Neuroprotection of dopamine neurons by xenon against low-level excitotoxic insults is not reproduced by other noble gases

Using midbrain cultures, we previously demonstrated that the noble gas xenon is robustly protective for dopamine (DA) neurons exposed to L-trans-pyrrolidine-2,4-dicarboxylate (PDC), an inhibitor of glutamate uptake used to generate sustained, low-level excitotoxic insults. DA cell rescue was observed in conditions where the control atmosphere for cell culture was substituted with a gas mix, comprising the same amount of oxygen (20%) and carbon dioxide (5%) but 75% of xenon instead of nitrogen. In the present study, we first aimed to determine whether DA cell rescue against PDC remains detectable when concentrations of xenon are progressively reduced in the cell culture atmosphere. Besides, we also sought to compare the effect of xenon to that of other noble gases, including helium, neon and krypton. Our results show that the protective effect of xenon for DA neurons was concentration-dependent with an IC50 estimated at about 44%. We also established that none of the other noble gases tested in this study protected DA neurons from PDC-mediated insults. Xenon's effectiveness was most probably due to its unique capacity to block NMDA glutamate receptors. Besides, mathematical modeling of gas diffusion in the culture medium revealed that the concentration reached by xenon at the cell layer level is the highest of all noble gases when neurodegeneration is underway. Altogether, our data suggest that xenon may be of potential therapeutic value in Parkinson disease, a chronic neurodegenerative condition where DA neurons appear vulnerable to slow excitotoxicity.

Characterization and Imaging of Lipid-Shelled Microbubbles for Ultrasound-Triggered Release of Xenon

Xenon (Xe) is a bioactive gas capable of reducing and stabilizing neurologic injury in stroke. The goal of this work was to develop lipid-shelled microbubbles for xenon loading and ultrasound-triggered release. Microbubbles loaded with either xenon (Xe-MB) or xenon and octafluoropropane (Xe-OFP-MB) (9:1 v/v) were synthesized by high-shear mixing. The size distribution and the frequency-dependent attenuation coefficient of Xe-MB and Xe-OFP-MB were measured using a Coulter counter and a broadband acoustic attenuation spectroscopy system, respectively. The Xe dose was evaluated using gas chromatography/mass spectrometry. The total Xe doses in Xe-MB and Xe-OFP-MB were 113.1 ± 13.5 and 145.6 ± 25.5 μl per mg of lipid, respectively. Co-encapsulation of OFP increased the total xenon dose, attenuation coefficient, microbubble stability (in an undersaturated solution), and shelf life of the agent. Triggered release of gas payload was demonstrated with 6-MHz duplex Doppler and 220-kHz pulsed ultrasound. These results constitute the first step toward the use of lipid-shelled microbubbles for applications such as neuroprotection in stroke.

Protection of xenon against postoperative oxygen impairment in adults undergoing Stanford Type-A acute aortic dissection surgery: Study protocol for a prospective, randomized controlled clinical trial

OBJECTIVES

The available evidence shows that hypoxemia after Stanford Type-A acute aortic dissection (AAD) surgery is a frequent cause of several adverse consequences. The pathogenesis of postoperative hypoxemia after AAD surgery is complex, and ischemia/reperfusion and inflammation are likely to be underlying risk factors. Xenon, recognized as an ideal anesthetic and anti-inflammatory treatment, might be a possible treatment for these adverse effects.

METHODS/DESIGN

The trial is a prospective, double-blind, 4-group, parallel, randomized controlled, a signal-center clinical trial. We will recruit 160 adult patients undergoing Stanford type-A AAD surgery. Patients will be allocated a study number and will be randomized on a 1:1:1:1 basis to receive 1 of the 3 treatment options (pulmonary inflated with 50% xenon, 75% xenon, or 100% xenon) or no treatment (control group, pulmonary inflated with 50% nitrogen). The aims of this study are to clarify the lung protection capability of xenon and its possible mechanisms in patients undergoing the Stanford type-A AAD surgery.

DISCUSSION

This trial uses an innovative design to account for the xenon effects of postoperative oxygen impairment, and it also delineates the mechanism for any benefit from xenon. The investigational xenon group is considered a treatment intervention, as it includes 3 groups of pulmonary static inflation with 50%, 75%, and 100% xenon. It is suggested that future trials might define an appropriate concentration of xenon for the best practice intervention.

Assessment of regional emphysema, air-trapping and Xenon-ventilation using dual-energy computed tomography in chronic obstructive pulmonary disease patients

OBJECTIVES

To compare the parenchymal attenuation change between inspiration/expiration CTs with dynamic ventilation change between xenon wash-in (WI) inspiration and wash-out (WO) expiration CTs.

METHODS

52 prospectively enrolled COPD patients underwent xenon ventilation dual-energy CT during WI and WO periods and pulmonary function tests (PFTs). The parenchymal attenuation parameters (emphysema index (EI), gas-trapping index (GTI) and air-trapping index (ATI)) and xenon ventilation parameters (xenon in WI (Xe-WI), xenon in WO (Xe-WO) and xenon dynamic (Xe-Dyna)) of whole lung and three divided areas (emphysema, hyperinflation and normal) were calculated on virtual non-contrast images and ventilation images. Pearson correlation, linear regression analysis and one-way ANOVA were performed.

RESULTS

EI, GTI and ATI showed a significant correlation with Xe-WI, Xe-WO and Xe-Dyna (EI R = -.744, -.562, -.737; GTI R = -.621, -.442, -.629; ATI R = -.600, -.421, -.610, respectively, p < 0.01). All CT parameters showed significant correlation with PFTs except forced vital capacity (FVC). There was a significant difference in GTI, ATI and Xe-Dyna in each lung area (p < 0.01).

CONCLUSIONS

The parenchymal attenuation change between inspiration/expiration CTs and xenon dynamic change between xenon WI- and WO-CTs correlate significantly. There are alterations in the dynamics of xenon ventilation between areas of emphysema.

KEY POINTS

• The xenon ventilation change correlates with the parenchymal attenuation change. • The xenon ventilation change shows the difference between three lung areas. • The combination of attenuation and xenon can predict more accurate PFTs.

Effect of Inhaled Xenon on Cerebral White Matter Damage in Comatose Survivors of Out-of-Hospital Cardiac Arrest: A Randomized Clinical Trial

IMPORTANCE

Evidence from preclinical models indicates that xenon gas can prevent the development of cerebral damage after acute global hypoxic-ischemic brain injury but, thus far, these putative neuroprotective properties have not been reported in human studies.

OBJECTIVE

To determine the effect of inhaled xenon on ischemic white matter damage assessed with magnetic resonance imaging (MRI).

DESIGN, SETTING, AND PARTICIPANTS

A randomized single-blind phase 2 clinical drug trial conducted between August 2009 and March 2015 at 2 multipurpose intensive care units in Finland. One hundred ten comatose patients (aged 24-76 years) who had experienced out-of-hospital cardiac arrest were randomized.

INTERVENTIONS

Patients were randomly assigned to receive either inhaled xenon combined with hypothermia (33°C) for 24 hours (n = 55 in the xenon group) or hypothermia treatment alone (n = 55 in the control group).

MAIN OUTCOMES AND MEASURES

The primary end point was cerebral white matter damage as evaluated by fractional anisotropy from diffusion tensor MRI scheduled to be performed between 36 and 52 hours after cardiac arrest. Secondary end points included neurological outcome assessed using the modified Rankin Scale (score 0 [no symptoms] through 6 [death]) and mortality at 6 months.

RESULTS

Among the 110 randomized patients (mean age, 61.5 years; 80 men [72.7%]), all completed the study. There were MRI data from 97 patients (88.2%) a median of 53 hours (interquartile range [IQR], 47-64 hours) after cardiac arrest. The mean global fractional anisotropy values were 0.433 (SD, 0.028) in the xenon group and 0.419 (SD, 0.033) in the control group. The age-, sex-, and site-adjusted mean global fractional anisotropy value was 3.8% higher (95% CI, 1.1%-6.4%) in the xenon group (adjusted mean difference, 0.016 [95% CI, 0.005-0.027], P = .006). At 6 months, 75 patients (68.2%) were alive. Secondary end points at 6 months did not reveal statistically significant differences between the groups. In ordinal analysis of the modified Rankin Scale, the median (IQR) value was 1 (1-6) in the xenon group and 1 (0-6) in the control group (median difference, 0 [95% CI, 0-0]; P = .68). The 6-month mortality rate was 27.3% (15/55) in the xenon group and 34.5% (19/55) in the control group (adjusted hazard ratio, 0.49 [95% CI, 0.23-1.01]; P = .053).

CONCLUSIONS AND RELEVANCE

Among comatose survivors of out-of-hospital cardiac arrest, inhaled xenon combined with hypothermia compared with hypothermia alone resulted in less white matter damage as measured by fractional anisotropy of diffusion tensor MRI. However, there was no statistically significant difference in neurological outcomes or mortality at 6 months. These preliminary findings require further evaluation in an adequately powered clinical trial designed to assess clinical outcomes associated with inhaled xenon among survivors of out-of-hospital cardiac arrest.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00879892.

[Intracranial and cerebral perfusion pressure in neurosurgical patients during anaesthesia with xenon]

Despite difficulties in providing xenon anaesthesia, xenon still seems to be attractive for neurosurgical procedures. But data upon its effect on intracranial (ICP) and cerebral perfusion pressure (CPP) remains controversial. We monitored ICP and CPP in patients with or without intracranial hypertension during xenon inhalation in different concentrations. Our results suggest that caution should be used while inhaling xenon in high anaesthetic concentration in patients wiith known intracranial hypertension. We also address new possibilities of xenon use, e.g., for sedation in neurosurgery. The study was supported by Russian Fund for Fundamental Research, grant number 13-04-01640.

[Practicing subnarcotic xenon dose inhalation in spa treatment of posttraumatic stress-induced disorders]

Purpose of the investigation was to compare and contrast effectiveness of xenon therapy of stress-induced neurotic disorders and traditional spa-based therapy. Patients of the experimental and control groups were people of risky professions who received drug therapy, psychotherapy and physiotherapy. The experimental group was additionally treated by inhalation therapeutic doses of medical xenon. Comparative analysis of qualitative and quantitative parameters of electroencephalogram (EEG), blood oxygen level, heart rate and blood pressure were compared in the groups before and after treatment. Recovery of the central nervous system functions, activation of parasympathetic involvement, abatement of main psychopathological and somatovegetative disorders in the experimental group were considered as signs of psychic improvement and return to the gestalt behavior.

[Anesthesia and sedation by admixture of xenon-oxygen in dentistry. Part I]

The modern out-patient dental treatment which is performed under combined anesthesia with of xenon-oxygen inhalations provides comfortable conditions for the doctor and the patient, effective anesthesia and safe level of the sedation controlled by dentist.

[Characteristics of perioperative period in Xenon-based combined general anaesthesia in neurosurgery]

Neuroprotection could be the aim to use Xenon for general anesthesia. However the experience of Xenon anesthesia in neurosurgery is quite limited. The appraisal of Xenon based anesthesia was accomplished in 12 patients during various brain surgery. Xe in concentration 65% was used to maintenance of anesthesia, other medication was avoided. As a resuIt there were 8 cases of arterial hypertension and 2 cases of superficial hypnotic state. Excitation (n = 3), hyperdynamic reaction (n = 8), PONV (n = 8) were detected in early postoperative period. An analysis of this study suggests a conclusion that studied method of Xenon-based anesthesia is inexpedient for neurosurgery.

[Effects of xenon anesthesia on cerebral blood flow in neurosurgical patients without intracranial hypertension]

Among anesthetic agents used in neurosurgery xenon appears to be the most advantageous. It preserves arterial blood pressure, assures rapid recovery and neuroprotection. But the data is lacking on xenon effect upon cerebral blood flow under anesthetic conditions. We measured flow velocity in middle cerebral artery in neurosurgical patients without intracranial hypertension during closed circuit xenon anesthesia comparing propofol and xenon effect in the same patients. In our study xenon didn't seem to induce clinically relevant changes in cerebral blood flow and preserved cerebral vascular reactivity thus proving its safety in patients without intracranial hypertension.

[Xenon and sevoflurane anti stress activity comparative assessment during elective anaesthesia in pediatric patients]

Research objective was to compare Xenon and Sevoflurane anti stress activities during elective anaesthesia in Pediatric patients.

MATERIAL AND METHODS

The results of anaesthesia in 42 patients in age from 1 to 18 years were analyzed. The clinical sings, BIS-index, Somatotropinum hormone and Cortisol levels in patient's blood were studied.

RESULTS

Xenon and Sevoflurane provide sufficient level of sedation, analgesia and do not cause Somatotropinum hormone and Cortisol levels increase.

CONCLUSION

Xenon and Sevoflurane have the same high anti stress activity However Xenon anaesthesia is characterized by more stable haemodynamics.

[A case of early detection of a giant postoperative posterior fossa hematoma after tumor excision under xenon anaesthesia]

We report a case of a life-threatening postoperative posterior fossa hematoma whose early detection and successful removal become possible owing to rapid awakening after xenon anesthesia and thorough postoperative follow-up in the recovery room. Postoperative management of neurosurgical patients and perspectives of xenon anesthesia in neurosurgery are discussed.

In vivo MR imaging of pulmonary perfusion and gas exchange in rats via continuous extracorporeal infusion of hyperpolarized 129Xe

BACKGROUND

Hyperpolarized (HP) (129)Xe magnetic resonance imaging (MRI) permits high resolution, regional visualization of pulmonary ventilation. Additionally, its reasonably high solubility (>10%) and large chemical shift range (>200 ppm) in tissues allow HP (129)Xe to serve as a regional probe of pulmonary perfusion and gas transport, when introduced directly into the vasculature. In earlier work, vascular delivery was accomplished in rats by first dissolving HP (129)Xe in a biologically compatible carrier solution, injecting the solution into the vasculature, and then detecting HP (129)Xe as it emerged into the alveolar airspaces. Although easily implemented, this approach was constrained by the tolerable injection volume and the duration of the HP (129)Xe signal.

METHODS AND PRINCIPAL FINDINGS

Here, we overcome the volume and temporal constraints imposed by injection, by using hydrophobic, microporous, gas-exchange membranes to directly and continuously infuse (129)Xe into the arterial blood of live rats with an extracorporeal (EC) circuit. The resulting gas-phase (129)Xe signal is sufficient to generate diffusive gas exchange- and pulmonary perfusion-dependent, 3D MR images with a nominal resolution of 2×2×2 mm(3). We also show that the (129)Xe signal dynamics during EC infusion are well described by an analytical model that incorporates both mass transport into the blood and longitudinal relaxation.

CONCLUSIONS

Extracorporeal infusion of HP (129)Xe enables rapid, 3D MR imaging of rat lungs and, when combined with ventilation imaging, will permit spatially resolved studies of the ventilation-perfusion ratio in small animals. Moreover, EC infusion should allow (129)Xe to be delivered elsewhere in the body and make possible functional and molecular imaging approaches that are currently not feasible using inhaled HP (129)Xe.

Xenon pretreatment may prevent early memory decline after isoflurane anesthesia and surgery in mice

Postoperative cognitive decline (POCD) is a common complication following surgery, but its aetiology remains unclear. We hypothesized that xenon pretreatment prevents POCD by suppressing the systemic inflammatory response or through an associated protective signaling pathway involving heat shock protein 72 (Hsp72) and PI3-kinase. Twenty-four hours after establishing long-term memory using fear conditioning training, C57BL/6 adult male mice (n = 12/group) received one of the following treatments: 1) no treatment group (control); 2) 1.8% isoflurane anesthesia; 3) 70% xenon anesthesia; 4) 1.8% isoflurane anesthesia with surgery of the right hind leg tibia that was pinned and fractured; or 5) pretreatment with 70% xenon for 20 minutes followed immediately by 1.8% isoflurane anesthesia with the surgery described above. Assessments of hippocampal-dependent memory were performed on days 1 and 7 after treatment. Hsp72 and PI3-kinase in hippocampus, and plasma IL-1β, were measured using western blotting and ELISA respectively, from different cohorts on day 1 after surgery. Isoflurane induced memory deficit after surgery was attenuated by xenon pretreatment. Xenon pretreatment prevented the memory deficit typically seen on day 1 (P = 0.04) but not on day 7 (P = 0.69) after surgery under isoflurane anesthesia, when compared with animals that underwent surgery without pretreatment. Xenon pretreatment modulated the expression of Hsp72 (P = 0.054) but had no significant effect on PI3-kinase (P = 0.54), when compared to control. Xenon pretreatment also reduced the plasma level increase of IL-1β induced by surgery (P = 0.028). Our data indicated that surgery and/or Isoflurane induced memory deficit was attenuated by xenon pretreatment. This was associated with a reduction in the plasma level of IL-1β and an upregulation of Hsp72 in the hippocampus.

Distribution of hyperpolarized xenon in the brain following sensory stimulation: preliminary MRI findings

In hyperpolarized xenon magnetic resonance imaging (HP (129)Xe MRI), the inhaled spin-1/2 isotope of xenon gas is used to generate the MR signal. Because hyperpolarized xenon is an MR signal source with properties very different from those generated from water-protons, HP (129)Xe MRI may yield structural and functional information not detectable by conventional proton-based MRI methods. Here we demonstrate the differential distribution of HP (129)Xe in the cerebral cortex of the rat following a pain stimulus evoked in the animal's forepaw. Areas of higher HP (129)Xe signal corresponded to those areas previously demonstrated by conventional functional MRI (fMRI) methods as being activated by a forepaw pain stimulus. The percent increase in HP (129)Xe signal over baseline was 13-28%, and was detectable with a single set of pre and post stimulus images. Recent innovations in the production of highly polarized (129)Xe should make feasible the emergence of HP (129)Xe MRI as a viable adjunct method to conventional MRI for the study of brain function and disease.

[Correction of the functional state of deck aviation pilots by the course of inhalation of therapeutic doses of xenon during long march]

The article deals with efficiency of the course of O2-Xe inhalation for correction of the functional state of deck aviation pilots in a long march. The course was shown to stabilize vagosympathetic balance in organism, to compensate functioning and to retain reserve of the cardiovascular system that resulted in significant psychoemotional animation attested by self-appreciation, amelioration and cheerfulness, and weakening of reactive anxiety. These observations point to applicability of xenon-based gas mixtures to correction of the pilot's functional state in the most intensive periods of service. Guidelines for broad adoption of the method by military medicine have been developed.

[Intracranial pressure changes during xenon anesthesia in neurosurgical patients without intracranial hypertention]

Xenon assures rapid awakening and stable hemodynamics, it also has some neuroprotective effect. This is the reason why it may become an anesthetic of choice in neurosurgery. Still there is little and controversial data on its impact upon ICP. This is the first study of xenon effect upon intracranial pressure, cerebral perfusion pressure and cerebrovascular reactivity during xenon anesthesia in neurosurgical patients without intracranial hypertension. We report a slight increase in intracranial and a slight decrease in cerebral perfusion pressure during xenon anesthesia and show that cerebrovascular reactivity is preserved. Thus we conclude that xenon anesthesia is safe for neurosurgical patients without intracranial hypertension.

[Impact of xenon anesthesia on cerebral oxygenation and metabolism in neurosurgical patients]

In recent years the background for xenon anesthesia implementation in neurosurgery has been created. A variety of researches have been conducted though very few of them concerned xenon effect upon cerebral metabolism. We assessed cerebral oxygenation and cerebral metabolism during propofol anesthesia followed by xenon closed circuit anesthesia in neurosurgical patients. Xenon inhalation was marked by higher jugular vein saturation, oxygen content and glucose level and lower arterio-venous difference. We conclude that compared to propofol xenon improves cerebral oxygenation and decreases cerebral metabolism in neurosurgical patients.

[Xenon for postoperative analgesia: why not?]

Xenon is widely used for maintenance of anesthesia, however the analgesic effect of this noble gas brings to an idea of its use in analgesic schemes. The first time antinociceptive features of Xe were described by B. Lachman and colleagues in 1988. It is well known that Xe realises its analgesic potential through powerful non-competitive blockade of NMDA-glutamate receptors, by that suppressing the development of hyperalgesia process in neurons of posterior horns of spinal cord, which take part in the process of pain transmission and forming of central sensitization and becoming the actual "gates of pain". In the given review the literature data on mechanisms, effectiveness, safety and farmacoeconomic justification of the use of Xe as an analgesic in clinical practice are brought up.

[Successful experience with xenon anesthesia in a patient with dilated cardiomyopathy and intramedullary spinal cord tumor]

The literature contains rare reports on anesthetic maintenance in non-cardiac operations in patients with dilated cardiomyopathy and an ejection fraction of less than 30%. Life-saving non-cardiosurgical interventions are performed in these patients since they are associated with a high risk for perioperative complications and fatal outcome. In these cases, anesthetic maintenance is performed with inotropic support; there is frequently a need to use a pacemaker, a cardioverter, or a LV assist device. The paper describes the first case of xenon anesthesia in a patient with dilated cardiomyopathy with an ejection fraction of less than 30% and rapidly progressing spinal cord tumor. The ability of xenon to maintain stable blood pressure and cardiac contractility could prevent perioperative infusion of inotropic agents. In 60-70% of cases, the maximum alveolar concentration of xenon enables anesthesia to be virtually performed as monoanesthesia without adding the anesthetics lowering cardiac contractility; the low blood-gas distribution coefficient ensures early emergence from anesthesia with early extubation and activation of a patient. In the author's opinion, xenon anesthesia has every reason to become the method of choice as anesthetic maintenance in patients with severe cardiac dysfunction.

Effect of low-xenon and krypton supplementation on signal/noise of regional CT-based ventilation measurements

Xenon computed tomography (Xe-CT) is used to estimate regional ventilation by measuring regional attenuation changes over multiple breaths while rebreathing a constant Xe concentration ([Xe]). Xe-CT has potential human applications, although anesthetic properties limit [Xe] to ≤35%. We investigate effects of lower [Xe], including a low [Xe]-krypton (Kr) combination, on time constant (TC) determination. Six anesthetized sheep were scanned prone and supine using multidetector row CT. Lungs were imaged by respiratory gating during washin of a 30%, 40%, 55% Xe, and a 30% Xe/30% Kr mixture. Using Kr avoids unwanted effects of Xe. Mean TCs, coefficients of variation (CV), and half confidence intervals (CI)/mean served as indexes of sensitivity to noise. Mean supine and prone TCs of three [Xe] values were not significantly different. Average CVs of TCs increased from 57% (55% Xe), 58% (40% Xe), and 73% (30% Xe) ( P < 0.05: paired t-tests; 30% Xe vs. higher [Xe]). Monte Carlo simulation indicated a CV based on inherent image noise was 8% for 55% Xe and 17% for 30% Xe ( P < 0.05). Adding 30% Kr to 30% Xe gave a washin signal equivalent to 40% Xe. Half CI/mean using the 30% Xe/30% Kr mixture was not significantly different from 55 and 40% Xe. Although average TCs were not affected by changes in [Xe], the higher CV and half CI/mean suggested reduced signal-to-noise ratio at the 30% [Xe]. The 30% Xe/30% Kr mixture was comparable to that of 40% Xe, providing an important agent for CT-based assessment of regional ventilation in humans.

[Effects of xenon and krypton-containing breathing mixtures on clinical and biochemical blood indices in animals]

Effects of 24-hr breathing air mixtures containing xenon (XBM) and krypton (KBM) were compared in terms of hormonal status, and blood biochemical indices and morphology in laboratory animals. Some changes observed in blood and hormone indices could be a nonspecific adaptive response. Hence, we should elicit whether these effects are quickly reversible or long. For several indices krypton was a more favorable factor than xenon. However, some of its effects invite to delve into effects of different krypton concentrations on organism.

Multicenter Randomized Comparison of Xenon and Isoflurane on Left Ventricular Function in Patients Undergoing Elective Surgery

Background

Volatile anesthetics are commonly used for general anesthesia. However, these can induce profound cardiovascular alterations. Xenon is a noble gas with potent anesthetic and analgesic properties. However, it is uncertain whether xenon alters myocardial function. The aim of this study was therefore to investigate left ventricular function during anesthesia with xenon compared with isoflurane.

Methods

The authors performed a randomized multicenter trial to compare xenon with isoflurane with respect to cardiovascular stability and adverse effects in patients without cardiac diseases scheduled for elective surgery. Two hundred fifty-nine patients were enrolled in this trial, of which 252 completed the study according to the protocol. Patients were anesthetized with xenon or isoflurane, respectively. Before administration of the study drugs and at four time points, the effects of both anesthetics on left ventricular function were investigated using transesophageal echocardiography.

Results

Global hemodynamic parameters were significantly altered using isoflurane (P &lt; 0.05 vs. baseline), whereas xenon only decreased heart rate (P &lt; 0.05 vs. baseline). In contrast to xenon, left ventricular end-systolic wall stress decreased significantly in the isoflurane group (P &lt; 0.05 vs. baseline). Velocity of circumferential fiber shortening was decreased significantly in the xenon group but showed a more pronounced reduction during isoflurane administration (P &lt; 0.05 vs. baseline). The contractile index (difference between expected and actually measured velocity of circumferential fiber shortening) as an independent parameter for left ventricular function was significantly decreased after isoflurane (P &lt; 0.0001) but unchanged using xenon.

Conclusions

Xenon did not reduce contractility, whereas isoflurane decreased the contractile index, indicating that xenon enables favorable cardiovascular stability in patients without cardiac diseases.

[Brain and spinal cord preconditioning for the protection against ischemic injury]

Recent studies have suggested that the brain preconditioning could induce tolerance to ischemia in humans. It has been believed that newly synthesized proteins are required for the acquisition of delayed tolerance in the brain and spinal cord. However, the mechanism other than the synthesis of neuroprotective proteins may also play a pivotal role. Preconditioning may reprogram the response to ischemic injury as seen during hibernation. Preconditioning with hyperbaric oxygen, volatile anesthetics, and xenon seems to be the focus of the attention from the standpoint of the clinical setting. Strong neuroprotection by the preconditioning with isoflurane and xenon is reported in animal experiments and may change the traditional idea of neuroprotection by anesthetics. The discovery that erythropoietin exerts neuroprotective properties has opened new therapeutic avenues. Erythropoietin is induced in the brain by hypoxic preconditioning and by the pharmacological preconditioning. In addition, the intravenous administration of erythropoietin has been shown to be safe and beneficial for acute stroke in humans. Therefore, erythropoietin is now one of the most promising neuroprotective agents. The research in the brain and spinal cord preconditioning will contribute to the elucidation of the mechanism of ischemic injury and to the establishment of new therapies for neuroprotection.

Asynchronous administration of xenon and hypothermia significantly reduces brain infarction in the neonatal rat

BACKGROUND

Neonatal asphyxia causes long-term neurological and behavioural impairment in the developing brain. Concurrent administration of xenon and hypothermia synergistically reduces long-term damage in a rat model of neonatal asphyxia. This study sought to investigate whether asynchronous administration of xenon and hypothermia is capable of combining synergistically to provide neuroprotection.

METHODS

Seven-day-old rats were subjected to right common carotid artery occlusion followed by 90 min hypoxia with 8% oxygen. After a 1 h recovery period, rats received asynchronous administration of mild hypothermia (35 degrees C) and xenon (20%) with a 1 or 5 h gap between interventions, xenon (20%) alone, or mild hypothermia (35 degrees C) alone. Infarct volume in the brain was measured 4 days after injury.

RESULTS

Administration of hypothermia or xenon alone, 1 and 6 h after the hypoxic ischaemic insult, respectively, provided no neuroprotection. Asynchronous administration of xenon and hypothermia at a 1 h interval produced a significant reduction in infarct volume [93 (7) vs 74 (8); P < 0.05]. Reduction in infarct volume was also present when hypothermia and xenon were asynchronously administered with an intervening gap of 5 h [97 (5) vs 83 (3); P < 0.05].

CONCLUSIONS

This finding provides a rationale for investigating the combined use of hypothermia and xenon in a progressive manner for the management of neonatal asphyxia. Thus, hypothermia can be administrated at the site of delivery and xenon can be administered later.

[Central hemodynamics, gas exchange, and gas oxygen-transporting function in combined anesthesia using xenon during operations under extracorporeal circulation]

The advantages of xenon include its good hemodynamic profile and possible cardioprotective properties. The investigation was undertaken to study central hemodynamics, lung gas exchange, and blood oxygen-transporting function in xenon anesthesia in patients operated on under extracorporeal circulation (EC). Fifteen patients aged 41-69 years operated on for coronary heart disease were examined. The severity of the patients' baseline status corresponded to NYHA functional classes I to IV. The duration of an operation was 251 +/- 10 min; that of EC was 97 +/- 5 min; aortic ligation lasted 59 +/- 3 min. After induction of anesthesia with propofol via concentration-regulated infusion (CRI) and with fentanyl, delivery of xenon was initiated at concentrations of 47 +/- 1 to 52.5 +/- 1%, which was mixed with oxygen. Propofol CRI was used during EC. After the latter, xenon was inhaled at concentrations of 47.7 +/- 1 to 53.3 +/- 1%. The mean arterial pressure (BP(mean)), heart rate (HR), and cardiac index (CI) remained unchanged during xenon anesthesia in the preperfusion period. After EC during xenon anesthesia, CI significantly rose with a moderate increase in HR without inotropic support. BP(mean) was moderately, but statistically significantly decreased. Prior to and following EC, there were no changes in the values of blood oxygen-transporting function.

[Changes in cerebral circulation in patients with coronary heart disease during myocardial revascularizing operations under combined xenon anesthesia]

Twenty-five patients with coronary heart disease were examined in the preperfusion stage of myocardial revascularing operations under extracorporeal circulation. All the patients received combined anesthesia with xenon (Xe) as minimum flow anesthesia with flow of gases: oxygen, 0.4 l/min; Xe, 0.9 to 0.4 l/min. Cerebral circulation was investigated by transcranial Doppler study. The following parameters of the circulation: maximum systolic and diastolic blood flow velocities and pulsatile index were bilaterally estimated, by insonating the middle cerebral artery (MCA). When the concentration of Xe was as high as 50-60%, systolic and diastolic blood flow velocities along the MCA increase and the pulsatile index decreased. Opposite results were obtained 8 minutes after Xe feed was stopped. The findings provide evidence that Xe increases cerebral circulation and has a significant hypnotic effect. The increased systolic and diastolic blood flow velocities with the decreased peripheral resistance index in the MCA suggest that Xe diminishes peripheral vascular resistance in the pial arteries of the brain.

Feasibility and Safety of Delivering Xenon to Patients Undergoing Coronary Artery Bypass Graft Surgery While on Cardiopulmonary Bypass

Background

Postoperative neurocognitive deficit is prevalent after cardiac surgery. Xenon may prevent or ameliorate acute neuronal injury, but it also may aggravate injury during cardiac surgery by increasing bubble embolism. Before embarking on a randomized clinical trial to test the safety and efficacy of xenon for postoperative neurocognitive deficit, we undertook a phase I study to investigate the safety of administering xenon to patients undergoing coronary artery bypass grafting while on cardiopulmonary bypass and to assess the practicability of our xenon delivery system.

Methods

Sixteen patients scheduled for coronary artery bypass grafting surgery with hypothermic cardiopulmonary bypass gave their informed consent to participate in an open-label dose-escalation study (0, 20, 35, 50% xenon in oxygen and air). Xenon was delivered throughout surgery using both a standard anesthetic breathing circuit and the oxygenator. Gaseous and blood xenon partial pressures were measured five times before, during, and after cardiopulmonary bypass. Middle cerebral artery Doppler was used to assess embolic load, and major organ system function was assessed before and after surgery.

Results

Middle cerebral artery Doppler showed no evidence of increased emboli with xenon. Patients receiving xenon had no major organ dysfunction: Troponin I and S100beta levels tended to be lower in patients receiving xenon. Up to 25 l xenon was used per patient. Xenon partial pressure in the blood tracked the delivered concentration throughout.

Conclusions

Xenon was safely and efficiently delivered to coronary artery bypass grafting patients while on cardiopulmonary bypass. Prevention of nervous system injury by xenon should be tested in a large placebo-controlled, randomized clinical trial.

[Effect of anesthesia with xenon and nitrous oxide with fentanyl on dynamics of cellular immunity and cytokines]

Immunological parameters were studied at randomization in 60 surgical patients during the similar operation--cholecystectomy made under combined endotracheal low-flow general anesthesia using N2O:O2+fentanyl in 32 patients and Xe:O2 in 28 patients. The time course of changes in cellular immunity and cytokines was closely related to the type of an anesthetic. Unlike N2O:O2+fentanyl, Xe did not show such a marked proinflammatory activity, exerted a mild normalizing effect on leuko- and lymphopoiesis, had an immunostimulating activity, and reduced the frequency of postoperative inflammatory complications and the length of stay at hospital. The differences in the action of the anesthetics were due to the fact that Xe had a greater narcotic potential, a protective action on neuroendocrine function, and no toxicity. Xe is indicated to patients with baseline immunodeficiency.

Xenon preconditioning reduces brain damage from neonatal asphyxia in rats

Xenon attenuates on-going neuronal injury in both in vitro and in vivo models of hypoxic-ischaemic injury when administered during and after the insult. In the present study, we sought to investigate whether the neuroprotective efficacy of xenon can be observed when administered before an insult, referred to as 'preconditioning'. In a neuronal-glial cell coculture, preexposure to xenon for 2 h caused a concentration-dependent reduction of lactate dehydrogenase release from cells deprived of oxygen and glucose 24 h later; xenon's preconditioning effect was abolished by cycloheximide, a protein synthesis inhibitor. Preconditioning with xenon decreased propidium iodide staining in a hippocampal slice culture model subjected to oxygen and glucose deprivation. In an in vivo model of neonatal asphyxia involving hypoxic-ischaemic injury to 7-day-old rats, preconditioning with xenon reduced infarction size when assessed 7 days after injury. Furthermore, a sustained improvement in neurologic function was also evident 30 days after injury. Phosphorylated cAMP (cyclic adenosine 3',5'-monophosphate)-response element binding protein (pCREB) was increased by xenon exposure. Also, the prosurvival proteins Bcl-2 and brain-derived neurotrophic factor were upregulated by xenon treatment. These studies provide evidence for xenon's preconditioning effect, which might be caused by a pCREB-regulated synthesis of proteins that promote survival against neuronal injury.

New measurement of hepatic blood flow by xenon CT system: an animal study with PGE1

BACKGROUND

A new Xenon computed tomography (CT) system was developed to measure both hepatic arterial and portal venous tissue blood flow (HATBF/PVTBF) non-invasively. Despite its clinical trial, the effect of prostaglandin E1 (PGE1) on hepatic hemodynamics is not well investigated. In a rabbit model, we evaluated the accuracy of this system by comparing it with the electromagnetic blood flowmeter (EMBF), the pharmacological effect of PGE1 on the fractional hepatic hemodynamics.

MATERIALS AND METHODS

Seven NZW-rabbits were used. Serial abdominal CT scan was obtained every min before and during the 4 min inhalation of the Xenon gas, followed by 5 min administration of oxygen air. From these images, HATBF and PVTBF were separately calculated with a special new imaging system. We also used EMBF during laparotomy, and directly measured the hepatic arterial and portal venous flow with or without PGE1 administration.

RESULTS

Xenon CT showed HATBF of 18.4 +/- 4.5 (ml/min/100 g) and PVTBF of 69.4 +/- 15.0, was almost identical with those of EMBF (19.8 +/- 5.7 and 67.2 +/- 19.1, respectively). After PGE1 administration, Xenon CT showed 22.9 +/- 4.6 and 76.5 +/- 20.5, while those with EMBF were 21.0 +/- 6.5 and 84.7 +/- 21.6, respectively. There were significant correlations (P < 0.01) in total HTBF, HATBF, and PVTBF between results of Xenon CT and EMBF.

CONCLUSIONS

Xenon CT with a newly developed imaging system enables us to measure the fractional hepatic tissue blood flow in rabbits, differentially and accurately. Venous administration of PGE1 increased total hepatic blood flow, mainly affecting the portal blood flow.

Quantitative tissue blood flow evaluation of pancreatic tumor: comparison between xenon CT technique and perfusion CT technique based on deconvolution analysis

PURPOSE

There has been one report that tissue blood flow (TBF) quantification with xenon CT was effective in predicting the therapeutic response to an anticancer drug in pancreatic cancer. The purpose of this study was to evaluate the correlation between the TBF of pancreatic tumors calculated with xenon CT and those with perfusion CT, in order to evaluate whether perfusion CT could replace xenon CT.

MATERIALS AND METHODS

Nine patients with pathologically proved pancreatic tumors who underwent both xenon CT and perfusion CT were included.

RESULTS

Quantitative TBF of pancreatic tumors measured by perfusion CT ranged from 22.1 to 196.2 ml/min/100 g (mean+/-SD, 52.6+/-54.8 ml/min/100 g). In contrast, those obtained by xenon CT ranged from 10.3 to 173.6 ml/min/100 g (mean+/-SD, 47.4+/-49.4 ml/min/100 g). There was a good linear correlation between xenon CT and perfusion CT (y=0.8537x+2.48, R2=0.895: p<0.05).

CONCLUSION

The TBF of pancreatic tumors measured by xenon CT and perfusion CT techniques showed a close linear correlation. We can expect that perfusion CT based on the deconvolution algorithm may replace xenon CT to predict the effect of pancreatic tumor treatment with anticancer drugs.

A cost-effective and versatile xenon gas dispenser

OBJECTIVE

To modify a commercial xenon gas dispenser so that two xenon unit-dose vials could be combined with a modified dispenser to deliver a recommended dose.

METHOD

To maintain the same operating mechanism, changes were made only to the vial shield and the needle port of the original gas dispenser. The modified gas dispenser consisted of two puncture needles and two vial holders shielded with the same thickness of lead as the commercial dispenser.

RESULTS

Our evaluation showed that the modified gas dispenser operated the same way as the commercial unit, and the average 133Xe residual activity in either one or two xenon unit-dose vials of the modified gas dispenser was not significantly different from that in one vial of the commercial xenon gas dispenser.

CONCLUSION

The modified xenon gas dispenser allows the stock of xenon gas vials to be managed cost-effectively. The modified unit can be used to dispense two low-activity xenon gas vials to deliver a standard dose to a patient. Also, the modified gas dispenser can be used to combine different amounts of xenon activity in two unit-dose vials in order to customize the dose delivered to patients with special needs (e.g., obese patients). Our modified device can also function as a single-dose dispenser by placing an empty vial alongside the unit-dose vial of radioactive xenon gas.

[To the effective concentration of xenon]

The present literature discusses what effective concentration of xenon may be used to induce adequate anesthesia. To examine the analgesic properties of the substance, 38 patients undergone laparoscopic operations for calculous cholecystitis under informational saturation EEG (INEEG) monitoring were included into this study. All the patients were divided into 3 groups in accordance to the mode of anesthesia maintenance and INEEG monitoring. In Groups 1 and 2, the concentration of xenon was maintained at 70%; INEEG monitoring was made in the of-line mode. In Group 3, the concentration of xenon was gradually decreased from 70% to the minimum value at which the level of INEEG was 40-50%, which corresponds to the adequate depth of anesthesia. The use of 70% xenon concentration and the standard doses offentanyl (3.1 +/- 1.6 microg/kg/h) resulted in excessively deep anesthesia (38 +/- 4% INEEG). Reduction of the dose of fentanyl on an average to 1.5 +/- 0.8 microg/kg/h permitted more adequate anesthesia; however, an excessively deep anesthesia is encountered in 40% of cases, as evidenced by INEEG. The active use of INEEG monitoring in Group 3 makes it possible to perform an adequate anesthesia (46 +/- 4% INEEG) and to determine the xenon concentration necessary for this, which is equivalent to 42 +/- 11% with the dose of fentanyl of 0.9 +/- 0.8 microg/kg/h.

Predicting Stroke Risk in Pediatric Moyamoya Disease with Xenon-enhanced Computed Tomography

OBJECTIVE:

To determine whether estimates of regional cerebral blood flow (rCBF) using xenon computed tomography (XeCT) in children with moyamoya disease can predict stroke risk before and after treatment.

METHOD:

Seven patients with moyamoya disease underwent 22 serial Xe computed tomographic scans. Estimates of rCBF were obtained at three computed tomographic levels by use of a 5-minute inhalation of 28% Xe. Acetazolamide challenge was performed in eight scans. For comparison of abnormal vessel distribution and areas of infarction, 17 intra-arterial digital subtraction angiograms, 47 computed tomographic scans, and 15 magnetic resonance imaging scans were available. Follow-up exceeded 36 months in all patients. Mean follow-up for the interventional group was 65.2 months (n =5; range, 37–109 mo) and 38 months for the nonoperative patients (n =2; 36 and 40 mo).

RESULTS:

Of six Xe computed tomographic scans obtained at diagnosis, four revealed regions of oligemia, augmented vertebrobasilar flow, and regions of carotid steal after acetazolamide. In the delay between diagnosis and treatment, three patients had strokes in ischemic areas identified by XeCT. Of the 10 posttreatment scans obtained from 4 patients, 2 revealed improved tissue perfusion with angiography confirming successful encephaloduroangiomyosynangiosis. In 2 others, XeCT performed 6 months posttreatment revealed improved perfusion without angiographic change, and angiography at 1 year revealed failed encephaloduroangiomyosynangiosis and new native collaterals. None of the patients with improved rCBF had new strokes. Eleven of 14 Xe computed tomographic scans were obtained within 30 days of angiography. Comparison of these studies demonstrates that regions of oligemia were confined to areas associated with vessel stenosis and little neovascularity or collateral pathways.

CONCLUSION:

XeCT, particularly with acetazolamide challenge, objectively quantifies rCBF. Our preliminary data suggest that it may permit assessment of stroke risk in children with moyamoya disease and may predict surgical outcome earlier than angiography.

Minimum anesthetic concentration of sevoflurane with different xenon concentrations in swine

In a previous study, we described a partial antagonism of xenon (Xe) in combination with isoflurane. One hypothetical explanation suggested that Xe and isoflurane probably induced anesthesia via different pathways at the neuronal level. This warranted investigating the combination of Xe with other inhaled anesthetics to examine the relationship between Xe and volatile anesthetics in general. We therefore investigated the influence of Xe on the minimum alveolar concentration (MAC) of sevoflurane. The study was performed in 10 swine (weight 30.8 kg +/- 2.6, mean +/- SD) ventilated with xenon 0%, 15%, 30%, 40%, 50%, and 65% in oxygen. At each Xe concentration, various concentrations of sevoflurane were administered in a stepwise design. For each a supramaximal pain stimulus (claw clamp) was applied. The appearance of a withdrawal reaction was recorded. The sevoflurane MAC was defined as the end-tidal concentration required to produce a 50% response rate. At each Xe concentration, the animals' responses to the pain stimulus were categorized and a logistic regression model was fitted to the results to determine sevoflurane MAC. Sevoflurane MAC was decreased by inhalation of Xe in a linear manner from 2.53 with 0% Xe to 1.54 with 65% Xe. In contrast to Xe and isoflurane, the anesthetic effects of Xe and sevoflurane appear to be simply linear.

IMPLICATIONS

We investigated the influence of the anesthetic gas, xenon, on the minimum alveolar concentration (MAC) for the volatile anesthetic sevoflurane. The study was performed in 10 swine ventilated with fixed xenon and various concentrations of isoflurane. The sevoflurane MAC is decreased by inhalation of xenon in a linear relationship.

The Neuroprotective Effect of Xenon Administration during Transient Middle Cerebral Artery Occlusion in Mice

Background

Xenon has been shown to be neuroprotective in several models of in vitro and in vivo neuronal injury. However, its putative neuroprotective properties have not been evaluated in focal cerebral ischemia. The purpose of this study was to determine if xenon offers neuroprotection in a mouse model of middle cerebral artery occlusion.

Methods

C57BL/6 mice underwent 60 min of middle cerebral artery occlusion. The animals (n = 21 per group) were randomized to receive either 70% xenon + 30% O2, 70% N2O + 30% O2, or 35% xenon + 35% N2O + 30% O2. After 24 h, functional neurologic outcome (on three independent scales: four-point, general, and focal deficit scales) and cerebral infarct size were evaluated.

Results

The 70% xenon + 30% O2 group showed improved functional outcome (median [interquartile range], four-point scale: 2 [2], 70% xenon + 30% O2 versus 3 [2], 70% N2O + 30% O2, P = 0.0061; general deficit scale: 9 [6], 70% xenon + 30% O2 versus 10 [4], 70% N2O + 30% O2, P = 0.0346). Total cerebral infarct volumes were reduced in the 70% xenon + 30% O2 group compared with the 70% N2O + 30% O2 group (45 +/- 17 mm3 versus 59 +/- 11 mm3, respectively; P = 0.0009).

Conclusions

In this model of transient focal cerebral ischemia, xenon administration improved both functional and histologic outcome.

Xenon incorporated in a lipid emulsion inhibits NMDA receptor channels

BACKGROUND

Over the past decade hyperpolarized (129)xenon incorporated in lipid emulsions has been studied for the purpose of imaging enhancement in radiology. Xenon (Xe), a NMDA (N-methyl-D-aspartate)-receptor antagonist, has neuroprotective properties even at subanesthetic concentrations. Thus, its intravenous administration for this purpose deserves further evaluation. In this study, we investigated in an in vitro model the effect of Xe, incorporated in a lipid emulsion (Lipofundin MCT(R) 20%), on the NMDA receptor channel of cortical neurons of the mouse.

METHODS

Pulses of 50 micro M of NMDA solution were extracellularly applied to the cells for 10 s, and the elicited membrane currents (I) were recorded while the membrane potential (V) was clamped at -80 mV. Either Lipofundin MCT(R) 20% or aqueous solution was loaded with Xe and applied simultaneously with the NMDA pulses by means of a multibarreled pipette attached to a battery of infusion-pumps.

RESULTS

Xenon equilibrated in Lipofundin(R) caused a concentration-dependent and reversible inhibition of NMDA-induced currents (maximal Xe content [Xemax]: 190 micro l ml-1). The inhibitory effect was equivalent compared with the effect of Xe dissolved in aqueous solution (Xemax: 89 micro l ml-1) even though the Xe content of the lipid solution was almost doubled. Further enhancement of the Xe content by saturating both the lipid emulsion and the aqueous solutions with Xe (Xemax: 256 micro l ml-1) did not increase the inhibitory action on NMDA-receptors.

CONCLUSION

The data demonstrate that Xe dissolved in Lipofundin MCT(R) 20% inhibits NMDA-receptors. Lipid emulsions enriched with Xe may serve as a carrier and a reservoir for Xe.

[A comparative evaluation of "cerebral oximetry" during anesthesia with xenon and other anesthetics]

The oxygen status dynamics during the general anesthesia is one of the most important issues of anesthetic monitoring. The set target was to study the cerebral oximetry (rSO2) in anesthesia with xenon as compared with other anesthetics. A total of 80 patients (class ASA I-II) were examined in the venectomy surgery. According to an anaesthetic used in induction and anesthesia management, the patients were divided into 3 groups. Group 1--40 patients with xenon mono-anesthesia; group 2--20 patients with propofol + N2O + neurolpangesia; and group 3--20 patients with N2O + ftorotan. At xenon induction, rSO2 went up by 6.4%. At propofol induction, there were no changes in rSO2. A biggest increase in the cerebral blood circulation was noted, at the anesthesia management stage, in the patients' group, who received ftorotan; a lesser increase was registered in xenon anesthesia. An increased rSO2 level was higher, during the wakening stage, in case of ftorotan administration than in the group, which received xenon; the process of recovering the initial parameters was slower in the former group. Xenon and ftorotan were shown to contribute to a higher oxygen status and an increased volume of the cerebral blood circulation. In case of xenon mono-anesthesia, there was a smaller increase in the cerebral blood circulation as compared to N2O + ftoratan anesthesia. Further special investigations are needed to give a final answer to the question on whether it is possible to use xenon in neuroanesthesiology and in intensive care of patients with a neuroresuscitation-type pathology of the brain.

[The method of low-flow xenon anesthesia]

Two variants of low-flow xenon (Xe) anesthesia was used in 150 patients operated on in general surgery, gynecology, urology, and vascular surgery; 116 patients received a combined endotracheal variant of Xe anesthesia and 34 patients received mask-type mono-narcosis. Limited possibilities of Russian-made apparatuses ("Polinarkon-2P") were shown in the process of minimizing the Xe consumption. An average Xe consumption reached, in a 2-hour anesthetic session, 42 l ($210). When foreign-made narcosis apparatuses ("Medimorph", "Anemat-8" etc.) were used, it was possible to minimize the Xe consumption during the same time period to 22 l ($110). When the endotracheal variant was in use, the Xe consumption was 15-16 l ($75-80) during 2 hours. When Xe was recycled by the desorption processor and fine cleaning at "Akela-N" Ltd. production facility, the cost of 2-hour anesthesia went down five-fold ($16-20). The article contains some recommendations made by authors to improve the method of low-flow Xe anesthesia as a method reducing the cost of Xe anesthesia in the routine medical practice.

[Comparison of cerebral blood flow with Xe-inhalation CT and perfusion CT]

Cerebral blood flow (ml/min/100g) (CBF) was detected by two methods, static xenon inhalation dynamic CT (Xe-CT) and perfusion CT, and a comparison of these two methods (Xe-CBF and perfusion CBF) was carried out in the same cases. Xe CT used 30% static xenon, 4 min wash-in, and 5 min wash-out, while perfusion CT was done by injecting 30 ml of non-ionic contrast medium at a rate of 9 ml/sec. Forty-eight patients underwent these examinations (30 serious cases and 18 mild). The correlation coefficients in the hemispheric area were r=0.713 (p<0.01) with Xe-CBF and perfusion CBF in mild cases and r=0.567 (p<0.01) in serious cases. The two CBF values were especially disparate in serious cases. The value for perfusion CBF was almost double that of Xe-CBF in these cases. Perfusion CT was a useful examination for the detection of CBF, but in serious cases, CBF needs to be determined by Xe-CT as well.

[Electrophysiological features of xenon anesthesia]

One of the central problems of zenon anesthesia is evaluation of its adequacy. The bispectral index (BIS) is estimated empirically on the basis of electroencephalograms of patients treated with vapor-forming anesthetics. We investigated clinical and electrophysiological parallels of xenon monoanesthesia by using the EEG bispectral index. The study was carried out in 40 patients (ASA I-II) during venectomy under Xe anesthesia. Electrophysiological parameters were stable during maintenance and corresponded to the depth of anesthesia. Hence, monitoring of BIS and SEF-95 provides for an adequate control of anesthesia, while during induction and awakening the values of these indices are doubtful. The incorrectness of EEG BIS at these stages of Xe anesthesia is due to specific electrophysiological mechanisms of Xe, affecting mainly HMDA and H-cholinergic receptors of the CNS.

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 effects of subanaesthetic concentrations of xenon in volunteers

This study reports the subjective, psychomotor and physiological properties of subanaesthetic concentrations of xenon. Ten healthy male volunteers received either xenon or nitrous oxide in a randomised crossover study design. The subjects breathed either xenon (Xe) or nitrous oxide (N2O) from a closed circuit breathing system, according to a randomised, double-blind protocol. The concentration of xenon required to produce sedation, ranged between 27 and 45% (median 35%). All subjects completed the xenon protocol. Subjects were tested using the Critical Flicker Fusion test and derived electroencephalogram parameters, however, neither test was found to reliably predict sedation. The respiratory rate decreased markedly during sedation with xenon. The subjects did not experience any airway irritability (coughing, breath-holding or laryngospasm) during administration of either gas. One subject required anti-emetic treatment in the N2O group compared to none in the Xe group. Eight subjects reported that they found sedation with xenon pleasant and preferable to nitrous oxide. Xenon sedation was well tolerated and was not associated with any adverse physiological effects, however, it was reported to be subjectively dissimilar to nitrous oxide.

Quantitative functional lung imaging with synchrotron radiation using inhaled xenon as contrast agent

Small airways play a key role in the distribution of ventilation and in the matching of ventilation to perfusion. The purpose of this study was to introduce an imaging method that allows measurement of regional lung ventilation and evaluation of the function of airways with a small diameter. The experiments were performed at the Medical Beamline of the European Synchrotron Radiation Facility. Monochromatic synchrotron radiation beams were used to obtain quantitative respiration-gated images of lungs and airways in two anaesthetized and mechanically ventilated rabbits using inhaled stable xenon (Xe) gas as a contrast agent. Two simultaneous images were acquired at two different energies, above and below the K-edge of Xe. Logarithmic subtraction of the two images yields absolute Xe concentrations. This technique is known as K-edge subtraction (KES) radiography. Two-dimensional planar and CT images were obtained showing spatial distribution of Xe concentrations within the airspaces, as well as the dynamics of filling with Xe. Bronchi down to 1 mm in diameter were visible both in the subtraction radiographs and in tomographic images. Absolute concentrations of Xe gas were calculated within the tube carrying the inhaled gas mixture, small and large bronchi, and lung tissue. Local time constants of ventilation with Xe were obtained by following the evolution of gas concentration in sequential computed tomography images. The results of this first animal study indicate that KES imaging of lungs with Xe gas as a contrast agent has great potential in studies of the distribution of ventilation within the lungs and of airway function, including airways with a small diameter.