Perfusion Computed Tomography as a Screening Tool for Pending Delayed Cerebral Ischemia in Comatose Patients After Aneurysmal Subarachnoid Hemorrhage: A Retrospective Cohort Study

BACKGROUND

Aneurysmal subarachnoid hemorrhage (aSAH) is frequently complicated by delayed cerebral ischemia (DCI), leading to poor outcomes. Early diagnosis of DCI is crucial for improving survival and outcomes but remains challenging in comatose patients. In this study, we aimed to evaluate computed tomography with angiography and perfusion (P-CT) as a screening modality on postictal days four and eight for impending DCI after aSAH in comatose patients using vasospasm with hypoperfusion (hVS) as a surrogate and DCI-related infarction as an outcome measure. Two objectives were set: (1) to evaluate the screening's ability to accurately risk stratify patients and (2) to assess the validity of P-CT screening.

METHODS

We conducted a retrospective review of the records of comatose patients with aSAH from January 2019 to December 2021 who were monitored with P-CT scans on days four and eight. The event rates of DCI-related infarction, hVS, and endovascular rescue therapy (ERT) were analyzed, and the sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV) for DCI were calculated. DCI-related infarction was defined as new secondary cerebral infarction > 48 h < 6 weeks post aSAH not attributable to other causes, and hVS was defined as arterial narrowing with corresponding hypoperfusion on P-CT.

RESULTS

Fifty-six comatose patients were included, and 98 P-CT scans were performed. The incidence of DCI-related infarction was 40%. Screening P-CT on days four and eight found vasospasm in 23% of all patients, including 11% with hVS. A positive hVS on day four or eight revealed a relative risk of 2.4 [95% confidence interval (CI) 1.13-5.11, p = 0.03], sensitivity of 23% (95% CI 8-45, p = 0.03), specificity of 95% (95% CI 36-100, p = 0.03), PPV of 0.83 (95% CI 0.36-1.00, p = 0.03), and NPV of 0.65 (95% CI 0.50-0.78). Six positive P-CT scans led to digital subtraction angiography in five patients, three of whom received ERT. All ERT-intervened patients developed DCI-related infarction.

CONCLUSIONS

P-CT resulted in few interventions and often resulted in late detection of DCI at an irreversible stage. Although a positive P-CT result accurately predicts impending DCI-related infarction, screening on days four and eight alone in comatose patients with aSAH often fails to timely detect impending DCI. Based on our analysis, we cannot recommend P-CT as a screening modality. P-CT is likely best used as a confirmatory test prior to invasive interventions when guided by continuous multimodal monitoring; however, prospective studies with comparison groups are warranted. The need for a reliable continuous screening modality is evident because of the high rate of deterioration and narrow treatment window.

Analysis of internal proteins of influenza A (H2N2) viruses isolated from birds in East Germany in 1983

Proteins and RNAs of influenza A (H2N2) viruses isolated from birds in 1983 in East Germany were compared antigenically with those of H2N2 human strains. The electrophoretic mobility of the viral proteins and of the S1-treated double-stranded RNAs from two human and six avian strains, as well as the results of EIA-tests using monoclonal antibodies to their matrix protein and nucleoproteins indicate an antigenic relationship between the avian isolates and human strains of H2N2 subtype. One of the avian strains had a reduced amount of matrix protein.

[The detection of antibodies to HIV protein p24 in human blood sera by the method of lanthanide immunofluorescent analysis]

A competitive time-resolved fluoroimmunoassay (TR-FIA) system for the detection of antibodies to protein p24 of HIV was developed on the basis of monoclonal antibodies. The advantages of this test system over analogous enzyme immunoassay system and commercial test system "Antigen" (USSR) were demonstrated. The newly developed test system of TR-FIA was used for examination of sera from HIV-infected persons.

[The strain-specific diagnosis of influenza by using lanthanide immunofluorescence analysis based on monoclonal antibodies to the hemagglutinin of the influenza A virus]

Nine monoclonal antibodies (MCA) to hemagglutinin of influenza A/Taiwan/1/86 (H1N1) virus and 5 MCA to influenza A/Mississippi/1/85 (H3N2) virus were generated and characterized. The MCA were used for the development of diagnostic test systems on the basis of time-resolved fluoroimmunoassay. The same MCA were used as primary and detecting antibodies in the test system specific for HA of the H1 serosubtype, whereas in the test system specific for influenza A serosubtype H3 virus MCA of different epitope appurtenance were used as primary and secondary antibodies. The sensitivity of the test system for HA of serosubtype H1 was found to be 10 ng/ml and that for serosubtype H3 5 nh/ml. The developed test systems were tried on the clinical material collected during the epidemic periods of 1983-1989.

[Standardization of conditions for detecting the internal proteins of the influenza virus in studying their antigenic properties in solid-phase immunoenzyme analysis]

The influence of the conditions of adsorption and virion destruction by freezing-thawing and detergents on the detection of M1 and NP proteins of different influenza virus strains by solid-phase enzyme immunoassay with direct virion adsorption on polystyrene was studied. It was found that for the detection of M1 protein the optimal conditions included virion disruption with detergent and adsorption to polystyrene at 4 degrees C, and for NP protein disruption by freezing-thawing at adsorption to polystyrene at 37 degrees C. In the study of the antigenic properties of protein M1 of different influenza virus strains using monoclonal antibodies it was shown to be necessary, first, to achieve maximum detection of proteins and, second, to standardize the amount of the adsorbed antigen with polyclonal antibodies.

[Indication of the influenza virus in clinical samples using immunoenzyme and lanthanide immunofluorescence analyses]

A comparative study of the potentials of enzyme-immunoassay (EIA) and lanthanide immunofluorescent assay (LIFA) for influenza virus detection in nasopharyngeal aspirates and nasopharyngeal washings was carried out. Monospecific and polyclonal antisera to hemagglutinin polyclonal antisera to matrix protein as well as polyclonal and monoclonal antisera to nucleoprotein were used. The nasopharyngeal aspirates were shown to contain virus-specific antigens in the amounts sufficient for influenza virus detection with polyclonal and monoclonal antibodies. There was a good correlation between chromophore results by EIA and fluorescence level in LIFA. The sensitivity of the test systems used (EIA and LIFA) was shown to be insufficient for the detection of virus-specific material in the nasopharyngeal washings. Besides, there was no correlation between the results obtained by different test systems. It was concluded that nasopharyngeal aspirates should be collected for rapid influenza diagnosis by EIA and LIFA.

[Stat-diagnosis of influenza using lanthanide immunofluorescence analysis]

A test system for influenza diagnosis has been developed on the basis of monoclonal antibodies to influenza A and B virus proteins using the principles of lanthanide immunofluorescence analysis. The diagnostic test system was shown to be highly specific in detecting influenza A and B virions in model systems. For the one-step variant of a double sandwich used in the study, the total time of diagnostic experiment using clinical materials was shown to be reduced to 15-20 min.

[Heterogeneous distribution of influenza A matrix protein in polyacrylamide gel, detected using an immunoblotting method with monoclonal antibodies]

The immune blotting method using monoclonal antibodies to Ml protein showed protein Ml to migrate in several bands in polyacrylamide gel electrophoresis (PGE) of influenza A virus polypeptides. The heterogeneous distribution of Ml protein in PGE is due to the formation of aggregates: dimers, trimers, and polymers of a higher order. The capacity of Ml protein for aggregation is typical not of all influenza virus strains and most likely is not associated with gel overloading. Since dimers and trimers of Ml protein comigrate in the gel with virus-specific proteins such as NP and proteins of a polymerase complex, this circumstance should be take into consideration in using PGE for isolation of pure influenza virus proteins.

Antigenic reactivity of matrix protein and nucleoprotein of influenza virus as detected by EIA after dissociation with different detergents

Solid phase enzyme-immunoassay (EIA) was employed to assess the antigenic reactivity of matrix protein (M) and nucleoprotein (NP) of influenza A virus adsorbed to polystyrene in the presence of different detergents such as beta-octaglucoside (OG), Triton X-100, Tween-20, sodium dodecylsulphate (SDS), sodium deoxycholate (Doch-Na), Nonidet P-40 (NP-40), and sarcosyl at concentrations ranging from 0 to 2%. The antigenic reactivity of NP was the highest in the absence of detergents. For M protein, Doch-Na, SDS, NP-40 and sarcosyl of 0.05-0.1% enhanced the chromatophoric response in EIA 1.5-2 times. In contrast, the antigenic reactivity of M protein remained unchanged after OG or Triton X-100 treatments, and it decreased in the presence of Tween-20.

[Isolation and characteristics of monoclonal antibodies to influenza virus types A and B]

Monoclonal antibodies (MCA) to influenza type A (10F) and B (5H and 6H) viruses have been prepared. By immunoblotting method, MCA 10F were found to be specific for NP-protein of influenza A virus, and MCA 5H and 6H to be specific for hemagglutinin of influenza B virus. It was established that the 10F clone interacted with all the investigated influenza A virus strains with different antigenic formulae (H1N1, H2N2, H3N2) and could be used for typing of this virus type. Clones 5H and 6H react specifically with hemagglutinins of influenza B viruses isolated in 1940, 1979, and 1983 which makes them useful for diagnosis of influenza B.

Simultaneous determination of the level of antibodies to influenza virus surface and internal proteins by enzyme-linked immunosorbent assay

Enzyme-linked immunosorbent assay (ELISA) has been adopted for simultaneous determination of the levels of antibodies to different influenza virus proteins in human sera with known haemagglutination-inhibition (HI) titre. Whole virus of serotypes H1N1 and H3N2, haemagglutinin (HA), matrix (M) and nucleoprotein (NP) proteins have been used as antigens. For detection of antibodies bound to the antigen, peroxidase labelled Staphylococcus protein A conjugate has been used. Correlation of the ELISA and HI titres of anti-HA antibody has been demonstrated. The use of isolated HA as antigen increased the specificity of ELISA. The analysis of human reconvalescent sera has shown that increase in the titre of antibodies to internal proteins does not always coincide with the increase of antibody level to HA. Out of 8 sera with significant increase of the HI titre to the H3 subtype 5 specimens showed 4-fold increase of antibody titre to NP protein. The antibody titre to M protein was elevated in 2 sera only, while 1 serum showed no rise of antibody response to the tested viral proteins.

The influence of the isolation technique of influenza virus nucleoprotein on its antigenic properties

ELISA has been used to study the antigenic properties 1. of influenza virus nucleoprotein (NP-1) isolated from virions with the help of preparative polyacrylamide gel electrophoresis (PAGE); 2. of virion ribonucleoprotein (NP-2), and 3. of NP structures prepared by dissociation of ribonucleoprotein into RNA and protein in sucrose gradient containing NaCl (NP-3). The investigation of immunologic cross-reactivity has shown complete identity of NP-2 and NP-3 and their striking difference from NP-1. In contrast to NP-2, NP-3 was not contaminated by other virus antigens, it was a good immunogen and could be used for preparation of monospecific antisera of high titre. NP-1 did not induce a high antibody response,however, like NP-2 and NP-3, it retained its capacity to react with antisera to native virus. Owing to its simple production and high yield, this protein can be used in serodiagnosis for testing the antibody level against NP-protein in convalescent sera.

[Possibility of detecting the matrix protein of the influenza virus in intact and disrupted virions by immunoenzyme analysis and immune electron microscopy]

ELISA and immune electron microscopy were used to study possible causes of the detection of antigenic reactivity of influenza virus matrix protein in purified virus suspension directly adsorbed on polystyrene. No interaction of antibody to M protein with the surface of virus and subvirus particles was observed. The process of virus sorption on polystyrene for a long period was shown not to lead to disruption of intact virus particles, and the detection of the internal matrix protein in preparations of purified influenza virus was due only to the presence of partially or completely destroyed virions in the viral suspension.

[Circular dichroism study of the ribonucleoprotein structure of Sendai virus isolated from infected chick embryo cells]

Thermostability and secondary structure of RNA, a component of ribonucleoprotein (RNP) of Sendai virus isolated from infected chick embryo cells (cRNP) and from virions (vRNP) were studied by the method of circular dichroism. The secondary structure of RNA in cRNP was shown to be practically no different from that of free RNA whereas incorporation of RNA into vRNP was accompanied by a significant decrease in the number of paired bases in it. Comparison of thermodenaturation parameters of cRNP and vRNP also revealed significant differences in their structural organization. Thus, melting of cRNP as well as of free RNA is of markedly non-cooperative nature indicating poor RNA-protein interactions in the complex. In contrast, the process of vRNP thermodenaturation occurs in a step-wise manner in a narrow temperature range indicating a significant role in the maintenance of this RNP structure of both RNA-protein and, apparently, protein-protein interactions.

[Effect of formaldehyde on the ribonucleoprotein structure of Sendai virus]

The effect of formaldehyde on the conformation of Sendai virus ribonucleoprotein (RNP) was studied by electron microscopy and a spectrophotometric method. The effect of formaldehyde on RNP conformation was found to depend strongly on the ionic strength of the solution. Under conditions of a low ionic strength in the presence of 1.5% formaldehyde the tightly coiled rods of RNP stained with uranyl acetate become loosely coiled or almost completely extended. At the same time, formaldehyde reaction with RNP results in a decrease in extinction of the RNP suspension in the 250 to 290 spectral region. However, RNP incubation with formaldehyde in the presence of 0.5M NaCl caused no changes in the morphology and spectral properties of the RNP under study. The results indicate that formaldehyde cannot be used for fixation of Sendai virus nucleocapsids before negative staining for electron microscopy examinations.

[Morphological and structural studies of Sendai virus ribonucleoprotein]

The structure and morphology of Sendai virus ribonucleoprotein (RNP) with native and split protein subunits were studied by the method of circular dichroism and electron microscopy. Cleavage of the polypeptide fragment from RNP protein subunits was shown to cause changes in the secondary structure of RNP in situ but not to affect the RNP morphology; when stained with uranyl acetate both RNP types had an appearance of spiral strands.

[Effect of the isolation method and staining procedure on the morphology of the virion ribonucleoprotein of Sendai virus]

Electron microscopic examinations of morphology of Sendai virus ribonucleoprotein (RNP) isolated from purified virions by two methods and simultaneous staining of the preparations with uranyl acetate and phosphotungstate acid (PTA) were carried out. The staining method was shown not to influence the kind of nucleoproteins which had been isolated from disrupted virions by sucrose density gradient centrifugation. With both strains RNP appeared as strongly helixed filaments. The staining method, however, strongly influenced morphology of RNP isolated from disrupted virions by equilibrium centrifugation in cesium chloride density gradient. After uranyl acetate staining RNP had an appearance of hard filaments whereas in the same preparation stained with PTA partially and completely unwound spirals of nucleocapsid were found alongside with strongly spiralized structures.

[Sedimentation and electron microscopic characteristics of RNA isolated from a highly concentrated suspension of Sendai virus]

Sedimentation analysis in a lineal (5%--30%) sucrose concentration gradient of an RNA preparation isolated from a highly concentrated Sendai virus suspension revealed an additional peak with sedimentation coefficient 69S apart from previously known peaks of 46S (genome RNA), 30S and 18S (incomplete virus RNA). Electron microscopy methods showed the single-stranded molecules of 46S RNA to have a marked hairpin structure. Molecules of double-stranded 69S RNA have a specific structure: lineal parts alternate with areas in the form of rosettes. It is suggested that molecules of of 69S RNA are a product of incomplete hybridization between "plus" and "minus" complementary chains of virion RNA.

Secondary structures of influenza and Sendai Virus RNAs

The secondary structures of influenza and Sendai virus RNAs were investigated by thermal denaturation, circular dichroism and proflavine binding methods. In 0.1 M NaCl about 60% of the bases of both RNAs were involved in secondary structure. The melting temperatures (Tm) of both viral RNAs were linear functions of the logarithm of the sodium ion concentration in solution, but under all ionic conditions the melting temperatures of Sendai virus RNA were higher than those of influenza virus RNA. At all ionic strengths the melting range of Sendai virus RNA was less than influenza virus RNA, indicating that the helical regions in Sendai virus RNA were longer than those in influenza virus RNA. Although Sendai virus RNA had a higher thermal stability than influenza virus RNA, hyperchromicity and circular dichroism data showed that Sendai virus RNA had less G+C content (34%) within the double stranded regions than influenza virus RNA (48%). The binding isotherms of Sendai and influenza virus RNA-proflavine complexes were studied at different ionic strengths. The number of binding sites of proflavine with influenza virus RNA were significantly lower than those with Sendai virus RNA. These results demonstrate the essential difference between the secondary and tertiary structures of the RNAs under study.

[Physico-chemical properties of the RNA of Sendai virus. III. Interaction with proflavin]

The binding isotherms of the Sendai virus single- and double-stranded RNA-proflavine complexes have been studied. The existence of two regions on the binding curves, corresponding to two subtypes of the strong complex (I1 and I2) has been demonstrated. The association constants and the numbers of binding sites for both subtypes were determined as a function of ionic strength. Both of the single- and for the double-stranded RNA the association constant for I1 complex were higher than those for I2 complex under all ionic strengths conditions. For the double-stranded RNA the variation of the ionic strength is more importance in case of the I1 complex formation. The total number of binding sites increases with a decrease of ionic strength. At low ionic strength (10(-4) M NaCl) the number of binding sites for single- and double-stranded RNA is practically the same and is equal to the number of binding sites for DNA at high ionic strength (1 molecule of proflavine per 3 nucleotides pairs). The heat denaturation of the RNA-proflavine complexes under different ionic conditions has been also investigated. The melting curves for double-stranded RNA-proflavine complex had two waves at high and low ionic strengths. For the single-stranded RNA the high temperature wave occured only at the high ionic strength. The dependence of heat denaturation of single-stranded RNA on ionic strength was examined for the evaluation of RNA structure. In these experiments a significant decrease of the width of melting interval under low ionic strength conditions was observed. It may reflect the existance in the RNA molecule of long helical regions. The occurence of such structures is likely to be responsible for an increase in the number of binding sites at low ionic strength and also for the appearance of the second wave on the melting curves of the single-stranded RNA-proflavine complexes at high ionic strength.

Physicochemical properties of Sendai virus RNA. II. Effect of ionic strength on thermostability of RNA

The dependence of the melting point (Tm) and width of the melting range (deltaTm) on the ionic strength and pH of the medium was investigated for the double-stranded RNA formed through self-hybridization during the isolation of RNA from Sendai virus. It was shown that Tm is a linear function of the logarithm of the sodium ion concentration in the range of concentrations from 10(-1) to 10(-4) M, with a slope of 11.5 degrees toward the abscissa for each order of magnitude. The width of the melting range increased slightly with a decrease in the ionic strength. A change in the pH of the solutions from 5 to 8 had almost no effect on the melting point or the width of the melting range. The degree of purification of the preparations of RNA and the presence of EDTA in the solutions affected the form of the dependence of the mp on the logarithm of the sodium ion concentration very strongly, especially in the region of low ionic strengths.