Cerebral blood flow velocity and systemic vascular resistance after acute reduction of low-density lipoprotein in familial hypercholesterolemia

Orthostatic hemodynamics in the vertebral artery and blood pressure in patients with orthostatic dizziness/vertigo

OBJECTIVES

Orthostatic dizziness/vertigo (ODV) is a common symptom and is believed to occur due to the cerebral hypoperfusion caused by orthostatic hypotension (OH). However, the detailed mechanism underlying ODV onset is poorly understood. The vertebral artery (VA) mainly supplies blood to the central vestibular system; therefore, the orthostatic decrease of VA blood flow could possibly lead to ODV. This study investigated the orthostatic blood pressure and VA hemodynamics in ODV patients to elucidate the hemodynamic mechanism underlying ODV onset. Furthermore, the influence of orthostatic hypotension (OH) on VA hemodynamics was examined because OH is probably the most common cause of ODV.

METHODS

This study included 181 patients with ODV and 73 control patients without ODV. All subjects underwent an active standing test to measure the extracranial Doppler (ECD) sonography spectrum of the VA and blood pressure (BP). VA blood flow velocity and BP were simultaneously measured for each patient in the supine static position and then in the upright standing positions following 3 min of standing. We investigated the orthostatic change in the average of flow velocity in bilateral VAs (VAFV) and BP for ODV patients compared with the control patients.

RESULT

VAFV in ODV patients was significantly reduced when standing up compared with the control patients. In the ODV patients, there was no difference in orthostatic decrease in VAFV between patients those with OH and without OH. However, the VAFV in the standing position was significantly lower in patients with OH than without OH. In cases with OH, the ODV patients exhibited a greater decrease in VAFV compared with the control patients, but this was not statistically significant. In the absence of OH, a significantly greater orthostatic decrease in VAFV was observed in ODV patients compared with the controls.

CONCLUSION

Our findings suggest that the orthostatic decrease of VA blood flow is deeply involved in the hemodynamic mechanism underlying ODV onset and is possibly associated with OH and other etiologies.

Systemic circulatory influences on retinal microvascular function in middle-age individuals with low to moderate cardiovascular risk

PURPOSE

To investigate the relationship between retinal microvascular reactivity, circulatory markers for CVD risk and systemic antioxidative defence capacity in healthy middle-aged individuals with low to moderate risk of CVD.

METHODS

Retinal vascular reactivity to flickering light was assessed in 102 healthy participants (46-60 years) by means of dynamic retinal vessel analysis (DVA). Other vascular assessments included carotid intima-media thickness (C-IMT) and blood pressure (BP) measurements. Total cholesterol (CHOL), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), triglycerides (TG) and blood glutathione levels in its reduced (GSH) and oxidized (GSSG) forms were also determined for each participant, along with Framingham risk scores (FRS).

RESULTS

Retinal arterial baseline diameter fluctuation (BDF) was independently, significantly and negatively influenced by LDL-C levels (β = -0.53, p = 0.027). Moreover, the arterial dilation slope (SlopeAD ) was independently, significantly and positively associated with redox index (GSH: GSSG ratio, β = 0.28, p = 0.016), while the arterial constriction slope (SlopeAC ) was significantly and negatively influenced by blood GSH levels (β = -0.20, p = 0.042), and positively associated with FRS (β = 0.25, p = 0.009). Venous BDF and dilation amplitude (DA) were also negatively influenced by plasma LDL-C levels (β = -0.83, p = 0.013; and β = -0.22, p = 0.028, respectively).

CONCLUSIONS

In otherwise healthy individuals with low to moderate cardiovascular risk, retinal microvascular dilation and constriction responses to stress levels are influenced by systemic antioxidant capacity, and circulating markers for cardiovascular risk.

Resting brain perfusion and selected vascular risk factors in healthy elderly subjects

Background and Purpose

Both cerebral hypoperfusion and vascular risk factors have been implicated in early aging of the brain and the development of neurodegenerative disease. However, the current knowledge of the importance of cardiovascular health on resting brain perfusion is limited. The aim of the present study was to elucidate the relation between brain perfusion variability and risk factors of endothelial dysfunction and atherosclerosis in healthy aged subjects.

Methods

Thirty-eight healthy subjects aged 50–75 years old were included. Mean global brain perfusion was measured using magnetic resonance phase contrast mapping and regional brain perfusion by use of arterial spin labeling.

Results

Mean global brain perfusion was inversely correlated with caffeine and hematocrit, and positively with end-tidal P_CO2. Furthermore, the mean global brain perfusion was inversely correlated with circulating homocysteine, but not with asymmetric dimethylarginine, dyslipidemia or the carotid intima-media thickness. The relative regional brain perfusion was associated with circulating homocysteine, with a relative parietal hypoperfusion and a frontal hyperperfusion. No effect on regional brain perfusion was observed for any of the other risk factors. A multiple regression model including homocysteine, caffeine, hematocrit and end-tidal P_CO2, explained nearly half of the observed variability.

Conclusion

Both intrinsic and extrinsic factors influenced global cerebral perfusion variation between subjects. Further, the results suggest that the inverse relation between homocysteine and brain perfusion is owing to other mechanisms, than reflected by asymmetric dimethylarginine, and that homocysteine may be a marker of cerebral perfusion in aging brains.

Hyperlipidemia disrupts cerebrovascular reflexes and worsens ischemic perfusion defect

Hyperlipidemia is a highly prevalent risk factor for coronary and cervical atherosclerosis and stroke. However, even in the absence of overt atherosclerosis, hyperlipidemia disrupts endothelial and smooth muscle function. We investigated the impact of hyperlipidemia on resting-brain perfusion, fundamental cerebrovascular reflexes, and dynamic perfusion defect during acute focal ischemia in hyperlipidemic apolipoprotein E knockout mice before the development of flow-limiting atherosclerotic stenoses. Despite elevated blood pressures, absolute resting cerebral blood flow was reduced by 20% in apolipoprotein E knockout compared with wild type when measured by [(14)C]-iodoamphetamine technique. Noninvasive, high spatiotemporal resolution laser speckle flow imaging revealed that the lower autoregulatory limit was elevated in apolipoprotein E knockout mice (60 vs. 40 mm Hg), and cortical hyperemic responses to hypercapnia and functional activation were attenuated by 30% and 64%, respectively. Distal middle cerebral artery occlusion caused significantly larger perfusion defects and infarct volumes in apolipoprotein E knockout compared with wild type. Cerebrovascular dysfunction showed a direct relationship to the duration of high-fat diet. These data suggest that hyperlipidemia disrupts cerebral blood flow regulation and diminishes collateral perfusion in acute stroke in the absence of hemodynamically significant atherosclerosis.

Doppler study of cerebral arteries in hypercholesterolemia

Background:

Hypercholesterolemia is one of the major modifiable risk factors for atherosclerosis of the coronary and carotid arteries. Although transcranial Doppler (TCD) studies of the cerebral arteries are indicative of decreased cerebral blood flow velocities in patients with hypercholesterolemia, the number of these studies has been limited. The aim of this study was to assess the hemodynamic status of the cerebral arteries in patients with hypercholesterolemia using TCD.

Methods:

In a case-control study, 60 individuals, including 30 hypercholesterolemic cases (low-density lipoprotein [LDL] > 160 mg/dL) and 30 healthy controls were enrolled. Other arterial risk factors, including diabetes mellitus, hypertension, smoking, and obesity (body mass index > 30), were evaluated and matched as well. TCD was used to assess the hemodynamics of the intracranial arteries as well as the internal carotid arteries. The mean blood flow velocity, pulsatility index, and resistance index were recorded in all the arteries.

Results:

The mean blood flow velocity, pulsatility index, and resistance index of the intracranial arteries and internal carotid arteries were not significantly different between the two groups (P > 0.05). However, those with higher levels of LDL (>180 mg/dL) showed significantly lower mean blood flow velocity and resistance index of the internal carotid arteries than the healthy controls. In addition, individuals with high-density lipoprotein (HDL) <35 mg/dL had significantly lower mean blood flow velocity in the internal carotid arteries.

Conclusion:

Hypercholesterolemia (LDL >160 mg/dL) does not seem to have a detrimental effect on the hemodynamic status of the intracranial arteries and internal carotid arteries. However, in cases of higher LDL (>180 mg/dL) and lower HDL, decreased TCD parameters in the internal carotid arteries, as a surrogate of the peripheral arteries, are prominent.

Relationships of transcranial blood flow Doppler parameters with major vascular risk factors: TCD study in patients with a recent TIA or nondisabling ischemic stroke

PURPOSE

The relationship between intracranial vascular disease and cardiovascular risk factors such as smoking, hypertension, diabetes mellitus, and total serum cholesterol in patients with recent cerebral ischemia is not well established. We used transcranial Doppler (TCD) sonography tests as parameters of intracranial vascular disease and investigated the relationship between these parameters and conventional cardiovascular risk factors.

METHODS

We prospectively studied 598 patients with a minor ischemic stroke or transient ischemic attack (TIA). In all patients, flow velocities in the left and right middle cerebral artery (MCA), and cerebrovascular reactivity to CO2 were measured by means of TCD sonography. Student's t-test and linear regression analysis were used to determine the relationship between the baseline characteristics, vascular risk factors, and TCD parameters.

RESULTS

After adjustment for other vascular risk factors, a statistically significant relationship with mean flow velocity in the MCA was found for age (3.5 cm/s/10 years of age; 95% CI, 2.5-4.5 cm/s/10 years of age; p < 0.0001), sex (-2.9 cm/s for male sex; 95% CI, -5.5 to -0.3 cm/s; p = 0.03), diabetes (5.6 cm/s for diabetics; 95% CI, 2.1-9.1 cm/s; p = 0.002), and total serum cholesterol (2.4 cm/s per mmol increase in total serum cholesterol; 95% CI, 1.4-3.5 cm/s; p < 0.0001). Total serum cholesterol and hypertension were related to cerebrovascular reactivity to CO2.

CONCLUSIONS

Cerebral flow velocity is influenced by multiple interacting factors. Results of TCD investigations should be adjusted for age, sex, diabetes, and cholesterol when used for diagnostic or prognostic purposes.

Clinical applications of long-term LDL-apheresis on and beyond refractory hypercholesterolemia

Premature coronary heart disease (CHD) can result from high LDL cholesterol levels even in the absence of any other risk factors. A striking example is found in children who have the homozygous form of familial hypercholesterolemia (FH) with extremely high levels of LDL-cholesterol, and severe atherosclerosis and CHD often develop during the first decades of life. LDL-apheresis was developed for the treatment of severe type of FH patients who are resistant to lipid-lowering drug therapy. Clinical efficacy and safety of the therapeutic tool which directly removes LDL from circulation have already been established in the treatment for refractory hypercholesterolemia in FH patients. The most recently developed method enables lipoproteins to be adsorbed directly from whole blood, using polyacrylate column. In addition to benefits derived from the stabilization or regression of arterial lesions, we highlight other possible clinical applications of LDL-apheresis. However, most of these clinical benefits came from case reports or retrospective studies. Mechanisms related these clinical improvement remain unclear, and prospective randomized controlled trials should be performed for the new clinical indications of LDL-apheresis.

LDL apheresis

Low density lipoprotein (LDL) apheresis provides a safe and effective means of treating patients with homozygous familial hypercholesterolaemia (FH). It also has a role in preventing the progression of coronary artery disease in heterozygotes and others with severe dyslipidaemia who are refractory to or intolerant of high doses of lipid-lowering drugs. Established methods involve either adsorption of apolipoprotein B-containing lipoproteins by affinity columns containing anti-apolipoprotein B antibodies or dextran sulphate, or their precipitation at low pH by heparin, in each instance after first separating plasma from blood cells with a cell separator. The most recently developed method enables lipoproteins to be adsorbed directly from whole blood, using polyacrylate columns. All 4 methods have proved to be similarly efficient when used weekly or biweekly to lower LDL cholesterol and Lp(a) without unduly reducing HDL cholesterol. Economic constraints restrict the use of LDL apheresis to the treatment of potentially fatal disorders such as FH, where there is clear evidence of benefit compared with conventional therapy. Widening the indications to include the treatment of other dyslipidaemic disorders such as steroid-resistant nephrotic syndrome, post-transplant donor vessel disease, stroke and prevention of re-stenosis after coronary angioplasty requires evidence from controlled trials that is currently lacking.

Beneficial effect of aggressive low-density lipoprotein apheresis in a familial hypercholesterolemic patient with severe diabetic scleredema

We present a 59-year-old woman with severe diabetic scleredema (DS) associated with heterozygous familial hypercholesterolemia (FH). She had been treated with drugs to lower blood glucose, with insulin for diabetes mellitus (DM), and with low-density lipoprotein (LDL) apheresis therapy monthly or every 2 weeks in addition to drugs to lower serum lipids for FH. However, her scleredema had not improved. After we had tried weekly LDL apheresis therapy for a period of 3 years to treat her hyperlipidemia, the levels of her serum lipids were reduced to normal ranges, and scleredema in her nape improved. We also demonstrated the histopathological improvement in dermis of her cervical skin. We conclude that weekly LDL apheresis therapy is effective for diabetic scleredema that is resistant to conventional treatments.

Low-density lipoprotein apheresis for the treatment of refractory hyperlipidemia

The advent of treatment with 3-hydroxy-3-methylglutaryl coenzyme A inhibitors has meant that, with a combination of diet and drug therapy, adequate control of serum cholesterol concentrations can be achieved in most patients with hypercholesterolemia. However, some patients, primarily those with familial hypercholesterolemia (FH), may require additional therapy to lower their cholesterol levels. In recent years, low-density lipoprotein (LDL) apheresis has emerged as an effective method of treatment in these patients. The criteria for commencement of LDL apheresis are LDL cholesterol levels of 500 mg/dL or higher for homozygous FH patients, 300 mg/dL or higher for heterozygous FH patients in whom medical therapy has failed, and 200 mg/dL or higher for heterozygous FH patients with documented coronary disease and in whom medical therapy has failed. In addition to cholesterol lowering in patients with FH, other indications for LDL apheresis are emerging. These include its use in the treatment of graft vascular disease in patients receiving cardiac transplants as well as in the treatment of certain glomerulonephritides. This review examines the role of LDL apheresis in the management of lipid disorders and the evidence available to support its use in clinical practice.

Effects of low-density lipoprotein apheresis on coronary and carotid atherosclerosis and diabetic scleredema in patients with severe hypercholesterolemia

Correlations between serum cholesterol levels and progression of coronary and peripheral atherosclerosis have been found in many recent studies. It has also been demonstrated that aggressive cholesterol-lowering therapy with low-density lipoprotein (LDL) apheresis, a method of LDL elimination by extracorporeal circulation, is effective not only for coronary artery disease, but also for systemic circulatory disturbance in severe hypercholesterolemic patients with familial hypercholesterolemia (FH) in particular. We found that LDL apheresis treatment with medical therapy improved coronary atherosclerotic lesions, based on coronary angiography evaluation and histopathological observation, suppressed progression of early carotid atherosclerotic lesions on annual B-mode ultrasonography, and improved diabetic scleredema in FH patients. This effectiveness of LDL apheresis appears to be due to recovery of vascular endothelial function and improvement of blood rheology. For diseases that are possibly due to circulation disturbance and that are intractable with drugs alone. LDL apheresis may be worth trying, particularly for patients complicated by hyperlipemia.

Transcranial doppler sonography and ambulatory blood pressure monitoring in patients with hypertension

To appraise the value of transcranial Doppler sonography (TCD) for assessment of hypertensive cerebrovascular damage, the relationship between ambulatory blood pressure (BP) and indices of cerebral circulation determined by TCD was investigated. Subjects were 55 inpatients with or without hypertension, including 13 patients with histories of cerebrovascular attacks. Mean flow velocity (MFV) in the middle cerebral artery was measured by TCD, then the cerebrovascular resistance index (CVRI; mean BP/MFV) and the Fourier PI1 (pulsatility index of the first Fourier harmonic of the flow-velocity waveform) were determined as indices of cerebrovascular resistance. CO2 reactivity of MFV was estimated as an index of cerebrovascular flow reserve. CVRI positively correlated with both daytime and nighttime BP as well as with age (p<0.01). Fourier PI1 positively correlated with nighttime BP and age (p<0.01). CO2 reactivity did not correlate with any of the ambulatory BP parameters, but negatively correlated with age (p<0.01). LV mass index significantly correlated with ambulatory BP parameters, CVRI, and Fourier PI1 but did not correlate with CO2 reactivity. Multiple regression analyses showed that nighttime systolic BP was a significant correlate for CVRI and Fourier PI1, but not for CO2 reactivity, and that history of cerebrovascular attack was significant for CVRI and CO2 reactivity. We conclude that cerebrovascular resistance determined by TCD accords with the results of ambulatory BP and LVMI, and thus could be successfully used to detect the early stage of hypertensive cerebrovascular change. Cerebrovascular flow reserve would be relatively preserved in hypertensive patients without cerebrovascular diseases.

Blood-flow velocities and their relationships in carotid and middle cerebral arteries

This study defines normative flow velocity (FV) ranges for the common carotid (CCA), internal carotid (ICA) and middle cerebral arteries (MCA), compares them to subjects with nonfocal vascular disease (mild to moderate hypertension, diabetes, hyperlipidemia or coronary artery disease), and clarifies the association between carotid and MCA FVs. FVs were measured by carotid and transcranial Doppler ultrasonography in 278 healthy and 190 vascular-disease subjects. Normative FV ranges for CCA, ICA and MCA were large in healthy subjects, with modest gender and age differences. Vascular-disease subjects had similar FVs to healthy controls. MCA FVs were significantly correlated with carotid FVs (r ranged 0.26-0.50), but were only weakly or not significantly associated with them (beta ranged 0.08-0.18) when controlling for age and gender. These findings suggest that normative FVs are not affected by the presence of nonfocal vascular disease, but carotid FVs do not aid in assessing MCA FVs.

Correction of erythrocyte shape abnormalities in familial hypercholesterolemia after LDL-apheresis: does it influence cerebral hemodynamics?

It is well known that red blood cells incubated in low-density lipoprotein (LDL)-rich medium show shape abnormalities that revert to normal after reincubation in normal plasma. Patients with homozygous familial hypercholesterolemia (HFH) have an increased percentage of abnormally-shaped erythrocytes (mostly stomatocytes, knisocytes, and crenated cells) compared to normocholesterolemic controls: 7.73+/-0.96 versus 3.52+/-0.52 (mean+/-SEM; P = 0.001). To confirm the role of high LDL concentration in inducing red cell shape abnormalities we determined the percentage of abnormally shaped erythrocytes in seven HFH patients 1 day after the procedure of LDL-apheresis with a 40% cholesterol decrease. A reduction in kniscocytes, stomatocytes, and crenated cells was observed in the patients treated by LDL-apheresis (P < 0.01). To investigate the possible benefit of a reduction in erythrocyte shape abnormality on cerebral hemodynamics, cerebral flow velocity, as evaluated by transcranial Doppler, was evaluated concomitantly and found to be remarkably increased after apheresis (P < 0.01). No significant change in hematocrit, plasma viscosity, blood viscosity, mean pressure, or cardiac output was detected, 1 day after apheresis. An inverse correlation was demonstrated (r = 0.55; P = 0.04) between changes in the percentage of knisocytes+stomatocytes +crenated cells and percent changes in middle cerebral artery peak systolic velocity. The correction of erythrocyte shape abnormalities after LDL-apheresis might be related to dramatic changes in plasma phospholipid concentration and proportion occurring after this procedure in HFH patients. The reduction of erythrocyte shape abnormalities could contribute, together with other hemorheological factors, to the improvement of cerebral hemodynamics after LDL-apheresis.

Effects of short-term reduction in serum cholesterol with simvastatin in patients with stable angina pectoris and mild to moderate hypercholesterolemia

To evaluate the effects of short-term cholesterol-lowering treatment on myocardial effort ischemia, 22 patients with stable effort ischemia and mild to moderate hypercholesterolemia (low density lipoprotein [LDL] cholesterol 160 to 220 mg/dl) were randomly allocated at baseline (TO) in 2 groups. Group A included 12 patients treated with simvastatin 10 mg bid; group B included 10 patients treated with placebo. All patients underwent a treadmill electrocardiography (ECG) test; total cholesterol, HDL and LDL cholesterol, triglycerides, plasma, and blood viscosity were measured. All tests were repeated after 4 and 12 weeks. For 18 of the same patients (11 taking simvastatin, 7 receiving placebo), forearm strain-gouge plethysmography was performed at baseline and after 4 weeks, both at rest and during reactive hyperemia. At 4 and 12 weeks, group A showed a significant reduction in total cholesterol (p <0.05) and LDL (p <0.05), with unchanged HDL, triglycerides, blood, and plasma viscosity. Effort was unmodified, ST-segment depression at peak effort and ischemic threshold were significantly improved after 4 and 12 weeks (all p <0.05) with unchanged heart rate x systolic blood pressure product. A significant increase in the excess flow response to reactive hyperemia was detected in group A (p <0.03); group B showed no changes in hematochemical and ergometric parameters. These data suggest that cholesterol-lowering treatment is associated with an improvement in myocardial effort ischemia; this might be explained by a more pronounced increase of coronary blood flow and capacity of vasodilation in response to effort.

Pregnancy in a patient with homozygous familial hypercholesterolemia treated with long-term low-density lipoprotein apheresis

The pregnancy and delivery of a subject with homozygous familial hypercholesterolemia (FH) and coronary artery disease (CAD) were monitored closely for signs of maternal and fetal distress. Biweekly treatment with low-density lipoprotein (LDL) apheresis using dextran-sulfate cellulose columns was continued throughout the pregnancy, and lipid and lipoprotein levels were evaluated. During the course of the pregnancy and delivery, no signs of maternal coronary insufficiency developed. Serial ultrasonographic measurements of fetal growth indices and the blood flow velocity waveforms (FVWs) of the uterine and umbilical artery did not reveal any sign of fetal growth retardation or insufficiency of the uteroplacental circulation, respectively. During pregnancy, time-averaged concentrations of serum total cholesterol (TC), LDL cholesterol (LDL-C), apolipoprotein (apo) B, and lipoprotein(a) [Lp(a)] showed a gradual decline. Notwithstanding LDL apheresis, a gradual twofold increase of serum triglyceride (TG) levels was found. In the second and third trimester, high-density lipoprotein cholesterol (HDL-C) levels showed a 55% increase that coincided with a 75% reduction in hepatic lipase activity in postheparin plasma, normalizing after parturition. After delivery, lp(a) levels showed an almost twofold increase, which could not be explained by the interruption of LDL apheresis alone, and may be caused by changes in gonadal steroids. Histologic examination of the placenta and the umbilical arteries revealed no atherosclerotic changes, infarctions, or lipid deposits. In general, long-term LDL apheresis in homozygous FH can delay the onset and complications of severe CAD. In case of a pregnancy, LDL apheresis seems feasible and should be continued during the pregnancy to prevent superimposed hyperlipidemia and placental insufficiency.