A cineradiographic study of lung ventilation in Alligator mississippiensis

Abstract

The skeletal and visceral kinematics of lung ventilation of the American alligator (Alligator mississippiensis) was examined using cineradiography, pneumotachometry, and intrapulmonary pressure recording. The respiratory pattern of A. mississippiensis is intermittent and diphasic. The inspiratory lung volume is retained during the non-ventilatory period through closure of the glottis. The aspiration pump of A. mississippiensis consists of multiple components: visceral movement, pubic rotation, gastralial movement, and costosternal movement, which vary independently in their contribution to lung ventilation. Vertebral flexion and extension is also observed, and may be a passive artifact of costal displacement. The amount of craniocaudal visceral movement during lung ventilation is variable, and can produce as much as 60% of the tidal volume. Pubic rotation is not directly coupled to visceral movement and contributes a relatively small percentage of the tidal volume, approximately 4% on average, as does vertebral flexion, which contributes less than 3%. Costosternal movement contributes the remaining majority of tidal volume, generally over 40%. The gastralia stiffen the abdominal wall and likely facilitate unified displacement of the abdominal wall. Tripartite ribs facilitate thoracic movement, allowing substantial excursion of the body wall. A relatively abrupt change in position of the vertebral parapophysis in the anterior thorax results in an increase in lateral rib movement in the posterior half of the thorax. The crocodylian aspiration pump appears to consist of a derived pelvic and diaphragmatic breathing pump combined with a basal costosternal and gastralial aspiration pump.

The accessory role of the diaphragmaticus muscle in lung ventilation in the estuarine crocodile Crocodylus porosus

“…These studies suggest that the diaphragmaticus muscle plays a primary role in inspiration. This argument is further supported by recent videoradiographic measurements of lung volume in resting alligators (Claessens, 2009), where the diaphragmatic contribution to lung inflation has been determined to range from 36% to 61% of inspired tidal volume.…”

“…Relatively large (up to 7.5kg) submerged caimans were used in studies that reported low EMG activity of the intercostals and a high reliance on the diaphragmaticus muscle for inspiration (Gans, 1971;Gans and Clark, 1976). Videoradiographic studies in juvenile alligators (mass 0.72-2.09kg) estimated that 36-61% of V T was attributable to diaphragmaticus activity and ~40% attributable to costosternal activity (Claessens, 2009), although it should be noted that these estimates were calculated for V T values 2-4-fold larger than those measured at rest in this study. While the diaphragmaticus muscle is well developed in adults, it is thin and translucent in juvenile crocodilians (S.L.M., personal observations).…”

“…Inspiration is driven by cranial rotation of tripartite ribs, which increases thoracic volume whereas caudal and medial rotation of the ribs decreases thoracic volume during expiration (Claessens, 2009). The abdominal muscles act to alter abdominal volume either by displacing the liver cranially during expiration or by providing room for the caudal displacement of the liver during inspiration.…”

“…The diaphragmaticus has been well described in caiman and alligator (Boelaert, 1942;Claessens, 2009;Farmer and Carrier, 2000a;Gans and Clark, 1976;Naifeh et al, 1970;Uriona and Farmer, 2006). In alligators, the two-paired strap-like muscles originate on the ischia and on the last gastralia and insert onto a connective tissue sheath that surrounds the liver (Farmer and Carrier, 2000a).…”

Evolution of Air Breathing: Oxygen Homeostasis and the Transitions from Water to Land and Sky

“…Pelvic aspiration and hepatic piston action are part of normal crocodilian breathing cycles (141). However, their involvement in buoyancy control suggests origination in an ancient aquatic crocodiliomorph lineage, that is, not a shared trait with archosaurs (759).…”