«PEKKA TIIHONEN Novel Portable Devices for Recording Sleep Apnea and Evaluating Altered Consciousness Doctoral dissertation To be presented by ...»
In addition to the technical and preliminary clinical tests with healthy volunteers included in Study IV, several clinical studies have been carried out with the device (Yppärilä 2002a, Yppärilä 2002b, Haenggi 2004, Yppärilä 2004a, Yppärilä 2004b, Westeren-Punnonen 2005). In these studies, the depths of sedation in adult patients under-going open-heart surgery (Yppärila 2002a) and sedation-induced changes in the EEG in children with adenoidectomy (Nieminen 2002) have been investigated. In addition, the device has been used for estimation of the effect of propofol sedation on ERPs and EEG in intensive care patients (Yppärila 2004b). In these studies, electromagnetic interference from other medical devices in ICU has been found to be relatively low and not to impair the clinical quality of the measurements.
In a case study of a patient suffering from an episode of postoperative ventricular fibrillation (Westeren-Punnonen 2005), the auditory ERPs recorded with Emma were found to recover faster than the EEG after the ventricular fibrillation and cardiac arrest.
The N100 component recovered to the baseline level within six hours after successful resuscitation, while the EEG still showed very slow and low-amplitude background activity. This is a clinically important finding, suggesting that devices like Emma can be of great benefit in the early prognostic assessment after different kinds of central nervous system insults.
The clinical applicability of Emma has been demonstrated in various clinical studies. However, the lack of a display and real-time signal processing enabling instantaneous evaluation of the status of the patient is the most evident shortcoming of the device. Moreover, recording of additional physiological parameters such as oxygen saturation, breathing movements and air flow would enable more comprehensive evaluation of central nervous system functions.
7.4 On the development of devices for clinical use in a hospitalenvironment
Clinical diagnostic devices are generally developed in research institutes and commercial companies. Although the developers strive to listen to the needs of the end users, many features of the devices are often not optimal for economic diagnostics.
Often the devices provide many diagnostically irrelevant features making them complicated and expensive. The interests of companies (profits) and hospitals (diagnosis and treatment of patients) rarely intersect. For example, the business consept of a manufacturer may be based on the maintenance of fragile devices and selling of expensive spare parts. The low durability and reliability of portable sleep monitors may be an example of these dubious commercial tactics. However, by searching for solutions from the user’s point of view, new ideas can arise.
Furthermore, commercial devices may be too complicated to use as they are often designed from engineers’ point of view. This can lead to failed recordings due to human
errors. The main goal of this work was to build robust, reliable, and easy to use devices.
Device development inside a hospital provides immediate connection to the end users, and the feedback is instant and honest. In hospitals, new ideas and devices (for example transducers) can be applied and clinically tested, because the appropriate reference instruments are readily available.
However, developing novel devices inside a hospital clinic is challenging.
Economics may have a significant role because the development of devices does entail some costs. Hospital organizations may have strict limitations and rules that can totally block this kind of work and prejudice attitudes can lead to serious limitations. Many influential administrators may believe that a hospital is for treating patients, not for scientific work or device development.
However, Studies I and IV reveal that development of devices or methods for clinical use can be conducted in a hospital environment and lead not only to scientific findings but also to commercial opportunities.
In this work, novel devices were designed, constructed and evaluated for use in the clinical diagnostics of sleep apnea and for monitoring of the depth of sedation or the level of consciousness.
1. The device developed in the Study I demonstrated similar diagnostic capabilities in the detection of sleep apnea as a commercial reference device. No statistical differences were found between the devices in evaluating the apnea hypopnea or in oxygen desaturation indices. Both the AHI and ODI values determined with the novel device and the reference instrument were highly linearly correlated. The developed device showed good technical reliability compared to devices evaluated in the literature.
2. The portable seven-channel recording device evaluated in Study II proved to be as good as the commercial reference device in detecting sleep apnea. No statistical differences were found in AHI or ODI values determined from simultaneous recordings with the reference instrument and the novel device. However, the technical reliability of the novel device was found to be superior to the values reported for other devices in the literature.
3. The reliability of automatic analysis of breathing events was found to be critically dependent on signal quality and therefore on the recording device. The comparison of automatic and manual analysis of ambulatory recordings of nocturnal breathing disorders revealed that an exclusion of obstructive sleep apnea should not be done based on automated analysis alone. However, automated analysis can greatly assist in the manual analysis, especially in severe cases.
Importantly, automatic analysis was found to fail in the detection of mixed and central apneas and those events should always be checked manually.
4. The device developed in Study IV was found to be suitable for safe and reliable measurement of ERP, EEG, and SEP. To our knowledge, no other portable instrument capable of ERP recordings in intensive care units has been described in the literature.
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Kuopio University Publications C. Natural and Environmental Sciences 261: 1 - 79 (2009)