Characteristics of pulse oximetry and arterial blood gas in patients with fibrotic interstitial lung disease

BACKGROUND

Fibrotic interstitial lung disease (ILD) is frequently associated with abnormal oxygenation; however, little is known about the accuracy of oxygen saturation by pulse oximetry (SpO2) compared with arterial blood gas (ABG) saturation (SaO2), the factors that influence the partial pressure of carbon dioxide (PaCO2) and the impact of PaCO2 on outcomes in patients with fibrotic ILD.

STUDY DESIGN AND METHODS

Patients with fibrotic ILD enrolled in a large prospective registry with a room air ABG were included. Prespecified analyses included testing the correlation between SaO2 and SpO2, the difference between SaO2 and SpO2, the association of baseline characteristics with both the difference between SaO2 and SpO2 and the PaCO2, the association of baseline characteristics with acid-base category, and the association of PaCO2 and acid-base category with time to death or transplant.

RESULTS

A total of 532 patients with fibrotic ILD were included. Mean resting SaO2 was 92±4% and SpO2 was 95±3%. Mean PaCO2 was 38±6 mmHg, with 135 patients having PaCO2 <35 mmHg and 62 having PaCO2 >45 mmHg. Correlation between SaO2 and SpO2 was mild to moderate (r=0.39), with SpO2 on average 3.0% higher than SaO2. No baseline characteristics were associated with the difference in SaO2 and SpO2. Variables associated with either elevated or abnormal (elevated or low) PaCO2 included higher smoking pack-years and lower baseline forced vital capacity (FVC). Lower baseline lung function was associated with an increased risk of chronic respiratory acidosis. PaCO2 and acid-base status were not associated with time to death or transplant.

INTERPRETATION

SaO2 and SpO2 are weakly-to-moderately correlated in fibrotic ILD, with limited ability to accurately predict this difference. Abnormal PaCO2 was associated with baseline FVC but was not associated with outcomes.

The Clinical Frailty Scale for Risk Stratification in Patients With Fibrotic Interstitial Lung Disease

BACKGROUND

Previous studies have shown the importance of frailty in patients with fibrotic interstitial lung disease (ILD).

RESEARCH QUESTION

Is the Clinical Frailty Scale (CFS) a valid tool to improve risk stratification in patients with fibrotic ILD?

STUDY DESIGN AND METHODS

Patients with fibrotic ILD were included from the prospective multicenter Canadian Registry for Pulmonary Fibrosis. The CFS was assessed using available information from initial ILD clinic visits. Patients were stratified into fit (CFS score 1-3), vulnerable (CFS score 4), and frail (CFS score 5-9) subgroups. Cox proportional hazards and logistic regression models with mixed effects were used to estimate time to death or lung transplantation. A derivation and validation cohort was used to establish prognostic performance. Trajectories of functional tests were compared using joint models.

RESULTS

Of the 1,587 patients with fibrotic ILD, 858 (54%) were fit, 400 (25%) were vulnerable, and 329 (21%) were frail. Frailty was a risk factor for early mortality (hazard ratio, 5.58; 95% CI, 3.64-5.76, P < .001) in the entire cohort, in individual ILD diagnoses, and after adjustment for potential confounders. Adding frailty to established risk prediction parameters improved the prognostic performance in derivation and validation cohorts. Patients in the frail subgroup had larger annual declines in FVC % predicted than patients in the fit subgroup (-2.32; 95% CI, -3.39 to -1.17 vs -1.55; 95% CI, -2.04 to -1.15, respectively; P = .02).

INTERPRETATION

The simple and practical CFS is associated with pulmonary and physical function decline in patients with fibrotic ILD and provides additional prognostic accuracy in clinical practice.

Lung imaging patterns in connective tissue disease-associated interstitial lung disease impact prognosis and immunosuppression response

OBJECTIVES

Interstitial lung disease (ILD) in connective tissue diseases (CTD) have highly variable morphology. We aimed to identify imaging features and their impact on ILD progression, mortality and immunosuppression response.

METHODS

Patients with CTD-ILD had high-resolution chest computed tomography (HRCT) reviewed by expert radiologists blinded to clinical data for overall imaging pattern (usual interstitial pneumonia [UIP]; non-specific interstitial pneumonia [NSIP]; organizing pneumonia [OP]; fibrotic hypersensitivity pneumonitis [fHP]; and other). Transplant-free survival and change in percent-predicted forced vital capacity (FVC) were compared using Cox and linear mixed effects models adjusted for age, sex, smoking, and baseline FVC. FVC decline after immunosuppression was compared with pre-treatment.

RESULTS

Of 645 CTD-ILD patients, the frequent CTDs were systemic sclerosis (n = 215), rheumatoid arthritis (n = 127), and inflammatory myopathies (n = 100). NSIP was the most common pattern (54%), followed by UIP (20%), fHP (9%), and OP (5%). Compared with UIP, FVC decline was slower for NSIP (1.1%/year, 95%CI 0.2, 1.9) and OP (3.5%/year, 95%CI 2.0, 4.9), and mortality was lower for NSIP (HR 0.65, 95%CI 0.45, 0.93) and OP (HR 0.18, 95%CI 0.05, 0.57), but higher in fHP (HR 1.58, 95%CI 1.01, 2.40). The extent of fibrosis also predicted FVC decline and mortality. After immunosuppression, FVC decline was slower compared with pre-treatment in NSIP (by 2.1%/year, 95%CI 1.4, 2.8), with no change for UIP or fHP.

CONCLUSION

Multiple radiologic patterns are possible in CTD-ILD, including a fHP pattern. NSIP and OP were associated with better outcomes and response to immunosuppression, while fHP had worse survival compared with UIP.

Impact of Antigen Exposure on Outcomes and Treatment Response in Fibrotic Hypersensitivity Pneumonitis

BACKGROUND

Patients with fibrotic hypersensitivity pneumonitis (fHP) are frequently treated with immunosuppression to slow lung function decline; however, the impact of this treatment has not been studied across different types of antigen exposure.

RESEARCH QUESTION

In patients with fHP, do disease outcomes and response to treatment vary by antigen type?.

STUDY DESIGN AND METHODS

A multicenter interstitial lung disease database (Canadian Registry for Pulmonary Fibrosis) was used to identify patients with fHP. The causative antigen was categorized as avian, mold, unknown, or other. Treatment was defined as mycophenolate ≥ 1,000 mg/d or azathioprine ≥ 75 mg/d for ≥ 30 days. Statistical analysis included t tests, χ2 tests, and one-way analysis of variance. Unadjusted and adjusted competing risks and Cox proportional hazards models were used to assess survival.

RESULTS

A total of 344 patients were identified with the following causative antigens: avian (n = 93; 27%), mold (n = 88; 26%), other (n = 15; 4%), and unknown (n = 148; 43%). Patient characteristics and lung function were similar among antigen groups with a mean FVC % predicted of 75 ± 20. The percent of patients treated with immunosuppression was similar between antigens with 58% of patients treated. There was no change in lung function or symptom scores with the initiation of immunosuppression in the full cohort. Immunosuppression was not associated with a change in survival for patients with avian or mold antigen (avian: hazard ratio, 0.41; 95% CI, 0.11-1.59; P = .20; mold: hazard ratio, 1.13; 95% CI, 0.26-4.97; P = .88). For patients with unknown causative antigen, survival was worse when treated with immunosuppression (hazard ratio, 2.65; 95% CI, 1.01-6.92; P = .047).

INTERPRETATION

Response to immunosuppression varies by antigen type in patients with fHP. Additional studies are needed to test the role of immunosuppression in fHP, and particularly in those with an unknown antigen.

Integration and Application of Radiologic Patterns From Clinical Practice Guidelines on Idiopathic Pulmonary Fibrosis and Fibrotic Hypersensitivity Pneumonitis

BACKGROUND

Clinical practice guidelines separately describe radiologic patterns of usual interstitial pneumonia (UIP) and fibrotic hypersensitivity pneumonitis (fHP), without direction on whether or how to apply these approaches concurrently within a single patient.

RESEARCH QUESTION

How can we integrate guideline-defined radiologic patterns to diagnose interstitial lung disease (ILD) and what are the pitfalls associated with described patterns that require reassessment in future guidelines?

STUDY DESIGN AND METHODS

Patients from the Canadian Registry for Pulmonary Fibrosis underwent detailed reevaluation in standardized multidisciplinary discussion. CT scan features were quantified by chest radiologists masked to clinical data, and guideline-defined patterns were assigned. Clinical data then were provided to the radiologist and an ILD clinician, who jointly determined the leading diagnosis.

RESULTS

Clinical-radiologic diagnosis in 1,593 patients was idiopathic pulmonary fibrosis (IPF) in 26%, fHP in 12%, connective tissue disease-associated ILD (CTD-ILD) in 34%, idiopathic pneumonia with autoimmune features in 12%, and unclassifiable ILD in 10%. Typical and probable UIP patterns corresponded to a diagnosis of IPF in 66% and 57% of patients, respectively. Typical fHP pattern corresponded to an fHP clinical diagnosis in 65% of patients, whereas compatible fHP was nonspecific and associated with CTD-ILD or IPAF in 48% of patients. No pattern ruled out CTD-ILD. Gas trapping affecting > 5% of lung parenchyma on expiratory imaging was an important feature broadly separating compatible and typical fHP from other patterns (sensitivity, 0.77; specificity, 0.91).

INTERPRETATION

An integrated approach to guideline-defined UIP and fHP patterns is feasible and supports > 5% gas trapping as an important branch point. Typical or probable UIP and typical fHP patterns have moderate predictive values for a corresponding diagnosis of IPF and fHP, although occasionally confounded by CTD-ILD; compatible fHP is nonspecific.

Pulmonary Apical Cap as a Potential Risk Factor for Pleuroparenchymal Fibroelastosis

Pleuroparenchymal fibroelastosis (PPFE) is a progressive and frequently fatal interstitial lung disease that involves the upper lobes. Although its cause remains unknown, the histopathologic evidence underlying PPFE bears striking resemblance to that of the pulmonary apical cap (PAC), a relatively common and benign entity. We describe the case of a patient with PAC that evolved into distinctly asymmetric PPFE over 6 years after unilateral surgical lung injury. Given the histologic similarity between these two conditions, we propose that these two entities underlie common biologic pathways of abnormal response to lung injury, with the presence of a PAC increasing susceptibility to the development of PPFE in the face of ongoing inflammatory insults. This case describes the histopathologic evolution of PAC to PPFE before and after an inciting injury.

Closed-Form Weak Localization Magnetoconductivity in Quantum Wells with Arbitrary Rashba and Dresselhaus Spin-Orbit Interactions

We derive a closed-form expression for the weak localization (WL) corrections to the magnetoconductivity of a 2D electron system with arbitrary Rashba α and Dresselhaus β (linear) and β_{3} (cubic) spin-orbit interaction couplings, in a perpendicular magnetic field geometry. In a system of reference with an in-plane z[over ^] axis chosen as the high spin-symmetry direction at α=β, we formulate a new algorithm to calculate the three independent contributions that lead to WL. The antilocalization is counterbalanced by the term associated with the spin relaxation along z[over ^], dependent only on α-β. The other term is generated by two identical scattering modes characterized by spin-relaxation rates which are explicit functions of the orientation of the scattered momentum. Excellent agreement is found with data from GaAs quantum wells, where, in particular, our theory correctly captures the shift of the minima of the WL curves as a function of α/β. This suggests that the anisotropy of the effective spin-relaxation rates is fundamental to understanding the effect of the spin-orbit coupling in transport.

Asymmetric Landau bands due to spin-orbit coupling

We show that the Landau bands obtained in a two-dimensional lateral semiconductor superlattice with spin-orbit coupling (SOC) of the Rashba/Dresselhaus type, linear in the electron momentum, placed in a tilted magnetic field, do not follow the symmetry of the spatial modulation. Moreover, this phenomenology is found to depend on the relative tilt of magnetic field and on the SOC type: (a) when only Rashba SOC exists and the magnetic field is tilted in the direction of the superlattice (b) Dresselhaus SOC exists and the magnetic field is tilted in the direction perpendicular to the superlattice. Consequently, measurable properties of the modulated system become anisotropic in a tilted magnetic field when the field is conically rotated around the z axis, at a fixed polar angle, as we demonstrate by calculating the resistivity and the magnetization.

Coulomb interaction effects on the Majorana states in quantum wires

The stability of the Majorana modes in the presence of a repulsive interaction is studied in the standard semiconductor wire-metallic superconductor configuration. The effects of short-range Coulomb interaction, which is incorporated using a purely repulsive δ-function to model the strong screening effect due to the presence of the superconductor, are determined within a Hartree-Fock approximation of the effective Bogoliubov-De Gennes Hamiltonian that describes the low-energy physics of the wire. Through a numerical diagonalization procedure we obtain interaction corrections to the single particle eigenstates and calculate the extended topological phase diagram in terms of the chemical potential and the Zeeman energy. We find that, for a fixed Zeeman energy, the interaction shifts the phase boundaries to a higher chemical potential, whereas for a fixed chemical potential this shift can occur either at lower or higher Zeeman energies. These effects can be interpreted as a renormalization of the g-factor due to the interaction. The minimum Zeeman energy needed to realize Majorana fermions decreases with the increasing strength of the Coulomb repulsion. Furthermore, we find that in wires with multi-band occupancy this effect can be enhanced by increasing the chemical potential, i.e. by occupying higher energy bands.

The thermoelectric power factor of a semiconductor superlattice with nanoparticle inclusions

We develop a phenomenological theory for cross-plane transport in a semiconductor superlattice (SL) doped with nanostructures to improve the thermoelectric properties. The SL consists of an array of quantum wells equally spaced along a spatial direction separated by narrow barriers, such that, in the presence of inter-well tunneling, a miniband energy structure is established. The semi-metallic ErAs nanoparticles are embedded inside the quantum wells in the process of growth of the SL, as reported in several recent experiments. Their effect on thermoelectric transport is considered through an additional contribution to the electron scattering rate, that is correlated with a process of resonant tunneling through the nanoparticle-semiconductor interface modeled as a Schottky barrier. In a semi-classical approximation of the miniband conduction regime, we calculate the electric conductivity, the thermopower and the power factor as a function of the barrier height and demonstrate the presence of a filtering effect, whereby the Seebeck coefficient is enhanced by the additional scattering.

Electron-dephasing time in a two-dimensional spin-polarized system with Rashba spin-orbit interaction

We calculate the dephasing time tau(phi)(B) of an electron in a two-dimensional system with a Rashba spin-orbit interaction, spin-polarized by an arbitrarily large magnetic field parallel to the layer. tau(phi)(B) is estimated from the logarithmic corrections to the conductivity within a perturbative approach that assumes weak, isotropic disorder scattering. For any value of the magnetic field, the dephasing rate changes with respect to its unpolarized-state value by a universal function whose parameter is 2E(Z)/E(SOI) (E(Z) is the Zeeman energy, while E(SOI) is the spin-orbit interaction), confirming the experimental report published in Phys. Rev. Lett. 94, 186805 (2005). In the high-field limit, when 2E(Z) >> E(SOI), the dephasing rate saturates and reaches asymptotically to a value equal to half the spin-relaxation rate.

Spin mass of an electron liquid

We show that in order to calculate correctly the spin current carried by a quasiparticle in an electron liquid one must use an effective "spin mass" m(s) that is larger than both the band mass m(b), which determines the charge current, and the quasiparticle effective mass m(*), which determines the heat capacity. We present two independent estimates of the spin mass enhancement, m(s)/m(b), in two- and three-dimensional electron liquids, based on (i) previously calculated values of the Landau parameters and (ii) a recent theory of the dynamical local field factor in the spin channel. Both methods yield a significant spin mass enhancement, which is larger in two dimensions than in three.

Identification of spherical virus particles in digitized images of entire electron micrographs

New methods are described that should facilitate high-resolution (5-10 A) image reconstructions from low-dose, low-contrast electron micrographs of frozen-hydrated specimens and processing of large, digital images produced by new imaging devices and modern electron microscopes. Existing techniques for automatic selection of images of individual biological macromolecules from electron micrographs are inefficient or unreliable. We describe the Crosspoint method (CP), which produces good quality solutions with relatively small miss rates and few false hits, and an extension of this method along with a procedure for refining its solution. Two algorithms for processing large images, one based on image subsampling, the other on image decomposition, are described. A large image is first compressed (e.g., by subsampling) and the CP method is applied to the compressed image to produce an initial solution. The information gathered at this stage is used to cut the original image into subimages and then to refine the particle coordinates in each subimage. An interactive environment for experimenting with particle identification methods is described.

Phase refinement and extension by means of non-crystallographic symmetry averaging using parallel computers

Electron-density averaging, fast Fourier synthesis and fast Fourier analysis programs have been adapted for parallel-computing systems. These have been linked to perform iterative phase improvement and extension utilizing non-crystallographic symmetry and solvent flattening. Various strategies for parallel algorithms have been tested on a variety of computers as a function of the number of computer nodes. Some experimental timing results are discussed.