Autonomic testing: which value for each cardiovascular test? An observational study.

AIMS: Cardiovascular autonomic testing is time consuming when adopting the entire Ewing battery of tests, hence, clinicians usually adopt an empirically reduced number of tests which may give controversial results. Our purpose was to examine the reliability of the cardiovascular tests most commonly used in autonomic diagnoses. METHODS: We tested 334 subjects, from an original group of 3745, who had shown an altered deep breathing test to both Lying to standing and Valsalva manoeuvre, assuming a value of postural hypotension of more than 15 mmHg as a sign of almost true dysautonomia. RESULTS: VM showed the highest sensitivity (85%) and, when coupled to LS, highest specificity (83%). CONCLUSIONS: VM could be useful when screening for possible or early autonomic neuropathy, VM + LS is useful as a diagnostic tool for probable or advanced autonomic neuropathy, and VM + LS + PH is useful for certain diagnosis of definite or late stage autonomic neuropathy.

Long-Acting GLP-1 Receptor Agonist Exenatide Influence on the Autonomic Cardiac Sympatho-Vagal Balance.

Long-acting glucagon-like peptide 1 receptor agonists are increasingly used to treat type 2 diabetes. An increase of heart rate (HR) has been observed with their use. To elucidate the role of the cardiac sympatho-vagal balance as a possible mediator of the reported increase in HR, we performed power spectral analysis of HR variability (HRV) in patients receiving exenatide extended-release (ER). Twenty-eight ambulatory patients with type 2 diabetes underwent evaluation at initiation of exenatide-ER and thereafter at 3 and at 6 months. To obtain spectral analyses of HRV, a computerized acquisition of 10 minutes of RR electrocardiogram intervals (mean values of ~700 RR intervals) were recorded both in lying and in standing positions. All patients showed a substantial increase of HR both in lying and in standing positions. Systolic blood pressure, body weight, and glycated hemoglobin A1c significantly decreased both at 3 and 6 months compared with basal levels. The low-frequency/high-frequency ratio varied from 3.05 ± 0.4 to 1.64 ± 0.2 (P < 0.001) after 3 months and to 1.57 ± 0.3 (P < 0.001) after 6 months in a lying position and from 4.56 ± 0.8 to 2.24 ± 0.3 (P < 0.001) after 3 months and to 2.38 ± 0.4 (P < 0.001) after 6 months in a standing position compared with basal values, respectively. HR variations, induced by exenatide-ER treatment, do not appear to be related to sympathetic autonomic tone. Of note, we observed a relative increase of vagal influence on the heart.

Modeling Pathological Hemodynamic Responses to the Valsalva Maneuver.

The Valsalva maneuver (VM) consisting in a forced expiration against closed airways is one of the most popular clinical tests of the autonomic nervous system function. When properly performed by a healthy subject, it features four characteristic phases of arterial blood pressure (BP) and heart rate (HR) variations, based on the magnitude of which the autonomic function may be assessed qualitatively and quantitatively. In patients with some disorders or in healthy patients subject to specific conditions, the pattern of BP and HR changes during the execution of the Valsalva maneuver may, however, differ from the typical sinusoidal-like pattern. Several types of such abnormal responses are well known and correspond to specific physiological conditions. In this paper, we use our earlier mathematical model of the cardiovascular response to the Valsalva maneuver to show that such pathological responses may be simulated by changing individual model parameters with a clear physiological meaning. The simulation results confirm the adaptability of our model and its usefulness for diagnostic or educational purposes.

Mathematical modelling of cardiovascular response to the Valsalva manoeuvre.

The Valsalva manoeuvre (VM) used for clinical autonomic testing results in a complex cardiovascular response with a concomitant action of several regulatory mechanisms whose nonlinear interactions are difficult to analyse without the aid of a mathematical model. The article presents a new non-pulsatile compartmental model of the human cardiovascular system with a variable intrathoracic pressure enabling the simulation of the haemodynamic response to the VM. The model is based on physiological data and includes three baroreflex mechanisms acting on heart rate, systemic resistance and venous unstressed volume. New nonlinear functions have been proposed to model cardiac output dependence on preload and afterload. Following the individual fitting of some parameters with a clear physiological meaning, the model is able to fit clinical data from patients with both typical and abnormal haemodynamic response to the VM. The sensitivity analysis showed that the model is most sensitive to the parameters describing the vascular pressure-volume relationships (the maximal volume of systemic veins and the relative level of vascular compliance). The use of nonlinear pressure-volume relationships for systemic veins proved crucial for the accurate modelling of the VM. On the contrary, the introduction of aroreflex time delays did not change significantly the haemodynamic response to the manoeuvre. The model can be a useful tool for aiding the interpretation of patient's response to the VM and provides a framework for analysing the interactions between the cardiovascular system and autonomic regulatory mechanisms.

Prevalence of Cardiovascular Autonomic Neuropathy in a Cohort of Patients With Newly Diagnosed Type 2 Diabetes: The Verona Newly Diagnosed Type 2 Diabetes Study (VNDS).

OBJECTIVE: Cardiovascular autonomic diabetic neuropathy (CAN) is a serious complication of diabetes. No reliable data on the prevalence of CAN among patients with newly diagnosed type 2 diabetes are available. Therefore, the aim of this study was to estimate the prevalence of CAN among patients with newly diagnosed type 2 diabetes. RESEARCH DESIGN AND METHODS: A cohort of 557 patients with newly diagnosed type 2 diabetes with cardiovascular autonomic test results available was selected. Early and confirmed neuropathy were assessed using a standardized methodology and their prevalences determined. A multivariate logistic regression analysis was modeled to study the factors associated with CAN. RESULTS: In the entire cohort, the prevalence of confirmed CAN was 1.8%, whereas that of early CAN was 15.3%. Prevalence did not differ between men and women. In the multivariate analyses BMI results were independently and significantly associated with CAN after adjusting for age, sex, hemoglobin A1c, pulse pressure, triglyceride-to-HDL cholesterol ratio, kidney function parameters, and antihypertensive treatment. CONCLUSIONS: CAN could be detected very early in type 2 diabetes. This study may suggest the importance of performing standardized cardiovascular autonomic tests after diagnosis of type 2 diabetes.

A new diagnostic and therapeutic approach to pericardial effusion: transbronchial needle aspiration.

Pericardiocentesis was introduced during the 19th century, and reached its current level of development with the introduction of two-dimensional echocardiography. Although there is general agreement that complications are rare with skilled operators, a diagnostic and therapeutic problem often occurs when there is a posterior pericardial effusion, as it is not easy to quantify by echocardiography, and difficult to drain through a percutaneous access; therefore, it is usually treated surgically. We describe a new approach to pericardial effusion by a transbronchial access through the left lower lobe bronchus (which allows both diagnosis and evacuation of abundant amounts of fluid), or through the distal trachea (for diagnostic purpose only, in the presence of pericardial effusions filling the aortic recess of the pericardium). The technique is rather easy for operators skilled in transbronchial needle aspiration, and is safe, economical, and well tolerated.