Real-space imaging of non-collinear antiferromagnetic order with a single-spin magnetometer.

Although ferromagnets have many applications, their large magnetization and the resulting energy cost for switching magnetic moments bring into question their suitability for reliable low-power spintronic devices. Non-collinear antiferromagnetic systems do not suffer from this problem, and often have extra functionalities: non-collinear spin order may break space-inversion symmetry and thus allow electric-field control of magnetism, or may produce emergent spin-orbit effects that enable efficient spin-charge interconversion. To harness these traits for next-generation spintronics, the nanoscale control and imaging capabilities that are now routine for ferromagnets must be developed for antiferromagnetic systems. Here, using a non-invasive, scanning single-spin magnetometer based on a nitrogen-vacancy defect in diamond, we demonstrate real-space visualization of non-collinear antiferromagnetic order in a magnetic thin film at room temperature. We image the spin cycloid of a multiferroic bismuth ferrite (BiFeO3) thin film and extract a period of about 70 nanometres, consistent with values determined by macroscopic diffraction. In addition, we take advantage of the magnetoelectric coupling present in BiFeO3 to manipulate the cycloid propagation direction by an electric field. Besides highlighting the potential of nitrogen-vacancy magnetometry for imaging complex antiferromagnetic orders at the nanoscale, these results demonstrate how BiFeO3 can be used in the design of reconfigurable nanoscale spin textures.

Effects of dentifrices differing in fluoride compounds on artificial enamel caries lesions in vitro.

The aim of this study was to compare the caries-preventive effect of a stabilized stannous fluoride/sodium fluoride dentifrice containing sodium hexametaphosphate with those of a regular, solely sodium fluoride-containing and amine fluoride-containing dentifrice on pre-demineralized bovine enamel specimens using a pH-cycling model. Bovine enamel specimens with two artificial lesions each were prepared. Baseline mineral loss of both lesions was analyzed using transversal microradiography (TMR). Eighty-five specimens with a mean (SD) baseline mineral loss of 3393 (683) vol% × µm were selected and randomly allocated to five groups (n = 13/15). Treatments during pH-cycling (28 days and 2 × 20 min demineralization/day) were: brushing twice daily with slurries of AmF (1400 ppm F-), NaF (1450 ppm F-), SnF2/NaF (1100 ppm F-/350 ppm F-), and fluoride-free (FF) dentifrices or they were immersed in distilled water and remained unbrushed (NB). Subsequently, from each specimen one lesion was covered with acid-resistant varnish, while the remaining lesion was demineralized for another 14 days. Differences in integrated mineral loss (∆∆Z) were calculated between values before and after pH-cycling (∆∆Z E1) as well as before pH-cycling and after second demineralization (∆∆Z E2) using TMR. Treatments AmF and NaF induced a significantly higher mineral gain (∆∆Z E1/∆∆Z E2) compared to treatments FF and NB (p < 0.05; ANOVA test). Except for treatments AmF and NaF no significant differences in mineral loss between before and after pH-cycling could be observed (p < 0.05; t test) [∆∆Z E1: AmF:1563 (767); NaF:1222 (1246); SnF2/NaF:258 (1259); FF:-52 (1223); NB:-151 (834)]. Both dentifrices with either AmF or NaF promoted remineralization, whereas SnF2/NaF dentifrice did not promote remineralization in a biofilm-free pH-cycling model.

Strain coupling of a nitrogen-vacancy center spin to a diamond mechanical oscillator.

We report on single electronic spins coupled to the motion of mechanical resonators by a novel mechanism based on crystal strain. Our device consists of single-crystal diamond cantilevers with embedded nitrogen-vacancy center spins. Using optically detected electron spin resonance, we determine the unknown spin-strain coupling constants and demonstrate that our system resides well within the resolved sideband regime. We realize coupling strengths exceeding 10 MHz under mechanical driving and show that our system has the potential to reach strong coupling. Our novel hybrid system forms a resource for future experiments on spin-based cantilever cooling and coherent spin-oscillator coupling.

[Heterotopic pancreas in the gallbladder. Diagnosis, therapy, and course of a rare developmental anomaly of the pancreas]. / Heterotopes Pankreasgewebe in der Gallenblase. Diagnostik, Therapie und Verlauf einer seltenen Entwicklungsanomalie der Bauchspeicheldrüse.

Ectopic pancreas is a rare entity but the second most prevalent pancreatic anomaly. Heterotopic pancreas is defined as the presence of pancreatic tissue without any anatomic or vascular continuity with the main body of the pancreas. Its aetiology is not clearly established. In 1916, Poppi published for the first time evidence of heterotopic pancreas in the gallbladder. A review of the literature up to the present showed only 28 more cases worldwide of ectopic pancreas in the gallbladder. Aberrant pancreas is incidentally discovered in 2% of autopsies and has been estimated to occur once in every 500 upper abdominal explorations. Ninety per cent of ectopic pancreas is found in the stomach, duodenum, and jejunum. Mostly it is asymptomatic and benign. For this reason, therapy is indicated only in patients with symptoms such as pyloric obstruction, bleeding, and malignant transformation. Surgical resection or endoscopic mucosal resection as a newer method are recommended.

Protection against adriamycin-induced skin necrosis in the rat by dimethyl sulfoxide and alpha-tocopherol.

Extravasation of Adriamycin during i.v. infusion can cause serious local complications. We have used a rat skin model to study the protection afforded by dimethyl sulfoxide and alpha-tocopherol (vitamin E) against Adriamycin-induced skin necrosis. Topical daily application of 1 ml dimethyl sulfoxide for 2 days produced a small decrease in ulcer diameter of up to 11% at 2 weeks. Topical daily applications of 1 ml 10% alpha-tocopherol succinate in dimethyl sulfoxide for 2 days produced a marked decrease in ulcer diameter at 2 weeks of up to 68%. Daily topical application of 1 ml 10% alpha-tocopherol succinate in dimethyl sulfoxide for 7 days offered no greater protection than 2-day application. alpha-Tocopherol acetate appeared to have activity slightly less than that of alpha-tocopherol succinate in reducing ulcer size, and both compounds were considerably more active than was alpha-tocopherol alcohol. Administration of alpha-tocopherol succinate or alpha-tocopherol acetate i.p. had no significant effect upon ulcer diameter. Topically applied dimethyl sulfoxide and alpha-tocopherol may provide an effective way of treating accidentally extravasated Adriamycin in cancer patients.

Activation and inactivation of cancer chemotherapeutic agents by rat hepatocytes cocultured with human tumor cell lines.

While colony formation assays provide sensitive indices of tumor cell proliferation and growth inhibition imposed by many chemotherapeutic agents, drugs which require metabolic activation lack activity in such assays. In the present study, we have utilized freshly isolated rat hepatocytes for the activation of drugs which are metabolized by hepatic microsomal as well as extra-microsomal enzymes. Hepatocytes in fluid medium are placed over soft-agarose matrix containing tumor-derived cells (e.g., A204, A549) within 35-mm culture dishes; drug and/or drug vehicle is added directly to the hepatocyte layer, and cultures are incubated for 24 hr prior to removal of the hepatocyte layer. Tumor cell colony formation is assessed following 7 to 10 days of incubation. Cyclophosphamide was used as a prototype agent to assess utility of the coculture methodology. In vivo treatment of rats with phenobarbital prior to hepatocyte isolation enhances cyclophosphamide toxicity in vitro, whereas pretreatment with carbon tetrachloride markedly reduced subsequent in vitro cyclophosphamide cytotoxicity. Hepatocyte:tumor cell cocultures provide an efficient means to detect metabolic activation and inactivation of several selected cancer chemotherapeutic agents as well. In the presence of hepatocytes, the 50% growth-inhibitory concentrations for cyclophosphamide, indicine N-oxide, and procarbazine are markedly decreased, whereas the 50% growth-inhibitory concentrations for [2,5-bis(1-aziridinyl)-3,6-diazo-1,4-cyclohexadiene-1,4-diyl]bis(c arbamic acid)diethyl ester, 1,3-bis-chloro(2-chloroethyl)-1-nitrosourea, dacarbazine, 5-fluorouracil, ftorafur, 1-(2-chloroethyl)-3-(4-methylcyclohexyl)-1-nitrosourea, and vincristine are significantly increased. By contrast, the 50% growth-inhibitory concentrations for actinomycin D, mitomycin C, 6-mercaptopurine, and other agents are unaffected by hepatocyte presence. Cryopreserved hepatocytes exhibit detectable levels of drug activation, although inadequate for routine use. Results suggest that hepatocyte:tumor cell cocultures may be well-suited for assessing the degree to which hepatic metabolism may activate or inactivate new anticancer drugs.

Quantitative nanoscale vortex imaging using a cryogenic quantum magnetometer.

Microscopic studies of superconductors and their vortices play a pivotal role in understanding the mechanisms underlying superconductivity. Local measurements of penetration depths or magnetic stray fields enable access to fundamental aspects such as nanoscale variations in superfluid densities or the order parameter symmetry of superconductors. However, experimental tools that offer quantitative, nanoscale magnetometry and operate over large ranges of temperature and magnetic fields are still lacking. Here, we demonstrate the first operation of a cryogenic scanning quantum sensor in the form of a single nitrogen-vacancy electronic spin in diamond, which is capable of overcoming these existing limitations. To demonstrate the power of our approach, we perform quantitative, nanoscale magnetic imaging of Pearl vortices in the cuprate superconductor YBa2Cu3O7-δ. With a sensor-to-sample distance of ∼10 nm, we observe striking deviations from the prevalent monopole approximation in our vortex stray-field images, and find excellent quantitative agreement with Pearl's analytic model. Our experiments provide a non-invasive and unambiguous determination of the system's local penetration depth and are readily extended to higher temperatures and magnetic fields. These results demonstrate the potential of quantitative quantum sensors in benchmarking microscopic models of complex electronic systems and open the door for further exploration of strongly correlated electron physics using scanning nitrogen-vacancy magnetometry.

Assessment of perfusion in the diabetic foot by regional transcutaneous oximetry.

Regional transcutaneous oximetry is a new, noninvasive diagnostic technique for the investigation of peripheral vascular disease (PVD) that uses differences in limb and trunk transcutaneous PO2 to assess the adequacy of local perfusion. The application of such measurements would be of great importance in diabetes, in which limb ischemia is commonly difficult to assess. A group of diabetic subjects with symptomatic PVD was studied with regional oximetry, Doppler-assisted blood pressure measurements, and arteriography. Doppler studies correlated poorly to symptom grade and angiographic data, while oximetry clearly demonstrated limb hypoxia under the functional conditions appropriate to the patients' clinical symptomatology. The superiority of oximetry to Doppler studies was highly significant (X2 = 12.64, P less than 0.001). Regional transcutaneous oximetry should therefore be the noninvasive diagnostic test of choice in the initial evaluation of the diabetic limb for PVD. Because of its dependence on the adequacy of local oxygenation, transcutaneous oximetry is a powerful tool for investigation of the pathophysiology of PVD and will, in the future, have wide-ranging applications to the diagnosis and therapy of PVD.

Digit-symbol performance in methadone-treated ex-heroin addicts.

The digit-symbol substituion task (DSST) of the WAIS was given to working (MW) and nonworking (MNW) patients on high-dose methadone maintenance and to two comparison groups to assess the function of attention in these patients. Mean DSST scores were significantly lower for the MNW group than for the other three groups, which did not differ. However, the scores for the MNW group were within the normal range. DSST scores and lenght of methadon treatment (range: 11 months to 8 years) were positively correlated, providing no evidence of deterioration with increasing duration of treatment.

Relationship of oxygen consumption and oxygen delivery in surgical patients with ARDS.

Previous studies have described oxygen delivery (DO2) and oxygen consumption (VO2) relationships in patients with ARDS and other acute diseases that suggest occasions when VO2 may be dependent on the supply of oxygen, ie, DO2. We studied 127 postoperative patients who developed ARDS to evaluate the relationship of DO2 to VO2. We found a weak correlation between DO2 and VO2 in the total series (r = 0.49) as well as in several clinical subgroups of patients with ARDS. Moreover, we observed similar relationships in a concurrent group of 218 postoperative patients who did not develop ARDS. We also examined the DO2/VO2 data of individual patients with ARDS to identify instances where flow-dependent VO2 patterns developed into flow-independent VO2 patterns. We were able to identify an apparent plateau in the DO2/VO2 relationships in 29/50 (58 percent) patients where multiple measurements were obtained over a short period of time. Our data are consistent with the concept that the DO2/VO2 relationship in acutely ill early postoperative patients with and without ARDS is affected by antecedent circulatory problems that may lead to tissue hypoxia and tissue oxygen deficiencies that are manifest by flow dependency.

Role of oxygen debt in the development of organ failure sepsis, and death in high-risk surgical patients.

In a series of 253 high-risk surgical patients, we measured the oxygen consumption (VO2) at frequent intervals before, during, and immediately after surgical operations and calculated the rate of VO2 deficit from the measured VO2 minus the VO2 need estimated from the patient's own resting preoperative control values corrected for both temperature and anesthesia. The calculated oxygen deficit was related to multiple organ failure, complications, and outcome. The 64 patients who died all had organ failure; their cumulative VO2 deficit averaged 33.2 +/- 4.0 L/m2 (+/- SEM) at its maximum, which occurred 17.8 +/- 2.2 h after surgery. In the 31 survivors with organ failure, the cumulative VO2 deficit averaged 21.6 +/- 3.7 L/m2 at its maximum, which occurred 10.1 +/- 2.7 h after surgery (p less than 0.05). In the 158 survivors without organ failure or major complications, the maximum cumulative VO2 deficit averaged 9.2 +/- 1.3 L/m2 at 4.1 +/- 0.6 h after surgery (p less than 0.05). In a prospective randomized clinical trial, a protocol group maintained at supranormal hemodynamic and oxygen transport values had significantly reduced oxygen debt (7.6 +/- 3.4 L/m2 vs 17.3 +/- 6.8 L/m2; p less than 0.05), fewer organ failures, and lower mortality (4 percent vs 33 percent; p less than 0.05) compared with a control group maintained at normal hemodynamic values. The data demonstrate a strong relationship between the magnitude and duration of the VO2 deficit in the intraoperative and early postoperative period and the subsequent appearance of organ failure and death. The latter may be reduced when oxygen debts were prevented or minimized by augmenting naturally occurring compensations that increased oxygen delivery.

Effects of prostaglandin E1 in postoperative surgical patients with circulatory deficiency.

Hemodynamic and oxygen transport effects of PGE1 were observed in the early postoperative period before development of ARDS in two series of general surgical patients with circulatory deficiencies. The first was a series of 19 studies in 18 patients, the second was a placebo-controlled series of 20 patients (ten received PGE1 and ten received a placebo). In the first series, PGE1 was given as a trial of therapy after fluid therapy to pulmonary wedge pressures greater than 15 mm Hg failed to correct satisfactorily circulatory and metabolic functions. There were two deaths in the placebo group and none in the PGE1 group. Previous studies indicated that PGE1 disaggregates platelets and reduces local vasoconstriction in pulmonary circulation; this study suggests that PGE1 improves tissue perfusion of systemic circulation. After fluid therapy to PAOP greater than 15 mm Hg fails to restore circulatory function to optimal values. PGE1 should be considered as ancillary therapy in critically ill postoperative patients.

Hemodynamic and oxygen transport patterns for outcome prediction, therapeutic goals, and clinical algorithms to improve outcome. Feasibility of artificial intelligence to customize algorithms.

A generalized decision tree or clinical algorithm for treatment of high-risk elective surgical patients was developed from a physiologic model based on empirical data. First, a large data bank was used to do the following: (1) describe temporal hemodynamic and oxygen transport patterns that interrelate cardiac, pulmonary, and tissue perfusion functions in survivors and nonsurvivors; (2) define optimal therapeutic goals based on the supranormal oxygen transport values of high-risk postoperative survivors; (3) compare the relative effectiveness of alternative therapies in a wide variety of clinical and physiologic conditions; and (4) to develop criteria for titration of therapy to the endpoints of the supranormal optimal goals using cardiac index (CI), oxygen delivery (DO2), and oxygen consumption (VO2) as proxy outcome measures. Second, a general purpose algorithm was generated from these data and tested in preoperatively randomized clinical trials of high-risk surgical patients. Improved outcome was demonstrated with this generalized algorithm. The concept that the supranormal values represent compensations that have survival value has been corroborated by several other groups. We now propose a unique approach to refine the generalized algorithm to develop customized algorithms and individualized decision analysis for each patient's unique problems. The present article describes a preliminary evaluation of the feasibility of artificial intelligence techniques to accomplish individualized algorithms that may further improve patient care and outcome.

Prospective trial of supranormal values of survivors as therapeutic goals in high-risk surgical patients.

Survivors of high-risk surgical operations were previously observed to have significantly higher mean CI, DO2, and VO2 than nonsurvivors. The hypothesis was proposed that increased CI and DO2 are circulatory compensations for increased postoperative metabolism. We tested this hypothesis in two series. In series 1, prospectively allocated by services, mortality and morbidity of the control group were significantly greater than those of the protocol group. In series 2, patients who fulfilled previously defined high-risk criteria were preoperatively randomized to one of three monitoring/treatment groups: CVP-control group, PA-control group and PA-protocol group. Postoperative mortalities in the CVP-control and PA-control groups were not statistically significantly different, but PA-protocol group mortality was significantly reduced compared with its control group. The PA-protocol group had reduced complications, duration of hospitalization, duration in ICU, and mechanical ventilation, and reduced costs when the PA catheter was placed preoperatively and used to augment circulatory responses.

Temporal hemodynamic and oxygen transport patterns in medical patients. Septic shock.

STUDY DESIGN: Because of the gradual insidious transitions between localized infection, generalized infection, and septic shock, it is difficult to compare data of patients in various stages and to differentiate primary from secondary and tertiary events. The aim of the present study was to describe the sequential pattern of hemodynamic and oxygen transport patterns of survivors and nonsurvivors of septic shock in order to evaluate possible physiologic mechanisms and to provide a template to relate the sequence of physiologic events to biochemical mediators. PROCEDURE: A previously described defined protocol was used prospectively to study the sequence of physiologic events using specific criteria to define stages as: (a) early period, the first recorded change in cardiac output; (b) middle period, time of maximal metabolic activity defined as the highest recorded oxygen consumption (VO2); and (c) late period, the time of death or recovery. In addition, three time lines were defined as the first time mean arterial pressure fell below 70 mm Hg, the first time temperature rose above 38 degrees C, and the earliest fall in VO2. Physiologic data were aligned in actual time before or after the time these criteria were met. Invasive hemodynamic and oxygen transport variables were measured with systemic and pulmonary artery catheters; intravascular pressures, arterial and mixed venous gas levels, cardiac output, and derived calculations were made at frequent intervals and keyed to the time of the cardiac output; each set of measurements in turn was keyed to the aforementioned time periods to describe the early, middle, and late periods. RESULTS: Beginning with increased cardiac index and oxygen delivery (DO2) as the early physiologic changes, there were progressive increases in cardiac index, DO2, and VO2 throughout the early and middle periods. They were maintained above the normal range in the late stage of survivors, but fell in the last 16 h in nonsurvivors. These values were greater in survivors than in nonsurvivors throughout. There were early transient reductions in VO2 that preceded the rise in temperature and the fall in mean arterial pressure (MAP). Although 84 percent of the septic patients were hyperdynamic, there were transient hypodynamic episodes defined as cardiac index of less than 2.5 L/min.m2 in approximately 10 percent of the measurements. There were also transient preterminal hypermetabolic periods in about 8 percent of the nonsurvivors. CONCLUSION: We conclude that increased cardiac index and DO2 represent compensations for circulatory inadequacies that limit body metabolism as reflected by VO2. Cardiac index, DO2, and VO2 values of survivors were higher than those of nonsurvivors and normal values. Therapy directed toward increasing cardiac index to supranormal values empirically determined by survivors has been reported to improve outcome. Additional studies to describe temporal relationships of biochemical mediators of these physiologic patterns are needed.

Comparison of hemodynamic and oxygen transport effects of dopamine and dobutamine in critically ill surgical patients.

Hemodynamic and oxygen transport effects of dopamine and dobutamine were studied in a series of 25 critically ill postoperative general surgical patients by a prospective, randomized crossover design after maximal response to fluids had been obtained. Dopamine increased MAP, HR, CI, PvO2, DO2, and Qsp while decreasing PaO2. Dobutamine increased HR, CI, SI, stroke work, DO2, VO2, and Qsp while decreasing PAWP and SVRI and PVRI. In general, the effects of the two drugs were greater in patients in the first 72 hours after surgery. The effects of dobutamine on flow and oxygen transport were greater than those of dopamine, especially in the early postoperative period. The effects were smaller and not significant in patients more than three days after surgery, as well as in those with sepsis, respiratory failure, renal failure, age over 65 years, and hyperdynamic states, in part because of the small number of patients in each group. These data are consistent with the hypothesis that the beta 2-adrenergic action of dobutamine vasodilates the previously constricted peripheral circulation, enhances tissue perfusion by improving micro-circulatory flow distribution, and improves DO2 and VO2.

Effects of prostaglandin E1 in adult respiratory distress syndrome.

Prostaglandin E1 (PGE1, Prostin VR) in doses of 30 ng/kg . min was studied in two series of severely ill surgical patients with adult respiratory distress syndrome (ARDS). First the drug was administered in an initial trial in six patients; then a prospective, randomized, blinded trial was conducted in 10 studies on nine patients. PGE1 markedly decreased pulmonary artery pressure, pulmonary and systemic vascular resistance indexed, and venous pressures, while increasing cardiac output, arterial PO2 (PaO2), oxygen delivery, and oxygen consumption when compared with the baseline preinfusion control values and with the response of the placebo-treated control series. The PGE1 responses were greater in patients whose ARDS was primarily attributed to the postoperative state with or without sepsis and least in patients with cirrhosis. The data are consistent with the concept that the drug reduces vasoconstriction primarily in the pulmonary circulation but also in the systemic circulation; improved PaO2 usually follows the hemodynamic effect. We conclude that PGE1 may be a useful adjunctive therapy for ARDS.

Pathophysiologic classification of peripheral vascular disease by positional changes in regional transcutaneous oxygen tension.

The clinical manifestations and prognosis of peripheral vascular disease (PVD) depend upon the severity of limb hypoxia. Transcutaneous oxygen tension (Ptco2) is related to tissue oxygenation, but limb Ptco2 varies with changes in systemic as well as peripheral oxygen delivery (Do2). Previously we have found that simultaneous assessment of limb and chest Ptco2 yields a ratio, or regional perfusion index (RPI), that is independent of systemic Do2 and accurately reflects the adequacy of limb perfusion. Analysis of segmental limb Ptco2, RPI, and position-induced RPI changes was performed in 24 control limbs and 14 limbs with intermittent claudication (IC), 8 limbs with rest pain (RP), and 7 limbs with gangrene (G). Control limbs had high RPI values that varied little with position. The IC group had modestly decreased RPIs in the supine position, but extremity RPIs decreased markedly during leg elevation. Patients with RP had ischemia while supine, but the RPI improved to nearly normal upon standing. Feet with G were hypoxic even in the standing position. Segmental RPI decreases correlated with the presence of significant arterial lesions. This correlation was unaffected by diabetes. Analysis of regional transcutaneous oximetry allows classification of PVD by quantitative criteria based upon the adequacy of limb perfusion under functional conditions. RPI is characteristically high in normal persons and low in persons with G. Limbs with marginally compensated perfusion may have nearly normal RPI values under some conditions, but typical ischemic changes are elicited by positional change and exercise. The ease of such provocation of RPI decreases constitutes an index of the severity of disease. Such quantitative assessments of limb hypoxia can form the basis for a physiologic approach to arterial reconstruction.

Measurement of tissue perfusion by oxygen transport patterns in experimental shock and in high-risk surgical patients.

Survivors of high-risk general (noncardiac) surgery were observed to have cardiac index (CI) values averaging 4.5 l/min.m2, oxygen delivery (DO2) of greater than 600 ml/min.m2, and oxygen consumption (VO2) of 170 ml/min.m2. In contrast, these values were relatively normal in patients who subsequently died. A very early predictive index based on these observations was found to predict outcome in 94% of high-risk patients. The hypotheses that increased DO2 and VO2 in the survivors represent compensatory physiologic responses and that these values were appropriate therapeutic goals were tested in prospective randomized clinical trials and found to reduce mortality and morbidity significantly. The optimal goals were more easily attained with colloids, red cells, dobutamine, and vasodilators, according to their capacity to improve tissue perfusion, as reflected by increased flow and oxygen transport. The extremely complex interactions between DO2 and VO2 are reviewed.

Determination of optimal positive end-expiratory pressure by means of conjunctival oximetry.

A method for determining the optimal level of positive end-expiratory pressure (PEEP) by means of noninvasive conjunctival oxygen (PcjO2) monitoring and arterial blood gas analysis was developed from the pattern of changes in PcjO2 tension, invasive hemodynamic parameters, and oxygen transport variables during PEEP titration in a series of patients with adult respiratory distress syndrome. All patients had radial and pulmonary artery (PA) catheters inserted and blood volume was measured with 125I serum albumin before each study. During progressive increases in the level of PEEP, PcjO2 tensions reflected changes in both PaO2 and cardiac index (CI), depending on whether PEEP produced a significant decrease in CI. In patients with a stable CI, PcjO2 tensions tracked PaO2 values (rw = 0.92); in patients with a greater than a 15% decrease in CI, the conjunctival index, CjI (defined as the PcjO2/PaO2 ratio), tracked CI (rw = 0.87), excluding one patient with high cardiac output-septic shock and severe hypoxemia. PcjO2 correlated with PaO2 in the latter patient (r = 0.99) probably because conjunctival oxygen transport was limited by arterial oxygen content (PaO2 = 34 torr) rather than blood flow (CI greater than 6 L/min X m2). In patients with a greater than a 10% decrease in CI as a result of PEEP, the greater the decrease in CI, the better CjI values correlated with CI. We conclude that PcjO2 monitoring combined with repeated arterial blood gas analysis may be used to titrate PEEP therapy in patients with adult respiratory distress syndrome. In patients whose CjI significantly decreases because of PEEP, PA catheterization and measurement of cardiac output are indicated because of the likelihood of a significant (greater than 15%) decrease in CI. In the absence of a significant decrease in the CjI, optimum PEEP occurs at the level producing maximum PcjO2. It is hoped that by following the described algorithm, many patients will be spared the cost and morbidity of unnecessary PA catheterization.