Dr. James Manos (MD)
February 20, 2016
Arterial compliance and risk of heart disease
Definition of arterial compliance
The classic definition by Spencer and Denison of compliance (C) is the change in arterial blood volume (ΔV) due to a given change in arterial blood pressure (ΔP), i.e., C = ΔV/ΔP (5).
Arterial compliance is an index of the elasticity of large arteries such as the thoracic aorta. Arterial compliance is an important cardiovascular risk factor. Compliance diminishes with age and menopause. Arterial compliance is measured by ultrasound as a pressure (carotid artery) and volume (outflow into the aorta) relationship (8).
Arterial Compliance is an action in which an artery yields to pressure or force without disruption. A measure of arterial compliance is used as an indication of arterial stiffening. An increase in age and systolic pressure is accompanied by decreased arterial compliance (3).
Arterial compliance is the relationship between changes in transmural pressure and the volume of an arterial segment, where high compliance signifies substantial changes in volume per change in transmural pressure. The relation between changes in transmural pressure and volume is far from linear, as compliance increases progressively with decreases in blood pressure. A change in compliance could indicate static changes in arterial wall composition, i.e., the relation between elastic and collagen fibers and accumulation of disease-related deposits or dynamic changes caused by alterations in muscular tone (13).
Arterial compliance and cardiovascular risk
Evidence has accumulated for several years that protecting endothelium is key to reducing cardiovascular (CV) disease risk. Endothelial dysfunction reduces compliance or increases arterial stiffness, particularly in the smaller arteries. This abnormality is characteristic of patients with hypertension but may also be seen in normotensive (with normal blood pressure) patients before the appearance of clinical disease. Reduced arterial compliance is also seen in patients with diabetes and in smokers and is part of a vicious cycle that further elevates blood pressure, aggravates atherosclerosis (hardening of the arteries), and leads to increased CV risk. Arterial compliance can be measured by several techniques, most invasive or otherwise not clinically appropriate. Pulse contour analysis is a newly developed noninvasive method that allows for easy, in-office measurement of arterial elasticity to identify patients at risk for CV events before the disease becomes clinically apparent (2).
Increasing arterial stiffness and decreasing arterial compliance are now thought to occur at the beginning of the hypertension disease process. Reduced arterial compliance is associated with isolated systolic blood pressure elevations. Many clinical trials of isolated systolic hypertension provide indirect evidence that improving compliance lowers the risk of cardiovascular disease. The Heart Outcomes Prevention Evaluation was a primary prevention study of the effect of an angiotensin-converting enzyme (ACE) inhibitor in subjects who were not necessarily hypertensive but were at risk for cardiovascular events. With minimal blood pressure lowering, Ramipril therapy provided significant risk reduction in all primary endpoints – overall mortality, stroke, myocardial infarction, and cardiovascular death. In conclusion, angiotensin-converting enzyme (ACE) inhibitors restore endothelial cell balance to improve arterial compliance. Thus, they can provide benefits beyond lowering blood pressure (11).
Abnormalities of peripheral arterial compliance are clinically useful markers of atherosclerosis and risk of vascular events. Computer-controlled pulse volume recordings (air plethysmography) can efficiently and accurately assess local peripheral arterial compliance in the clinic. A study investigated the relationship between clinical cardiovascular risk factors, a surrogate of atherosclerotic burden, and peripheral arterial compliance in the thigh and calf determined by quantification of local pulse volume recordings in patients undergoing coronary angiography. The results showed that pulse volume recordings detected decreased local arterial compliance in the thigh associated with a history of hypertension, diabetes mellitus, and hyperlipidemia. In the calf, this arterial compliance measure was associated with a history of hypertension and diabetes mellitus. Females had lower arterial compliance than males in the thigh and calf. Limited evidence of lower arterial compliance in the thigh was found for those with obesity. This procedure also demonstrated that subjects with multiple cardiovascular risk factors had lower arterial compliance in the thigh than subjects with no or 1 risk factor. In conclusion, peripheral arterial compliance determined by air plethysmography is strongly associated with standard cardiovascular risk factors. The non-invasive measurement of local arterial compliance by regional pulse volume recording may be a useful adjunct for cardiovascular risk stratification early in the course of the disease and for monitoring vascular response to therapy (12).
Measurement of arterial compliance
Measurement of arterial compliance is of interest in evaluating patients with atherosclerosis and other diseases that affect the vessels. The most used method reflecting arterial compliance is pulse wave velocity measurement. However, the pulse wave velocity method measures compliance at ambient transmural pressures and is affected by the actual blood pressure and the rate of pressure change. Another commonly used method employs the echo-tracking technique to measure the arterial diameter simultaneously with continuous blood pressure monitoring. This method makes it possible to calculate arterial compliance for continuous pressure values between the diastole and the systole. The volume-oscillometry method is based on the fact that the artery can collapse at the end of the diastole by an occlusive cuff. At the same time, it remains open in a pressure-dependent manner during the rest of the cardiac cycle.
Changes in the arterial volume are transmitted to the cuff, where it induces a measurable difference in pressure. Hence, the volume of the artery can be calculated at different values of transmural pressures. Using this method on normal subjects has shown that arterial compliance decreases with age and that females have lower compliance than males primarily due to a smaller diameter of their arteries. It has also been shown that patients with essential (diastolic) hypertension have compliances that are higher or equal to those of healthy subjects and that patients with systolic hypertension have lower arterial compliances than healthy subjects. The former finding contrasts with pulse wave velocity measurements, where diastolic hypertension was associated with low arterial compliance (13).
In a study, seven classic and recently proposed methods used to estimate total arterial compliance have been evaluated for accuracy and applicability in different physiological conditions. The results showed that the methods based on the two-element windkessel (WK) model are more accurate than those based on the three-element WK model. The classic exponential decay and the diastolic area method yield substantially comparable results, and their compliance estimates are correct within 10% except at high heart rates. The later part of the diastole (from the time that the systolic pressure wave has reached all peripheral beds) gives the best results. The newly proposed two-area and pulse pressure methods, based on the two-element WK model, are accurate (errors, generally, < 10%) and can be applied to other locations in the arterial tree where the decay time and area method can’t. Methods based on the three-element WK model consistently overestimate total arterial compliance (> or = 25%) (1).
In a study, arterial compliance was determined in eight healthy subjects and 23 patients with hypertension and vascular disease by two independent techniques: (a) with a plethysmography strain gauge (to measure pulsatile forearm volume changes as representing intra-arterial volume changes) and an automated sphygmomanometer system (to measure pulse pressure) and (b) calculation of the local pulse wave velocity and the dimension of the brachial artery measured by pulsed wave Doppler ultrasound. The results showed that arterial compliance measured by the plethysmographic technique and calculated from the pulse wave velocity was reduced in subjects with hypertension and vascular disease compared to healthy subjects. The good correlation validates the plethysmography technique to determine arterial compliance (14).
Arterial compliance is measured by ultrasound as a pressure (carotid artery) and volume (outflow into the aorta) relationship (8).
Abnormalities of peripheral arterial compliance are clinically useful markers of atherosclerosis and risk of vascular events. Local peripheral arterial compliance can be efficiently and accurately assessed in the clinic by computer-controlled pulse volume recordings (air plethysmography) (12).
Arterial stiffness is a significant contributor to cardiovascular diseases. Because current methods of measuring arterial stiffness are technically demanding, a study aimed to develop an effortless way of evaluating arterial stiffness using oscillometric blood pressure measurement. Blood pressure was conventionally measured in the upper left arm of 173 individuals using an inflatable cuff. Using the time series of occlusive cuff pressure and the amplitudes of pulse oscillations, the scientists calculated the local slopes of the curve between the decreasing cuff pressure and corresponding arterial volume. The whole pressure-volume curve was derived from the numerical integration of the local slopes.
The curve was fitted using an equation, and they identified a differential coefficient of the equation as an index of arterial stiffness (Arterial Pressure-volume Index, API). Using a vascular testing device, they also measured brachial-ankle (baPWV) PWV and carotid-femoral (cfPWV) PWV and compared the values with API. Furthermore, they assessed carotid arterial compliance using ultrasound images to compare with API. The study's results suggest that their method can merely and simultaneously evaluate arterial stiffness and blood pressure based on oscillometric blood pressure measurements (23).
Methods of attenuation of the reduction in arterial compliance
a) Exercise
A reduction in compliance of the large-sized cardiothoracic (central) arteries is an independent risk factor for the development of cardiovascular disease with advancing age. A study used cross-sectional and interventional approaches to determine the role of habitual exercise on the age-related decrease in central arterial compliance. The study concluded that regular aerobic endurance exercise attenuates age-related reductions in central arterial compliance and restore levels in previously sedentary healthy middle-aged and older men. This may be one mechanism by which regular exercise lowers the risk of cardiovascular disease in this population (6).
A study aimed to determine the effects of moderate resistance training and the combined resistance and aerobic training intervention on carotid arterial compliance. Resistance training has become a favorite exercise mode, but intense weight training is shown to stiffen carotid arteries. The study concluded that simultaneously performing aerobic exercise training could prevent the stiffening of carotid arteries caused by resistance training in healthy young men (9).
Exercise training elevates arterial compliance at rest, but the effects of acute exercise in this regard are unknown. A study investigated the impact of a single 30-minute bout of cycling exercise at 65% of maximal oxygen consumption on indexes of arterial compliance. Whole-body arterial compliance was determined noninvasively from simultaneous measurements of aortic flow. The carotid pressure was elevated at 0.5 hours post (after) exercise, followed by a decline to baseline 1 hour after exercise. Mean arterial pressure was unchanged; however, central systolic blood pressure was reduced post-exercise. Cardiac output was elevated via heart rate elevation after exercise, whereas stroke volume was constant. Total peripheral resistance was, therefore, reduced and would be expected to contribute to a height in arterial compliance. In conclusion, a single bout of cycling exercise increased whole-body arterial compliance by mechanisms that may relate to vasodilation (vessel dilation) (18).
Swimming is ideal for older adults because it includes minimum weight-bearing stress and decreased heat load. A study assessed if regular swimming exercise would decrease arterial blood pressure (BP) and improve vascular function. Forty-three otherwise healthy adults >50 years old with prehypertension or stage 1 hypertension and not on any medication were randomly assigned to 12 weeks of swimming exercise or attention time controls. The results showed that swimming exercise produced a 21% increase in carotid artery compliance. Flow-mediated dilation and cardiovagal baroreflex sensitivity improved after the swim training program. In conclusion, swimming exercise elicits hypotensive (blood pressure lowering) effects and improvements in vascular function in previously sedentary older adults (22).
Exercise which can improve muscle strength while not compromising arterial compliance, is especially needed for older adults. Tai Chi (an internal Chinese martial art) practitioners are known to have better than average arterial compliance and muscle strength. A single-blind randomized clinical trial was designed to establish a cause-and-effect relationship between Tai Chi training and increased arterial compliance and muscle strength. In the study, thirty-one elderly women were randomly assigned to receive either Tai Chi training or an education program, three sessions per week for 16 weeks. The study concluded that practicing Tai Chi (an internal Chinese martial art) can improve the eccentric knee extensor strength and arterial compliance of elderly women. Thus, Tai Chi may be a useful exercise choice to improve the cardiovascular health and muscle strength of the elderly (21).
Although acute high-intensity resistance exercise to exhaustion decreases arterial compliance and increases arterial stiffness, the effect of low-intensity resistance exercise (LRE) to exhaustion on arterial compliance and stiffness remains unknown. A study investigated the acute effects of LRE on arterial compliance and stiffness. Ten healthy individuals (age 26 ± 5 years) performed LRE (40 % of 1 repetition maximum) and control (CON: seated rest in the exercise room) trials on separate days in a randomized controlled crossover fashion. The LRE comprised three sets of bench presses to exhaustion with an inter-set rest period of 2 min.
In the CON trial, LRE was not performed. Carotid arterial compliance, the beta-stiffness index (via simultaneous B-mode ultrasound and applanation tonometry), carotid and brachial blood pressure, and heart rate were measured before and at 30 and 60 min after both trials. The results showed that carotid arterial compliance and the beta-stiffness index significantly increased and decreased, respectively, at 30 and 60 min after the LRE trials, but neither significantly differed after the CON trials. Carotid and brachial blood pressure and heart rate did not change at 30 and 60 min after both trials from baseline. The study concluded that the results suggest that low-intensity resistance exercise (LRE) acutely increases arterial compliance and decreases arterial stiffness (30).
b) Medications
Diabetes is associated with large stiff arteries, playing a vital role in the pathogenesis of vascular disease, and is the primary cause of mortality and morbidity with type 2 diabetes. Similarly, after menopause, women experience a dramatic increase in large artery stiffness and the rate of cardiovascular disease. Thiazolidinediones modulate glucose homeostasis and exhibit some potential antiatherogenic actions, the collective effects of which remain fully elucidated in humans. A randomized, double-blind, placebo-controlled study investigated whether rosiglitazone, the second member of the thiazolidinediones group, would improve blood pressure and arterial compliance, measured by distensibility index, in postmenopausal (after menopause) women with type 2 diabetes. In the study, 31 women with diabetes diagnosed 1–12 years prior were tested before and after 12 weeks of treatment with 4 mg rosiglitazone daily (n = 21 subjects) or matching placebo (n = 10 subjects).
The main findings of this study are that for postmenopausal women with type 2 diabetes, rosiglitazone improves glycemic control, reduces blood pressure, and increases compliance of large proximal arteries. Strict glycemic control delays the onset and moderates the progression of vascular complications. This may partly explain the increases in arterial compliance and reductions in blood pressure with rosiglitazone; however, rosiglitazone may improve cardiovascular parameters independently of glycemic changes. Decreased blood pressure and increased large proximal artery compliance may reduce the risk of coronary artery disease. In conclusion, rosiglitazone is an effective treatment to improve glycemic control (blood sugar control) and reduce the risk of cardiovascular disease in postmenopausal (after menopause) women with type 2 diabetes (24).
A study investigated the effect of amlodipine (an anti-hypertensive drug) on arterial compliance (AC), and the effect of atorvastatin on AC when given in combination with amlodipine. In the study, twenty-one consecutive hypertensive hyperlipidemic (with high blood lipids) patients were included. Patients were followed every month for 6 months (3 months of amlodipine therapy and 3 months of amlodipine and atorvastatin combination). The study concluded that amlodipine improves large and small arterial compliance (AC), and the beneficial effect of atorvastatin on small AC is additive to the effect achieved by amlodipine (25).
A study investigated the effect of amlodipine (an anti-hypertensive drug) on arterial compliance (AC), and the effect of atorvastatin on AC when given in combination with amlodipine. In the study, twenty-one consecutive hypertensive hyperlipidemic (with high blood lipids) patients were included. Patients were followed every month for 6 months (3 months of amlodipine therapy and 3 months of amlodipine and atorvastatin combination). The study concluded that amlodipine improves large and small arterial compliance (AC), and the beneficial effect of atorvastatin on small AC is additive to the effect achieved by amlodipine (25).
A study assessed whether a diuretic or an angiotensin-converting enzyme inhibitor (ACEI) based treatment can reduce arterial wall hypertrophy of a distal muscular, medium-sized artery—the radial artery—and the stiffness of a proximal large elastic artery—the common carotid artery. Large-artery wall thickness and stiffness are increased during sustained essential hypertension and contribute to the increased risk of complications. In the study, seventy-seven elderly hypertensive patients were randomized to receive 9 months of double-blind treatment with perindopril or the diuretic combination of hydrochlorothiazide plus amiloride after a 1-month placebo washout period. The study results indicate that in elderly hypertensive patients, angiotensin-converting enzyme inhibitor (ACEI) and diuretic combination-based treatments can reduce radial artery wall hypertrophy and improve carotid artery compliance (4).
Arterial stiffness is increased in chronic kidney disease (CKD). Intervention studies aimed at reducing arterial stiffness in dialysis patients have been disappointing. A study investigated the effect of pravastatin (a ΄΄statin΄΄ – a cholesterol-lowering agent), vitamin E, and homocysteine-lowering on arterial compliance and distensibility coefficients in mild-to-moderate CKD. The study concluded that in patients with mild-to-moderate chronic kidney disease (CKD), 18 months of treatment consisting of pravastatin, vitamin E, and homocysteine-lowering resulted in significant improvement of compliance and distensibility in the common carotid artery (CCA) and femoral artery (FA). Since pravastatin was used throughout the observation period, it remains unclear whether the beneficial effects are attributable solely to the ongoing impact of pravastatin treatment or if the additional interventions further slowed the progression of vascular stiffness (15).
Note: homocysteine may be lowered with folic acid, vitamin B6 (pyridoxine) & vitamin B12.
Arterial stiffening with increased pulse pressure is a leading risk factor for cardiovascular disease in the elderly. A study tested whether ALT-711, a novel non-enzymatic breaker of advanced glycation end-product crosslinks, selectively improves arterial compliance and lowers pulse pressure in older individuals with vascular stiffening. In the study, nine US centers recruited and randomly assigned subjects with resting arterial pulse pressures >60 mm Hg and systolic pressures >140 mm Hg to once-daily ALT-711 (210 mg; n=62 subjects) or placebo (n=31 subjects) for 56 days. The study concluded that ALT-711 improves total arterial compliance in aged humans with vascular stiffening. It may provide a novel therapeutic approach for this abnormality, which occurs with aging, diabetes, and isolated systolic hypertension (16).
c) Herbs & dietary supplements
A double-blind, placebo-controlled study investigated the effects of dietary fish oil supplementation on arterial wall characteristics in twenty patients with non-insulin-dependent diabetes mellitus. The study's results support the hypothesis that fish oils alter vascular reactivity and favorably influence arterial wall characteristics in patients with non-insulin-dependent diabetes mellitus. These direct vascular effects, expressed at the level of the vessel wall, may contribute to the cardioprotective (protective for the heart) actions of fish oil in humans (7).
The compliance or elasticity of the arterial system, an essential index of circulatory function, diminishes with increased cardiovascular risk. Conversely, systemic arterial compliance improves by eating fish and fish oil. A study tested the value of a high intake of alpha-linolenic acid (ALA, an omega-3 fatty acid), the plant precursor of fish fatty acids. Fifteen obese people with markers for insulin resistance ate, in turn, four diets of 4 weeks each: saturated/high fat (SHF), alpha-linolenic acid/low fat (ALF), oleic/low fat (OLF), and SHF. Daily intake of alpha-linolenic acid was 20 g from margarine products based on flax oil.
Systemic arterial compliance was calculated from aortic flow velocity and aortic root driving pressure. Systemic arterial compliance rose significantly to 0.78 +/- 0.28 with ALF; systemic arterial compliance with OLF was 0.62 +/- 0.19, lower than with ALF. Also, insulin sensitivity and HDL cholesterol diminished, and LDL oxidability increased with ALF. The marked rise in arterial compliance, at least with alpha-linolenic acid, reflected a rapid functional improvement in systemic arterial circulation despite increased LDL oxidability. Dietary omega-3 (n-3) fatty acids in flax oil thus confer a novel approach to improving arterial function (17).
Aortic stiffness predicts cardiovascular mortality and may be influenced by dietary fat composition. The hypothesis that plasma fat composition influences arterial stiffness and subsequent death was tested in a prospective study. A total of 174 randomly sampled non-diabetic participants aged 45 to 74 years were recruited from local populations, stratified by ethnicity and gender, and followed up for mortality. Aortic pulse wave velocity (PWV), blood pressure, and fatty acid composition of plasma lipids were measured at baseline. PWV was associated with increased cardiovascular mortality and inversely related to the proportions of docosahexaenoic (DHA; an omega-6 fatty acid) and arachidonic acid (AA; an omega-6 fatty acid) in plasma lipids.
Principal component analyses identified a cluster characterized by higher proportions of palmitate, palmitoleic, and oleic acid and lower proportions of linoleic, dihomo-gamma linolenic, and arachidonic acids. This cluster was positively associated with PWV, central adiposity, smoking, and increased mortality. These data suggest that plasma fatty acid profiles characterized by a higher proportion of long-chain polyunsaturated fatty acids (PUFAs) are associated with decreased cardiovascular mortality, independent of the impact of aortic pulse wave velocity (PWV). The results are consistent with the effect of dietary sources of n-3 (omega-3) long-chain polyunsaturated fatty acids influencing arterial stiffness and mortality (27).
The possibility that the heightened cardiovascular risk associated with menopause can be reduced by increasing dietary isoflavone intake was tested in 17 women by measuring arterial compliance, an index of the elasticity of large arteries such as the thoracic aorta. Compliance diminishes with age and menopause. An initial 3- to 4-week run-in period and a 5-week placebo period were followed by two 5-week periods of active treatment with 40 mg and then 80 mg isoflavones derived from red clover containing genistein, daidzein, biochanin, and formononetin in 14 and 13 women, respectively, with 3 others serving as placebo controls throughout. Arterial compliance, measured by ultrasound as a pressure (carotid artery) and volume (outflow into the aorta) relationship, was determined after each period. The study concluded that an important cardiovascular risk factor, arterial compliance, which diminishes with menopause, was significantly improved with red clover isoflavones. As diminished compliance leads to systolic hypertension and may increase left ventricular work, the findings indicate a potential new therapeutic approach for improved cardiovascular function after menopause (8).
The possibility that the heightened cardiovascular risk associated with menopause, which is said to be ameliorated by soybeans, can be reduced with soy isoflavones was tested in 21 women. A placebo-controlled crossover trial examined the effects of 80 mg daily isoflavones (45 mg genistein) over 5- to 10-week periods. The study concluded that a critical measure of arterial health, systemic arterial compliance, was significantly improved in perimenopausal and menopausal women taking soy isoflavones to about the same extent as is achieved with conventional hormone replacement therapy (10).
Dietary soy protein has been shown to have several beneficial effects on cardiovascular health. The best-documented impact is on plasma lipid and lipoprotein concentrations, with reductions of approximately 10% in LDL cholesterol (΄΄bad΄΄ – cholesterol) levels and small increases in HDL cholesterol (΄΄good΄΄ – cholesterol) concentrations. Dietary soy protein improves flow-mediated arterial dilation of postmenopausal women but worsens that of men. Soy isoflavone extracts improve systemic arterial compliance, an indicator of atherosclerosis extent. Complete soy protein but not alcohol-washed soy protein reduces atherosclerosis in postmenopausal monkeys. No definite experimental evidence exists to establish that soy protein's cardiovascular benefits are accounted for by its isoflavones (19).
Although a high intake of some flavonoid subclasses may reduce cardiovascular disease mortality, data regarding the in vivo mechanisms of action are limited. A study examined associations between habitual flavonoid intakes and direct measures of arterial stiffness, central blood pressure, and atherosclerosis. In a cross-sectional study of 1898 women aged 18 –75 from the TwinsUK registry, intakes of total flavonoids and their subclasses (flavanones, anthocyanins, flavan-3-ols, polymers, flavonols, and flavones) were calculated. Data, which include direct measures of arterial stiffness and thickness, suggest that a higher intake of anthocyanins and flavones is inversely associated with lower arterial stiffness. The intake of anthocyanins related to these findings could be incorporated into the diet by consuming 1 – 2 portions of berries daily. Therefore, relevant for public health strategies to reduce cardiovascular disease risk (13).
A study observed the effect of Chinese herbal medicine for calming Gan and suppressing hyperactive yang (CGSHY) on arterial elasticity function and the circadian rhythm of blood pressure in patients with essential hypertension (EH; hypertension that has no identifiable cause). Adopting a parallel, randomized design, sixty-four patients with EH of stages I and II were randomly divided into two groups according to a random number table, with 32 in each group. The patients in the treatment group were treated with CGSHY, and those in the control group were treated with Enalapril [an angiotensin-converting enzyme inhibitor (ACEI)]. The study concluded that Chinese herbal medicine for calming Gan and suppressing hyperactive yang (CGSHY) may lower the blood pressure (BP) smoothly and recover the circadian rhythm of blood pressure in patients with essential hypertension (EH; hypertension that has no identifiable cause). They may also improve the carotid elasticity of EH patients, similar to that of Enalapril [an angiotensin-converting enzyme inhibitor (ACEI)]. The mechanism of action of Chinese herbs on EH might be related to regulating vascular endothelium function (20).
Preclinical studies indicate the role of Korean red ginseng (KRG) in the modulation of vascular function; however, clinical evidence is scarce. An acute randomized, controlled, double-blind, crossover study investigated the effect of KRG root on peripheral blood pressure (BP) and augmentation index (AI), an emerging method to assess cardiovascular risk beyond conventional BP measurements. Furthermore, to elucidate which of the major components of KRG is responsible for these effects, the ginsenoside and polysaccharide fractions isolated from the same KRG root were also investigated. In the study participated 17 healthy fasted individuals. The study concluded that although preliminary, it is the first to demonstrate that Korean red ginseng (KRG) may improve arterial stiffness as measured by the augmentation index (AI). Also, ginsenosides may be the principal pharmacologically active component of the root rather than the polysaccharide fraction. This study supports the results seen with KRG in the preclinical studies and warrants further investigation on acute and long-term endothelial parameters (28).
Substantial preclinical and some clinical data show that Asian ginseng (Panax ginseng C.A. Meyer) varieties or their ginsenosides exert a vasodilatation effect and thus may modulate vascular function. However, the clinical evidence for American ginseng (Panax quinquefolius L.) is scarce. A study evaluated the effect of American ginseng (AG) on arterial stiffness, as measured by augmentation index (AI), and blood pressure (BP), in type 2 diabetes patients with concomitant hypertension. Using a double-blind, placebo-controlled, parallel design, each participant was randomized to either the selected AG extract or placebo at a daily dose of 3 grams for 12 weeks as an adjunct to their usual antihypertensive and antidiabetic therapy (diet and/or medications). The study concluded that the addition of American ginseng (AG) extract to conventional therapy in diabetes with concomitant hypertension improved arterial stiffness and attenuated systolic blood pressure (BP), thus warrants further investigation on long-term endothelial parameters before being recommended as an adjunct treatment (29).
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