A servo-controlled respiration system for inhalation studies in anesthetized animals

Rosenthal, Frank S., and Changhong Li. Aservo-controlled respiration system for inhalation studies inanesthetized animals. J. Appl.Physiol. 83(5): 1768-1774, 1997.To facilitate aerosol deposition experiments and aerosol exposures in anesthetized animals, a servo-controlled respiration system was developed and tested. The system induces ventilation by varying extrathoracic pressure in a whole body respirator in which an intubated animal isplaced. The pressure inside the whole body respirator is varied with athree-way servo-controlled spool valve connected to sources of positiveand negative pressure. A computer-based system detects respiratory flowand computes the controlling signal for the valve by using aproportional-integral-derivative algorithm, to achieve desired patternsof flow and volume vs. time. The system was used with dogs and found toaccurately induce various single-breath breathing patterns involvingconstant-flow inspirations and expirations as well as breath-holdperiods. A similar system was used to induced repeated breaths withdesired parameters for continuous exposure to particles and forventilation of animals between experiments.

     

A custom restraining device for small animals

A full-body restraining device was constructed that permits the short-term recording of physiologic data (respiration, electrocardiogram, arterial blood pressure, and electroencephalogram) in unanesthetized rats. A plaster cast of a freshly killed 160 g rat was made and cut to yield a base and two side pieces. Using the assembled cast as a custom tray, an alginate impression of the rat was taken. Replicas of the cast pieces were then made of plastic. Animals to be tested were anesthetized briefly, placed in the restraining device, and allowed to waken. Results with 400 animals demonstrate the feasibility of recording physiologic data during acute studies in conscious rats.     

A new airway device for small laboratory animals

There is a need for a device for improved management of the airway of small laboratory animals during general anaesthesia. This report introduces such a device, referred to here as the airway device (AD). The AD has some similarity to the laryngeal mask airway (LMA) developed for human patients, but the mask portion of the device is specifically designed for small laboratory animals. In addition, the device has an oesophageal extension and unlike the LMA does not have a cuff associated with the mask. This report also shares experience of tests of one prototype AD with six New Zealand white rabbits. The AD was used for administering isoflurane and its effectiveness was evaluated during conditions of spontaneous and controlled intermittent positive pressure ventilation. The results provide encouragement for further development of the AD for airway management of small laboratory animals.     

The absolute eosinophil count in experimental animals.

The values of the absolute eosinophil count in certain laboratory animals were examined and were compared with values in healthy humans. The method and the results extend the possibility of detecting and studying changes in biological processes in the organism of experimental animals.     

Responses to negative pressure surrounding the neck in anesthetized animals

Continuous positive pressure applied at the nose has been shown to cause a decrease in upper airway resistance. The present study was designed to determine whether a similar positive transmural pressure gradient, generated by applying a negative pressure at the body surface around the neck, altered upper airway patency. Studies were performed in nine spontaneously breathing anesthetized supine dogs. Airflow was measured with a pneumotachograph mounted on an airtight muzzle placed over the nose and mouth of each animal. Upper airway pressure was measured as the differential pressure between the extrathoracic trachea and the inside of the muzzle. Upper airway resistance was monitored as an index of airway patency. Negative pressure (-2 to -20 cmH2O) was applied around the neck by using a cuirass extending from the jaw to the thorax. In each animal, increasingly negative pressures were transmitted to the airway wall in a progressive, although not linear, fashion. Decreasing the pressure produced a progressive fall in upper airway resistance, without causing a significant change in respiratory drive or respiratory timing. At -5 cmH2O pressure, there occurred a significant fall in upper airway resistance, comparable with the response of a single, intravenous injection of sodium cyanide (0.5-3.0 mg), a respiratory stimulant that produces substantial increases in respiratory drive. We conclude that upper airway resistance is influenced by the transmural pressure across the airway wall and that such a gradient can be accomplished by making the extraluminal pressure more negative.(ABSTRACT TRUNCATED AT 250 WORDS)