AJP - Regulatory, Integrative and Comparative Physiology, Vol 257, Issue 1 156-R161, Copyright © 1989 by American Physiological Society
Effect of upper airway CO2 pattern on ventilatory frequency in tegu lizards
G. O. Ballam and E. L. Coates
Biomedical Research Division, Lovelace Medical Foundation, Albuquerque, New Mexico 87108.
Nasal CO2-sensitive receptors are reported to depress ventilatory frequency
in several reptilian species in response to constant low levels of inspired
CO2. The purpose of this study was to determine the influence of phasic
patterns of CO2 in the upper airways on ventilation. Awake lizards
(Tupinambis nigropunctatus) breathed through an endotracheal tube from an
isolated gas source. A second gas mixture was forced at constant flow into
the external nares. A concentration of 4% CO2 was intermittently pulsed
through the nares in a square-wave pattern with a frequency of 60, 12, 6,
4.2, 1.8, and 0.6 cycles/min. Concentrations of 2, 3, 4, and 6% CO2 were
also pulsed through the nares at 12 cycles/min and compared with sustained
levels of 1, 1.5, 2, and 3%. Additionally, 0 or 3% CO2 was forced through
the upper airways with a servo system designed to mimic normal ventilatory
flow and gas concentrations. No changes in breathing pattern were noted
during any of the pulsing protocols, although a significant breathing
frequency depression was present with sustained levels of CO2 of comparable
mean concentrations. We conclude that ventilatory control is selectively
responsive to sustained levels of environmental CO2 but not to phasic
changes in upper airway CO2 concentration.
