Evaluation of the early stage of carotid atherosclerosis using the vascular response to nitroglycerin and high-resolution ultrasonography

Simple Models of Complex Mechanics for Improved Hypertension Care: Learning to De-stiffen Arteries

Arteries can stiffen via different mechanisms due to the distending effects of blood pressure, the extracellular (ECM) and vascular smooth muscle cells (VSMC). This short review discusses how these simple models can be applied to the complex biomechanics of arteries to gain physiological insight into why an individual's arteries are stiff and identify new therapeutic strategies. In the Multi-Ethnic Study of Atherosclerosis, the important question of whether arteries stiffen with aging due to load-dependent or structural stiffening was investigated. Structural stiffening was consistently observed with aging, but load-dependent stiffening was highly variable. Importantly, the high load-dependent stiffness was associated with future cardiovascular disease events, but structural stiffness was not. Clinical studies in older, hypertensive adults surprisingly show that decreasing vascular smooth muscle tone can cause clinically significant increases in arterial stiffness. To understand this paradox, the author developed a model simple enough for clinical data but with biologically relevant extracellular matrix (ECM) and vascular smooth muscle cell (VSMC) stiffness parameters. The effect of VSMC tone on arterial stiffness depends on the ECM-VSMC stiffness ratio. Future research is needed to develop a framework that incorporates both the blood pressure dependence of arterial stiffness and the VSMC-ECM interaction on hemodynamics. This could result in personalized arterial stiffness treatments and improved CVD outcomes. The subtitle of this review is "Learning to De-Stiffen Arteries" because our results have so far only shown that we can acutely make arteries stiffer. We are optimistic though that the findings and the analytic techniques covered here will be one of the many steps along the path of the arterial stiffness research community learning how to de-stiffen arteries.

Exercise increases arterial stiffness independent of blood pressure in older Veterans

BACKGROUND

Exercise-induced changes in arterial function could contribute to a hypertensive response to exercise (HRE) in older individuals. We performed the present analysis to define the acute arterial stiffness response to exercise in ambulatory older adults.

METHODS

Thirty-nine Veterans (>60 years old), without known cardiovascular disease, participated in this study, including 19 Veterans who were hypertensive (70.8 ± 6.8 years, 53% women) and 20 Veterans who were normotensive (72.0 ± 9.3 years, 40% women). Arterial stiffness parameters were measured locally with carotid artery ultrasound and regionally with carotid-femoral pulse wave velocity (cfPWV) before and during the 10 min after participants performed a Balke maximal exercise treadmill stress test.

RESULTS

The arterial stiffness response to exercise was similar for control and hypertensive participants. At 6 min postexercise, cfPWV was significantly increased (Δ1.5 ± 1.9 m/s, P  = 0.004) despite mean blood pressure (BP) having returned to its baseline value (Δ1 ± 8 mmHg, P  = 0.79). Arterial mechanics modeling also showed BP-independent increases in arterial stiffness with exercise ( P  < 0.05). Postexercise cfPWV was correlated with postexercise SBP ( r  = 0.50, P  = 0.004) while baseline cfPWV ( r  = 0.13, P  = 1.00), and postexercise total peripheral resistance ( r  = -0.18, P  = 1.00) were not.

CONCLUSION

In older Veterans, exercise increases arterial stiffness independently of BP and the arterial stiffness increase with exercise is associated with increased postexercise SBP. BP-independent increases in arterial stiffness with exercise could contribute to a HRE in older adults.

Effects of nitroglycerin-induced vasodilation on elastic and muscular artery stiffness in older Veterans

Vascular smooth muscle tone may play an important role in the physiology of increased arterial stiffness that occurs with aging. This study evaluated the impact of smooth muscle tone on arterial stiffness in older individuals following nitroglycerin-induced vasodilation in elastic and muscular arteries. Forty older Veterans (≥60 years old) without known cardiovascular disease were included in this study. Twenty Veterans were included as hypertensive participants (70.8 ± 6.6 years, 10 females), and 20 were included as normotensive controls (72.0 ± 9.3 years, 8 females). Nitroglycerin (NTG)-induced changes in arterial stiffness were measured locally with vascular ultrasound in the carotid and brachial arteries and regionally by carotid-femoral pulse wave velocity (cfPWV) with tonometry. With NTG treatment, both hypertensive participants and normotensive controls Veterans showed increased carotid PWV (6.4 ± 1.3 m/s to 7.2 ± 1.4 m/s, Δ 0.8 ± 1.1 m/s, p = 0.007) and cfPWV (8.6 ± 1.9 m/s to 9.5 ± 2.4 m/s, Δ 0.9 ± 2.3 m/s, p = 0.020) but did not show changes in brachial PWV (11.2 ± 2.4 m/s to 11.1 ± 2.2 m/s, Δ -0.2 ± 2.5 m/s, p = 0.72). The carotid artery was dilated more in control participants than hypertensive Veterans (Δ 0.54 ± 0.19 mm vs. 0.42 ± 0.12 mm, p = 0.022). Brachial artery dilation was similar between the two groups (Δ 0.55 ± 0.26 mm vs. 0.51 ± 0.20 mm, p = 0.46). In older Veterans without known cardiovascular disease, NTG-induced vasodilation increased elastic artery stiffness but did not change muscular artery stiffness. Increased central arterial stiffness and a decrease in the arterial stiffness gradient could offset some of the benefits of lowering blood pressure in older patients who are prescribed vasodilators as an antihypertensive therapy. Elastic artery stiffening with vasodilation warrants further investigation, as it may be important for antihypertensive medication selection and influence CVD development.

A systematic literature review of the effect of carotid atherosclerosis on local vessel stiffness and elasticity

OBJECTIVE

This systematic literature review sought to determine the effects of carotid atherosclerotic plaque on local arterial stiffness.

METHODS

MedLine, EMBASE, and grey literature were searched with the following term: ("atherosclerosis" or "carotid atherosclerosis" or "carotid artery disease" or "carotid plaque") AND ("distensibility" or "elasticity" or "stiffness" or "compliance") NOT ("pulse wave velocity" or "PWV" or "carotid-ankle" or "ankle-brachial" or "augmentation index" or "cardio-ankle" or "CAVI" or "flow mediated dilation" or "FMD"). Results were restricted to English language articles reporting local arterial stiffness in human subjects with carotid atherosclerosis.

RESULTS

Of the 1466 search results, 1085 abstracts were screened and 191 full-text articles were reviewed for relevance. The results of the 50 studies that assessed some measure of carotid arterial elasticity or stiffness in patients with carotid plaque were synthesized and reviewed.

DISCUSSION

A number of different measures of carotid elasticity were found in the literature. Regardless of which metric was used, the majority of studies found increased carotid stiffness (or decreased distensibility) to be associated with carotid plaque presence, the degree of atherosclerosis, and incident stroke.

CONCLUSION

Carotid artery mechanics are influenced by the presence of atherosclerotic plaque. The clinical applicability of carotid elasticity measures may be limited by the lack of reference values and standardized techniques.

Relationship between Nitrate-Induced Headache and Coronary Artery Lesion Complexity

OBJECTIVE

The aim of the present study was to investigate the association between nitrate-induced headache (NIH) and the complexity of coronary artery lesions in patients with stable coronary artery disease (CAD).

SUBJECTS AND METHODS

Two hundred and seventy-five patients with anginal chest pain who underwent coronary angiography were enrolled in the present study. NIH was defined as the presence of headache due to nitrate treatment (isosorbide mononitrate 40 mg) after excluding confounding factors. Coronary artery lesion complexity was assessed by the SYNTAX score (SXscore) using a dedicated computer software system.

RESULTS

The mean SXscore was lower in the patients with NIH than in patients without NIH (7.3 ± 5.2 vs. 14.4 ± 8.5, respectively; p < 0.001). Additionally, patients with NIH had a lower rate of multivessel disease compared with those without NIH (the mean number of diseased vessels was 1.5 ± 0.7 and 2.0 ± 07, respectively; p < 0.001). In multivariate analysis, increasing age (p = 0.02) and headache (p = 0.001) were found to be independent determinants of SXscore.

CONCLUSION

The present study demonstrated an independent inverse association between NIH and SXscore. The NIH could provide important predictive information about coronary artery lesion complexity in patients with stable CAD.

WISE 2005: responses of women to sublingual nitroglycerin before and after 56 days of 6° head-down bed rest

This study tested the hypothesis that cardiovascular effects of sublingual nitroglycerin (NG) would be exaggerated after 56 days of 6° head-down bed rest (HDBR) in women, and that an aerobic and resistive exercise countermeasure (EX, n = 8) would reduce the effect compared with HDBR without exercise (CON, n = 7). Middle cerebral artery maximal blood flow velocity (CBFV), cardiac stroke volume (SV), and superficial femoral artery blood flow (Doppler ultrasound) were recorded at baseline rest and for 5 min following 0.3 mg sublingual NG. Post-HDBR, NG caused greater increases in heart rate (HR) in CON compared with EX (+24.9 ± 7.7 and +18.8 ± 6.6 beats/min, respectively, P < 0.0001). The increase in HR combined with reductions in SV to maintain cardiac output. Systolic, mean, and pulse pressures were reduced 5-10 mmHg by NG, but total peripheral resistance was only slightly reduced at 3 min after NG. Reductions in CBFV of -12.5 ± 3.8 cm/s were seen after NG, but a reduction in the Doppler resistance index suggested dilation of the middle cerebral artery with no differences after HDBR. The femoral artery dilated with NG and blood flow was reduced ∼50% with the appearance of large negative waves suggesting a marked increase in downstream resistance, but there were no effects of HDBR. In general, responses of women to NG were not altered by HDBR; the greater increase in HR in CON but not EX was probably a consequence of cardiovascular deconditioning. These results contrast with the hypothesis and a previous investigation of men after HDBR by revealing no change in cardiovascular responses to exogenous nitric oxide.

Diagnostic value of nitroglycerin-induced headache as a negative predictor of coronary atherosclerosis

The purpose of the present study was to clarify the possible relationship between nitroglycerin (NTG)-induced headache and both vascular functional and organic atherosclerosis. The study included 96 patients with NTG-induced headache (group I: 54.7±9.5 years, 52 males) and 204 patients without headache (group II: 58.1±9.1 years, 127 males) who suffered from new-onset chest pain. Flow-mediated dilation and nitroglycerin-mediated dilation were significantly greater in group I than in group II (8.8±4.1% vs. 7.1±3.5%, p=0.001, and 23.1±7.3% vs. 17.1±11.8%, p<0.001, respectively). The carotid intima-media thickness was significantly smaller in group I than in group II (0.55±0.15 mm vs. 0.67±0.22 mm, p=0.001). Heart-carotid pulse wave velocity was significantly lower in group I than in group II (784.5±160.1 m/s vs. 979.1±215.6 m/s, p=0.003). In the multiple regression analysis, the absence of NTG-induced headache was a predictor of coronary artery disease (CAD) (odds ratio: 17.89, 95% confidence interval: 7.89-40.02, p<0.001). NTG-induced headache developed more frequently in patients with normal coronary arteries or minimal CAD than in patients with obstructive CAD. The presence of NTG-induced headache might be helpful and provide additional information in evaluating patients with chest pain syndrome.

Headache response to glyceryl trinitrate in patients with and without obstructive coronary artery disease

OBJECTIVES

To examine the hypothesis that glyceryl trinitrate (GTN) may cause headache in patients with normal coronary arteries more often than in patients with obstructive coronary artery disease (CAD). This simple assessment may aid clinicians in the initial evaluation of chest pain syndrome and possible CAD.

PATIENTS AND METHODS

118 patients (66 men and 52 women) with new onset of chest pain were enrolled in this study. Patients were excluded from the study if they had a history of chronic headache, long term nitrates use, or any coronary artery procedures. Mean age of the patients was 62.5 years. Coronary angiography was performed within one month of GTN administration with the usual clinical indications such as recurrent chest pain, abnormal ECG, or abnormal results of stress tests. Thirty patients had normal coronary arteries or minimal or non-obstructive CAD. Eighty eight patients had obstructive CAD defined as luminal narrowing greater than 50% in any one or more of the left or right coronary arteries or their major branches. All the patients had a varying degree of relief of chest pain with GTN administration within 10 minutes. 36% of patients reported significant headache after GTN administration.

RESULTS

In patients with normal coronary arteries or minimal CAD, 73% had significant headache caused by sublingual GTN. In patients with obstructive CAD, only 23% had significant headache after GTN use (p < 0.001). There were no differences in patients' sex and vascular risk factors concerning the frequency of headache in patients with or without obstructive CAD.

CONCLUSIONS

GTN causes significantly more frequent headache episodes in patients with normal coronary arteries or minimal CAD than in patients with obstructive CAD. This unique finding may provide clinicians with an additional tool for the differential diagnosis of patients with chest pain syndrome.

Association between plasma homocysteine concentration and carotid atherosclerosis in hemodialysis patients

Accelerated atherosclerosis is a major risk for uremic patients undergoing long-term hemodialysis. Because hyperhomocysteinemia may influence this condition, 168 such patients were examined for a possible association between plasma total homocysteine concentration (tHcy) and conventional cardiovascular risk factors. Generalized atherosclerosis was indicated by excessive intimal-medial wall thickness (IMT) of the extracranial carotid artery as measured by B-mode ultrasonography. The results documented tHcy in these patients of 33.0+/-16.9 micromol/L, a significantly higher amount than that of healthy subjects (11.0+/-3.1 micromol/L, p<0.0001). The patients' carotid maximum IMT was 1.79+/-1.16 mm. In multiple regression analyses with forward elimination procedure, carotid maximum IMT was clearly related to age (r = 0.417, p<0.0001), systolic blood pressure (r = 0.262, p = 0.0043), smoking (r = 0.177, p = 0.0076), duration of hemodialysis (r = 0.083, p = 0.0045), and tHcy (r = 0.195, p = 0.0021). These 5 factors accounted for 36.0% of the variation in carotid maximum IMT. Factors determined as unrelated were male gender, diastolic blood pressure, body mass index, total and HDL cholesterol, triglyceride, lipoprotein(a), uric acid, calcium, inorganic phosphate, and parathyroid hormone. Therefore hyperhomocysteinemia, along with advanced age, systolic hypertension and smoking aggravates atherosclerosis in chronic uremic patients.