Search PubMed⌕ Search

Biomedical subjects

R R Diehl

Publications and source records attributed to R R Diehl.

At least 19 recordsLinked to original sources
PubMed2006

Recovery of the blood pressure - cerebral flow relation after carotid stenting in elderly patients.

BACKGROUND: As a sensitive and convenient means for the cerebral hemodynamic monitoring, dynamic cerebral autoregulation testing could be especially useful in medical conditions where less invasive diagnostics and therapies are preferred. This study analysed the effect of carotid stenting on dynamic autoregulation in elderly patients focussing on the relation between blood pressure and cerebral blood flow velocity. METHODS: We examined 20 patients age 69 +/- 8 years with coexisting cerebrovascular and medical risk factors before and at least six month after stenting of severe carotid stenoses. Data were compared to 24 age-matched healthy controls. Slow spontaneous oscillations were studied in continuous recordings of Transcranial Doppler and beat-to-beat blood pressure. Analysis was based on the "high-pass filter model", which predicts a positive phase relationship between these oscillations. FINDINGS: Whereas phase shift angles were diminished (20.4 +/- 14.1 degrees ) before stenting, after stenting these values were significantly increased to normal (48.1 +/- 16.6 degrees ), to the level of controls (46.7 +/- 15.9 degrees ). Medical conditions such as coronary artery disease, arterial hypertension, and dyslipidemia did not diminish this recovery. The level of increase was inversely correlated with the initial autoregulatory deficit (r = -0.68) which was largest with insufficient collateral blood supply and symptomatic carotid stenoses. CONCLUSIONS: The study showed that an impaired cerebral autoregulation may recover after stent-guided carotid angioplasty even in the elderly with co-existing medical conditions. In this respect to regain vasomotor capability, patients with cerebrovascular risk factors seemed to benefit particularly.

Aged↗
PubMed2005

Impact of vertebral artery disease on dynamic cerebral autoregulation.

OBJECTIVES: This study applied dynamic cerebral autoregulation (DCA) testing distally to severe bilateral vertebral artery disease (BVAD). METHODS: Using continuous monitoring of beat-to-beat blood pressure and transcranial Doppler of the posterior cerebral arteries (PCA) were examined in 20 patients with BVAD and 22 controls. DCA testing was based on the 'high-pass filter model', which predicts a positive phase relationship between spontaneous oscillations (M-waves 3-9 cpm and R-waves 9-20 cpm) in blood pressure and cerebral blood flow velocity. RESULTS: In patients with BVAD, DCA testing detected autoregulatory deficits of different degrees. The lowest M-wave phase shift angles were found in the PCA territory distally to intracranial BVAD. CONCLUSION: This study suggests that DCA testing of the PCA could help to quantify the hemodynamic impact of BVAD. It highlights the relevance of functional TCD sonography as a useful diagnostic tool for the hemodynamic evaluation of vertebrobasilar disease.

Aged↗
PubMed2004

Dynamic autoregulation testing in the posterior cerebral artery.

BACKGROUND AND PURPOSE: Dynamic autoregulation has been studied predominantly in the middle cerebral artery (MCA). Because certain clinical conditions, ie, presyncopal symptoms or hypertensive encephalopathy, suggest a higher vulnerability of autoregulation within posterior parts of the brain, we investigated whether the cerebral blood flow velocity (CBFV) is modulated differently within the posterior cerebral artery (PCA). METHODS: Spontaneous oscillations of CBFV and arterial blood pressure (ABP) in the frequency range of 0.5 to 20 cycles per minute were studied in 30 volunteers (supine and tilted positions). Analysis was based on the "high-pass filter model," which predicts a specific frequency-dependent phase and amplitude relationship between oscillations in CBFV to ABP. These parameters, characterized as phase shift angles and transfer function gains, were calculated from simultaneously recorded beat-to-beat blood pressure and transcranial Doppler signals of the PCA and MCA by means of cross-spectrum analysis. RESULTS: In the MCA and PCA, phase shift angles were decreased, and gains were elevated with increasing oscillation frequency. The PCA gain values in supine and tilted positions were significantly higher than in the MCA. CONCLUSIONS: The phase and amplitude relationship between CBFV and ABP showed a frequency dependence in the PCA similar to that in the MCA. The study therefore suggests that the high-pass filter model of dynamic cerebral autoregulation can be applied to the PCA. In this model the generally higher gain values in the PCA indicate a lower damping of ABP oscillations, which are transmitted to the posterior part of cerebral circulation.

Aged↗
PubMed2004

M-wave analysis and passive tilt in patients with different degrees of carotid artery disease.

BACKGROUND AND PURPOSE: Carotid artery disease (CAD) is able to critically impair cerebral autoregulation which increases the risk for stroke. As therapeutic strategy largely depends on the degree of CAD, we investigated whether this gradation is also related to significant changes in autoregulatory capacity. We applied cross-spectral analysis (CSA) of spontaneous Mayer-wave (M-wave) oscillations and passive tilting (PT) to test cerebral autoregulation. METHODS: Cerebral autoregulation was tested in 102 patients with carotid stenosis (> or =70%) or occlusion and 14 controls by comparison of continuous transcranial Doppler sonography of the middle cerebral artery and beat-to-beat arterial blood pressure (ABP) during PT to 80 degrees head-up position as well as by CSA of M-waves (3-9 cpm). RESULTS: The orthostatic decrease of cerebral blood flow velocity (CBFV) was not correlated with the degree of CAD and showed a lower sensitivity and specificity than phase angle shifts between M-waves in ABP and CBFV (sensitivity: 75-80%, specificity: 86%). Phase angles were gradually lowered in carotid stenoses > 70%, but apparently, they were only moderately correlated with the degree of CAD (r = -0.35, P < 0.01). An additional influencing factor seemed to be the sufficiency of collateralization. CONCLUSIONS: The results show that CSA of M-waves is more appropriate for testing autoregulation than PT. CSA suggests that the capacity to autoregulate depends to a certain extent on the degree of CAD but is also influenced by the sufficiency of collateral pathways and pre-existing strokes.

Adult↗
PubMed2003

Dynamic autoregulation testing in patients with middle cerebral artery stenosis.

BACKGROUND AND PURPOSE: Cross-spectral analysis (CSA) of spontaneous oscillations in cerebral blood flow velocity (CBFV) and arterial blood pressure is considered a sensitive and convenient method for dynamic autoregulation testing. So far, it has been unclear whether CSA can be used to assess stenoses of the intracranial arteries. METHODS: This study for the first time applies CSA to 26 patients with low-, moderate-, and high-degree M1 stenoses and 14 normal control subjects. Using CSA, we studied spontaneous oscillations (M waves, 3 to 9 cpm; B waves, 0.5 to 3 cpm) in continuous recordings of transcranial Doppler of the middle cerebral artery and simultaneously recorded beat-to-beat blood pressure. RESULTS: A gradual decrease in pulsatility indexes confirmed the increasing hemodynamic relevance of the stenoses. Compared with control subjects, M-wave phase shifts between CBFV and blood pressure were gradually reduced with increasing degree of M1 stenosis (control subjects, 44.6+/-21.1 degrees; high-degree stenosis, 16.7+/-19.5 degrees ). The phase relation between B waves in blood pressure and CBFV was shifted to positive values (low-degree stenosis, -9.7+/-108.4 degrees; high-degree stenosis, 50.9+/-43.8 degrees ). CONCLUSIONS: Because B- and M-wave phase shifts seem to characterize the degree of autonomy of CBFV modulation, this study suggests that with increasing degree of M1 stenosis, the arteriolar function is impaired. It shows that CSA is of indicative use for the assessment of intracranial artery stenosis.

Arterioles↗
PubMed2003

[Determinants for the prognosis of median cerebral artery processes--a retrospective analysis of 90 patients].

The data of 825 consecutive patients with ischemic stroke or TIA were retrospectively reviewed for ultrasound findings of stenoses or occlusions of the middle cerebral artery (MCA). Using survival statistics,we studied the influence of various factors on the prognosis of MCA findings. We identified 90 subjects with MCA stenosis or occlusion. Microembolic signals were demonstrated in 33% and spontaneous flow variations in 7%. Symptomatic MCA findings normalized more quickly than asymptomatic findings. Microembolic signals occurred only in symptomatic stenoses. Spontaneous flow variations strongly predicted the disappearance of a stenosis. Atherogenic risk factors were associated with stable ultrasound findings. These data suggest that different types of MCA findings exist: (1) dynamic, emboligenic stenoses or occlusions with early normalization and a high risk for ischemic events and (2) static, nonemboligenic stenoses with rare normalization and a low risk of ischemic events. A high percentage of the former may be of embolic origin, and the latter may be atherosclerotic plaques.

Adult↗
PubMed2003

[Dementia].

Explore the source record for details and available documents.

Activities of Daily Living↗
PubMed2002

Dynamics and embolic activity of symptomatic intra-cranial cerebral artery stenoses.

OBJECTIVE: To investigate the occurrence of microembolic signals (MES) and hemodynamic features in patients with acute symptomatic intracranial cerebral artery stenoses by transcranial Doppler (TCD). MATERIAL AND METHODS: Twelve patients with acute hemispheric ischemic events and corresponding intracranial cerebral artery stenoses as identified by TCD, and exclusion of extracranial or cardiac emboli sources were repeatedly studied by TCD monitoring of the affected and the contralateral vessel. The occurrence of MES and MES clusters (> or =3 MES per second) and of flow velocity changes was examined. RESULTS: Nine patients presented with MES in the affected artery during the first measurement. In seven patients sudden flow velocity changes could be detected in the affected vessel. In five patients these changes were accompanied by MES clusters. MES and velocity changes disappeared in all patients during follow-up, and the degree of stenosis decreased in nine patients. CONCLUSIONS: The high prevalence of MES and sudden velocity changes in acute intracranial cerebral artery stenoses indicates that acute intracranial stenoses may be formed at least in part by mobile thrombotic material.

Adult↗
PubMed2001

Cerebral autoregulation testing after aneurysmal subarachnoid hemorrhage: the phase relationship between arterial blood pressure and cerebral blood flow velocity.

OBJECTIVE: Impairment of cerebral autoregulation (CA) appears to be an important cause for secondary ischemia after subarachnoid hemorrhage (SAH). It has been shown that graded CA impairment is predictive of outcome. Little is known about whether such impairment is present, what causes CA impairment, whether it precedes vasospasm, and whether it is predictive of outcome in patients with severe aneurysmal SAH. DESIGN: Prospective, controlled study. SETTING: Neurosurgical intensive care unit. PATIENTS: Twelve patients after aneurysmal subarachnoid hemorrhage, 40 controls. INTERVENTIONS: Recording of cerebral blood flow velocities and continuous measurement of arterial blood pressure at a controlled ventilatory frequency of six per minute to standardize the influence of intrathoracic pressure changes on blood pressure. MEASUREMENTS AND MAIN RESULTS: We calculated the phase shift angles (deltaphidegrees) between slow (0.1 Hz) arterial blood pressure and cerebral blood flow velocity waves measured by transcranial Doppler ultrasound in the middle cerebral artery during a) posthemorrhage days (PHD) 1-6 (early or prevasospasm phase), and b) during PHD 7-13 (late or vasospasm phase) using a 6/min ventilation protocol, and in 40 controls spontaneously ventilating at the same rate. deltaphi <30 degrees indicated lost CA. Mean flow velocities >100 cm/sec were considered vasospasm. We combined early and late measurements to assess the CA relationship with low cerebral perfusion pressure (CPP) and/or vasospasm. We assessed the Glasgow Outcome Scale (GOS) score at discharge (1 = worst, 5 = best). The admission Hunt and Hess score was 3.6 +/- 0.7. GOS scores were n = 3 (GOS 1), n = 2 (GOS 2), n = 5 (GOS 3), n = 1 (GOS 4), and n = 1 (GOS 5). In the early phase, deltaphi was 40.4 +/- 19.8 degrees (left), and 40.4 +/- 19.2 degrees (right). CPP was 69.4 +/- 10.9, intracranial pressure (ICP) was 6.7 +/- 2.8 mm Hg. In the late phase, deltaphi worsened in six patients and none improved: 32.1 +/- 21 degrees (left), and 26.9 +/- 17.2 degrees (right); CPP was 68.1 +/- 12.1, ICP was 7.5 +/- 3.7 mm Hg. CA was significantly impaired in both phases when compared with normal subjects (deltaphi: 65.7 +/- 24.5 degrees; p < .01 for early, p < .001 for late phase). In the early phase, seven of eight patients in whom autoregulation was intact had a GOS >2 at discharge and disturbed CA on at least one side was predictive of either vegetative condition at discharge or death (p < .01). In the late phase, deltaphi was no longer predictive of outcome. Spasm was present in 8 of 17 vessels (47%) in which CA was lost; no spasm was found in 25 of 28 vessels (89%) in which CA was intact (p < .01). A low CPP was present in 6 of 17 vessels (35%) in which CA was lost; a normal CPP was found in 21 of 27 vessels (78%) in which CA was intact (p > .05, NS). However, 14 of 17 vessels (82%) with lost CA showed spasm and/or low CPP while only 8 of 27 cases (30%) with intact CA had either spasm or low CPP (p < .001). CONCLUSIONS: CA can be assessed in a graded fashion in SAH patients. CA impairment precedes vasospasm; ongoing vasospasm worsens CA. CA assessment early after subarachnoid hemorrhage, within PHD 1-6, is predictive of outcome whereas late assessment is not. CA impairment is associated with cerebral vasospasm and low CPP.

Adult↗
PubMed2001

Spontaneous oscillations in cerebral blood flow velocity give evidence of different autonomic dysfunctions in various types of headache.

OBJECTIVES: Our objectives were to determine if: (1) patients with migraine have B wave abnormalities in comparison to normal controls and patients with chronic tension headache and (2) patients with chronic tension headache have an imbalance in autonomic activity that is reflected in differences in Mayer wave activity in comparison to normal controls. BACKGROUND: B waves and Mayer waves are spontaneous oscillations in cerebral blood flow velocity with a frequency of 0.5 to 3 or 4 to 7 cycles per minute, respectively, and can be measured by transcranial Doppler sonography. There is experimental evidence that B waves are generated by certain brain stem nuclei which modulate the lumen of the small intracerebral vessels via monoaminergic nerve endings. In contrast, Mayer waves in cerebral blood flow velocity have no central generator but mirror the Mayer waves in arterial blood pressure which represent peripheral autonomic activity. Migraine may be attributed to a neurotransmitter imbalance in brain stem nuclei. Dysfunctions of the peripheral autonomic nervous system are known in patients with chronic tension headache. METHODS: Using bilateral transcranial Doppler monitoring of the middle cerebral artery B waves and Mayer waves were studied in 30 patients with migraine without aura, 28 subjects with tension-type headache, and 30 normal controls. Coefficient of variation as a quantitative parameter for amplitude of waves and the mean frequency were calculated from the envelope curves of the Doppler spectra. RESULTS: The coefficient of variation of B waves was higher in migrainous patients compared with patients with tension-type headache and normal controls (P<.05), indicating an increase in activity of brain stem nuclei in migraine only. Patients with chronic tension headaches had lower values for Mayer wave activity in comparison with normal controls (P<.05), a sign of an impairment of sympathetic activity. CONCLUSIONS: Our data support the dysfunction of the brain stem monoaminergic/serotonergic system in migraine. In contrast, patients with chronic tension headache have an autonomic dysfunction of peripheral origin presenting as a decrease of sympathetic activity.

Adult↗
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

[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↗
PubMed1999

Spontaneous oscillations of arterial blood pressure, cerebral and peripheral blood flow in healthy and comatose subjects.

Slow and rhythmic spontaneous oscillations of cerebral and peripheral blood flow occur within frequencies of 0.5-3 min-1 (0.008-0.05 Hz, B-waves) and 3-9 min-1 (0.05-0.15 Hz, M-waves). The generators and pathways of such oscillations are not fully understood. We compared the coefficient of variance (CoV), which serves as an indicator for the amplitude of oscillations and is calculated as the percent standard deviation of oscillations within a particular frequency band from the mean, to study the impairment of generators or pathways of such oscillations in normal subjects and comatose patients in a controlled fashion. With local ethic committee approval, data were collected from 19 healthy volunteers and nine comatose patients suffering from severe traumatic brain injury (n = 3), severe subarachnoid hemorrhage (n = 3), and intracerebral hemorrhage (n = 3). Cerebral blood flow velocities were measured by transcranial Doppler ultrasound (TCD), peripheral vasomotion by finger tip laser Doppler flowmetry (LDF), and ABP by either non-invasive continuous blood pressure recordings (Finapres method) in control subjects, or by direct radial artery recordings in comatose patients. Each recording session lasted approximately 20-30 min. Data were stored in the TCD device for offline analysis of CoV. For CoV in the cerebral B-wave frequency range there was no difference between coma patients and controls, however there was a highly significant reduction in the amplitude of peripheral B-wave LDF and ABP vasomotion (3.8 +/- 2.1 vs. 28.2 +/- 16.1 for LDF, p < 0.001; and 1.2 +/- 0.7 vs. 4.6 +/- 2.8 for ABP, p < 0.001). This observation was confirmed for spontaneous cerebral and peripheral oscillations in the M-wave frequency range. The CoV reduction in peripheral LDF and ABP oscillations suggest a severe impairment of the proposed sympathetic pathway in comatose patients. The preservation of central TCD oscillations argues in favor of different pathways and/or generators of cerebral and peripheral B- and M-waves.

Adult↗
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↗