Kais Hamza

Abnormal vocal cord function in difficult-to-treat asthma.

RATIONALE Upper airway dysfunction may complicate asthma but has been largely ignored as an etiological factor. Diagnosis using endoscopic evaluation of vocal cord function is difficult to quantify, with limited clinical application. OBJECTIVES A novel imaging technique, dynamic 320-slice computerized tomography (CT), was used to examine laryngeal behavior in healthy individuals and individuals with asthma. METHODS Vocal cord movement was imaged using 320-slice CT larynx. Healthy volunteers were studied to develop and validate an analysis algorithm for quantification of normal vocal cord function. Further studies were then conducted in 46 patients with difficult-to-treat asthma. MEASUREMENTS AND MAIN RESULTS Vocal cord movement was quantified over the breathing cycle by CT using the ratio of vocal cord diameter to tracheal diameter. Normal limits were calculated, validated, and applied to evaluate difficult-to-treat asthma. Vocal cord movement was abnormal with excessive narrowing in 23 of 46 (50%) patients with asthma and severe in 9 (19%) patients (abnormal > 50% of inspiration or expiration time). Imaging also revealed that laryngeal dysfunction characterized the movement abnormality rather than isolated vocal cord dysfunction. CONCLUSIONS Noninvasive quantification of laryngeal movement was achieved using CT larynx. Significant numbers of patients with difficult-to-treat asthma had excessive narrowing of the vocal cords. This new approach has identified frequent upper airway dysfunction in asthma with potential implications for disease control and treatment.

Phenotypes of patients with mild to moderate obstructive sleep apnoea as confirmed by cluster analysis

Background and objective:  Patients with OSA manifest different patterns of disease. However, this heterogeneity is more evident in patients with mild‐moderate OSA than in those with severe disease and a high total AHI. We hypothesized that mild‐moderate OSA can be categorized into discreet disease phenotypes, and the aim of this study was to comprehensively describe the pattern of OSA phenotypes through the use of cluster analysis techniques.

The smallest uniform upper bound on the distance between the mean and the median of the binomial and Poisson distributions

We show that for the binomial and Poisson distributions, the distance between the mean and the median is always less than ln 2.

Some Properties and Generalizations of Non-negative Bayesian Time Series Models

We study the most basic Bayesian forecasting model for exponential family time series, the power steady model (PSM) of Smith, in terms of observable properties of one-step forecast distributions and sample paths. The PSM implies a constraint between location and spread of the forecast distribution. Including a scale parameter in the models does not always give an exact solution free of this problem, but it does suggest how to define related models free of the constraint. We define such a class of models which contains the PSM. We concentrate on the case where observations are non-negative. Probability theory and simulation show that under very mild conditions almost all sample paths of these models converge to some constant, making them unsuitable for modelling in many situations. The results apply more generally to non-negative models defined in terms of exponentially weighted moving averages. We use these and related results to motivate, define and apply very simple models based on directly specifying the forecast distributions.

A Family of Non-Gaussian Martingales with Gaussian Marginals

We construct a family of martingales with Gaussian marginal distributions. We give a weak construction as Markov, inhomogeneous in time processes, and compute their infinitesimal generators. We give the predictable quadratic variation and show that the paths are not continuous. The construction uses distributions Gσ having a log-convolution semigroup property. Further, we categorize these processes as belonging to one of two classes, one of which is made up of piecewise deterministic pure jump processes. This class includes the case where Gσ is an inverse log-Poisson distribution. The processes in the second class include the case where Gσ is an inverse log-gamma distribution. The richness of the family has the potential to allow for the imposition of specifications other than the marginal distributions.

CONDITIONS FOR INTEGRABILITY OF MARKOV CHAINS

We give simple sufficient conditions for integrability of continuous-time Markov chains in terms of their infinitesimal parameters. Similar conditions for regularity are stated first, and a simple proof given.

Night-to-night repeatability of supine-related obstructive sleep apnea.

RATIONALE Patients with obstructive sleep apnea (OSA) experience respiratory events with greater frequency and severity while in the supine sleeping position. Postural modification devices (PMDs) prevent supine sleep, although there is a paucity of guidance to help clinicians decide when to use PMDs for their patients. In order for PMDs to treat OSA effectively, patients must experience respiratory events in the supine sleeping position consistently from night to night and must have a low nonsupine apnea and hypopnea index (AHINS). OBJECTIVES To document the repeatability of traditionally defined supine predominant OSA on consecutive polysomnography, to determine whether the consistency of the supine-predominant phenotype can be improved by altering the definition of it, and to determine whether a low AHINS is repeatable from night to night. METHODS We recruited 75 patients for polysomnography on two separate nights. Patients were classified as having supine OSA on each night on the basis of traditional and novel definitions, and the classification systems used were compared on the basis of agreement from night to night. MEASUREMENTS AND MAIN RESULTS The definition of supine OSA with the highest level of agreement from night to night incorporates a supine AHI (AHIS) to AHINS ratio ≥4:1. In addition, agreement exists for males, but there is poor agreement for female patients, regardless of the definition applied. An AHINS <10 events/hour is highly repeatable from night to night. CONCLUSIONS Males with an AHIS:AHINS ratio ≥4:1 and an AHINS <10 events/hour represent a consistent supine-predominant OSA phenotype from night to night. This patient group is likely to benefit from treatment with PMD.

Exacerbation phenotyping in chronic obstructive pulmonary disease

Acute exacerbations of chronic obstructive pulmonary disease (AECOPD) are crucial events but causes remain poorly defined. A method to clinically ‘phenotype’ AECOPD have been proposed, and 52 hospitalized chronic obstructive pulmonary disease exacerbations according to underlying aetiology have now been prospectively phenotyped. Multiple exacerbation phenotypes were identified. A subpopulation coinfected with virus and bacteria had a significantly longer length of hospital stay, and this pilot study indicates that exacerbation phenotyping may be advantageous.

Abnormal vocal cord movement treated with botulinum toxin in patients with asthma resistant to optimised management

Abnormal vocal cord movement may coexist with asthma and cause additional upper/middle airway obstruction. The condition may be a form of muscular dystonia that could contribute to asthma resistant to optimised treatments. Botulinum toxin causes temporary paralysis of muscle and may be an effective local treatment that improves asthma control.

Evaluation of the role of lung volume and airway size and shape in supine‐predominant obstructive sleep apnoea patients

This study aimed to evaluate the involvement of airway cross‐sectional area and shape, and functional residual capacity (FRC), in the genesis of obstructive sleep apnoea (OSA) in patients with supine‐predominant OSA.