Study protocol of an individual thresholding procedure assessing respiratory interoception using non-invasive resistances and occlusions

Background: Altered interoception may play an important role in
symptom generation. Understanding the psychobiological mechanisms
underlying symptoms, however, necessitates the assessment of
interoceptive indicators for different stages of processing. Therefore,
we developed a protocol to assess multiple stages of interoceptive
signal processing in the respiratory domain.
Methods: Respiratory stimuli are required to elicit respiratory-related
evoked potentials (RREPs) for early sensory-perceptual processing (Stage
1) and late affective-cognitive processing (Stage 3), as well as present a
tangible behavioral component (interoceptive accuracy/IAc), with conscious
sensory-perceptual feedback (Stage 2), in line with established
methods used in other organ domains. The nature of the stimuli used
were full occlusions (100%, 250ms duration with 84ms rise time, 100ms
onset delay after start of inhalation, 2-4 non-occluded breaths) of a
breathing tube for stages 1 & 3, and resistances (5~95%, 2000ms
duration with 4~80ms rise time, 100ms onset delay) for stage 2.
Resistances were based on a percentage of a full occlusion of the
breathing tube. A personal resistance threshold was determined by
presenting decreasing resistances in steps of 5%, until a resistance was
detected <50%. The measure was repeated with single-step presentation
of the last increment to determine a precise personal threshold.
Based on the threshold, resistances were presented at 50%, 25%, 12.5%
and 6.25% of maximal resistance above threshold, at 6.25%, 12.5% and
25% of minimal resistance below threshold, as well as maximal (95%)
and minimal (5%) resistance and the threshold-level itself. The order of
resistances and occlusions was counterbalanced to control for a reciprocal
effect.