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Biomedical subjects

D Linden

Publications and source records attributed to D Linden.

At least 19 recordsLinked to original sources
PubMed2000

Valsalva-induced syncope during apnea diving.

A young man had two dangerous episodes of transient loss of consciousness during apnea diving in a swimming pool. Medical and neurologic examination results were normal. Standard autonomic test results (including heart rate variability, baroreflex sensitivity, tilt-table test, and Valsalva ratio) were unremarkable, with the exception of an increased blood pressure decrease during early phase II of the Valsalva maneuver. Syncope with arrhythmic myoclonic jerks could be evoked by a strong straining maneuver. Simultaneous physiologic recordings showed extreme blood pressure and cerebral blood flow velocity decreases and electroencephalographic slowing during syncope. The electrocardiogram showed a continuous sinus rhythm with a progressive tachycardia. The authors' findings were not compatible with baroreflex failure or vasovagal mechanisms (Bezold-Jarisch reflex activation) as the underlying causes. The authors concluded that mechanical factors (strong reduction of blood reflux to the heart) in combination with a reduced threshold of the brain for developing ischemia-related arrhythmic myoclonic jerks were responsible for Valsalva-induced syncope in the patient.

Adult↗
PubMed1999

Cerebrovascular mechanisms in neurocardiogenic syncope with and without postural tachycardia syndrome.

BACKGROUND AND PURPOSE: Recent transcranial Doppler studies in patients with neurocardiogenic syncopes (NCS) have demonstrated that the cerebrovascular response to sudden systemic hypotension is vasoconstriction instead of compensatory vasodilation (autoregulation). We tried to characterize the conditions leading to this unexpected response in NCS patients further by continuously monitoring autoregulation and autonomic parameters during a standardized tilt-table test (TTT). METHODS: Sixteen patients below the age of 50 years with a history of at least three syncopes of undetermined cause and tilt-table verified NCS and 20 normal controls were studied. Arterial blood pressure (ABP) and heart rate (HR) were monitored by Finapres and cerebral blood flow velocity (CBFV) of the left middle cerebral artery by transcranial Doppler. Baroreflex sensitivity and autoregulation parameters were measured continuously, using cross-spectral analysis of Mayer waves (3-9 cycles per minute oscillations) in ABP, HR and CBFV, respectively. Pulsatility indices (PI) of CBFV and ABP were determined continuously. Measurements were taken during 5 min in supine and during 5 min in tilted position. In patients, tilting was continued for a maximum of 45 min until the onset of syncope or presyncope. RESULTS: According to the maximum increase in heart rate (deltaHR) during the first 5 min of standing, heart rate responses were classified as postural tachycardia syndrome (POTS) (deltaHR > 35/min) or as normal. Only one out of 20 control subjects showed a POTS (5%) in contrast to seven patients (44%). Patients with a POTS had significantly lower PI values in ABP and higher ratios between the PI of CBFV and the PI of ABP both in supine and in tilted positions. Baroreflex sensitivity during standing decreased significantly in POTS patients when compared to controls. Although autoregulation remained intact during standing, mean CBFV decreased significantly and continuously. The nine patients without a POTS showed almost the same cardiovascular and cerebrovascular responses as the control subjects. All 16 patients showed similar circulatory responses during syncope (sudden hypotension, relative or absolute bradycardia, reduced CBFV and increased PI in CBFV). CONCLUSIONS: The development of a POTS during tilting indicates a high risk for fainting. The characteristic hemodynamic features in the initial phase of standing in these patients can be interpreted in terms of central hypovolemia (low PI of ABP) with sufficient ABP regulation and increased cerebrovascular resistance (defined as the ratio between PI of CBFV and ABP). Cerebral autoregulation seems not to be affected in patients suffering from NCS.

Adult↗
PubMed1999

Facial nerve dysfunction in hereditary motor and sensory neuropathy type I and III.

Facial nerve function was studied in 19 patients with hereditary motor and sensory neuropathy type I (HMSN I) and 2 patients with hereditary motor and sensory neuropathy type III (HMSN III, Déjérine-Sottas), and compared to that in 24 patients with Guillain-Barré syndrome (GBS). The facial nerve was stimulated electrically at the stylomastoid fossa, and magnetically in its proximal intracanalicular segment. Additionally, the face-associated motor cortex was stimulated magnetically. The facial nerve motor neurography was abnormal in 17 of 19 HMSN I patients and in both HMSN III patients, revealing moderate to marked conduction slowing in both the extracranial and intracranial nerve segments, along with variable reductions of compound muscle action potential (CMAP) amplitudes. The facial nerve conduction slowing paralleled that of limb nerves, but was not associated with clinical dysfunction of facial muscles, because none of the HMSN I patients had facial palsy. Conduction slowing was most severe in the HMSN III patients, but only slight facial weakness was present. In GBS, conduction slowing was less marked, but facial weakness exceeded that in HMSN patients in all cases. We conclude that involvement of the facial nerve is common in HMSN I and HMSN III. It affects the intra- and extracranial part of the facial nerve and is mostly subclinical.

Adult↗
PubMed1999

[Differential orthostatic dysregulation disorders diagnosis].

Orthostatic circulatory disorders are frequently the cause of orthostatic intolerance, syncope or dangerous falls. A sufficient therapy should be based on a differential diagnosis by means of an active standing test or a tilt-table test. Three typical pathological reactions of blood pressure and heart rate can be differentiated. The hypoadrenergic orthostatic hypotension is characterised by an immediate drop in blood pressure (systolic drop > 20 mmHg below base line within 3 min) with or without compensatory tachycardia. It is caused by peripheral or central sympathetic dysfunction. Tachycardia (> 30 beats per minute above base line within 10 min) without significant blood pressure drop but with a fall of cerebral blood flow indicates a postural tachycardia syndrome. In general, there is no further somatic dysfunction. Increased venous pooling is thought to be the assumed pathomechanism. A reflex mechanism evokes the neurocardiogenic syncope after a certain time of standing: sympathetic inhibition yields a strong blood pressure drop and vagal activation bradycardia. Proved therapies include use of the mineralocorticoide fludrocortison (hypoadrenergic orthostatic hypotension), of the alpha-agonist midodrin (postural tachycardia syndrome) and of beta-blockers (neurocardiogenic syncope).

Diagnosis, Differential↗
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↗