Postictal Pulmonary Edema Requires Pulmonary Vascular Pressure Increases

Summary: The pathogenesis of neurogenic pulmonary edema has been debated for many years. Whether cardiogenic mechanisms and increased pulmonary vascular pressures are primary or even necessary for the production of pulmonary edema has been argued. We used postictal pulmonary edema to study this problem in a sheep model of neurogenic pulmonary edema with bicucullin-induced status epilepticus. Seizure-induced increases in pulmonary vascular pressures were averted with a reservoir system to maintain left atrial pressure (LAP) and pulmonary artery pressure (PAP) at preseizure levels. No increase in lung lymph flow occurred during seizures, in contrast to the doubling of lung lymph flow that occurred during seizures when ictal pulmonary vascular hypertension was not blocked. These data support a primary role of pulmonary vascular pressure increases in the production of neurogenic pulmonary edema.     

Pulmonary lymphatic flow alterations during intracranial hypertension in sheep

The role of intracranial hypertension in the genesis of neurogenic pulmonary edema was studied in 25 sheep; cardiopulmonary hemodynamics (aortic, pulmonary arterial, and left atrial pressures and cardiac output) and fluid and protein movement across the pulmonary capillary bed (efferent pulmonary lymph flow and lymph/plasma protein ratio) were monitored. Only when intracranial pressure was raised to equal the baseline mean systemic pressure (75 to 120 Torr) did we observe the expected Cushing response of increased aortic pressure, or any alteration in pulmonary hemodynamics or fluid movement. When pulmonary changes did occur, they included an increase in pulmonary arterial pressure of between 5 and 15 Torr without any notable rise in left atrial pressure, and a sustained doubling of the pulmonary lymph flow with no dilution of the lymph/plasma protein ratio. In 3 additional animals cerebral ischemia alone produced an elevation in systemic pressure (74 Torr over baseline) without change in pulmonary arterial pressure, left atrial pressure, or pulmonary lymph flow. Thus, intracranial hypertension and ischemia both affect systemic pressure, but only the elevated intracranial pressure is followed by changes in the pulmonary circuit. We suggest that these changes in pulmonary vascular pressure, independent of changes in left atrial pressure, produce increased pulmonary transcapillary fluid flux that may result in neurogenic pulmonary edema.     

Sildenafil improves dynamic vascular function in the brain: studies in patients with pulmonary hypertension

BACKGROUND: Prostaglandins and nitric oxide play a pivotal role in the regulation of macro- and microcirculatory blood flow distribution. Interference with both mediator systems have been implicated in cerebrovascular dysfunction. Inhaled iloprost (long-acting prostacyclin analogue) and the phosphodiesterase-5 inhibitor sildenafil have recently shown efficacy in the treatment of chronic pulmonary hypertension. We investigated the impact of these agents on cerebral microcirculatory regulation in patients suffering from this disease. METHODS: In 11 patients suffering from severe pulmonary hypertension, a functional transcranial Doppler test utilizing a visual stimulation paradigm was undertaken to measure the evoked flow velocity in the posterior cerebral artery. Measurements were performed in parallel to right heart catheterization and pharmacological testing of the pulmonary vasoreactivity. After assessment of baseline measurements, inhaled iloprost and oral sildenafil were given consecutively for testing of cerebral and pulmonary vascular function. The data gained from the Doppler measurements were compared to data from 22 healthy volunteers. RESULTS: Both substances provoked a significant reduction of pulmonary arterial pressure and vascular resistance, accompanied by minor changes in systemic vascular resistance. In contrast to these superimposable hemodynamic profiles opposite effects were observed regarding cerebral vascular tone: cerebral microvascular reactivity, as assessed by attenuation and time rate parameters, was significantly improved by sildenafil, but slightly worsened by iloprost. CONCLUSIONS: Sildenafil has beneficial effects on cerebral vascular reactivity indicative of an improvement in neurovascular coupling in patients with pulmonary hypertension. These results warrant further investigations of the influence of sildenafil on dynamic vascular function in the brain independent of the underlying disease.     

Lesions of the AV3V region attenuate sympathetic activation but not the hypertension elicited by destruction of the nucleus tractus solitarius

Previous studies have implicated a functionally defined area of the forebrain, the anteroventral third ventricle (AV3V) region as being involved in the regulation of blood pressure and required for the expression of neurogenic hypertension. The present study re-examined the effect of AV3V lesion on hypertension caused by the destruction of the nucleus tractus solitarius (NTS), focussing on whether ablation of the AV3V region altered either the sympathoadrenal or vasopressin (VP) components of NTS hypertension. Bilateral electrolytic lesions of the NTS elicited acute severe hypertension in conscious, freely moving rats whether or not the animals had received AV3V or Sham lesions 14 days previously. Mean arterial pressure (MAP) measured 45 min following NTS lesion was 157 +/- 6 mm Hg in AV3V + NTS lesioned rats and 161 +/- 7 mm Hg in SHAM + NTS lesioned rats. Plasma VP levels were similarly elevated in the two groups of NTS lesioned animals, and the contribution of VP to the hypertensive response (as assessed by the decrease in arterial pressure in response to a VP pressor antagonist) was the same in both groups. In contrast, NTS lesion appeared to produce a lesser degree of sympathetic nervous system activation in AV3V lesioned rats, as evidenced by a substantially smaller increase in plasma norepinephrine (NE) levels. These results demonstrate that AV3V lesions do not attenuate or prevent NTS hypertension. However, AV3V lesions do appear to attenuate the sympathoadrenal activation caused by NTS lesions.     

Modulation of the carotid baroreceptor reflex by substance P in the nucleus tractus solitarius

Previous studies have shown that administration of substance P (SP) into the nucleus tractus solitarius (NTS) can evoke a depressor response similar to that produced by activation of the arterial baroreceptors. In addition, some studies have suggested that SP increases the reflex responses to activation of baroreceptor input. The present study was performed to determine the effects of SP on the carotid sinus baroreceptor reflex at the level of the NTS by examining the effects of both exogenous SP microinjected into different rostrocaudal locations in the NTS and blockade of the effects of endogenous SP, through the microinjection of a substance P antagonist (SPa; [D-Pro, D-Trp]-substance P). Changes in pressure in an isolated carotid sinus in anesthetized dogs were used to evoke baroreflex changes in arterial blood pressure (BP) before and after microinjection of SP (0.5 microM) or SPa (10 microM) into barosensitive regions of the NTS. Microinjection of SP or its antagonist did not alter baseline, resting BP but did produce significant changes in baroreflex sensitivity. Microinjection of SP into different rostrocaudal regions of the NTS produced different responses, with rostral and caudal NTS microinjections producing significant increases in sensitivity. No effects on baroreflex sensitivity were obtained in response to SP microinjections into the intermediate NTS. Unlike SP, microinjection of the SPa significantly decreased baroreflex sensitivity at all rostrocaudal levels of the NTS. These data demonstrated that SP has the capability to modulate the carotid baroreflex at the level of the NTS and support a physiological role for endogenously released SP.     

Systemic and pulmonary vascular pressures during generalized seizures in sheep

The systemic vascular response to seizures in known but information on the hemodynamics of the pulmonary circulation is lacking, clouding an understanding of the pathophysiology of postical pulmonary edema. We investigated this problem using electrically induced single seizures and bicuculline-induced status epilecticus in halothaneanesthetized sheep. Aortic, pulmonary arterial, and left atrial pressures were recorded throughout the seizure activity, and the responses of the systemic and pulmonary pressures were compared. All monitored pressures rose precipitously with the onset of seizures. In all types of seizure the pulmonary pressure elevation was brief, lasting only one-third as long as did the systemic. Pulmonary microvascular pressures rose well above the level of plasma oncotic pressure. Pulmonary vascular pressures were elevated in proportion to the duration of the seizure stimulus, while the systemic response did not so vary. Cervical spinal cord transection abolished all systemic and pulmonary vascular response to seizures, demonstrating ultimate neural mediation.     

Abolition of the behavioral effects of cholecystokinin following bilateral radiofrequency lesions of the parvocellular subdivision of the nucleus tractus solitarius

Cholecystokinin (CCK) has been implicated as a signal for the syndrome of satiety in a variety of species. Several lines of evidence point to a peripheral site of action for the behavioral effects of CCK. Peripheral CCK receptors appear to activate a gut-brain pathway involving the sensory fibers of the vagus nerve. To investigate the central anatomical substrate of this visceral-behavioral control system, the terminal regions of the sensory tract of the vagus were lesioned. Selective destruction of the parvocellular subdivisions of the nucleus tractus solitarius (NTS) blocked the effects of acute doses of CCK on exploratory behaviors. Sham lesions and lesions destroying only the remaining regions of the NTS or the vagal motor nuclei had no effect on baseline exploratory behaviors and did not influence the ability of CCK to decrease spontaneous exploratory behaviors. These findings delineate the first central site along the ascending sensory pathway which appears to mediate the satiety-related behavioral effects of CCK.     

EXPERIMENTAL BRAIN DAMAGE FROM FLUID PRESSURES DUE TO IMPACT ACCELERATION. 3. Morphological Observations

"Contre-coup" lesions occurring particularly in the frontal and temporal lobes following head injury have been claimed to be caused by sudden negative pressure transients, as part of the "contre-coup" end pressures occurring in the brain tissue at an occipital impact. With a new experimental model such impact acceleration pressure (near-1 atm) could be generated in the rabbit brain through a parietal opening. Resulting morphological changes were evaluated with various microscopical methods, including Evan's blue-albumin technique for observations on vascular permeability changes. Regardless of the magnitude of the negative pressure transients no changes characteristic of "contre-coup" lesions were seen in temporal lobes, i.e. in areas where preparative artefacts are absent in control animals. Therefore such negative pressure transients per se do not appear to be of major importance for the development of contre-coup lesions. However, vascular permeability changes were frequently observed in the brain stem and upper cervical cord and are presumably related to the flow of tissue in the cranio-spinal junction.     

Cardiovascular and neuroendocrine responses to behavioral stress after central or peripheral barodenervation in rats

The cardiovascular and neuroendocrine responses to acute behavioral stress were evaluated in rats after disruption of the baro reflexes by electrolytic lesions of the nucleus tractus solitarii (NTS) or sinoaortic denervation (SAD). Rats with NTS lesions or SAD showed significantly greater increases in mean arterial pressure (MAP) and plasma norepinephrine (NE) concentrations than control rats during a single 30-min escape-avoidance test. In addition, the increases in MAP and plasma NE concentration of NTS lesion rats were significantly greater than those of SAD rats. However, NTS lesion raats showed no increase in plasma renin activity (PRA), as observed in the other groups. Thus, disruption of the baroreflexes by NTS lesions oraugments the arterial pressure and plasma NE responses to stress. Additionally, NTS lesions appeared to eliminate the neurons or fibers of passage participating in the sympathetically mediated increase in PRA.     

Epileptic Sudden Death: Animal Models

Summary: The pathologic hallmark of sudden unexpected death in epilepsy (SUDEP) in humans is pulmonary edema. In an animal model of seizures, pulmonary vascular pressure, but not systemic pressure, increases in proportion to seizure duration. The induced pulmonary vascular hypertension drives fluid out of the vascular compartment into the lung parenchyma. Blocking intraictal pulmonary vascular pressure elevations prevents changes in the observed doubling of the pulmonary transcapillary fluid flux. In this animal model, the main difference between surviving animals and those that die during the seizure is apnea, with a precipitous fall in the partial pressure of oxygen (p0₂) and a parallel elevation in the partial pressure of carbon dioxide (pC0₂) recorded in nonsurvivors. Pulmonary artery and left atrial pressures in animals that die are double those of surviving animals, with a resultant increase in extra-vascular lung water at postmortem examination. The pulmonary edema is due to the combined effects of seizure- and hypoxia-induced pulmonary vascular hypertension. This animal model reproduces both death during epilepsy and pulmonary edema at postmortem examination. The etiology of the pulmonary edema appears to be that of pulmonary vascular hypertension, and the etiology of sudden death appears to be that of centrally induced apnea.     

Modulation of cardiovascular and electrocortical activity through serotonergic mechanisms in the nucleus tractus solitarius of the rat

The nucleus tractus solitarius (NTS) is an integral part of the baroreceptor reflex arc. Thus, stimulation of the NTS elicits changes in arterial pressure and heart rate as well as in numerous other physiologic parameters including electrocortical activity. Serotonin (5-HT), which has been implicated in cardiovascular and electrocortical control, is present in nerve terminals within the NTS. Therefore, this study was designed to determine whether 5-HT may effect that control within the NTS. Serotonin injected into the NTS of anesthetized rats produced marked changes in the EEG, arterial pressure, and heart rate. EEG activity changed from irregular 1-5 Hz, 350-500 microV waves with an overlying 13-15 Hz, low voltage rhythm to a regular, 5 Hz, 250-300 microV rhythm. The dose-dependent cardiovascular changes were maximal at a dose of 400 pmol which produced a fall of mean arterial pressure of 48 +/- 2 mm Hg from a baseline of 96 +/- 4 mm Hg and of heart rate of 90 +/- 9 bpm from a baseline of 400 +/- 18 bpm (n = 6; P less than 0.001). Both the cardiovascular and EEG effects of 5-HT injected into the NTS were blocked by the prior injection of the 5-HT antagonist metergoline at the same site. However, the bilateral microinjection of metergoline into the NTS did not affect the baroreceptor reflex. Thus, although serotonergic mechanisms in the NTS may be involved in the modulation of electrocortical and cardiovascular activity, they are not integral to the baroreceptor reflex arc.     

Anteroventral third ventricle lesions impair cardiovascular responses to intravenous hypertonic saline infusion

The anteroventral third ventricle (AV3V) region is a critical area of the forebrain, acting on fluid and electrolyte balance and maintaining cardiovascular homeostasis. The purpose of this study was to determine the effects of lesions to the anteroventral third ventricle region on cardiovascular responses to intravenous hypertonic saline (HS) infusion. Male Wistar rats were anesthetized with urethane. The femoral artery and jugular vein were cannulated to record mean arterial pressure (MAP) and infuse hypertonic saline (3M NaCl, 0.18 mL/100 g bw, over 1 min), respectively. Renal blood flow (RBF) was recorded by ultrasonic transit-time flow probes. Renal vascular conductance (RVC) was calculated as renal blood flow to mean arterial pressure ratio and expressed as percentage of baseline. After hypertonic saline infusion in sham animals, renal blood flow and renal vascular conductance increased to 137+10% and 125+7% (10 min), and 141+/-10% and 133+/-10% (60 min), respectively. Increases in mean arterial pressure (20-min peak: 12+/-3 mm Hg) were also observed. An acute lesion in the AV3V region (DC, 2 mA 25s) 30 min before infusion abrogated the effects of hypertonic saline. Mean arterial pressure was unchanged and renal blood flow and renal vascular conductance were 107+/-7% and 103+/-6% (10 min), and 107+/-4 and 106+/-4% (60 min), respectively. Marked tachycardia was observed immediately after lesion. Responses of chronic sham or lesioned rats were similar to those of acute animals. However, in chronic lesioned rats, hypertonic saline induced sustained hypertension. These results demonstrate that integrity of the AV3V region is essential for the renal vasodilation that follows acute changes in extracellular fluid compartment composition.     

Cardiovascular responses to microinjection of L-glutamate into the NTS in AV3V-lesioned rats

The excitatory amino acid L-glutamate injected into the nucleus of the solitary tract (NTS) in unanesthetized rats similar to peripheral chemoreceptor activation increases mean arterial pressure (MAP) and reduces heart rate. In this study, we investigated the effects of acute (1 day) and chronic (15 days) electrolytic lesions of the preoptic-periventricular tissue surrounding the anteroventral third ventricle (AV3V region) on the pressor and bradycardic responses induced by injections of L-glutamate into the NTS or peripheral chemoreceptor activation in unanesthetized rats. Male Holtzman rats with sham or electrolytic AV3V lesions and a stainless steel cannula implanted into the NTS were used. Differently from the pressor responses (28+/-3 mm Hg) produced by injections into the NTS of sham-lesioned rats, L-glutamate (5 nmol/100 nl) injected into the NTS reduced MAP (-26+/-8 mm Hg) or produced no effect (2+/-7 mm Hg) in acute and chronic AV3V-lesioned rats, respectively. The bradycardia to l-glutamate into the NTS and the cardiovascular responses to chemoreflex activation with intravenous potassium cyanide or to baroreflex activation with intravenous phenylephrine or sodium nitroprusside were not modified by AV3V lesions. The results show that the integrity of the AV3V region is essential for the pressor responses to L-glutamate into the NTS but not for the pressor responses to chemoreflex activation, suggesting dissociation between the central mechanisms involved in these responses.     

Effect of phenylephrine injected into the nucleus tractus solitarius of Sprague-Dawley rats and spontaneously hypertensive rats

In alpha-chloralose-anesthetized Sprague-Dawley (SD) rats with unilateral nucleus tractus solitarius (NTS) lesions, injection of the alpha(1)-adrenergic receptor agonist phenylephrine into the contralateral NTS dose-dependently increased arterial pressure (AP). Bunazosin (0.1 nmol) or prazosin (0.36 nmol), an alpha(1)-adrenergic receptor antagonist, also increased AP. When injected into the NTS, pre-treatment with phenylephrine (10 nmol) or both antagonists abolished the cardiovascular effects of glutamate and acetylcholine. In contrast, pre-treatment with prazosin or methylatropine did not alter the effect of phenylephrine. Phenylephrine (30 nmol) injected into the NTS abolished aortic depressor nerve (ADN) evoked-responses. The pressor effect of phenylephrine in the NTS was exaggerated in spontaneously hypertensive rats (SHR). These results suggest that when injected into the NTS, the effect of phenylephrine may be due to a baroreflex blockade resulting from direct modulatory actions or non-specific neuronal alterations rather than stimulating the alpha(1)-adrenergic receptor. Additionally, this effect is enhanced in SHR.     

Uptake blockade of endocannabinoids in the NTS modulates baroreflex-evoked sympathoinhibition

Previous studies supporting a possible physiological role for an endogenous cannabinoid, arachidonylethanolamide (AEA, anandamide), showed a significant increase in AEA content in the nucleus tractus solitarius (NTS) after an increase in blood pressure (BP) and prolonged baroreflex inhibition of renal sympathetic nerve activity (RSNA) after exogenous AEA microinjections into the NTS. These results, along with other studies, support the hypothesis that endogenous AEA can modulate the baroreflex through cannabinoid CB(1) receptor activation within the NTS. This study was performed to characterize the physiological role of endogenously released cannabinoids (endocannabinoids) in regulating baroreflex control of RSNA through actions in the NTS. Endocannabinoid effects were assessed by measuring the RSNA baroreflex response to increased pressure after bilateral microinjections of AM404, an endocannabinoid transport inhibitor, into the NTS of adult male Sprague Dawley rats. AM404 blocks uptake of endocannabinoids and enhances the effects of any endocannabinoids released [M. Beltramo, et al., Functional role of high-affinity anandamide transport, as revealed by selective inhibition, Science 277 (5329) (1997) 1094-1097.] into the NTS. Therefore, it was hypothesized that microinjections of AM404 should exhibit effects similar to microinjections of exogenous AEA. In this study, AM404 microinjections into the NTS were found to significantly prolong baroreflex inhibition of RSNA compared to control, similar to effects of exogenous AEA. This effect is thought to result from an increased endocannabinoid presence in the NTS, leading to prolonged CB(1) receptor activation. These results indicate that endocannabinoids released in the NTS have the potential to modulate baroreflex control at this site in the central baroreflex pathway.     

Increasing pressure of external counterpulsation augments blood pressure but not cerebral blood flow velocity in ischemic stroke

External counterpulsation (ECP) is a noninvasive method used to augment cerebral perfusion but the optimal use of ECP in ischemic stroke has not been well documented. We aimed to investigate the effects of ECP treatment pressure on cerebral blood flow and blood pressure (BP). We recruited 38 ischemic stroke patients with large artery occlusive disease and 20 elderly controls. We commenced ECP treatment pressure at 150 mmHg and gradually increased to 187.5, 225 and 262.5 mmHg. Mean cerebral blood flow velocities (CBFV) of bilateral middle cerebral arteries and continuous beat-to-beat BP were recorded before ECP and during each pressure increment for 3 minutes. Patient CBFV data was analyzed based on whether it was ipsilateral or contralateral to the infarct. Mean BP significantly increased from baseline in both stroke and control groups after ECP commenced. BP increased in both groups following raised ECP pressure and reached maximum at 262.5 mmHg (patients 16.9% increase versus controls 16.52%). The ipsilateral CBFV of patients increased 5.15%, 4.35%, 4.55% and 3.52% from baseline under the four pressures, respectively. All were significantly higher than baseline but did not differ among different ECP pressures; contralateral CBFV changed likewise. Control CBFV did not increase under variable pressures of ECP. ECP did increase CBFV of our patients to a roughly equal degree regardless of ECP pressure. Among the four ECP pressures tested, we recommend 150 mmHg as the optimal treatment pressure for ischemic stroke due to higher risks of hypertension-related complications with higher pressures.     

Autonomic regulation of organ vascular resistances during hypoxemia in the cat

This study aimed to dissect the roles played by the autonomic interoreceptors, the carotid bodies (cbs) and the aortic bodies (abs) on the vascular resistances of several organs in anesthetized, paralyzed, artificially ventilated cats challenged by systemic hypoxemia. Two 15 min challenges stimulated each of 5 animals in two different groups: (1) in the intact group hypoxic hypoxia (10% O₂ in N₂; HH) stimulated both abs and cbs, increasing neural output to the nucleus tractus solitarius (NTS); (2) in this group carbon monoxide hypoxia (30% O₂ in N₂ with the addition of CO; COH) stimulated only the abs, increasing neural output to the NTS. (3) In the second group in which their bilateral aortic depressor nerves had been transected only the cbs increased neural output to the NTS during the HH challenge; (4) in this aortic body resected group during COH neither abs nor cbs increased neural traffic to the NTS. CO and 10% O₂ reduced Hb saturation to the same level. With the use of radiolabeled microspheres blood flow was measured in a variety of organs. Organ vascular resistance was calculated by dividing the aortic pressure by that organ's blood flow. The spleen and pancreas revealed a vasoconstriction in the face of systemic hypoxemia, thought to be sympathetic nervous system (SNS)-mediated. The adrenals and the eyes vasodilated only when cbs were stimulated. Vasodilation in the heart and diaphragm showed no effect of chemoreceptor stimulated increase in SNS output. Different chemoreceptor involvement had different effects on the organs.     

Status epilepticus: Divergence of sympathetic activity and cardiovascular response

To study changes in plasma catecholamine concentrations and their relationship to changes in systemic and pulmonary vascular pressures, we induced status epilepticus by intravenous administration of bicuculline in 5 anesthetized, paralyzed, ventilated adult sheep. Status epilepticus was accompanied by marked elevations in plasma epinephrine and norepinephrine levels (390-fold and 163-fold, respectively) and by marked elevations in systemic and pulmonary vascular pressures. Vascular pressure returned to normal in 60 minutes, despite plasma catecholamine levels that remained elevated for the 3-hour duration of the study. Mild metabolic acidosis and hyperkalemia were also noted. We discuss the implications of these findings with regard to the management of hypotension during status epilepticus.     

Activation by hypotension of neurons in the hypothalamic paraventricular nucleus that project to the brainstem

To investigate the involvement of neuronal nitric oxide (NO) in the response of the brain to changes in blood pressure, we studied the activation of putative NO-producing neurons in the paraventricular nucleus of the hypothalamus (PVN) in rats whose mean arterial pressures (MAPs) were decreased by 40–50% with hemorrhage (HEM) or infusion of sodium nitroprusside (NP). Activation was assessed on the basis of expression of the immediate early gene, c-fos; putative NO-producing neurons were identified with the histochemical stain for nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d); and the proportions of neurons projecting to the nucleus of the tractus solitarius (NTS) and/or caudal ventrolateral medulla (CVLM) were determined with retrograde tracing techniques. No differences were found for results obtained from HEM and NP animals. Three to four percent of activated PVN neurons projected to the NTS or CVLM. Conversely, approximately 33% and 16% of neurons projecting to the NTS and CVLM, respectively, were activated. About 43% of NADPH-d neurons in the PVN were activated. Of PVN neurons projecting to the NTS or CVLM, 38% and 32%, respectively, were NADPH-d positive. About 11% of NADPH-d PVN neurons projected to the NTS or CVLM. An average of 3 NADPH-d neurons per section were activated and projected to either target. Finally, 7 PVN cells per section sent collateral branches to the NTS and CVLM; 2 or 3 of these cells per section were also activated by decreases in arterial pressure. No NADPH-d cells were found that sent collateral branches to the NTS and CVLM. This study shows that decreases in MAP activate PVN neurons that project, singly and through collaterals, to the NTS and CVLM. A relatively high proportion of the singly projecting neurons is NADPH-d positive. These results support the contention that descending projections from the PVN to the brainstem play an important role in the physiological response to decreases in arterial pressure and suggest that NO may participate in this response. J. Comp. Neurol. 385:285–296, 1997. © 1997 Wiley-Liss, Inc.     

Blood pressure fluctuations in the dysautonomia of Guillain-Barré syndrome

A 76-year-old man with severe Guillain-Barré syndrome had extremes of hypotension alternating with hypertension. His blood pressure paralleled both systemic vascular resistance and cardiac output. Heart rate, rather than stroke volume, was the major determinant of cardiac output over a wide range of blood pressures. It was at times invariant for several hours and was unresponsive to carotid massage or respiratory cycles, but slowed slightly with each episode of hypotension. Trend monitoring indicated that hypotension preceded reductions in pulmonary artery diastolic pressure. These findings suggest that hypotension resulted from a vasodepressor response with a vagotomized heart and that hypertension was the result of increased sympathetic activity. Both extremes were caused by parallel changes in vascular resistance and heart rate. Dysfunction of baroreflex buffering may have accounted for the rapid swings in pressure.