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Arterial Stiffness and Pulse Wave Velocity in Hypertension: A Literature Review

1. Introduction

Arterial stiffness is increasingly recognized as a central mechanism in the pathogenesis of hypertension and a powerful independent predictor of cardiovascular (CV) morbidity and mortality. It reflects structural and functional deterioration of the arterial wall — primarily the loss of elastic fibres and their replacement by less distensible collagen — causing large elastic arteries to lose their cushioning function. The most widely used non-invasive measure of arterial stiffness is carotid-femoral pulse wave velocity (cf-PWV), while the augmentation index (AIx) serves as a complementary surrogate of wave reflection. Together, these indices provide important clinical information that extends beyond conventional brachial blood pressure (BP) measurement. This review synthesises current evidence on the role of arterial stiffness in hypertension, its assessment methods, age- and gender-related patterns, pharmacological modulation, and the challenges of measurement standardisation.

2. Pathophysiology of Arterial Stiffness in Hypertension

Arterial stiffness develops from structural changes in large elastic arteries, including fragmentation of elastin fibres, collagen cross-linking, smooth muscle cell changes, and calcification. Factors strongly associated with arterial stiffening include ageing, hypertension, diabetes mellitus, chronic kidney disease (CKD), smoking, and high sodium intake (Brenner and Rector's The Kidney).
The classical view held that arterial stiffness was a consequence of sustained elevated BP — chronic pulsatile mechanical load fractures elastin and recruits stiffer collagen fibres. However, emerging evidence suggests a bidirectional or even reverse relationship. Data from the Framingham Heart Study demonstrated that markers of arterial stiffness (cf-PWV and forward pressure wave amplitude) were associated with a 30–60% increased risk for incident hypertension over 7 years of follow-up, while baseline BP levels were not significantly associated with future changes in arterial stiffness (Brenner and Rector's The Kidney). Diaz et al. (2018) similarly noted that differences in PWV between young hypertensive and normotensive patients support the hypothesis, first proposed by Simon and Levenson in the 1980s, that arterial damage may precede the development of hypertension — a concept subsequently reinforced by findings from the Framingham Study and recent epidemiological data.

3. Pulse Wave Velocity: Gold Standard Measurement

PWV is considered the gold standard for measuring arterial stiffness due to its simplicity, accuracy, reproducibility, and predictive value (Diaz et al., 2018; Shimizu & Kario, 2008). It is calculated as the distance between two arterial recording sites divided by the transit time of the pulse wave. Carotid-femoral PWV (cf-PWV) is the most validated method, reflecting predominantly aortic stiffness, which is the haemodynamically most relevant segment.
The traditional mechanism by which increased PWV predicts CV events operates through wave reflection: faster PWV causes the reflected pressure wave to return to the central circulation before the end of systole, augmenting central systolic BP, increasing left ventricular (LV) afterload, and reducing diastolic pressure, thereby impairing coronary perfusion. However, more recent analyses emphasise that increased amplitude of the forward wave and increased characteristic impedance of the proximal aorta also contribute substantially; the relative contribution of wave reflection to age-dependent pulse pressure change has been estimated at only 4–11% (Brenner and Rector's The Kidney).
Multiple meta-analyses confirm the prognostic value of PWV. Ben Shlomo et al. (2014), cited by Diaz et al. (2018), showed in an individual participant meta-analysis of 17,635 subjects that aortic PWV is a stronger risk factor among younger individuals. Vlachopoulos et al. (2010) demonstrated in a systematic review and meta-analysis that arterial stiffness predicts CV events and all-cause mortality independently of other risk factors.

4. Reference Values and Age-Related Changes in PWV

Establishing population-specific reference values for PWV is critical, given that a single threshold (10 m/s) lacks age-sensitivity. Diaz et al. (2018) conducted a cross-sectional population-based study in Tandil, Argentina, enrolling 1,079 patients divided into normotensive (NT, n=780) and hypertensive (HT, n=299) groups, with careful exclusion of confounding risk factors. Mean aortic PWV in the NT group was 6.85 ± 1.66 m/s, increasing linearly with age (R²=0.62, p<0.05). A critical inflection point was observed at 50 years of age: PWV was significantly higher in patients over 50 years versus younger patients (8.35 vs. 5.92 m/s, p<0.001). The rate of PWV increase was 0.44 m/s per decade in normotensives compared with 0.93 m/s per decade in hypertensives (p<0.001).
These Argentine reference values are notably lower than European reference values, particularly at the 90th percentile in patients older than 60 years (Argentine vs. European difference: −2.59 to −2.7 m/s, p<0.05). This underscores the need to normalise PWV reference values according to ethnicity and population, as lifestyle and CV risk profiles significantly influence arterial stiffness (Diaz et al., 2018). Using the single cut-off of 10 m/s, only 3.72% of apparently normal patients and 11.7% of hypertensive patients would be classified as having elevated PWV — demonstrating that a single threshold misses a substantial proportion of individuals with true arterial ageing.

5. Impact of Isolated Hypertension on Arterial Stiffness

Diaz et al. (2018) uniquely investigated the effect of isolated, untreated hypertension as the sole risk factor on PWV — an aspect previously understudied. Mean PWV in hypertensive patients was 8.04 ± 1.8 m/s, significantly higher than normotensives (p<0.001) across all age groups. Even in the youngest patients (<20 years), hypertensives showed significantly higher PWV than normotensive counterparts, indicating early impairment of arterial compliance before end-organ damage is clinically apparent.
Multivariate regression analysis confirmed that PWV is independently related to age and mean BP, but not to heart rate. Correcting for mean BP eliminated the difference in PWV between NT and HT groups, suggesting that the haemodynamic elevation in BP (rather than a structural difference per se) partly mediates the stiffness difference. Nevertheless, the greater rate of PWV increase per decade in hypertensives implies that sustained BP elevation accelerates arterial wall structural deterioration, especially after age 50 — a period of convergent vascular ageing and hypertension-driven stiffening.

6. Augmentation Index: Physiology, Measurement, and Clinical Relevance

The augmentation index (AIx) is defined as the ratio of the augmented pressure (AP) to pulse pressure (PP): AIx (%) = AP/PP × 100, where AP represents the incremental systolic pressure attributable to the reflected wave returning before the end of systole (Shimizu & Kario, 2008; Papaioannou et al., 2019). Unlike PWV, which primarily reflects arterial wall stiffness, AIx captures the functional consequence of wave reflection, incorporating both the velocity of transmission and the amplitude of the reflected wave.
AIx is influenced by multiple factors:
  • Arterial stiffness: stiffening increases PWV, causing earlier return of reflected waves
  • Body height: shorter individuals have reflecting sites closer to the heart, increasing AIx
  • Heart rate: higher rates shorten ejection duration, delaying the reflected wave relative to the cardiac cycle and reducing AIx (hence the importance of heart rate correction, expressed as AIx@75 — AIx adjusted to 75 bpm)
  • Peripheral vascular tone: vasodilators reduce wave reflection amplitude
  • Age and sex: AIx increases steeply in younger subjects and reaches a plateau in older age (Shimizu & Kario, 2008)
Importantly, AIx is higher in women than in men even after adjusting for height, a sex difference that persists across populations and likely reflects additional hormonal or structural vascular determinants (Shimizu & Kario, 2008). This contrasts with PWV, for which Diaz et al. (2018) found no significant gender difference in either normotensive or hypertensive populations.
The non-linear age-AIx relationship is a clinically important feature: AIx increases steeply from early to middle adulthood, more gradually from age 50–60, and then plateaus or even declines in elderly subjects. This plateau is partly explained by a distal shift of the effective reflecting site — as aortic stiffness increases disproportionately relative to peripheral arterial stiffness with ageing, the impedance mismatch diminishes, moving the major reflection point toward the periphery (Shimizu & Kario, 2008). This also means AIx may underestimate vascular deterioration in the elderly, and its clinical utility may be most prominent in younger individuals (McEniery et al., 2005, as cited by Shimizu & Kario).

7. AIx as a Predictor of Target Organ Damage and Cardiovascular Events

Multiple longitudinal studies confirm that AIx independently predicts adverse CV outcomes. London et al. (2001) demonstrated that a 10% increase in carotid AIx was associated with a hazard ratio of 1.48 for CV mortality and 1.51 for total mortality in end-stage renal disease (ESRD) patients. Weber et al. (2005) found that patients in the highest versus lowest AIx tertile had a hazard ratio of 1.80 for death/MI/clinical restenosis after percutaneous coronary intervention. Chirinos et al. (2005) reported a hazard ratio of 1.28 per 10% increase in invasive aortic AIx for major adverse cardiac events (MACE) in patients undergoing coronary angiography (Shimizu & Kario, 2008, Table 1).
AIx has also been associated with target organ damage including:
  • Left ventricular hypertrophy in normotensives, ESRD patients, and essential hypertensives
  • Carotid intima-media thickness (a surrogate of atherosclerosis)
  • Coronary artery disease severity
  • Urinary albumin excretion and diabetic retinopathy — suggesting microvasular involvement (Shimizu & Kario, 2008, Table 2)
Santos et al. (2021) extended this evidence to paediatric populations, finding that AIx@75 is an independent predictor of future cardiovascular events and all-cause mortality even in healthy children and adolescents, and is increased in conditions such as arterial hypertension, CKD, diabetes, asthma, and obesity.

8. AIx Reference Values in Children and Adolescents

Santos et al. (2021) conducted a cross-sectional observational study of 134 healthy Brazilian children and adolescents (ages 9–19 years) from Belo Horizonte, using the Mobil-O-Graph device to assess AIx@75. Key findings include:
  • Mean AIx@75 in the total sample was 22.21 ± 7.96%, with no significant difference between males (22.60±8%) and females (21.80±7.97%)
  • Mean PWV ranged from 4.50–4.59 m/s, similar to values reported by Hivédgi et al. in children aged 3–18 years
  • AIx@75 correlated negatively with height across all groups — consistent with the known inverse relationship between body height and wave reflection distance
  • AIx@75 correlated inversely with systolic volume (SV) across all subgroups, and positively with total vascular resistance (TVR)
  • Independent predictors of AIx@75 in the whole sample (R²=80.47%) were: age, peripheral diastolic BP, mean arterial pressure, pulse pressure amplification (PPA), SV, cardiac index, and PWV
  • PPA (the pPP/cPP ratio) was a key predictor in most subgroups except males; reductions in PPA are associated with ageing, hypertension, organ damage, and mortality, making it a sensitive early marker
This study provides the first AIx@75 reference equations for Brazilian children and adolescents stratified by sex and age, enabling early detection of subclinical atherosclerosis and objective assessment of vascular therapeutic effects in this population.

9. Device Comparability and Measurement Standardisation

A critical methodological challenge in the field is the lack of interchangeability between devices measuring central AIx. Papaioannou et al. (2019) compared AIx measurements from three commercially used devices — Arteriograph (TensioMed, oscillometry, cuff-based), Complior (Alam Medical, tonometry, direct carotid recording), and Mobil-O-Graph (IEM GmbH, oscillometry with ARCSolver transfer function) — in 211 subjects undergoing diagnostic cardiovascular assessment.
The key findings were striking:
ComparisonMean BiasLimits of Agreement
Mobil-O-Graph vs Complior−2.1%−31.1% to +26.9%
Arteriograph vs Complior+12.9%−15.7% to +41.5%
Mobil-O-Graph vs Arteriograph−10.8%−43.9% to +22.3%
The Arteriograph significantly overestimated AIx compared to both Complior (p<0.001) and Mobil-O-Graph (p<0.001). The Mobil-O-Graph showed the closest agreement with Complior (lowest bias of −2.1%), though even this comparison yielded wide limits of agreement. Intraclass correlation coefficients were below 0.4 for all pairwise comparisons, indicating poor agreement. These differences are attributable to fundamental methodological divergences: acquisition technique (tonometry vs. oscillometry), arterial site of measurement (carotid vs. brachial), and pulse wave analysis algorithm (direct waveform analysis vs. transfer function).
This finding has direct implications for clinical practice and research: AIx values derived by different devices cannot be used interchangeably, and longitudinal monitoring of individual patients must employ the same device throughout. The field currently lacks an established gold standard for non-invasive central AIx estimation (Papaioannou et al., 2019).

10. Pharmacological Effects on AIx and Central BP

Different antihypertensive drug classes exert differential effects on AIx and central BP, even when equivalent reductions in brachial BP are achieved. This represents a clinically important distinction, as central BP more strongly predicts CV events than brachial BP (Roman et al., 2007; Williams et al., 2006, as cited by Shimizu & Kario, 2008).
ACE inhibitors (e.g., perindopril, captopril, enalapril), angiotensin receptor blockers (ARBs) (e.g., valsartan, eprosartan), calcium channel blockers (CCBs) (e.g., nitrendipine), and nitrates reduce AIx. Diuretics have minimal or no effect on AIx, while beta-blockers (e.g., atenolol) paradoxically increase AIx — likely because bradycardia shifts the reflected wave to arrive earlier in systole relative to the cardiac cycle, worsening systolic augmentation (Shimizu & Kario, 2008, Table 3).
Miyoshi et al. (2017) examined whether adding aliskiren (a direct renin inhibitor) or trichlormethiazide (a diuretic) to valsartan (ARB) produced different effects on radial AIx in 97 hypertensive patients over 24 weeks. Both combinations significantly reduced central BP and AI@75, with no significant between-group difference in AIx reduction (mean difference −2.3%, 95% CI −6.9% to 2.2%, p=0.31) or in arterial stiffness measured by the cardio-ankle vascular index (CAVI). However, the valsartan+aliskiren combination achieved significantly greater reduction in urinary 8-OHdG/Cr ratio (a marker of oxidative stress), suggesting a pleiotropic anti-oxidative benefit of dual RAS blockade beyond pure haemodynamic effects. This is consistent with the hypothesis that chronic oxidative stress is a major driver of vascular remodelling and arterial stiffening.
The CAFE study had previously established that CCB-based therapy reduces central aortic pressure and AIx more than beta-blocker-based therapy, despite identical brachial BP reduction — a finding with major implications for personalised antihypertensive selection (Williams et al., 2006, cited in Miyoshi et al. and Shimizu & Kario).

11. Non-Pharmacological Interventions

Non-pharmacological strategies also influence AIx. Endurance exercise has been consistently shown to reduce AIx and attenuate age-related increases in arterial stiffness. In contrast, isometric resistance training (e.g., bench pressing) increases AIx. Dietary sodium restriction significantly reduces carotid AIx. Smoking cessation is associated with linear reduction of AIx proportional to cessation duration (Shimizu & Kario, 2008). These observations support lifestyle modification as a meaningful intervention target for vascular ageing, particularly in younger patients where the clinical benefit of AIx reduction is likely greatest.

12. Synthesis and Clinical Implications

The convergent evidence from these studies supports several key clinical conclusions:
  1. Arterial stiffness is both a cause and consequence of hypertension, with a bidirectional relationship whose relative dominance shifts across the lifespan — in younger patients, stiffness may precede and drive hypertension, while in older patients, chronic hypertension further accelerates stiffening.
  2. PWV and AIx provide complementary information: PWV primarily reflects structural wall stiffness and is the gold standard for arterial ageing assessment; AIx captures the haemodynamic consequences of wave reflection and is more sensitive to vasomotor and pharmacological changes, particularly in younger individuals.
  3. Age- and population-specific reference values are essential: a single PWV cut-off of 10 m/s is clinically inadequate and will miss a significant proportion of patients with elevated arterial stiffness, particularly in younger age groups and non-European populations (Diaz et al., 2018).
  4. Hypertension amplifies the age-dependent increase in PWV at a rate more than double that of normotensives (0.93 vs. 0.44 m/s per decade), and this acceleration begins even in adolescence — underscoring the value of early detection and treatment.
  5. Device standardisation remains an unresolved challenge: AIx measurements cannot be compared across different devices, and no gold standard currently exists (Papaioannou et al., 2019). Longitudinal studies and clinical monitoring require consistent use of a single validated device.
  6. Antihypertensive drug selection matters beyond BP reduction: CCBs, ACE inhibitors, and ARBs favourably reduce central BP and AIx; beta-blockers worsen AIx despite adequate brachial BP control, a distinction with prognostic significance.

References

  1. Diaz A, Tringler M, Wray S, Ramirez AJ, Cabrera Fischer EI. The effects of age on pulse wave velocity in untreated hypertension. J Clin Hypertens. 2018;20:258–265.
  2. Santos LM, Gomes IC, Pinho JF, Neves-Alves CM, Magalhães GS, Campagnole-Santos MJ, Rodrigues-Machado MG. Predictors and reference equations for augmentation index, an arterial stiffness marker, in healthy children and adolescents. Clinics (Sao Paulo). 2021;76:e2350.
  3. Shimizu M, Kario K. Role of the augmentation index in hypertension. Ther Adv Cardiovasc Dis. 2008;2(1):25–35.
  4. Papaioannou TG, Thymis J, Benas D, et al. Measurement of central augmentation index by three different methods and techniques: Agreement among Arteriograph, Complior, and Mobil-O-Graph devices. J Clin Hypertens. 2019;21:1386–1392.
  5. Miyoshi T, Murakami T, Sakuragi S, et al. Comparable effect of aliskiren or a diuretic added on an angiotensin II receptor blocker on augmentation index in hypertension: a multicentre, prospective, randomised study. Open Heart. 2017;4:e000591.
  6. Brenner and Rector's The Kidney, 2-Volume Set. Section: Arterial Stiffness in Hypertension, pp. 2052–2053.
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