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                 Increase in intracranial pressure by application of a rigid cervical collar 191
gency medical service physicians since 2012. Both performed over 25 ONSD examinations before our study. Sonographers were also blinded to each other’s measurements (Figure 9.1 and Figure 9.2). The upper part of the volunteer’s head (from the nose up) was presented to the operators through a narrow opening in the center of a room dividing screen. Between every session, the sonographer was not allowed to see the participant, while a collar was be- ing applied or not as per randomization. All four sessions of measurements were performed with the volunteers in a supine position on a table: two with and two without application of a Stifneck® (Laerdal Medical AS, Stavanger, Norway) rigid cervical collar.
Measurements were performed within two minutes after the application of the collar. Volun- teers were instructed to breathe normally and not to talk or cough during the measurements. If coughing occurred, measurements were repeated. Randomization was achieved by rolling a die in one of six collar regimes (Table 9.1). A third researcher (BV) on the other side of the screen adjusted the size of the adaptable Stifneck® and applied it to the participants’ neck as prescribed in the user manual (version and year). The cervical collar Velcro was opened and closed again before every measurement, independent of application to the volunteer’s neck
Figure 9.2 Research set-up
In the center of the image, the screen is shown that blocked the view to the subjects’ necks.
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