Journal of Applied Physiology, Vol 77, Issue 6 2703-2708, Copyright © 1994 by American Physiological Society
Relationship between Cr and breathing pattern in mechanically ventilated patients
H. Burnet, M. Bascou-Bussac, C. Martin and Y. Jammes
Laboratoire de Physiopathologie Respiratoire, Unite de Recherche Associee 1630, Centre National de la Recherche Scientifique, Institut Jean Roche, Faculte de Medecine-Nord, Marseille.
In mechanically ventilated patients the natural gas-conditioning process of
the upper airways is bypassed by the use of an endotracheal tube or a
tracheostomy. We hypothesized that under these conditions the breathing
pattern may greatly influence the convective respiratory heat loss (Cr). Cr
values were computed from minute ventilation (VE) and inspiratory and
expiratory gas temperatures, which were measured in six patients under
mechanical ventilation for the management of cranial trauma. In each
patient the effects of 11-20 different breathing patterns were
investigated. Relationships between Cr and VE and between combined tidal
volume and respiratory frequency were obtained by simple and multiple
linear regression methods, respectively. Comparison of the standard errors
of estimate indicated that multiple linear regression gives the best fit.
Thus, Cr was highly dependent on the breathing pattern and was not related
only to VE. For the same VE value, Cr was higher when VE was achieved with
high tidal volume and low respiratory frequency. These data are consistent
with previous studies in which thermal exchanges through the upper airways
were taxed by hyperventilation of frigid air.
