Respiration Physiology 120 (2000) 179 – 183
Short communication
Continuous circadian measurements of ventilation in
behaving adult rats
Erin L. Seifert, John Knowles, Jacopo P. Mortola *
Room 1121, Department of Physiology, McIntyre Basic Sciences Building, McGill Uniersity, 3655 Drummond Street, Montreal,
Que, Canada H3G 1Y6
Accepted 15 February 2000
Abstract
Body temperature (Tb) and oxygen consumption (V
O
2
) are important determinants of ventilation (V E). While the
circadian rhythms in Tb and V
O
2
have been well described, the daily pattern of V E has not due to limitations in the
available methods for measuring V E. Here we describe an adaptation of the barometric method using a chamber in
which a large flow through very small restrictions was generated by the combined action of a positive pressure pump
on the entrance and a negative pressure pump at the outlet. In this way the chamber effectively behaved as a closed
system, despite having a high enough flow for long-term recording in freely moving, undisturbed small animals. This
system was then used to test the hypothesis that V E oscillates with a circadian pattern similar to that of Tb
.
Measurements of tidal volume (VT) and breathing rate (f), in combination with Tb and activity by telemetry, were
made in eight adult rats over 4–6 days under 12:12 light:dark conditions. Both VT, f, and thus V E, showed a circadian
pattern similar to that of Tb and activity; that is, values were higher during the dark compared to the light phase.
The differences in V E levels according to the time of the day suggest that mechanisms involved in the control of
breathing may also have circadian patterns. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Control of breathing; Rhythm; Mammals, rat; Metabolism, circadian rhythm; Methods, barometric, ventilation; Pattern
of breathing; Rhythm, circadian
www.elsevier.com/locate/resphysiol
1. Introduction
Body temperature (Tb) and oxygen consump-
tion (V
O
2
) are among the many physiological
parameters that show a circadian rhythm. That is,
both variables oscillate with a 24-h period in
the absence of external cues such as the light-dark
cycle. In addition, while correlated with the activ-
ity cycle, neither rhythm depends on it (Aschoff
and Pohl, 1970; Decoursey et al., 1998). There are
numerous examples where pulmonary ventilation
(V E) changes in parallel with V
O
2
, the best docu-
* Corresponding author. Tel.: +1-514-3984335; fax: +1-
514-3987452.
E-mail address: jacopo@med.mcgill.ca (J.P. Mortola)
0034-5687/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII:S0034-5687(00)00108-0