Study objectives: To ascertain whether inspiratory
pressure support (IPS) can be triggered reliably from and targeted at
esophageal pressures (Pes), and to compare the work of breathing and
time delay to initiation of inspiratory flow between conventional
pressure support and esophageal-directed pressure support (EDPS).
Design: Prospective laboratory study.
Setting: University medical school.
participants: Five normal volunteers.
Interventions: IPS at a level to achieve tidal volume of 10
mL/kg, and EDPS with a target Pes of 0 cm H2O via full
Measurements and results: Pes, airway
pressure, and inspiratory flow were measured during spontaneous
breathing. Peak Pes and pressure time product (PTP) of Pes were
calculated during spontaneous breathing and through linear resistances.
Measurements were repeated during IPS and EDPS ventilation. At rest,
PTP was 7.56 (± 3.6) and peak Pes was −5.8 cm H2O
(± 1.44). When subjects were breathing through the resistors, PTP
increased to 12.4 (± 8.1) and 30.3 (± 8.9) and peak Pes decreased
to −7.2 and −15.3 cm H2O respectively. With facemask IPS,
unloaded PTP fell to 1.7 (± 1.3) and peak Pes fell to −3.3 cm
H2O (± 1.3). When ventilated through the highest
resistance with IPS, mean PTP increased to 21.9 and peak Pes increased
to −11.9 (± 4.2) cm H2O relative to baseline. During
EDPS with the resistor, PTP fell to 1.5 ± 1.1 (p < 0.007) and peak
Pes fell to −1.9 ± 1.1 cm H2O (p < 0.0001).
Conclusions: It was possible to initiate supported
breathing from Pes values. The work performed, as measured by PTP, was
lower during EDPS than during either unsupported breathing or
Abbreviations: EDPS = esophageal-directed pressure
support; IPS = inspiratory pressure support; PEEP = positive
end-expiratory pressure; Pes = esophageal pressure; PTP = pressure