Cognitive performance and cerebrohemodynamics associated with the Persian Gulf Syndrome.

The Persian Gulf Syndrome generally manifests as a set of nonspecific complaints with emphasis on central nervous system impairment. The purpose of this study was to determine if cognitive performance and middle cerebral artery blood flow velocity (MCABFV) were altered in symptomatic Gulf War veterans (sGWVs) and asymptomatic Gulf War veterans (aGWVs) by exposure to low levels of acetone. MCABFV was assessed in male aGWVs (n = 8) and sGWVs (n = 8) during cognitive challenges while breathing 1) clean air, 2) a clean air placebo, and 3) a mixture of air and 40 parts per million (ppm) acetone. Pulmonary function was also evaluated. Pulmonary function tests showed no statistical differences between aGWVs and sGWVs while breathing clean air or 40 ppm acetone in air. Cognitive performance was similar during the clean air, placebo, and acetone test conditions for sGWVs and aGWVs. Data pooled across test conditions for each group indicated a statistically significant (P < 0.05) poorer performance primarily in memory and executive function tasks by sGWVs. sGWVs had a 34.2% higher baseline MCABFV than aGWVs (P < 0.05). Increases in MCABFV for aGWVs (averaged over all cognitive tasks for each test condition) ranged between 7.8% and 8.8%, and were not statistically significant. Increases for sGWVs ranged between 0.3% and 4.8%, averaged over all cognitive tasks for each test condition. No significant differences were noted between the clean air and placebo test conditions but both were significantly different to the acetone condition. Differences in MCABFV increases for each of the test conditions between aGWVs and sGWVs were also statistically significant. sGWV did not appear to demonstrate pulmonary dysfunction following exposure to acetone. They did, however, appear to have generally lower cognitive function as compared to aGWVs. sGWVs appeared to have a significant degree of autoregulatory disruption in cerebral perfusion, resulting in reduced cognitive reserve capacity and potentially impaired ability to handle complex cognitive tasks.

A rat model of neurobehavioral sensitization to toluene.

Some individuals report that, following either a single high-level or repeated lower-level exposures to chemicals (initiation), subsequent exposure to very low concentrations of chemicals (triggering) produces a variety of adverse effects, including disruption of cognitive processes. Our objective was to model this two-step process in a laboratory animal. Two groups of 16 rats, eight male and eight female, received whole-body inhalation exposure to toluene, either at 80 ppm for 6 h/day for 4 weeks (Repeat group) or to 1600 ppm for 6 h/day on one day only (Acute group). Two other groups (Trigger group and Clean group) of 16 were sham-exposed. After 17 days without toluene exposure, the Acute, Repeat and Trigger groups began a series of daily toluene 'trigger' exposures (10 ppm for 1 h) followed immediately by testing on an operant repeated-acquisitions task requiring learning within and across sessions. The Clean group was sham-exposed prior to operant testing. Trigger or sham exposures and operant testing continued 5 days/week for 17 sessions. Analysis of variance revealed a variety of statistically significant (P < 0.05) differences between treatment groups. Furthermore, the patterns of differences between groups differed (P < 0.05) for female and male rats. For example, male rats of the Trigger group made the most responses, and female rats of the Repeat group responded most slowly. The observation of important changes in the operant behavior of female and male rats previously exposed to toluene, at relatively low concentrations (80 or 1600 ppm) and then later re-exposed at very low concentrations (10 ppm), is consistent with the experiences of humans reporting cognitive difficulties following acute or chronic exposures to chemicals.

Three-dimensional laser imaging system for measuring wound geometry.

BACKGROUND AND OBJECTIVE: A low cost laser imager was designed and fabricated for measurement of wound geometry. METHODS: The accuracy of the imager was validated using reference depressions of known dimensions. Perimeter, area, and volume were compared to planimetric and packing techniques on simulated wound models. RESULTS: Wound tracing and alginate measurement methods required approximately 20 times longer for the reference standards, and 11 times longer for the simulated wounds than with the laser scanning method (LSM). LSM consistently overestimated the reference perimeter by 0.73+/-0.20 cm and the area by 0.98+/-0.62 cm2. Volume estimates were not statistically different. The tracing method underestimated the perimeter by 0.34+/-0.27 cm and the area by 1.07+/-1.09 cm2. Volume measurements by the alginate method were not statistically different. The perimeters of the simulated wounds averaged 1.29+/-0.27 cm greater using the LSM than obtained by the tracing method, and areas greater by 2.02+/-1.30 cm2. Volume scans averaged 1.04+/-0.61 cm3 greater than by the alginate method.

Physiologic, histologic, and neurologic responses to simultaneous bilateral cerebral vessel Doppler imaging at high beam intensity.

This study evaluates physiological fluid heating during continuous bilateral insonation at 530 mW/cm2 for 8 h in a bench simulation. It also examines the physiologic, histopathologic, and neurologic effects of bilateral Doppler imaging of middle cerebral artery (MCA) blood flow velocity using ultrasonic beams with 530 mW/cm2 intensity in a canine model immediately after and 2 weeks after insonation. In saline-filled containers, instrumented with opposing Doppler probes angled 10 degrees off axis, temperature was recorded at 15-min intervals for approximately 8 h at the intersection of the Doppler probe axes. Three conditions were tested: 1) an ambient control, 2) continuous bilateral insonation at 530 mW/cm2 per channel with the thermistor in position, and 3) intermittent thermistor insertion. In one group of canines, physiopathologic responses during continuous bilateral insonation of the MCAs for 8 h at 2 MHz and 530 mW/cm2 were studied. Brains were prepared for histologic examination immediately after insonation. Cerebral temperature; arterial, venous, pulmonary artery, and capillary wedge pressures; electrocardiogram; cardiac output; MCA velocity; and arterial blood gases were monitored. In a second group of canines, a neurologic evaluation was performed before and after insonation and again after 2 weeks. Brain tissue was evaluated histologically after the last neurologic examination. Light microscopic study was used for all histologic evaluations. In the bench experiments, a net temperature rise in the fluid of the simulation amounted to 0.0075 degrees C/h in the overlap region after correction for ambient temperature effects and artifact thermistor heating. In canines, brain temperature (after correction for core body temperature changes and artifact heating of the thermistor) rose a mean of 0.2 degrees C (p < 0.05) by the first hour, thereafter unchanging. No significant changes in the physiologic, neurologic, or histologic evaluations were observed in either of the experimental groups.

Twelve-hour canine heart preservation with a simple, portable hypothermic organ perfusion device.

BACKGROUND: Cardiac transplantation is limited to an ischemic time of around 6 hours by available preservation solution and technique. Complex organ preservation devices have been developed that extend this time to 24 hours or more, but are clinically impractical. This study evaluates a portable oxygen-driven organ perfusion device weighing approximately 13.5 kg. METHODS: Organs are perfused with the University of Wisconsin solution at low perfusion pressure using less than 400 L of oxygen per 12 hours. Left ventricular parameters were measured in anesthetized adult beagles to establish control values (n = 5). Hearts were procured after cardioplegia with 4 degrees C University of Wisconsin solution, weighed, then stored for 12 hours in University of Wisconsin solution at 4 degrees C. Hearts were perfused (n = 3) or nonperfused (n = 2) during storage. Organ temperature, partial pressure of oxygen in the aorta and right atrium, perfusion pressure, and aortic flow were recorded hourly in perfused hearts. After 12 hours, hearts were transplanted into littermates and left ventricular parameters measured after stabilization off bypass. RESULTS: Organ weight for both groups was unchanged. Nonperfused hearts required both pump and pharmacologic support with significantly depressed left ventricular function. Perfused hearts needed minimal pharmacologic support, with left ventricular end-diastolic pressure, cardiac output, and rate of change of left ventricular pressure showing no statistical difference from control. CONCLUSIONS: These findings confirm the potential for extended metabolic support for ischemia-intolerant organs in a small, lightweight, easily portable preservation system.

The effect of anesthetics on neurologic outcome during the recovery period of spinal cord injury in rats.

We evaluated the effects of anesthetics on neurologic outcome in a model of recoverable experimental spinal cord injury (SCI). Adult rats were implanted with various sizes of hygroscopic plastic material at the T12 spinal level to determine the dimensions that would produce a progressive neurologic deficit from which recovery could occur. Neurologic evaluation was conducted on an inclined plane, noting the maximum angle at which an animal was able to maintain orientation perpendicular to the longitudinal midline. Scores were statistically modeled for each group to develop profiles of neurologic deficits. Rats were subjected to a 4-h exposure to isoflurane, fentanyl/nitrous oxide, or ketamine 7 or 8 days postimplantation. Neurologic outcomes were compared to a SCI reference group which received no postimplant anesthesia. An animal weight/desiccated implant volume (Wa/Vi) ratio of 53 to 73 g/mm3 produced postimplant neurologic deficits which deteriorated to near maximum within 3 days, followed by a gradual improvement beginning at Day 8 and returning to near normal between 21 and 25 days. Final outcome was based on modeled ramp scores for each group and reported in degrees +/- SD: reference, 71.2 +/- 1.1; fentanyl/N2O, 70.4 +/- 0.3; isoflurane, 72.6 +/- 1.1; and ketamine, 64.9 +/- 0.6. The fentanyl group attained maximum recovery first (P > 0.05) but did not recover to a level different on the average from the reference group. The ketamine group demonstrated a poorer (P > 0.05) recovery level relative to the other anesthetic protocols.

Detection and volume estimation of embolic air in the middle cerebral artery using transcranial Doppler sonography.

BACKGROUND AND PURPOSE: Cerebral embolism has been implicated in the development of cognitive and neurological deficits following bypass surgery. This study proposes methodology for estimating cerebral air embolus volume using transcranial Doppler sonography. METHODS: Transcranial Doppler audio signals of air bubbles in the middle cerebral artery obtained from in vivo experiments were subjected to a fast-Fourier transform analysis. Audio segments when no air was present as well as artifact resulting from electrocautery and sensor movement were also subjected to fast-Fourier transform analysis. Spectra were compared, and frequency and power differences were noted and used for development of audio band-pass filters for isolation of frequencies associated with air emboli. In a bench model of the middle cerebral artery circulation, repetitive injections of various air volumes between 0.5 and 500 microL were made. Transcranial Doppler audio output was band-pass filtered, acquired digitally, then subjected to a fast-Fourier transform power spectrum analysis and power spectrum integration. A linear least-squares correlation was performed on the data. RESULTS: Fast-Fourier transform analysis of audio segments indicated that frequencies between 250 and 500 Hz are consistently dominant in the spectrum when air emboli are present. Background frequencies appear to be below 240 Hz, and artifact resulting from sensor movement and electrocautery appears to be below 300 Hz. Data from the middle cerebral artery model filtered through a 307- to 450-Hz band-pass filter yielded a linear relation between emboli volume and the integrated value of the power spectrum near 40 microL. Detection of emboli less than 0.5 microL was inconsistent, and embolus volumes greater than 40 microL were indistinguishable from one another. CONCLUSIONS: The preliminary technique described in this study may represent a starting point from which automated detection and volume estimation of cerebral emboli might be approached.

Canine tracheal blood flow after endotracheal tube cuff inflation during normotension and hypotension.

Tracheal tissue damage associated with endotracheal intubation may be a direct result of high mucosal contact pressure (MCP) generated by the endotracheal tube cuff. Tracheal blood flow (TBF) was measured at MCPs in the normotensive and hypotensive (mean arterial blood pressure, 50 mm Hg) canine model. Control TBFs through the individual rings in contact with the endotracheal tube cuff ranged between 26.6 +/- 2.7 and 44.5 +/- 5.0 with a mean of 35.0 +/- 2.5 mL.min-1 x 100 g-1 during normotension, and 15.0 +/- 4.9 and 22.5 +/- 5.0 with a mean of 18.9 +/- 0.9 mL.min-1 x 100 g-1 during hypotension. TBF was reduced significantly at all elevated MCPs in both groups. TBF also was measured during normotension and hypotension after cuff inflation to 15 mm Hg MCP at 1-h intervals for 3 h. TBF was reduced significantly from control to 14.9 +/- 1.5 mL.min-1 x 100 g-1 after 1 h during normotension, and continued to decline to 6.1 +/- 0.9 mL.min-1 x 100 g-1 after 3 h. During hypotension, TBF decreased significantly from control to 6.1 +/- 0.6 mL.min-1 x 100 g-1 at 1 h and remained unchanged at 3 h. These findings suggest that even at 20 mm Hg MCP, significant reductions in TBF may occur. For prolonged endotracheal intubation, especially during hypotension, significant reductions in TBF may occur at even lower MCP.

Anatomy of a defective barrier: sequential glove leak detection in a surgical and dental environment.

OBJECTIVES: a) To determine the frequency of perforations in latex surgical gloves before, during, and after surgical and dental procedures; b) to evaluate the topographical distribution of perforations in latex surgical gloves after surgical and dental procedures; and c) to validate methods of testing for latex surgical glove patency. DESIGN: Multitrial tests under in vitro conditions and a prospective sequential patient study using consecutive testing. SETTING: An outpatient dental clinic at a university dental school, the operating suite in a medical school affiliated with the Veteran's Hospital, and a biomechanics laboratory. PERSONNEL: Surgeons, scrub nurses, and dental technicians participating in 50 surgical and 50 dental procedures. METHODS: We collected 679 latex surgical gloves after surgical procedures and tested them for patency by using a water pressure test. We also employed an electronic glove leak detector before donning, after sequential time intervals, and upon termination of 47 surgical (sequential surgical), 50 dental (sequential dental), and in three orthopedic cases where double gloving was used. The electronic glove leak detector was validated by using electronic point-by-point surface probing, fluorescein dye diffusion, as well as detecting glove punctures made with a 27-gauge needle. RESULTS: The random study indicated a leak rate of 33.0% (224 out of 679) in latex surgical gloves; the sequential surgical study demonstrated patency in 203 out of 347 gloves (58.5%); the sequential dental study showed 34 leaks in the 106 gloves used (32.1%); and with double gloving, the leak rate decreased to 25.0% (13 of 52 gloves tested). While the allowable FDA defect rate for unused latex surgical gloves is 1.5%, we noted defect rates in unused gloves of 5.5% in the sequential surgical, 1.9% in the sequential dental, and 4.0% in our electronic glove leak detector validating study. In the sequential surgical study, 52% of the leaks had occurred by 75 mins, and in the sequential dental study, 75% of the leaks developed by 30 mins. In terms of the anatomical localization, the thumb and forefinger accounted for more than 60% of the defects. There were no differences in the frequency of glove leaks between the left and right hand. Leak rates were highest for the surgeon (52%), followed by the first assistant (29%) and the scrub nurse (25%). No false negatives were noted using the electronic glove leak detector; one false positive was seen out of 225 gloves tested (0.44%), as noted in our validation studies. CONCLUSIONS: Significantly high glove leak rates were noted after surgical and dental procedures, indicating that the present day latex surgical gloves can become an incompetent barrier once they are used. Unused latex surgical gloves demonstrated a higher rate of defects than allowed by the Food and Drug Administration standards, indicating substantial noncompliance of quality control standards by manufacturers as well as inadequate governmental oversight. Double gloving, or the use of thicker latex surgical gloves, would probably reduce the frequency of glove leaks. Latex surgical gloves should be tested for patency before use and during surgical and dental procedures.

Pulmonary effects of body position, PEEP, and surfactant depletion in dogs.

The influence of position (sphinx, lateral, supine), surfactant depletion, and different positive end-expiratory pressure (PEEP) on functional residual capacity (FRC), series dead space (VdS) and compliance of the respiratory system (Crs) were evaluated in five dogs. Ventilation homogeneity as measured by an index (multiple breath alveolar mixing efficiency), oxygenation, and cardiovascular hemodynamics were additionally examined. The dogs were anesthetized with halothane, paralyzed, and mechanically ventilated. FRC and VdS were found to be notably large in dogs, 45 +/- 8 ml/kg and 6 +/- 1 ml/kg, respectively. FRC and ventilation homogeneity were improved in the sphinx position (prone position with upright head). Surfactant depletion by lung lavage with 37 degrees C saline caused an immediate and stable decrease in FRC, Crs, and oxygenation (P less than 0.05, respectively) for about 5 h without marked effects on the circulatory system. FRC and VdS increased with increasing PEEP. At the highest PEEP, 10 cmH2O (1 kPa), Crs decreased (P less than 0.05) and ventilation became more uneven, indicating alveolar overdistension.

Intermittent-flow expiratory ventilation (IFEV): delivery technique and principles of action--a preliminary communication.

The ventilator support utilized in acute respiratory failure can exacerbate an underlying lung injury. Various ventilation techniques have been introduced to prevent such damage by limiting tidal volume and inflation pressure, ensuring uniform expansion of the lung, and stabilizing lung volume during expiration. Acceptance of such methods has been limited. Intermittent-flow expiratory ventilation (IFEV) is the latest development in limited-excursion pulmonary ventilation. The method involves the delivery of fresh gas to the respiratory tree during expiration, thereby flushing out the anatomic deadspace and ensuring that the gas initially delivered to the alveolus with the succeeding inspiration is able to participate in gas exchange. By eliminating end-tidal gas in the conducting air passages, series deadspace is functionally reduced, permitting lowering of tidal volume and airway pressures without a corresponding reduction in CO2 removal. This effect may benefit patients who have acute lung injury by permitting ventilator settings with lower tidal volumes and peak airway pressures. The technique of IFEV delivery, a successful clinical application, and possible ways to improve IFEV efficiency are discussed.

Intracranial and spinal cord hemodynamics in the sitting position in dogs in the presence and absence of increased intracranial pressure.

The effect of the sitting position on cerebral blood flow (CBF), spinal cord blood flow (SCBF), and cerebral metabolic rate for oxygen (CMRo2) was studied in anesthetized dogs with and without increased intracranial pressure. Blood flow measurements were made at four time periods: (a) initial supine; (b) after 5 min in the sitting position; (c) after 60 min in the sitting position; and (d) 15 min after resuming the supine position. Six dogs (group 1) served as a control group with a normal intracranial pressure (ICP). In five dogs (group 2) ICP was elevated with a parietal epidural balloon 1 h before the first measurements of blood flows were made. Saline was injected incrementally into the balloon so as to reach a steady-state ICP of 30 mm Hg for 1 h. Elevation of ICP in group 2 resulted in significantly lower CBF, SCBF, and CMRo2 compared with group 1. Postural changes in group 1 did not result in any significant change in blood flow measurements whereas in group 2, after 1 h in the sitting position, there were significant decreases in CBF and SCBF compared with the initial supine measurements. There was, however, no corresponding decrease in CMRo2 in group 2 with change in position. These data suggest that both the brain and spinal cord may be at risk for ischemia during sitting position procedures under general anesthesia in the presence of elevated ICP.

The effect of magnesium sulfate administration on cerebral and cardiac toxicity of bupivacaine in dogs.

The effect of acutely elevated serum magnesium on the CNS and cardiac toxicity of bupivacaine was studied. Anesthesia was induced in mongrel dogs with thiopental, 25 mg/kg, and ventilation was controlled. Sedation was maintained with fentanyl (25 micrograms/kg bolus and 5 micrograms.kg-1h-1) and pancuronium (0.15 mg/kg bolus and 0.05 mg.kg-1h-1) provided paralysis. Two hours after the thiopental bolus, all animals received an intravenous (iv) infusion of bupivacaine (1 mg.kg-1 min-1). The control group (5 animals) received bupivacaine only. The Mg++ group (5 animals) received MgSO4 140 mg/kg iv and 80 mg.kg-1 h-1 15 min prior to beginning the bupivacaine infusion. Lead II ECG, cardiac hemodynamics, and two-channel EEG were continuously monitored. Serum magnesium concentrations in the Mg++ group rose from 0.67 mM (1.3 mEq/L) to 2.42 mM (4.8 mEq/L). The bupivacaine infusion caused PR and QRS interval prolongation in both groups, but QRS widening was greater in the control group. QT interval corrected for heart rate (QTIc) lengthened only in the control group. A depression of left ventricular stroke work index (LVSWI) occurred to an equal extent in both groups. The seizure dose of bupivacaine was not different between the two groups: 12.9 +/- 2.3 (SEM) mg/kg in the control group and 13.9 +/- 2.5 mg/kg in the Mg++ group.(ABSTRACT TRUNCATED AT 250 WORDS)

Continuous-flow apneic ventilation with small endobronchial catheters.

This study compares gas exchange and hemodynamic parameters during bronchial insufflation with two different internal diameter (ID) catheters (2.5 and 1.4 mm) at a constant mean gas exit velocity. Anesthetized, paralyzed dogs were instrumented to monitor arterial, central venous, and airway pressures, blood gases, temperature, ECG, and ventilated using continuous flow apneic ventilation (CFAV) via 2.5-mm or 1.4-mm ID bronchial insufflation catheters positioned 1.25 bronchial diameter units (BDU) beyond the carina. Initially, flow was adjusted to provide adequate oxygenation and ventilation through the 2.5-mm ID catheters. After a 30-min stabilization, physiological parameters were recorded and the mean gas exit velocity was calculated. The 2.5-mm ID insufflation catheters were then replaced by 1.4-mm ID catheters and the bronchial insufflation flow adjusted so as to produce the same mean gas exit velocity as for the 2.5-mm ID catheters. After a 30-min stabilization period, physiological parameters were again recorded. No significant differences were noted in arterial, central venous, or airway pressures, temperature, heart rate, pH, PaCO2, and PaO2 between the 2.5-mm and 1.4-mm ID bronchial insufflation catheters. However, significantly less bronchial insufflation flow (69.7%) was required to maintain oxygenation and ventilation for the 1.4-mm ID bronchial insufflation catheters.