Intrapulmonary CO2-rise time and ventilation in ducks

Abstract

Many investigators have reported finding intrapulmonary chemoreceptors (IPCs) in several species of birds and reptiles; however, the role of IPCs in ventilatory control in birds has not been identified. This study was undertaken to assess the role of intrapulmonary CO2 dynamics on the control of breathing. Ducks were unidirectionally ventilated, and their breathing was monitored with a pneumotachograph connected to a personal computer. A gas-mixing system controlled by the computer adjusted the rate of rise of airway CO2 concentration ([CO2]). On inspiration, the computer removed CO2 from the ventilating gas for 1.5 s, followed by a controlled [CO2] rise. Breathing frequency was directly related to the rate of rise of airway [CO2]. Tidal volume, however, was not correlated with CO2-rise time but was related to the peak airway [CO2]. This response is likely mediated by IPCs because preventing airway [CO2] from falling during inspiration immediately altered that breath. An increase in CO2 production (as in exercise) will lead to an increase in the rate of CO2 excretion into the lung. The resulting alteration of breathing frequency would thus maintain acid-base balance. The observed response, therefore, may represent a link between ventilation and metabolism.

Cerebral areas associated with motor control of speech in humans

“…This study shows a relationship between dynamic C02 ventilatory response and cough receptor sensitivity for the first time. In birds, dynamic C02 sensitivity is mediated by receptors within the airways themselves (Furilla & Bernstein, 1995). In man, dynamic C02 sensitivity is probably mediated by peripheral chemoreceptors; our results support a link between their stimulation and the airway cough receptor.…”

Patterns of respiration in diving penguins: is the last gasp an inspired tactic?

“…Our observations that penguins in the laboratory invariably exhaled with the beak minimally open and that the wave form of the beak angle in the breathing cycle deviated from a true sine wave by having long, low troughs, may reflect control of the speed of exhalation. Slow ventilation in the little penguin probably increases the efficiency of oxygen extraction (Stahel and Nicol, 1988), and slowing exhalation may prevent reflex inhibition of ventilation by intrapulmonary chemoreceptors that are stimulated when airway CO2 levels are reduced, as by rapid air passage (Furilla and Bernstein, 1995). Finally, partial beak closure during exhalation when tidal volumes are high may also reduce water and heat losses substantially by forcing air to exit through the nasal turbinates, The relationships for the other individuals are shown in Table·3.…”

Benzolamide, acetazolamide, and signal transduction in avian intrapulmonary chemoreceptors

“…A similar response is seen in mammalian CO 2 -sensitive laryngeal mechanoreceptors (5) and reptilian IPC (29). One interpretation is that CA inhibition causes alkalosis that mimics low PCO 2 and stimulates IPC discharge (9,25). These observations and others (2,4) suggest that H ϩ from hydrated CO 2 , rather than CO 2 itself, is the signal transduced by IPC.…”

“…Afferents from IPC are carried centrally in the vagus and provide phasic and tonic sensory feedback important for the control of breathing. The CO 2 stimulus detected by IPC varies during the breathing cycle (25) under the influence of inspired PCO 2 , venous PCO 2 , pulmonary ventilation and perfusion, and metabolism (1,9,12,30,32). IPC are therefore in a good position to detect CO 2 changes that help to match breathing to environmental and metabolic demands.…”