Analysis Of Respiratory Pattern During Panting In Fowl, Gallus Domesticus

Abstract

ABSTRACT When exposed to hot environments, birds depend mostly on respiratory evaporative cooling in order to maintain body temperature since cutaneous evaporation is limited for most species because they lack sweat glands. As well as serving this thermoregulatory function the respiratory system must also accommodate the obligatory requirement of adequate gaseous exchange. The hyperthermic bird must increase ventilation rates over evaporative surfaces in the respiratory system and buccopharynx for cooling purposes and yet avoid a severe blood hypocapnia and alkalosis (Calder & Schmidt-Nielsen, 1968). Recently Bech, Johansen & Maloiy (1979) showed that flamingoes, Phoenicopterus ruber, avoid hypocapnia during panting by restricting hyperventilation to the respiratory dead-space. This is achieved by increasing respiratory frequency, f, but reducing tidal volume, VT, to a value which closely matches the tracheal dead-space volume, VD. AS a result of the diminished VT, carbon dioxide accumulated within the respiratory system and rapid, shallow panting was periodically interrupted by bursts of 1–3 deeper breaths which served to flush out the excess carbon dioxide. A similar pattern of breathing has been observed in domestic fowl by Gleeson & Brackenbury (1983). These authors showed that the carbon dioxide accumulated during rapid shallow breathing in the posterior (abdominal) air sacs as a result of the increase in the VD/VT ratio. Other authors have reported an increased f and reduced VT in the panting fowl (Kassim & Sykes, 1982; Arad & Marder, 1983) but the diphasic pattern of breathing during panting has not been adequately described or quantified although its presence is apparent from earlier records of breathing movements in the panting fowl (Romijn & Lokhorst, 1961). Some forms of diphasic panting also occur in other species of bird, although there is considerable variation in the frequency and regularity of the alternating patterns of breathing between species (for a review see Bech et al. 1979).