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A chest-lung model, consisting of a human laryngo-tracheo-bronchial tree cast (4 or 5 bronchial generations) tightly enclosed in a 100 l rigid box was used to assess the potential efficiency of high frequency jet ventilation in patients with upper tracheal stenosis. The elasticity of the air in the box stimulated normal adult chestlung compliance. Diaphragms (0.5 or 1.5 cm thick) were inserted into the upper trachea to simulate stenoses of 0.7, 1, 1.5 and 1.75 cm inner diameter. A rigid injectorcatheter (5 mm outside diameter) was directed in the axis of the trachea with its tip 2.5 cm beneath the stenosis. The end inspiratory alveolar pressure (PA), the end expiratory pressure (PEEP) and the tidal volume (VT) were measured at a rate of 100/min and 30% inspiratory to total periods ratio. Entrained flow, Vem, measured at the start of air insufflation, was compared to that calculated (\(\dot Vec\)) from a simple model. For a given setting of the ventilator, PEEP, PA — PEEP and VT were approximately linearly related to the difference in diameters of stenosis and injector. While PEEP decreased, both PA — PEEP and VT increased with increasing diameter of stenosis. When the diameter of the stenosis was higher than 1.5 cm no changes in PA — PEEP and VT were observed, owing to the narrowest section of the larynx.\(\dot Vec\) was always higher than\(\dot Vem\). The thickness of the stenosis did not affect the results, and the diameter of the stenosis appeared to be the main factor affecting the ventilatory parameters under our experimental coditions. This suggests that a stenosis diameter under 10 mm could affect the efficiency of jet ventilation in clinical practice.

Hyperbaric oxygen therapy is one of the numerous therapies which have been proposed in the management of sudden deafness. It is presumptuous to claim the efficiency of any treatment in a pathology where both the origin and the actual rate of spontaneous recovery are unknown. The grounds of therapies are therefore empirical but the need of urgent therapy is dictated by ethics. This study compares the effects of hyperbaric oxygen therapy in two groups of patients; according ot their order in randomization the subjects were treated either at a rate of 1 session or 2 sessions per day. Hyperbaric oxygen therapy was associated with infusion of Naftidrofuryl to counteract the vasoconstrictive effect of increased oxygen pressure in blood. Steroids were also administered simultaneously to avoid, for the same reasons, cerebral oedema. Normovolemic hemodilution (Dauman et al. 1983) was systemically performed in all the patients preliminarily to hyperbaric oxygen therapy, in order to reduce the haematocrit and thus facilitate blood supply. The efficiency and the side effects were similar in the two groups, provided that some principles in the selection and the monitoring of the patients were respected. The rate of 2 sessions of hyperbaric oxygen therapy per day has obvious advantages in view of health policy, but it requires the hospitalization of the patient and should be restricted to the younger subjects.

Alteration in flow and pressure in a chest-lung model during jet ventilation was studied from a theoretical and experimental standpoint. The model consisted of a stiff box, with an inserted cast of the bronchial tree, simulating either normal or low compliance of the human chest-lung. Airway resistances in the model could be altered. A constant driving flow (Vd) was applied through the opening of the trachea at various rates. The driving flow drew in a constant flow (entrained flow = Ve) and increased the box pressure (PA), which in turn induced an increasing back flow (Vr). Vd, Ve-Vr and PA were measured. Theoretical analysis of time variation in box pressure showed a monoexponential pattern which was confirmed experimentally. Tr, the time at which back flow and entrained flow become equal could be predicted taking the physical characteristics of the experimental set-up and the values of Vd and Ve into account. Tr values depended mainly on the compliance of the experimental set-up. Increasing the resistances was found to reduce Ve. In practice, the efficiency of jet ventilation for gas exchange at a frequency below 4 Hz is known to be mainly related to the volume of gas flowing in the trachea towards the alveoli. This efficiency generally depends on the values of Tr and the inspiratory period (TI). A value of TI less than or equal to Tr will thus improve the jet ventilation efficiency.

After the apparition of a sudden deafness, 45 patients (22 men and 23 women, with a mean age of 44 +/- 14.9 years) were treated with normovolaemic haemodilution performed with dextran 60. They were placed into 4 groups depending on their hearing loss: total loss: 10 cases; severe loss: 90 to 70 db. 13 cases; moderates loss: 65 to 40 db, 14 cases, slight loss: less than or equal to 35 db, 8 cases. The mean time between the onset of the hearing loss and treatment was 9.3 +/- 12.4 days. The initial mean haematocrit was 44.8 +/- 3.8% and mean haematocrit after haemodilution was 33.1 +/- 2.8%. For 51% of the patients, an almost total recovery was obtained. In 15.5% of cases, recovery was between 25 to 50% of the hearing loss, and in 33.3% of the patients recovery was negligible. We did not find any relationship between hearing recovery and initial haematocrit. The best results were obtained in the group of patients treated early. Hearing gain was significatively better if delay in starting treatment was less than 7 days. There was a relationship between the initial hearing loss and the final recuperation. These results suggested that haemodilution increased labyrinth microcirculation and oxygenation of the cochlear sensory cells, reversing the ischaemic insult to these cells.

An experimental and clinical study of an endotracheal tube with a foam-filled cuff has been carried out. The experimental study showed that, during inspiration, the cuff was insufflated through the "T piece" connecting the cuff in the inspiratory limb of the ventilator circuit, preventing inspiratory leak. The intracuff pressure was equal to airway pressure. During expiration the gas insufflated into cuff leaked out through the "T piece" and intracuff pressure rapidly returned to zero. When N2O in 50% O2 was used for one hour, intracuff pressure did not increase. Twenty patients intubated with a foam-filled cuff tube, for ENT surgery, have been studied. The mean intubating time was 151 min +/- 36 and two patients were intubed, respectively, 26 hours and 28 hours. No complications were noted, 24 hours after extubation, during laryngeal fibroscopic control. Only two patients had light edema of the vocal cords and three of them had a light inflammation of the subglottic mucosa, without sore throat. No tracheal ischaemic damage nor tracheal mucosal inflammation were observed.