title: Measurement of pressure-time product during spontaneous assisted breathing by rapid interrupter technique.
abstract: BACKGROUND
  Measuring the work of breathing of patients undergoing spontaneous assisted ventilation can be useful to monitor and titrate ventilatory support. The aim of this study was to obtain measurements of the pressure generated by the respiratory muscles (PMUSC) and the derived pressure-time product (PTP; a good indicator of the metabolic work of breathing), performing the rapid interrupter technique with a commercial ventilator.
  
  
  METHODS
  A Draeger Evita 4 ventilator (Draeger Medical, Lubeck, Germany) was controlled by a personal computer to rapidly interrupt the airway flow at different times and volumes of the respiratory cycle during pressure-support ventilation. From the airway pressure tracing after the occlusion, the authors estimated the alveolar pressure and PMUSC; the integration of PMUSC values over the inspiratory time yields the measurement of PTP. Esophageal pressure measurements were used as a reference. After a bench study of the valves' performance, the authors performed 11 measurement sequences in eight patients.
  
  
  RESULTS
  The closure times for the inspiratory and expiratory valves were 74 +/- 10 and 61 +/- 13 ms, respectively. The interrupter technique provided a reliable estimate of PMUSC (PMUSC, occl = 1.00 . PMUSC, pes + 0.19; r = 0.88; 95% confidence interval for agreement, +5.49/-5.32 cm H2O). PTPoccl tightly correlated with PTPpes (PTPoccl = 0.95 . PTPpes + 0.13; r = 0.96; 95% confidence interval, 1.94/-1.61 cm H2O . s).
  
  
  CONCLUSIONS
  The rapid interrupter technique can be performed by means of a commercial ventilator, providing reliable measurement of PMUSC and PTP.
authors.affiliation: Dipartimento di Medicina Sperimentale, Ambientale e Biotecnologie Mediche, Università degli Studi Milano Bicocca, Ospedale San Gerardo, Italy.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Bellani
authors.forename: Nicolò
authors.initials: N
authors.lastname: Patroniti
authors.forename: Dieter
authors.initials: D
authors.lastname: Weismann
authors.forename: Lucia
authors.initials: L
authors.lastname: Galbiati
authors.forename: Francesco
authors.initials: F
authors.lastname: Curto
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Foti
authors.forename: Antonio
authors.initials: A
authors.lastname: Pesenti
mesh_terms: D000208:Acute Disease; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007384:Intermittent Positive-Pressure Breathing / Q000295:instrumentation / Q000379:methods*; D008297:Male; D008838:Microcomputers; D008875:Middle Aged; D012131:Respiratory Insufficiency / Q000503:physiopathology / Q000628:therapy*; D015656:Respiratory Mechanics; D012132:Respiratory Muscles; D013990:Tidal Volume; D013997:Time Factors; D014939:Work of Breathing