Distribution of innervation and circulation in porcine cervical trachea

The circulation and innervation to porcine cervical trachea were studied in 54 animals in situ. The antemortem response of porcine tracheal muscle was measured isometrically during selective injection of acetylcholine into the cranial thyroid arterial circulation. A predominantly unilateral (70.4%), rather than bilateral (3.7%), arterial circulation was identified; a cranial thyroid artery was not demonstrated in 25.9% of swine, suggesting dominant perfusion from the caudal thyroid circulation. After animals were killed, dye injection through the dominant cranial thyroid trunk demonstrated homogeneous perfusion of the muscle in all instances. In 20 of these animals, the distribution of parasympathetic innervation to porcine tracheal muscle was studied by selective electrical stimulation of the vagus nerves in situ. Tracheal smooth muscle response was measured isometrically, using settings (20 v, 20 Hz) causing maximal contractile force. Bilateral electrical stimulation caused active tracheal tension of 23.2 +/- 1.9 g/cm. Unilateral stimulation of the left vagus nerve caused 17.8 +/- 1.5 g/cm contraction, which was significantly greater than the response caused by selective stimulation of the right vagus nerve (12.1 +/- 1.6 g/cm; P less than 0.001). Innervation to porcine cervical trachea, although bilateral, is derived predominantly from the left vagus nerve; circulation is derived almost always from the left cranial thyroid artery.