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PubMedDate not supplied

Local cortical blood flow and oxygen consumption during isoflurane-induced hypotension. Results in patients undergoing intracranial aneurysm clipping.

Cerebral cortical blood flow (lCoBF) and metabolic rate for oxygen (lCoMRO2) were studied in eight patients undergoing intracranial aneurysm clipping. The patients were anesthetized with fentanyl 10 micrograms/kg and 70% nitrous oxide combined with 30% oxygen. Hypotension was induced with isoflurane. A thermal diffusion probe was used to measure lCoBF, and arterial and cerebral venous blood samples were obtained for measurement of arterio-cerebral venous O2 content difference. Measurements were made prior to hypotension, during hypotension (to mean arterial pressure approximately 50 mmHg), and posthypotension. Mean lCoBF decreased from 69 +/- 20 mL/100 g/min at normotension to 59 +/- 13 mL/100 g/min during hypotension (P less than .03, NS) and was 61 +/- 18 mL/100 g/min upon return to normotension (all values mean +/- 1 SD). The lCoMRO2 averaged 3.9 +/- 1.6 mL/100 g/min and 3.1 +/- 1.5 mL/100 g/min, respectively (P less than .03, NS) for normotension upsilon hypotension. Values for cerebral venous PO2 and O2 saturation also did not differ significantly between study periods. These results indicate that isoflurane-induced hypotension during fentanyl-nitrous oxide anesthesia allows maintenance of a constant lCoBF and oxygen delivery.

Adult↗

PubMed1998

A methodology for examining the plausibility of accelerated aging protocols for UHMWPE components.

In light of the time-intensive nature of using real-time shelf-aged specimens in research into property changes of ultra-high-molecular-weight polyethylene (UHMWPE), accelerated thermal diffusion oxidative aging (usually referred to as accelerated aging) is frequently resorted to. A number of such aging protocols have been reported in the literature, with various claims for their producing changes in the properties of the polymer being the same as or similar to those seen in real-time shelf-aged samples. The thrust of the present work is the presentation of a methodology for examining such claims. The methodology is applied to six properties (% crystallinity, melting temperature, oxidation index, ultimate tensile strength, ultimate tensile elongation, and tensile toughness) of 4150HP UHMWPE grade, sterilized using six different methods, prior to and following the use of a specific accelerated aging protocol (oxygen gas at 70 degrees C and 507 kPa pressure; 14 d.). These six properties have been identified in the literature as being strongly correlated with the clinical wear of UHMWPE articular components. It is shown that the claim for the protocol used in the present work (in terms of the simulated equivalent shelf aging time) is plausible. It needs to be emphasized, however, that this conclusion is tentative given the paucity of the relevant literature results that are currently available and which are vital to the application of the methodology.

Biocompatible Materials↗

PubMed1999

Autoregulation of cortical blood flow during surgery for ruptured intracranial aneurysms.

BACKGROUND: Little information is available about the extent and the time course of possible impairment of cerebral circulation occurring after aneurysmal subarachnoid haemorrhage (SAH). The aim of this study was to correlate cerebral autoregulation, neurological impairment at surgery and timing of surgery in patients with ruptured intracerebral aneurysms. METHODS: Cortical blood flow (CoBF) was measured intraoperatively by a thermal diffusion probe in 77 patients during surgery for ruptured supratentorial aneurysms, who were operated on at different time intervals after bleeding. An autoregulation index (AI), expressed as the ratio between the change in CoBF and the change of mean arterial blood pressure at the time of rising the systemic blood pressure after occlusion of the aneurysm(s), was determined in each case. RESULTS: Among good-grade patients (WFNS grade I-II), those operated on days 0-2 after SAH had a significantly better autoregulatory response, compared either with patients who underwent surgery on days 3-7 after bleeding (p<0.01), or with those whose aneurysm was occluded more than 7 days after rupture (p<0.03). The mean AI of poor-grade patients (WFNS grade IV-V), who received surgery on days 0-2 after SAH, was significantly higher (p<0.01) compared with the corresponding value of good-grade patients. No significant difference was found between the mean AIs of patients who subsequently did, or did not, develop symptomatic vasospasm. CONCLUSIONS: It is concluded that good-grade patients operated on within 48 hours after bleeding take advantage of a preserved autoregulatory function during controlled hypotension.

Adult↗

PubMed2000

Anesthesia with deep hypothermic circulatory arrest for giant basilar aneurysm surgery.

The application of deep hypothermic circulatory arrest (DHCA) as an adjutant technique in anesthetic management for surgery of giant and complex cerebral aneurysm has been clinically recognized with piling up experience in many institutes. DHCA provides the advantages such as a bloodless surgical field and protection of the brain, all of which make a precise clipping of the aneurysm possible and thus it lowers the mortality rate which could be extremely high without it. Nevertheless, in application, the disadvantages of this technique includes comparatively inefficient and uneven cooling or rewarming, severe physiological change, cardiac distension and arrhythmia during cardiopulmonary bypass (CPB), hemorrhage from systemic heparinization and brain damage due to inadequate protection, none of which has ever been stressed. Since many giant aneurysms are found inoperable during exploration with application of DHCA, it would change the fate of the patients, and the clinical value of DHCA in such an instance becomes contradictive and disputable. We would like to present our experience in a case who, because of a giant basilar aneurysm, underwent surgical correction under DHCA retrograde cerebral perfusion (RCP) with cerebral function monitoring including electroencephalography (EEG), brainstem auditory evoked potentials (BAEP), thermal diffusion cerebral blood flowmetry, study of the change of extracellular concentration of excitatory amino acid, glutamate and aspartate, and off-line neurochemical analysis with cerebral microdialysis technique.

Adult↗

PubMed2001

Xenon-induced flow activation in patients with cerebral insult who undergo xenon-enhanced CT blood flow studies.

BACKGROUND AND PURPOSE: Stable xenon-enhanced CT ((s)Xe/CT) has gained wide acceptance in the assessment of regional cerebral blood flow (rCBF) in patients with intracranial abnormalities. The aim of this study was to test whether the contrast medium (ie, (s)Xe) itself directly induces relevant changes in rCBF, thereby distorting any valid determination of cerebral perfusion by using (s)Xe/CT. METHODS: To characterize the degree and temporal dynamics of (s)Xe-induced flow activation, a thermal diffusion (TD)-based microprobe was placed subcortically into the frontal lobe on either hemisphere to assess rCBF (TD-rCBF) continuously in 23 patients (mean age, 55 +/- 18 years) with severe intracranial insult who were undergoing (s)Xe/CT. RESULTS: In 35, the (s)Xe/CT studies TD-rCBF rose from 25 +/- 17 mL/100 g per minute (range, 5-42 mL/100 g per minute) before (s)Xe administration to 28 +/- 21 mL/100 g per minute (range, 6-46 mL/100 g per minute) after arterial (s)Xe saturation was reached. Analysis of the flow activation curve showed a logarithmic shape with an increase in TD-rCBF between 3% and 7% within the first 76 seconds of (s)Xe wash-in (12% after 190 seconds) and showed no further augmentation until the end of the blood flow study. CONCLUSION: The observed (s)Xe-induced rCBF activation, which showed significant inter- and intraindividual variability, might lead to overestimation of rCBF in patients with severe intracranial insult. The obtained flow activation curve provides essential information that may allow subsequent refinement of the methodology, aiming to further minimize the influence of (s)Xe-induced rCBF activation on rCBF calculations when using (s)Xe/CT technology.

Administration, Inhalation↗

PubMed1989

Safety and ECT Stimulus Electrodes: I. Heat Liberation at the Electrode-Skin Interface.

Calculations reveal that the electroconvulsive therapy (ECT) stimulus cannot cause burn injury to brain tissue, but poor electrode-skin contact is a risk for skin burn. This article reviews factors that influence skin temperature, including electrical charge, skin impedance, topographic conformity between electrode and skin, electrode surface area, and thermal diffusivity of electrode material.

Journal Article↗

PubMed1975

Measurement of venous blood flow and pressure using thermoelectric and pressure transducers.

In order to simplify procedures for testing the circulatory function of a patient, changes in the venous blood flow as well as venous pressure following exercise were continuously observed using the thermoelectric flowmeter. The level of zero flow necessary for evaluation of the velocity of flow was successfully indicated without occlusion of blood vessels by means of a form of compensation for thermal diffusion devised by the authors.

Blood Flow Velocity↗

PubMed1992

[Local cerebral blood flow and its CO2 reactivity in the ischemic cerebrovascular diseases before and after bypass].

We evaluated the effects of the STA-MCA anastomosis on local cerebral blood flow (LCBF) and CO2 cerebrovascular reactivity (CVR) in ischemic cerebrovascular diseases (CVD). [Patients and Methods] We examined the LCBF and CVR of 21 patients with ischemic CVD subjected standard STA-MCA anastomosis. During surgery, LCBF was continuously measured using the thermal diffusion method sometimes in a state of decreased PaCO2 (median: 7.2mmHg) before and after bypass. CVR was represented as % delta LCBF/delta CO2. [Results] 1) In the control group (with non-ruptured aneurysm, n = 7), LCBF was 58.6 +/- 14.1 ml/100g/min and % delta LCBF/delta CO2 was 4.68 +/- 1.68%/mmHg. 2) Before bypass, LCBF was 46.7 +/- 10.3ml/100g/min. It was significantly (p < 0.05) lower than control level. After bypass, LCBF increased significantly (p < 0.05) to 62.0 +/- 14.3 ml/100g/min. 3) Before bypass, % delta LCBF/delta CO2 was -1.36 +/- 4.34%/mmHg. In the 14 cases (66.7%), % delta LCBF/delta CO2 was below the 0%/mmHg (inverse steal effect). 4) After bypass, it increased to 0.08 +/- 2.73%/mmHg. 11 cases (52.4%) showed % delta LCBF/delta CO2 was above the 0%/mmHg. 5) In the group with a preoperative % delta LCBF/delta CO2 of less than 0%/mmHg, preoperative LCBF was 43.6 +/- 9.3 ml/100g/min, which was significantly low (p < 0.01) compared to that in the group with higher % delta LCBF/delta CO2. After bypass, LCBF and % delta LCBF/delta CO2 remarkably increased in the group with % delta LCBF/delta CO2 below 0%/mmHg. [Conclusion] Before bypass, LCBF was low and CVR was severely disturbed. In the 14 cases % delta LCBF/delta CO2 was below 0%/mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

[Effects of topically applied bunazosin hydrochloride on choroidal capillary blood flow and intraocular pressure of rabbit eye].

The effects of topically applied bunazosin hydrochloride, a selective alpha 1 blocker under development as a drug to treat glaucoma, were studied in regard to the choroidal capillary blood flow, intraocular pressure (IOP), and blood pressure in albino rabbit eyes in comparison with propranolol hydrochloride, a non-selective beta blocker. The capillary blood flow was measured using a thermal diffusion flowmeter. Single instillations (50 ul) of 0.005% bunazosin hydrochloride, lowered the IOP to almost the same degree as did 1.0% propranolol hydrochloride. The maximum decreases from initial IOP were 3.3 +/- 1.2, 3.6 +/- 1.7 mmHg for bunazosin hydrochloride and propranolol hydrochloride, respectively. No significant effect on mean blood pressure was observed with these instillations. The choroidal capillary blood flow was reduced by propranolol hydrochloride for 3 hours after instillation (maximum rate of decrease was 10.0 +/- 4.6%), while it was increased by bunazosin hydrochloride for 150 min. (maximum rate of increase was 8.3 +/- 3.8%). When phenylephrine hydrochloride (0.5%), an alpha 1 agonist, was instilled with bunazosin hydrochloride (0.005%), the choroidal capillary blood flow showed no significant change. This was felt to imply an action mechanism involving the alpha 1 receptor.

Administration, Topical↗

PubMed1990

[Response to CO2 and autoregulation of cortical cerebral blood flow during isoflurane anesthesia].

Response to CO2 and autoregulation of cortical cerebral blood flow (CBF) during isoflurane anesthesia were studied in 10 patients undergoing neurosurgery. The patients were anesthetized with 0.5 to 1.2% end-tidal isoflurane and 66% nitrous oxide in oxygen. The CBF was measured by thermal diffusion using a flow probe with a Peltier stack. PaCO2 was controlled to produce hypocarbia, normocarbia and hypercarbia by changing tidal volume and respiratory rate. Arterial blood pressure was altered. Hypotension was achieved by intravenous infusion of trimetaphan and hypertension was induced by intravenous administration of metaraminol. During isoflurane anesthesia the response to CO2 of CBF was kept at PaCO2 between 27.8 and 53.9 mmHg. The following relationship was obtained. CBF = 2.54 x PaCO2-53.0, r = 0.59, n = 131 The autoregulation of CBF was evaluated in 7 patients, and in 2 patients, the autoregulation of CBF was abolished.

Anesthesia, Inhalation↗

PubMed1990

[Effects of controlled hypotension induced by prostaglandin E1 on the cerebral blood flow].

The effect of controlled hypotension induced by prostaglandin E1 (PGE1) on the cerebral blood flow (CBF) was studied in 14 patients undergoing neurosurgery. CBF was measured by thermal diffusion using a flow probe with a Peltier stack. PGE1 was injected i.v. continuously, at a dose of 0.05, 0.1 and 0.2 micrograms.kg-1.min-1. CBF tended to increase dose-dependently but not significantly by PGE1 administration. Cerebral vascular resistance was reduced significantly by every dose of PGE1 administered. Therefore, the results indicate that the cerebral vascular beds are dilated directly by PGE1. In conclusion, this study suggests that PGE1 can be used safely to control hypotension without reducing CBF during neurosurgery.

Adult↗

PubMed1990

[Cerebral microcirculation during increased intracranial pressure--assessment with reflectance photometry].

The cerebral microcirculation under increased intracranial pressure was evaluated by using reflectance photometric method. The values of tissue hemoglobin (IHb) and its oxygen saturation (ISO2) detected by this method were evaluated in cat brain tissue. The correlation between IHb and content of cortical hemoglobin subunits in vitro was high. High correlation between ISO2 and blood oxygen saturation in superior sagittal sinus was also noted in hypoxic hypoxia. Thus, the reflectance photometric method was revealed to be applicable for evaluation of regional hemoglobin content and oxygen saturation. Using this method the cerebral microcirculation was studied in an increased intracranial pressure model produced by injection of artificial CSF into the cisterna magna in cats. Regional cortical cerebral blood flow (CBF) was measured simultaneously by thermal diffusion method. During decrease of perfusion pressure down to 40 mmHg with preservation of CBF, compensatory increase of IHb was not observed, but IHb rather gradually decreased. The decrease of IHb would be due collapse of capacitance vessels by increased intracranial pressure. Cerebral ISO2 was stable as well as CBF. Less than 40 mmHg of perfusion pressure, ISO2 started to decrease in association with CBF and IHb. Since ISO2 seems to be closely related to the tissue oxygen extraction the change of ISO2 reflect the CBF and tissue cerebral oxygen metabolism. Present study suggest the evaluations of IHb and ISO2 were an useful monitoring indexes in various cerebral disorders.

Animals↗

PubMed1990

Hand-arm vibration, noise, temperature and static load--an experimental study of peripheral circulation while operating chain-saws.

From the viewpoint of elucidating the etiological mechanism of vibration-induced white finger (VWF), a model experiment was designed using a chain-saw under laboratory conditions. Finger skin temperature and finger blood flow were measured simultaneously as indicators of peripheral circulatory movement, using a thermister and an apparatus for measuring tissue blood flow based on the thermal diffusion method. In the first project (Experiment A), five healthy subjects operated a chain-saw at a high working speed with-out actually cutting anything. In the second project (Experiment B), seven healthy subjects were exposed to three different kinds of experiments with combinations of hand-arm vibration, noise and tool weight at about 15 degrees C room temperature. In the third project (Experiment C), the effects of tool weight and grip force were examined. In the fourth project (Experiment D), patients suffering from vibration disease were exposed to hand-arm vibration and the noise of a chain-saw for 2 minutes. In experiment A, the mean value of the normalized finger skin temperature decreased gradually with cyclic changes corresponding to each exposure and break period. Changes in finger blood flow had almost the same pattern as the changes of skin temperature, but the recovery of blood flow during a 30 sec break period was notable and a slight elevation of the base line was observed. In experiment B, the mean value for the normalized finger skin temperature decreased much more when the subjects operated a chain-saw at a high working speed than when they operated the chain-saw with the noise isolated by double hearing protection. On the other hand, the results obtained in experiment C indicated that the effect of tool weight should be considered as an important factor for investigating the acute changes in peripheral circulation. In experiment D, some patients showed an unusual pattern in the change of blood flow during a post exposure period which was not seen in healthy subjects.

Adult↗

PubMed1988

[Reversibility of cerebral cortical function after recirculation in experimental cerebral ischemia].

Several kinds of monitoring systems to evaluate cerebral function have been introduced such as somatosensory evoked potential, visual evoked potential and auditory brain stem response. Although these monitoring systems are employed in practice in neurosurgical operations, the reversibility of these cerebral functions after ischemia insult is little known. In this study the reversibility of direct cortical response (DCR) as well as EEG from global ischemia was investigated using total 60 cats. Cortical cerebral blood flow was also measured continuously by the thermal diffusion flow probe with a peltier stack calibrated by hydrogen clearance. Global ischemia was made by the occlusion of innominate and left subclavian arteries. Although the EEG was abolished soon after occlusion of these arteries, DCR was preserved and it started to decay at the cortical CBF of about 21 ml/100 g/min. It had completely disappeared at the CBF of about 8 ml/100 g/min. Recovery of DCR was not correlated with the occlusion time, but it was well correlated with the interval of loss of DCR. When the DCR was not completely lost, DCR amplitude was completely recovered about 3 hours after ischemia insult with the CBF below 20 ml/100 g/min. Moreover, in all 8 cats which were recirculated within 5 minutes after loss of DCR, complete recovery of DCR amplitude was obtained. However, it was observed in 10 of 12 cats (83%) with 10 minutes loss of DCR, 5 of 12 cats (42%) with 15 minutes loss of DCR, 4 of 14 cats (29%) with 20 minutes loss of DCR, and only one of 11 cats (10%) with 30 minutes loss of DCR.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1979

[Soluble high molecular weight derivatives of pancreatic inhibitors. Kinetic-thermodynamic studies of inhibitors linked to differently charged matrices].

The effects of electrostatic charge of the matrix on the pH-dependence of interactions of commercial trypsin with preparations of pancreatic inhibitor modified by soluble polysaccharide coupling were studied. It was shown that the rate constants of trypsin association with native and modified pancreatic inhibitor preparations as well as the rate constants of dissociation of their complexes and, consequently, the inhibition constants are identical. The invariability of the rate constants for the association reaction after the increase in the molecular weight of pancreatic inhibitor may be probably accounted for by the fact that the limiting step of a stable trypsin-inhibitor complex formation is not controlled by diffusion. Thermal denaturation of pancreatic inhibitor preparations modified by binding to polysaccharides (pH 4.7--8.0, 97 degrees C) suggests an essential role of the negative charge of matrix in stabilization of the protein inhibitor globule.

Animals↗

PubMed1986

[Experimental coronary angioplasty using hematoporphyrin coloration simultaneously with a pulsed laser beam].

The setting up of a reliable method for angioplasty by laser irradiation is based. On the one hand, on the simultaneous control of the observed thermal, mechanical and photochemical effects within the atheromatous material and, on the other, on the demonstration of the absence of effects damaging to the arterial tunica. Theoretical modelling and experimental use have together proved the unique importance of pulsed emission, which strongly reduces thermal diffusion. Labelling of the atheromatous plaque by a hematoporphyrin derivative (HPD), as exemplified in the carcinological process, cancels the superficial reflectivity and strongly reduces the diffusion coefficient in the plaque. It confers on it a spectral absorption characteristic which is the basis of the exact physical coupling between the frequency of the exciting radiation and the absorption which generates vaporization in the pathological material. The preparation of chemically more homogeneous HPD and the spectrometric study of other colouring agents in vivo point to a further development of this technique of angioplasty.

Coronary Disease↗

PubMed1985

[Physical and technical bases of tumor hemostasis with a CO2 laser in neurosurgery].

The particular thermal properties of CO2 laser make it an useful instrument for neurological surgery. Necrosis and carbonization zones, as well as its thermal diffusion in the nervous tissue are dramatically less important with a CO2-laser unit than with other lasers (Nd-Yag or Argon) and moreover with the electrical mono--or bipolar coagulator. That is why the authors chosed this instrumentation for achieving a good hemostasis. It was particularly useful during removal of intracranial tumors situated close to the functional structures of the basis of the brain and the brainstem. The authors present their experience with the french CO2-laser unit Ercelas 80 (Robert et Carrière Biomedical) that they have been using routinely since 1983 in 60 neurosurgical procedures. They present the technical standards necessary to perform such an hemostasis either with the hand-piece or using the micromanipulator. In all cases the output power must be much lower for hemostasis than for tumoral cutting or vaporization. Depending on the type of tumor, radiation power should vary from 2 to 10 watts if a linear emission is used, and from 10 to 30 watts in case of pulsed emission. On the other hand, CO2-laser beam must be unfocussed so as to avoid cutting the vessels less than 0.5 mm in diameter before coagulating them properly.

Carbon Dioxide↗

PubMed1986

[Effect of hypoxia and hyperoxia on cortical oxidative metabolism in relation to cerebral blood flow autoregulation].

Our earlier studies have shown that local cortical blood flow (CoBF) in the rabbit has been autoregulated in a narrow range of mean arterial blood pressure (MABP) and autoregulation of cortical oxygen tension (bPO2) has been maintained in a wider range (75-110 mmHg) than that of CoBF. In the present studies, bPO2, NAD/NADH redox state, and CoBF were measured under the various conditions of hypoxia and hyperoxia to discuss the critical level of cortical oxidative metabolism and autoregulation of CoBF in relation to oxidative metabolism. New Zealand white rabbits were anesthetized with pentobarbital sodium intraperitoneally and paralyzed with gallamine triethiodide intravenously. They were ventilated artificially maintaining normal blood gas analysis. NAD/NADH redox state was measured with a compensated fluorometer with a reflectance device to correct for hemodynamic artefacts and bPO2 was monitored continuously with the polarographical method. They were measured simultaneously. CoBF was monitored with the thermal diffusion cerebral blood flow monitor of Flowtronics. Hypoxia and hyperoxia were produced by decreasing or increasing the inspired oxygen concentration. Arterial blood samples were obtained for blood gas determination before and during the episode of hypoxia or hyperoxia. A definite reduction of NADH began at a 50% decrease of PaO2. It corresponded to 70 mmHg of PaO2. Below 50% decrease of PaO2, NADH was reduced largely. This was statistically significant (p less than 0.01). Although, the oxidation of NADH occurred in the moderate hyperoxic state, no oxidation of NADH occurred more than 6.1% of full scale even in the condition of higher PaO2.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗