Photoplethysmographic assessment of pulse wave reflection: blunted response to endothelium-dependent beta2-adrenergic vasodilation in type II diabetes mellitus

Noninvasive continuous monitoring of digital pulse waves during hemodialysis

Intermittent hemodynamic instability during hemodialysis treatment is a frequent complication in patients with end-stage renal failure. A noninvasive method for continuous hemodynamic monitoring is needed. We used noninvasive digital photoplethysmography and an algorithm for continuous, investigator-independent, automatic analysis of digital volume pulse in 10 healthy subjects and in 20 patients with end-stage renal failure during the hemodialysis session. The reflective index was defined representing the diastolic component of the digital pulse wave. The properties of the reflective index were studied in healthy control subjects (n=10). An increased reflective index was due to increased peripheral pulse wave reflection (e.g., vasoconstriction). During a hemodialysis session, the reflective index increased significantly from 36+/-3 arbitrary units to 41+/-3 arbitrary units (n=20; p<0.05) measured using digital photoplethysmography. This increase appeared in 15 of the 20 patients with end-stage renal failure. Our data establish digital photoplethysmography as a noninvasive, reliable, and sensitive method for continuous monitoring during the hemodialysis session.

Asymmetric dimethyl arginine levels correlate with cardiovascular risk factors in patients with erectile dysfunction

BACKGROUND

Erectile dysfunction is related to penile arterial endothelial nitric oxide production. Asymmetric dimethylarginine (ADMA) and E-selectin are often considered plasma markers of endothelial function.

OBJECTIVE

This study investigated the relationship between these plasma markers and cardiovascular risk factors in patients with erectile dysfunction.

METHODS AND RESULTS

Cardiovascular risk factors, ADMA and E-selectin were assessed in 45 patients with erectile dysfunction. Plasma markers showed associations with baseline risk factors. E-selectin levels showed an inverse relationship with age (p = 0.005) and statin therapy (p = 0.03) and a weak association with concomitant beta-blocker therapy (p = 0.05). Compared to these relatively weak associations with cardiovascular risk factors, ADMA levels showed strong associations with pulse pressure (p < 0.001), lack of smoking (p = 0.002) and lipoprotein (a) (p = 0.004) concentrations and weak associations with LDL-cholesterol (p = 0.02), and C-reactive protein levels (p = 0.04). ADMA levels correlated with E-selectin (partial r = 0.76; p < 0.001) after adjustment for lipoprotein (a), pulse pressure and smoking. No change in E-selectin or ADMA levels was seen after 70 days therapy with sildenafil and no relationship was found between either plasma marker and the acute pulse wave response to a single challenge dose of sildenafil.

CONCLUSION

ADMA levels correlate at baseline with some cardiovascular risk factors including inflammatory markers and lipoprotein (a) in patients with erectile dysfunction.

Effects of intravenous PD 123319 on haemodynamic and arterial stiffness indices in healthy volunteers

Relatively little is known about the functional expression of cardiovascular angiotensin type 2 (AT2)-receptors in healthy young adult humans. We performed a randomised, placebo-controlled crossover study of the effects of intravenous administration of the selective AT2-receptor antagonist PD 123319 on haemodynamics and arterial stiffness in normal volunteers. Sixteen normal subjects aged 29.9+/-13.8 years (range 18-30 years) received an intravenous infusion of PD 123319 (10 mcg/minute for 5 minutes) and placebo, separated by one week. Haemodynamics (cardiac index, stroke index and systemic vascular resistance) were measured non-invasively using a BioZ.com thoracic impedance detection system. Blood pressure was measured from an arm cuff using oscillometry. Stiffness index, a measure of arterial stiffness, was measured using a Pulse Trace recorder. No significant changes in blood pressure (p=0.92), cardiac index (p=0.52), stroke index (p=0.61), systemic vascular resistance index (p=0.32) or stiffness index (p=0.57) was demonstrated following PD 123319 infusion, compared with placebo. The results of this study do not support the functional presence of cardiovascular AT2-receptors that mediate acute haemodynamic effects in healthy young adults. It remains possible that higher doses of PD 123319 may be required to demonstrate functional cardiovascular AT2-receptors in this population, if they are present.

The role of inheritance and environment in predisposition to vascular disease in people of African descent

OBJECTIVES

This study sought to compare vascular reactivity and carotid intima media thickness (CIMT) between Afro-Caribbean people in the United Kingdom (UK) and the West Indies and Afro-Caribbean and Caucasian people in the UK.

BACKGROUND

Attenuated vascular reactivity and increased CIMT in black patients is seen as evidence for predisposition to vascular disease, but no comparisons exist between Afro-Caribbean people in different settings, which can provide insight into non-inherited determinants of increased ethnic susceptibility.

METHODS

A representative community sample of 81 healthy Afro-Caribbean people and 101 Caucasian people in the UK was compared with 197 matched Afro-Caribbean people in Jamaica. Small vessel reactivity was assessed by measuring the absolute change from baseline in the reflection index (RI) of the digital volume pulse during intravenous infusion of albuterol (5 microg/min, DeltaRI(ALB)) and glyceryl trinitrate (5 microg/min, DeltaRI(GTN)). The CIMT was measured ultrasonographically in the distal 1 cm of the common carotid artery.

RESULTS

Mean DeltaRI(ALB) was 4.2 percentage points (95% confidence interval [CI], 2.3 to 6.1, p < 0.001) lower in UK Afro-Caribbean people compared with Jamaican Afro-Caribbean people and 2.6 percentage points (95% CI, 0.4 to 4.7, p = 0.02) lower compared with Caucasian people, after adjusting for vascular risk profile. Adjusted mean CIMT of UK Afro-Caribbean people was 0.13 mm (95% CI, 0.08 to 0.17, p < 0.001) greater compared with Jamaican Afro-Caribbean people and 0.05 mm (95% CI, 0.01 to 0.10, p = 0.02) greater compared with Caucasian people.

CONCLUSIONS

Healthy UK Afro-Caribbean people have greater and Jamaican Afro-Caribbean people have less impairment of vascular reactivity and intima media thickness compared with UK Caucasian people, suggesting that potentially modifiable environmental interactions may contribute to excess vascular disease in Afro-Caribbean people.

Effect of moderate-intensity exercise, whole-body periodic acceleration, and passive cycling on nitric oxide release into circulation

STUDY OBJECTIVE

To determine if a 3-min bout of moderately intensive supine bicycle exercise, whole-body periodic acceleration (pGz), and passive motorized cycling cause nitric oxide (NO) release into the circulation, as detected by dicrotic notch descent on the diastolic limb of a finger pulse wave.

PARTICIPANTS

Fourteen healthy adults underwent two levels of supine bicycle ergometry that caused heart rate to rise to 56% (light moderate exercise) and 67% (heavy moderate exercise) of maximum predicted heart rate, and a single bout of pGz. Several months later, 9 of the 14 subjects underwent passive motorized cycling.

METHODS

The ECG and finger pulse wave were recorded. The dicrotic notch position was computed from the amplitude of the digital pulse wave (a) divided by the height of the dicrotic notch above the end-diastolic level (b) and designated the a/b ratio. Increase of the a/b ratio due to dicrotic notch descent reflects the vasodilator action of NO on resistance vessels. The last 30 s of baseline, exercise or pGz, and recovery periods were analyzed.

RESULTS

Compared to baseline, light moderate exercise produced a nonsignificant rise of the a/b ratio. Both heavy moderate exercise and pGz produced statistically significant rises of peak and mean a/b ratios over baseline. Heavy moderate exercise produced a greater mean a/b ratio than pGz, but the peak a/b ratio did not differ between the two. Episodic rises and falls of a/b ratios were more common during pGz than exercise. Passive motorized cycling did not alter the a/b ratio.

CONCLUSIONS

Dicrotic notch descent occurs during a brief bout of moderate cycling exercise, consistent with NO release into circulation. pGz produces comparable descent, but passive motorized cycling does not. In terms of the beneficial effects of NO, this suggests that pGz might serve as a substitute in subjects who are physically incapable of exercising.

Ethnic Differences in Arterial Responses and Inflammatory Markers in Afro-Caribbean and Caucasian Subjects

OBJECTIVE

Small vessel disease is more common in Afro-Caribbeans than Caucasians. We investigated underlying differences in metabolic, inflammatory, and vascular responses that may predispose Afro-Caribbeans to small vessel pathology.

METHODS AND RESULTS

Seventy-eight Afro-Caribbeans aged 35-75 years, with no vascular disease or medications, were compared with 82 matched Caucasians for metabolic variables, fasting insulin, interleukin 6, tumor necrosis factor (TNF) alpha, and cytoplasmic repressor protein levels. Carotid intima media thickness (CIMT) was measured ultrasonographically. Small vessel function was assessed by measuring the absolute change from baseline in the reflectance index (RI) of the digital volume pulse during IV infusion of albuterol (5 microg/min, DeltaRIALB) and glyceryl tri nitrate (5 microg/min, DeltaRIGTN). Large artery elasticity was measured as the stiffness index (SI) and derived from the time to pulse wave reflection adjusted for subject height. Afro-Caribbeans had significantly higher diastolic blood pressure (80.3 versus 77.6 mm Hg; P=0.033), fasting insulin (14.0 versus 10.6 microU/mL; P=0.026), TNF-alpha (6.7 versus 4.3; pg/mL; P=0.001), and interleukin 6 (2.3 versus 1.5 pg/mL; P=0.036) levels compared with Caucasians. CIMT was greater (0.81+/-0.20 versus 0.75+/-0.18 mm; P=0.02) and small vessel reactivity attenuated (mean DeltaRIALB 6.8+/-8.0% versus 12.3+/-8.%; P<0.0001) in Afro-Caribbeans, but their large artery elasticity (mean index of large artery stiffness 9.9 versus 9.7 m/s; P=0.48) was comparable with Caucasians. CIMT was independently associated with an index of large artery stiffness (beta=0.03; P=0.002) in Caucasians but not in Afro-Caribbeans. There were independent relationships among Afro-Caribbean ethnicity, TNF-alpha, and insulin levels.

CONCLUSIONS

Selective impairment of small artery function may contribute to excess small vessel disease in Afro-Caribbeans.

A Comparison of Three Different Methods to Evaluate Endothelium-Dependent Vasodilation in the Elderly

Background— Three different techniques to evaluate endothelium-dependent vasodilation in the peripheral circulation have been described but not simultaneously tested in a large-scale population-based setting. This study aimed to evaluate the feasibility and usefulness of these techniques in the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study.

Methods and Results— In the population-based PIVUS study (1016 subjects aged 70 years), the invasive forearm technique with acetylcholine given in the brachial artery (EDV), the brachial artery ultrasound technique with measurement of flow-mediated dilatation (FMD), and the pulse wave analysis method with β-2-agonist (terbutaline) provocation were successfully used in 87%, 97%, and 86% of the sample, respectively. The results of EDV and pulse wave analysis were interrelated ( r =0.12, P =0.0013), but no relationships were found with FMD measurements. All 3 techniques were correlated to the Framingham risk score ( r =0.10 to 0.12, P =0.0007 to 0.001). In multiple regression analysis, however, only EDV and FMD were independently associated with the Framingham score.

Conclusions— All 3 evaluated techniques were feasible to perform in a general elderly population. Both the invasive forearm technique and FMD were independently associated with increased coronary risk, suggesting that information on conduit artery and resistance artery endothelial function carry different, but important, information in the elderly. If the invasive technique cannot be used, the pulse wave based technique is an alternative.

Endothelial function and baroreflex sensitivity according to the oral glucose tolerance test in patients with coronary artery disease and normal fasting glucose levels

Endothelial dysfunction and reduced BRS (baroreflex sensitivity) may be present in patients with CAD (coronary artery disease). The normal fasting glucose level does not exclude abnormal glucose metabolism in patients with CAD. The aim of present study was to evaluate endothelial function and BRS according to glucose metabolism in patients with normal fasting plasma glucose and stable CAD subjected to PTCA (percutaneous transluminal coronary angioplasty). Forty-six consecutive patients who underwent elective PTCA were studied (37 men; mean age 56 years). Endothelial function was assessed non-invasively using the arterial vasodilator response to salbutamol (albuterol). BRS was measured using a cross-correlation method. The extent of coronary narrowing was estimated by calculation of the Gensini score. All patients underwent a 75 g OGTT (oral glucose tolerance test). IGT (impaired glucose tolerance) or diabetes was present in approx. 60% of patients. The vasodilator response to salbutamol, as a measure of endothelial dysfunction, was significantly impaired in patients with IGT or diabetes compared with those with normal glucose tolerance (−0.5±1.6% compared with −7.9±2.2; P=0.01). Glucose metabolism and age were significant predictors of endothelial dysfunction (R2=35.2%, P=0.02). BRS did not differ significantly between patients with normal glucose tolerance and those with IGT or diabetes (6.9±1.2 compared with 6.1±0.6 ms/mmHg respectively; P=0.669). BRS was negatively correlated with age (r=−0.34, P=0.021) and the Gensini score (r=−0.34, P=0.022). The significant predictors of BRS were Gensini score, age and past myocardial infarction (R2=37.02%, P=0.002). Patients with established CAD, normal fasting glucose and IGT or diabetes demonstrated impaired endothelial function which did not correlate with the extent of coronary artery involvement. Conversely, BRS in the study population was not affected by glucose metabolism, but showed an interaction with the extent of coronary narrowing.

Reduction in visceral adiposity is highly related to improvement in vascular endothelial dysfunction among obese women: an assessment of endothelial function by radial artery pulse wave analysis

Because obesity is frequently complicated by other cardiovascular risk factors, the impact of a reduction in visceral adiposity on vascular endothelial dysfunction (VED) in obese patients is difficult to determine. In the present study, we evaluated the impact of a reduction in visceral adiposity on VED in obese women. Thirty-six premenopausal obese women (BMI >/= 25 kg/m2) without complications were enrolled in the study. VED was evaluated by determining the augmentation index (AIx) from radial artery pulse waves obtained by applanation tonometry. Changes in AIx in response to nitroglycerin- induced endothelium-independent vasodilatation (DeltaAIx-NTG) and in response to salbutamol administration (DeltaAIx-Salb) were determined before and after weight reduction. After a 12-week weight reduction program, the average weight loss was 7.96 +/- 3.47 kg, with losses of 21.88 +/- 20.39 cm2 in visceral fat areas (p < 0.001). Pulse wave analysis combined with provocative pharmacological testing demonstrated preserved endothelium-independent vasodilation in healthy premenopausal obese women (DeltaAIx-NTG: 31.36 +/- 9.80% before weight reduction vs. 28.25 +/- 11.21% after weight reduction, p > 0.1) and an improvement in endothelial-dependent vasodilation following weight reduction (DeltaAIx-Salb: 10.03 +/- 6.49% before weight reduction vs. 19.33 +/- 9.28% after reduction, p < 0.001). A reduction in visceral adipose tissue was found to be most significantly related to an increase in DeltaAIx-Salb (beta=-0.57, p < 0.001). A reduction in visceral adiposity was significantly related to an improvement in VED. This finding suggests that reduction of visceral adiposity may be as important as the control of other major risk factors in the prevention of atherosclerosis in obese women.

Pulse wave analysis during supine rest may identify subjects with recurrent vasovagal syncope

In the present study, we studied whether analysis of the FAP (finger arterial pressure) waveform during supine rest discriminates subjects with recurrent VVS (vasovagal syncope) from healthy controls. Signal-averaged FAP waveforms (Finapres) were obtained in 32 head-up tilt-test-positive subjects with recurrent VVS (35±13 years) and in 32 sex- and age-matched healthy controls. The DT (time delay) between the systolic and diastolic peaks of the FAP waveform was measured and large artery SI (stiffness index) was calculated as a ratio of body height and DT. VVS patients had significantly shorter DT compared with controls (303±31 compared with 329±18 ms; P<0.001) and higher SI (5.79±0.70 compared with 5.20±0.36 m/s; P<0.001). The differences were independent of heart rate and blood pressure. SI >5.45 m/s identified subjects with syncope with a sensitivity of 72% and a specificity of 84%. Age-corrected DT (cDT=DT+age−350) identified subjects with syncope with a sensitivity of 75% and a specificity of 84%. Combined use of cDT <0 ms and SI >5.45 m/s increased sensitivity and specificity to 81% and 96% respectively. The discriminative power of FAP descriptors improved further when younger subjects were excluded. In subjects aged >30 years (median age), the combination of cDT and SI identified subjects with syncope with a sensitivity of 93% and a specificity of 100%. These results suggest that FAP descriptors during supine rest might be useful in the diagnosis of VVS in middle-aged subjects.

Comparative effects of glyceryl trinitrate and amyl nitrite on pulse wave reflection and augmentation index

AIMS

The influence of vasodilators on augmentation index (AIx) offers a simple, rapid and noninvasive method of evaluating vascular function. Glyceryl trinitrate (GTN) is widely used as an endothelium-independent vasodilator, although other nitrates that are shorter acting may have advantages in clinical studies. The aim of this study was to compare the effects of two short-acting nitrates, GTN and amyl nitrite, which have differing pharmacodynamic profiles.

METHODS

Twenty-one healthy volunteers (15 male; mean age 35 years, range 21-56 years) attended on three occasions and received sublingual GTN (0.5 mg for 3 min), inhaled amyl nitrite (0.2 ml inhaled for 30 s), or no treatment in a randomized cross-over design. Haemodynamic responses of AIx, blood pressure and thoracic bioimpedance (heart rate, cardiac index) were assessed by measurement at baseline, every 60 s for the first 5 min, and then every 5 min for a further 55 min.

RESULTS

AIx was reduced by amyl nitrite (peak effect -9 +/- 2% at 1 min, P < 0.002) and GTN (peak effect -12 +/- 3% at 4 min, P < 0.05). Compared with amyl nitrite, the onset and offset of action of GTN was slower. Amyl nitrite initially increased heart rate by 27 +/- 4% (P < 0.001) and cardiac index by 13 +/- 3% (P < 0.001) whereas GTN had no significant effect (P > 0.05). Neither agent affected blood pressure.

CONCLUSIONS

GTN causes a slower and more sustained reduction in AIx than amyl nitrite. Although amyl nitrite causes a more rapid fall and recovery in AIx, it induces a reflex tachycardia that may limit interpretation of the initial (1 min) but not later (2 min) changes in AIx. The prolonged offset of GTN suggests that a sufficient washout period must be included when making repeated measures or when assessing the subsequent effects of other agents.

Association of pulse waveform characteristics with birth weight in young adults

OBJECTIVE

An association between birth weight and blood pressure has been reported in many studies, but the strength of this association has been disputed. Birth weight could, however, be associated with alterations in the proximal arterial tree that have little effect on blood pressure. The objective of this study was to examine the relationship between birth weight and characteristics of the proximal arterial tree determined by pulse wave analysis.

METHODS

An optically derived digital volume pulse was used to obtain indices of pressure wave reflection (reflection index; RI) determined by characteristics of small/medium sized arteries and of large artery stiffness (stiffness index; SI) in healthy young adults (n = 220, 111 women, aged 16-26 years). Birth weight was obtained from maternal recall.

RESULTS

Diastolic blood pressure was significantly correlated with birth weight (P < 0.001) but birth weight accounted for only 5% of the variance in diastolic blood pressure. RI was significantly correlated with birth weight in women (r = -0.33, P < 0.001) but not in men, and there was a significant interaction between birth weight and sex (P < 0.001). SI was significantly independently correlated with birth weight in both men and women (r = -0.41 and -0.49, each P < 0.0001) and birth weight accounted for 17% of the overall (men and women) variance in SI.

CONCLUSIONS

These results suggest a close association between birth weight and characteristics of the arterial tree proximal to resistance vessels in young adults and a sex-specific association with characteristics influencing arterial pressure wave reflection.

Endothelial function and dysfunction. Part I: Methodological issues for assessment in the different vascular beds: a statement by the Working Group on Endothelin and Endothelial Factors of the European Society of Hypertension

An enormous number of studies in the last two decades have been devoted to investigating the role of the endothelium in cardiovascular diseases. Nonetheless, the optimal methodology for investigating the multifaceted aspects of endothelial dysfunction is still under debate. Biochemical markers, molecular genetic tests and invasive and non-invasive tools with and without pharmacological and physiological stimuli have been introduced. Furthermore newer pharmacological tools have been proposed. However, the application of these methodologies should fulfil a number of requirements in order to provide conclusive answers in this area of research. Thus, the most relevant methodological issues in the research on endothelial function and dysfunction are summarized in this paper.

Digital pulse contour analysis: investigating age-dependent indices of arterial compliance

The resting peripheral volume pulse wave of 44 subjects within three age categories (30-39, 40-49, 50) has been characterized using a novel algorithm for the automated determination of a mean pulse function. The contour of this resting mean pulse has been analyzed with regard to its systolic and diastolic characteristics. Previously described indices of arterial stiffness and viscoelasticity have been investigated for age-dependent variations associated with arterial mechanical properties. Measures of the minimum rise time (MRT) and the stiffness index (SI) demonstrated strong correlations with age and each other, although their derivations are unrelated. While significant correlations existed (|r| = 0.50-0.78, p < or = 0.002), pairwise comparisons between the right and left hands did not demonstrate significant differences for the minimum rise time parameter; however, the stiffness index was significantly lower in the left hand versus the right (p = 0.009). With regard to age, the youngest age group had significantly lower MRT and SI values than the two older groups. For these data, this was only demonstrated in parameters calculated for the right hand because of higher variability within age groups for the left hand. A normalized average mean pulse for each age group was determined which visually illustrated the contour changes associated with the MRT and SI parameters that occur in both the systolic and diastolic portions of the pulse. The finding that differences between the age groups were significantly more evident for the right hand suggests that the physical site for such testing may be an important consideration. This study provides further evidence regarding the merit of using contour analysis when assessing the peripheral volume pulse and the importance of establishing ageing indices for such analysis.

A review of methods currently used for assessment of in vivo endothelial function

An intact vascular endothelium is critical to the maintenance of normal arterial tone and coagulation status. Endothelial injury leading to dysfunction is thought to be a precursor to most if not all vascular disease, and has been implicated as a critical event in atherosclerosis. At present there are several methods available for detection of in vivo endothelial function, and the aim of this study was to critically review these methods. Five distinct methods were identified and studied in detail. These methods are diverse and each assesses a different vascular bed. Importantly there is no uniformity among investigators over choice of method and protocol, making it difficult to compare in vivo enothelial dysfunction between groups. These issues need to be addressed in large scale comparative analyses so that investigators can agree a common approach to endothelial function assessment.

Nitric oxide is released into circulation with whole-body, periodic acceleration

STUDY OBJECTIVE

To determine if comfortably applied, whole-body, periodic acceleration releases significant amounts of nitric oxide (NO) into the circulation of healthy subjects and patients with inflammatory diseases.

MATERIALS

Fourteen healthy adults and 40 adult patients with inflammatory diseases underwent single 45-min trials of whole-body, periodic acceleration with a new "passive exercise" device, while an ECG and a digital pulse wave were obtained with a photoelectric-plethysmograph sensor.

METHODS

The position of the dicrotic notch from the pulse waveform was computed from the amplitude of the pulse divided by the height of the dicrotic notch above the end-diastolic level (a/b ratio). Increase of the a/b ratio reflects the vasodilator action of NO that causes downward movement of the dicrotic notch in the diastolic limb of the digital pulse, thereby elevating the a/b ratio.

RESULTS

Application of whole-body, periodic acceleration was well tolerated in all participants, and all completed the 45-min treatment. The peak value of the a/b ratio markedly rose during periodic acceleration and returned to baseline during a 5-min recovery period in all healthy subjects and patients with inflammatory diseases.

CONCLUSIONS

Whole-body, periodic acceleration increased pulsatile shear stress to the endothelium leading to vasodilatation and a fall in the dicrotic notch, consistent with increased NO bioactivity in every healthy adult and adult patient with inflammatory disease so treated. Therefore, passive exercise using whole-body, periodic acceleration produces an important benefit that occurs with active exercise.

Vascular endothelial dysfunction tested by blunted response to endothelium-dependent vasodilation by salbutamol and its related factors in uncomplicated pre-menopausal obese women

BACKGROUND

Vascular endothelial dysfunction (VED) plays a pivotal role in the pathogenesis of atherosclerosis and is associated with insulin resistance and visceral obesity. We examined the predicting factors of VED in uncomplicated premenopausal obese women using analysis of endothelium-dependent vasodilation by radial artery pulse wave obtained through applanation tonometry.

METHODS

The subjects included a group of 33 obese women body mass index ((BMI) > or = 25) and another age-matched control group of 25 nonobese women (BMI: 18.5-22.9) of Asian origin. All uncomplicated premenopausal (20-45 y) obese women were sedentary (<1 h/week of physical activity). Anthropometric measurements were performed, and regional distributions of adipose tissue and metabolic variables were measured. Endothelial function was measured by pulse wave analysis after salbutamol administration, which reflects endothelium-mediated vasodilation, contributed partially by nitric oxide release from beta2-adrenergic stimulation. Radial artery wave forms were recorded and from a derived aortic wave forms augmentation index (AIx, defined as the pressure difference between the first and second peaks of the central arterial wave form, expressed as a percentage of the pulse pressure) was calculated. The subjects received sublingual nitroglycerine (NTG) (0.6 mg), followed by nebulized salbutamol (2.5 mg).

RESULTS

AIx fell significantly after the administration of salbutamol, which causes endothelium-dependent vasodilatation. This value was significantly reduced in obese women compared with the controls (10.3+/-6.7 vs 17.2+/-6.8%, P=0.0003). NTG, which causes endothelium-independent vasodilatation, did not produce significant changes (P=0.917). As for our obese subjects, the visceral adipose tissue area was a significant predictor of VED independent of BMI, percent body fat, and other metabolic variables including high-sensitivity C-reactive protein (beta = -0.141, P=0.002, Adj-R(2)=0.41).

CONCLUSION

Increased abdominal adiposity is a powerful independent predictor of VED in uncomplicated obese women. Further studies are warranted to determine the pathophysiological link between visceral adipose tissue and VED.

Nitric oxide-dependent beta2-adrenergic dilatation of rat aorta is mediated through activation of both protein kinase A and Akt

Vasorelaxation to beta(2)-adrenoceptor stimulation occurs through both endothelium-dependent and endothelium-independent mechanisms, and the former is mediated through Ca(2+)-independent activation of endothelial-type nitric oxide synthase (NOS-3). Since Ca(2+)-independent NOS-3 activation may occur through its serine phosphorylation via protein kinase A (PKA) or Akt, we determined the PKA and Akt dependency of beta(2)-adrenergic relaxation of rat aorta. Rat aortic rings were pre-incubated with the PKA inhibitor H-89 (10(-7) m), the phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin (5 x 10(-7) m), Akt inhibitor (10(-5) m), or vehicle, in the absence or presence of the NOS inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME, 10(-4) m). Rings were then contracted with phenylephrine (10(-7) m), and concentration-relaxation responses determined to the beta(2)-adrenoceptor agonist albuterol. Rings exhibited a concentration-dependent relaxation to albuterol: pEC(50) 6.9+/-0.2, E(max) 88.2+/-4.0%. l-NAME attenuated E(max) to 60.2+/-3.5% (P<0.001). In the presence of l-NAME, wortmannin or Akt inhibitor did not influence albuterol responses, whereas H-89 reduced E(max) further, to 27.5+/-2.2% (P<0.001). In the absence of l-NAME, E(max) to albuterol was reduced by H-89, wortmannin or Akt inhibitor, to 56.2+/-2.2, 56.0+/-1.6 and 55.4+/-1.8%, respectively (P<0.001 for each); the combinations H-89 plus wortmannin or H-89 plus Akt inhibitor reduced E(max) further still. Western blotting of NOS-3 immunoprecipitates from rat aortas confirmed that albuterol increased serine phosphorylation of NOS-3, and this increase was attenuated by H-89 or Akt inhibitor. Our results indicate that beta(2)-adrenoceptor stimulation relaxes rat aorta through both NO-dependent and independent mechanisms. The latter is predominantly PKA-mediated, whereas the former occurs through both PKA and PI3K/Akt activation.

Oral L-arginine and vitamins E and C improve endothelial function in women with type 2 diabetes

Endothelial dilator function is impaired in people with type 2 diabetes mellitus (T2DM). Prior research indicates that this can be improved with intravenous administration of ascorbate or L-arginine, but whether these agents have this effect when administered by the clinically practical oral route is unknown. To investigate this question, 10 premenopausal women with T2DM and 10 healthy, premenopausal, non-diabetic women received, in random sequence, a 1-week administration of oral L-arginine (9 g daily) or vitamins E (1800 mg) and C (1000 mg) with an intervening 1-week washout period. Flow-mediated brachial artery dilation (FMD) was measured by ultrasonography and forearm blood flow was measured by plethysmography before and following blood pressure cuff-induced forearm ischemia before and after each week of treatment. At baseline, the women with T2DM had lesser FMD responses (0.028 +/- 0.006 cm vs 0.056 +/- 0.008 cm, p < 0.05). Post-ischemic forearm hyperemia was reduced at baseline in T2DM compared with controls (16.4 +/- 1.8 vs 26.0 +/- 1.4 ml 100 ml(-1) min(-1), p < 0.05). Administration of L-arginine caused a 50 +/- 12% increase in FMD in T2DM (p < 0.05) and raised post-ischemic forearm blood flow by 29 +/- 8% (p < 0.05). No significant changes were seen in controls. Administration of vitamins E and C in women with T2DM produced an increase in the brachial artery diameter response of 79 +/- 15% (p < 0.05), but did not significantly increase the hyperemic blood flow response (p = NS). No significant changes in the responses of controls from pre to post vitamin administration were observed. We concluded that administration of two types of oral agents improved measures of endothelial function in people with T2DM.

Acute systemic effects of inhaled salbutamol in asthmatic subjects expressing common homozygous beta2-adrenoceptor haplotypes at positions 16 and 27

AIMS

The relationship between beta2-adrenoceptor polymorphisms at positions 16 and 27, and the acute systemic beta2-adrenoceptor effects of inhaled salbutamol is unclear. We therefore elected to evaluate the influence of common homozygous beta2-adrenoceptor haplotypes on the acute systemic beta2-adrenoceptor effects following inhaled salbutamol in asthmatic subjects.

METHODS

An initial database search of 531 asthmatic subjects identified the two commonest homozygous haplotypes at positions 16 and 27 to be Arg16-Gln27 (12%) and Gly16-Glu27 (19%). After a 1-week washout period where all beta2-adrenoceptor agonists were withdrawn, 16 Caucasian subjects (Arg16-Gln27: n = 8 and Gly16-Glu27: n = 8) were given a single dose of inhaled salbutamol (1200 microg), followed by serial blood sampling for serum potassium, along with measurements of diastolic blood pressure and heart rate, at 5-min intervals for 20 min.

RESULTS

The two groups were well matched for age, sex, FEV1, and inhaled corticosteroid dose. Baseline values for serum potassium, diastolic blood pressure and heart rate were not significantly different comparing Arg16-Gln27 vs Gly16-Glu27. The mean +/- SEM maximum serum potassium change from baseline over 20 min was significantly greater (P = 0.04) for Arg16-Gln27: -0.37 +/- 0.05 mmol l(-1) vs Gly16-Glu27: -0.23 +/- 0.04 mmol l(-1); 95% CI for difference: -0.01 to -0.28 mmol l(-1). The maximum diastolic blood pressure change from baseline over 20 min was significantly greater (P = 0.0008) for Arg16-Gln27: -13 +/- 1 mmHg vs Gly16-Glu27: -4 +/- 2 mmHg; 95% CI for difference: -5, 14 mmHg. There was no significant difference comparing the maximum heart rate change from baseline for Arg16-Gln27: 10 +/- 3 beats min(-1) vs Gly16-Glu27: 10 +/- 3 beats min(-1).

CONCLUSIONS

Caucasian asthmatic subjects with the Arg16-Gln27 haplotype exhibited a greater systemic response to inhaled salbutamol, compared with those with the Gly16-Glu27 haplotype. The attenuated beta2-adrenoceptor response in the Gly16-Glu27 haplotype would be in keeping with increased susceptibility to prior down-regulation by endogenous catecholamines.

Haemodialysis acutely improves endothelium-independent vasomotor function without significantly influencing the endothelium-mediated abnormal response to a 2-agonist

BACKGROUND

Increased aortic stiffness markers--aortic pulse wave velocity (PWV) and augmentation index (AIx)--have emerged as powerful predictors of survival in haemodialysis (HD). Various and often contradictory abnormalities of endothelium-dependent (ED) and endothelium-independent (EID) vasomotor function, have been described in dialysis subjects, pre- and post-dialysis, using methods that are difficult to export to the clinical setting or to large prospective trials assessing their relevance. Therefore, we determined the influence of a HD session on PWV and the ED and EID vascular reactivity, employing pulse wave analysis (PWA) of the aortic waveforms, combined with provocative pharmacological stimuli known to reduce wave reflection.

METHODS

PWV and aortic AIx (difference between the first and second systolic peak on the aortic pressure waveform divided by the pulse wave height) were determined from PWA of arterial waveforms recorded by applanation tonometry using a SphygmoCor device in 41 HD (20 males, age 41.8 years) and in 20 controls with essential hypertension (10 males, age 43.6 years). ED and EID vascular reactivity were assessed by changes in AIx following inhaled salbutamol and sublingual nitroglycerin (GTN), respectively, pre- and post-dialysis session. Echocardiography was performed in all patients, pre-HD and before the PWV recordings.

RESULTS

Pre-HD AIx (27.9+/-11.9%) was significantly higher compared with hypertensive patients with normal renal function (16.5+/-17%, P<0.05). Dialysis significantly reduced AIx to 18.2+/-18.3% (P<0.05 compared with pre-HD AIx), a level comparable with non-renal subjects (P = NS). Overall, PWV increased following HD to 7.89+/-2.09 m/s (P = 0.004 vs pre-HD, 6.34+/-1.32 m/s in essential hypertensive patients, P<0.05); however, a 19.1% increase was seen in 29 subjects and a 9.1% decrease in the remaining 12 subjects, both P<0.05. In HD patients, either pre- or post-HD, the EID vascular reactivity is significantly greater than the ED vasodilatation elicited by a beta 2-agonist. Moreover, when compared with hypertensive patients with normal renal function, the dialysis session only improved the EID abnormality (post-HD GTN AIx(HD) = -20.8+/-22.9% vs post-GTN AIx(hypertensive) = -14.2+/-5.7%, P = NS), while it had a non-additive effect on the ED response. A smaller response to a GTN challenge was associated with a greater left ventricular mass: r =-0.42, P = 0.007. In contrast, a diminished response to a beta 2-agonist did not represent a marker for cardiac abnormalities.

CONCLUSIONS

The HD session acutely restores EID but not ED vasomotor function comparable with essential hypertensive patients. Pulse-wave analysis methodology, combined with provocative pharmacological testing may be used to unveil subsets of patients with more severe cardiac structural abnormalities.

Acetylcysteine Reduces Plasma Homocysteine Concentration and Improves Pulse Pressure and Endothelial Function in Patients With End-Stage Renal Failure

Background— Increased oxidative stress, elevated plasma homocysteine concentration, increased pulse pressure, and impaired endothelial function constitute risk factors for increased mortality in patients with end-stage renal failure.

Methods and Results— We investigated the metabolic and hemodynamic effects of intravenous administration of acetylcysteine, a thiol-containing antioxidant, during a hemodialysis session in a prospective, randomized, placebo-controlled crossover study in 20 patients with end-stage renal failure. Under control conditions, a hemodialysis session reduced plasma homocysteine concentration to 58±22% predialysis (mean±SD), whereas in the presence of acetylcysteine, the plasma homocysteine concentration was significantly more reduced to 12±7% predialysis ( P <0.01). The reduction of plasma homocysteine concentration was significantly correlated with a reduction of pulse pressure. A 10% decrease in plasma homocysteine concentration was associated with a decrease of pulse pressure by 2.5 mm Hg. Analysis of the second derivative of photoplethysmogram waveform showed changes of arterial wave reflectance during hemodialysis in the presence of acetylcysteine, indicating improved endothelial function.

Conclusions— Acetylcysteine-dependent increase of homocysteine removal during a hemodialysis session improves plasma homocysteine concentration, pulse pressure, and endothelial function in patients with end-stage renal failure.

Say NO to fibromyalgia and chronic fatigue syndrome: an alternative and complementary therapy to aerobic exercise

Increased shear stress to the endothelium increases activity of endothelial nitric oxide synthase (eNOS) with subsequent release of small quantities (nMol) of nitric oxide (NO) into the circulation. It occurs during moderate aerobic exercise mostly as a result of laminar shear stress and with whole body, periodic acceleration as a result of pulsatile shear stress. The latter is administered by means of a new, non-invasive, passive exercise device. Moderate exercise has long been known to alleviate the symptoms of fibromyalgia and chronic fatigue syndrome and in the current study, whole body, periodic acceleration did as well. Since NO through action of eNOS has potent anti-inflammatory properties mainly by suppressing nuclear factor kappabeta activity, it is hypothesized that both diseases have chronic inflammation as their basis. Whole body periodic acceleration can be applied separately or supplementary to aerobic exercise in the treatment of fibromyalgia and chronic fatigue syndrome.

Effect of time of day and rabbit strain on patterns of aortic wall permeability

Lipid deposits occur more frequently downstream of branch points than upstream in immature rabbit and human aortas but the opposite pattern is seen in mature vessels. These distributions correlate spatially with age-related patterns of aortic permeability, observed in rabbits, and may be determined by them. The mature but not the immature pattern of permeability is dependent on endogenous nitric oxide synthesis. Although the transport patterns have hitherto seemed robust, recent studies have given the upstream pattern in some mature rabbits but the downstream pattern in others. Here we show that transport in mature rabbits is significantly skewed to the downstream pattern in the afternoon compared with the morning (P < 0.05), and switches from a downstream to an upstream pattern at around 21 months in rabbits of the Murex strain, but at twice this age in Highgate rabbits (P < 0.001). The effect of time of day was not explained by changes in nitric oxide production, assessed from plasma levels of nitrate and nitrate, nor did it correlate with conduit artery tone, assessed from the shape of the peripheral pulse wave. The effect of strain could not be explained by variation in nitric oxide production nor by differences in wall structure. The effects of time of day and rabbit strain on permeability patterns explain recent discrepancies, provide a useful tool for investigating underlying mechanisms and may have implications for human disease.

Successful renal transplantation decreases aortic stiffness and increases vascular reactivity in dialysis patients

BACKGROUND

Patients with end-stage renal disease on dialysis have among the highest cardiovascular event rates documented. Abnormal nitric oxide (NO)-dependent endothelial reactivity and increased arterial stiffness are commonly described in hemodialysis (HD) patients. Measures of aortic stiffness--aortic pulse wave velocity (PWV) and augmentation index (AGI)--have been shown to be powerful predictors of survival on hemodialysis. It is not known how these parameters interfere with successful renal transplantation.

METHODS

PWV and aortic AGI (difference between the first and second systolic peak on the aortic pressure waveform divided by the pulse wave height) were determined from contour analysis of arterial waveforms recorded by applanation tonometry using a SphygmoCor device in 41 HD patients (20 men; age, 41.8 years) and in a control group of 20 patients with essential hypertension (HTA) (10 men; age, 43.6 years). Twenty of the HD patients (10 men; age, 39.7 years) received live-related renal transplants (RTx) and were restudied (3 months after RTx, normal serum creatinine). NO-dependent and NO-independent vascular reactivity were assessed by changes in AGI after challenges with inhaled salbutamol (SAL) and sublingual nitroglycerin (NTG), respectively.

RESULTS

AGI values were significantly lower in RTx patients compared with subjects on hemodialysis (15.9 +/- 13.9% vs. 27.9 +/- 11.9%, P<0.05), but similar to essential HTA controls (16.5 +/- 17%). Serial AGI measurements showed that successful renal transplantation is associated with a decrease in AGI in all cases, from a mean of 25.1 +/- 7.8% while on dialysis to 15.9 +/- 7.0% 3 months after transplantation (P<0.0001). The responsiveness to both endothelium-dependent stimuli (inhaled SAL) and endothelium-independent stimuli (sublingual NTG) was greater in transplant patients than in hemodialysis patients (SAL-induced decrease in AGI -82.3 +/- 65.7% vs. 45 +/- 72.3%, P<0.01; and NTG-induced decrease in AGI 197 +/- 108 vs. -129.0 +/- 215.5%, P<0.01). PWV values in dialysis patients (7.19 +/- 1.88 m/sec) were significantly higher than those measured in essential HTA patients (6.34 +/- 1.32 m/sec, P<0.05) with normal renal function (despite similar blood pressure levels). PWV after RTx was 6.59 +/- 1.62 m/sec, significantly different from pretransplantation (dialysis) values (P<0.05 for comparison) but similar to the control group of essential HTA patients.

CONCLUSIONS

Renal transplantation is associated with marked improvements in vascular structure and function to a profile comparable to essential HTA patients.

Effects of inhibition of basal nitric oxide synthesis on carotid-femoral pulse wave velocity and augmentation index in humans

Aortic stiffness, as measured by carotid-femoral pulse wave velocity (PWV), is a powerful, independent predictor of vascular risk. PWV in muscular arteries is influenced by basal nitric oxide (NO) release. It is not known whether NO also influences carotid-femoral PWV. We examined the effects of an NO synthase inhibitor, NG-monomethyl-l-arginine (L-NMMA), on carotid-femoral PWV and aortic augmentation index (AIx, an indirect measure of arterial stiffness). To control for effects of L-NMMA on distending pressure, we used doses of norepinephrine and dobutamine that caused similar changes in mean arterial blood pressure (MAP). Healthy men (32 to 48 years old, n=8) were studied on 4 occasions and received, in random order, vehicle, L-NMMA (3 mg x kg(-1) by intravenous bolus followed by 3 mg x kg(-1) x h(-1)), norepinephrine (50 ng x kg(-1) x min(-1)), and dobutamine (2.5 to 10 microg x kg(-1) x min(-1)), each for 30 minutes. PWV and AIx were measured by carotid-femoral PWV and radial tonometry, respectively. L-NMMA and norepinephrine increased MAP by 7.8+/-1.7 and 9.7+/-2.1 mm Hg, respectively (each P<0.05 vs vehicle) and increased PWV by 0.7+/-0.2 and 1.0+/-0.3 m x s(-1) (each P<0.01 vs vehicle). Dobutamine, at doses that produced a similar increase in MAP (9.6+/-2.9 mm Hg), increased PWV by 0.8+/-0.2 m x s(-1) (P<0.01 vs vehicle). Changes in PWV caused by the 3 pressor agents were closely correlated with changes in MAP (R>0.99, P<0.0001). L-NMMA and norepinephrine increased AIx, but dobutamine decreased AIx (P<0.01 vs norepinephrine and L-NMMA). Effects of inhibition of basal NO release on carotid-femoral PWV can be explained by the change in MAP that this causes rather than any specific effect of NO inhibition within the aorta.

Assessment of peripheral vascular endothelial function with finger arterial pulse wave amplitude

BACKGROUND

Abnormalities in pulse wave amplitude (PWA) have been described in subjects with atherosclerosis and may be a marker of future cardiac events. We evaluated the relationship between changes in PWA of the finger and peripheral endothelial function.

METHODS

We performed measurements of PWA with a novel finger plethysmograph (peripheral arterial tonometry [PAT]) and compared the findings with a simultaneous noninvasive measurement of peripheral endothelial function with brachial artery ultrasound scanning (BAUS) in 89 subjects. The PAT hyperemia ratio was defined as the ratio of PWA during reactive hyperemia relative to the baseline. Flow-mediated dilation (FMD) was defined by BAUS as the ratio of the brachial artery diameter during reactive hyperemia relative to the baseline. Sixty-eight subjects underwent exercise myocardial perfusion imaging (ExMPI).

RESULTS

Fifty-four men and 35 women were examined. There was a linear relationship between the PAT hyperemia ratio and FMD during the same episode of reactive hyperemia (r = 0.55, P <.0001). Subjects in the lowest FMD quartile had the lowest PAT hyperemia ratio, whereas subjects in the highest FMD quartile had the highest PAT hyperemia ratio (P <.001 for trend). Similar to BAUS, the PAT hyperemia ratio was more impaired in subjects with cardiovascular risk factors and in subjects with ExMPI studies that were indicative of coronary artery disease.

CONCLUSIONS

Assessment of PWA with PAT demonstrates patterns of abnormality similar to that of BAUS assessment of FMD. PWA during reactive hyperemia is influenced by factors known to affect endothelial function, including cardiovascular risk factors and coronary artery disease. These findings support the concept that analysis of PWA with PAT during reactive hyperemia may be used to study peripheral vascular endothelial function.

Noninvasive assessment of arterial stiffness and risk of atherosclerotic events

Investigation of arterial stiffness, especially of the large arteries, has gathered pace in recent years with the development of readily available noninvasive assessment techniques. These include the measurement of pulse wave velocity, the use of ultrasound to relate the change in diameter or area of an artery to distending pressure, and analysis of arterial waveforms obtained by applanation tonometry. Here, we describe each of these techniques and their limitations and discuss how the measured parameters relate to established cardiovascular risk factors and clinical outcome. We also consider which techniques might be most appropriate for wider clinical application. Finally, the effects of current and future cardiovascular drugs on arterial stiffness are also discussed, as is the relationship between arterial elasticity and endothelial function.

Influence of nervous blockade on insulin-mediated glucose uptake in the human forearm

This study was undertaken to investigate if a nonpharmacologic increase in forearm blood flow (FBF) could increase forearm glucose uptake (FGU) during hyperinsulinemia. In 10 young volunteers, FBF and the arterial-venous glucose difference were measured in both arms during a 2-hour euglycemic hyperinsulinemic clamp procedure when 1 of the arms was subjected to axillary plexus nervous blockade with local anesthesia. FBF was measured in both arms by venous occlusion plethysmography. Nervous blockade, increasing FBF by more than 3-fold, did not improve insulin-mediated FGU. On the contrary, a tendency towards a reduced FGU compared with the control arm was seen (P =.07). Furthermore, while insulin increased FBF to a similar degree in both arms (+ 3.0 and 4.4 mL/min/100 mL tissue, P <.01 for both arms), nervous blockade abolished the rapid increase in glucose extraction seen in the control arm when insulin infusion was initiated. The present study showed that an increase in FBF induced by nervous blockade did not increase insulin-mediated FGU. On the contrary, a tendency towards a reduction was seen. Furthermore, insulin induced vasodilation in the blocked arm, but delayed the ability of insulin to promote glucose extraction, suggesting that the well-documented increase in skeletal muscle sympathetic nerve activity seen during acute hyperinsulinemia has metabolic rather than hemodynamic consequences.

Analysis of endothelium-dependent vasodilation by use of the radial artery pulse wave obtained by applanation tonometry

OBJECTIVES

To evaluate applanation tonometry as a method to obtain arterial pulse waves suitable for pulse wave analysis of the height of the diastolic inflection point (IP), and to use this technique to study endothelium-mediated vasodilation by evaluation of the contribution of nitric oxide (NO) to the reduction in the height of the IP induced by beta2-adrenergic stimulation.

METHODS

The radial artery pulse waveform was recorded by applanation tonometry in young healthy subjects before and after interventions both locally in the forearm and systemically by different vasodilators and vasoconstrictors, and vasodilatation was analysed as a change in the height of the IP. The mechanism behind the reduction in the height of the IP induced by terbutaline was investigated by systemic interventions with both N(G)-monomethyl-l-arginine (l-NMMA) and noradrenaline (NA).

RESULTS

Applanation tonometry was a convenient method to obtain radial artery pulse waves of good quality. The reduction in IP was substantially more pronounced when vasodilators were given systemically than when given locally in the forearm, indicating that the effect was obtained through an effect on peripheral pulse wave reflection. Systemically given l-NMMA, but not NA, increased the IP (P<0.05). Systemically given l-NMMA also caused a more pronounced attenuation than NA of the reduction in IP following terbutaline injection (P<0.05).

CONCLUSION

Changes in IP following beta2-adrenergic stimulation appears to be a measurement of pulse wave reflection mainly governed by NO. Applanation tonometry and pulse wave analysis is a minimally invasive method suitable to assess endothelium-dependent vasodilation in large-scale studies.

Insulin-induced decreases in aortic wave reflection and central systolic pressure are impaired in type 2 diabetes

OBJECTIVE

To determine whether large arteries are resistant to insulin.

RESEARCH DESIGN AND METHODS

Insulin normally acutely decreases central systolic pressure by decreasing wave reflection in vivo. This effect occurs before any changes in peripheral vascular resistance or heart rate under normoglycemic conditions. We determined whether the ability of insulin to decrease central aortic pressure is altered in uncomplicated type 2 diabetes. The study subjects consisted of 16 type 2 diabetic patients (age 54 +/- 2 years, BMI 29 +/- 1 kg/m(2)) and 19 matched nondiabetic individuals (51 +/- 2 years, 29 +/- 1 kg/m(2)) studied under normoglycemic-hyperinsulinemic conditions. Central aortic pressure waveforms were synthesized from those recorded in the periphery using applanation tonometry and a validated reverse transfer function to construct the central aortic pressure waveform every 30 min. This method allowed determination of aortic augmentation (the pressure difference between the first and second central systolic pressure waves) and the augmentation index (augmentation divided by pulse pressure).

RESULTS

Whole-body insulin sensitivity was 31% lower (P < 0.05) in the type 2 diabetic patients than in the normal subjects. Basally, before the insulin infusion, augmentation averaged 8.9 +/- 1.3 and 11.1 +/- 1.2 mmHg (NS) and the augmentation index averaged 23.1 +/- 2.1 and 27.5 +/- 2.1% (NS) in the normal subjects and diabetic patients, respectively. After 30 min of hyperinsulinemia, augmentation decreased significantly to 6.1 +/- 1.1 mmHg (P < 0.001) in the normal subjects but remained unchanged at 9.1 +/- 1.1 mmHg (NS) in type 2 diabetic patients. At 30 min, the augmentation index had decreased significantly (30 +/- 7% decrease) to 17.9 +/- 2.6% in the normal subjects but remained at 24.4 +/- 2.4% in the diabetic patients (13 +/- 4% decrease, P < 0.05 for change vs. normal subjects). Central systolic pressure decreased significantly by 30 min in the normal subjects but only after 120 min in the type 2 diabetic patients. There were no significant changes in heart rate, pulse pressure, or forearm blood flow during the first 120 min of the insulin infusion.

CONCLUSIONS

Insulin resistance in type 2 diabetes involves a delay in the ability of insulin to decrease central aortic pressure. This defect could predispose these patients to develop systolic hypertension.

Aortic pulse-wave velocity and its relationship to mortality in diabetes and glucose intolerance: an integrated index of vascular function?

BACKGROUND

Arterial distensibility measures, generally from pulse-wave velocity (PWV), are widely used with little knowledge of relationships to patient outcome. We tested whether aortic PWV predicts cardiovascular and all-cause mortality in type 2 diabetes and glucose-tolerance-tested (GTT) multiethnic population samples.

METHODS AND RESULTS

Participants were randomly sampled from (1) a type 2 diabetes outpatient clinic and (2) primary care population registers, from which nondiabetic control subjects were given a GTT. Brachial blood pressures and Doppler-derived aortic PWV were measured. Mortality data over 10 years' follow-up were obtained. At any level of systolic blood pressure (SBP), aortic PWV was greater in subjects with diabetes than in controls. Mortality risk doubled in subjects with diabetes (hazard ratio 2.34, 95% CI 1.5 to 3.74) and in those with glucose intolerance (2.12, 95% CI 1.11 to 4.0) compared with controls. For all groups combined, age, sex, and SBP predicted mortality; the addition of PWV independently predicted all-cause and cardiovascular mortality (hazard ratio 1.08, 95% CI 1.03 to 1.14 for each 1 m/s increase) but displaced SBP. Glucose tolerance status and smoking were other independent contributors, with African-Caribbeans experiencing reduced mortality risk (hazard ratio 0.41, 95% CI 0.25 to 0.69).

CONCLUSIONS

Aortic PWV is a powerful independent predictor of mortality in both diabetes and GTT population samples. In displacing SBP as a prognostic factor, aortic PWV is probably further along the causal pathway for arterial disease and may represent a useful integrated index of vascular status and hence cardiovascular risk.

Assessment of endothelial function using peripheral waveform analysis: a clinical application

OBJECTIVES

The study was done to determine whether radial artery applanation tonometry can be used as a noninvasive method of assessing global endothelial function. BACKGROUND; It is known that beta(2)-receptor stimulation results in endothelial release of nitric oxide. Furthermore, for over a century glyceryl trinitrate (GTN) has been known to markedly affect the arterial pressure waveform, even in the absence of significant blood pressure (BP) changes. Therefore, it was hypothesized that the change in the peripheral pressure waveform, as measured using tonometry and quantified using the augmentation index (AIx) and in response to Salbutamol (Salb), would allow assessment of global endothelial function.

METHODS

The study contained three parts. In the first study, Salb (400 microg) was administered to 11 healthy subjects via inhalation after either intravenous N-omega-nitro-monomethyl-L-arginine (L-NMMA) (3 mg/kg over 5 min) or control solution (normal saline) in the supine, rested, fasted condition. The BP, heart rate and waveform responses were recorded each 5 min following Salb for 20 min. Next, GTN was given and responses recorded 5 min later. In the second study, both the reproducibility of Salb and the GTN responses were assessed in 9 subjects studied twice on separate days. In the third study, the Salb and GTN responses of 12 subjects with angiographic coronary artery disease (CAD) were compared with 10 age-matched control subjects with no atherosclerotic risk factors.

RESULTS

After control infusion, AIx decreased following Salb, from 50.8 +/- 4.3% to 44.8 +/- 4.2%, a change of -11.8 +/- 3.7%, p < 0.01. After L-NMMA, AIx did not significantly change following Salb (54.2 +/- 5.1% vs. 52.9 +/- 5.3%, -2.0 +/- 3.1%). The GTN-induced decreases in AIx were similar after either infusion (35.1 +/- 3.3% vs. 36.5 +/- 3.3%). Reproducibility of Salb-induced changes in AIx between studies performed on separate days was good (r = 0.80, p < 0.01). Salb-induced changes in AIx in CAD patients were significantly less compared to control subjects (-2.4 +/- 1.9% vs. -13.2 +/- 2.4%, respectively, p < 0.002). The GTN-induced changes were not significantly different (-27.6 +/- 4.2 vs. -38.9 +/- 4.4%, p = 0.07).

CONCLUSIONS

The peripheral arterial pressure waveform is sensitive to beta(2)-stimulation. Changes are related to nitric oxide release, are reproducible and can distinguish between clinical subject groups. Arterial waveform changes following Salb may thus provide a noninvasive method of measuring "global" arterial endothelial function.

Quantification of glyceryl trinitrate effect through analysis of the synthesised ascending aortic pressure waveform

OBJECTIVE

To establish through analysis of the radial pressure pulse waveform the dose dependent effects of glyceryl trinitrate (GTN) on properties of different blood vessels.

DESIGN

Radial pulse waveform was measured in randomised order before, during a five hour application of a GTN patch delivering 0.104-0.625 mg/h, and for two hours after patch removal. The radial pressure waveform (Millar applanation tonometer) was convolved into an ascending aortic wave using a generalised transfer function (SphygmoCor process) enabling measurement of aortic systolic, diastolic, pulse, mean, and augmented pressure and left ventricular ejection duration in addition to standard brachial cuff pressures.

SETTING

Fu Wai and Ren Ming hospitals in Beijing, China.

PATIENTS

46 recumbent hospitalised patients aged 56 (9) years, awaiting electrophysiological or other diagnostic studies, fasting, and with other treatments suspended.

MAJOR OUTCOME MEASURES

Conventional brachial pressure measures and data from the synthesised aortic pulse.

RESULTS

There was no consistent change in heart rate or brachial pressures except for a decrease in systolic and pulse pressures (p < 0.01) at dose > 0.416 mg/h. In contrast, there were substantial and significant (p < 0.0001) decreases in aortic systolic, pulse, and augmented pressures at all doses, mean pressure (p < 0.001) at doses > 0.416 mg/h, and ejection duration (p < 0.001) at doses > 0.208 mg/h.

CONCLUSIONS

Pulse waveform analysis exposes dose dependent effects of GTN on the aortic waveform, suggesting muscular conduit arterial dilatation with reduced wave reflection at the lowest dose, arteriolar dilatation and decreased peripheral resistance at the highest dose, and venous dilatation at the intermediate dose.

Can a clinically useful aortic pressure wave be derived from a radial pressure wave?

BACKGROUND

The information contained in arterial pressure waveforms is probably underused by most clinicians who manage critically ill patients. It is not generally known that an aortic pressure wave can be synthesized by applying a generalized transfer function to the radial arterial pressure wave. We validated a commercially available system, SphygmoCo (PWV Medical, Sydney).

METHODS

Ascending aortic pressure waves were synthesized and comparisons were made between the synthesized aortic waveforms, the measured aortic and radial arterial waveforms. Ascending aortic pressure waves (catheter-tip manometer) and radial artery pressure waves (short fluid-filled catheter) were recorded simultaneously in 12 patients with angina pectoris (age 62-76 years) undergoing cardiac catheterization. Patients were studied at rest, following midazolam, sublingual nitroglycerin and during Valsalva manoeuvres.

RESULTS

Both midazolam and nitroglycerin lowered mean arterial pressure but nitroglycerin caused a more selective decrease in the measured and synthesized aortic systolic pressures than in the radial artery pressure. The synthesized aortic systolic pressure was less, by 6-8 mm Hg (SD 2-3) and the synthesized aortic diastolic pressure greater, by 4 mm Hg (SD 2). Despite these differences in pulse pressure, the synthesized waveform tracked the measured waveform before and during interventions.

CONCLUSIONS

By deriving an aortic waveform from the radial pulse, monitoring of left ventricular afterload can improve without more invasive means.

Pulse-wave analysis: clinical evaluation of a noninvasive, widely applicable method for assessing endothelial function

Current methods for assessing vasomotor endothelial function are impractical for use in large studies. We tested the hypothesis that pulse-wave analysis (PWA) combined with provocative pharmacological testing might provide an alternative method. Radial artery waveforms were recorded and augmentation index (AIx) was calculated from derived aortic waveforms. Thirteen subjects received sublingual nitroglycerin (NTG), inhaled albuterol, or placebo. Twelve subjects received NTG, albuterol, and placebo separately during an infusion of N(G)-monomethyl-L-arginine (LNMMA) or norepinephrine. Twenty-seven hypercholesterolemic subjects and 27 controls received NTG followed by albuterol. Endothelial function was assessed by PWA and forearm blood flow in 27 subjects. Albuterol and NTG both significantly and repeatably reduced AIx (P<0.001). Only the response to albuterol was inhibited by LNMMA (-9.8+/-5.5% vs -4.7+/-2.7%; P=0.02). Baseline AIx was higher in the hypercholesterolemic subjects, who exhibited a reduced response to albuterol (P=0.02) but not to NTG when compared with matched controls. The responses to albuterol and acetylcholine were correlated (r=0.5, P=0.02). Consistent with an endothelium-dependent effect, the response to albuterol was substantially inhibited by LNMMA. Importantly, the response to albuterol was reduced in subjects with hypercholesterolemia and was correlated to that of intra-arterial acetylcholine. This methodology provides a simple, repeatable, noninvasive means of assessing endothelial function in vivo.

Strain-dependent differences in the pattern of aortic lipid deposition in cholesterol-fed rabbits

Spontaneous lesions develop downstream of branch points in immature human and rabbit aortas, but occur more frequently at the sides and upstream of these sites in mature vessels. Cholesterol-induced lesions in mature rabbits, however, have shown the downstream distribution in one trial and the more upstream distribution in another. We tested the hypothesis that this discrepancy reflected a difference in the degree of impairment of the nitric oxide pathway. Mature rabbits were fed cholesterol-enhanced versions of the two base diets used in the previous trials, and some were given additional vitamin E or l-arginine to protect the NO pathway or L-NAME to inhibit it. Unexpectedly, the rabbits developed a lesion pattern intermediate between the two previously described, and this distribution was unaffected by the base diet or supplements. Consequently, an exploratory study was conducted to investigate possible effects of other differences between the two earlier trials. These were the precise age of the mature rabbits and the feeding protocol employed; both base diets again were used. Two different lesion patterns were observed in this trial, but there was no systematic effect of any of the controlled variables. Instead, there appeared to be an influence of the supplier from which the rabbits had been obtained. A multivariate analysis of all four trials confirmed that the pattern of disease was associated with rabbit strain, and not with base diet, cholesterol level, or precise age.

Vasoactive drugs influence aortic augmentation index independently of pulse-wave velocity in healthy men

Aortic augmentation index, a measure of central systolic blood pressure augmentation arising mainly from pressure-wave reflection, increases with vascular aging. The augmentation index is influenced by aortic pulse-wave velocity (related to aortic stiffness) and by the site and extent of wave reflection. To clarify the relative influence of pulse-wave velocity and wave reflection on the augmentation index, we studied the association between augmentation index, pulse-wave velocity, and age and examined the effects of vasoactive drugs to determine whether altering vascular tone has differential effects on pulse-wave velocity and the augmentation index. We made simultaneous measurements of the augmentation index and carotid-to-femoral pulse-wave velocity in 50 asymptomatic men aged 19 to 74 years at baseline and, in a subset, during the administration of nitroglycerin, angiotensin II, and saline vehicle. The aortic augmentation index was obtained by radial tonometry (Sphygmocor device, PWV Medical) with the use of an inbuilt radial to aortic transfer function. In multiple regression analysis, the aortic augmentation index was independently correlated only with age (R=0.58, P<0.0001). Nitroglycerin (3 to 300 microg/min IV) reduced the aortic augmentation index from 4.8+/-2.3% to -11.9+/-5.3% (n=10, P<0.002). Angiotensin II (75 to 300 ng/min IV) increased the aortic augmentation index from 9.3+/-2.4% to 18.3+/-2.9% (n=12, P<0.001). These drugs had small effects on aortic pulse-wave velocity, producing mean changes from baseline of <1 m/s (each P<0.05). In healthy men, vasoactive drugs may change aortic augmentation index independently from aortic pulse-wave velocity.

Characteristics of the pulse waveform during altered nitric oxide synthesis in the rabbit

Nitrovasodilators produce characteristic changes in the shape of the peripheral pulse wave. Similar changes might also be caused by alteration of endogenous NO activity, which would allow such activity to be assessed in vivo. We investigated whether manipulation of the NO pathway influences the pulse waveform, and the mechanisms involved. The pulse wave in the ear of normal rabbits was examined by reflectance photoplethysmography before and during infusion of vasoactive agents. Pulse wave velocity was assessed by using an additional sensor on the rear foot. A diastolic peak was observed in the ear pulse; its timing was consistent with it being a reflection of the systolic peak from the lower body. The height of the dicrotic notch marking the start of this diastolic wave was decreased by acetylcholine or an NO donor, and further decreased by a phosphodiesterase type V inhibitor. The acetylcholine-induced decreases were blocked by inhibiting NO synthesis with N(G)-nitro-L-arginine methyl ester (L-NAME) but were unaffected by the inactive enantiomer D-NAME. These data demonstrate that NO influences the height of the notch in the pulse wave. Heart rate and blood pressure were altered during acetylcholine or L-NAME infusion, but there were no changes in pulse wave amplitude or velocity, or in the timing of the diastolic peak or dicrotic notch. The slope of the pulse wave between the systolic peak and notch changed substantially. These effects are most convincingly explained by changes in wave reflection, not only from the lower body but also from more proximal sites.

Noninvasive assessment of the digital volume pulse. Comparison with the peripheral pressure pulse

The digital volume pulse can be recorded simply and noninvasively by photoplethysmography. The objective of the present study was to determine whether a generalized transfer function can be used to relate the digital volume pulse to the peripheral pressure pulse and, hence, to determine whether both volume and pressure pulse waveforms are influenced by the same mechanism. The digital volume pulse was recorded by photoplethysmography in 60 subjects (10 women, aged 24 to 80 years), including 20 subjects with previously diagnosed hypertension. Simultaneous recordings of the peripheral radial pulse and digital artery pulse were obtained by applanation tonometry and a servocontrolled pressure cuff (Finapres), respectively. In 20 normotensive subjects, measurements were obtained after the administration of nitroglycerin (NTG, 500 microgram sublingually). Transfer functions obtained by Fourier analysis of the waveforms were similar in normotensive and hypertensive subjects. In normotensive subjects, transfer functions were similar before and after NTG. By use of a single generalized transfer function for all subjects, the radial and digital artery pressure waveforms could be predicted from the volume pulse with an average root mean square error of 4.4+/-2.0 and 4.3+/-1.9 mm Hg (mean+/-SD) for radial and digital artery waveforms, respectively, similar to the error between the 2 pressure waveforms (4.4+/-1.4 mm Hg). The peripheral pressure pulse is related to the digital volume pulse by a transfer function, which is not influenced by effects of hypertension or NTG. Effects of NTG on the volume pulse and pressure pulse are likely to be determined by a similar mechanism.