title: Relationship between tidal volume and deadspace during high frequency ventilation.
abstract: Physiological (VDphys) and anatomical (VDanat) deadspaces were measured in seven anaesthetized, paralysed and intubated adult patients ventilated at normal and high frequencies. To maintain a constant PaCO2 while increasing the ventilation frequency from 15 to 120 b.p.m., the mean VT was decreased from 454 +/- 62 ml (mean +/- SD) to 117 +/- 9 ml. The mean VDanat and VDphys decreased from 130 +/- 11 ml to 74 +/- 12 ml and 165 +/- 24 ml to 92 +/- 3 ml, respectively, by 80 b.p.m., above which frequency there was no further significant reduction in either. The mean VD/VT ratio increased from 0.36 +/- 0.04 to 0.76 +/- 0.05. This study showed that the deadspace volume measured conventionally was not a constant factor, was mainly a function of VT and was a determinant of tidal and minute volume requirement even during high frequency ventilation. The variable VDphys showed a wide variation between subjects, and appeared to have a mean minimal value of approximately 1.1 ml kg-1 at 80 b.p.m. in adult human subjects with a tracheal tube in situ--a value about half the VDphys measured at conventional normal tidal volumes and ventilation frequencies.
authors.forename: M K
authors.initials: MK
authors.lastname: Chakrabarti
authors.forename: G
authors.initials: G
authors.lastname: Gordon
authors.forename: J G
authors.initials: JG
authors.lastname: Whitwam
mesh_terms: D002245:Carbon Dioxide / Q000097:blood; D006801:Humans; D007442:Intubation, Intratracheal; D008176:Lung Volume Measurements; D008875:Middle Aged; D012121:Respiration, Artificial; D012126:Respiratory Dead Space; D013990:Tidal Volume
chemical_list: D002245:Carbon Dioxide