Respiratory related changes in electrodermal activity

Nepeari Skin electrical conductance (SC) reflects autonomically controlled sweat gland activity. Phasic changes in SC (skin conductance response - SCR) can be evoked by various stimuli (eg visual, auditory) and decrease with repetitive stimulation (habituation). SCRs are also known to be associated with deep inspiration, however, the mechanisms linking SCR and respiration have not been studied. Methods: We measured SCR, mouth pressure (P) and inspired airflow and volume (V) in 5 normal adult subjects who performed inspiratory efforts via a mouthpiece to reach target mouth pressures of -5, -10 and -15cm H2O against either an external resistance or an occlusion. Each condition was repeated 3 times and the resulting 18 inspiratory events were randomly presented within a session but in a fixed order across subjects. Results: During tidal mouth breathing, group mean SC was 5.7 ji Siemens (S; range: 4.3-8.1 (iS) and was unaffected by phase of respiration. During inspiratory efforts, however, an SCR was evoked in 76% of events with responses occurring during both occluded (0.38 ,nS (0.09(SEM)) and unoccluded efforts (0.64 jiS (0.10); n=45, p<0.005, unpaired t-test). Furthermore, SCR progressively decreased as the number of inspiratory efforts performed increased. During occlusion, multiple regression analysis showed that SCR was negatively related to the temporal position of the event (E; n=42, p<0.0005) but not related to mouth pressure. For efforts against an external resistance there was a significant relationship between SCR and E (n=42, p<0.041) and V (n=42, p<0.0005) [SCR(S)=0.40+0.42V(1)-0.029E; r=0.46, p<0.0005]. Conclusion: We have confirmed that inspiratory efforts during partial or complete occlusion can elicit SCRs. However, it is unlikely that inspiratory airflow, lung volume change, or the level of mouth pressure are unique factors influencing SCR. Respiratory related SCR shows habituation, a hallmark of a central process. We speculate that the demonstrated relationship between volume change and SCR may reflect the degree of applied effort.