Assessing the validity of two-dimensional carotid ultrasound to detect the presence and absence of a pulse.

BACKGROUND: Traditional assessment of return of cardiac output in cardiac arrest by manual palpation has poor accuracy. Point of care ultrasound of a major artery has been suggested as an alternative. We conducted a diagnostic accuracy study of two-dimensional carotid ultrasound to detect the presence or absence of a pulse, using cardiopulmonary bypass patients for pulse and pulseless states. METHODS: A cross-sectional multi-patient, multi-reader repeated measures diagnostic study was conducted. For patients undergoing routine cardiopulmonary bypass, a portable ultrasound was used to record four 10-s videos the common carotid artery, three aimed for a pulse in high (>90 mmHg), medium (70-90 mmHg) and low (<70 mmHg) systolic blood pressure (SBP) ranges, and a pulseless video was recorded on cardiopulmonary bypass. Critical care physicians viewed the videos and were asked to nominate within 10 s if a pulse was present. True pulse-status was determined via the arterial-line waveform. RESULTS: Twenty-three patients had all four videos collected. Median patient age was 64 (IQR 14), sixteen were male (70%) and median BMI was 27. The median SBP in high-, medium- and low-SBP groups were 120 mmHg, 83 mmHg and 69 mmHg respectively. Forty-six physicians reviewed a subset of 24 videos. Overall sensitivity was 0.91 (95% confidence interval 0.89-0.93) and specificity 0.90 (95% CI 0.86-0.93). Sensitivity was highest in the high-SBP group (0.96, 95% CI 0.93-0.98) and lowest in the low-SBP group (0.83, 95% CI 0.78-0.87). CONCLUSION: 2D ultrasound of the common carotid artery is both sensitive and specific for detection of the presence or absence of a pulse.

In Vivo Optical Detection and Spectral Triangulation of Carbon Nanotubes.

In the first in vivo demonstration of spectral triangulation, biocompatible composites of single-walled carbon nanotubes in Matrigel have been surgically implanted into mouse ovaries and then noninvasively detected and located. This optical method deduces the three-dimensional position of a short-wave IR emission source from the wavelength-dependent attenuation of fluorescence in tissues. Measurements were performed with a second-generation optical scanner that uses a light-emitting diode matrix emitting at 736 nm for diffuse specimen excitation. The intrinsic short-wave IR fluorescence of the nanotubes was collected at various positions on the specimen surface, spectrally filtered, and detected by a photon-counting InGaAs avalanche photodiode. Sensitivity studies showed a detection limit of ∼120 pg of nanotubes located beneath ∼3 mm of tissue. In addition, the mass and location of implanted nanotubes could be deduced through spectral triangulation with sub-millimeter accuracy, as validated with the aid of magnetic resonance imaging (MRI) data. Dual-modality imaging combining spectral triangulation with computed tomography or MRI will allow accurate registration of emission centers with anatomical features. These results are a step toward the future use of probes with targeting agents such as antibodies linked to nanotube tags for the noninvasive detection and imaging of tumors in preclinical research on small animals. Translation to the clinic could aid in early detection of ovarian cancer and identification of metastases for resection during primary surgery.

Skewness Analysis in Variance Spectroscopy Measures Nanoparticle Individualization.

An important enabling step in nanoparticle studies is the sorting of heterogeneous mixtures to prepare structurally homogeneous samples. It is also necessary to detect and monitor aggregation of the individual nanoparticles. Although variance spectroscopy provides a simple optical method for finding low concentrations of heteroaggregates in samples such as single-walled carbon nanotube dispersions, it cannot detect the homoaggregates that are relevant for well-sorted samples. Here we demonstrate that variance spectral data can be further analyzed to find third moments of intensity distributions (skewness), which reveal the presence of emissive homoaggregates. Using experimental measurements on variously processed nanotube dispersions, we deduce a simple numerical standard for recognizing aggregation in the highly sorted samples that are increasingly available to nanoscience researchers.

(n,m)-Specific Absorption Cross Sections of Single-Walled Carbon Nanotubes Measured by Variance Spectroscopy.

A new method based on variance spectroscopy has enabled the determination of absolute absorption cross sections for the first electronic transition of 12 (n,m) structural species of semiconducting single-walled carbon nanotubes (SWCNTs). Spectrally resolved measurements of fluorescence variance in dilute bulk samples provided particle number concentrations of specific SWCNT species. These values were converted to carbon concentrations and correlated with resonant components in the absorbance spectrum to deduce (n,m)-specific absorption cross sections (absorptivities) for nanotubes ranging in diameter from 0.69 to 1.03 nm. The measured cross sections per atom tend to vary inversely with nanotube diameter and are slightly greater for structures of mod 1 type than for mod 2. Directly measured and extrapolated values are now available to support quantitative analysis of SWCNT samples through absorption spectroscopy.

Variance Spectroscopy.

Spectroscopic analysis and study of nanoparticle samples is often hampered by structural diversity that presents a complex superposition of spectral signatures. By probing the spectra of small volumes within dilute samples, we can expose statistical variations in composition to obtain information unavailable from bulk spectroscopy. This new approach is demonstrated using fluorescence spectra of unsorted single-walled carbon nanotube samples to deduce structure-specific abundances and emissive efficiencies. Furthermore, correlations between intensity variations at different wavelengths provide two-dimensional covariance maps that isolate the spectra of homogeneous subpopulations. Covariance analysis is also a sensitive probe of particle aggregation. It shows that well-dispersed nanotube samples can spontaneously form loose aggregates of a type not previously recognized. Variance spectroscopy is a simple and practical technique that should find application in many nanoparticle studies.

The dimerization domain in DapE enzymes is required for catalysis.

The emergence of antibiotic-resistant bacterial strains underscores the importance of identifying new drug targets and developing new antimicrobial compounds. Lysine and meso-diaminopimelic acid are essential for protein production and bacterial peptidoglycan cell wall remodeling and are synthesized in bacteria by enzymes encoded within dap operon. Therefore dap enzymes may serve as excellent targets for developing a new class of antimicrobial agents. The dapE-encoded N-succinyl-L,L-diaminopimelic acid desuccinylase (DapE) converts N-succinyl-L,L-diaminopimelic acid to L,L-diaminopimelic acid and succinate. The enzyme is composed of catalytic and dimerization domains, and belongs to the M20 peptidase family. To understand the specific role of each domain of the enzyme we engineered dimerization domain deletion mutants of DapEs from Haemophilus influenzae and Vibrio cholerae, and characterized these proteins structurally and biochemically. No activity was observed for all deletion mutants. Structural comparisons of wild-type, inactive monomeric DapE enzymes with other M20 peptidases suggest that the dimerization domain is essential for DapE enzymatic activity. Structural analysis and molecular dynamics simulations indicate that removal of the dimerization domain increased the flexibility of a conserved active site loop that may provide critical interactions with the substrate.