Preservation of autoregulation of cerebral blood flow in autonomic failure

Elevated cerebral blood flow in patients with pure autonomic failure

PURPOSE

Pure autonomic failure (PAF) results from an impaired peripheral autonomic nervous system, and clinical symptoms present with orthostatic hypotension. While the impact on cardiovascular indices of orthostatic intolerance are well-characterized, more limited information is available regarding cerebral hemodynamic dysfunction in PAF. The objective of this study was to test the hypothesis that cerebral blood flow (CBF) is reduced in PAF, and to quantify the relationship between CBF and clinical indicators of disease severity, including peripheral supine arterial blood pressure.

METHODS

Participants with PAF (n = 17) and age- and sex-matched normotensive healthy controls (n = 17) were examined using established clinical rating scales, cardiovascular autonomic function tests, and 3T MRI measurements of CBF. CBF-weighted images were also used to determine the prevalence of venous hyperintensities from the major dural sinuses as evidence of abnormal capillary flow. Nonparametric tests and general linear models were used to evaluate differences and correlations between study variables.

RESULTS

Gray matter CBF was higher in PAF (51.1 ± 13.4 mL/100 g/min) compared to controls (42.9 ± 6.5 mL/100 g/min, p = 0.007). Venous hyperintensities were more prevalent in PAF relative to controls, and the presence and degree of venous hyperintensities was associated with higher mean CBF (p = 0.027). In PAF participants, CBF and supine systolic blood pressure were inversely related (Spearman's rho = -0.545, p = 0.024).

CONCLUSIONS

Findings suggest that PAF patients may exhibit elevated CBF and provide evidence that this condition exerts a hemodynamic impact in the central nervous system.

Symptom Recognition Is Impaired in Patients With Orthostatic Hypotension

Failure to recognize symptoms of orthostatic hypotension (OH) may result in falls, syncope, and injuries. The relationship between orthostatic changes in blood pressure and symptom occurrence and severity is not known. The goal of the present study was to define the relationship between the occurrence and severity of the symptoms of orthostatic hypotension (OH) and (1) the upright systolic blood pressure (SBP) and (2) the fall in SBP after tilting in patients with OH. We prospectively studied 89 patients with OH. Reported BP values include the lowest BP in the first 3 minutes of tilt and the change in blood pressure during tilt. Subjects were queried about symptoms of orthostatic intolerance while supine and during the first 3 minutes of tilt testing using Question 1 of the Orthostatic Hypotension Questionnaire. Mean tilted SBP was 101.6±26.1 mm Hg and mean SBP fall 47.9±18.1 mm Hg. Mean symptom scores when upright were: light-headedness (2.3/10±2.7), dizziness (1.6/10±2.5), and impending blackout (0.8/10±1.9). The majority of patients were asymptomatic or mildly symptomatic and no discrete cutoff for symptoms was observed. The magnitude of the SBP fall (r=-0.07, P=NS) and the lowest upright SBP (r=0.08, P=NS) did not correlate with any reported symptom. These results suggest a poor relationship between the magnitude of the orthostatic BP fall, the upright orthostatic BP, and symptoms. Many patients are asymptomatic despite substantial SBP falls and low orthostatic blood pressures. These findings have implications for clinical care of patients with OH and clinical trials to treat patients with OH.

Timing of Circulatory and Neurological Events in Syncope

Syncope usually lasts less than a minute, in which short time arterial blood pressure temporarily falls enough to decrease brain perfusion so much that loss of consciousness ensues. Blood pressure decreases quickest when the heart suddenly stops pumping, which happens in arrhythmia and in severe cardioinhibitory reflex syncope. Loss of consciousness starts about 8 s after the last heart beat and circulatory standstill occurs after 10-15 s. A much slower blood pressure decrease can occur in syncope due to orthostatic hypotension Standing blood pressure can then stabilize at low values often causing more subtle signs (i.e., inability to act) but often not low enough to cause loss of consciousness. Cerebral autoregulation attempts to keep cerebral blood flow constant when blood pressure decreases. In reflex syncope both the quick blood pressure decrease and its low absolute value mean that cerebral autoregulation cannot prevent syncope. It has more protective value in orthostatic hypotension. Neurological signs are related to the severity and timing of cerebral hypoperfusion. Several unanswered pathophysiological questions with possible clinical implications are identified.

Efficacy of Servo-Controlled Splanchnic Venous Compression in the Treatment of Orthostatic Hypotension: A Randomized Comparison With Midodrine

Splanchnic venous pooling is a major hemodynamic determinant of orthostatic hypotension, but is not specifically targeted by pressor agents, the mainstay of treatment. We developed an automated inflatable abdominal binder that provides sustained servo-controlled venous compression (40 mm Hg) and can be activated only on standing. We tested the efficacy of this device against placebo and compared it to midodrine in 19 autonomic failure patients randomized to receive either placebo, midodrine (2.5-10 mg), or placebo combined with binder on separate days in a single-blind, crossover study. Systolic blood pressure (SBP) was measured seated and standing before and 1-hour post medication; the binder was inflated immediately before standing. Only midodrine increased seated SBP (31±5 versus 9±4 placebo and 7±5 binder, P=0.003), whereas orthostatic tolerance (defined as area under the curve of upright SBP [AUCSBP]) improved similarly with binder and midodrine (AUCSBP, 195±35 and 197±41 versus 19±38 mm Hg×minute for placebo; P=0.003). Orthostatic symptom burden decreased with the binder (from 21.9±3.6 to 16.3±3.1, P=0.032) and midodrine (from 25.6±3.4 to 14.2±3.3, P<0.001), but not with placebo (from 19.6±3.5 to 20.1±3.3, P=0.756). We also compared the combination of midodrine and binder with midodrine alone. The combination produced a greater increase in orthostatic tolerance (AUCSBP, 326±65 versus 140±53 mm Hg×minute for midodrine alone; P=0.028, n=21) and decreased orthostatic symptoms (from 21.8±3.2 to 12.9±2.9, P<0.001). In conclusion, servo-controlled abdominal venous compression with an automated inflatable binder is as effective as midodrine, the standard of care, in the management of orthostatic hypotension. Combining both therapies produces greater improvement in orthostatic tolerance.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT00223691.

Cerebral autoregulation and white matter lesions in Parkinson's disease and multiple system atrophy

Cerebral autoregulation is a complex homeostatic process which ensures constant brain blood supply, despite continuous blood pressure fluctuations. Recent evidence suggests that in Parkinson's disease (PD) and multiple system atrophy (MSA) this process is maintained in a broadened range of blood pressure values, consistent with an adaptive mechanism to increase tolerance to orthostatic hypotension. In PD and MSA orthostatic hypotension may be accompanied by supine hypertension which has been recently linked with cerebral white matter lesions in these conditions. We hypothesize that cerebral autoregulation adaptation to chronic orthostatic hypotension may be directly related with an increase susceptibility to hypertensive peaks. Evaluation of cerebral autoregulatory behavior may thus represent a novel approach to simultaneously target orthostatic symptoms and silent end-organ damage in alpha-synucleinopathies, with a beneficial impact on cerebrovascular and cognitive outcome.

Hypotension and environmental noise: a replication study

Up to now, traffic noise effect studies focused on hypertension as health outcome. Hypotension has not been considered as a potential health outcome although in experiments some people also responded to noise with decreases of blood pressure. Currently, the characteristics of these persons are not known and whether this down regulation of blood pressure is an experimental artifact, selection, or can also be observed in population studies is unanswered. In a cross-sectional replication study, we randomly sampled participants (age 20–75, N = 807) from circular areas (radius = 500 m) around 31 noise measurement sites from four noise exposure strata (35–44, 45–54, 55–64, >64 Leq, dBA). Repeated blood pressure measurements were available for a smaller sample (N = 570). Standardized information on socio-demographics, housing, life style and health was obtained by door to door visits including anthropometric measurements. Noise and air pollution exposure was assigned by GIS based on both calculation and measurements. Reported hypotension or hypotension medication past year was the main outcome studied. Exposure-effect relationships were modeled with multiple non-linear logistic regression techniques using separate noise estimations for total, highway and rail exposure. Reported hypotension was significantly associated with rail and total noise exposure and strongly modified by weather sensitivity. Reported hypotension medication showed associations of similar size with rail and total noise exposure without effect modification by weather sensitivity. The size of the associations in the smaller sample with BMI as additional covariate was similar. Other important cofactors (sex, age, BMI, health) and moderators (weather sensitivity, adjacent main roads and associated annoyance) need to be considered as indispensible part of the observed relationship. This study confirms a potential new noise effect pathway and discusses potential patho-physiological routes of actions.

Combined counter-maneuvers accelerate recovery from orthostatic hypotension in familial dysautonomia

BACKGROUND

In patients with familial dysautonomia (FD), prominent orthostatic hypotension (OH) endangers cerebral perfusion. Supine repositioning or abdominal compression improves systolic and diastolic blood pressure (BPsys and BPdia).

OBJECTIVE

To determine whether OH recovers faster with combined supine repositioning and abdominal compression than with supine repositioning alone.

METHODS

In 9 patients with FD (17.8 ± 3.9 years) and 10 healthy controls (18.8 ± 5 years), we assessed 2-min averages of BPsys, BPdia, and heart rate (HR) during supine rest, standing, supine repositioning, another supine rest, second standing, and supine repositioning with abdominal compression by leg elevation and flexion. We determined BPsys- and BPdia-recovery-times as intervals from return to supine until BP reached values equivalent to each participant's 2-min average at supine rest minus two standard deviations. Differences in signal values and BP-recovery-times between groups and positions were assessed by ANOVA and post hoc testing (significance: P < 0.05).

RESULTS

Patients with FD had pronounced OH that improved with supine repositioning. However, BP only reached supine rest values with additional abdominal compression. In controls, BP was stable during positional changes. Without abdominal compression, BP-recovery-times were longer in patients with FD than those in controls, but similar to control values with compression (BPsys: 83.7 ± 64.1 vs 36.6 ± 49.5 s; P = 0.013; BPdia: 84.6 ± 65.2 vs 35.3 ± 48.9 s; P = 0.009).

CONCLUSION

Combining supine repositioning with abdominal compression significantly accelerates recovery from OH and thus lowers the risk of hypotension-induced cerebral hypoperfusion.

Brain hypoperfusion in a girl with systemic lupus erythematosus

We describe an adolescent girl with systemic lupus erythematosus, presenting with severe cardiovascular autonomic dysfunction and incapacitating orthostatic hypotension to a degree not previously reported. Further evaluation of cerebral blood flow velocity, using transcranial Doppler testing, demonstrated an abnormal hypercapnic cerebrovascular response. Both the orthostatic hypotension and the abnormal cerebrovascular hypercapnic response improved with intensive medical treatment of her systemic lupus erythematosus. Additional studies are necessary to elucidate the pathogenesis of these cerebrovascular and autonomic abnormalities, especially considering the potential consequences they may exert on cerebral perfusion, which may be subtle, underrecognized, and capable of affecting cognition.

The changing face of orthostatic and neurocardiogenic syncope with age

AIM

Reports of the outcomes of syncope assessment across a broad spectrum of ages in a single population are scarce. It is our objective to chart the varying prevalence of orthostatic and neurocardiogenic syncope (NCS) as a patient ages.

METHODS

This was a retrospective study. All consecutive patients referred to a tertiary referral syncope unit over a decade were included. Patients were referred with recurrent falls or orthostatic intolerance. Tilt tests and carotid sinus massage (CSM) were performed in accordance with best practice guidelines.

RESULTS

A total of 3002 patients were included (1451 short tilt, 127 active stand, 1042 CSM and 382 prolonged tilt). Ages ranged from 11 to 91 years with a median (IQR) of 75 (62-81) years. There were 1914 females; 1088 males. Orthostatic hypotension (OH) was the most commonly observed abnormality (test positivity of 60.3%). Those with OH had a median (IQR) age of 78 (71-83) years. Symptomatic patients were significantly younger than asymptomatic (P = 0.03). NCS demonstrated a bimodal age distribution. Of 194 patients with carotid sinus hypersensitivity, the median age (IQR) was 77 (68-82) years. Those with vasovagal syncope (n = 80) had a median (IQR) age of 30 (19-44) years. There were 57 patients with isolated postural orthostatic tachycardia syndrome. Of the total patients, 75% were female. They had a median (IQR) age of 23 (17-29) years.

CONCLUSION

We have confirmed, in a single population, a changing pattern in the aetiology of syncope as a person ages. The burden of disease is greatest in the elderly.

Autonomic dysfunction affects cerebral neurovascular coupling

OBJECTIVE

Autonomic failure (AF) affects the peripheral vascular system, but little is known about its influence on cerebrovascular regulation. Patients with familial amyloidotic polyneuropathy (FAP) were studied as a model for AF.

METHODS

Ten mild (FAPm), 10 severe (FAPs) autonomic dysfunction FAP patients, and 15 healthy controls were monitored in supine and sitting positions for arterial blood pressure (ABP) and heart rate (HR) with arterial volume clamping, and for blood flow velocity (BFV) in posterior (PCA) and contralateral middle cerebral arteries (MCA) with transcranial Doppler. Analysis included resting BFV, cerebrovascular resistance parameters (cerebrovascular resistance index, CVRi; resistance area product, RAP; and critical closing pressure, CrCP), and neurovascular coupling through visually evoked BFV responses in PCA (gain, rate time, attenuation, and natural frequency).

RESULTS

In non-stimulation conditions, in each position, there were no significant differences between the groups, regarding HR, BP, resting BFV, and vascular resistance parameters. Sitting ABP was higher than in supine in the three groups, although only significantly in controls. Mean BFV was lower in sitting in all the groups, lacking statistical significance only in FAPs PCA. CVRi and CrCP increased with sitting in all the groups, while RAP increased in controls but decreased in FAPm and FAPs. In visual stimulation conditions, FAPs comparing to controls had a significant decrease of natural frequency, in supine and sitting, and of rate time and gain in sitting position.

INTERPRETATION

These results demonstrate that cerebrovascular regulation is affected in FAP subjects with AF, and that it worsens with orthostasis.

Postprandial hypotension in clinical geriatric patients and healthy elderly: prevalence related to patient selection and diagnostic criteria

The aims of this study were to find out whether Postprandial hypotension (PPH) occurs more frequently in patients admitted to a geriatric ward than in healthy elderly individuals, what the optimal interval between blood pressure measurements is in order to diagnose PPH and how often it is associated with symptoms.The result of this study indicates that PPH is present in a high number of frail elderly, but also in a few healthy older persons. Measuring blood pressure at least every 10 minutes for 60 minutes after breakfast will adequately diagnose PPH, defined as >20 mmHg systolic fall, in most patients. However with definition of PPH as >30 mmHg systolic fall, measuring blood pressure every 10 minutes will miss PPH in one of three patients. With the latter definition of PPH the presence of postprandial complaints is not associated with the existence of PPH.

Central and cerebrovascular effects of leg crossing in humans with sympathetic failure

Leg crossing increases arterial pressure and combats symptomatic orthostatic hypotension in patients with sympathetic failure. This study compared the central and cerebrovascular effects of leg crossing in patients with sympathetic failure and healthy controls. We addressed the relationship between MCA V_mean (middle cerebral artery blood velocity; using transcranial Doppler ultrasound), frontal lobe oxygenation [O₂Hb (oxyhaemoglobin)] and MAP (mean arterial pressure), CO (cardiac output) and TPR (total peripheral resistance) in six patients (aged 37–67 years; three women) and age- and gender-matched controls during leg crossing. In the patients, leg crossing increased MAP from 58 (42–79) to 72 (52–89) compared with 84 (70–95) to 90 (74–94) mmHg in the controls. MCA V_mean increased from 55 (38–77) to 63 (45–80) and from 56 (46–77) to 64 (46–80) cm/s respectively (P<0.05), with a larger rise in O₂Hb [1.12 (0.52–3.27)] in the patients compared with the controls [0.83 (−0.11 to 2.04) μmol/l]. In the control subjects, CO increased 11% (P<0.05) with no change in TPR. By contrast, in the patients, CO increased 9% (P<0.05), but also TPR increased by 13% (P<0.05). In conclusion, leg crossing improves cerebral perfusion and oxygenation both in patients with sympathetic failure and in healthy subjects. However, in healthy subjects, cerebral perfusion and oxygenation were improved by a rise in CO without significant changes in TPR or MAP, whereas in patients with sympathetic failure, cerebral perfusion and oxygenation were improved through a rise in MAP due to increments in both CO and TPR.

Pathophysiology, diagnosis, and treatment of orthostatic hypotension and vasovagal syncope

Orthostatic hypotension (OH) occurs in 0.5% of individuals and as many as 7-17% of patients in acute care settings. Moreover, OH may be more prevalent in the elderly due to the increased use of vasoactive medications and the concomitant decrease in physiologic function, such as baroreceptor sensitivity. OH may result in the genesis of a presyncopal state or result in syncope. OH is defined as a reduction of systolic blood pressure (SBP) of at least 20 mm Hg or diastolic blood pressure (DBP) of at least 10 mm Hg within 3 minutes of standing. A review of symptoms, and measurement of supine and standing BP with appropriate clinical tests should narrow the differential diagnosis and the cause of OH. The fall in BP seen in OH results from the inability of the autonomic nervous system (ANS) to achieve adequate venous return and appropriate vasoconstriction sufficient to maintain BP. An evaluation of patients with OH should consider hypovolemia, removal of offending medications, primary autonomic disorders, secondary autonomic disorders, and vasovagal syncope, the most common cause of syncope. Although further research is necessary to rectify the disease process responsible for OH, patients suffering from this disorder can effectively be treated with a combination of nonpharmacologic treatment, pharmacologic treatment, and patient education. Agents such as fludrocortisone, midodrine, and selective serotonin reuptake inhibitors have shown promising results. Treatment for recurrent vasovagal syncope includes increased salt and water intake and various drug treatments, most of which are still under investigation.

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.

Multiple system atrophy as a cause of upper airway obstruction

A patient presented to the ear, nose and throat department with inspiratory stridor, dysphagia and a sore throat. Clinical and radiological examination was normal. During induction of anaesthesia for a planned microlaryngoscopy, the patient developed complete upper airway obstruction that was overcome by applying positive pressure via a facepiece until awake. He subsequently developed respiratory failure, requiring mechanical ventilatory support. An elective tracheostomy was inserted for his symptoms. Neurological opinion confirmed the diagnosis of multiple system atrophy with akinetic rigid syndrome. We review this obscure condition and how it may occasionally present to anaesthetists.

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.

A Clinical, Physiology and Pharmacology Evaluation of Orthostatic Hypotension in the Elderly

Orthostatic hypotension is very common in the elderly. It increases morbidity and is an independant predictor of all cause mortality. It is defined as a fall in systolic blood pressure greater than 20 mm Hg or a fall in diastolic blood pressure greater than 10 mm Hg within 3 minutes of standing. Symptoms include light headedness, weakness, blurred vision, fatigue and lethargy and falls. Most patients have orthostatic hypotension due to non neurogenic causes. Drugs like antihypertensives and tricyclic antidepressants are very common causes of orthostatic hypotension. Diagnosis is based on the history and a thorough clinical examination. Based on the history and physical examination, further testing of the heart, kidneys and autonomic nervous system may be required in selected patients. Non pharmacological methods like slow position change, increased fluid and sodium intake, compression stockings and elevation of head of the bed are the key to management of orthostatic hypotension. After these methods, pharmacological treatment with fludrocortisone and midodrine should be tried. Other drugs like desmopresin acetate, xamoterol, erythropoetin and ocreotide can be used as second line agents in selected patients.

Should we screen hospice inpatients for orthostatic hypotension?

Orthostatic hypotension (OH) is defined as a reduction in systolic blood pressure of at least 20 mm Hg or a reduction in diastolic blood pressure of at least 10 mm Hg within three minutes of standing, with a reported prevalence of 40% in the hospice setting. Dizziness, falls and fractures have been attributed to OH and some cases of symptomatic OH might be reversible. This study explored the case for screening hospice inpatients for OH. Fifty-nine patients were screened up to five times and, whilst the detection rate was 27%, in no case was it reproducible. There was no statistical association between orthostatic symptoms and the detection of OH, and no patients benefited from the screening process. On closer examination of the literature, the current definition of OH might benefit from revision, sphygmomanometry is an unsatisfactory screening method and there is currently no case for screening hospice inpatients for OH.

Treatment of vasodepressor carotid sinus syndrome with midodrine: a randomized, controlled pilot study

OBJECTIVES

To evaluate the efficacy of treatment of the vasodepressor form of carotid sinus hypersensitivity (carotid sinus syndrome (CSS)) with midodrine.

DESIGN

A prospective, double-blind, randomized, controlled trial of crossover design.

SETTING

A dedicated outpatient facility with access to tilt-table, digital arterial photoplethysmography, and 24-hour ambulatory blood pressure (BP) monitoring equipment.

PARTICIPANTS

Ten older adults (4 male, 6 female, mean age 75, range 66-86 years) with a history of unexplained syncope who displayed an asymptomatic decrease in systolic BP (SBP) of more than 50 mmHg or a symptomatic decrease of more than 30 mmHg within 30 seconds of carotid sinus massage (CSM).

MEASUREMENTS

Symptom reproduction and BP and heart rate changes were evaluated after CSM in supine and semierect positions on the right and then left sides. These measurements were performed on the final day of placebo and active-treatment phases. Ambulatory 24-hour BP monitoring took place on the penultimate and final days of each treatment phase.

RESULTS

Eight patients were symptomatic after their initial CSM. The mean+/-standard deviation SBP decrease after initial CSM was 54+/-22 mmHg. Initial mean 24-hour ambulatory BP was 127/70+/-7/5 mmHg. Eight patients reported symptoms after CSM at the end of the placebo phase. The mean SBP decrease at the end of the placebo phase was 49+/-12 mmHg. The mean 24-hour ambulatory BP was 127/69+/-9/7 mmHg. One patient reported symptoms after CSM at the end of the active-treatment phase. The mean SBP decrease at the end of the active-treatment phase was 36+/-9 mmHg. The mean 24-hour ambulatory BP at the end of the treatment phase was 133/75+/-7/6 mmHg. The differences in symptom reporting and mean SBP decrease after CSM were both significant (P<.01 and P=.03, respectively).

CONCLUSION

The results of this pilot study suggest that treatment of vasodepressor CSS with midodrine significantly reduced the rate of symptom reporting and attenuated SBP decreases after CSM but increased mean 24-hour ambulatory BP.

Multiple system atrophy

Multiple system atrophy (MSA) is a sporadic neurodegenerative disorder characterised clinically by any combination of parkinsonian, autonomic, cerebellar, or pyramidal signs and pathologically by cell loss, gliosis, and glial cytoplasmic inclusions in several CNS structures. Owing to the recent advances in its molecular pathogenesis, MSA has been firmly established as an alpha-synucleinopathy along with other neurodegenerative diseases. In parallel, the clinical recognition of MSA has improved and the recent consensus diagnostic criteria have been widely established in the research community as well as movement disorders clinics. Although the diagnosis of this disorder is largely based on clinical expertise, several investigations have been proposed in the past decade to assist in early differential diagnosis. Symptomatic therapeutic strategies are still limited; however, several candidate neuroprotective agents have entered phase II and phase III clinical trials.

Effect of Posture on Blood and Intraocular Pressures in Multiple System Atrophy, Pure Autonomic Failure, and Baroreflex Failure

Background— Intraocular pressure (IOP) may be partially under systemic vascular control. This study examined whether a correlation exists between blood and intraocular pressures in patients with autonomic dysfunction.

Methods and Results— Eleven patients with 3 types of confirmed autonomic dysfunction (multiple system atrophy, pure autonomic failure, and baroreflex failure) were compared with age- and gender-matched controls and had IOP, systolic blood pressure, diastolic blood pressure, heart rates, and calculated mean arterial pressures (MAP) and mean ocular perfusion pressures (MOPP) measured in the supine, sitting, and standing positions. Data were analyzed with a general linear model repeated-measures ANOVA. All pressures for patients showed a dramatic decline ( P <0.001) from supine to standing (MAP −31±14 mm Hg; IOP −6±3 mm Hg; MOPP −25±14 mm Hg) compared with controls (MAP +4±7 mm Hg; IOP −1±2 mm Hg; MOPP +6±7 mm Hg). There was no significant change in heart rate from supine to standing for patients compared with controls ( P =0.648). Within both the multiple system atrophy (n=5) and pure autonomic failure (n=4) groups, all initial pressures were similar to control pressures in the supine position, whereas patients with baroreflex failure (n=2) had higher mean pressures than respective controls in the supine position.

Conclusions— In autonomic dysfunction, a large decrease in MAP correlated with a large decrease in IOP. These data suggest that the autonomic nervous system, perhaps through an influence on systemic blood pressure, has a significant role in IOP regulation.

Syncope, cerebral perfusion, and oxygenation

During standing, both the position of the cerebral circulation and the reductions in mean arterial pressure (MAP) and cardiac output challenge cerebral autoregulatory (CA) mechanisms. Syncope is most often associated with the upright position and can be provoked by any condition that jeopardizes cerebral blood flow (CBF) and regional cerebral tissue oxygenation (cO(2)Hb). Reflex (vasovagal) responses, cardiac arrhythmias, and autonomic failure are common causes. An important defense against a critical reduction in the central blood volume is that of muscle activity ("the muscle pump"), and if it is not applied even normal humans faint. Continuous tracking of CBF by transcranial Doppler-determined cerebral blood velocity (V(mean)) and near-infrared spectroscopy-determined cO(2)Hb contribute to understanding the cerebrovascular adjustments to postural stress; e.g., MAP does not necessarily reflect the cerebrovascular phenomena associated with (pre)syncope. CA may be interpreted as a frequency-dependent phenomenon with attenuated transfer of oscillations in MAP to V(mean) at low frequencies. The clinical implication is that CA does not respond to rapid changes in MAP; e.g., there is a transient fall in V(mean) on standing up and therefore a feeling of lightheadedness that even healthy humans sometimes experience. In subjects with recurrent vasovagal syncope, dynamic CA seems not different from that of healthy controls even during the last minutes before the syncope. Redistribution of cardiac output may affect cerebral perfusion by increased cerebral vascular resistance, supporting the view that cerebral perfusion depends on arterial inflow pressure provided that there is a sufficient cardiac output.

Drug treatment of orthostatic hypotension and vasovagal syncope

Orthostatic hypotension is a common problem, estimated to occur in 5 out of every 1000 individuals and in as many as 7% to 17% of patients in an acute care setting. Moreover, orthostatic hypotension may be more prominent in elderly patients due to the increased intake of vasoactive medications and concomitant decrease in physiologic function, such as baroreceptor sensitivity, often seen with aging. Orthostatic hypotension is a fall in blood pressure on assuming an upright position. Absolute cutoffs for the drop in blood pressure are often difficult to determine because different patients exhibit varying degrees of tolerance to falls in blood pressure. Therefore, strict numerical criteria may lead to underdiagnosis and improper intervention. A thorough review of patient symptomatology combined with appropriate clinical tests should be employed to narrow the vast differential diagnosis and pinpoint the etiology. The fall in blood pressure seen in orthostatic hypotension results from the inability of the autonomic nervous system to adequately compensate for the 500 mL blood that is estimated to pool in the lower extremities on assuming an upright posture. The decrease in venous return results in a concomitant decrease in cardiac output and thus hypoperfusion of the cerebral circulation, possibly resulting in syncope or various other symptoms. A complete investigation should consider hypovolemia, removal of offending medications, primary autonomic disorders, secondary autonomic disorders and, of course, vasovagal syncope, the most common cause of syncope. Although further research is still necessary to rectify the disease process responsible for orthostatic hypotension, patients suffering from this disorder can effectively be treated through a combination of nonpharmacologic treatment, pharmacologic treatment and patient education. Agents such as fludrocortisone, midodrine and erythropoietin show promising results as therapeutic adjuncts. Treatment for recurrent vasovagal syncope includes increased salt intake, and various drug treatments, most of which are still under investigation.

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.

The symptomatic treatment of multiple system atrophy

Multiple system atrophy (MSA) is a neurodegenerative disease of undetermined aetiology that occurs sporadically and manifests itself as a combination of parkinsonian, autonomic, cerebellar and pyramidal signs. Despite the lack of any effective therapy to reverse this condition, some of the symptoms may be, at least temporarily, improved with adequate symptomatic therapies. Medical treatment is largely aimed at mitigating the parkinsonian and autonomic features. The therapeutic results of levodopa therapy in cases of MSA are difficult to interpret because of their variability. Nevertheless, the statement that patients with MSA are non or poorly levodopa-responsive is misleading. Clinical and pathologically proven series document about 40-60% levodopa efficacy in patients with MSA presenting with predominant parkinsonian features. Unfortunately, other antiparkinsonian compounds (dopamine agonists, amantadine) are not more effective than levodopa. Orthostatic hypotension (OH) can be suspected from the patient's history and subsequently documented in the clinic by measuring lying and standing blood pressure. The diagnosis ideally should be confirmed in the laboratory with additional tests to determine the cause and evaluate the functional deficit, so as to aid treatment. A variety of pharmacological agents with different mechanisms of action have been used in MSA to reduce OH when this is symptomatic. OH can also be alleviated by avoiding aggravating factors, such as the effects of food, micturition, exposure to a warm environment and physiological diurnal changes and by using other non-pharmacological strategies. The treatment of the very common genito-urinary symptoms (incontinence, retention, impotence) should also be considered in order to improve the quality of life of these patients.

Normal cerebral hemodynamic response to orthostasis in Parkinson's disease

In patients with Idiopathic Parkinson's Disease (IPD) without a history of syncope the cardiovascular and cerebrovascular response to orthostatic stress was studied to search for subclinical impairment of autoregulatory mechanisms. Fifteen patients with IPD and 15 healthy age-matched controls were studied at rest and during head-up tilt (HUT). Heart rate, mean arterial blood pressure (MAP) and mean blood flow velocity (MBFV) in the middle cerebral artery were measured simultaneously. Changes of MAP and MBFV and the relationship between both were assessed. During HUT, heart rate increased less in patients than in healthy subjects (16.3% versus 24.2%, p=0.03). In the first minute of orthostasis MAP decreased more in patients than in healthy subjects (-4.0% versus -0.6%, p=0.04). MAP reached the pre-tilt values within 2 min in healthy subjects and 5 min in patients. Cerebral blood flow velocities fell to a similar degree and with similar time characteristics in patients and controls (-15.4% versus -16.7%, p=0.3). In both groups, patients and controls, changes of MAP did not correlate with changes of MBFV. It can be concluded that in IPD patients without symptoms of orthostatic dysregulation the autonomic circulatory control is impaired while the cerebral hemodynamic regulation during orthostasis is unaffected.

Autoregulatory cerebral vasodilation occurs during orthostatic hypotension in patients with primary autonomic failure

It is unclear whether patients with autonomic failure autoregulate cerebral blood flow during hypotension. The objective in this study was to examine cerebral autoregulatory capacity in patients with autonomic failure by studying changes in middle cerebral artery blood flow velocity using transcranial Doppler ultrasonography before, during, and after tilt-induced hypotension. Nine patients with primary autonomic failure were evaluated. Mean arterial pressure and middle cerebral artery blood flow velocity were simultaneously recorded while the patients were in the supine position, during 60 degrees head-up tilt, and after they were returned to the horizontal position. The results were as follows: during tilt-induced hypotension, mean arterial pressure decreased significantly more than middle cerebral artery mean blood flow velocity (58% versus 36%, p <0.0002). After return to the horizontal position, mean arterial pressure returned to baseline, and middle cerebral artery blood flow velocity transiently increased above pretilt value (p <0.02). It is concluded that cerebral autoregulatory vasodilation occurs in patients with autonomic failure. This was demonstrated by a more pronounced decline in mean arterial pressure than in middle cerebral artery blood flow velocity during hypotension and by a transient increase in middle cerebral artery blood flow velocity (ie, hyperemic response) after blood pressure was restored.

Cerebral autoregulation in orthostatic intolerance

Many of the primary symptoms of orthostatic intolerance (fatigue, diminished concentration) as well as some of the premonitory symptoms of neurally mediated syncope (NMS) are thought to be due to cerebral hypoperfusion. Transcranial Doppler measurements of middle cerebral artery blood velocity (CBV) is at present the only technique for assessing rapid changes in cerebral blood flow, and hence for evaluating dynamic cerebral autoregulation. However, controversies exist regarding data interpretation. At syncope, during the collapse of blood pressure (BP), diastolic CBV diminishes, whereas systolic CBV is maintained. Some consider this increase in CBV pulsatility to be indicative of a paradoxical increase in cerebrovascular resistance (CVR) prior to syncope. Others note that mean CBV decreases much less than does mean BP, implying that cerebral autoregulatory mechanisms are intact and functioning at syncope. Similarly, there is no evidence of impaired dynamic cerebral autoregulation, as measured by standard linear transfer-function analysis, in patients with NMS. Some patients with exaggerated postural tachycardia (POTS) have been found to have an excessive decrease in CBV during head-up tilt. Controversy exists as to whether this decrease results from an excessive sympathetic outflow to the cerebral vasculature or from hyperventilation. However, many other equally symptomatic patients with a similar hemodynamic profile of exaggerated tachycardia during head-up tilt have normal CBV changes during this maneuver and have normal dynamic cerebral autoregulation as determined by transfer-function analysis. Whether these discrepancies reflect different pathologies in patients with POTS is currently unknown.

Orthostatic tolerance, cerebral oxygenation, and blood velocity in humans with sympathetic failure

BACKGROUND AND PURPOSE

Patients with orthostatic hypotension due to sympathetic failure become symptomatic when standing, although their capability to maintain cerebral blood flow is reported to be preserved. We tested the hypothesis that in patients with sympathetic failure, orthostatic symptoms reflect reduced cerebral perfusion with insufficient oxygen supply.

METHODS

This study addressed the relationship between orthostatic tolerance, mean cerebral artery blood velocity (V(mean), determined by transcranial Doppler ultrasonography), oxygenation (oxyhemoglobin [O(2)Hb], determined by near-infrared spectroscopy), and mean arterial pressure at brain level (MAP(MCA), determined by finger arterial pressure monitoring [Finapres]) in 9 patients (aged 37 to 70 years; 4 women) and their age- and sex-matched controls during 5 minutes of standing.

RESULTS

Supine MAP(MCA) (108+/-14 versus 86+/-14 mm Hg) and V(mean) (84+/-21 versus 62+/-13 cm. s(-1)) were higher in the patients. After 5 minutes of standing, MAP(MCA) was lower in the patients (31+/-14 versus 72+/-14 mm Hg), as was V(mean) (51+/-8 versus 59+/-9 cm. s(-1)), with a larger reduction in O(2)Hb (-11. 6+/-4 versus -6.7+/-4.5 micromol. L(-1)). Four patients terminated standing after 1 to 3.5 minutes. In these symptomatic patients, the orthostatic fall in V(mean) was greater (45+/-6 versus 64+/-10 cm. s(-1)), and the orthostatic decrease in O(2)Hb (-12.0+/-3.3 versus -7.6+/-3.9 micromol. L(-1)) tended to be larger. The reduction in MAP(MCA) was larger after 10 seconds of standing, and MAP(MCA) was lower after 1 minute (25+/-8 versus 40+/-6 mm Hg).

CONCLUSIONS

In patients with sympathetic failure, the orthostatic reduction in cerebral blood velocity and oxygenation is larger. Patients who become symptomatic within 5 minutes of standing are characterized by a pronounced orthostatic fall in blood pressure, cerebral blood velocity, and oxygenation manifest within the first 10 seconds of standing.

Contrasting actions of pressor agents in severe autonomic failure

BACKGROUND

Orthostatic hypotension is the most disabling symptom of autonomic failure. The choice of a pressor agent is largely empiric, and it would be of great value to define predictors of a response.

PATIENTS AND METHODS

In 35 patients with severe orthostatic hypotension due to multiple system atrophy or pure autonomic failure, we determined the effect on seated systolic blood pressure (SBP) of placebo, phenylpropanolamine (12.5 mg and 25 mg), yohimbine (5.4 mg), indomethacin (50 mg), ibuprofen (600 mg), caffeine (250 mg), and methylphenidate (5 mg). In a subgroup of patients, we compared the pressor effect of midodrine (5 mg) with the effect of phenylpropanolamine (12.5 mg).

RESULTS

There were no significant differences in the pressor responses between patients with multiple system atrophy or pure autonomic failure. When compared with placebo, the pressor response was significant for phenylpropanolamine, yohimbine, and indomethacin. In a subgroup of patients, we confirmed that this pressor effect of phenylpropanolamine, yohimbine, and indomethacin corresponded to a significant increase in standing SBP. The pressor responses to ibuprofen, caffeine, and methylphenidate were not significantly different from placebo. Phenylpropanolamine and midodrine elicited similar pressor responses. There were no significant associations between drug response and autonomic function testing, postprandial hypotension, or plasma catecholamine levels.

CONCLUSIONS

We conclude that significant increases in systolic blood pressure can be obtained in patients with orthostatic hypotension due to primary autonomic failure with phenylpropanolamine in low doses or yohimbine or indomethacin in moderate doses. The response to a pressor agent cannot be predicted by autonomic function testing or plasma catecholamines. Therefore, empiric testing with a sequence of medications, based on the risk of side effects in the individual patient and the probability of a response, is a useful approach.

Autoregulation of cerebral blood flow in orthostatic hypotension

BACKGROUND AND PURPOSE

We sought to evaluate cerebral autoregulation in patients with orthostatic hypotension (OH).

METHODS

We studied 21 patients (aged 52 to 78 years) with neurogenic OH during 80 degrees head-up tilt. Blood flow velocities (BFV) from the middle cerebral artery were continuously monitored with transcranial Doppler sonography, as were heart rate, blood pressure (BP), cardiac output, stroke volume, CO2, total peripheral resistance, and cerebrovascular resistance.

RESULTS

All OH patients had lower BP (P<.0001), BFV_diastolic (P<.05), CVR (P<.007), and TPR (P<.02) during head-up tilt than control subjects. In control subjects, no correlations between BFV and BP were found during head-up tilt, suggesting normal autoregulation. OH patients could be separated into those with normal or expanded autoregulation (OH_NA; n=16) and those with autoregulatory failure (OH_AF; n=5). The OH_NA group showed either no correlation between BFV and BP (n=8) or had a positive BFV/BP correlation (R2>.75) but with a flat slope. An expansion of the "autoregulated" range was seen in some patients. The OH_AF group was characterized by a profound fall in BFV in response to a small reduction in BP (mean deltaBP <40 mm Hg; R2>.75).

CONCLUSIONS

The most common patterns of cerebral response to OH are autoregulatory failure with a flat flow-pressure relationship or intact autoregulation with an expanded autoregulated range. The least common pattern is autoregulatory failure with a steep flow-pressure relationship. Patients with patterns 1 and 2 have an enhanced capacity to cope with OH, while those with pattern 3 have reduced capacity.

Effect of perturbations and a meal on superior mesenteric artery flow in patients with orthostatic hypotension

Our aims were to evaluate to role of superior mesenteric blood flow in the pathophysiology of orthostatic hypotension in patients with generalized autonomic failure.

METHODS

Twelve patients with symptomatic neurogenic orthostatic hypotension and 12 healthy controls underwent superior mesenteric artery flow measurements using Doppler ultrasonography during head-up tilt and tilt plus meal ingestion. Autonomic failure was assessed using standard tests of the function of the sympathetic adrenergic, cardiovagal and postganglionic sympathetic sudomotor function.

RESULTS

Superior mesenteric flow volume and time-averaged velocity were similar in patients and controls at supine rest; however, responses to cold pressor test and upright tilt were attenuated (p < 0.05) in patients compared to controls. Head-up tilt after the meal evoked a profound fall of blood pressure and mesenteric blood flow in the patients; the reduction of mesenteric blood flow correlated (r = 0.89) with the fall of blood pressure in these patients, providing another manifestation of failed baroreflexes. We make the novel finding that the severity of postprandial orthostatic hypotension regressed negatively with the postprandial increase in mesenteric flow in patients with orthostatic hypotension.

CONCLUSION

Mesenteric flow is under baroreflex control, which when defective, results in, or worsens orthostatic hypotension. Its large size and baroreflexivity renders it quantitatively important in the maintenance of postural normotension. The effects of orthostatic stress can be significantly attenuated by reducing the splanchnic-mesenteric volume increase in response to food. Evaluation of mesenteric flow in response to eating and head-up tilt provide important information on intra-abdominal sympathetic adrenergic function, and the ability of the patient to cope with orthostatic stress.

Complexity of middle cerebral artery blood flow velocity: effects of tilt and autonomic failure

We examined spectral fractal characteristics of middle cerebral artery (MCA) mean blood flow velocity (MFV) and mean arterial blood pressure adjusted to the level of the brain (MAPbrain) during graded tilt (5 min supine, -10 degrees, 10 degrees, 30 degrees, 60 degrees, -10 degrees, supine) in eight autonomic failure patients and age- and sex-matched controls. From supine to 60 degrees, patients had a larger drop in MAPbrain (62 +/- 4.7 vs. 23 +/- 4.5 mmHg, P < 0.001; means +/- SE) and MFV (16.4 +/- 3.8 vs. 7.0 +/- 2.5 cm/s, P < 0.001) than in controls. From supine to 60 degrees, there was a trend toward a decrease in the slope of the fractal component (beta) of MFV (MFV-beta) in both the patients and the controls, but only the patients had a significant decrease in MFV-beta (supine: patient = 2.21 +/- 0.18, control = 1.99 +/- 0.60; 60 degrees: patient = 1.46 +/- 0.24, control = 1.62 +/- 0.19). The beta value of MAPbrain (MAPbrain-beta; 2.19 +/- 0.05) was not significantly different between patients and controls and did not change with tilt. High and low degrees of regulatory complexity are indicated by values of beta close to 1.0 and 2.0, respectively. The increase in fractal complexity of cerebral MFV in the patients with tilt suggests an increase in the degree of autoregulation in the patients. This may be related to the drop in MAPbrain. The different response of MFV-beta compared with that of MAPbrain-beta also indicates that MFV-beta is related to the regulation of cerebral vascular resistance and not systemic blood pressure.

Cerebrovascular and cardiovascular responses to graded tilt in patients with autonomic failure

BACKGROUND AND PURPOSE

Patients with autonomic nervous system failure often experience symptoms of orthostatic intolerance while standing. It is not known whether these episodes are caused primarily by a reduced ability to regulate arterial blood pressure or whether changes in cerebral autoregulation may also be implicated.

METHODS

Eleven patients and eight healthy age- and sex-matched control subjects were studied during a graded-tilt protocol. Changes in their steady state middle cerebral artery mean flow velocities (MFV), measured by transcranial Doppler, brain-level mean arterial blood pressures (MABPbrain), and the relationship between the two were assessed.

RESULTS

Significant differences between patients and control subjects (P < .05) were found in both their MFV and MABPbrain responses to tilt. Patients' MFV dropped from 60 +/- 10.2 cm/s in the supine position to 44 +/- 14.0 cm/s at 60 degrees head-up tilt, whereas MABPbrain fell from 109 +/- 11.7 to 42 +/- 16.9 mm Hg. By comparison, controls' MFV dropped from 54 +/- 7.8 cm/s supine to 51 +/- 8.8 cm/s at 60 degrees, whereas MABPbrain went from 90 +/- 11.2 to 67 +/- 8.2 mm Hg. Linear regression showed no significant difference in the MFV-MABPbrain relationship between patients and control subjects, with slopes of 0.228 +/- 0.09 cm.s-1.mm Hg-1 for patients and 0.136 +/- 0.16 cm.s-1.mm Hg-1 for control subjects.

CONCLUSIONS

The present study found significant differences between patients and control subjects in their MFV and MABPbrain responses to tilt but no difference in the autoregulatory MFV-MABPbrain relationship. These results suggest that patients' decreased orthostatic tolerance may primarily be the result of impaired blood pressure regulation rather than a deficiency in cerebral autoregulation.

Transfer function analysis of cerebral autoregulation dynamics in autonomic failure patients

BACKGROUND AND PURPOSE

Autonomic nervous system diseases affect systemic blood pressure regulation. Patients with autonomic nervous system diseases have consistently larger drops in blood pressure associated with standing than the normal population. Autonomic dysfunction and/or these changes in blood pressure may affect dynamic cerebral autoregulation.

METHODS

Heart rate, mean blood flow velocity (MBFV) of the middle cerebral artery via transcranial Doppler ultrasound, mean arterial blood pressure adjusted to brain level (MABPbrain) via Finapres, and end tidal CO2 were measured continuously during graded tilt (after 5 minutes in supine position as baseline, -10 degrees, +10 degrees, +30 degrees, +60 degrees, -10 degrees, and supine recovery) in autonomic failure patients and their age- and sex-matched control subjects. The dynamic response of MBFV to spontaneous variations in MABPbrain was investigated by cross-spectral analysis. The transfer gain and phase relationships between MBFV and MABPbrain were determined from the final 256 beats of each 5-minute-tilt segment. The transfer gain was normalized to mean MABPbrain and MBFV and then converted to decibels (dB).

RESULTS

MBFV variation (0.03 to 0.14 Hz) preceded MABPbrain by similar phase angles in patients and control subjects and in all tilt conditions (patients: 31 +/- 5 degrees; control subjects: 30 +/- 5 degrees; mean +/- SEM). Patients had a higher supine gain than control subjects (P < .05). Both patients and control subjects showed a significant decrease in gain with tilt and by 60 degrees the patients were not different from the control subjects (supine to 60 degrees: patients = 5.23 +/- 0.77 to -1.65 +/- 0.89 dB; control subjects = 1.74 +/- 0.82 to -1.80 +/- 0.62 dB).

CONCLUSIONS

These data indicate an altered, yet present, autoregulatory response with autonomic failure.

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.

Improved orthostatic tolerance in familial amyloidotic polyneuropathy with unnatural noradrenaline precursor L-threo-3,4-dihydroxyphenylserine

Disabling orthostatic hypotension, due to insufficiency of the autonomic nervous system, is a common complication of type I familial amyloidotic polyneuropathy (FAP). We investigated whether oral treatment with L-threo-3,4-dihydroxyphenylserine (L-threo-Dops), a noradrenaline precursor, might be of therapeutical benefit. In twenty untreated FAP patients, aged 33 to 44 years, who, because of severe orthostatic hypotension, were bedridden or constrained to a sitting life, supine and erect blood pressure (BP), plasma noradrenaline and tilting time, defined as the interval (s) between the beginning of a 60 degrees head-up tilt and the occurrence of orthostatic symptoms (dizziness, blurred vision or near syncope) were determined before and at repeated intervals during oral treatment with L-threo-Dops, 100 mg bid, for 6 months. Before treatment supine mean BP was 80 (76-85) mmHg (mean and 95% CI), supine plasma noradrenaline was low, 59 (41-77) pg/ml and tilting time ranged from 38 to 118 s. In response to tilt, mean BP immediately fell by 36 (31-41) mmHg, whereas plasma noradrenaline increased by only 11 (0-21) pg/ml (p = 0.05). After 3 to 5 days of treatment with L-threo-Dops all patients experienced marked improvement of their orthostatic tolerance as reflected by their ability to walk freely around. This effect sustained throughout the six months of treatment. Plasma noradrenaline increased moderately by 37 (11-63) pg/ml (p = 0.02) and supine mean BP increased by 8.6 (5.8-12.4) mmHg (p < 0.001) during chronic treatment. Supine or nocturnal hypertension did not develop, the fall in mean BP in response to tilt diminished by 12.5 (6.5-17.3) mmHg (p < 0.001) and tilting time became longer than 600 s in all patients. Because of its efficacy, its sustained duration of action and the lack of side effects, L-threo-Dops is advocated to improve orthostatic tolerance in patients with autonomic insufficiency due to FAP.

Paroxysmal staring and masticatory automatisms during postural hypotension in a patient with multiple system atrophy

PURPOSE

We studied a 51-year-old man with multiple system atrophy and autonomic insufficiency. He had repeated episodes of loss of contact, staring, and masticatory automatisms.

METHODS

Blood pressure during these events documented a systolic pressure of 60 mm Hg. Cardiovascular reflex tests provided evidence of autonomic failure. Head computed tomography (CT) revealed moderate, diffuse cortical and cerebellar atrophy.

RESULTS

These events were strictly related to blood pressure decreases and could be reproduced consistently by having the patient sit up after a meal. Ictal polygraphic recordings showed EEG changes consistent with anoxia, preceded by sudden hypotension with fixed heart rate.

CONCLUSIONS

Cerebral anoxia during a syncopal attack may therefore precipitate transient, sudden neurologic dysfunction that closely mimics complex partial seizures. Masticatory automatisms may represent a release phenomenon resulting from inactivation of neocortical structures by cerebral anoxia or reticular disconnection.

Autoregulation in the middle meningeal artery

In cats anesthetized with alpha-chloralose, autoregulation of blood flow (F) in the middle meningeal and common carotid arteries was assessed by bleeding and subsequently reinfusing the animals to achieve a 25% step reduction in mean arterial blood pressure (P), while maintaining the systolic blood pressure >80 mmHg. The integrity of autoregulation was assessed by calculating the gain factor Gf = 1 - [(deltaF/F)/(deltaP/P)]. Cats were examined intact, after hexamethonium (10 mg/kg), and after papaverine (6 mg/kg). Reduction of blood pressure of 25 to 60 mmHg produced equivalent drops in carotid blood flow (Gf = 0.041 +/- 0.34; mean +/- standard deviation, n = 12). There were only small changes in flow in the middle meningeal artery during this procedure (Gf = 0.91 +/- 0.29). Hexamethonium did not block autoregulation in the middle meningeal artery (Gf = 0.92 +/- 0.13, n = 4). However, papaverine almost completely abolished the ability of the artery to autoregulate (Gf = 0.10 +/- 0.16, n = 7). The results suggest that the middle meningeal artery possesses an ability similar to that of the cortical circulation to autoregulate its blood flow through intrinsic, non-neuronal mechanisms. This will have important implications for the study of disturbances of dural arterial control in migraine and other headaches.

Simultaneous cerebrovascular and cardiovascular responses during presyncope

BACKGROUND AND PURPOSE

Presyncope, characterized by symptoms and signs indicative of imminent syncope, can be aborted in many situations before loss of consciousness occurs. The plasticity of cerebral autoregulation in healthy humans and its behavior during this syncopal prodrome are unclear, although systemic hemodynamic instability has been suggested as a key factor in the precipitation of syncope. Using lower body negative pressure (LBNP) to simulate central hypovolemia, we previously observed falling mean flow velocities (MFVs) with maintained mean arterial blood pressure (MABP). These findings, and recent reports suggesting increased vascular tone within the cerebral vasculature at presyncope, cannot be explained by the classic static cerebral autoregulation curve; neither can they be totally explained by a recent suggestion of a rightward shift in this curve.

METHODS

Four male and five female healthy volunteers were exposed to presyncopal LBNP to evaluate their cerebrovascular and cardiovascular responses by use of continuous acquisition of MFV from the right middle cerebral artery with transcranial Doppler sonography, MABP (Finapres), and heart rate (ECG).

RESULTS

At presyncope, MFV dropped on average by 27.3 +/- 14% of its baseline value (P < .05), while MABP remained at 2.0 +/- 27% above its baseline level. Estimated cerebrovascular resistance increased during LBNP. The percentage change from baseline to presyncope in MFV and MABP revealed consistent decreases in MFV before MABP.

CONCLUSIONS

Increased estimated cerebrovascular resistance, falling MFV, and constant MABP are evidence of an increase in cerebral vascular tone with falling flow, suggesting a downward shift in the cerebral autoregulation curve. Cerebral vessels may have a differential sensitivity to sympathetic drive or more than one type of sympathetic innervation. Future work to induce dynamic changes in MABP during LBNP may help in assessing the plasticity of the cerebral autoregulation mechanism.

Postural hypotension in diabetic autonomic neuropathy: a review

Postural hypotension is uncommon in diabetes but can occur secondary to autonomic neuropathy. Symptoms are rare and include dizziness, weakness, blurred vision, tiredness, and loss of consciousness. The pathophysiology of postural hypotension is not clear, but changes in intravascular volume, heart rate, cardiac output, and splanchnic vascular resistance are similar in patients and controls. The main factors producing hypotension are a blunted catecholamine response to standing, and failure of lower limb vascular resistance to increase adequately. Treatment for symptomatic postural hypotension includes avoidance of dehydration, adequate salt intake, and fludrocortisone. Other treatments are reviewed but are less helpful. Patients with postural hypotension have intermittent symptoms over the years but rarely become severely disabled. They have a poorer prognosis than patients with symptomatic autonomic neuropathy without postural hypotension.

Autonomic hyperreflexia with spinal cord injury

Autonomic hyperreflexia occurs in up to 85 percent of individuals with spinal cord injuries above the major splanchnic sympathetic outflow. In such cases, paroxysmal reflex sympathetic activity develops in response to noxious stimuli below the level of the neurologic lesion. The clinical features of autonomic hyperreflexia are due largely to reflex sympathetic adrenergic and cholinergic discharges with dysfunctional supraspinal regulatory control. Cephalgia, diaphoresis, flushing, tachycardia or bradycardia, and paroxysmal hypertension are most commonly observed. Although a variety of stimuli can provoke autonomic responses of variable magnitudes, bladder and bowel distention continue to account for most episodes. Removal of the offending stimulus is important to restoring the autonomic nervous system to its baseline activity. Current understanding of the pathophysiology, clinical features, and medical management of this fascinating but potentially serious complication of spinal cord injury are reviewed.

The cerebral hemodynamics of normotensive hypovolemia during lower-body negative pressure

Although severe hypovolemia can lead to hypotension and neurological decline, many patients with neurosurgical disorders experience a significant hypovolemia while autonomic compensatory mechanisms maintain a normal blood pressure. To assess the effects of normotensive hypovolemia upon cerebral hemodynamics, transcranial Doppler ultrasound monitoring of 13 healthy volunteers was performed during graded lower-body negative pressure of up to -50 mm Hg, an accepted laboratory model for reproducing the physiological effects of hypovolemia. Middle cerebral artery flow velocity declined by 16% +/- 4% (mean +/- standard error of the mean) and the ratio between transcranial Doppler ultrasound pulsatility and systemic pulsatility rose 22% +/- 8%, suggesting cerebral small-vessel vasoconstriction in response to the sympathetic activation unmasked by lower-body negative pressure. This vasoconstriction may interfere with the autoregulatory response to a sudden fall in blood pressure, and may explain the common observation of neurological deficit during hypovolemia even with a normal blood pressure.

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.