Initial drop of blood pressure during head-up tilt in patients with cerebrovascular accidents

Autonomic dysfunction after mild acute ischemic stroke and six months after: a prospective observational cohort study

INTRODUCTION

Autonomic dysfunction is prevalent in ischemic stroke patients and associated with a worse clinical outcome. We aimed to evaluate autonomic dysfunction over time and the tolerability of the head-up tilt table test in an acute stroke setting to optimize patient care.

PATIENTS AND METHOD

In a prospective observational cohort study, patients were consecutively recruited from an acute stroke unit. The patients underwent heart rate and blood pressure analysis during the Valsalva maneuver, deep breathing, active standing, and head-up tilt table test if active standing was tolerated. In addition, heart rate variability and catecholamines were measured. All tests were performed within seven days after index ischemic stroke and repeated at six months follow-up.

RESULTS

The cohort was comprised of 91 acute stroke patients, mean (SD) age 66 (11) years, median (IQR) initial National Institute of Health Stroke Scale 2 (1-4) and modified Ranking Scale 2 (1-3). The head-up tilt table test revealed 7 patients (10%) with orthostatic hypotension. The examination was terminated before it was completed in 15%, but none developed neurological symptoms. In the acute state the prevalence of autonomic dysfunction varied between 10-100% depending on the test. No changes were found in presence and severity of autonomic dysfunction over time.

CONCLUSION

In this cohort study of patients with mild stroke, autonomic dysfunction was highly prevalent and persisted six months after index stroke. Head-up tilt table test may be used in patients who tolerate active standing. Autonomic dysfunction should be recognized and handled in the early phase after stroke.

Using Kalman Filtering to Predict Time-Varying Parameters in a Model Predicting Baroreflex Regulation During Head-Up Tilt

The cardiovascular control system is continuously engaged to maintain homeostasis, but it is known to fail in a large cohort of patients suffering from orthostatic intolerance. Numerous clinical studies have been put forward to understand how the system fails, yet noninvasive clinical data are sparse, typical studies only include measurements of heart rate and blood pressure, as a result it is difficult to determine what mechanisms that are impaired. It is known, that blood pressure regulation is mediated by changes in heart rate, vascular resistance, cardiac contractility, and a number of other factors. Given that numerous factors contribute to changing these quantities, it is difficult to devise a physiological model describing how they change in time. One way is to build a model that allows these controlled quantities to change and to compare dynamics between subject groups. To do so, it requires more knowledge of how these quantities change for healthy subjects. This study compares two methods predicting time-varying changes in cardiac contractility and vascular resistance during head-up tilt. Similar to the study by Williams et al. [51], the first method uses piecewise linear splines, while the second uses the ensemble transform Kalman filter (ETKF) [1], [11], [12], [33]. In addition, we show that the delayed rejection adaptive Metropolis (DRAM) algorithm can be used for predicting parameter uncertainties within the spline methodology, which is compared with the variability obtained with the ETKF. While the spline method is easier to set up, this study shows that the ETKF has a significantly shorter computational time. Moreover, while uncertainty of predictions can be augmented to spline predictions using DRAM, these are readily available with the ETKF.

Carotid blood flow, cardiovascular and endocrine responses during head-up tilt in patients with acute cerebrovascular diseases

The purpose of this study was to define common carotid blood flow (CBF), cardiovascular and endocrine responses during head-up tilt (HUT) in patients with acute cerebrovascular diseases (CVD). In 31 male patients with acute CVD (damage of the supratentorial area) and 21 age-matched control male subjects, we measured CBF, mean blood pressure (MBP), heart rate, stroke volume and cardiac output responses before (baseline), during and after HUT. We also measured plasma levels of antidiuretic hormone, adrenaline, noradrenaline, aldosterone and plasma renin activity. After obtaining baseline measurements during 3-minutes horizontal position, HUT was performed for 5 minutes, followed by continuation of recording for 3 more minutes in the horizontal position. During HUT, CBF decreased significantly and equally in both groups. MBP did not change during HUT in both groups. The endocrine responses were also not different between the two groups. The results suggest that damage to the supratentorial area in patients with acute CVD do not alter the CBF, cardiovascular and endocrine responses. In other words, HUT does not predispose patients with acute CVD to serious falls in MBP and CBF at upright posture.