reduced Wave Reflection Research Articles

The impact of consecutive freshwater trimix dives at altitude on human cardiovascular function

Self-contained underwater breathing apparatus (SCUBA) diving is regularly associated with numerous asymptomatic changes in cardiovascular function. Freshwater SCUBA diving presents unique challenges compared with open sea diving related to differences in water density and the potential for dive locations at altitude. The aim of this study was to evaluate the impact of freshwater trimix diving at altitude on human cardiovascular function. Ten divers performed two dives in consecutive days at 294 m altitude with the surface interval of 24 h. Both dives were at a depth of 45 m with total dive time 29 and 26 min for the first and second dive, respectively. Assessment of venous gas embolization, hydration status, cardiac function and arterial stiffness was performed. Production of venous gas emboli was low, and there were no significant differences between the dives. After the first dive, diastolic blood pressure was significantly reduced, which persisted up to 24 h. Left ventricular stroke volume decreased, and heart rate increased after both dives. Pulse wave velocity was unchanged following the dives. However, the central and peripheral augmentation index became more negative after both dives, indicating reduced wave reflection. Ejection duration and round trip travel time were prolonged 24 h after the first dive, suggesting longer-lasting suppression of cardiac and endothelial function. This study shows that freshwater trimix dives with conservative profiles and low venous gas bubble loads can result in multiple asymptomatic acute cardiovascular changes some of which were present up to 24 h after dive.

Separation method of bi-directional reflected waves and oblique incident regular waves

Wave reflection is one of the key problems affecting wave simulation quality in ocean engineering basin. The deep ocean engineering basin is equipped with two-sided segmented wavemakers and two wave absorbing beaches, which are located opposite to wave generators to reduce wave reflection effects. When an oblique long-crested wave is made by two-sided segmented wavemakers in a wave basin, two bi-directional reflected waves with the same azimuth but opposite propagation directions are generated. According to this feature, based on the two-point approach developed by Goda, a method to separate an incident regular wave from two bi-directional reflected waves using three wave gauges is proposed. The validity of this method is proved by numerical composite waves. The results indicate that the method can separate incident wave from reflected waves effectively. The method can be used to determine the reflection coefficient and verify the capacity of wave absorbing beaches in deep ocean engineering basin.

347 THE VIS-A-TERGO FOR CEREBRAL PERFUSION

Background: While requiring high steady flow, the brain is perfused in a pulsatile manner. Changes in flow pulsation have been linked to stroke. Flow pulsations in normal subjects have not been characterised, nor their relationship to pulsatile perfusion pressure. Methods: Data were obtained in 200 persons (age 52 years, 94 males), undergoing 24-hour BP monitoring for outpatient evaluation. Flow waveforms were recorded by transcranial Doppler in the right and left Anterior Cerebral, Middle Cerebral, and Basilar Arteries (ACA, MCA and BA, respectively). Radial artery tonometry was used with SphygmoCorTM to generate Ascending Aortic Pressure waveform (AP). Results: Similar flow waveforms were seen on the right and left sides for ACA and MCA. Mean flow velocity was high in all (ACA 54, MCA 61 and BA 38 cm/s, respectively), and continued throughout diastole. Flow waves showed prominent late systolic augmentation, more marked in the smaller BA than ACA or MCA. Flow augmentation index (FAI), calculated in similar fashion to aortic pressure, increased with age at all sites, but was higher in smaller (BA; 112%) than larger arteries (ACA; MCA; 93%) and in all, systematically greater than Pressure Augmentation Index. Conclusions: Wave reflection from the lower body increases Ascending Aortic pressure in late systole. This is caused by wave reflection from the lower body (vis-a-tergo). Wave reflection also boosts late systolic flow in the major cerebral arteries. Value of reduction in wave reflection by arterial dilating drugs needs be explored.

Marina di Cecina Urban Beach: a Shore Protection Project

AMINTI, P.L., BARTOLETTI, E., BERRIOLO, G., BINI, A., BONINSEGNI, G., MORI, E., PRANZINI, E and VANNUCCHI, V., 2011. Marina Di Cecina Urban Beach: a Shore Protection Project. In: Micallef, A. (ed.), MCRR3-2010 Conference Proceedings, Journal of Coastal Research, Special Issue, No. 61, pp. 282–289. Grosseto, Tuscany, Italy, ISSN 0749-0208.Marina di Cecina is a tourist town built on the southern side of Cecina river mouth. Its urban beach has been undergoing severe erosion since the early 20th century as a consequence of reduced river sediment input. Some groins were constructed after the collapse of the first line of houses near the waterline. Immediately the shoreline assumed a characteristic saw-tooth shape and beach use and recreational facilities had to adapt to this uneven sand distribution. In 1990 two of the three main groins were extended with submerged segments and limited artificial nourishment was also performed. Some discontinuous submerged detached breakwaters were added later within the groin field, which resulted in sediment dispersion offshore. The beach was maintained with occasional nourishment, but its width could not support profitable recreational activities and some tourism facilities are still being damaged today by waves during severe storms. To solve these problems, the Livorno Province administration within the Regional shore protection plan, has performed a rehabilitation project at this urban beach. The project is based on the reconfiguration of the whole defence system, removing parallel structures and modifying the groin field; varying the lengths to reach a new alignment of the tips, in order to stabilise a new and more uniform beach to be obtained by means of artificial nourishment. Groin tips will be asymmetric, to reduce wave reflection on the exposed side; some of them will be extended with a long submerged segment made with T-shape concrete precast elements. Groins will be constructed using large flat-faced stones in order to obtain regular slopes, whereas a central pathway made of concrete will allow easy access to pedestrians. Moreover, at the extremities of the field, where parking facilities are present, groins will end with a mildly sloped ramp to give wheelchair users access to the sea.

The L-arginine/asymmetric dimethylarginine (ADMA) ratio is improved during anti-Tumor Necrosis Factor–α therapy in patients with inflammatory arthropathies: Association with aortic stiffness

p< 0.05), augmentation index (AIx, 22.0 7.0 vs 13.1 5.2%, p<0.01) and pressure-dependent elastic modulus. After barnidipine, in hypertensive patients, office BP fell from 159 14/95 11 to 138 16/81 9 mmHg (p<0.001), due to a significant reduction in forward and backward pressures, and AIx decreased to 17.0 8.0% (p<0.01), without changes in arterial stiffness indices. A significant direct relationship between AIx and pulse pressure observed in hypertensive patients at baseline disappeared after therapy (rZ0.45 before and 0.25 after therapy). Conclusions. These data suggest that a reduced wave reflection during therapy with the calcium antagonist barnidipine is depending on its effects on muscular artery tone rather than on large artery stiffness.

Arterial stiffness, pressure and flow pulsatility and brain structure and function: the Age, Gene/Environment Susceptibility – Reykjavik Study

Aortic stiffness increases with age and vascular risk factor exposure and is associated with increased risk for structural and functional abnormalities in the brain. High ambient flow and low impedance are thought to sensitize the cerebral microcirculation to harmful effects of excessive pressure and flow pulsatility. However, haemodynamic mechanisms contributing to structural brain lesions and cognitive impairment in the presence of high aortic stiffness remain unclear. We hypothesized that disproportionate stiffening of the proximal aorta as compared with the carotid arteries reduces wave reflection at this important interface and thereby facilitates transmission of excessive pulsatile energy into the cerebral microcirculation, leading to microvascular damage and impaired function. To assess this hypothesis, we evaluated carotid pressure and flow, carotid-femoral pulse wave velocity, brain magnetic resonance images and cognitive scores in participants in the community-based Age, Gene/Environment Susceptibility--Reykjavik study who had no history of stroke, transient ischaemic attack or dementia (n = 668, 378 females, 69-93 years of age). Aortic characteristic impedance was assessed in a random subset (n = 422) and the reflection coefficient at the aorta-carotid interface was computed. Carotid flow pulsatility index was negatively related to the aorta-carotid reflection coefficient (R = -0.66, P<0.001). Carotid pulse pressure, pulsatility index and carotid-femoral pulse wave velocity were each associated with increased risk for silent subcortical infarcts (hazard ratios of 1.62-1.71 per standard deviation, P<0.002). Carotid-femoral pulse wave velocity was associated with higher white matter hyperintensity volume (0.108 ± 0.045 SD/SD, P = 0.018). Pulsatility index was associated with lower whole brain (-0.127 ± 0.037 SD/SD, P<0.001), grey matter (-0.079 ± 0.038 SD/SD, P = 0.038) and white matter (-0.128 ± 0.039 SD/SD, P<0.001) volumes. Carotid-femoral pulse wave velocity (-0.095 ± 0.043 SD/SD, P = 0.028) and carotid pulse pressure (-0.114 ± 0.045 SD/SD, P = 0.013) were associated with lower memory scores. Pulsatility index was associated with lower memory scores (-0.165 ± 0.039 SD/SD, P<0.001), slower processing speed (-0.118 ± 0.033 SD/SD, P<0.001) and worse performance on tests assessing executive function (-0.155 ± 0.041 SD/SD, P<0.001). When magnetic resonance imaging measures (grey and white matter volumes, white matter hyperintensity volumes and prevalent subcortical infarcts) were included in cognitive models, haemodynamic associations were attenuated or no longer significant, consistent with the hypothesis that increased aortic stiffness and excessive flow pulsatility damage the microcirculation, leading to quantifiable tissue damage and reduced cognitive performance. Marked stiffening of the aorta is associated with reduced wave reflection at the interface between carotid and aorta, transmission of excessive flow pulsatility into the brain, microvascular structural brain damage and lower scores in various cognitive domains.

Evaluation of Carotid Wave Intensity in Firefighters Following Firefighting

Sudden cardiac events are the number one cause of line-of-duty firefighter deaths, but little information exists elucidating the physiologic response to firefighting. Wave intensity (WI) is a new hemodynamic index that provides information about the dynamic behavior of the heart and the vascular system and their interaction. The larger first peak wave (W1) occurs during early systole and is associated with cardiac contractility. The second smaller peak (W2) follows a period of relatively little net wave production during mid-systole and is associated with end systole/early diastole. A small backward-traveling compression wave occurs after the first peak of wave intensity referred as negative area (NA), caused by reflected waves from the peripheral vascular tone and resistance. PURPOSE: To examine changes in arterial ventricular coupling associated with firefighting. METHODS: We examined 39 firefighters (2 females) with a mean age of 28 ± 1 yrs and BMI of 26.6 ± 0.7 kg/m2 at rest and immediately after 4 hours of live firefighting drills. WI was assessed on the right common carotid artery using an Aloka alpha 10 high-resolution ultrasound scanner with color Doppler system for blood flow velocity measurement combined with an echo-tracking method for detecting vessel diameter changes. The vessel changes were automatically converted to pressure waveforms by calibrating its peak and minimum values by systolic and diastolic carotid blood pressure. Carotid blood pressure was measured by applanation tonometery. RESULTS: The magnitude of the W1 decreased significantly from 15925 ± 1341 to 11540 ± 886 mmHg m s-2, p<.05. The magnitude of W2 remained unchanged (W2: from 2080± 200 to 2144 ± 358 mmHg m s-2). Net NA decreased from 53 ± 5 to 40 ± 4 mmHg m s-2. Carotid blood pressures did not change significantly (carotid SBP: from 126 ± 2 to 122 ± 2mmHg; carotid DBP: from 79 ± 1 to 78 ± 1 mmHg). CONCLUSIONS: Cardiac contractility deteriorated after live firefighting drills reflected by reduced W1. This was partly offset by a reduction in wave reflection but without changes in early diastole or carotid pressure. The decrease in cardiac contractility (or altered ventricular-arterial coupling) may be associated with clinical events during firefighting, but this needs further investigation. Supported by Dept of Homeland Security EMW2006FP02459

Passive Vibration Reduces Wave Reflection and Wasted Left Ventricular Pressure Energy in Healthy Young Adults

The augmentation index (AIx), an index of wave reflection, has been associated with increased cardiovascular risk. Wasted left ventricular energy (ΔEw) is considered an additional energy expended by the left ventricle to overcome increased wave reflection. The AIx and ΔEw decrease following acute endurance and resistance exercise performed to fatigue. Similarly, AIx decreases 30 min after an acute bout of ten 1-min sets of static squat exercise with whole-body vibration (WBV). However, the effects of passive vibration (PV) on wave reflection remain unknown. PURPOSE: To test the hypothesis that PV applied to the legs would acutely decrease AIx, augmented pressure (AG), and ΔEw. METHODS: Twenty (M=9,F=11) healthy young (22 ± 3 yr.) volunteers were randomly assigned to rest supine with their legs over a vibration platform (Power Plate) for 10 min with or without PV. The vibration frequency and peak-to-peak displacement were set at 25 Hz and 2 mm, respectively (peak-to-peak acceleration of ∼5.37 G). Subjects remained in the supine position during 33 min of recovery. Radial waveforms were obtained by applanation tonometry to obtain indices of wave reflection before 10 min of PV or a no vibration control (CON). Thereafter, pressure wave forms were collected at 3-5 min (Post-3) and 30-33min (Post-30) of recovery. RESULTS: Brachial and aortic blood pressure (BP), the first systolic peak pressure, and heart rate did not change after either trial. There were significant trialby- time interactions (P<0.01) at Post-30 for AP, AIx, and ΔEw. At Post-30, there were significant reductions (P<0.01) in AP (2.3 mmHg), AIx (7%), and ΔEw (881dynes s/cm2) in the PV trial, with no changes in the CON trial. There was a significant time-by-trial interaction (P<0.05) for the second systolic peak pressure (P2) at Post-30 such that it decreased (P<0.05) in the PV trial, but did not change in the CON trial. CONCLUSIONS: These findings suggest that PV applied to the lower extremities decreases wave reflection and ΔEw in young adults. Prospective research is warrant to evaluate the potential beneficial effects of PV on arterial function in individuals with cardiovascular diseases that are unable to perform conventional exercise.

Reflecting on posture

Cardiovascular parameters are most often assessed at rest, and in many cases in the supine position. This generally facilitates measurement procedures and obviates the need to account for external and usually complex confounding factors, other than those related to the inherent physiology being investigated. Although the supine resting position may be relevant for some part of circadian living, a large part of human activity is characterized by locomotion and the upright posture. Physiological adaptations to locomotion are studied under controlled conditions and at varying degrees of exercise. However, although primary measures of basic physiological quantities (e.g. stroke volume) can be obtained with some level of confidence at rest in supine position, it becomes extremely difficult to measure them during exercise, and so they are generally derived from other measurable quantities, with the associated errors. Notwithstanding this, the large body of work done so far on the physiological response to exercise has been extremely beneficial in elucidating both underlying and adaptive mechanisms for the function of the circulatory system. On the other hand, assessment of the changes occurring in cardiovascular variables when shifting from supine to standing is the procedure most commonly adopted to explore the response of cardiovascular control mechanisms to gravitational challenges, both when investigating physiological adaptations to the upright posture in healthy individuals and when assessing alterations in cardiovascular regulation in patients with a variety of diseases.

Active standing reduces wave reflection in the presence of increased peripheral resistance in young and old healthy individuals

Pressure wave reflections are age-dependent and generally assumed to increase with increasing peripheral resistance. We sought to determine the effect of standing on wave reflection in healthy older and younger individuals and the influence of increased peripheral resistance. During supine rest and active standing, continuous finger arterial blood pressure was measured. Data obtained in the supine period and after 1 and 5 min standing were analysed. Aortic pressure and flow, calculated from finger pressure, were used to derive forward and backward pressure waves, reflection magnitude (ratio of backward and forward pressure waves), augmentation index, and peripheral resistance. Fifteen healthy older (aged 53±7 years) and 15 healthy younger (aged 29±5 years) individuals were included. In both groups, upon standing, stroke volume, cardiac output and pulse pressure decreased with an increase in heart rate and in diastolic pressure. In the older group peripheral resistance increased from 1.3±0.4 to 1.5±0.4 and 1.5±0.4 for supine, 1 and 5 min standing, whereas reflection magnitude decreased from 0.67±0.1 to 0.61±0.1 and 0.61±0.1, and augmentation index from 33±11 to 23±12 and 25±11. In the younger group peripheral resistance increased from 0.9±0.2 to 1.1±0.2 and 1.1±0.2, whereas reflection magnitude decreased from 0.55±0.05 to 0.48±0.05 and 0.49±0.05 and augmentation index from 18±11 to 1±18 and 4±19. With standing, haemodynamic variables change similarly in older and younger individuals. The opposite changes in reflection magnitude and peripheral resistance suggest that reflection and pressure augmentation are not solely dependent on peripheral resistance.

An experimental study of compressed air generation using a pendulum wave energy converter

This study describes a novel system of compressed air generation using a pendulum wave energy converter installed in a coastal defense structure. The objective of this study is to understand how much energy from the incoming waves can be captured for use by the system. Laboratory experiments were carried out to determine the effects of wave and system load conditions on energy conversion efficiency and wave reflection. The test results show that the system can operate with a high degree of efficiency under standing wave and high-load conditions. A reduction of wave reflection can be achieved by the system under a wide range of wave conditions.

Arterial aging—hemodynamic changes and therapeutic options

Arterial aging can be attributed to two different pathophysiological changes--increase in arterial stiffness and disturbed wave reflections. The capacity of the aorta to absorb the force exerted by the left ventricular ejection and dampen pulsatile flow becomes diminished with advancing age, owing to the progressive hardening of the arterial wall. These changes contribute to increase blood pressure, mainly systolic blood pressure and pulse pressure, which can trigger cardiovascular events. Understanding the pulsatile arterial hemodynamics that elevate cardiovascular risk has led to the use of pharmacological therapies, which prevent arterial stiffness and reduce wave reflections, and improve cardiovascular morbidity and mortality. Antifibrotic agents, such as those that block the renin-angiotensin-aldosterone pathway, are often given in association with diuretics, calcium-channel blockers, or both, but not with standard beta-blockers. Consistent reductions in cardiovascular outcomes obtained using these agents can be predicted through noninvasive measurements of central systolic blood pressure and pulse pressure.

Some mechanical aspects of arterial aging: physiological overview based on pulse wave analysis

Aging has a striking impact on the arterial structure and function. The principal structural change with age is medial degeneration that leads to a progressive stiffening of the large elastic arteries. Large artery stiffening increases aortic systolic and pulse pressures through an increase in the forward incident wave and an early return of the backward reflected wave. Peripheral muscular arteries/arterioles are only minimally affected in structure by aging itself, but impaired vasomotor function can alter their impedance properties and thereby increase reflection magnitude. An augmented aortic pressure due to enhanced wave reflection increases wasted left ventricular effort and causes cardiac hypertrophy. Increased pulsatile pressure and flow stresses extend to the vulnerable microcirculation of vasodilated organs such as the brain and kidneys, and can predispose to cerebral lacunar infarction and albuminuria. Although most currently available vasodilators appear to have little direct effect on degenerated elastic arteries, they can act instead on less-degenerated muscular arteries to markedly reduce peripheral wave reflection magnitude and central aortic pressure, and thus contribute to the regression of left ventricular hypertrophy. Further studies are necessary to examine whether the effect of vasodilator therapy on reducing wave reflection contributes similarly to the prevention of microvascular damage in the brain and kidneys.

Actions of Selected Cardiovascular Hormones on Arterial Stiffness and Wave Reflections

The large conduit arteries of the thorax and abdomen are elastic while those in the arms and legs are muscular. Alterations in wall properties of elastic arteries occur over time and are usually permanent in nature; acute changes can, however, occur is response to a change in transmural pressure. Chronic alterations in properties of muscular arteries are minimal but changes (e.g vasoconstriction, vasodilation or tone) do occur in response to smooth muscle cell (SMC) stimulation. In general an increase in arterial stiffness (and wave reflection) increases systolic blood pressure (BP) and is detrimental while a decrease is beneficial. The augmentation in systolic BP increases left ventricular (LV) mass, wasted energy, tension-time index (TTI) and myocardial oxygen demand while the fall in diastolic BP decreases coronary artery perfusion causing a mismatch in ventricular/vascular coupling and an imbalance in the myocardial oxygen supply/demand ratio. Cardiovascular hormones such as renin, angiotensin, aldosterone, parathormone, sympathomimetic amines and endothelin induce vasoconstriction and increase arterial stiffness while insulin, thyroxine, testosterone, atrial natriuretic peptide (ANP), estrogen and nitric oxide (NO) have the opposite effect. The undesirable effects can be reversed with selected blocking agents. Vasodilator drugs have little direct active effect on large elastic arteries and unaugmented BP but can markedly reduce wave reflection amplitude and duration and augmentation index by decreasing stiffness of the muscular arteries and reducing transmission velocity of the reflected wave from the periphery to the heart. This decrease in amplitude and increase in travel time (or delay) of the reflected wave causes a generalized decrease in systolic BP, arterial wall stress, wasted LV energy and TTI.

-Blockers Reduce Aortic Stiffness in Hypertension but Nebivolol, Not Atenolol, Reduces Wave Reflection

There is conflicting information with regard to the effect of beta-blockers on arterial stiffness and wave reflection. We compared a vasodilating beta-blocker, nebivolol, with atenolol. We randomized 40 subjects with untreated hypertension (mean +/- s.e.m. systolic/diastolic blood pressure (BP) of 160 +/- 3/98 +/- 1 mm Hg, age 49 +/- 1 years) 16 of whom were women, to atenolol 50 mg or nebivolol 5 mg daily for 4 weeks. Arterial stiffness was assessed in terms of carotid-femoral pulse wave velocity (PWV, Complior) and arterial wave reflection (augmentation index (AIx) by applanation tonometry, Sphygmocor). Both beta-blockers produced an equal reduction in brachial BP but aortic pulse pressure (PP) was reduced to a greater extent by nebivolol (P < 0.05). PWV was decreased significantly by both therapies (nebivolol: from 11.5 +/- 0.5 to 9.9 +/- 0.5 m/s; atenolol: from 11.1 +/- 0.4 to 9.8 +/- 0.4 m/s; P < 0.01) but only nebivolol significantly reduced AIx (from 35 +/- 5 to 28 +/- 2%, P < 0.05). In addition, whereas PP amplification (PP, mm Hg) decreased with atenolol therapy (from 10 +/- 1 to 7 +/- 1, P < 0.01), it increased with nebivolol therapy (from 8 +/- 1 to 14 +/- 3, P < 0.01). Atenolol reduced heart rate to a greater extent than nebivolol did (14 +/- 3/min reduction by atenolol vs. 8 +/- 2/min reduction by nebivolol, P < 0.05). There was no difference between the two treatments in respect of the effect on transit time. The beta-blockers, atenolol and nebivolol, have a similar effect in reducing arterial stiffness in the large elastic aorta, largely secondary to BP reduction. Nebivolol, in contrast to atenolol, has an effect on small muscular arteries, increasing PP amplification and reducing wave reflection, possibly because of increased levels of nitric oxide (NO). Such ancillary properties may impart important distinct hemodynamic effects, and therefore beta-blockers cannot be regarded as a homogeneous group.

Optimal Treatment of Hypertension with Diastolic Heart Failure

Approximately 5 million people in the United States have heart failure. Epidemiologic studies have demonstrated that at least one half of patients who have clinically overt heart failure have diastolic heart failure (DHF), or heart failure with preserved ejection fraction. DHF is characterized by concentric remodeling with normal left ventricular end-diastolic volume, abnormalities of active relaxation, and increased passive ventricular stiffness. Diuretics are an essential component of therapy for most patients who have DHF, and treatment of hypertension is a cornerstone of therapy designed to prevent or to treat DHF. Several antihypertensive agents have been shown to effectively reduce wave reflection, including angiotensin-converting enzyme inhibitors, angiotensin-receptor blockers, calcium antagonists, and nitrates. Lifestyle changes may also be helpful.

Modelling and simulation of wave transformation in porous structures using VOF based two-phase flow model

This paper represents the results of wave transformation in porous structures and hydraulic performance of a vertical porous seawall. The study was carried out using a VOF based two-phase numerical hydrodynamic model. The model was developed by coupling an ordinary porous flow model based on extended Navier–Stokes equations for porous media, and a two-phase flow model. A unique solution domain was established with proper treatment of the interface boundary between water, air and the structure. The VOF method with an improved fluid advection algorithm was used to trace the interface between water and air. The resistance to flow caused by the presence of structural material was modeled in terms of drag and inertia forces. The parameters that govern resistance to flow in a porous media were calibrated for a typical structural setup and then the computational efficacy of the model was evaluated for several wave and structural conditions other than the calibrated setup. A set of comparisons of wave properties in and around the structure showed that the model reproduced reasonably good agreement between computed results and measured data. The model was then applied to investigate wave transformation in a vertical porous structure. The role of porosity and width of a structure in reducing wave reflection and increasing energy dissipation was investigated. It is confirmed that there exists an optimum value of structure width and porosity that can maximize hydraulic performances of a porous seawall.

Monitoring of Antihypertensive Therapy for Reduction in Left Ventricular Mass

Pressure pulse waveform features may predict treatment-induced regression of left ventricular (LV) mass better than casual brachial blood pressure (BP). We compared predictive power for LV mass reduction between the putative optimal pulse waveform feature (pulse amplification) and the putative optimal brachial cuff measurement (self BP monitoring at home). Forty-three patients with hypertension received standard medical treatment for 1 year. Self BP monitoring was used to determine home morning and evening BPs. Radial pressure waveforms recorded with applanation tonometry in the clinic were transformed to aortic waveforms, and pulse amplification (upper limb pulse pressure/central pulse pressure) was calculated. Antihypertensive therapy significantly (P < .05) reduced LV load, manifest by a decrease in both home BPs and by an increase in amplification. These changes were accompanied by significant reduction in echocardiographically determined LV mass index (LVMI). However, treatment-induced LVMI change did not correlate with change in any component of home BPs, but closely correlated with change in amplification (r = -0.54, P < .001). Amplification was a strong determinant of LVMI reduction, independent of age, gender, and home BP. Estimated subject numbers required for predicting a significant LVMI reduction were far less when the pulse waves were used rather than home BP; for alpha = 0.05 and beta = 0.20, numbers were 25 subjects for amplification but more than 1000 for home BP. Regression of LV mass is closely associated with reduction in wave reflection, and can be assessed more precisely and easily from radial tonometry than use of the brachial cuff measurement, even in the home setting.

Abstract 2741: Paradoxical Reduction in Pulse Wave Reflection Following Maximal Exercise in Patients with Type 2 Diabetes Mellitus: Association with Exercise Central Blood Pressure

Background: Patients with type 2 diabetes mellitus (T2DM) have increased large artery stiffness and exaggerated brachial and central systolic blood pressure (SBP) responses to exercise. Elevations in exercise central SBP may be a result of increased arterial wave reflections and this study aimed to test this hypothesis. Methods: Maximal exercise stress tests were conducted in 50 T2DM patients (55 ± 8y, 70% males) and 50 controls (56 ± 8y, 70% males) matched by age, gender, maximal exercise brachial SBP and heart rate. Brachial and central BP were measured at rest and immediately post-exercise. Augmentation index (AIx), augmented pressure (AP; markers of wave reflection) and central SBP were recorded by radial tonometry. Results: Despite no significant differences between groups in maximal exercise brachial or central SBP, AIx and AP were significantly lower in T2DM patients (Table ). Exercise central SBP was inversely and independently associated with exercise AIx in the T2DM patients (β= -0.32; p=0.05) but not controls (β= -0.10; p=0.49). The presence of T2DM was also identified as a weak but significant independent determinant of exercise AIx (β= -0.19) and central SBP (β= 0.10; p&lt;0.05 both). Conclusions: Patients with T2DM have 1) a paradoxical reduction in wave reflection at maximal exercise and 2) a significant inverse association between wave reflection and exercise central SBP that is not observed in controls. The reduced reflected pressure waves may indicate an increase in peripheral vasodilation to offset high exercise central BP. Exercise hemodynamics in T2DM patients and controls

Augmentation Index and Central Aortic Stiffness in Middle-Aged to Elderly Individuals

Increased aortic stiffness contributes to systolic hypertension and increased cardiovascular risk. The augmentation index (AI), ie, the percentage of central pulse pressure attributed to reflected wave overlap in systole, was proposed as a noninvasive indicator of increased arterial stiffness. We evaluated this hypothesis by investigating relations between AI and other direct measures of aortic stiffness. Tonometric carotid- and femoral-pressure waveforms, Doppler aortic flow, and aortic-root diameter were assessed in 123 individuals with uncomplicated systolic hypertension and 29 controls of comparable age and sex. Carotid-femoral pulse-wave velocity (PWV) was assessed from the carotid-femoral time delay and body-surface measurements. Aortic PWV was assessed from the ratio of the upstroke of carotid pressure and aortic flow velocity and was used to calculate proximal aortic compliance as [aortic area]/[1.06 x (aortic PWV)(2)]. Partial correlations (adjusted for age, sex, presence of hypertension, height, weight, and systolic ejection period) showed no association between AI and carotid-femoral PWV (R = -0.05, P = .54). The AI was significantly though weakly related directly with aortic compliance (R = 0.21, P = .012) and inversely with aortic PWV (R = -0.198, P = .017). However, higher stiffness (lower compliance and higher PWV) was associated with lower AI. Increased AI is not a reliable surrogate for increased aortic stiffness. Decreasing AI with decreasing compliance (increasing aortic stiffness) may be attributable to impedance matching and reduced wave reflection at the interface between the aorta and the muscular arteries.