P300 from inspiratory occlusion reflects orienting but not startle

The role of nicotine on respiratory sensory gating measured by respiratory-related evoked potentials

Respiratory perception can be altered by changes in emotional or psychological states. This may be due to affective (i.e., anxiety) modulation of respiratory sensory gating. Nicotine withdrawal induces elevated anxiety and decreased somatosensory gating. Respiratory sensory gating is evidenced by decreased amplitude of the respiratory-related evoked potentials (RREP) N1 peak for the second occlusion (S2) when two 150-ms occlusions are presented with a 500-ms interval during an inspiration. The N1 peak amplitude ratio of the S2 and first occlusion (S1) (S2/S1) is <0.5 and due to central neural sensory gating. We hypothesized that withdrawal from nicotine is anxiogenic and reduces respiratory gating in smokers. The RREP was recorded in smokers with 12-h withdrawal from nicotine and nonsmokers using a paired occlusion protocol. In smokers, the RREP was measured after nicotine withdrawal, then with either nicotine or placebo gum, followed by the second RREP trial. Nonsmokers received only placebo gum. After nicotine withdrawal, the smokers had a higher state anxiety compared with nonsmokers. There was a significant interaction between groups (nonsmokers vs. smokers with nicotine vs. smokers with placebo) and test (pre- vs. posttreatment) in RREP N1 peak amplitude S2/S1. The S2/S1 in the smokers were larger than in nonsmokers before treatment. After gum treatment, the smoker-with-placebo group had a significantly larger S2/S1 than the other two groups. The S2/S1 was significantly decreased after the administration of nicotine gum in smokers due to significantly decreased S2 amplitudes. The RREP Nf and P1 peaks were unaffected. These results demonstrated that respiratory sensory gating was decreased in smokers after nicotine withdrawal. Nicotine increased respiratory sensory gating in smokers with a S2/S1 similar to that of the nonsmokers. Nicotine did not change respiratory sensory information arrival, but secondary information processing in respiratory sensation.

The impact of panic disorder on interoception and dyspnea reports in chronic obstructive pulmonary disease

The prevalence of panic disorder (PD) in patients with chronic obstructive pulmonary disease (COPD) is significantly higher than that in the general population. Comorbid anxiety disorders in COPD are associated with a number of worse outcomes, however little is known about the mechanisms by which PD affects patients with COPD. We hypothesized that patients with COPD and PD would have greater dyspnea severity, but not greater somatosensory sensitivity, to dyspneic stimuli. We studied 10 patients with COPD and PD, 9 patients with COPD without PD, and 9 healthy, matched controls. Participants were administered the Anxiety Sensitivity Index-3. We tested interoceptive sensitivity using a respiratory load detection protocol and dyspnea ratings in response to inspiratory resistive loads. Participants with COPD and PD had higher anxiety sensitivity scores and reported greater dyspnea in response to resistive loads. However no group differences were found in resistive load detection threshold. Anxiety sensitivity scores accounted for a significant amount of the variance in the group difference in dyspnea ratings. Patients with COPD and PD do not show heightened interoceptive sensitivity, but report greater dyspnea to inspiratory resistive loads. Emotional responses to dyspneic sensations may account for higher dyspnea ratings in patients with PD and COPD.

Respiratory-related evoked potential measures of respiratory sensory gating

The purpose of this study was to demonstrate a neural respiratory gating system using a paired stimuli paradigm. The N1 peak of the respiratory-related evoked potential (RREP) represents early perceptual processing of respiratory sensory information. This is similar to the N100 peak shown with tactile sensation, where the second peak amplitude (S2) of the N100 peak from the somatosensory evoked potential (SEP) was smaller than the first peak amplitude (S1) when the stimuli were presented 500 ms apart. We hypothesized that paired inspiratory occlusions would result in a reduced amplitude of the S2 N1 RREP peak amplitude, indicating respiratory central neural gating. Twenty healthy subjects (10 men and 10 women; 25.8 +/- 6.5 yr old) completed the paired inspiratory occlusion (RREP) trial. Thirteen of the subjects also completed the paired mouth air puffs [mouth-evoked potential (MEP) trial], and the paired hand air puffs (SEP) trial. All paired presentations were separated by 500 ms. The N1 peak amplitudes of the RREP trial and the N100 peak amplitudes of the MEP and SEP trials for S1 and S2 and the S2/S1 ratios were determined. The S1 RREP N1 peak amplitude was significantly greater than S2, and the S2/S1 ratio was 0.43. The S1 MEP and SEP N100 peak amplitudes were significantly greater than S2, and the N100 ratio was 0.49 and 0.49, respectively. These results are consistent with central neural gating of respiratory afferent input. The RREP gating response is similar to somatosensory mechanoreceptor gating.

Detection threshold for inspiratory resistive loads and respiratory-related evoked potentials

The relationship between detection threshold of inspiratory resistive loads and the peaks of the respiratory-related evoked potential (RREP) is unknown. It was hypothesized that the short-latency and long-latency peaks of the RREP would only be elicited by inspiratory loads that exceeded the detection threshold. The detection threshold for inspiratory resistive loads was measured in healthy subjects with inspiratory-interruption or onset load presentations. In a separate protocol, the RREPs were recorded with resistive loads that spanned the detection threshold. The loads were presented in stimulus attend and ignore sessions. Onset and interruption load presentations had the same resistive load detection threshold. The P1, Nf, and N1 peaks of the RREP were observed with loads that exceeded the detection threshold in both attend and ignore conditions. The P300 was present with loads that exceeded the detection threshold only in the attend condition. No RREP components were elicited with subthreshold loads. The P1, Nf, and P300 amplitudes varied with resistive load magnitude. The results support the hypothesis that there is a resistive load threshold for eliciting the RREPs. The amplitude of the RREP peaks vary as a function of load magnitude. The cognitive P300 RREP peak is present only for detectable loads and when the subject attends to the stimulus. The absence of the RREP with loads below the detection threshold and the presence of the RREP elicited by suprathreshold loads are consistent with the gating of these neural measures of respiratory mechanosensory information processing.