Objective: Because of concerns regarding the effects of deep hypothermia and circulatory arrest on the neonatal brain, we have developed a technique of regional low-flow perfusion that provides ...cerebral circulatory support during neonatal aortic arch reconstruction.
Methods: We studied the effects of regional low-flow perfusion on cerebral oxygen saturation and blood volume as measured by near-infrared spectroscopy in 6 neonates who underwent aortic arch reconstruction and compared these effects with 6 children who underwent cardiac repair with deep hypothermia and circulatory arrest.
Results: All the children survived with no observed neurologic sequelae. Near-infrared spectroscopy documented significant decreases in both cerebral blood volume and oxygen saturations in children who underwent repair with deep hypothermia and circulatory arrest as compared with children with regional low-flow perfusion. Reacquisition of baseline cerebral blood volume and cerebral oxygen saturations were accomplished with a regional low-flow perfusion rate of 20 mL · kg
–1 · min
–1.
Conclusions: Regional low-flow perfusion is a safe and simple bypass management technique that provides cerebral circulatory support during neonatal aortic arch reconstruction. The reduction of deep hypothermia and circulatory arrest time required may reduce the risk of cognitive and psychomotor deficits. (J Thorac Cardiovasc Surg 2000;119:331-9)
High-frequency pulsed electromagnetic field stimulation is an emerging noninvasive therapy being used clinically to facilitate bone and cutaneous wound healing. Although the mechanisms of action of ...pulsed electromagnetic fields (PEMF) are unknown, some studies suggest that its effects are mediated by increased nitric oxide (NO), a well-known vasodilator. The authors hypothesized that in the brain, PEMF increase NO, which induces vasodilation, enhances microvascular perfusion and tissue oxygenation, and may be a useful adjunct therapy in stroke and traumatic brain injury. To test this hypothesis, they studied the effect of PEMF on a healthy rat brain with and without NO synthase (NOS) inhibition.
In vivo two-photon laser scanning microscopy (2PLSM) was used on the parietal cortex of rat brains to measure microvascular tone and red blood cell (RBC) flow velocity in microvessels with diameters ranging from 3 to 50 μm, which includes capillaries, arterioles, and venules. Tissue oxygenation (reduced nicotinamide adenine dinucleotide NADH fluorescence) was also measured before and for 3 hours after PEMF treatment using the FDA-cleared SofPulse device (Ivivi Health Sciences, LLC). To test NO involvement, the NOS inhibitor N(G)-nitro-l-arginine methyl ester (L-NAME) was intravenously injected (10 mg/kg). In a time control group, PEMF were not used. Doppler flux (0.8-mm probe diameter), brain and rectal temperatures, arterial blood pressure, blood gases, hematocrit, and electrolytes were monitored.
Pulsed electromagnetic field stimulation significantly dilated cerebral arterioles from a baseline average diameter of 26.4 ± 0.84 μm to 29.1 ± 0.91 μm (11 rats, p < 0.01). Increased blood volume flow through dilated arterioles enhanced capillary flow with an average increase in RBC flow velocity by 5.5% ± 1.3% (p < 0.01). Enhanced microvascular flow increased tissue oxygenation as reflected by a decrease in NADH autofluorescence to 94.7% ± 1.6% of baseline (p < 0.05). Nitric oxide synthase inhibition by L-NAME prevented PEMF-induced changes in arteriolar diameter, microvascular perfusion, and tissue oxygenation (7 rats). No changes in measured parameters were observed throughout the study in the untreated time controls (5 rats).
This is the first demonstration of the acute effects of PEMF on cerebral cortical microvascular perfusion and metabolism. Thirty minutes of PEMF treatment induced cerebral arteriolar dilation leading to an increase in microvascular blood flow and tissue oxygenation that persisted for at least 3 hours. The effects of PEMF were mediated by NO, as we have shown in NOS inhibition experiments. These results suggest that PEMF may be an effective treatment for patients after traumatic or ischemic brain injury. Studies on the effect of PEMF on the injured brain are in progress.
Recent theoretical work has highlighted the importance of multi-scale forcing of the flow for altering the nature of turbulence energy transfer and dissipation. In particular, fractal types of ...forcing have been studied. This is potentially of real significance in environmental fluid mechanics where multi-scale forcing is perhaps more common than the excitation of a specific mode. In this paper we report the first results studying the detail of the wake structure behind fences in a boundary layer where, for a constant porosity, we vary the average spacing of the struts and also introduce fractal fences. As expected, to first order, and in the far-wake region, in particular, the response of the fences is governed by their porosity. However, we show that there are some significant differences in the detail of the turbulent structure between the fractal and non-fractal fences and that these override differences in porosity. In the near wake, the structure of the fence dominates porosity effects and a modified wake interaction length seems to have potential for collapsing the data. With regards to the intermittency of the velocities, the fractal fences behave more similarly to homogeneous, isotropic turbulence. In addition, there is a high amount of dissipation for the fractal fences over scales that, based on the energy spectrum, should be dominated by inter-scale transfers. This latter result is consistent with numerical simulations of flow forced at multiple scales and shows that what appears to be an “inertial regime” cannot be as production and dissipation are both high.
The effectiveness of cerebrospinal fluid (CSF) drainage in lowering high intracranial pressure (ICP) is well established in severe traumatic brain injury (TBI). Recently, however, the use of external ...ventricular drains (EVDs) and ICP monitors in TBI has come under question. The aim of this retrospective study was to investigate the effect of CSF drainage on brain tissue oxygenation (PbtO
). Using a multi-modality monitoring system, we continuously monitored PbtO
and parenchymal ICP during CSF drainage events via a ventriculostomy in 40 patients with severe TBI. Measurements were time-locked continuous recordings on a Component Neuromonitoring System in a neuroscience intensive care unit. We further selected for therapeutic CSF drainage events initiated at ICP values above 25 mm Hg and analyzed the 4-min periods before and after drainage for the physiologic variables ICP, cerebral perfusion pressure (CPP), and PbtO
. We retrospectively identified 204 CSF drainage events for ICP EVD-opening values greater than 25 mm Hg in 23 patients. During the 4 min of opened EVD, ICP decreased by 5.7 ± 0.6 mm Hg, CPP increased by 4.1 ± 1.2 mm Hg, and PbtO
increased by 1.15 ± 0.26 mm Hg. ICP, CPP, and PbtO
all improved with CSF drainage at ICP EVD-opening values above 25 mm Hg. Although the average PbtO
changes were small, a clinically significant change in PbtO
of 5 mm Hg or greater occurred in 12% of CSF drainage events, which was correlated with larger decreases in ICP, displaying a complex relationship between ICP and PbtO
that warrants further studies.
To address the ability and reliability of the INVOS 3100A (Somanetics, Troy, MI) cerebral oximeter to detect cerebral desaturation in patients and the interpretation of cerebral oximetry measurements ...using the INVOS 3100A in stroke and cardiac arrest.
Case reports of two patients.
Neurologic Intensive Care Unit of a University Hospital.
Two patients suffering occlusive strokes of the middle cerebral artery. One later suffered a cardiac arrest.
The first case, a patient who suffered cardiac arrest while undergoing continuous cerebral oximetry, clearly demonstrated the ability of the INVOS 3100A to detect rapid tissue vascular oxyhemoglobin desaturation in the brain during circulatory arrest. In the second case, oximetry readings were obtained in a patient with a right internal carotid artery occlusion and an infarct in the middle cerebral artery territory. The circulation of the anterior cerebral artery (ACA) territory was intact. Stable xenon-computed tomography of local cerebral blood flow showed no perfusion in the infarct, and oximetry readings were between 60 and 65. In the border zone between the middle cerebral artery and the ACA, readings of 35 to 40 were obtained, and over the ACA territory, the readings were in the 60s.
Oximetry by near infrared spectroscopy reflects the balance between regional oxygen supply and demand. In dead or infarcted nonmetabolizing brain, saturation may be near normal because of sequestered cerebral venous blood in capillaries and venous capacitance vessels and contribution from overlying tissue. In regionally or globally ischemic, but metabolizing brain, saturation decreases because oxygen supply is insufficient to meet metabolic demand. These observations are supported by previously reported "normal" readings in unperfused or dead brains.
Display omitted
Middle cerebral artery occlusion (MCAO) by the intraluminal suture method is widely used to model ischemic stroke in rats. Current methods include transection or ligation of the ...external carotid or common carotid artery and thus result in partial restoration of perfusion after transient MCAO. Since incomplete reperfusion may influence recovery and thus confound studies of the impact of neuroprotective compounds and therapies on outcomes after stroke, we have devised a novel method to induce transient MCAO with complete reperfusion. Advantages of the method include:
•MCAO is achieved through insertion of an intraluminal suture into the internal carotid artery through the common carotid artery.•At the end of the occlusion period, the suture is withdrawn and the incision in the common carotid artery is closed with cyanoacrylate tissue adhesive and complete reperfusion is established.•No residual subcutaneous sutures remain during recovery.•Vasculature is restored to the preoperative state.
The Carotid Occlusion Surgery Study (COSS) was an improvement over the Extracranial-Intracranial Bypass Study, which did not utilize physiological selection. To assess possible reasons for early ...closure of the COSS trial, we reviewed COSS methods used to identify high-risk patients and compared results with separate quantitative data.
Increased oxygen extraction fraction (OEF) by positron emission tomography is a gold standard for ischemia, but the specific thresholds and equivalency of the semiquantitative OEF ratio utilized in COSS and quantitative OEF are at issue.
The semiquantitative hemispheric OEF ratio used in COSS did not identify the same group of patients as did quantitative OEF using a threshold of 50%.
The failure of COSS is likely caused by a failure of the semiquantitative, hemispheric OEF ratio method rather than by the selection for bypass based on hemodynamic compromise.
Genetic variation in humans probably plays a role in determining the range of individual susceptibility to age-related hearing loss (AHL), but no contributing loci have been identified because of the ...difficulties of dissecting complex traits in humans. This paper reports mapping of an AHL locus using a panel of consomic mice between C57BL/6J (B6) and MSM strains, which covered more than a half of chromosome sets. B6 strain exhibited AHL beginning at 10 months of age whereas MSM strain, derived from Japanese wild mice, had normal hearing throughout life. Individuals in the panel were examined with auditory brainstem response (ABR) at various months of age, revealing that one particular strain (B6-Chr17
MSM) substituting the chromosome 17 with the MSM-derived one showed a prominent resistance, having still good hearing at 18 months of age. Subsequent mapping using 89 individuals in the cross between B6-Chr17
MSM and B6 was performed, which showed a significant association of ABR thresholds with loci in the vicinity of
D17Mit119. These results show a novel AHL-resistant locus, designated as
Ahl3, on the chromosome 17.
PDF
