Feature selectivity is stable in primary visual cortex across a range of spatial frequencies

Reliable perception of environmental signals is a critical first step to generating appropriate responses and actions in awake behaving animals. The extent to which stimulus features are stably represented at the level of individual neurons is not well understood. To address this issue, we investigated the persistence of stimulus response tuning over the course of 1–2 weeks in the primary visual cortex of awake, adult mice. Using 2-photon calcium imaging, we directly compared tuning stability to two stimulus features (orientation and spatial frequency) within the same neurons, specifically in layer 2/3 excitatory neurons. The majority of neurons that were tracked and tuned on consecutive imaging sessions maintained stable orientation and spatial frequency preferences (83% and 76% of the population, respectively) over a 2-week period. Selectivity, measured as orientation and spatial frequency bandwidth, was also stable. Taking into account all 4 parameters, we found that the proportion of stable neurons was less than two thirds (57%). Thus, a substantial fraction of neurons (43%) were unstable in at least one parameter. Furthermore, we found that instability of orientation preference was not predictive of instability of spatial frequency preference within the same neurons. Population analysis revealed that noise correlation values were stable well beyond the estimated decline in monosynaptic connectivity (~250–300 microns). Our results demonstrate that orientation preference is stable across a range of spatial frequencies and that the tuning of distinct stimulus features can be independently maintained within a single neuron.

Treatment of severe systemic inflammatory response syndrome and sepsis with a novel bradykinin antagonist, deltibant (CP-0127). Results of a randomized, double-blind, placebo-controlled trial. CP-0127 SIRS and Sepsis Study Group

OBJECTIVE

To test the effect of a novel bradykinin antagonist, deltibant (CP-0127), on survival, organ dysfunction, and other outcomes in patients with the systemic inflammatory response syndrome (SIRS) and presumed sepsis.

DESIGN

Multicenter, randomized, placebo-controlled, double-blind, parallel, dose-ranging trial. Follow-up for 28 days or until death.

SETTING

A total of 47 US referral hospitals.

PATIENTS

A total of 504 patients with SIRS and documented evidence of infection plus either hypotension or dysfunction of 2 organ systems.

INTERVENTIONS

Three-day continuous intravenous infusion of either placebo or 1 of 3 doses (0.3, 1.0, or 3.0 microg x kg(-1) x min(-1)) of deltibant. Concurrent therapy at the discretion of the treating physician.

MAIN OUTCOME MEASURE

Risk-adjusted, 28-day, log-normal intent-to-treat survival analysis. Risk adjustment was performed using a study-specific risk model derived from the APACHE III database.

RESULTS

Deltibant had no significant effect on risk-adjusted 28-day survival. In a posthoc analysis, risk-adjusted 7-day survival showed a nonsignificant trend toward improvement (P=.09). The 28-day risk-adjusted survival in the prospectively defined subset of patients with gram-negative infections showed a statistically significant improvement (P=.005).

CONCLUSIONS

Deltibant may have some effect on survival in patients with SIRS and gram-negative sepsis; however, additional studies would be required to prove this.

Cromolyn sodium is effective in adult chronic asthmatics

We studied 68 chronic asthmatic patients, 18 to 76 yr of age, with a percent predicted FEV1 between 33 and 81, comparing cromolyn sodium with placebo. We used a double-blind, comparative group trial design. A 4-wk baseline period was followed by 3 months of active treatment or placebo. Patients recorded symptom severity and frequency of study drug and concomitant medication usage on daily diary cards. At each clinic visit, patients independently assessed the effectiveness of the test medication in controlling their asthma. Physicians also assessed the severity of the patients' symptoms, pulmonary function, and effectiveness of test medication at monthly intervals. Methacholine challenges were done pre- and post-treatment. Use of concomitant therapy was reduced according to a specified schedule. There was significant improvement in the severity of daytime asthma, nighttime asthma, and cough as assessed by the patients in the cromolyn sodium group. Mean use of concomitant medications decreased significantly in cromolyn sodium patients. Despite the reductions in the use of bronchodilators, pulmonary function (FEV1, FVC, FEF25-75) improved significantly in the cromolyn sodium group. Similar improvements did not occur in the control group. The physicians' assessments of symptoms showed significant improvement in favor of the cromolyn sodium group. Both physicians and patients judged cromolyn sodium to be moderately or very effective for 61% of the patients as compared to 27% (by physicians) and 24% (by patients) in the placebo group. There was no significant difference in methacholine response between the two groups, although the mean value for methacholine sensitivity in the cromolyn sodium group was significantly less at the end of the study than at baseline.(ABSTRACT TRUNCATED AT 250 WORDS)

Pleural fluid pH in malignant effusions. Diagnostic, prognostic, and therapeutic implications

STUDY OBJECTIVE

To determine whether the measurement of pleural fluid pH in malignant effusions has diagnostic use, predicts survival, and has therapeutic implications.

DESIGN

A prospective comparison of cytologic examinations and pleural biopsy results, survival, and response to chemical pleurodesis with tetracycline in patients with normal-pH (7.30 or greater) and low-pH (less than 7.30) malignant pleural effusions.

SETTING

Academic medical center, university referral hospital, city hospital, and Veterans Administration hospital.

PATIENTS

Sixty patients with malignant pleural effusions, proven at either initial thoracentesis by cytologic examination or within 4 months of initial thoracentesis by repeat thoracentesis, thoracotomy, or autopsy, were followed until death.

INTERVENTION

Twenty-one patients, 12 with normal pleural fluid pH and 9 with low pleural fluid pH, were treated with tube thoracostomy and intrapleural tetracycline for symptomatic, recurrent pleural effusions.

MAIN RESULTS

The 20 patients with low-pH malignant effusions had a significantly greater positivity on initial pleural fluid cytologic evaluation, a shorter mean survival, and a poorer response to tetracycline pleurodesis compared with 40 patients with normal-pH malignant effusions.

CONCLUSIONS

Determination of pleural fluid pH in malignant effusions provides a rational approach to further diagnostic testing, prognostic information, and a rationale for palliative treatment.

Peritoneovenous shunt in the management of the hepatorenal syndrome

The hepatorenal syndrome (HRS) is a terminal complication of severe liver disease associated with a mortality of 80 to 90%. Although the renal functional abnormalities in the HRS suggest prerenal azotemia, volume expansion with saline, albumin or ascitic fluid rarely results in reversal of the HRS because fluid redistributes from the vascular space. Since the peritoneovenous (PV) shunt causes sustained central volume expansion, it has been advocated for the treatment of the HRS. We prospectively compared the PV shunt (N = 10) to Medical Therapy (MED) (N = 10) on renal function and mortality in 20 patients with the HRS associated with alcoholic liver disease. The HRS was diagnosed on the basis of clinical, hemodynamic, and laboratory criteria. The insertion of a PV shunt resulted in an increase in pulmonary capillary wedge pressure (4.2 +/- 1.1 vs. -1.5 +/- 1.0 mm Hg, P less than 0.01) and in cardiac index (0.8 +/- 0.3 vs. -0.2 +/- 0.3 1/min/m2, P less than 0.05). After 48 to 72 hours, weight (+3.1 +/- 1.1 kg) and serum creatinine (3.9 +/- 0.5 to 5.5 +/- 0.7 mg/dl, P less than 0.001) were increased with MED therapy and decreased (weight: -3.7 +/- 0.7 kg; serum creatinine: 3.6 +/- 0.4 to 3.0 +/- 0.5, P less than 0.05) with the PV shunt. Despite improvement in renal function, only one patient with the PV shunt had prolonged survival (210 days). In the remainder, survival was 13.8 +/- 2.2 days compared to 4.1 +/- 0.6 days with MED therapy. We conclude that the PV shunt often stabilizes renal function, but does not prolong life in patients with the HRS.

Demand and continuous flow intermittent mandatory ventilation systems

A mechanical lung was used to evaluate the pressure and flow characteristics of four demand and two continuous flow intermittent mandatory ventilation (IMV) systems. The amount of negative pressure required to initiate inspiratory flow and peak expiratory resistance were measured. The inspiratory pressure required to initiate flow in the demand mode was also compared to pressures generated in the assist mode. In addition, the peak expiratory resistance was measured with four commercially available exhalation valves. Results showed that the ventilator manometer measuring internal machine pressures significantly underestimated the amount of negative pressure required to open the demand valve (p less than 0.01). There are major differences in the flow and pressure characteristics among demand and continuous flow IMV systems. Systems that impose high inspiratory elastic threshold loads and expiratory flow resistive loads may have a deleterious effect on the mechanics of breathing, and thereby limit weaning success and eventually impair the recovery of certain patients in respiratory failure. The basic methodology, especially the simple technique of inserting an aneroid manometer in line next to a patient's ET tube, for measuring proximal negative inspiratory force (NIF test) can be easily applied to any and all ventilators at any practitioner's individual institution.

The pathogenesis of low glucose, low pH malignant effusions

Possible mechanisms to explain the finding of a low pH, low glucose, malignant pleural effusion include: use of glucose and acid production by pleural fluid constituents including leukocytes and free malignant cells; pleural membrane metabolism, especially by malignant cells; abnormal transfer of glucose, carbon dioxide, and hydrogen ion across a diseased pleural membrane. To determine the pathogenesis of low glucose, low pH effusions, we performed incubation and glucose and gas transport studies in 5 patients with malignant effusions, 3 with a low pH (less than 7.30) and 2 with a pH greater than 7.30 (control patients). After 24 h of incubation, there was no significant difference in the metabolic activity of pleural fluid between low pH fluids and control fluids. Transport studies confirmed impaired glucose transfer both into and out of the pleural space and impaired efflux of CO2 from the pleural space in patients with low pH effusions, whereas control patients demonstrated free transfer across the pleural membrane. It appears that an abnormal pleural membrane (tumor or fibrosis), rather than increased acid production, results in a low glucose concentration from impaired glucose transfer from blood to pleural fluid and a low pH from impaired hydrogen ion efflux in some malignant effusions.

Naloxone: effects on hypoxic pulmonary vasoconstriction

To determine the effect of naloxone on the hypoxic pulmonary vasoconstrictive response, six mongrel dogs were rendered hypoxic with 10% oxygen and were given either saline or naloxone. Following hypoxia all dogs had significant increases in mean pulmonary artery pressure (PAP) and pulmonary arterial resistance index (PARI) without changes in cardiac output or systemic blood pressure. Beta endorphins did not change at any time following hypoxia. Dogs receiving naloxone had significant lowering of PAP and PARI without changes in plasma beta endorphin levels. We conclude that naloxone attenuates hypoxic pulmonary vasoconstriction without measurable alterations of plasma beta endorphin levels.

Lupus pleuritis. Clinical features and pleural fluid characteristics with special reference to pleural fluid antinuclear antibodies

Eighteen patients with lupus erythematosus (LE) and pleural effusions were evaluated. Fourteen patients had lupus pleuritis and four had pleural effusions of other etiologies. All patients were symptomatic, and the presenting signs and symptoms did not help distinguish between lupus pleuritis and pleural effusions of other causes. The presence of LE cells confirmed the diagnosis of lupus pleuritis in seven of eight patients. In 11 of 13 patients with lupus pleuritis, the pleural fluid antinuclear antibody (ANA) titer was greater than or equal to 1:160, and in nine of 13 patients with lupus pleuritis, the pleural fluid to serum (PF/S) ANA ratio was greater than or equal to 1. In the four patients with LE and a pleural effusion of another etiology, the pleural fluid ANA titer was negative in two and low titer in two (1:40, 1:80); the pleural fluid to serum ANA titer was always less than one. Of 67 patients with pleural effusions of other etiologies, the pleural fluid ANA was negative. The signs and symptoms of lupus pleuritis are nonspecific, however; the findings of LE cells in pleural fluid confirms the diagnosis and a high pleural fluid ANA titer (greater than or equal to 1:160) and a PF/S ANA ratio of greater than or equal to 1 strongly supports the diagnosis.

The contribution of leukocytes and bacteria to the low pH of empyema fluid

Empyema fluid characteristically has a low pleural fluid pH, and it has been demonstrated that this fluid has a high acid-generating capacity. To evaluate the contribution of leukocytes and bacteria to the low pH of empyema fluid, an experimental model of empyema was used. After the production of a sterile pleural effusion by turpentine in both normal and neutropenic New Zealand white rabbits, either live Streptococcus pneumoniae, killed Streptococcus pneumoniae, or Acinetobacter, an organism that does not undergo fermentation or produce substantial acid, were injected into the pleural fluid. With these manipulations, the contribution of leukocytes and bacteria alone could be assessed. The results showed that both leukocyte phagocytosis and bacterial metabolism contribute to the low pH of empyema fluid and that the number of polymorphonuclear leukocytes per se in clinically observed ranges is not critical to the change in pleural fluid pH.

The pathogenesis of the low pleural fluid pH in esophageal rupture

To determine the possible mechanisms responsible for the low pH pleural effusion associated with esophageal rupture we evaluated the following possibilities: (1) gastric acid reflux, (2) bacterial metabolism, and (3) leukocyte metabolism. Neither elimination of gastric hydrogen ion contribution by distal esophageal ligation nor elimination of bacteria with antibiotics prevented the progressive fall in pleural fluid pH after esophageal rupture. Only elimination of polymorphonuclear leukocytes from the pleural space by rendering animals leukopenic with nitrogen mustard, prevented a low pH effusion after esophageal rupture. It appears that pleural fluid leukocyte metabolism is primarily responsible for the low pH effusion associated with esophageal rupture.

Adult respiratory distress syndrome: risk with common predispositions

A 1-year survey of patients in three hospitals identified 936 patients who had one predisposition and 57 who had several predispositions to the adult respiratory distress syndrome. From the total predisposed population of 993 patients, 68 subsequently developed the syndrome. An additional 20 patients developed the syndrome from causes other than eight identified predispositions, to bring the total of patients studied to 88. A highly significant difference (p less than 0.0001) was found in the incidence rates of the syndrome between patients with one and several predispositions (5.8 versus 24.6 per 100 patients). Within 72 hours of onset of predisposition, 89.5% of patients who developed the syndrome had been intubated and placed on mechanical ventilation. Fifty-seven of the 88 patients (64.8%) with the syndrome died. By the 14th day 90% of deaths had occurred. There were no age- or sex-specific differences in either incidence or mortality rates. Case fatality rates of the syndrome were high in all predisposed groups.

Inflammatory responses in experimental tuberculosis pleurisy

A model of tuberculous pleurisy in New Zealand white rabbits was developed to describe the sequential cellular and biochemical changes in pleural fluid. Bacille Calmette-Guérin (BCG) in 4 X 10(7) colony-forming units was introduced into the right pleural space of rabbits previously sensitized by intradermal BCG. Pleural fluid was obtained via serial thoracenteses. A normal-pH, normal-glucose, exudative effusion was seen through 144 hours. Polymorphonuclear leukocytes were the first cells to respond to the introduction of tubercle bacilli in the pleural space; they remained the predominant cell for the first 24 hours and were followed by macrophages, which peaked at 96 hours, and then by lymphocytes. Numerous granulomata were observed on both the visceral and parietal pleura ten days following intrapleural instillation of BCG. We propose that the polymorphonuclear leukocyte influx is not a nonspecific response to pleural injury and that such a leukocyte response, either itself or through its interaction with the macrophage, plays a role in host defense mechanisms against the tubercle bacilli.

Mixed venous and arterial pH: a comparison during hemorrhagic shock and hypothermia

Under normal conditions a linear relationship exists between venous and arterial pH values. However, with severe metabolic and hemodynamic stress this correlation has not been established. To evaluate this relationship, nine dogs were subjected to 60 minutes of hemorrhagic shock at a mean arterial pressure of 30 mm Hg and were then resuscitated. Seven dogs were rendered hypothermic by surface cooling. Serial arterial and mixed venous samples for blood gas analysis were obtained from the femoral artery, superior vena cava (SVC), right atrium (RA), and pulmonary artery (PA). There were no statistical differences between mixed venous pH values obtained from SVC, RA, and PA during any study time. The differences between arterial and mixed venous pH (AVpH) had a significant linear relationship (r greater than 0.90, P less than 0.01). The AVpH during hypothermia was +.03 to +.04 pH units. The greatest AVpH occurred during shock, and ranged from +.08 to +.20 pH units. During recovery AVpH was intermediate at +.04 to +.13. It appears that during hemorrhagic shock and moderate hypothermia, a significant relationship persists between mixed venous and arterial pH. The mixed venous sample can be obtained from the superior vena cava, right atrium, or pulmonary artery.

Superior vena cava syndrome as a cause of pleural effusion

The development in the postoperative period of the superior vena cava syndrome resulted in a persistent right-sided, transudative pleural effusion. It appears that the increased systemic venous pressure from left innominate thrombosis leading to superior vena cava obstruction in association with chest tube drainage connected to suction (increased intrapleural negative pressure) produced hydrostatic imbalances that resulted in increased pleural fluid formation and collection.

Tuberculosis in association with pregnancy

A review was made of the records of 27 patients admitted to National Jewish Hospital who developed or experienced a reactivation of pulmonary tuberculosis during pregnancy or the first 12 month post partum. Sixteen patients had drug-resistant disease, and 11 had drug-susceptible disease. The drug-resistant group had more extensive radiographic abnormalities(p less than 0.01), longer sputum conversion times (p less than 0.05), and a higher incidence of pulmonary complications and death (p = 0.05). Patients with tuberculosis associated with pregnancy have the same clinical presentation as nonpregnant patients. Tuberculosis during pregnancy should be treated, and the drugs that appear to be safest for the fetus include isoniazid, para-aminosalicylic acid, ethambutol, and rifampin.

The effect of common sclerosing agents on the rabbit pleural space

New Zealand white rabbits received intrapleural instillations of either tetracycline (7, 20, and 35 mg/kg), HCI (0.01N), quinacrine (10 mg/kg), nitrogen mustard (0.2 mg/kg), bleomycin (1.5 mg/kg), or NaOH (0.5%). All sclerosing agents produced a neutrophil-predominant, exudative pleural effusion within 12 h of instillation. By 48 h the pleural fluid was predominantly mononuclear. Despite the large pH range of the sclerosing agents (tetracycline, 2.0; NaOH, 13.0), the pleural fluid pH was always between 7.40 and 7.49 during the 144-h observation period. There was no difference in protein concentration, leukocyte count, or neutrophil differential with either the 3 different doses of tetracycline or the 5 other sclerosing agents. Autopsies at 30 days showed that only the 35 mg/kg dose of tetracycline produced pleural symphysis. We concluded that the common sclerosing agents produce a similar type of pleural effusion, but only tetracycline leads to pleural fibrosis; this effect appears to be dose-dependent. The pH of the sclerosing agent per se probably has little effect on the development of pleural symphysis.

Rheumatoid pleurisy. observations on the development of low pleural fluid pH and glucose level

A patient with rheumatoid pleurisy provided the opportunity to observe the time course of development of the low glucose level and low pH characteristic of these pleural effusions. During six days, the effusion evolved from one with a normal glucose value and pH to one with a glucose value of 20 mg/dL and a pH of 6.78. The mechanisms responsible for these phenomena probably are (1) a selective block to glucose transport from blood to pleural fluid, (2) enhanced glucose use by rheumatoid pleura, and (3) an efflux block to the end products of pleural space glucose metabolism. Once the low glucose value-low pH rheumatoid effusion develops, it seems not to revert to an effusion with a normal glucose level and pH.

The diagnostic value of pleural fluid pH

One hundred eighty-three patients had simultaneous blood and pleural fluid pH determinations. Thirty-six effusions were transudates, and 147 were exudates. In 46 effusions, the pleural fluid pH was less than 7.30; all 46 were exudates. A pleural fluid pH less than 7.30 was associated with the following six diagnoses: (1) empyema; (2) malignancy; (3) collagen vascular disease; (4) tuberculosis; (5) esophageal rupture; and (6) hemothorax. The results of pleural fluid pH determination are immediately available, narrow the differential diagnosis of the exudate, and may expedite patient management. The pH of pleural fluid should be measured whenever a diagnostic thoracocentesis is performed.

A model of immune complex-mediated pleuropulmonary injury; evidence of deposition of circulating immune complexes in the lung

Severe acute, diffuse lung inflammation was induced in rabbits immunized to bovine serum albumin (BSA) and subsequently challenged with BSA intrapleurally. Evidence suggesting involvement of circulating immune complexes in the pathogenesis of lung injury in these rabbits include 1) positive lung immunofluorescence, 2) a fall in serum hemolytic complement, 3) diffuse bilateral involvement despite unilateral antigen challenge, and 4) absence of these findings in control rabbits. Further investigation with this model may provide insight into the processes involved in the deposition of immune complexes in the lung and the mechanisms of lung injury provoked by immune complex deposition.

Office spirometry

The practicality of the office spirometer as an effective, inexpensive diagnostic device is well established. It can be used in a matter of seconds by minimally trained office personnel. Two basic parameters can be quickly and accurately measured: forced vital capacity (FVC), a test of volume indicative of restrictive lung disease, and forced expiratory volume in one second (FEV1), a test of flow rate indicative of obstructive lung disease. The FEV1/FVC ratio is a valuable screening measurement that indicates the likelihood of progressive deterioration of pulmonary function.

The routine use of positive end-expiratory pressure after open heart surgery

Because atelectasis of the left lower lobe is a frequent complication of open heart surgery, we evaluated the efficacy of routine therapy with positive end-expiratory pressure (PEEP) to prevent this complication. Twenty-four patients were randomly assigned to either a group receiving therapy with PEEP (ten patients) or to a group with no PEEP (14 patients). The two groups could not be distinguished by age, weight, the forced expiratory volume in one second (FEV1), the ratio of FEV1 over the forced vital capacity, the time on the pump, the units of blood transfused, the tidal volume, or the hours of mechanical ventilation. There was no significant roentgenographic difference between the two groups in either the degree or frequency of left lower lobe atelectasis. While the arterial-alveolar ratios tended to improve over time in those patients receiving therapy with PEEP, this improvement was not clinically significant. No complications were encountered with the use of PEEP. We conclude that the routine use of PEEP following open heart surgery is safe but offers no advantage over standard ventilatory techniques.

The pH of sclerosing agents: a determinant of pleural symphysis

The rate of success in producing pleural symphysis with intrapleural instillation of sclerosing agents has been variable. Differences in the designs of studies probably account for some of the variability, but the reasons for the remainder are not clear. Since a low pH of the pleural fluid is associated with pleural adhesions and loculations, the pH of the commonly used solutions of sclerosing agents was determined, both in their usual concentrations and when diluted with large quantities of exudative pleural fluid. The buffered solution of tetracycline hydrochloride had the most acidic pH (2.0) and showed little change when diluted by pleural fluid. A 0.5 percent solution of sodium hydroxide had the highest pH (13.0). The remainder of the sclerosing solutions showed a range of pH from 4.3 to 8.7. Experimental and clinical experience suggests that tetracycline consistently has the highest rate of success in producing pleural symphysis. It appears that when proper technique is employed, the pH of the solution of the sclerosing agent is an important determinant of the production of pleural symphysis.

Emergency room intubations--complications and survival

Forty-three consecutive patients requiring endotracheal intubation in an emergency room were studied prospectively to define the complications associated with intubation and the survival of these patients, and to evaluate emergency room policies. The indications for intubation were acute respiratory failure (ARF) in 22 patients and cardiopulmonary arrest (CPA) in 21 patients. Thirty-eight complications occurred in 24 of the 43 patients. The department or level of training of the intubator did not affect the rate of complications. Furthermore, specific complications did not influence survival. Seventeen patients survived, all in the ARF group. Age less than 40 years and admission PaO2 greater than 40 mm Hg also were associated with increased survival. We conclude that the complication rate of emergency room intubations is high and would not appear to be lowered by limiting intubations to physicians from specific departments or with certain levels of training. The underlying diagnosis and condition on admission to the emergency room appear to be more important factors relating to survival than complications during intubation.