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Ventilation and Acid-Base Status during Thermal Panting in Pigeons (Columba livia)

Marvin H. Bernstein and Felipe C. Samaniego
Physiological Zoology
Vol. 54, No. 3 (Jul., 1981), pp. 308-315
Stable URL: http://www.jstor.org/stable/30159945
Page Count: 8
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Ventilation and Acid-Base Status during Thermal Panting in Pigeons (Columba livia)
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Abstract

During heat exposure, the respiratory system of a panting bird must fulfill the potentially conflicting requirements of dissipating heat and maintaining arterial carbon dioxide tension ($Pa_{CO_{2}}$). To investigate these functions in panting pigeons (Columba livia, mass 0.34 kg), we simultaneously measured respiratory volumes, $Pa_{CO_{2}}$, and arterial blood acidity (pHa). At body temperatures ($T_{b}$) of 41 and 42 C, we observed no panting. At $T_{b}$ of 43, 44, and 45 C, a compound pattern of ventilation containing two components replaced resting breathing. One component had approximately the same frequency (f), 28-39 min⁻¹, and tidal volume ($V_{T}$), 2.5-3.0 cm³ body temperature and pressure, saturated with water vapor (BTPS), as at lower $T_{b}$; the other was rapid, about 500 mi⁻¹, and shallow, 1.1 cm³ BTPS or less, resulting in a ventilation of 550 cm³ air BTPS·min⁻¹. Since this $V_{T}$ approximates tracheal dead space, the rapid component of ventilation, although five times greater than the slow component, was confined to the non-gas-exchanging, evaporative surfaces of the anterior respiratory tract. Over this entire range of $T_{b}$, 41-45 C, neither $Pa_{CO_{2}}$ nor pHa varied significantly, averaging 25.8 torr and 7.50, respectively. Compound panting in moderate heat stress thus elevates respiratory evaporation while sustaining normal pulmonary ventilation and blood acid-base status. At $T_{b}$ of 46 C, the rapid component increased $V_{T}$ well beyond the dead space, and the slow component was abandoned, with a consequent hypocapnic alkalosis ($Pa_{CO_{2}}$ 18 torr, pHa 7.63) due to excessive CO₂ washout.

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