Use of a New Laser Plethysmograph in Assessment of Chest Wall Function

Abstract

Respiratory disease is the leading cause of death in the UK. Methods for assessing pulmonary function and chest wall movement are essential for accurate diagnosis, as well as monitoring response to treatment, operative procedures and rehabilitation. Despite this, there is a lack of low-cost devices for rapid assessment. Spirometry is used to measure air flow expired, but cannot infer or directly measure full chest wall motion. This paper presents the development of a low-cost chest wall motion assessment system. The prototype was developed using four Microsoft Kinect sensors to create a 3D time-varying representation of a patient’s torso. An evaluation of the system in two phases is also presented. Initially, static volume of a resuscitation mannequin with that of a Nikon laser scanner is performed. This showed the system has slight underprediction of 0.441 %. Next, a dynamic analysis through the comparison of results from the prototype and a spirometer in nine cystic fibrosis patients and thirteen healthy subjects was performed. This showed an agreement with correlation coefficients above 0.8656 in all participants. The system shows promise as a method for assessing respiratory disease in a cost-effective and timely manner. Further work must now be performed to develop the prototype and provide further evaluations.

Description

Respiratory disease, including lung cancer, is the leading cause of death in the UK, accounting for 920,000 disability-adjusted life years lost [10]. It is the most frequent cause of disease in primary care in all age groups and the second most common cause of chronic conditions.

For patients who report to A&E, a quick and low-cost method of assessment is required. One process currently used to assess respiratory disease in a low-cost and time-effective manner is spirometry [14]. Spirometry allows for the measurement of expired airflow from the lungs, enabling physicians to better characterise the cause of breathlessness and to assess progression of respiratory disease over time.

However, spirometry can have significant limitations. Firstly, forced spirometric efforts allow assessment of initial diaphragm/muscle strength and can only measure total airflow in and out of the lungs; it therefore provides a limited amount of feedback and does not allow physicians to identify motion at the chest and the relative contribution of different areas of each lung to the subjects’ respiratory function [16]. This is particularly important in subjects with more focal lung abnormalities, such as emphysematous bullae, collapsed lung segments and previous surgical lung resection. Secondly, the effect of chest wall abnormalities, such as respiratory muscle weakness and pectus excavatum, as well as diaphragm movement cannot be assessed by spirometry [21]. Thirdly, since it is an effort-dependent procedure, there is a potential for inaccurate results in subjects unable to reliably perform a forced expiratory manoeuvre [12] (e.g. children, the elderly and subjects with hearing impairments, learning difficulties or a language barrier). Fourthly, subjects with facial abnormalities or muscle weakness are often unable to form a tight seal around the mouthpiece, preventing spirometry being accurately performed [8].