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Susceptibility to periodic breathing with assisted ventilation during sleep in normal subjects
Authors:Meza  Sonia; Mendez  Manuel; Ostrowski  Michele; Younes  Magdy
Abstract:Assisted ventilation with pressure support (PSV)or proportional assist (PAV) ventilation has the potential to produceperiodic breathing (PB) during sleep. We hypothesized that PB willdevelop when PSV level exceeds the product of spontaneous tidal volume (VT) and elastance(VTsp · E)but that the actual level at which PB will developPSV(PB)] will be influenced by theDelta PCO2 (difference between eupneicPCO2 andCO2 apneic threshold) and by Delta RRresponse of respiratory rate (RR) to PSV]. We also wishedto determine the PAV level at which PB develops to assess inherentventilatory stability in normal subjects. Twelve normal subjectsunderwent polysomnography while connected to a PSV/PAV ventilatorprototype. Level of assist with either mode was increased in smallsteps (2-5 min each) until PB developed or the subject awakened.End-tidal PCO2,VT, RR, and airway pressure (Paw) were continuously monitored, and the pressure generated byrespiratory muscle (Pmus) was calculated. The pressure amplification factor (PAF) at the highest PAV level was calculated from(Delta Paw + Pmus)/Pmus], where Delta Paw is peak Paw - continuous positive airway pressure. PB with central apneas developedin 11 of 12 subjects on PSV. Delta PCO2ranged from 1.5 to 5.8 Torr. Changes in RR with PSV were small andbidirectional (+1.1 to -3.5min-1). With use ofstepwise regression, PSV(PB) was significantly correlated withVTsp(P = 0.001), E(P = 0.00009),Delta PCO2 (P = 0.007), and Delta RR(P = 0.006). The final regressionmodel was as follows: PSV(PB) = 11.1 VTsp + 0.3E - 0.4 Delta PCO2 - 0.34 Delta RR - 3.4 (r = 0.98). PBdeveloped in five subjects on PAV at amplification factors of1.5-3.4. It failed to occur in seven subjects, despite PAF of upto 7.6. We conclude that 1) aPCO2 apneic threshold exists duringsleep at 1.5-5.8 Torr below eupneicPCO2,2) the development of PB during PSVis entirely predictable during sleep, and3) the inherent susceptibility to PBvaries considerably among normal subjects.

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