Isotope labelled microspheres were used to study the capillary blood perfusion of the rabbit tracheal mucosa. Under resting conditions the perfusion was about 0.3 ml/min - g (i.e. about 60% of the relative cerebral blood flow). Irritation of the tracheal mucosa by an endotracheal tube caused a steep rise in blood flow, tenfold or more. This was probably due to relaxation of the arterioles caused by a release of histamine-like substances. When an endotracheal tube is equipped with a small cuff (small resting diameter, low residual volume), the part of the mucosa in contact with the cuff, i.e. the mucosa covering the surface and edges of the cartilages, will be ischaemic at a cuff to tracheal wall pressure (C-T pressure) of greater than 30 millimeters of mercury. This abrupt ischaemia threshold contributes to the risk of deep mucosal damage with subsequent tracheal scarring, possibly proceeding to stenosis. Our present studies indicate that the ideal large cuff, with properties resembling those of an air cushion, will allow the major part of the arterial pressure to be propagated as far down as the capillaries. Under these conditions the cuff would permit some of the capillary blood perfusion of the tracheal mucosa covering the cartilages also at C-T pressures exceeding 30 mmHg. Although this investigation supports the concept that the ideal thin-walled large cuff interferes much less with the mucosal blood perfusion than the small cuff, we recommend that the cuff pressure be monitored and kept below 20 mmHg.
Since 1972 a series of experiments (Skoog, Ohlsén & Sohn, 1972; 1975; Ohlsén, 1976) has been performed to elucidate the potential of perichondrial grafts to generate cartilage. In 1974 Sohn & Ohlsén demonstrated in rabbits that tracheal cartilage could be reconstructed from free perichondrial grafts. As these studies were carried out with an intact tracheal mucosa a series of experiments was conducted in rabbits, and reported in this paper, in which a tracheal section containing two cartiliages and the covering mucous membrane was removed and replaced with a free perichondrial graft taken from the ear. New cartilege formed in all animals. The reconstructed portion of trachea was partly covered by ciliated cells of normal appearance, partly by low epithelium with microvilli. These latter areas were mainly within the central parts of the regenerated mucosa. The use of perichondrial grafts for tracheal reconstruction was also studied in two series of dogs. In four dogs a tracheal section, consisting of two comlete cartilages with the covering mucosa, was completely removed. The circumferential defect was reconstructed by free perichondrial grafats from rib cartilage. They were placed on two fascial flaps which had been raised from the adjacent muscles, rotated into the defect and sutured for complete coverage. Regeneration of cartilage occurred in all dogs, producing a biologic framework. The lining of the reconstructed tracheal section was completely restored by epithelialization from the surrounding mucosa. Low epithelial cells were successively replaced by columnar ciliated cells typical of the respiratory tract. The morphological development of the regenerated epithelium was demonstrated by electron microscopy. The regenerated mucosa exhibited normal function by passing mucus across the reconstructed area. This was recorded by filming at low speed using Cardio-green as indicator. All the animals of this series developed tracheal stenosis within the reconstructed portion. Another experiment was therefore carried out in which four dogs were subjected to the same operative procedure. Postoperatively, however, during the phase of healing, a silicon tube was inserted and left in situ to maintain expansion of the reconstructed portion. By this means stenosis could be prevented with good regeneration of the mucosal lining.
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