Minimally Invasive Detection of a Sleep Apnoea

Obstructive sleep apnoea (OSA) is characterised by recurrent nocturnal respiratory interruptions, resulting from the total or partial collapse of the upper respiratory ways. This results into sleep fragmentation, metabolic and biological disorders, which alter the neuropsychological and cardiovascular systems. Nowadays, 24% of men and 9% of women aged 30 to 60 years disclose already an asymptomatic and underdiagnosed sleep disorder breathing (SDB). In subjects suffering from cardiovascular disease, prevalence of SDB is higher than in the general population, reaching 87% in people with resistant hypertension, 51% in those with heart failure and 62% in those with atrial fibrillation (to cite a few).The current diagnostic tool for SDB is polysomnography (PSG), but this is an expensive, time-consuming and uncomfortable tool, which limits its wide-spread use despite the high frequency of SDB in general and, even more, in patients suffering from cardiovascular diseases. Several screening devices exist in order to test those patients at risk of SDB, but these have several limitations, since they are not recommended in patients who are asymptomatic for apnoea, in those with cardiorespiratory diseases, nocturnal arrhythmias or neurological and metabolic co-morbidities. In other words, nowadays there isn't an efficient screening tool of SDB, mainly for those with a low pre-test probability of having SDB.

Preliminary evidence suggests that the seismocardiography (SCG) and the ballistocardiography (BCG) can detect nocturnal awakening and sleep disturbances with a good sensitivity and accuracy as compared to the state-of-the-art PSG. Simultaneous recording of SCG and BCG is called kinocardiography (KCG) and has not been performed yet during sleep.

The main hypothesis tested in this study is that the KCG provides sensitive and accurate measures of obstructive and central apnoea as compared to the state-of-the-art PSG. The secondary hypotheses are related to modifications in the SCG and BCG signals during the apnoea and the effects of continuous positive air pressure (CPAP) therapy. These hypotheses will be tested through a series of studies in normal volunteers and patients, as follow:

• Group RESPIRATOIRYSIMUL (Study A): voluntary end-expiratory breathing cessations periods and obstructive voluntary apnoea's (n=46);
• Group SBD (Study B): patients admitted for complains of sleep disturbances without cardiovascular and/or respiratory abnormalities which could induce artifacts in the KCG recording (n=50);
• Group nCPAP (Study C): patients treated by nCPAP therapy (n=50);
• Group UNSELECTED (Study D): unselected consecutive patients (n=100), without recruitment restrictions.

Study A is an interventional study on voluntary breath holding in normal volunteers. Studies B, C and D are observational investigations recruiting subjects referred for PSG as required by their medical condition. Because the KCG device is not intrusive, the investigators do not anticipate difficulties in the enrollment. This study will not affect in any manner the regular medical care of the patients admitted to the sleep laboratory.

To conclude, SDB is a widespread disease with detrimental health effects and its prevalence is supposed to increase in future years. PSG is the gold standard for diagnosis of SDB but it is an expensive, uncomfortable and time-consuming tool, limiting its use in daily clinical practice. For subjects with a high pre-test probability of SDB, portable, inexpensive and easy-to-use tools have been proposed as sleep monitoring and seem to provide accurate estimates of SDB. Although such devices seem promising, they disclose also several limitations and are not universally accepted as SDB screening devices, mainly in case of low pre-test probability of SBD. The less cumbersome KCG may screen patients for SDB accurately. One of its unique features is also that it can directly identify the consequences of SDB and nCPAP therapy on the cardiovascular system, and in especially the presence of frequently associated cardiac arrhythmias. With a more efficient pre-screening, those who are most likely to be eligible for nCPAP therapy will have a better access to the currently existing sleep laboratory facilities. The present research project has thus the potential of improving SDB patients care and health, at no additional societal costs.