title: Physiologic evaluation of different levels of assistance during noninvasive ventilation delivered through a helmet.
abstract: OBJECTIVE
  To evaluate the effects of various levels of pressure support (PS) during noninvasive ventilation delivered through a helmet on breathing pattern, inspiratory effort, CO2 rebreathing, and comfort.
  
  
  METHODS
  Physiologic study.
  
  
  METHODS
  University-affiliated hospital.
  
  
  METHODS
  Eight healthy volunteers.
  
  
  METHODS
  Volunteers received ventilation through a helmet with four different PS/positive end-expiratory pressure combinations (5/5 cm H2O, 10/5 cm H2O, 15/5 cm H2O, and 10/10 cm H2O) applied in random order.
  
  
  RESULTS
  The ventilatory respiratory rate, esophageal respiratory rate (RRpes), airway pressure, esophageal pressure tracings, esophageal swing, and pressure-time product (PTP) [PTP per breath, PTP per minute, and PTP per liter] were evaluated. We also measured the partial pressure of inspired CO2 (Pi(CO2)) at the airway opening, mean partial pressure of expired CO2 (Pe(CO2)), CO2 production (V(CO2)), minute ventilation (V(E)) delivered to the helmet (V(E)h), and the true inspired V(E). By subtracting V(E) from V(E)h, we obtained the Ve washing the helmet (V(E)wh). A visual analog scale (from 0 to 10) was used to evaluate comfort. Compared to spontaneous breathing, different levels of PS progressively increased tidal volume (V(T)) and decreased RRpes, reducing inspiratory effort. The increased levels of assistance did not produce significant changes in Pi(CO2), end-tidal CO2, and V(CO2). Pe(CO2) had a slight decrease when increasing the level of PS from 5 to 10 cm H2O (p < 0.05). Despite the presence of constant values of Ve, the increase of PS produced an increase in V(E)wh, without significant differences comparing 10 cm H2O and 15 cm H2O of PS. The subjects had a slight but not significant increase in discomfort by augmenting the level of assistance. At the highest level of PS (15 cm H2O), the discomfort was significantly higher (p < 0.001) than at the other levels of assistance.
  
  
  CONCLUSIONS
  In volunteers, the helmet is efficient in ventilation, allowing a Vt increase and RRpes reduction. A significant discomfort was present only at the highest level of assistance; however, it did not affect patient/ventilator interaction.
authors.affiliation: Dipartimento di Anestesia e Rianimazione, Università Cattolica del S. Cuore, Policlinico A. Gemelli, Largo A. Gemelli 8, 00168 Rome, Italy.
authors.forename: Roberta
authors.initials: R
authors.lastname: Costa
authors.forename: Paolo
authors.initials: P
authors.lastname: Navalesi
authors.forename: Massimo
authors.initials: M
authors.lastname: Antonelli
authors.forename: Franco
authors.initials: F
authors.lastname: Cavaliere
authors.forename: Andrea
authors.initials: A
authors.lastname: Craba
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Proietti
authors.forename: Giorgio
authors.initials: G
authors.lastname: Conti
mesh_terms: D000328:Adult; D002245:Carbon Dioxide / Q000032:analysis; D004867:Equipment Design; D005260:Female; D006260:Head Protective Devices; D006801:Humans; D007385:Intermittent Positive-Pressure Ventilation / Q000295:instrumentation / Q000379:methods; D008297:Male; D011175:Positive-Pressure Respiration / Q000295:instrumentation* / Q000379:methods; D012016:Reference Values; D012143:Respiratory Physiological Phenomena
chemical_list: D002245:Carbon Dioxide