2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
108
PERFORMANCE OF AN END-TIDAL FORCING SYSTEM FOR
ASSESSMENT OF HUMAN PULMONARY VENTILATION
RESPONSES
Koehle M.S., Giles L.V., Walsh M.L., Curtis C.N., White M.D.
Laboratory for Exercise and Environmental Physiology,
School of Kinesiology, Simon Fraser University, Burnaby, BC, Canada
Contact person: koehle@interchange.ubc.ca
INTRODUCTION
To measure chemosensitivity, ventilatory or cardiovascular responses in humans, it is
often desirable to closely control end-tidal O2 (PETO2) and CO2 (PETCO2). The endtidal
forcing (ETF) technique is an established method of manipulating end-tidal
gases. Unfortunately, it usually requires large volumes of compressed gases and a
significant amount of equipment, rendering it unusable for fieldwork and most
clinical/laboratory applications. The purpose of the present study was to develop and
validate a compact, simplified portable ETF system capable of reliably controlling
end-tidal gases in field and clinical /laboratory conditions.
METHODS
The compact ETF system developed consisted of 3 compressed gas sources (air, N2
and CO2) connected via computer-controlled solenoid valves to a gas humidification
chamber and inspiratory reservoir bag from which participant breathed. The
computer-controlled system compared actual end-tidal gas partial pressures (assessed
by a BXB metabolic cart), with target end-tidal gas partial pressures and based on the
size of this error mixed the appropriate gases for the participant’s next breath. Eight
participants underwent 2 different 30-min protocols that included each possible
combination of end-tidal O2 and CO2 control at 2 levels of both PETO2 (55 and 75 mm
Hg) and PETCO2 (4 and 7 mmHg above resting). End-tidal pressures and target values
were compared using one-sample t-tests and across conditions with a repeated
measures ANOVA and paired t-tests. The alpha level was set at 0.05.
RESULTS
The mean standard deviations for PETCO 2 and PETO 2 over the last 2 min of each
control stage were 0.61 mm Hg and 1.78 mm Hg. Ninety-five percent confidence
intervals for PETCO2 and PETO2 were ±1.2 mm Hg and ±3.5 mm Hg, respectively.
During control of O2 and CO2, mean (SD) time constant for the transitions were 10.6
(9.6) s for CO2 and 8.3 (14.6) s for O2.
DISCUSSION
These data demonstrate the validity of a system for control of end-tidal CO2 and O2
gas partial pressures. The device represents a compact and economical alternative to
the classical end-tidal forcing system and it can be employed in field and
clinical/laboratory conditions.
ACKNOWLEDGEMENTS
This research was supported by: Canadian Institutes of Health Research (SafetyNet),
Natural Sciences and Engineering Council of Canada and the Canadian Foundation
for Innovation.