Bowel-sound pattern analysis using wavelets and neural networks with application to long-term, unsupervised, gastrointestinal motility monitoring

Abstract

This work focuses on the implementation of an autonomous system appropriate for long-term, unsupervised monitoring of bowel sounds, captured by means of abdominal surface vibrations. The autonomous intestinal motility analysis system (AIMAS) promises to deliver new potentials in gastrointestinal auscultation, towards the establishment of novel non-invasive methods for prolonged intestinal monitoring and diagnosis over functional disorders. The system was developed utilizing time–frequency features and wavelet-adapted parameters in combination with multi-layer perceptrons, that exhibit remarkable adaptation in pattern classification applications. Various network topologies and sizes were tested in combination with different features’ sets. Quantitative analysis and validation results showed that the implemented system exhibits an overall recognition accuracy of 94.84%, while the error in separating bowel sounds from other sound patterns, representing interfering noises, was 2.19%.

Introduction

During the last decades, the field of biomedical engineering has received a lot of attention from researchers, allowing technology improvements to have a positive impact on medical knowledge and practice. Expert systems and artificial intelligence methods have been implemented in a variety of applications (Aruna et al., 2005, İçer et al., 2006, Jiang and Choi, 2006, Polat et al., 2006, Turkoglu et al., 2002, Subasi, 2006, Yan et al., 2006), offering better knowledge handling and diagnostic decisions support utilities. These benefits are observed in various fields of medical expertise, including the critical area of gastroenterology, where computer assisted expert systems have been reported for delivering e-health services (Aruna et al., in press, Huang and Chen, 2006, Kuo et al., 2004). However, there is a lack of a reliable and easy to apply method for long-term monitoring of intestinal contractile activity that still makes difficult to study the gastrointestinal motility physiology (Drossman, 1999, Talley et al., 2000). As a result, there are certain gastrointestinal functional disorders that are still diagnosed indirectly, via elimination of other diseases. The irritable bowel syndrome (IBS) is the most representative case, while other functional disorders such as abdominal bloating, functional dyspepsia, diarrhea, constipation and abdominal pain fall in the same category (Drossman, 1999, Talley et al., 2000). Most of these symptoms are strongly affected by various factors like nutrition, medication and stress; their influence to intestinal motility is another issue needs further research (Drossman, 1999, Holtmann and Enck, 1991).

Manometry and electromyography stand as the most common investigative methods that have been tested for medical knowledge extraction and diagnosis of the related abnormalities (Chen et al., 1993, Kellow et al., 1990, Sharna, 1989, Vantrappen et al., 1986, Weisbrodt, 1987). Their utilization has been mainly restricted to research studies, since they exhibit certain disadvantages to be used in clinical practice. Intraluminal manometry is painful and inconvenient to apply on human subjects, due to its invasiveness. Nevertheless, it is still capable of “clean”, multi-site pressure recordings. Operative electromyography seems to feature similar advantages and disadvantages. As a result, research efforts have been concentrated on non-invasive methods like cutaneous electromyography (Garcia-Casado, Martinez-de-Juan, & Ponce, 2005), as well as recording and analysis of gastrointestinal sounds (Craine et al., 1999, Craine et al., 2001, Craine et al., 2002, Dimoulas et al., 1999, Hadjileontiadis et al., 2000, Hadjileontiadis, 2005a, Hadjileontiadis, 2005b, Pastiadis et al., 1998, Tomomasa et al., 1999, Dimoulas, 1997, Campbell et al., 1989).

Bowel sound (BS) auscultation was proposed as an alternative medical study approach, in order to overcome the previous stated obstacles. There are direct relationships between manometry, electromyography and abdominal surface vibration (ASV) sensing, in how they monitor intestinal motility. All methods measure the effects of muscular convulsions, which produce pressure alterations over time and electrical myogenic activity. Implementation of BS monitoring has many advantages over traditional diagnosis methods (including X-ray screening approaches), because it is easier to apply, non-invasive, painless, does not cause discomfort to subjects, its influence to other psycho-physiology issues is limited, and can be applied for prolonged periods. However, knowledge and interpretation of BS has advanced little since Cannon’s pioneering work (Cannon, 1905), so that there is a lack of a reliable and accurate method for use in clinical practice. Most researchers seem to agree that this is not due to redundancy of diagnostic information of BS, but due to insufficient scientific support (Hadjileontiadis et al., 2000).