Cerebrovascular regulation in preganglionic and postganglionic autonomic insufficiency

The cerebrovascular response to norepinephrine: A scoping systematic review of the animal and human literature

Intravenous norepinephrine (NE) is utilized commonly in critical care for cardiovascular support. NE's impact on cerebrovasculature is unclear and may carry important implications during states of critical neurological illness. The aim of the study was to perform a scoping review of the literature on the cerebrovascular/cerebral blood flow (CBF) effects of NE. A search of MEDLINE, BIOSIS, EMBASE, Global Health, SCOPUS, and Cochrane Library from inception to December 2019 was performed. All manuscripts pertaining to the administration of NE, in which the impact on CBF/cerebral vasculature was recorded, were included. We identified 62 animal studies and 26 human studies. Overall, there was a trend to a direct vasoconstriction effect of NE on the cerebral vasculature, with conflicting studies having demonstrated both increases and decreases in regional CBF (rCBF) or global CBF. Healthy animals and those undergoing cardiopulmonary resuscitation demonstrated a dose-dependent increase in CBF with NE administration. However, animal models and human patients with acquired brain injury had varied responses in CBF to NE administration. The animal models indicate an increase in cerebral vasoconstriction with NE administration through the alpha receptors in vessels. Global and rCBF during the injection of NE displays a wide variation depending on treatment and model/patient.

Pure Autonomic Failure

Pure autonomic failure (PAF) is a rare sporadic neurodegenerative autonomic disorder characterized by slowly progressive pan autonomic failure without other features of neurologic dysfunctions. The main clinical symptoms result from neurogenic orthostatic hypotension and urinary and gastrointestinal autonomic dysfunctions. Autonomic failure in PAF is caused by neuronal degeneration of pre- and postganglionic sympathetic and parasympathetic neurons in the thoracic spinal cord and paravertebral autonomic ganglia. The presence of Lewy bodies and α-synuclein deposits in these neural structures suggests that PAF is one of Lewy body synucleinopathies, examples of which include multiple system atrophy, Parkinson disease, and Lewy body disease. There is currently no specific treatment to stop progression in PAF. Management of autonomic symptoms is the mainstay of treatment and includes management of orthostatic hypotension and supine hypertension. The prognosis for survival of PAF is better than for the other synucleinopathies.

Dynamic cerebral autoregulation in stroke patients with a central sympathetic deficit

OBJECTIVE

To investigate the functional role of the sympathetic innervation on cerebral autoregulation.

MATERIALS AND METHODS

Seventeen patients with infarction of the dorsolateral medulla oblongata affecting central sympathetic pathways (Wallenberg's syndrome) and 21 healthy controls were included in the study. Cerebral blood flow velocity (CBFV) in the medial cerebral artery was investigated using transcranial Doppler ultrasound during decrease in cerebral perfusion pressure induced by leg-cuff test and tilt table.

RESULTS

Upon leg-cuff test, changes of cerebral blood flow and mean arterial blood pressure as well as autoregulatory index did not differ between patients or controls. No differences were found in changes of CBFV, mean arterial blood pressure and heart rate between patients or controls during the tilt table test.

CONCLUSIONS

We suggest that the sympathetic nervous system does not have an influence on cerebral autoregulation after decrease in perfusion pressure under normotonous conditions.

Autonomic related vertigo

OBJECTIVES

To demonstrate clinical evidence that vestibular symptomatology can occur in relation to autonomic dysfunction. Characterization of clinical findings and treatment response would then allow autonomic related vertigo to be differentiated from other vertiginous conditions that present in a like manner.

STUDY DESIGN

This was a retrospective review of 113 patients that described symptoms consistent with spontaneous, rotational vertigo and autonomic dysfunction.

METHODS

Vestibular, otologic, and autonomic symptoms are presented along with the results of audiologic, orthostatic, and autonomic testing. Medical management included fluid loading, dietary changes, exercise, and patient education. Treatment results were analyzed according to the effectiveness in control of vestibular and otologic symptoms. Results were compared with a control group that demonstrated a similar vestibular and otologic presentation without autonomic symptomatology.

RESULTS

All patients described spontaneous, rotational vertigo, with complete or substantial vertigo control obtained in 93 (85%) of 110 patients. Postural vertigo and distinct lightheadedness were also documented in 53% and 97% of cases, respectively. Vertigo failed to improve or worsened with prior treatment of low sodium diet or diuretic in 53 (91%) of 58 cases. Vertigo improvement was subsequently achieved in 48 (86%) of 56 cases with an autonomic treatment regimen. Long-term vertigo control was obtained in 56 (88%) of 64 patients followed for at least 18 months. Tinnitus was reported in 97 (86%) patients, aural fullness in 93 (82%) patients, and subjective hearing loss (HL) in 46 (41%) of 111 cases. Bilateral tinnitus and aural fullness occurred in 65% and 63%, respectively. Tinnitus improved with treatment in 56 (67%) of 84 patients, whereas aural fullness improved in 59 (74%) of 80 patients. Autonomic symptoms included palpitations in 103 (91%) patients, chronic fatigue in 102 (90%) patients, cold extremities in 91 (81%) patients, and previous fainting in 72 (64%) patients. A history of mitral valve prolapse was documented in 51 (45%) of cases and demonstrated with echocardiogram in 68 (93%) of the 73 patients tested. Audiologic testing was normal in 104 (95%) of 109 patients, and electrocochleography was abnormal in 42 (40%) of 105 patients. Orthostatic blood pressure and heart rate testing met the criteria for orthostatic hypotension in 16 (15%) of 104 patients. Autonomic testing was obtained in 34 cases, with orthostatic intolerance demonstrated in 33 (97%) patients and orthostatic hypotension demonstrated in 13 (38%) patients. Overall, orthostatic hypotension was documented through combined testing results in 23 (21%) of 107 patients. Vertigo was reproduced during autonomic testing in 17 (77%) of 22 patients, and otologic symptoms were reproduce in 9 (47%) of 19 patients. Comparison of the study population with a control group without autonomic symptoms revealed statistically significant differences in orthostatic testing and treatment results. There was no statistical difference noted in findings between patients of this study that demonstrated or failed to demonstrate orthostatic hypotension.

CONCLUSIONS

There is a subgroup of patients with spontaneous vertigo who also demonstrate symptoms and findings consistent with poor autonomic regulation. These patients report vertigo improvement with a treatment strategy that aims to improve autonomic dysfunction through expansion of effective circulating volume. Clinical findings and treatment results of this study suggest an underlying autonomic influence in the production of vertigo and otologic symptoms.

Cerebral oxygenation monitoring for detecting critical cerebral hypoperfusion in patients with multiple system atrophy during the head-up tilt test

OBJECTIVE

Near infrared spectroscopy (NIRS) is a non-invasive optical technique to monitor cerebral tissue oxygen saturation (ScO(2)). The purpose of this study was to reveal the usefulness of ScO(2) monitoring in evaluating cerebral circulation in patients with autonomic failure.

METHODS

Nineteen patients with multiple system atrophy (MSA), who had autonomic failure, and 10 age-matched normal control subjects participated. In addition to blood pressure monitoring, ScO(2) was recorded by a near-infrared spectroscopy instrument during head-up tilt (HUT) test.

RESULTS

HUT tests induced postural symptoms in 9 MSA patients (presyncopal group), but not in 10 MSA patients (non-presyncopal group) or in any of the controls. ScO(2), which decreased slightly in the controls and MSA patients, did not differ significantly between the MSA and control groups. With regard to MSA subgroups, the ScO(2) reduction in the presyncopal group (-3.1+/-1.7%) was significantly larger than in the non-presyncopal group (-0.9+/-0.5%, P<0.005) and controls (-1.1+/-1.0%, P<0.05). The systolic blood pressure decreases during HUT in the non-presyncopal (-35.2+/-16.1 mmHg, P<0.01) and presyncopal (-54.3+/-27.5 mmHg, P<0.0005) groups were significantly greater than that in the control group (4.0+/-10.7 mmHg), but the difference between presyncopal and non-presyncopal groups was not significant.

CONCLUSION

In our study, ScO(2) reduction seemed to be associated with presyncopal symptoms. ScO(2) monitoring may be useful to detect cerebral hypoperfusion in MSA patients with autonomic failure.

Cerebral blood flow and oxygenation during head-up tilt in patients with multiple system atrophy and healthy control subjects

To assess cerebral hemodynamics in patients with multiple system atrophy (MSA), cerebral blood flow and oxygenation were evaluated in 7 MSA patients and 9 healthy controls during a head-up tilt test (HUT) by means of transcranial Doppler ultrasonography and near-infrared spectrophotometry. In the MSA patients examined, the perfusion pressure reduction during HUT was marked, but severe reduction in blood flow velocity was prevented because of a decrease in cerebrovascular resistance. The MSA patients showed no severe reduction in cerebral oxygenation during HUT. These findings indicate that our MSA patients exhibited a compensatory cerebral vasodilatation response to orthostatic hypotension.

Cerebral vasomotor reactivity in Parkinson's disease, multiple system atrophy and pure autonomic failure

Parkinson's disease (PD), multiple system atrophy (MSA) and pure autonomic failure (PAF) are neurodegenerative disorders frequently associated with orthostatic hypotension and syncope, though with different underlying mechanisms. Cerebral hemodynamic responses in these three neurodegenerative diseases are still incompletely studied and it is possible that they would be differentially affected. We measured blood flow velocity (BFV) in the middle cerebral artery (MCA) and vertebral artery (VA) in patients with these disorders and investigated whether cerebral vasomotor reactivity (VMR) differs in these three disorders. Twenty-four patients (9 with PD, 10 with MSA and 5 with PAF) were studied. VMR was assessed in the MCA and VA, using transcranial Doppler (TCD) and Diamox test (injection of 1 g acetazolamide i.v.) with the patients in a recumbent position. The percent difference between BFV before and after acetazolamide injection was defined as VMR% and the results were compared by ANOVA. The mean MCA and VA blood flow velocities were similar in the three disorders and within normal limits for our laboratory. The mean MCA VMR values were 37.5+/-24.0%, 27.9+/-28.0% and 38.0+/-33.9% in PD, MSA and PAF, respectively. The VA VMR values were 22.9+/-23.6%, 32.4+/-38.0% and 18.9+/-18.3%, respectively, with no significant differences between the groups. We conclude that BFV is normal in PD, MSA and PAF and that the VMR, as investigated by TCD and the Diamox test, did not disclose differences in cerebral vasomotor responses between these conditions.

Impairment of cerebral autoregulation in diabetic patients with cardiovascular autonomic neuropathy and orthostatic hypotension

AIMS

Impaired cerebrovascular reactivity and autoregulation has been previously reported in patients with diabetes mellitus. However, the contribution of cardiovascular diabetic autonomic neuropathy and orthostatic hypotension to the pathogenesis of such disturbances is not known. The purpose of this study was to evaluate cerebral blood flow velocity in response to standing in patients with diabetes and cardiovascular autonomic neuropathy with or without orthostatic hypotension.

METHODS

We studied 27 patients with diabetes--eight had cardiovascular autonomic neuropathy and orthostatic hypotension (age 46.4 +/- 13.5 years, diabetes duration 25.0 +/- 11.0 years), seven had autonomic neuropathy without hypotension (age 47.3 +/- 12.7 years, diabetes duration 26.4 +/- 12.1 years), and 12 had no evidence of autonomic neuropathy (age 44.1 +/- 13.8 years, diabetes duration 17.1 +/- 10.2 years)-and 12 control subjects (age 42.6 +/- 9.7 years). Flow velocity was recorded in the right middle cerebral artery using transcranial Doppler sonography in the supine position and after active standing.

RESULTS

Cerebral flow velocity in the supine position was not different between the groups studied. Active standing resulted in a significant drop of mean and diastolic flow velocities in autonomic neuropathy patients with orthostatic hypotension, while there were no such changes in the other groups. The relative changes in mean flow velocity 1 min after standing up were -22.7 +/- 16.25% in patients with neuropathy and orthostatic hypotension, +0.02 +/- 9.8% in those with neuropathy without hypotension, -2.8 +/- 14.05% in patients without neuropathy, and -9.2 +/- 15.1% in controls.

CONCLUSIONS

Patients with diabetes and cardiovascular autonomic neuropathy with orthostatic hypotension show instability in cerebral blood flow upon active standing, which suggests impaired cerebral autoregulation.

Regulation of cerebral blood flow in patients with autonomic dysfunction and severe postural hypotension

BACKGROUND

Whether cerebral blood flow (CBF) autoregulation is maintained in autonomic dysfunction has been debated for a long time, and the rather sparse data available are equivocal. The relationship between CBF and mean arterial blood pressure (MABP) was therefore tested in eight patients with symptoms and signs of severe cardiovascular autonomic dysfunction.

PATIENTS AND METHODS

Eight patients were included, three of whom had Parkinson's disease, three diabetes, one pure autonomic failure and the last one had multiple system atrophy. By the use of two techniques, the arteriovenous oxygen [(a-v)O2] method and xenon-inhalation with single photon emission tomography, 15 measurements (range 10-20) and three to four CBF measurements, respectively, were obtained in each patient. Following CBF measurements during baseline, MABP was raised gradually using intravenous noradrenaline infusion, and then lowered by application of lower body negative pressure. From the (a-v)O2 samples the CBF response to changes in MABP was evaluated using a computer program fitting one or two regression lines through the plot.

RESULTS AND CONCLUSION

Preserved autoregulation was observed in three patients, while the remaining five patients showed a linear relationship between CBF and MABP. Comparison of the results of the tomographic CBF measurements to the (a-v)O2 data demonstrated that it is not possible to assess whether CBF is autoregulated or not with only three to four pairs of data.

Orthostatic dysregulation in progressive autonomic failure--a transcranial Doppler sonography monitoring

Hemodynamic changes associated with orthostatic hypotension in one patient with pure progressive autonomic failure (PAF) were studied by a passive (70 degrees tilt of the upper part of the body) and an active orthostatic tests. Mean blood pressure (MBP), heart rate (HR) and mean blood flow velocity (MFV) during transcranial Doppler sonography monitoring of the right middle cerebral artery (RMCA) were determined after 10 minutes of rest and after 1, 10 and 60 minutes passive 70 degrees tilt or active standing. Simultaneously, plasma norepinephrine (NE) levels during recumbency and after 1 and 10 min of the orthostatic manoeuvres were measured. Stand-up tilting induced slight decrease in MBP and MFV without changes in HR. Changes of systemic hemodynamics occurred during the first minute of passive standing and they increased within the first hour however the cerebral hemodynamics remained relatively stable. Active standing was accompanied by a severe decrease in the MBP and the MFV in RMCA, and an increase in vascular resistance immediately after the upright position. The hemodynamic changes were not followed by a secondary cardiac acceleration; they increased within the first minute of active standing and evoked a syncope. During squatting as a self-selected preventive mechanism in our patient an increase in MBP and MFV in RMCA occurred. Plasma NE levels in recumbency were lower than the reference values; they decreased with 12.1% after 10 min of passive tilting and with 24.8% after the first minute of active standing. These results showed that PAF is accompanied by a severe orthostatic dysregulation during active standing, associated with a progressive peripheral autonomic deficiency and disturbed mechanisms against gravitational pooling of the blood to the lower extremities. The orthostatic autoregulation of the cerebral hemodynamics seems to be preserved.

Influence of cerebrovascular sympathetic, parasympathetic, and sensory nerves on autoregulation and spontaneous vasomotion

The effect of removal of cerebrovascular sympathetic, parasympathetic or sensory nerve on brain cortical blood flow and spontaneous vasomotion during changes in systemic blood pressure was studied by laser-Doppler flowmetry in anaesthetized rats. Selective section of sympathetic fibres along the internal carotid artery markedly affected the ability to autoregulate, as measured in microvessels of the middle cerebral arterial territory. Removal of the parasympathetic nerves tended to reduce the ability to autoregulate, whereas no significant influence was found after sensory denervation. Following the denervations, spontaneous vasomotion was not significantly affected in frequency or amplitude.

Cholinergic dysfunction in Shy-Drager syndrome: effect of the parasympathomimetic agent, bethanechol

To determine the frequency, severity and organ distribution of cholinergic dysfunction in the Shy-Drager syndrome, eleven patients were prospectively studied. In addition to documenting adrenergic insufficiency, a battery of twelve tests was employed to assess cholinergic function. Six tests demonstrated pupillary, lacrimal, salivary, urinary bladder, sexual and sudomotor dysfunction in the majority of patients. Cardiac vagal function as studied by the heart rate response to deep breathing, the Valsalva manoeuvre, cold face test, apnoeic facial immersion and atropine test was affected in all patients. Oesophageal motility was abnormal in six patients. Cholinergic dysfunction in patients with the Shy-Drager syndrome was widespread but of variable severity and distribution. Subcutaneous administration of the parasympathomimetic agent bethanechol demonstrated hyperresponsiveness of lacrimal, salivary, oesophageal, bowel, bladder and sudomotor functions. It is suggested that the Shy-Drager syndrome is primarily a preganglionic cholinergic disorder with transsynaptic degeneration accounting for the development of postganglionic cholinergic as well as adrenergic dysfunction.

Cerebral autoregulation in patients with orthostatic hypotension

The present study was conducted to determine the relationship between autonomic nervous function and cerebral autoregulation in 17 patients with vertigo or dizziness. Autonomic nervous function was examined by measuring systolic blood pressure response and dynamic electrocardiogram R-peak to R-peak response upon standing up. Regional cerebral autoregulation was examined by comparing cerebral blood flow in both supine and standing positions with single photon emission computed tomography. Moreover, the relationship of each of these three measures to postural provocation of symptoms was studied. The findings indicated that autonomic nervous dysfunction does not influence cerebral autoregulation, but autonomic nervous dysfunction was related to postural provocation of symptoms. This might indicate that impaired autoregulation in the brain stem or the peripheral vestibule, which could not be detected by the single photon emission computed tomography, played a role in inducing vertigo or dizziness in patients with orthostatic hypotension.

Orthostatic changes of cerebral blood flow velocity in patients with autonomic dysfunction

Simultaneous registrations of intracranial blood flow velocity parameters achieved by transcranial Doppler sonography and basic cardiovascular parameters were carried out during orthostatic changes in normal controls, diabetic patients and patients with pandysautonomia. Normal subjects had a rapid increase in heart rate at a constant blood pressure and a slight decrease in cerebral blood flow velocities associated with a mild increase of the pulsatility index (PI) after being tilted from a horizontal to a vertical position. Diabetics showed a fixed heart rate reflecting the disturbed autonomic innervation but only minor changes of cerebral blood flow velocity, which is similar to normal cerebrovascular autonomic regulation. Patients with pandysautonomia had a fixed heart rate associated with a decrease of systemic blood pressure but a failure of compensatory cerebral autoregulation to maintain normal flow velocity values after standing up. The results suggest that in diabetics cerebrovascular autonomic regulation is intact in contrast to cardiac autonomic function, while in patients with pandysautonomia both functions are disturbed. Criteria for the interpretation of autonomic regulatory mechanisms involved in cerebrovascular flow measurements are discussed.

Transcranial Doppler sonographic studies of cerebral autoregulation in Shy-Drager syndrome

A study is reported of mean arterial blood pressure and heart rate in four patients suffering from Shy-Drager syndrome. Blood flow velocity in the middle cerebral artery (MCA) was recorded by transcranial Doppler sonography. Concomitant changes in cerebral blood flow and the effect of cerebral autoregulation were thus examined. During tilt (60 degrees, head up) mean arterial blood pressure decreased by 40 mm Hg or 35%, while MCA blood flow velocity dropped by 14 cm/s or 28% (mean values). The lower percentage reduction in flow velocity may indicate a preserved cerebral autoregulation in central autonomic insufficiency.

The effect of orthostatic hypotension on cerebral blood flow and middle cerebral artery velocity in autonomic failure, with observations on the action of ephedrine

Cerebral blood flow (CBF) and middle cerebral artery velocity (MCAv) have been measured using 133xenon washout and transcranial Doppler in ten patients with autonomic failure. Four pure autonomic failure and four multiple system atrophy patients behaved similarly: tilting them sufficiently to induce significant orthostatic hypotension without causing syncopal symptoms led to a significant fall in their mean MCAv, but no change in their mean CBF. These findings suggest that cerebral autoregulation is preserved in autonomic failure, orthostatic hypotension resulting in a reactive vasodilatation which lowers MCAv, reduces vascular resistance, and maintains CBF. Ephedrine helped to correct the orthostatic hypotension, but had no direct effect on CBF. Two siblings with orthostatic hypotension secondary to dopamine-beta-hydroxylase deficiency also had preserved cerebral autoregulation, but ephedrine led to paradoxical hypotension in these patients.

Cerebral blood flow increases during insulin-induced hypoglycaemia in type 1 (insulin-dependent) diabetic patients and control subjects

The effect of insulin-induced hypoglycaemia on cerebral blood flow was examined using the intravenous xenon-clearance technique in 9 patients with Type 1 (insulin-dependent) diabetes (aged 20 to 43 years) and 9 age-matched control subjects before, during and after hypoglycaemia. Cerebral blood flow rose in both groups. The mean basal cerebral flood flow values were not significantly different and during hypoglycaemia mean cerebral blood flow increased by 17% (p = 0.008) in the diabetic patients and by 21% (p = 0.0003) in the control subjects. The results suggest that in young diabetic patients without autonomic neuropathy or microangiopathy cerebral vessels dilate normally in response to hypoglycaemia. The physiological importance of an increase in cerebral blood flow during hypoglycaemia is uncertain; but glucose availability is increased.

Equilibrium disorders and R-R intervals in ECG

We have measured RR intervals on patients with equilibrium disorders to check the function of the autonomic nervous system. And we have obtained two parameters (coefficient of variation "CV%" (the static function of the autonomic nervous system] and "A-B" (the dynamic function of the autonomic nervous system). The dynamic function of the autonomic nervous system (A-B) further deteriorated in elderly patients with central nervous system disorders. We concluded that disorders in the dynamic function of the autonomic nervous system affected the autoregulation which caused the central nervous system disorders, especially in elderly patients.

Constipation with colonic inertia. A manifestation of systemic disease?

Transit of radiopaque markers was delayed in the ascending colon of 51 females and 3 males treated for severe idiopathic constipation. Onset of symptoms was between age 10 and 20 in more than half of the patients. Eighteen percent had previously undergone unnecessary laparotomy for large bowel pseudoobstruction. Stool frequency ranged from 1 stool every three days to 1 every 2 months. Twenty-six percent suffered from fecal incontinence. In addition, 30% had orthostatic hypotension and 15% galactorrhea of idiopathic origin. Patients had a higher than normal anal pressure (P less than 0.001). They all had a rectoanal inhibitory reflex, but it was abnormal in 76%. In the upper esophageal sphincter, resting pressure was higher (P less than 0.02), and coordination poorer (P less than 0.05) than in normal control subjects. Incidence of spontaneous tertiary contractions in the body of the esophagus was greater than normal (P less than 0.03). In the lower esophageal sphincter, resting pressure was lower (P = 0.001) and gastroesophageal gradient weaker (P = 0.05). Closing pressure of the sphincter was lower (P less than 0.001) and coordination less adequate (P less than 0.02). After subcutaneous injection of 0.035 mg/kg bethanechol, urinary bladder intraluminal pressure increased by over 15 cm H2O in 31% of patients but never did in controls, and average maximal pressure was greater (P less than 0.025). Time taken to reach peak pressure was shorter (P less than 0.01). This study provides evidence that patients who suffer from constipation with colonic inertia also have abnormal function in other hollow viscera.(ABSTRACT TRUNCATED AT 250 WORDS)

Prognostic value of cerebral blood flow autoregulation in the long-term prognosis of ischemic cerebrovascular disease

The correlation between long-term prognosis, cerebral blood flow (CBF) and CBF autoregulation was studied in 34 patients with cerebral infarction (mean age, 64 years). CBF was measured by the nitrous oxide method 1-6 months (mean 87 days) after disease onset. CBF autoregulation was evaluated quantitatively from the Dysautoregulation Index (DI) (delta CBF/delta effective MABP). Reductions in effective MABP were induced with a tilt table. No significant correlation was noted among CBF, DI and activities of daily living at the time of measurement. The patients' physical condition was reevaluated by questionnaire 2 years or more (mean 32 months) later. Better functional state at follow-up was related to higher CBF and lower DI values although the differences were not significant. The relationships among CBF, DI and changes in physical condition during the period were evaluated. The mean CBF values in patients with a better prognosis exceeded those of poor prognosis patients. The CBF values in the group who became independent significantly exceeded those in the group that deteriorated (P less than 0.05). The CBF values in the latter showed small but significant decreases during head-up tilting (P less than 0.05). The DI in this group was significantly higher than in the groups with a less severe outcome (P less than 0.01, P less than 0.05, respectively). In conclusion, determinations of CBF autoregulation, together with flow values, in the chronic state may have some value in predicting the long-term prognosis in cerebral infarction.

Preservation of autoregulation of cerebral blood flow in autonomic failure

Cerebral blood flow (CBF) measurements have been made at systolic pressures between 40 and 170 mm Hg in 8 patients with chronic autonomic failure and widespread sympathetic efferent defects. Hypotension was produced by head up tilt. Cerebral autoregulation was preserved over a wide range and only failed at a systolic pressure close to 60 mm Hg, which is below the level at which it fails in normal subjects. Therefore, although autoregulation is probably mediated largely by local myogenic factors, its lower limit appears to be reduced by defective sympathetic function. These findings help to explain the remarkable tolerance of severe postural hypotension in autonomic failure.

Cerebral hemodynamics in Shy-Drager syndrome: variability of cerebral blood flow dysautoregulation and the compensatory role of chemical control in dysautoregulation

Cerebrovascular autoregulation and CO2 reactivity were measured repeatedly in 3 patients with the multiple system atrophy type of autonomic insufficiency (Shy-Drager syndrome) by means of the 133Xe injection method. The degree of cerebral blood flow (CBF) dysautoregulation showed day-to-day variations in 2 of the 3 patients. The CO2 reactivity was normal or supernormal in the supine position in patients with impaired autoregulation. In the head-up position the response to CO2 was slightly suppressed in 2 of the patients, suggesting that chemical control may have tended to compensate for CBF dysautoregulation. It is concluded that the mechanism of chemical control of the cerebrovasculature is different from that which controls autoregulation and may have partially compensated for CBF dysautoregulation.

The sympathetic-nervous-system defect in primary orthostatic hypotension

We sought to elucidate further the neurologic defect of idiopathic orthostatic hypotension, which appears to represent two distinct clinical entities. While recumbent, patients with multiple central-nervous-system defects, as well as peripheral autonomic nervous dysfunction, have normal plasma levels of norepinephrine that fail to increase normally after standing or exertion (P less than 0.001 by t-test as compared to controls). While recumbent, patients with peripheral autonomic insufficiency without signs of central-nervous-system defects have low levels of plasma norepinephrine (P less than 0.001) that also fail to increase normally after standing or exercising (P less than 0.001). Both groups have low levels of plasma dopamine-beta-hydroxylase (P less than 0.02). These findings are consistent with other pathological and pharmacologic observations suggesting that patients with central-nervous-system disease are unable to activate appropriately an otherwise intact sympathetic nervous system, whereas in patients without signs of central-nervous-system disease the deficit affects peripheral sympathetic nerves.

Atherosclerotic cerebral infarction: pathophysiologic aspects

When the supply of substrate to the brain is threatened, homeostatic mechanisms induce cerebral vasodilatation to compensate for the insufficiency. When a region of the brain is rendered completely ischemic, local infarction occurs. The size of the infarct depends partly on the availability of collateral circulation and the adequacy of the homeostatic mechanisms controlling blood flow in stillpatent vessels. Several approaches to acute-phase treatment of stroke derive from clinical and experimental studies of cerebral blood flow and metabolism. We must conclude that both surgical and nonsurgical therapeutic measures have been of limited value in the treatment of cerebral infarction and that the basic therapy for completed stroke remains good medical management of complications and attentive nursing care.

Neurogenic Regulation of Cerebral Blood Flow Following Ischemia

To elicit evidence concerning neurogenic control, regional cerebral blood flow determined by measurement of cortical temperature was examined in monkeys. Following three hours of temporary occlusion of the MCA, pressure autoregulation was preserved in all control animals. Presumptive partial chemical sympathectomy, produced by the administration of either L-alphamethyl-tyrosine or 3-alpha-dimethyl-tyrosine methyl ester HCl, was associated with loss of pressure autoregulation following 1.5 hours of occlusion of the MCA on only the side of the occlusion. Failure of pressure autoregulation in the treated animals implies that sympathetic control was a partial requirement of proper postischemic pressure autoregulation.

[Idiopathic orthostatic hypotension (Shy-Drager syndrome). Results of regional cerebral blood flow measurements (author's transl)]

Using a gamma camera and the stochastic method, regional cerebral blood flow was measured in a patient with the diagnosis of idiopathic orthostatic hypotension. Blood pressure was altered by tilting the patient in supine position head-up and head-down. A partial defect in the autoregulation and CO2 sensitivity was found. Sensitivity to Norepinephrine was checked by intravenous infusion of 0.02 mug/min/kg body weight. An immediate marked rise in blood pressure was observed. Clinical symptoms, therapeutic guidelines, and histopathological findings are discussed.

Cerebrospinal-fluid acid-base and electrolyte changes resulting from cerebral anoxia in man

To study metabolic changes in the central nervous system after profound anoxia, we measured changes in cisternal and lumbar cerebrospinal fluid. Acid-base values and electrolyte concentrations were determined in cisternal and lumbar fluid from 12 severely anoxic patients (cardiac arrest), and from 15 within 24 hours after cardiac resuscitation. In the severely anoxia patients the normal cisternal-lumbar pH gradient was reversed, cisternal fluid was more acid (pH 6.815 vs. 6.953), and cisternal potassium concentration was twice that of lumbar (6.7 vs 3.5 mEq per liter). These findings indicate that during anoxia potassium and hydrogen ion flow from brain cells into the brain extracellular fluid, and that acute changes are reflected more accurately by cisternal than by lumbar fluid. In resuscitated patients cisternal fluid was normal, and normal cisternal-lumbar differences were found; thus, the normal milieu of brain cells is rapidly reestablished after resuscitation.

Chronically impaired autoregulation of cerebral blood flow in long-term diabetics

Using the arteriovenous oxygen difference method autoregulation of cerebral blood flow (CBF) was tested in 16 long-term diabetics and eight control patients. Blood pressure was raised by angiotensin infusion and lowered by trimethaphan camsylate infusion, in some cases combined with head-up tilting of the patient. Regression analysis was carried out on the results in order to quantify autoregulatory capacity. In the control patients CBF did not vary with moderate blood pressure variations, indicating normal autoregulation. In four of the 16 diabetic patients CBF showed significant pressure dependency, indicating impaired autoregulation. The cause of impaired autoregulation in some long-term diabetics is believed to be diffuse or multifocal dysfunction of cerebral arterioles due to diabetic vascular disease. Other conditions with impaired autoregulation are discussed and compared with that seen in long-term diabetes.

The role of the peripheral sympathetic nervous system in cerebral blood flow autoregulation

The effect of chronic, unilateral superior cervical ganglionectomy on cerebral blood flow and blood flow autoregulaiton to changes in perfusion pressure was examined in seven phencyclidine anesthetized monkeys. Ten to 14 days prior to the experiments Doppler ultrasonic flow transducers were placed on both carotid arteries after ligation of the external carotid branches and removal of one superior cervical ganglion. Autoregulation was tested by exsanguination and metaraminol infusion with the monkeys inspiring from air, 9% and 12% carbon dioxide in air. Immediately following experimentation the cerebral vessels were examined for the presence of noradrenergic fibers. The results of the study demonstrate that: (1) superior cervical ganglionectomy produces a significant reduction in the noradrenergic innervation of ipsilateral extraparenchymal arteries: (2) the peripheral sympathetic nervous system contrivutes to overall cerebral vascular resistance primarily by affecting resistance in extraparenchymal arteries; and (3) as a result, it determines the contribution of the extraparenchymal arteries to overall cerebral blood flow autoregulation.