Xenon alters right ventricular function

Background: In contrast to other volatile anesthetics, xenon produces less cardiovascular depression with fewer fluctuations of various hemodynamic parameters, but reduces cardiac output (CO) in vivo . Besides an increase in left ventricular afterload and reduction of heart rate, an impairment of the right ventricular function might be an additional pathophysiological mechanism for the reduction of CO. Therefore, we used an animal model to study the effects of xenon as a supplemental anesthetic on right ventricular function, especially right ventricular afterload.
Methods: Right ventricular function was monitored with a volumetric pulmonary artery catheter in 11 pigs during general anesthesia with thiopental. Six animals received additional 70% (volume) xenon (equivalent to 0.55 MAC minimum alveolar concentration). Parameters for systolic function, afterload, and preload were calculated at baseline and during 50 min of xenon application, and in a corresponding control group. Significant differences were detected by multivariate analyses of variance for repeated measures.
Results: Xenon reduced CO on average by 30% and increased pulmonary arterial elastance by 60%, which led to a reduction of the right ventricular ejection fraction by 25%. Whereas right ventricular preload remained stable, maximal slope of pulmonary artery pressure and the right ventricular elastance increased. No effect on the ratio of stroke work and end-diastolic volume was found.
Conclusion: The reduction in CO during xenon anesthesia was partly due to an impairment of the right ventricular function, mainly caused by an increased afterload, without an impairment of systolic ventricular function.     

Measurement of 129Xe gas apparent diffusion coefficient anisotropy in an elastase‐instilled rat model of emphysema

Hyperpolarized noble gas (³He and ¹²⁹Xe) apparent diffusion coefficient (ADC) measurements have shown remarkable sensitivity to microstructural (i.e., alveolar) changes in the lung, particularly emphysema. The ADC of hyperpolarized noble gases depends strongly on the diffusion time (Δ), and ³He ADC has been shown to be anisotropic for Δ ranging from a few milliseconds down to a few hundred microseconds. In this study, the anisotropic nature of ¹²⁹Xe diffusion and its dependence on Δ were investigated both numerically, in a budded cylinder model, and in vivo, in an elastase‐instilled rat model of emphysema. Whole lung longitudinal ADC (D_L) and transverse ADC (D_T) were measured for Δ = 6, 50, and 100 ms at 73.5 mT, and correlated with measurements of the mean linear intercept (L_m) obtained from lung histology. A significant increase (P = 0.0021) in D_T was measured for Δ = 6 ms between the sham (0.0021 ± 0.0005 cm²/s) and elastase‐instilled (0.005 ± 0.001 cm²/s) cohorts, and a strong correlation was measured between D_T (Δ = 6 ms) and L_m, with a Pearson's correlation coefficient of 0.90. This study confirms that ¹²⁹Xe D_T increases correlate with alveolar space enlargement due to elastase instillation in rats. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

129Xe spectra from the heads of rats with and without ligation of the external carotid and pterygopalatine arteries.

After rats inhaled hyperpolarized (129)Xe gas, in vivo spectra from their heads revealed a dominant peak around 195 ppm, another easily resolvable peak near 189 ppm, a broad peak around 210 ppm, and two minor peaks around 198 ppm and 192 ppm. However, the source of each peak remains controversial. To further study the origin of each peak, we compared spectra obtained from the heads of normal rats with spectra taken from the heads of rats that had undergone ligation of the external carotid (ECA) and pterygopalatine (PPA) arteries, the major feeding vessels of nonbrain tissue in the rat head. The amplitude of the peak at around 189 ppm was greatly reduced in the ECA/PPA-ligated rats, while the peak around 195 ppm persisted. We conclude that the signal that originates from the rat brain after inhalation of (129)Xe gas is overwhelmingly dominated by the single resonance at 195 ppm.     

Regional ventilation mapping of the rat lung using hyperpolarized (129) Xe magnetic resonance imaging

Lung ventilation was mapped in seven healthy male Sprague‐Dawley rats (433 ± 24 g) using hyperpolarized ¹²⁹Xe magnetic resonance imaging (MRI) at 3.0 T, and validated with hyperpolarized ³He MRI under similar ventilator conditions. Ventilation maps were obtained using flip angle variation for offset of RF and relaxation (FAVOR) which is a multiple breath imaging technique that extracts the fractional ventilation parameter, r, on a pixel‐by‐pixel basis from the dynamic signal enhancement. r is defined as the fractional refreshment of gas per breath. Under the ventilator conditions used in this work, whole‐lung measurements of fractional ventilation obtained using hyperpolarized ¹²⁹Xe were not significantly different from those obtained using hyperpolarized ³He (p = 0.8125 by a Wilcoxon matched pairs test). Fractional ventilation gradients calculated in the superior/inferior (S/I) and anterior/posterior (A/P) directions obtained using hyperpolarized ¹²⁹Xe were not significantly different from those obtained using hyperpolarized ³He (p = 0.9375 and p = 0.1563, for the S/I and A/P directions, respectively). Following baseline fractional ventilation measurements, one representative rat was challenged with methacholine and fractional ventilation measurements were performed over a time course of 10 min. A reduction and subsequent recovery in whole‐lung r values were detected using the FAVOR method. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.     

Comparative study of regional cerebral blood flow values measured by Xe CT and Xe SPECT

The regional cerebral blood flow (rBCF) values measured by stable xenon-enhanced computed tomography (Xe XT) and by radioactive xenon-133 single photon emission computed tomography (Xe SPECT) were compared in 16 patients with cerebral infarct. On the non-lesion side Xe SPECT recorded 10.7% higher rCBF values than Xe CT in the anterior cerebral artery territory while Xe CT recorded 9.6% higher values than Xe SPECT in the middle cerebral artery territory. These differences were not statistically significant. Although the rCBF values were almost the same no correlation was found between the two methods in the posterior cerebral artery territory and the basal ganglia. Only hemispheric CBF on the non-lesion side showed the same value and a good correlation between the Xe CT and the Xe SPECT. There was a good correlation in the hemispheric CBF values on the lesion side, too. The difference of rCBF between the non-lesion side and the lesion side was expressed smaller in the Xe SPECT than in the Xe CT. This is in agreement with the previous reports that Xe SPECT overestimates the flow in the low flow areas. The higher rCBF values in the anterior cerebral artery territory measured by the Xe SPECT was ascribed to the artifact from the radioactivities in the inhalation mask and the air passages as reported previously. In conclusion, there is no good correlation between the rCBF values measured by the Xe CT and by the Xe SPECT. Only hemispheric CBF shows a good correlation between the two methods.     

Local cerebral blood flow and partition coefficients measured in cerebral astrocytomas of different grades of malignancy

Local cerebral blood flow and local partition coefficients were measured in patients with different grades of malignant cerebral astrocytomas (n = 5) who inhaled 35% stable xenon during computed tomography scanning. Results were compared with those in age-matched normal subjects (n = 5. Mean values for local cerebral blood flow in the gray matter in patients with astrocytomas were decreased throughout the tumor mass and surrounding brain that was apparently free of tumor. Patients with highly malignant glioblastoma multiforme (astrocytoma grade IV; n = 2) showed more variable values for local cerebral blood flow and local partition coefficients compared to those with astrocytomas of lower grades (grades I-II; n = 3). Local partition coefficients in gray matter invaded by grade IV astrocytoma were significantly higher than those in gray matter invaded by grade I-III astrocytomas. Local cerebral blood flow and local partition coefficients in the brain tissue surrounding grade IV astrocytomas were reduced to a greater extent than those in more benign tumors.     

A randomized clinical trial of feeder vessel photocoagulation of proliferative sickle cell retinopathy. I. Preliminary results

A randomized prospective clinical trial of feeder vessel photocoagulation for proliferative sickle cell retinopathy was performed. In Chicago there were 34 argon laser-treated eyes and 30 control eyes. In Kingston there were 53 xenon arc treated eyes and 50 control eyes. Prolonged loss of visual acuity was rare in both photocoagulated and control eyes. Argon laser and xenon arc feeder vessel photocoagulation reduced the incidence of vitreous hemorrhage and visual loss from vitreous hemorrhage. However, photocoagulation was associated with an increased risk of choroidal neovascularization (xenon arc greater than argon laser) and retinal detachment (argon laser), although visual loss from these complications has not been seen in these patients so far.     

Gas,tubes and flow

Optimizing the flow of both liquids and gases is crucial to many areas of anaesthetic and critical care practice. In this article, we describe the physical principles that govern the flow of gases and present scenarios from clinical practice to illustrate these concepts. The difference between laminar and turbulent flow is explained, along with the factors that determine the nature of the fluid flow. The Venturi effect, Bernoulli principle and Coanda effect are also described with reference to their clinical applications and their relevance to medical devices.