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Biomedical subjects

D Linden

Publications and source records attributed to D Linden.

At least 19 recordsLinked to original sources
PubMed1998

Spontaneous blood pressure oscillations and cerebral autoregulation.

The relationship between spontaneous oscillations in cerebral blood flow velocity (CBFV) and arterial blood pressure (ABP) was analysed in normal subjects in order to evaluate whether these relationships provide information about cerebral autoregulation. CBFV was measured using transcranial Doppler sonography and continuous ABP and heart rate using Finapres in 50 volunteers. Measurements were made over 5 min in a supine position and 6 min in a tilted position. Coefficients of variation were calculated using power- and cross-spectral analysis in order to quantify amplitudes within two frequency ranges: 3-9 cycles per min (cpm) (M-waves); and 9-20 cpm (R-waves). Correlations, coherence values, phase angle shifts and gains were also computed between corresponding waves in CBFV and in ABP. A clear correlation was seen for M-waves and R-waves between CBFV and ABP and coherence values were large enough to calculate phase angle shifts and gains. Phase angles for M-waves were larger and gains lower than was the case for R-waves, either tilted or supine. These data are consistent with a highpass filter model of cerebral autoregulation. Relatively high CBFV/ABP gain values (between 1.4 and 2.0) suggest that the principle of frequency-dependent vascular input impedances has to be considered in addition to autoregulatory feedback mechanisms. Spontaneous ABP oscillations in the M-wave and R-wave ranges may serve as a basis for continuous autoregulation monitoring.

Adult↗
PubMed1998

Reduced baroreflex sensitivity and cardiorespiratory transfer in amyotrophic lateral sclerosis.

INTRODUCTION: Clinically relevant autonomic disturbances have been reported for respirator-dependent ALS patients while subclinical involvement may be present in the early course. METHODS: Eighteen patients with early-stage ALS and 18 age-matched controls were studied by means of standard autonomic tests (heart off + response to deep breathing and tilt-table testing), and spectral analysis of heart rate (HR) and arterial blood pressure (ABP), using the associated transfer function as a measure of baroreflex sensitivity for the mid-frequency band (MF band, 0.05-0.15 Hz) and as a measure of cardiorespiratory transfer for the high-frequency band (HF band, 0.15-0.33 Hz). RESULTS: Mean HR and ABP were increased in ALS, while results of standard autonomic tests were similar for ALS and controls. Transfer function analysis revealed reduced baroreflex sensitivity and diminished cardiorespiratory transfer during normal breathing. CONCLUSIONS: Cardiovascular autonomic functions are intact in patients with ALS. There is evidence of sympathetic enhancement and vagal withdrawal, accompanied by reduced baroreflex sensitivity. These findings are similar to those reported for essential hypertension and may point to a common central autonomic derangement in both disorders.

Aged↗
PubMed1997

Autonomic evaluation by means of standard tests and power spectral analysis in multiple sclerosis.

Standard autonomic tests [heart rate response to deep breathing (HRDB), change in systolic blood pressure due to tilt], and spectral analysis of heart rate (HR), arterial blood pressure (ABP), and the associated transfer function analysis (gains and phases) were performed in 20 patients with multiple sclerosis to determine their diagnostic value. Transfer function analysis suggested impairment of baroreflex function in 7 patients and an alteration of cardiorespiratory coupling on a brain stem level in 4 patients. In addition, sympathetic vasomotor outflow was reduced in 2 patients (spectral ABP measures in the mid frequency band) and a decrease of vagal outflow was suggested by abnormal respiratory HR parameters in another 2 patients. An abnormal HRDB was present in 5 patients and was probably due to a central alteration (cardiorespiratory coupling) in 2 patients and due to diminished respiratory effort in 1 patient. Spectral analysis of both HR and ABP oscillations and their transfer function may considerably improve the pathophysiological interpretation of cardiovascular autonomic dysfunction in patients with central nervous system disease.

Adult↗
PubMed1997

Sympathetic cardiovascular dysfunction in long-standing idiopathic Parkinson's disease.

Standard autonomic tests (heart rate response to deep breathing--HRDB, heart rate and systolic blood pressure response to tilt--delta HR and delta SBP) and spectral analysis of heart rate and arterial blood pressure and their transfer function (for the mid-frequency band a measure of baroreflex sensitivity) were performed in 20 patients with idiopathic Parkinson's disease (IPD) and 20 age-matched controls. Patients showed significantly diminished delta SBP, and reduced sympathetic vasomotor and cardiomotor outflow (diminished Mayer waves), consistent with an alteration of the efferent arc of the baroreflex. These results were only significant in long-standing IPD (IPD-l, > 5 years), whereas patients with short disease duration (IPD-s, < 5 years) showed values comparable to controls. Respiratory-related heart rate variability was slightly reduced in IPD-1 but this was mainly due to diminished respiratory effort, indicated by low respiratory-related blood pressure variability. We conclude that autonomic abnormalities are only present in long-standing IPD and consist in reduced sympathetic vasomotor and cardiomotor outflow.

Aged↗
PubMed1997

Determinants of heart rate variability during deep breathing: basic findings and clinical applications.

The measurement of heart rate variation during forced breathing (HRDB) is a well-known clinical test of parasympathetic function. It is known that normal values of HRDB are strongly dependent on age. However, little is known about other physiological factors that may lead to reduced HRDB values that may mimic parasympathetic failure. Thirty-two normal subjects (age 56.7 +/- 12.4 years) and 32 neurological patients with pathological autonomic test findings (age 57.9 +/- 10.2) were studied. Oscillations in heart rate and in mean arterial blood pressure were recorded in the supine position during forced breathing (6 cycles/min) using the Finapres monitor. Amplitudes of heart rate and blood pressure waves at 6 cycles/min (HR6 and ABP6) as well as gain values (Gain6 = HR6/ABP6) and phase differences (delta phi 6) between HR and ABP waves were calculated by means of spectral analysis. The mean (+/-SD) HR6 in normal subjects was 6.34 +/- 3.36 cycles/min with a mean ABP6 of 5.11 +/- 2.49 mmHg. HR6 correlated significantly with age (r = -0.426) and with ABP6 (r = 0.602). No significant correlation was found between HR6 and mean blood pressure, mean heart rate or sex. From 24 patients with pathological findings in the classical HRDB value, only nine could be classified as pathological when the effect of ABP6 was considered. In conclusion, ABP variations significantly influence the amplitude of heart rate variations during forced breathing. We interpret these findings in terms of a baroreflex mechanism of HRDB including both vagal and sympathetic efferents. Normal reference value tables for clinical HRDB studies should not only consider age but also the amplitude of blood pressure variations.

Autonomic Nervous System↗
PubMed1996

Comparison of standard autonomic tests and power spectral analysis in normal adults.

Standard autonomic measures [heart rate response to deep breathing (HR[DB]), systolic blood pressure response to orthostatic load, the 30:15 ratio, and the Valsalva ratio (VR)] and spectral measures of the heart rate (HR) and the arterial blood pressure (ABP) (MF: mid-frequency band at 0.05-0.15 Hz; HF: high-frequency band at 0.15-0.33 Hz) were performed in 50 healthy subjects. The supine HR-HF and the tilt ABP-MF were taken as indicators of parasympathetic and sympathetic outflow, respectively. The transfer function magnitude of HR related to the ABP in the mid-frequency band estimated the baroreflex sensitivity. The HR[DB] and the 30:15 ratio were correlated with the parasympathetic spectral measure, and the VR was, surprisingly, only correlated with the sympathetic spectral measure. Significant baroreflex contribution was only evident for the 30:15 ratio. The spectral HR data were highly correlated with their corresponding spectral data of ABP. These results provide insights into autonomic regulation, but further studies on both basic physiological mechanisms of these methods and their clinical value have to be performed before a broad application can be recommended.

Adult↗
PubMed1996

Spinal arteriovenous malformations: clinical and neurophysiological findings.

Eighteen patients with dural arteriovenous fistulas or intradural arteriovenous malformations underwent clinical and neurophysiological examination. Bladder disturbances, pain, sensory abnormalities and involvement of both upper and lower motor neurons were commonly observed. Abnormal findings were obtained both in electromyography (11/18) and somatosensory evoked potentials (16/18). The motor evoked potentials were abnormal in all but one patient and showed a prolonged central (n = 14) or peripheral motor conduction time (n = 6). In three cases both values were prolonged. The results of nerve conduction studies in the patients with prolonged peripheral motor conduction times were normal. These neurophysiological findings may indicate root involvement in some patients, probably due to venous congestion and consequent hypoxia, as there were no signs of root compression on neuroradiological evaluation in any of these six patients. Motor evoked potentials may provide an additional clue to the diagnosis, although patients with spinal stenosis or motor neuron disease may present with similar findings.

Adult↗
PubMed1996

Estimation of baroreflex sensitivity using transfer function analysis: normal values and theoretical considerations.

Human baroreflex sensitivity is traditionally derived from changes in heart rate due to alterations of the baroreceptor input (pharmacologically or physically induced blood pressure changes). Transfer function analysis (TFA) of changes in heart rate (output function) and physiological blood pressure oscillations (input function) at approximately 0.1 Hz (Mayer waves) has already been accepted as a measure of baroreflex sensitivity (BRS). Transfer function analysis provides gain and phase shift values for each frequency band and body position. We performed TFA in 50 normal subjects in the supine and tilted positions, at mid-frequency (0.05-0.15 Hz) and high-frequency (0.15-0.33 Hz) bands, recording heart rate and blood pressure continuously with a Finapres device. Gain values were in accordance with previous studies. Phase shifts lay within a narrow range for all frequency bands and positions. High correlations were found between phase shifts of the same frequency band, but not for those of the same position. This supports the idea that the transfer mechanisms for the two frequency bands may, in part, be different. There was a poor correlation between gain and phase values on the one hand and, on the other hand, further spectral measures and the results of standard autonomic tests. This suggests that TFA may not only be a measure of BRS, but also a complementary tool for evaluation of autonomic function.

Adult↗
PubMed1996

Transcranial Doppler during neurocardiogenic syncope.

The purpose of the present study was to investigate changes in cerebral circulation during neurocardiogenic syncope (NCS). Twenty patients with a history of unexplained syncopes were studied over a 45 min period in a tilted position. Heart rate and arterial blood pressure were recorded non-invasively using Finapres. Cerebral blood flow velocity of both middle cerebral arteries was measured with transcranial Doppler (TCD). Ten patients (50%) developed a NCS during the tilt test, with a strong reduction in blood pressure (mean, 48/34 mmHg) and heart rate (mean, 54 beats/min). Simultaneously, diastolic blood flow velocities dropped to values close to zero. However, systolic blood flow velocities did not decrease. In consequence, the pulsatility index (PI) increased considerably from 0.93 to 2.01. The increase in PI suggests that there is a constriction of cerebral resistance vessels during NCS. Despite the drop in blood pressure and the putative increase in cerebrovascular resistance, systolic blood flow velocities remained unchanged in the TCD records. This fact can be explained by a lumen narrowing of the middle cerebral artery at the site of insonation. In conclusion, the typical changes in cerebral blood flow velocity during NCS are probably due to a strong constriction of both the proximal and the peripheral segments of cerebral arteries. It is clear that, in addition to vasodepression and cardiac inhibition, cerebral vasoconstriction is a further mechanism in the pathogenesis of a NCS.

Adult↗
PubMed1995

Subclinical autonomic disturbances in multiple sclerosis.

We compared results from non-invasive autonomic testing [sympathetic skin responses (SSR), heart beat variation during deep breathing, and orthostatic manoeuvre with transcranial Doppler monitoring in 22 patients] with motor and somatosensory evoked potentials (MEP and SEP) in 30 unselected patients with multiple sclerosis. We found a similarly high yield of pathological results for SSR, MEP and SEP (66.7%, 65.5%, and 69%, respectively). When analysed for each limb (n = 120), SSR were highly correlated with MEP and SEP (for both P < 0.001). Heart beat variation was reduced in only 3 patients. In 4 of 22 patients orthostatic manoeuvre induced a pathological decrease in cerebral blood flow velocity despite normal systemic blood pressure being maintained. We conclude that SSR may be a useful additional diagnostic tool in patients with multiple sclerosis. Cerebral dysautoregulation is a rather frequent finding, although its significance is not known.

Adolescent↗
PubMed1995

Sympathetic skin responses (SSRs) in monofocal brain lesions: topographical aspects of central sympathetic pathways.

Lesions of the central sympathetic pathways are likely to be of clinical relevance. In patients with acute stroke, in particular, they may be responsible for the partially deleterious cardiac arrhythmia. There is little knowledge of the central organization of sympathetic pathways above the brainstem level for both cardio-efferent and sudomotor fibers. We studied the sympathetic skin response (SSR) in 29 patients with brainstem stroke or infarction in the territory of the middle cerebral artery (MCA) in order to evaluate the pathways mediating emotional sweating. In 24 patients (82.8%) the SSR was pathological. These abnormalities were bilateral with no clear asymmetry in 10 patients (34.5%), bilateral with marked contralateral pathology in 8 patients (27.6%), purely contralateral in 5 patients (17.2%) and purely ipsilateral in one patient (3.5%). Bilateral abnormalities were more frequent and more marked in brainstem than in MCA stroke. This is probably indicative of a more generalized sympathetic dysfunction. In contrast, contralateral abnormalities were more pronounced in MCA than in brainstem infarcts. Our results show that sympathetic skin responses are suppressed in the majority of stroke patients. Asymmetric responses may indicate that sudomotor fibers mediating emotional sweating have their origin or receive input from the contralateral MCA territory.

Adult↗
PubMed1995

Phase relationship between cerebral blood flow velocity and blood pressure. A clinical test of autoregulation.

BACKGROUND AND PURPOSE: This study investigates the usefulness, as a test of dynamic autoregulation, of phase shift angle analysis between oscillations in cerebral blood flow velocity (CBFV) and in arterial blood pressure (ABP) during deep breathing. METHODS: Fifty healthy volunteers, 20 patients with occlusive cerebrovascular diseases (OCD), and 10 patients with arteriovenous malformations (AVM) took part in the study. All subjects received transcranial Doppler monitoring of both middle cerebral arteries (MCAs). In addition, continuous blood pressure monitoring was performed with the use of noninvasive servo-controlled infrared finger plethysmography during deep breathing at a rate of 6/min. With the use of a high-pass filter model of autoregulation, autoregulation was quantified as phase shift angle between oscillations in CBFV and ABP at a frequency of 6/min. A phase shift angle of 0 degrees indicates total absence of autoregulation, while 90 degrees can be gauged as optimal autoregulation. In addition, vasomotor reactivity of both MCAs to CO2 stimulation was assessed among patients and calculated as percent increase in CBFV per millimeter of mercury of increase in CO2. RESULTS: All normal subjects showed positive phase shift angles between CBFV and ABP (mean +/- SD, 70.5 +/- 29.8 degrees). OCD patients presented with significantly decreased phase shift angles for the MCA only on the pathological side (51.7 +/- 35.1 degrees; P < .05). Patients with AVM showed significantly reduced phase shift angles on both the affected side (26.8 +/- 13.5 degrees; P < .001) and the unaffected side (40.6 +/- 26.6 degrees; P < .01). In patients' groups, phase shift angle and vasomotor reactivity correlated significantly (r = .66; P < .001) after results from all MCAs were pooled. CONCLUSIONS: Results confirm the high-pass filter model of cerebral autoregulation: Normal subjects showed predicted positive phase shift angles between CBFV and ABP oscillations. Patients with expected autoregulatory disturbances showed significant decreases in phase shift angles. Close correlations existed between autoregulation and CO2-induced vasomotor reactivity.

Adult↗
PubMed1994

Magnetic motor evoked potentials (MEP) in diseases of the spinal cord.

Transcranial magnetic stimulation (TMS) is a non-invasive diagnostic method particularly suited to investigation of the long motor tracts. The clinical value of this method in many cortical and subcortical diseases has been well established, but comparable studies for most spinal cord diseases have still to be made. Forty patients in whom spinal cord disease was established by clinical examination, cerebrospinal fluid examination, and magnetic resonance imaging (MRI) were studied by means of somatosensory evoked potentials (SEP, median and tibial nerve stimulation) and magnetic motor evoked potentials (MEP, first dorsal interosseus and tibialis anterior muscle recordings after transcranial and spinal stimulation). The underlying pathology was neoplastic (n = 16), inflammatory (n = 15) or ischemic (n = 9). Clinical signs and symptoms ranged from slight sensory disturbances to complete paraplegia and had developed within minutes (ischemia) or over many years (benign neoplastic disease). The overall frequency of pathological SEP was slightly higher than that of MEP (78% vs 68%) which was statistically not significant (p > 0.05). This was also true for the subgroups, except for pure motor disorders, which gave the same yield for both methods. Decreased amplitudes or absence of MEP were more frequent in neoplastic than in inflammatory lesions (75% vs 33%, p < 0.05). In the latter, however, MEP more often occurred with increased latencies (40% vs 31%, p > 0.05, n.s.). Pathological SEP were found in 75% of patients presenting with pure motor abnormalities, while pathological MEP were found in 30% of patients with pure sensory disturbances.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗