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Interest was focussed on maximal inspiratory efforts which anesthetized rabbits are able to display when acutely made dyspnoic by prolonged tracheal occlusion. Such efforts were characterized by the mean intrapleural pressure decrease per breath and by the maximum of intrapleural pressure decrease reached during inspiration. These efforts could not be intensified by additional biochemical and/or biophysical means such as hypercapnia, hypoxia, artificial pneumothorax, thoracic compression, etc. They were most pronounced around the 25th second after onset of tracheal occlusion.

Experiments have been conducted to investigate whether electrical activity of medullary inspiratory neurones is altered on the first breath following mechanical loading of inspiration. The predominant effect of resistive loading was an increase in both rate and duration of neurone activity. This facilitation was completely eliminated by vagotomy suggesting that the vagi are the only source of sensory information impinging on the inspiratory neurones conveying information about the loaded breath. In the intact animal, elastic loading and tracheal occlusion elicited the following responses : 1) an extended firing time of all neurones, 2) increased rate of unit activity in one population of neurones, 3) a decreased rate of unit activity in another population of neurones. Following vagotomy the only response noted with these types of loading was a decrease in the firing rate of some neurones. A probable source of the observed inhibition are the tendon organs of the diaphragm and /or external intercostal muscles via dorsal root pathways.

Levy, L. S. (1971).Brit. J. industr. Med.,28, 164-171. Physiological changes during electrical asphyxiation. In this study of death caused by electric shock the rabbit has been used as an experimental animal to elucidate some of the physiological changes that occur in the blood gas, acid-base, and cardiorespiratory systems during long, non-fibrillating electric shocks. The results obtained were compared with known and confirmed observations for obstructive asphyxiation produced by tracheal occlusion. The main finding was that in electrical asphyxiation the lack of respiratory movements during the shock coupled with the rapid development of a very severe metabolic acidosis caused very early cardiac standstill. This indicates the urgent need for the instigation of resuscitatory procedures after such accidents.

Primary benign tumors of the trachea are uncommon. These tumors may cause tracheal occlusion and lead to a misdiagnosis of asthma. Ectopic parathyroid adenoma (EPA) can be seen anywhere between the mandibular angle and the mediastinum. The distal part of the trachea is a rare location for EPA, and EPA obstructing the endotracheal lumen has not been reported in the literature. We herein describe a 52-year-old female with a several-year history of asthma treatment who presented with progressive dyspnea. Computed tomography revealed a mass that was obstructing the tracheal lumen. Total mass excision was performed via endobronchial treatment, and pathologic examination revealed EPA.

The inspiration inhibiting vagal reflex as elicited in rabbits by tracheal occlusion in inspiratory position, is strongly increased by etorphine and its derivatives, the 19-isoamylderivative benig of outstanding activity.

The present investigation was undertaken to study the interaction of CO2 and body temperature on phrenic activity (moving average) and tracheal occlusion pressure. Studies were performed on spontaneously ventilated cats anesthetized with pentobarbital sodium at different body temperatures (32–41 degrees C) while breathing room air, 2 and 4% CO2 in 50% O2. At any given chemical drive, increased body temperature caused a similar increase in rate of phrenic activity and tracheal occlusion pressure, while their peak values remained virtually unchanged. At any given body temperature, increased chemical drive caused an increase in both rate of rise and peak values of phrenic activity and tracheal occlusion pressure. These results confirm previous findings that body temperature affects the rate of rise of the central inspiratory activity (CIA), but not the inspiratory “off-switch” threshold, while CO2 increases both the rate of rise of CIA and off-switch threshold. In addition the results indicate that tracheal occlusion pressure provides a similar index of CIA as “integrated” phrenic activity.

Tolerance to the Combined Effects of Hypothermia, Anoxia, and Ionizing Radiation. An experimental study on rats was undertaken in order to evaluate to what extent severe anoxia, made tolerable by virtue of hypothermia, may prove of protective value against lethal effects of ionizing radiation. A protective factor approaching 3 proved to be obtainable by the combination of deep but spontaneously reversible hypothermia and a severe but easily tolerable anoxia, provoked by tracheal occlusion. Terminal respiratory movements were recorded and changes of brain ATP, ADP, AMP, creatine phosphate and lactate levels were followed during the course of anoxia, so that degrees of protection, afforded by different phases of the post-occlusion period, could be correlated with biochemical and physiological parameters.

Thirty-three anesthetized dogs of varying weights were subjected to complete asphyxia by tracheal occlusion to produce uniform anoxia of the heart. Eleven showed electrocardiographic evidence of ventricular fibrillation while the other twenty-two demonstrated cardiac arrest. The development of ventricular fibrillation correlated with the heavier body and heart weights and with a lower average right atrial serum potassium level as compared to the dogs not fibrillating. Other serum electrolytes, pH, body temperature and sex showed no correlation with the arrhythmia. The importance of the fact that large dogs have a greater susceptibility to develop ventricular fibrillation during uniform anoxia of the heart is discussed in relation to experimental research on dogs and to a current theory of the cause of ventricular fibrillation.

To assess respiratory muscle fatigue in acute respiratory failure in patients with chronic obstructive pulmonary disease and evaluate its influence on weaning patients from mechanical ventilation.We studied the time course of tracheal occlusion pressure (P0.1) and high-to-low ratio of the diaphragmatic electromyogram in 16 patients in acute respiratory failure with chronic obstructive pulmonary disease.All patients were intubated and studied during a 15-minute weaning period from ventilation. Minute ventilation (VE), arterial blood gases, P0.1 and high-to-low ratio of the diaphragm were measured every day from the onset to the end of acute failure (before extubation) at 5 and 15 minutes into the weaning period. The diaphragmatic electromyogram was recorded with an esophageal electrode and the high-to-low ratio of the electrical signal analyzed to assess diaphragmatic fatigue.In all patients P0.1 was markedly increased (7.1 +/- 2.4 cm H2O, mean +/- SE) on the first day of acute failure and did not change during weaning. In 11 patients, P0.1 had decreased to 4.7 +/- 1.8 cm H2O (P less than or equal to 0.002) before extubation (which was done after 5 to 9 days). In these patients, the high-to-low ratio of the diaphragm decreased rapidly-during the first minutes of weaning on the first day of acute failure and remained low throughout weaning, whereas before extubation no decrease in high-to-low ratio was seen during weaning. In 5 patients, P0.1 did not change significantly from the onset of acute failure and the high-to-low ratio remained low before extubation. These 5 patients had to be reintubated within 2 to 6 days. In both groups of patients, VE did not change significantly from the first to last day of acute failure (10.3 +/- 3 compared with 10.7 +/- 2.1 min-1), whereas blood gases during room air breathing improved significantly from the first to last day of acute failure, respectively, in each group (arterial oxygen pressure [PaO2], 33.5 +/- 1.5 compared with 44 +/- 9 mm Hg (P less than or equal to 0.05) and PaO2 56 +/- 2.3 compared with 49 +/- 2 mm Hg (P less than 0.005).Extubation should not be done in patients with respiratory muscle fatigue despite improvement in arterial blood gases and clinical status; and P0.1 provides a valid and simple index to assess the likelihood of respiratory muscle fatigue.

Excerpt To the Editor:Murciano and colleagues (1) showed that tracheal occlusion pressure (P0.1) provided a better predictive index for successful extubation than classic weaning criteria in patien...