Blood pressure variability responses to tilt are buffered by cardiac autonomic control

Variability in blood pressure (BPV) is influenced by vascular sympathetic drive as well as autonomic control of the heart. Evidence suggests that elimination of cardiac autonomic control, as measured by heart period variability (HPV), produces a reduction in BPV at rest but an increase in BPV during challenge. We recently showed that the BPV response to psychological challenge, which principally produces cardiac parasympathetic withdrawal, was inversely related to the subject's level of cardiac control. In the current study we examined the BPV response to orthostatic tilt, a sympathetic stressor. Subjects were 22 healthy men and women who differed in cardiac control due in part to differences in aerobic capacity. HPV and BPV were measured noninvasively on a beat-to-beat basis. Tilt produced significant increases in heart rate and diastolic blood pressure and a significant decrease in high frequency HPV. As predicted, changes in BPV in response to tilt were inversely related to resting HPV. Results are interpreted in terms of a model of cardiovascular control which holds that BPV originates from feedforward effects of central control of the heart, feedback effects mediated through the baroreflexes, and direct sympathetic vascular effects.

Cardiac autonomic control is inversely related to blood pressure variability responses to psychological challenge

Blood pressure exhibits variability (BPV) at low (0.02- to 0.07-Hz), mid (0.07- to 0.15-Hz)-, and high (0.15- to 0.50-Hz) frequencies. Evidence suggests that BPV responses to challenge are inversely related to cardiac autonomic control. We tested this hypothesis by examining the BPV responses to psychological stressors in 22 normal subjects who differed in cardiac control, operationalized as resting heart period variability (HPV). HPV and BPV were measured noninvasively or a beat-to-beat basis. The stressors produced a significant increase in heart rate and a small but significant increase in diastolic blood pressure. As predicted, the changes in BPV in response to the stressors were inversely related to resting HPV. The results are interpreted in terms of a model of cardiovascular control that holds that BPV originates from feedforward effects of central control of the heart, feedback effects mediated through the baroreflexes, and direct sympathetic vascular effects.

Dementia after stroke increases the risk of long-term stroke recurrence

BACKGROUND

Although risk factors for first stroke have been identified, the predictors of long-term stroke recurrence are less well understood. We performed the present study to determine whether dementia diagnosed three months after stroke onset is an independent risk factor for long-term stroke recurrence.

METHODS

We examined 242 patients (age = 72.0 +/- 8.7 years) hospitalized with acute ischemic stroke who had survived the first three months without recurrence and followed them to identify predictors of long-term stroke recurrence. We diagnosed dementia three months after stroke using modified DSM-III-R criteria based on neuropsychological and functional assessments. The effects of conventional stroke risk factors and dementia status on survival free of recurrence were estimated using Kaplan-Meier analyses, and the relative risks (RR) of recurrence were calculated using Cox proportional hazards models.

RESULTS

Dementia (RR = 2.71, 95% CI = 1.36 to 5.42); cardiac disease (RR = 2.18, CI = 1.15 to 4.12); and sex, with women at higher risk (RR = 2.03, CI = 1.01 to 4.10), were significant independent predictors of recurrence, while education (RR = 1.90, CI = 0.77 to 4.68), admission systolic blood pressure >160 mm Hg (RR = 1.80, CI = 0.94 to 3.44) and alcohol intake exceeding 160 grams per week (RR = 1.86, CI = 0.79 to 4.38) were weakly related.

CONCLUSIONS

Our results suggest that dementia significantly increases the risk of long-term stroke recurrence, with additional independent contributions by cardiac disease and sex. Cognitive impairment may be a surrogate marker for multiple vascular risk factors and larger infarct volume that may serve to increase the risk of recurrence. Alternatively, less aggressive medical management of stroke patients with cognitive impairment or noncompliance of such patients with medical therapy may be bases for an increased rate of stroke recurrence.

The multisite field trial of the consultation-liaison psychiatry assessment instrument

A multisite field trial was conducted at 11 institutions to test the clinical reliability of a 29-item consultation-liaison (C-L) psychiatry assessment instrument. Twenty-five raters viewed videotapes of two "trainees" conducting clinical interviews with a simulated patient. One trainee was a medical student, the other was a fellow in psychiatry. Raters completed the 29-item assessment instrument for each trainee. The mean value scores reflected the skill of each trainee. The medical student had a mean score of 1.93, whereas the C-L fellow had a mean score of 3.13 which parallels the expected level of skill for the two interviewers. Eighty-six percent of the items (25/29) had a standard deviation (SD) of less than 1.0. Each of the remaining four items (14%) had a SD minimally greater than 1.0. These results reflect clear wording of items with measurable parameters defined for assessing trainees' skills. The authors present different uses for the assessment instrument, including giving feedback to trainees regarding interviewing techniques and skills; setting "gold" and "lead" standards for clinical C-L interviewing skills; and training supervisors in evaluation using a standardized assessment instrument.

Risk factors for incident dementia after stroke. Role of hypoxic and ischemic disorders

BACKGROUND AND PURPOSE

Stroke significantly increases the risk of dementia in the elderly, yet the risk factors for incident dementia after ischemic stroke are not well understood. We attempted to determine whether hypoxic-ischemic (HI) disorders, which may result from comorbid medical conditions (eg. seizures, cardiac arrhythmias, pneumonia), would be an independent risk factor for the development of new dementia after stroke.

METHODS

We prospectively followed 185 initially nondemented patients with ischemic stroke (age, 70.3 +/- 7.7 years) for a maximum of 52.8 months. We diagnosed the presence of dementia at annual examinations based on neuropsychological testing and modified DSM-III-R criteria. HI disorders were identified by record review or examination during hospitalization. We used Kaplan-Meier analysis to determine the cumulative proportion of patients with and without HI disorders who survived free of dementia and used Cox models to estimate the relative risk of dementia associated with HI disorders.

RESULTS

The cumulative proportion (+/- SE) surviving without dementia was 51.7 +/- 10.9% in the HI group versus 78.2 +/- 4.3% in the non-HI group after 52.8 months of observation. The relative risk of incident dementia associated with HI events was 4.3 (95% confidence interval = 1.9 to 9.6) after we adjusted for demographic factors, recurrent stroke, and baseline cognitive function.

CONCLUSIONS

We conclude that HI disorders may be a significant independent risk factor for incident dementia after stroke, even after adjustment for other recognized predictors of cognitive decline. Recognition of HI cerebral damage as a possible pathogenic mechanism for dementia after stroke may allow targeted therapeutic interventions to prevent subsequent cognitive deterioration.

Heart rate reactivity and heart period variability throughout the first year after heart transplantation

Heart rate reactivity to mental stress is substantially blunted early after heart transplantation, suggesting that the loss of neural modulation limits the cardiovascular response to mental stress. We tested whether reactivity to mental stress recovers during the first year after heart transplantation. Hemodynamic and respiratory responses to mental arithmetic challenge were studied in 20 heart transplant recipients 3, 6, and 12 months after surgery. A normal comparison group was studied at equivalent intervals. Heart rate reactivity to mental arithmetic was significantly reduced in the cardiac transplant group compared to the normal subjects. This effect persisted up to 1 year after transplantation. Heart period variability in the heart transplant recipients was minimal in all three test sessions. The findings suggest that no functional reinnervation or other compensatory adaptation occurs up to 1 year after heart transplantation.

Relationships between circulating catecholamines and low frequency heart period variability as indices of cardiac sympathetic activity during mental stress

Heart rate increases during psychological stress are the product of cardiac sympathetic activation and parasympathetic withdrawal. Levels of plasma epinephrine (E) and norepinephrine (NE) have a long history as indicators of cardiac adrenergic activity and, accordingly, generally increase in response to psychological challenge. Recently, several investigators have suggested that indices derived from power spectral analysis of heart period variability (HPV) also may provide estimates of cardiac sympathetic nervous system activity. These indices include power in the low frequency band (0.04-0.15 Hz, LF), and the ratio of low to high frequency (0.15-0.50 Hz, HF) power (LF/HF). The relationship between spectral and neurohumoral indices during psychological stress has not been investigated. This issue was addressed by studying spectrally defined measures of HPV and levels of plasma E and NE in 34 normal subjects who participated in a study of responsiveness to a psychologically challenging arithmetic task. Heart rate (HR), LF and HF power, the LF/HF ratio, and blood pressure were measured during the 5-minute baseline and 5-minute task periods. Integrated samples of forearm venous blood were collected for both periods. E and NE were analyzed by high performance liquid chromatography. The task produced significant increases in HR, systolic and diastolic pressures, and NE. Of the 12 Pearson correlation coefficients used to examine the relationships between power spectral measures and catecholamines for the baseline, task, and delta values, none achieved statistical significance, suggesting little relationship between neurohumoral and spectral estimates of cardiac sympathetic activity. We conclude that under conditions of psychological stress, LF power provides no useful information about cardiac sympathetic activity, both because power in this frequency band falls whereas HR rises and because there is no relationship between LF power and plasma NE.

Consistency of heart rate and sympathovagal reactivity across different autonomic contexts

Theories that psychophysiological reactivity constitutes a risk factor for coronary artery disease assume that reactivity is a consistent individual characteristic. We tested this assumption by measuring reactivity to three psychologically challenging tasks performed by 22 healthy subjects across different autonomic contexts produced by positional change. Dependent variables included heart rate (HR), low-frequency (LF; 0.04-0.15 Hz) and high-frequency (HF; 0.15-0.50 Hz) heart period variability, and the LF/HF ratio. HR (r = .44, p < .05) and LF/HF ratio (r = .48, p = .03) reactivity were modestly correlated across the different autonomic contexts, but HF and LF power reactivity were not. These findings suggest that HR reactivity to psychological challenge is a modestly consistent characteristic of individuals, despite differences in autonomic context. Although the same is true of cardiac sympathovagal balance, reactivity of HF and LF power were less consistent.

Temporal stability of heart period variability during a resting baseline and in response to psychological challenge

Central to the psychophysiologic reactivity hypothesis of the etiology of coronary artery disease is the assumption that reactivity is an individual characteristic that is stable over time. Although heart rate (HR) and blood pressure reactivity appear to meet this criterion, temporal stability of cardiac autonomic control as measured by analysis of heart period variability (HPV) has not been assessed. In this study, we tested the stability of HPV, measured in both the time and frequency domain, during a quiet, resting baseline and in response to 5-min mental arithmetic and reaction time tasks, in 20 normal subjects measured in three testing sessions during a 9-month period. Stability, assessed by the intraclass correlation coefficient (ICC), was excellent for resting baseline measures of HR and HPV, with ICCs of 0.68-0.86. However, HR and HPV reactivity to either arithmetic or reaction time tasks generally was less stable, with ICCs of 0.17-0.73, in contrast to results of previous studies demonstrating long-term stability of HR responses to psychological challenge. Stability of aggregated reactivity scores was only slightly improved. Whether for individual tasks or aggregated measures, reactivity of total and low-frequency measures of HPV was moderately stable but stability of high-frequency HPV reactivity was poor.

Dementia after stroke is a predictor of long-term survival

BACKGROUND AND PURPOSE

The aim of this study was to determine whether dementia after stroke adversely influences long-term survival.

METHODS

Subjects were 251 patients > or = 60 years of age with ischemic stroke who were given neurological, neuropsychological, and functional examinations 3 months after hospitalization and were followed up prospectively. Using criteria modified from the Diagnostic and Statistical Manual of Mental Disorders-III-R, dementia was found in 66 (26.3%) patients at the 3-month baseline examination. Life-table methods were used to estimate mortality rates in the groups with and without dementia after 1 to 5 years of follow-up, Kaplan-Meier curves to estimate the cumulative proportion surviving with and without dementia, and Cox proportional-hazards analysis to compute the relative risk of mortality associated with dementia at baseline, after adjusting for other potential predictors of stroke mortality.

RESULTS

The mortality rate was 19.8 deaths per 100 person-years with dementia compared with 6.9 deaths per 100 person-years without dementia. The cumulative proportion surviving after a median follow-up of 58.6 months was 38.9 +/- 0.08% for those with dementia and 74.5 +/- 0.04% for those without dementia. The relative risk associated with dementia was 3.11 (95% confidence interval, 1.79 to 5.41) after adjusting for the effects of demographic factors, cardiac disease, severity of stroke (Barthel Index), stroke type (lacunar versus nonlacunar), and recurrent stroke (examined as a time-dependent variable). When the Mini-Mental State Examination score at baseline was examined instead of the diagnosis of dementia, the results of the model were similar.

CONCLUSION

Our study is the first to demonstrate that dementia or cognitive impairment adversely influences long-term survival after stroke, even after adjusting for other commonly accepted predictors of stroke mortality. Impairment in intellectual function after stroke, independent of physical disability, has a significant impact on prognosis. Both cognitive and physical functions should be assessed in clinical studies of stroke outcome.

Risk of dementia after stroke in a hospitalized cohort: results of a longitudinal study

Stroke is considered the second most common cause of dementia, but the magnitude of the risk posed by stroke has not been fully clarified. The aim of this study was to determine the long-term risk of developing dementia after stroke onset in a hospitalized cohort. We prospectively examined 185 nondemented patients aged > or = 60 years hospitalized with ischemic stroke and 241 age-matched nondemented controls without stroke from the same community using neurologic, neuropsychological, and functional assessments given annually. Using criteria modified from the DSM-III-R, we diagnosed incident dementia based on the annual examination findings. We used life-table methods to estimate incidence in the two groups, Kaplan-Meier analysis to determine the proportion surviving without dementia, and Cox proportional-hazards analysis to compute the relative risk (RR) of dementia after 1 to 4 years of follow-up. The incidence of dementia was 8.4 per 100 person-years in the stroke group and 1.3 per 100 person-years in the control group. After 52 months of follow-up, the cumulative proportion (+/- SE) surviving without dementia was 66.3 +/- 5.5% for stroke and 90.3 +/- 4.3% for control subjects. The RR of dementia associated with stroke compared with controls was 5.5 (95% CI, 2.5 to 11.1) after adjusting for demographic factors. Older age at stroke onset and fewer years of education were significant covariates, but sex and race were not. A low score on the Mini-Mental State Examination at baseline was a significant predictor when added to this model.(ABSTRACT TRUNCATED AT 250 WORDS)

Brief interval heart period variability by different methods of analysis correlates highly with 24 h analyses in normals

Heart period variability (HPV) measured from 24 h ECG recordings predicts mortality following myocardial infarction and may be a measure of cardiovascular health in the general population. Since epidemiologic evaluation of healthy people will require alternatives less intensive than 24 h recording, we investigated the relationship between HPV derived from 24 h and 5 min recordings, using two approaches for obtaining RR intervals. Template-matching (TM) algorithms were applied to 24 h ECG recordings from 41 normal subjects (mean age 35.7 +/- 13 years). Five min of ECG data during this 24 h period also were collected by an on-line microcomputer-based system for peak detection (PD) analysis. Intraclass correlations comparing the TM and PD approaches on the 5 min period were .80 or greater for all measures of HPV. Pearson correlation coefficients between the 5 min (TM) estimates and 24 h data and 5 min (PD) estimates and 24 h data exceeded .60 and .55, respectively, for all but one variable, with all p values < .05. Thus, in healthy adults, TM and PD approaches to HPV estimation from short segments of ECG data are highly consistent and the correlations between HPV obtained from brief intervals and 24 h measures were substantial, suggesting that assessment of HPV as a screening measure of cardiac autonomic control in healthy adults may be feasible.

Cardiac denervation and cardiovascular reactivity to psychological stress

OBJECTIVE

This study investigated the mechanisms responsible for increases in heart rate and blood pressure during psychological stress, which are incompletely understood. Since cardiac transplant patients have denervated hearts, they provide a unique model for isolating central versus peripheral influences on the cardiovascular response to stress.

METHODS

The authors compared the responses to two laboratory stressors of 20 ambulatory heart transplant recipients and two groups of normal subjects, one whose ages were matched to the ages of the transplant patients (mean = 46 years) and one whose ages were matched to the ages of the heart donors (mean = 27 years). The three groups of subjects performed mental arithmetic and reaction time tasks.

RESULTS

Heart rate increase during the mental arithmetic task was significantly attenuated in the transplant recipients. During stress, stroke volume increased in the transplant recipients but decreased in both groups of comparison subjects. The difference in age between the heart recipients and donors did not account for the difference in reactivity between the heart transplant patients and the normal subjects.

CONCLUSIONS

Direct neural stimulation of the heart is more important than peripherally circulating factors in producing tachycardia during psychological stress. Cardiac but not vascular responses to psychological stress are altered by cardiac denervation.

Effect of mental stress throughout the day on cardiac autonomic control

Although many laboratory studies have demonstrated changes in cardiac autonomic control during psychological stress, few have attempted to demonstrate this effect in ambulatory subjects. To address this issue, 24-h electrocardiographic recordings of 33 healthy subjects were analyzed for RR interval and heart period variability (HPV) responses associated with periodic diary entries measuring physical position, negative effect, and time of day. A total of 362 diary entries were made during the 24-h sessions, each in response to a device which signaled on an average of once per hour. HPV was analyzed in the frequency domain, yielding estimates of spectral power in low (LF) and high (HF) frequency bands, as well as the LF/HF ratio. Because of the high correlations of the measures of negative affect (alpha = 0.91), they were combined to create a single index of stress. Multivariate analysis was used to assess the effect of individual subject differences, physical position, and stress on RR interval and HPV. Results revealed significant effects of individual differences, stress, and physical position on RR interval, with increases in stress associated with decreases in RR interval as expected. HF power was significantly lower and the LF/HF ratio significantly higher in the standing compared with the sitting position. Psychological stress was significantly associated with an increase in the LF/HF ratio, suggesting increases in the relative predominance of sympathetic nervous system activity during stressful periods of the day. Overall, these findings suggest that in ambulatory normal subjects, cardiac autonomic control varies throughout the day as a function of self-reported stress.

Cognitive impairment after stroke: frequency, patterns, and relationship to functional abilities

Cognitive function was examined in 227 patients three months after admission to hospital for ischaemic stroke, and in 240 stroke-free controls, using 17 scored items that assessed memory, orientation, verbal skills, visuospatial ability, abstract reasoning, and attentional skills. After adjusting for demographic factors with standardised residual scores in all subjects, the fifth percentile was used for controls as the criterion for failure on each item. The mean (SD) number of failed items was 3.4 (3.6) for patients with stroke and 0.8 (1.3) for controls (p < 0.001). Cognitive impairment, defined as failure on any four or more items, occurred in 35.2% of patients with stroke and 3.8% of controls (p < 0.001). Cognitive domains most likely to be defective in stroke compared with control subjects were memory, orientation, language, and attention. Among patients with stroke, cognitive impairment was most frequently associated with major cortical syndromes and with infarctions in the left anterior and posterior cerebral artery territories. Functional impairment was greater with cognitive impairment, and dependent living after discharge either at home or nursing home was more likely (55.0% with, v 32.7% without cognitive impairment, p = 0.001). In a logistic model examining the risks related to dependent living after stroke, cognitive impairment was a significant independent correlate (odds ratio, OR = 2.4), after adjusting for age (OR = 5.2, 80 + v 60-70 years) and physical impairment (OR = 3.7, Barthel index < or = 40 v > 40). It is concluded that cognitive impairment occurs frequently after stroke, commonly involving memory, orientation, language, and attention. The presence of cognitive impairment in patients with strike has important functional consequences, independent of the effects of physical impairment. Studies of stroke outcome and intervention should take into account both cognitive and physical impairments.

L-carnitine and platelet aggregation in uremic patients subjected to hemodialysis

It has been reported that treatment with L-carnitine at a daily dose of 3 g orally may cause a rise in platelet aggregation and serum triglyceride concentration in hemodialyzed patients. The present double-blind cross-over study has been performed to evaluate the influence of L-carnitine when compared with placebo on platelet aggregation and plasma concentrations of various factors involved in platelet activation. In addition, the concentration of triglycerides, cholesterol and HDL-cholesterol has been evaluated. 18 uremic patients on maintenance hemodialysis for at least 1 year were randomly allocated either to a control group receiving placebo or to a group treated with L-carnitine. Statistical analysis performed by means of ANOVA did not show any significant change in the serum concentration of cholesterol, HDL-cholesterol and triglycerides. Furthermore, platelet aggregation tests (performed with adenosine 5'-diphosphate, epinephrine, thrombin and collagen) and plasma beta-thromboglobulin concentration did not show any statistically significant difference. In addition, the plasma concentration of several coagulation markers, such as factor VIIIc, antithrombin III, alpha 2-antiplasmin, and fibrinopeptide A, did not show any significant variation. The results suggest that under our experimental conditions L-carnitine neither increases the risk of thromboembolism nor alters the serum lipid content in uremic patients on chronic hemodialysis.

High doses of L-carnitine in acute myocardial infarction: metabolic and antiarrhythmic effects

Fatty acids accumulate in the muscle cells in some carnitine deficiency syndromes due to a variety of genetic defects in intermediary metabolism. L-Carnitine administration may relieve this excess by transporting acyl compounds out of the cell as acylcarnitine. Similar fatty acid accumulation occurs during myocardial ischaemia because of the decreased rate of beta-oxidation, and this has been put forward as a cause of ventricular arrhythmias. This study was carried out to investigate whether administration of high doses of i.v. L-carnitine in patients with acute myocardial infarction could increase urinary excretion of acylcarnitine and reduce early ventricular arrhythmias. Fifty-six patients suffering from acute myocardial infarction, admitted to the Coronary Unit between 3 and 12 h after the onset of symptoms, were included in the study. The design of the study was double blind, parallel and placebo controlled. Allocation of treatment to patients was done randomly after stratification (time from onset of pain and site of infarction). The first group (28 patients) received intravenous L-carnitine at a dose of 100 mg kg-1 b.w. every 12 h for 36 h while the second group (28 patients) received placebo intravenously. Immediately before starting treatment two blood samples were taken (at 5-min intervals) and a further 16 samples were taken at regular intervals over the following 48 h. Patients' urine was collected over the same period of time. Concentrations of free carnitine, short chain acylcarnitine esters and long chain acylcarnitine esters in serum and urine were measured.(ABSTRACT TRUNCATED AT 250 WORDS)

L-carnitine addition to dialysis fluid. A therapeutic alternative for hemodialysis patients

L-Carnitine has been reported to have beneficial effects in the reduction of serum triglycerides and increases high-density lipoprotein cholesterol in hemodialysis patients. The published reports are, however, equivocal. Paradoxical increases in serum triglycerides following intravenous administration of L-carnitine have been observed. It has been suggested that the paradoxical rise in triglycerides may result from the high doses used and intravenous administration, both of which may cause abnormally high tissue concentrations. In the present study 22 hemodialysis patients were selected. All patients had been treated intravenously with 2 g of L-carnitine administered at the end of dialysis for a minimum of 12 months. Treatment with L-carnitine was then discontinued during a 4-month washout period. The patients were then divided into two equal subgroups and placed on L-carnitine therapy (1 g i.v.) at the end of dialysis for 1 month. Thereafter, L-carnitine was added to the dialysate (2 g in group 1, 4 g in group 2) for 3 months. Serum and muscle carnitine levels were determined throughout the study as were lipid parameters, serum chemistry, and hematology. Muscle biopsies obtained at baseline revealed supranormal levels of carnitine which decreased to normal levels following the 4-month washout period. When therapy with L-carnitine was resumed, intravenous administration or in dialysate, the muscle carnitine levels remained within the normal range. Similarly, serum carnitine was markedly elevated at baseline and decreased to normal during the washout period. When L-carnitine was added to the dialysate, total carnitine was observed to significantly increase in the group receiving 4 g.(ABSTRACT TRUNCATED AT 250 WORDS)