An ethylene-induced cDNA encoding a lipase expressed at the onset of senescence

A cDNA clone encoding a lipase (lipolytic acyl hydrolase) expressed at the onset of petal senescence has been isolated by screening a cDNA expression library prepared from carnation flowers (Dianthus caryophyllus). The cDNA contains the lipase consensus sequence, ITFAGHSLGA, and encodes a 447-amino acid polypeptide with a calculated molecular mass of 50.2 kDa that appears to be a cytosolic protein. Over-expression of the clone in Escherichia coli yielded a protein of the expected molecular weight that proved capable of deesterifying fatty acids from p-nitrophenylpalmitate, tri-linolein, soybean phospholipid, and Tween in both in vitro and in situ assays of enzyme activity. The abundance of the lipase mRNA increases just as carnation flowers begin to senesce, and expression of the gene is also induced by treatment with ethylene. Southern blot analyses of carnation genomic DNA have indicated that the lipase is a single copy gene. The lipase gene is also expressed in carnation leaves and is up-regulated when the leaves are treated with ethylene. Deesterification of membrane lipids and ensuing loss of membrane structural integrity are well established early events of plant senescence, and the expression pattern of this lipase gene together with the lipolytic activity of its cognate protein indicate that it plays a fundamentally central role in mediating the onset of senescence.

The effects of early and repeated prone positioning in pediatric patients with acute lung injury

STUDY OBJECTIVE

To describe the physiologic changes and to evaluate the safety of placing pediatric patients with acute lung injury (ALI) prone for 20 h/d during the acute phase of their illness.

DESIGN

Single-center prospective case series.

SETTING

Tertiary-level pediatric ICU.

PATIENTS

Consecutive patients with bilateral pulmonary parenchymal disease requiring intubation and mechanical ventilation with a PaO(2)/fraction of inspired oxygen (FIO(2)) ratio </= 300 mm Hg.

INTERVENTIONS

Patients were enrolled as soon as possible after meeting criteria and were placed in a prone position for 20 h/d daily until clinical improvement or death occurred.

MEASUREMENTS AND RESULTS

Twenty-five pediatric patients who had ALI/ARDS, ranging in age from 2 months to 17 years, were placed in a prone position within 19 h of meeting the study criteria for a median time of 4 days, which accounted for 47% of their time receiving mechanical ventilation. Eighty-four percent of patients (n = 21) were categorized as overall responders to prone positioning because they experienced more days of increases of >/= 20 mm Hg in PaO(2)/FIO(2) ratio or a decrease of >/= 10% in oxygenation index when shifted from a supine to a prone position during the study period. During the 107 patient-days and 214 positioning cycles, no critical incidents occurred. Furthermore, no patient experienced a persistent decrease in oxygen saturation as measured by pulse oximetry (SpO(2)) of > 10% from values obtained when in the supine position, failed to keep their SpO(2) at > 85%, or experienced an increased respiratory rate of > 40 breaths/min when prone. Using the COMFORT score, patients were objectively rated to be equally comfortable in both the supine and prone positions. Patients also were able to resume spontaneous ventilation and to progress toward endotracheal extubation while in the prone position. Iatrogenic injury associated with prolonged prone positioning included stage II pressure ulcers in six patients (24%).

CONCLUSIONS

The pediatric patients in this series demonstrated improvements in oxygenation without serious iatrogenic injury after prone positioning. This study provides a foundation for a prospective randomized study investigating the effect of early and repeated prone positioning on clinical outcomes in pediatric patients with ALI.

Evidence for covalent linkage between xyloglucan and acidic pectins in suspension-cultured rose cells

Neutral xyloglucan was purified from the cell walls of suspension-cultured rose (Rosa sp. 'Paul's Scarlet') cells by alkali extraction, ethanol precipitation and anion-exchange chromatography on 'Q-Sepharose FastFlow'. The procedure recovered 70% of the total xyloglucan at about 95% purity in the neutral fraction. The remaining 30% of the xyloglucan was anionic, as demonstrated both by anion-exchange chromatography at pH 4.7 and by high-voltage electrophoresis at pH 6.5. Alkali did not cause neutral xyloglucan to become anionic, indicating that the anionic nature of the rose xyloglucan was not an artefact of the extraction procedure. Pre-incubation of neutral [3H]xyloglucan with any of ten non-radioactive acidic polysaccharides did not cause the radioactive material to become anionic as judged by electrophoresis, indicating that stable complexes between neutral xyloglucan and acidic polysaccharides were not readily formed in vitro. The anionic xyloglucan did not lose its charge in the presence of 8 M urea or after a second treatment with NaOH, indicating that its anionic nature was not due to hydrogen-bonding of xyloglucan to an acidic polymer. Proteinase did not affect the anionic xyloglucan, indicating that it was not associated with an acidic protein. Cellulase converted the anionic xyloglucan to the expected neutral nonasaccharide and heptasaccharide, indicating that the repeatunits of the xyloglucan did not contain acidic residues. Endo-polygalacturonase converted about 40% of the anionic xyloglucan to neutral material. Arabinanase and galactanase also converted appreciable proportions of the anionic xyloglucan to neutral material. These results show that about 30% of the xyloglucan in the cell walls of suspension-cultured rose cells exists in covalently-linked complexes with acidic pectins.

Single-breath CO2 analysis as a predictor of lung volume change in a model of acute lung injury

OBJECTIVE

To examine the utility of single-breath CO2 analysis as a measure of lung volume change in a model of acute lung injury.

SETTING

Animal laboratory in a university-affiliated medical center.

DESIGN

Prospective, animal cohort study comparing 21 variables derived from single-breath CO2 analysis with lung volume measurements determined by nitrogen washout.

SUBJECTS

Seven lambs with saline lavage-induced acute lung injury.

METHODS

Animals were treated with repetitive saline lavage to achieve a uniform degree of acute lung injury (PaO2 < 100 torr [13.32 kPa] on FiO2 of 1.0). Twenty-one derived components of the CO2 expirogram were evaluated as predictors of lung volume change. Lung volume was manipulated by 3-cm H2O incremental increases in positive end-expiratory pressure from 0 to 21 cm H2O and ranged between 90 and 765 mL.

MEASUREMENTS AND MAIN RESULTS

Fifty-five measurements of lung volume were available for comparison with derived variables from the CO2 expirogram. Stepwise linear regression identified five variables that were most predictive of lung volume change: a) dynamic lung compliance; b) the slope of phase III; c) the slope of phase II divided by the mixed expired CO2 concentration; d) airway deadspace; and e) PaO2/FIO2 ratio. The multivariate equation was highly statistically significant and explained 94% of the variance (adjusted r2 = .94, p < .0001). The bias and precision of the calculated lung volume were 10.9 and 55.9, respectively. The mean percentage difference for the lung volume estimate derived from the single-breath CO2 analysis station was 3.3%.

CONCLUSIONS

Our data indicate that analysis of the CO2 expirogram can yield accurate information about lung volume in animals with saline lavage-induced acute lung injury. Specifically, five variables derived from a plot of expired CO2 concentration vs. expired volume predict changes in lung volume in healthy lambs with an adjusted coefficient of determination of 0.94. We hope to further define the utility of this technique by prospective application of this methodology in the clinical setting.

Production of tomato flavor volatiles from a crude enzyme preparation using a hollow-fiber reactor

In recent years there has been an increase in the interest in the production of compounds by isolation from natural sources or through processes that can be deemed "natural". This is of particular interest in the food and beverage industry for flavors and aromas. Hexanal, organoleptically known to possess "green character", is of considerable commercial interest. The objective of this study was to determine if the enzyme template known to be responsible for the synthesis of hexanal from linoleic acid (18:2) in tomato fruits could be harnessed using a hollow-fiber reactor. A hollow-fiber reactor system was set up and consisted of a XAMPLER ultrafiltration module coupled to a reservoir. The enzyme template was extracted from ripe tomato fruits and processed through an ultrafiltration unit (NMWC of 100 kDa) to produce a retentate enriched in soluble and membrane-associated lipoxygenase (LOX) and hydroperoxide lyase (HPL). This extract was recirculated through the lumen of the hollow-fiber ultrafiltration unit with the addition of substrate in the form of linoleic acid, with buffer addition to the reaction flask to maintain a constant retentate volume. Product formation was measured in the permeate using solid phase microextraction (SPME) developed for this system. At exogenous substrate concentrations of 16 mM and a transmembrane pressure of 70 kPa, hexanal production rates are in the order of 5.1 microg/min. Addition of Triton X-100 resulted in membrane fouling and reduced flux. The reactor system has been run for periods of up to 1 week and has been shown to be stable over this period.

Pediatric trauma management in a rural Wisconsin trauma center

OBJECTIVE

To determine the results of pediatric trauma care managed with a cooperative effort by general surgeons and pediatric intensivists in comparison to national standards.

DESIGN

Retrospective chart review.

SETTING

Referral level II trauma center in rural Wisconsin.

PATIENTS

All pediatric trauma patients age 16 and younger admitted to the hospital from 1990 to 1993.

METHODS

Demographics, mechanisms of injury, revised trauma score (RTS), injury severity score (ISS), surgical procedures, need for intensive care, and outcome were examined. All patients were primarily managed by the trauma surgery service. Those patients requiring intensive care were managed jointly by the trauma surgery service and pediatric intensivists. Outcome was predicted by TRISS analysis; patients identified as "unexpected deaths" underwent critical clinical review to determine potential for survival.

RESULTS

There were 531 pediatric trauma admissions. The mean age was 9.0 +/- 6.2 (SEM) years and two thirds of the patients were boys. Over half of all injuries were from falls, recreational activities, and motor vehicle crashes. There were few penetrating injuries. The mean RTS was 7.58 +/- 0.05, and the majority of patients had an ISS below 10. Sixty-two percent of patients required surgical procedures, most of which were orthopedic. Fourteen percent of patients were admitted to the pediatric intensive care unit. There were 13 deaths for a mortality rate of 2.4%. TRISS analysis identified six deaths as unexpected. Four drownings were not included in TRISS analysis, and there were no unexpected survivors. Of the six unexpected deaths, there were no significant management errors identified on careful review.

CONCLUSIONS

Cooperation between general surgeons and pediatric intensivists can result in excellent pediatric trauma care in a rural level II trauma center.

Same admission colon resection with primary anastomosis for acute diverticulitis

Current standard of care for complicated diverticulitis includes urgent resection with colostomy versus antibiotic treatment, followed by delayed resection with primary anastomosis at a second admission. In certain circumstances, it is possible to perform resection and anastomosis on the same admission for acute diverticulitis. A retrospective review was completed for patients undergoing surgery for diverticulitis from 1991 to 1998. Groups included: 1) sigmoid resection with primary anastomosis on same admission (n = 18); 2) resection with protective end colostomy (n = 16); and 3) in-patient antibiotic treatment alone, followed by a second admission for resection with primary anastomosis (n = 5). Four patients initially treated with antibiotics worsened symptomatically or developed radiographic evidence of perforation and required resection with colostomy. Five patients in Group 1 had abscesses or contained perforations based on radiographic studies. Findings on CT scans did not predict treatment. Group 1 patients had uneventful recoveries and few minor complications (wound infections and an incisional hernia). One anastomotic leak occurred in Group 2 after colostomy closure. Although there will continue to be a role for emergent operation for diverticulitis, same admission sigmoid resection with primary anastomosis after antibiotic treatment is safe, uses a shorter course of antibiotics, and has a low complication rate.

A fully human antibody neutralising biologically active human TGFbeta2 for use in therapy

Phage display provides a methodology for obtaining fully human antibodies directed against human transforming growth factor-beta (TGFbeta) suitable for the treatment of fibrotic disorders. The strategy employed was to isolate a human single chain Fv (scFv) fragment that neutralises human TGFbeta2 from a phage display repertoire, convert it into a human IgG4 and then determine its TGFbeta binding and neutralisation properties and its physical characteristics. Several scFv fragments binding to TGFbeta2 were isolated by panning of an antibody phage display repertoire, and subsequent chain shuffling of the selected V(H) domains with a library of V(L) domains. The three most potent neutralising antibodies were chosen for conversion to IgG4 format. The IgG4 antibodies were ranked for their ability to neutralise TGFbeta2 and the most potent, 6B1 IgG4, was chosen for further characterisation. 6B1 IgG4 has a high affinity for TGFbeta2 with a dissociation constant of 0.89 nM as determined using the BIAcore biosensor and only 9% cross-reactivity with TGFbeta3 (dissociation constant, 10 nM). There was no detectable binding to TGFbeta1. 6B1 IgG4 strongly neutralises (IC50 = 2 nM) the anti-proliferative effect of TGFbeta2 in bioassays using TF1 human erythroleukaemia cells. Similarly, there was strong inhibition of binding of TGFbeta2 to cell surface receptors in a radioreceptor assay using A549 cells. 6B1 IgG4 shows no detectable cross-reactivity with related or unrelated antigens by immunocytochemistry or ELISA. The 6B1 V(L) domain has entirely germline framework regions and the V(H) domain has only three non-germline framework amino acids. This, together with its fully human nature, should minimise any potential immunogenicity of 6B1 IgG4 when used in therapy of fibrotic diseases mediated by TGFbeta2.

Rapid determination of aspartate enantiomers in tissue samples by microdialysis coupled on-line with capillary electrophoresis

Microdialysis was coupled on-line with derivatization by o-phthalaldehyde and beta-mercaptoethanol and optically gated capillary electrophoresis to determine D- and L-aspartate in tissue samples obtained from rats. The microdialysis probe was inserted into a homogenized tissue sample which allowed generation of a continuous sample stream that was filtered and deproteinated. With 7.5 mM beta-cyclodextrin (CD) in the electrophoresis buffer, the enantiomers of interest could be resolved in 3 s with an electric field of 2500 V/cm over a separation length of 15 mm. Values of D- and L-aspartate in different tissues agreed well with those obtained by an HPLC procedure that required protein precipitation, centrifugation, and extraction. The speed and compatibility with automation of the microdialysis/CE method may make it a general approach for a variety of applications involving high-throughput analysis or sensorlike operation.

Surgical approach to cecal diverticulitis

BACKGROUND

Cecal diverticulitis is a rare condition in the Western world, with a higher incidence in people of Asian descent. The treatment for cecal diverticulitis has ranged from expectant medical management, which is similar to uncomplicated left-sided diverticulitis, to right hemicolectomy.

STUDY DESIGN

A retrospective chart review was conducted of the 49 patients treated for cecal diverticulitis at Olive View-UCLA Medical Center from 1976 to 1998. This was the largest-ever single-institution review of cecal diverticulitis reported in the mainland US.

RESULTS

The clinical presentation was similar to that of acute appendicitis, with abdominal pain, low-grade fever, nausea/vomiting, abdominal tenderness, and leukocytosis. Operations performed included right hemicolectomy in 39 patients (80%), diverticulectomy in 7 patients (14%), and appendectomy with drainage of intraabdominal abscess in 3 patients (6%). Of the 7 patients who had diverticulectomy, 1 required right hemicolectomy at 6 months followup for continued symptoms. Of the three patients who underwent appendectomy with drainage, all required subsequent hemicolectomy for continued inflammation. Of the 39 patients who received immediate hemicolectomies, there were complications in 7 (18%), with no mortality.

CONCLUSIONS

We endorse an aggressive operative approach to the management of cecal diverticulitis, with the resection of all clinically apparent disease at the time of the initial operation. In cases of a solitary diverticulum, we recommend the use of diverticulectomy when it is technically feasible. When confronted with multiple diverticuli and cecal phlegmon, or when neoplastic disease cannot be excluded, we advocate immediate right hemicolectomy. This procedure can be safely performed in the unprepared colon with few complications. Excisional treatment for cecal diverticulitis prevents the recurrence of symptoms, which may be more common in the Western population.

Ticarcillin/clavulanate versus imipenem/cilistatin for the treatment of infections associated with gangrenous and perforated appendicitis

The objective of this study was to compare ticarcillin/clavulanate given at 3.1 g every 6 hours with imipenem/cilistatin given at 500 mg every 6 hours for the treatment of infections associated with gangrenous or perforated appendicitis. One hundred thirty-seven patients were found to have gangrenous or perforated appendicitis and received the study medication for 3 to 5 days in a double-blinded, randomized manner. Clinical success was similar for the two treatment groups, 96.9 and 95.9 per cent in the ticarcillin/clavulanate and imipenem/cilistatin groups, respectively (P=0.99; 95% confidence interval for the difference was -5.6% to 7.6%). Bacteriologic success at the end of therapy was similar in the two groups, 100 and 98.4 per cent in the ticarcillin/clavulanate and imipenem/ cilistatin groups, respectively (P=0.99; 95% confidence interval for the difference was -1.8% to 4.7%). The occurrence of adverse events related to treatment was similar for the two groups (P=0.31) and led to study withdrawal for four patients (one with ticarcillin/clavulanate and three with imipenem/ cilistatin). Ticarcillin/clavulanate given at 3.1 g every 6 hours is as effective and as safe as imipenem/ cilistatin given at 500 mg every 6 hours for treatment of gangrenous or perforated appendicitis.

A new ventilator improves CO2 removal in newborn lambs with congenital diaphragmatic hernia

OBJECTIVES

To demonstrate improved ventilation with intratracheal pulmonary ventilation (ITPV) in new-born lambs with congenital diaphragmatic hernia, using a new microprocessor controlled ITPV-specific ventilator.

DESIGN

Prospective study, with each animal serving as its own control (paired data).

SETTING

Large animal research laboratory.

SUBJECTS

Diaphragmatic hernias were created surgically in seven fetal sheep on gestational day 100 (term = 145 days).

INTERVENTIONS

Lambs (2.7 to 5.0 kg) were delivered by cesarean section anywhere between gestational days 136 and 140. Arterial and venous catheterizations, bilateral chest tube thoracostomies, and tracheostomies were performed while the lambs received placental bypass. Initially, congenital diaphragmatic hernia lambs were supported on conventional pressure control mechanical ventilation to achieve steady state with measurements of baseline vital signs, arterial blood gases, and ventilatory settings. ITPV was instituted while maintaining constant peak carinal pressures and oxygen saturations. Statistical comparisons were made using the paired t-test.

MEASUREMENTS AND MAIN RESULTS

Postductal Paco2 decreased from 110+/-21 (SD) torr (14.7+/-2.8 kPa) to 52+/-24 torr (6.93+/-3.2 kPa; p= .0014) on ITPV. Simultaneously, pH improved from 7.04+/-0.07 to 7.31+/-0.15 (p = .0012) and minute ventilation increased from 0.66+/-0.40 to 4.00+/-1.35 L/min (p = .0016). Peak carinal pressures and postductal Pao2 were unchanged.

CONCLUSIONS

ITPV significantly improved CO2 removal in newborn lambs with diaphragmatic hernias without increasing airway pressures or changing oxygenation. Based on these results, we are conducting human clinical trials.

His...Asp catalytic dyad of ribonuclease A: conformational stability of the wild-type, D121N, D121A, and H119A enzymes

Residue His119 acts as an acid/base during the cleavage/hydrolysis reactions catalyzed by bovine pancreatic ribonuclease A (RNase A). In the native enzyme, His119 forms a hydrogen bond with Asp121. This His...Asp dyad is conserved in all homologous pancreatic ribonucleases of known sequence. Yet, replacing Asp121 with an asparagine or alanine residue does not have a substantial effect on either structure or function [Schultz, L. W., Quirk, D. J., and Raines, R. T. (1998) Biochemistry 37, 8886-8898]. Here, the pH dependencies of the conformational stabilities of wild-type RNase A and the D121N, D121A, and H119A variants were determined by monitoring thermal stability over the pH range 1.2-6.0. Replacing Asp121 with an asparagine or alanine residue results in a loss of conformational stability at pH 6.0 of deltadeltaG(o) = 2.0 kcal/mol, from a total of 9.0 kcal/mol. The magnitude of this loss is similar to that to transition-state binding during catalysis. As the pH decreases, the aspartate residue becomes protonated and deltadeltaG(o) decreases. D121N RNase A and D121A RNase A are approximately equivalent in conformational stability. This equivalence arises from compensating changes to enthalpy and entropy. A general analytical method was developed to determine the value of the pKa of a residue in the native and denatured states of a protein by comparing the pH-stability profile of the wild-type protein with that of a variant in which the ionizable residue is replaced with a nonionizable one. Accordingly, Asp121 was found to have pKa values of approximately 2.4 and 3.4 in the native and denatured states, respectively, of wild-type RNase A. This change in pKa can account fully for the differential effects of pH on the conformational stabilities of the wild-type and variant proteins. We conclude that the His...Asp catalytic dyad in pancreatic ribonucleases has two significant roles: (1) to position the proper tautomer of His119 for catalysis and (2) to enhance the conformational stability of the native enzyme. Most enzymic residues contribute to catalysis or stability (or neither). Asp121 of RNase A is a rare example of a residue that contributes equally to both.

White blood cell count is a poor predictor of severity of disease in the diagnosis of appendicitis

The white blood cell (WBC) count is considered to be a useful test in the diagnosis of appendicitis. The purpose of this study was to examine the clinical features of patients with normal WBC appendicitis and also to determine whether a higher WBC count correlates with a more advanced stage of appendicitis. Patients with pathologically confirmed appendicitis from January 1989 to December 1994 were included in the study (n = 1919). The age, gender, temperature, length of hospital stay, and severity of disease (1 = acute appendicitis; 2 = gangrenous appendicitis; 3 = perforated appendicitis with abscess formation; 4 = appendicitis with diffuse peritonitis) were compared for patients with a normal WBC count (range, 3.8-10.9) versus those who had an elevated WBC count. A normal WBC count was seen in 11 per cent of patients (n = 209). There was no difference in age, temperature, gender, or severity of disease in the patients with a normal WBC count compared with those with an elevated WBC count (P > 0.05). The severity of disease of patients with a normal WBC count were: 1 = 58 per cent; 2 = 13 per cent; 3 = 7 per cent; and 4 = 22 per cent. For patients with an elevated WBC count the scores were: 1 = 57 per cent; 2 = 17 per cent; 3 = 13 per cent; and 4 = 14 per cent. The proportion of gangrenous and perforated appendicitis in the patients with a normal WBC count is the same as in the patients with an elevated WBC count.

Faculty Preparation: A New Solution to an Old Problem

Concern regarding adequate faculty preparation has been an issue in nursing for many years. Because of the small number of nurses with educational preparation, expert clinicians rather than educators increasingly have filled faculty positions. Although the clinical expertise of this faculty is extremely valuable, they lack critical educational skills. This creates a dilemma for administrators, senior faculty, and the clinicians themselves. This article presents a new solution to this continuing problem. The development, purpose, and outcomes of the Teacher Education Center at the University of Pennsylvania are described. This center has met with success in preparing a specific group of expert clinicians, nurse practitioners, and nurse midwives for their faculty roles.

Association of an intracranial arteriovenous malformation and a meningioma

A case of a simultaneously discovered arteriovenous malformation (AVM) and a meningioma is presented. A review of the literature revealed only four similar cases, but there have been 30 reports of other intracranial tumors in association with AVM. The possible mechanisms of this rare association are discussed.

Molecular characterization of an Arabidopsis gene encoding hydroperoxide lyase, a cytochrome P-450 that is wound inducible

Hydroperoxide lyase (HPL) cleaves lipid hydroperoxides to produce volatile flavor molecules and also potential signal molecules. We have characterized a gene from Arabidopsis that is homologous to a recently cloned HPL from green pepper (Capsicum annuum). The deduced protein sequence indicates that this gene encodes a cytochrome P-450 with a structure similar to that of allene oxide synthase. The gene was cloned into an expression vector and expressed in Escherichia coli to demonstrate HPL activity. Significant HPL activity was evident when 13S-hydroperoxy-9(Z),11(E),15(Z)-octadecatrienoic acid was used as the substrate, whereas activity with 13S-hydroperoxy-9(Z),11(E)-octadecadienoic acid was approximately 10-fold lower. Analysis of headspace volatiles by gas chromatography-mass spectrometry, after addition of the substrate to E. coli extracts expressing the protein, confirmed enzyme-activity data, since cis-3-hexenal was produced by the enzymatic activity of the encoded protein, whereas hexanal production was limited. Molecular characterization of this gene indicates that it is expressed at high levels in floral tissue and is wound inducible but, unlike allene oxide synthase, it is not induced by treatment with methyl jasmonate.

Single-breath CO2 analysis as a predictor of lung volume in a healthy animal model during controlled ventilation

OBJECTIVE

To examine the utility of single-breath CO2 analysis as a measure of lung volume.

DESIGN

A prospective, animal cohort study comparing 21 parameters derived from single-breath CO2 analysis with lung volume measurements determined by nitrogen washout in animals during controlled ventilation.

SETTING

An animal laboratory in a university-affiliated medical center.

SUBJECTS

Seven healthy lambs.

INTERVENTIONS

The single-breath CO2 analysis station consists of a mainstream capnometer, a variable orifice pneumotachometer, a signal processor and computer software with capability for both on- and off-line data analysis. Twenty-one derived components of the CO2 expirogram were evaluated as predictors of lung volume. Lung volume was manipulated by 3 cm H2O incremental increases in positive end-expiratory pressure from 0 to 21 cm H2O, and ranged between 147 and 942 mL.

MEASUREMENTS AND MAIN RESULTS

Fifty-five measurements of lung volume were available for comparison with derived variables from the CO2 expirogam. Stepwise linear regression identified four variables that were most predictive of lung volume: a) dynamic lung compliance; b) the slope of phase 3; c) the slope of phase 2 divided by the mixed expired CO2 tension; and d) airway deadspace. The multivariate equation was highly statistically significant and explained 94% of the variance (adjusted r2 =.94, p < .0001). The bias and precision of the calculated lung volume was .00 and 51, respectively. The mean percent difference for the lung volume estimate derived from the single-breath CO2 analysis station was 0.79%.

CONCLUSIONS

Our data indicate that analysis of the CO2 expirogram can yield accurate information about lung volume. Specifically, four variables derived from a plot of expired CO2 concentration vs. expired volume predict changes in lung volume in healthy lambs with an adjusted coefficient of determination of .94. Prospective application of this technology in the setting of lung injury and rapidly changing physiology is essential in determining the clinical usefulness of the technique.

Pulmonary blood flow distribution during partial liquid ventilation

Regional pulmonary blood flow was investigated with radiolabeled microspheres in four supine lambs during the transition from conventional mechanical ventilation (CMV) to partial liquid ventilation (PLV) and with incremental dosing of perfluorocarbon liquid to a cumulative dose of 30 ml/kg. Four lambs supported with CMV served as controls. Formalin-fixed, air-dried lungs were sectioned according to a grid; activity was quantitated with a multichannel scintillation counter, corrected for weight, and normalized to mean flow. During CMV, flow in apical and hilar regions favored dependent lung (P < 0.001), with no gradient across transverse planes from apex to diaphragm. During PLV the gradient within transverse planes found during CMV reversed, most notably in the hilar region, favoring nondependent lung (P = 0.03). Also during PLV, flow was profoundly reduced near the diaphragm (P < 0.001), and across transverse planes from apex to diaphragm a dose-augmented flow gradient developed favoring apical lung (P < 0.01). We conclude that regional flow patterns during PLV partially reverse those noted during CMV and vary dramatically within the lung from apex to diaphragm.

Usefulness of proton MR spectroscopy in the evaluation of temporal lobe epilepsy

OBJECTIVE

The purpose of our study was to compare the ability of MR spectroscopy with that of standard presurgical methods to accurately lateralize the abnormal hippocampus in a group of patients with complex partial seizures.

SUBJECTS AND METHODS

Ten healthy volunteers (five male, five female) without a history of seizures, significant head trauma, or other neurologic abnormalities were chosen to participate in the study. Twelve consecutive patients (three male, nine female) having intractable temporal lobe epilepsy and undergoing presurgical evaluation for temporal lobectomy were chosen to participate in the study. The condition of all patients was refractory to medications. All patients underwent presurgical examination with interictal and video ictal electroencephalography, ictal single-photon emission computed tomography, interictal positron emission tomography, MR imaging, and neuropsychologic testing. When noninvasive data were inconclusive, depth or grid recordings were performed. The results of MR spectroscopy were also compared with postsurgical seizure control as defined by the Engel classification.

RESULTS

Nine (90%) of 10 control subjects showed no significant difference in N-acetyl aspartate. One control subject showed 16% asymmetry in N-acetyl aspartate between sides. The control group showed no statistically significant differences in ratios of N-acetyl aspartate:creatine, N-acetyl aspartate:choline, or creatine:choline when comparing sides (p < .05). All 12 patients showed clearly lateralizing values identified by the index of asymmetry in N-acetyl aspartate (range, 24-93%), with a mean difference of 51% (SD, 22) (p = .01). Additionally, as a group, statistically significant indexes of asymmetry (p = .01) were seen in ratios of N-acetyl aspartate:choline (mean, 42; SD, 22%), N-acetyl aspartate:creatine (mean, 41; SD, 27), and N-acetyl aspartate:creatine + choline (mean, 42; SD, 22). Using an N-acetyl aspartate index of asymmetry of greater than 15%, which represents the mean index of asymmetry of the control subjects +/- two SDs, as our cutoff level for lateralization, the correct side was identified in all patients. When comparing both hippocampi using an asymmetry index of 15% for N-acetyl aspartate:choline + creatine, 11 (92%) of 12 were correctly lateralized. When comparing the unaffected temporal lobes between patients and control subjects, no statistically significant differences were detected in any metabolites or ratios.

CONCLUSION

Our study agrees with others in showing decreased N-acetyl aspartate in the hippocampus of seizure patients when compared with control subjects. Using N-acetyl aspartate, N-acetyl aspartate:creatine, N-acetyl aspartate:choline, and N-acetyl aspartate:creatine + choline as our parameters, patients with mesial temporal lobe epilepsy were correctly lateralized with MR spectroscopy when compared with clinical consensus criteria. We consider MR spectroscopy to be complementary to MR imaging. Both studies can be performed as a single integrated examination.

MR spectroscopy in the evaluation of epilepsy

MR spectroscopy may be a helpful, reliable, noninvasive test with which to lateralize the seizure focus in patients with partial complex seizures. MR spectroscopy is complementary to other studies, especially MR imaging, and both may be performed in a single integrated examination and result in improved surgical management and outcome.