RESPIRATORY CHALLENGE INDUCES HIGH-FREQUENCY SPIKING ON THE STATIC CHARGE SENSITIVE BED (SCSB)

The static charge sensitive bed (SCSB) is a simple and noninvasive dev ice used for the detection of sleep apnoea. In addition to episodes of apnoea or hypopnoea, heavy snorers commonly present with episodes of high frequency spiking on the SCSB. These spiking episodes have been c laimed to represent partial upper airway obstruction during sleep, but the mechanism of their appearance is not known, We studied the SCSB s piking phenomenon in awake subjects during experimental respiratory ch allenge. One female and five male volunteers were studied whilst breat hing freely, during hypoxia, hypercapnia and inspiratory and expirator y loading, Oxygen saturation, end-tidal carbon dioxide tension, minute ventilation oesophageal pressure, electrocardiographic activity (ECG) , blood pressure and the SCSB signals were monitored. During free brea thing, the SCSB high frequency signal consisted of low amplitude compl exes with close time relationship to the cardiac cycle, During respira tory challenge, spiking occurred, These spikes showed no time relation ship to the cardiac cycle, but were time-linked to the onset of inspir ation or expiration, Spike amplitude correlated with breathing frequen cy (r(2)=0.59; p<0.005) and variation in oesophageal pressure (r(2)=0. 57; p<0.005). We conclude that during quiet, unobstructed breathing th e static charge sensitive bed high frequency signal represents cardiac activity (ballistocardiogram), whereas during high-drive breathing hi gh frequency spikes are produced, These spikes are respiratory in orig in and are likely to represent fast components of respiratory movement s, Our results support the use of static charge sensitive bed spiking as a noninvasive measure of breathing stimulation.