Optimal phasic tracheal gas insufflation timing: an experimental and mathematical analysis.
OBJECTIVE
To investigate the modulation of CO2 clearance by changes in the duration of tracheal gas flow application during tracheal gas insufflation (TGI).


METHODS
Combination of bench studies using a commercial test lung and a commercially available intensive care ventilator and mathematical analysis using a clearance model derived from first principles.


METHODS
University pulmonary research laboratory.


METHODS
None.


METHODS
Experiments using TGI were performed on a test lung at two combinations of tidal volume and frequency. TGI was limited to part of the expiratory phase (the terminal 10-100% of expiration), and two different TGI catheter flow rates were studied. Permutations over a range of compliances, dead-space volumes, catheter flows, and TGI durations were collected. A mathematical model incorporating key ventilatory and TGI-related variables was developed to provide a first-principles theoretical foundation for interpreting the experimental results.


RESULTS
In the physical model, alveolar Pco2 attained a minimum value with TGI flow applied during the terminal 40-60% of the expiratory phase, a finding that was consistent over an almost eight-fold range of expiratory time constants. The mathematical model shows the same qualitative pattern as the experimental model, indicating that the observed behaviors are not an experimental artifact.


CONCLUSIONS
The optimal duration of expiratory TGI flow application is stable over a wide range of impedance characteristics. Such stability suggests that near maximal effect of expiratory TGI could be obtained by applying TGI flow solely within the final 50% of the expiratory phase. Such uniform restriction of the application profile might both simplify technique implementation and decrease adverse consequences.
Hota
S
S
Department of Mathematics, Fisk University, Nashville, TN, USA.
Crooke
P S
PS
Adams
A B
AB
Hotchkiss
J R
JR
D002245:Carbon Dioxide / Q000032:analysis*; D007327:Insufflation / Q000379:methods*; D008954:Models, Biological; D010313:Partial Pressure; D011175:Positive-Pressure Respiration / Q000379:methods*; D015656:Respiratory Mechanics / Q000502:physiology; D013990:Tidal Volume; D014132:Trachea
D002245:Carbon Dioxide