Baroreflex control of heart rate during sleep in severe obstructive sleep apnoea: effects of acute CPAP

Baroreflex control of heart rate during sleep (baroreflex sensitivity; BRS) has been shown to be depressed in obstructive sleep apnoea (OSA), and improved after treatment with continuous positive airway pressure (CPAP). Whether CPAP also acutely affects BRS during sleep in uncomplicated severe OSA is still debatable. Blood pressure was monitored during nocturnal polysomnography in 18 patients at baseline and during first-time CPAP application. Spontaneous BRS was analysed by the sequence method, and estimated as the mean sequence slope. CPAP did not acutely affect mean blood pressure or heart rate but decreased cardiovascular variability during sleep. Mean BRS increased slightly during CPAP application (from 6.5+/-2.4 to 7.5+/-2.9 ms x mmHg(-1)), mostly in response to decreasing blood pressure. The change in BRS did not correlate with changes in arterial oxygen saturation or apnoea/hypopnoea index. The small change in baroreflex control of heart rate during sleep at first application of continuous positive airway pressure in severe obstructive sleep apnoea was unrelated to the acute resolution of nocturnal hypoxaemia, and might reflect autonomic adjustments to positive intrathoracic pressure, and/or improved sleep architecture. The small increase in baroreflex control of heart rate during sleep may be of clinical relevance as it was accompanied by reduced cardiovascular variability, which is acknowledged as an independent cardiovascular risk factor.

[Possible interaction of environment and genetic factors in work-related diseases: the case of hypertension]

BACKGROUND

Cardiovascular diseases are the most important cause of death and invalidity during the course of working life. The major risk factor for cardiovascular diseases is arterial hypertension, a typical example of multifactorial and polygenic disease, involving genetic, environmental, and demographic factors.

OBJECTIVES

A review of studies performed sofar on hypertension which can be also defined as a work-related disease.

METHODS

Several studies on association or linkage analysis showed an association between genetic polymorphisms and increased risk of hypertension.

RESULTS

Till now no studies have identified one or more "major" candidate genes involved in the pathogenesis of hypertension. Recently the interaction between genetics and environment have attracted much interest since the genotypes predisposingfor hypertension have different effects according to the patient's environment and life style.

CONCLUSIONS

It is likely that the aspects covered in this review will, in the near future, be studied more extensively. The identification of any correlations between genes and environment will also be influenced by the accuracy in measuring environmental exposure, where the occupational physician will play a significant role.

Neuroadrenergic and reflex abnormalities in patients with metabolic syndrome

AIMS/HYPOTHESIS

Previous studies have shown that alterations in vascular, metabolic, inflammatory and haemocoagulative functions characterise the metabolic syndrome. Whether this is also the case for sympathetic function is not clear. We therefore aimed to clarify this issue and to determine whether metabolic or reflex mechanisms might be responsible for the possible adrenergic dysfunction.

METHODS

In 43 healthy control subjects (age 48.2+/-1.0 years, mean+/-SEM) and in 48 untreated age-matched subjects with metabolic syndrome (National Cholesterol Education Program's Adult Treatment Panel III Report criteria) we measured, along with anthropometric and metabolic variables, blood pressure (Finapres), heart rate (ECG) and efferent postganglionic muscle sympathetic nerve activity (microneurography) at rest and during baroreceptor manipulation (vasoactive drug infusion technique).

RESULTS

Compared with control subjects, subjects with metabolic syndrome had higher BMI, waist circumference, blood pressure, cholesterol, triglycerides, insulin and homeostasis model assessment (HOMA) index values but lower HDL cholesterol values. Sympathetic nerve traffic was significantly greater in subjects with metabolic syndrome than in control subjects (61.1+/-2.6 vs 43.8+/-2.8 bursts/100 heartbeats, p<0.01), the presence of sympathetic activation also being detectable when the metabolic syndrome did not include hypertension as a component. Muscle sympathetic nerve traffic correlated directly and significantly with waist circumference (r=0.46, p<0.001) and HOMA index (r=0.49, p<0.001) and was inversely related to baroreflex sensitivity (r=-0.44, p<0.001), which was impaired in the metabolic syndrome.

CONCLUSIONS/INTERPRETATION

These data provide evidence that the metabolic syndrome is characterised by sympathetic activation and that this abnormality (1) is also detectable when blood pressure is normal and (2) depends on insulin resistance as well as on reflex alterations.

Time-course of diastolic dysfunction in different stages of chronic HCV related liver diseases

AIM

A hyperdynamic circulatory pattern in advanced liver disease is known since a long time. The first studies evaluating cardiac function in cirrhosis were performed in patients with alcoholic liver disease and thus this condition was attributed to the toxic effects of ethanol. A reduced performance of the left ventricle after physical and pharmacological strains along with an altered diastolic function has been demonstrated also in postviral cirrhosis. Many factors are involved in advanced cirrhosis whereas little is known in the earlier stages of disease.

METHODS

To this aim we have investigated patients with different stages of hepatitis C virus (HCV)-related liver disease to detect the time-course of diastolic dysfunction. An impaired relaxation and increased thickness of left ventricular walls along with an altered pattern of transmitral flow can be easily detected by means of echocardiography.

RESULTS

In chronic hepatitis diastolic function is preserved but increased thickness of left ventricle parietal walls can be detected in patients with fibrosis on liver biopsy. The typical pattern of diastolic dysfunction is observed in Child A cirrhotic patients and in Child C ascitic patients but thickness of parietal walls is more relevant in the former group. Chronic aldosterone blockade could exert favourable effects in heart remodeling suggesting a potential role of these drugs in cirrhotic cardiomyopathy.

CONCLUSIONS

The presence of increased thickness of left ventricle parietal walls in chronic hepatitis C in the precirrhotic stage point to a putative role of HCV in this heart structural abnormality that can become a co-factor in the more advanced stages of cirrhosis when portal hypertension and its deleterious effects on systemic hemodynamics, cardiac function and structure become manifest.

Hypertension, antihypertensive treatment and stroke prevention

Despite intensive research efforts, few effective treatments are available once stroke has occurred. Thus, stroke prevention should be a primary focus for all health care provides. The purpose of this article is to review the pathophysiological relevance of hypertension as a leading cause of stroke. This will be followed by an analysis of the evidence that blood pressure lowering with different antihypertensive drugs reduces the risk. Finally recent data suggest that the angiotensin II (ATII)-receptor antagonist losartan may offer advantages beyond blood pressure lowering, including attenuation of the central aortic reflected pressure wave, molecule-specific properties and neural protective influences on brain ATII type 2 receptors.

The association of hypertension and diabetes: prevalence, cardiovascular risk and protection by blood pressure reduction

Diabetes and hypertension frequently coexist, and their combination provides additive increases in the risk of life-threatening cardiovascular events. Recent guidelines agree on the need for early, aggressive reduction of blood pressure, with a goal of <130/80 mmHg, in patients with diabetes. The mechanism that underpins the increased sensitivity of diabetic subjects to hypertension is not known, but may involve impaired autoregulation or attenuated nocturnal decrease of blood pressure. All classes of antihypertensive agents are effective in reducing blood pressure in diabetic subjects, and all show evidence of a concomitant reduction in cardiovascular risk. Although there is some evidence that agents that interrupt the renin-angiotensin system (RAS) provide greater protective effects, the data are not conclusive. However, most diabetic subjects will require combination therapy to reach goal blood pressure. Antihypertensive drugs can also significantly influence the probability that otherwise healthy individuals will develop metabolic syndrome or type 2 diabetes. While diuretics and betablockers have a prodiabetic effect, angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers may prevent diabetes more effectively than the metabolically neutral calcium channel blockers. Given that diabetes is an important cardiovascular risk factor, there is the potential for reductions in risk due to reduced blood pressure to be offset by an increased risk due to the development of diabetes. Such concerns should be considered in the selection of antihypertensive therapy.

Left ventricular and carotid structure in untreated, uncomplicated essential hypertension: results from the Assessment Prognostic Risk Observational Survey (APROS)

The impact of hypertension on left ventricular (LV) and vascular structure and the relation of left ventricular hypertrophy (LVH) with vascular changes in untreated essential hypertensives has not been fully explored. This study investigated the prevalence of structural abnormalities of LV and carotid arteries and their determinants in a large population of untreated, uncomplicated essential hypertensive patients. The Assessment of Prognostic Risk Observational Survey was a multicentre (44 centres) prospective study including 1142 untreated hypertensives classified as low or medium cardiovascular risk on the basis of the routine diagnostic work-up recommended by the 1999 World Health Organization/International Society of Hypertension guidelines. All patients underwent ultrasound examinations of the heart and carotid arteries. LVH and carotid structural changes were diagnosed when: (1) LV mass index exceeded 125 g/m(2) in men and 110 g/m(2) in women; (2) there was at least one plaque (focal thickening>1.3 mm) in any segment of either carotid artery or a diffuse common carotid intima-media thickness (IMT) (average of IMT>/=0.8 mm) was present. Overall, 1074 patients (504 women, mean age 48.1+/-11.4 years) completed the study with ultrasonographic examinations of good technical quality. The prevalences of LVH and LV concentric remodelling in the total population were 26.8 and 10.7%, respectively. Eccentric hypertrophy was more prevalent than concentric hypertrophy (15.2 vs 11.6%). One or more carotid plaques or thickening were present in 27.4% of the patients. A stepwise increase in IM thickness occurred from the lowest values in patients with normal cardiac mass and geometry (0.68 mm) to intermediate in those with LV remodelling (0.76 mm) and eccentric LVH (0.81 mm) and to the highest level in patients with concentric LVH (0.87 mm). Patients with LV concentric remodelling and concentric LVH had a significantly greater relative carotid wall thickness than those with normal geometry and eccentric LVH (0.25 and 0.26 vs 0.18 and 0.19, respectively, P<0.01). According to a multivariate analysis age, blood glucose, systolic BP and pulse pressure were the main independent predictors of LVH, while age, systolic BP and total cholesterol were the variables with the greatest impact on IM thickening. To conclude, this study shows that: (1) altered patterns of LV structure and geometry and carotid structural changes occur in a large fraction of patients with untreated essential hypertension; (2) there is a significant association between carotid wall thickening and LVH; (3) the probability of LVH or carotid thickening is significantly greater in elderly, in patients with higher systolic BP and in patients with associated metabolic risk factors.

Acute Effect of High-Fat Meal on Endothelial Function in Moderately Dyslipidemic Subjects

OBJECTIVE

Hypercholesterolemia markedly impairs endothelial function. Whether this is the case for hypertriglyceridemia is less clear, however, and limited evidence exists on the effect of an acute increase in triglyceridemia caused by a high-fat meal.

METHODS AND RESULTS

In 16 normotensive subjects with an untreated mild hypertriglyceridemia and dyslipidemia and in 7 normal controls, we measured radial artery diameter and blood flow by an echo-tracking device (NIUS02). Data were obtained at baseline, at the release of a 4-minute ischemia of the hand, which causes an increase in arterial diameter dependent on nitric oxide (NO) secretion, and at the release of a 12-minute exclusion of the arm by an arm cuff to obtain a larger increase in arterial diameter mainly of nonendothelial nature. Measurements were performed before and 6 hours after a high-fat meal (680 kcal/m(2) body surface; 82% lipids). In mild dyslipidemic hypertriglyceridemic subjects, the high-fat meal did not alter baseline blood pressure (beat-to-beat finger measurement), heart rate, radial artery diameter, and blood flow. It also did not alter the increase in blood flow induced by the 4-minute ischemia (+42.7+/-10.4 and +43.7+/-10.4 mL/min), whereas it markedly attenuated the concomitant increase in arterial diameter (+0.31+/-0.06 versus 0.13+/-0.06 mm; P<0.05). The alteration of the diameter response did not correlate with changes in total cholesterol, but it showed a significant correlation with the increase in serum triglycerides induced by high-fat meal (r=0.49, P<0.05). This attenuation was not seen in control subjects and in subjects in whom measurements were repeated after a 6-hour observation period. It was also not paralleled by an alteration of the endothelially independent response to a 12-minute ischemia whose larger effects on arterial diameter and blood flow were similar before and after the high-fat meal.

CONCLUSIONS

Endothelial function is markedly impaired by a high-fat meal that causes an acute hypertriglyceridemia. This impairment is evident in dyslipidemic patients with baseline hypertriglyceridemia but not in normotriglyceridemic controls. An oral fat load was administered to 55 HIV-positive and 10 HIV-negative individuals. Postprandial clearance of triglyceride-rich lipoproteins was delayed in HIV-positive individuals. Compared with HIV-positive subjects not on PIs, those taking PIs do not have increased postprandial triglyceride-rich lipoproteins but do have increased postprandial intermediate-density and low-density lipoproteins. Hypercholesterolemia impairs endothelial function, whereas the effect of hypertriglyceridemia is less clear. In normotensive subjects with an untreated hypertriglyceridemia and hypercholesterolemia, we measured endothelial function before and 6 hours after a high-fat meal. The results demonstrate that in moderately dyslipidemic patients, endothelial function is impaired by acute hypertriglyceridemia.