Ventilatory accommodation of oxygen demand and respiratory water loss in a large bird,the emu (Dromaius novaehollandiae), and a re-examination of ventilatory allometry for birds |
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Authors: | S K Maloney T J Dawson |
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Institution: | (1) School of Biological Science, University of New South Wales, PO Box 1, 2033 Kensington, Australia;(2) Present address: Brain Function Research Unit, University of the Witwatersrand, 7 York Road, 2193 Parktown, South Africa |
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Abstract: | Ventilation was studied in the emu, a large flightless bird of mass 40kg, within the range of ambient temperatures from-5 to 45°C. Data for the emu and 21 other species were used to calculate allometric relationships for resting ventilatory parameters in birds (breath frequency=13.5 mass-0.314; tidal volume=20.7 mass1.0). At low ambient temperatures the ventilatory system must accommodate the increased metabolic demand for oxygen. In the emu this was achieved by a combination of increased tidal volume and increased oxygen extraction. Data from emus sitting and standing at-5°C, when metabolism is 1.5x and 2.6x basal metabolic rate, respectively, indicate that at least in the emu an increase in oxygen extraction can be stimulated by low temperature independent of oxygen demand. At higher ambient temperatures ventilation was increased to facilitate respiratory water loss. The emu achieved this by increased respiratory frequency. At moderate heat loads (30–35°C) tidal volume fell. This is usually interpreted as a mechanism whereby respiratory water loss can be increased without increasing parabronchial ventilation. At 45°C tidal volume increased; however, past studies have shown that CO2 washout is minimal under these conditions. The mechanism whereby this is possible is discussed.Abbreviations BMR
basal metabolic rate
- BTPS
body temperature, ambient pressure, saturated
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EO
2
oxygen extraction
- EWL
evaporative water loss
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f
R
ventilation frequency
- RH
relative humidity
- RHL
respiratory heat loss
- SEM
standard error of the mean
- SNK
student-Newman-Keuls multiple range test
- STPD
standard temperature and pressure, dry
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T
a
ambient temperatures(s)
-
T
b
body temperature(s)
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T
ex
expired air temperature(s)
-
T
rh
chamber excurrent air temperature
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V
J
ventilation
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VO2
oxygen consumption
-
V
T
tidal volume
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V/Q
air ventilation to blood perfusion ratio |
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Keywords: | Allometry Thermoregulation Ventilation Emu Dromaius novaehollandiae |
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