Emfit movement sensor in evaluating nocturnal breathing

Highlights

• The movement sensors (SCSB, Emfit) have been used to classify periodic breathing.

• Those sensors offer additional information on the degree of negative intrathoracic pressure during apneas or hypopneas.

• The Emfit pattern scoring correlates with excellent accuracy in detecting subjects with AHI 15/h or more.

• The Emfit would enhance the diagnostic accuracy of clinically significant sleep-disordered breathing.

Abstract

Obstructive sleep apnea (OSA) diagnostics by the movement sensors static charge-sensitive bed (SCSB) and electromechanical film transducer (Emfit) is based on dividing the signal into different breathing patterns. The usage of non-invasive mattress sensors in diagnosing OSA is particularly tempting if patient has many other non sleep-related monitoring sensors. However, a systematic comparison of the apnea–hypopnea index (AHI) with Emfit-parameters is lacking. In addition to periodic breathing, SCSB and Emfit visualize episodes of sustained negative increases in intrathoracic pressure (increased respiratory resistance, IRR), of which relevance is still ambiguous. Our aim is to compare Emfit-parameters with the AHI and to provide a description of the patients suffering from IRR.

Time percentage with all obstructive periodic Emfit breathing patterns (OPTotal%) showed the best correlation with the AHI. The OPTotal percentage of 21 yielded to excellent accuracy in detecting subjects with an AHI of 15/h or more. Patients with IRR received high scores in GHQ-12-questionnaire.

An Emfit movement sensor might offer additional information in OSA diagnostics especially if nasal pressure transducer cannot be used.

Introduction

Usually quantization of nocturnal sleep-disordered breathing (SDB) is based on the apnea–hypopnea index (number of respiratory events per hour of sleep), the arousal index (number of cortical microarousals per hour of sleep) and the oxygen desaturation index calculated from the polysomnography (PSG). The diagnostic sensitivity of the SDB analysis can be improved, for example, by calculating respiratory related arousals (RERAs) as is done when researching the upper airway resistance syndrome (UARS) (Iber et al., 2007). UARS patients have inspiratory flow limitation which leads to progressive increases in respiratory effort terminated by a sudden decrease in negative oesophageal pressure and arousal (Guilleminault et al., 1993). Repetitive respiratory events can also be detected with noninvasive movement sensors such as the static charge-sensitive bed (SCSB) and the Emfit (electromechanical film transducer) sensor, which are widely used in Finland in diagnosing SDB and periodic leg movements (Anttalainen et al., 2007b, Kirjavainen et al., 1996, Rauhala et al., 2009, Tenhunen et al., 2011). The suitability of SCSB movement sensor in sleep apnea diagnostics has been evaluated in many studies and it has been shown to identify obstructive apneas with high sensitivity (Anttalainen et al., 2010, Lojander et al., 1998, Polo et al., 1988, Polo, 1992, Salmi et al., 1989, Svanborg et al., 1990). In mattress scoring episodes of periodic apneas/hypopneas are named as obstructive periodic patterns (OP-patterns) by Polo et al. (1988).

Attention has recently been paid to another type of SDB; prolonged or sustained partial upper airway obstruction (Anttalainen et al., 2007a, Anttalainen et al., 2010, Bao and Guilleminault, 2004). This phenomenon can be assessed either by sustained negative increase in oesophageal pressure or by prolonged flow limitation pattern in the nasal pressure transducer signal (Bao and Guilleminault, 2004, Hernandez et al., 2001). Also the SCSB and the Emfit can serve as non-invasive means to detect prolonged partial obstruction (Kirjavainen et al., 1996, Polo, 1992, Polo et al., 1991, Tenhunen et al., 2011). Increased negative intrathoracic pressure induces respiratory-related spikes to the SCSB and the Emfit signal (Kirjavainen et al., 1996, Tenhunen et al., 2011), and the sustained partial upper airway obstruction with sustained spiking has been entitled “increased respiratory resistance, IRR” (Alihanka et al., 1981, Alihanka, 1987, Polo, 1992). IRR is clearly distinguishable from the OP-patterns (Fig. 1). In our recent work we discovered that during IRR there is a sustained negative increase in the oesophageal pressure but arousals and apneas/hypopneas are sparse. During OP-patterns oesophageal pressure is also increased, but apneas/hyponeas and arousals are frequent (Tenhunen et al., 2011).

The smaller Emfit bed sensor has replaced the SCSB in many laboratories, and because a systematic comparison between the AHI measured by the PSG and obstructive breathing periods measured with the Emfit has not been done, the main aim of the present study was to evaluate the feasibility of the Emfit-sensor in diagnosing obstructive sleep apnea (OSA) using the PSG with a nasal pressure transducer as a reference method. As there is only little epidemiologic data from prolonged partial obstruction, the other aim was to examine the prevalence of prolonged partial obstruction (IRR) among adult patients who were referred to a full polysomnography. The third aim was to compare polysomnographic and demographic parameters between obstructive sleep apnea syndrome–patients (OSAS) and patients with prolonged partial obstruction.