Tracheal Dynamics in Infants with Respiratory Distress, Stridor, and Collapsing Trachea

Abstract

The purpose of this investigation was to evaluate the tracheal “collapse” commonly seen during roentgenoscopy of newborn and older infants. It was hoped this would lead to a better understanding of the mechanism of changes in lumen dimensions and their relation to “tracheomalacia,” stridor, and respiratory distress. While the trachea and bronchi normally dilate on inspiration and narrow on expiration, they are also observed to “collapse” on cough and the Valsalva and similar maneuvers. Measurements of the bronchial and tracheal diameters in normal subjects have emphasized the wide range of variation (1–3). Prior to cineroentgenography, observations of luminal changes were made under conditions which in themselves influence these changes by adding airway resistance, as through a bronchoscope or other intraluminal hardware. No such factors were brought into practice in our observations other than the introduction of one to one and a half cubic centimeters of bronchographic contrast media into the trachea In recent years, laboratory studies of the airway have contributed substantially to our knowledge and indicate that the physical changes in the tracheal bronchial system can be predicated on known aerodynamic and physical principles (3–6). Experimental work in dogs emphasizes the role that pressure and flow may play in the variations of the tracheal diameters. Controlled pressure changes of from 5 to 15 cm of water produce up to 40 per cent variation in the tracheal diameter and 75 per cent in the bronchi (7, 8). The tracheal lumen, it should be clear, is determined at any given instance by its inherent rigidity and the deforming force exerted upon it (4, 9, 10). Its “rigidity” or the ease with which it can be deformed is expressed as compliance; the deforming force is the transmural pressure. Compliance is a physical property, elasticity or resiliency, determined by the structural anatomy and fixation of the trachea. I t is measured as internal volume change per unit pressure change (unit: liters per cm H20) . Compliance decreases with age (10) as well as with longitudinal stretching of the trachea as in inspiratory effort, cervical extension, or deglutition. The deforming force, transmural pressure, is illustrated and further defined in Figure 1, A. The cervical and intrathoracic portions of the trachea are subject to different external pressures. We have observed, as has also been pointed out by Van Hayek (11), that at the level of the cervicothoracic junction the behavior of the trachea is quite different from that in either the cervical or thoracic segments. This illdefined anatomic area is further explained and illustrated in Figure 1, B. Material and Methods To check the findings in the normal trachea, tracheal cineroentgenograms were obtained of 8 normal infants, from newborn to eighteen months of age, and 28 healthy puppies two and half to ten weeks old. The study was carried out in an identical manner in every instance.