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Figure 1 (Upper panel) The placement of the tilt switches in the sensor unit. Four tilt switches are placed inside the box. The two switches (HL, HR) are used to detect the recumbent positions. When the body turns sideways more than 30 degrees, one of these switches turns on. Consequently, it changes the frequency of the oscillator output. Another pair of switches (VL, VR) can be used to detect whether the patient is standing or not. In the case of standing (or lying in the prone position), both switches turn off; as a result, the oscillator is stopped. (Lower panel) An example of the recorded waves. The output voltage of the pulse is 3 mV peak-to-peak, with the frequency selectable between 0.5, 1, and 2 Hz depending on the combination of the status of the tilt switches. Each frequency of 0.5, 1, and 2 Hz corresponds to the left lateral decubitus position, supine position, and right lateral decubitus position, respectively.
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