Ventilation
When the lung is placed in the artificial thoracic chamber and ventilated at negative pressure, the ventilation head is removed and replaced by the pneumotachometer for the measurement of respiratory flow. The ventilation medium (air or gas mixture) is constantly flowing past the distal end of the pneumotachometer. The breathing frequency can be varied between 30 and 60 breaths/min. In addition, the inspiratory time as a percentage of each breath, can be set between 10 and 90% in 10% steps. The end-inspiratory, end-expiratory, and deep breath (hyperinflationary) negative pressure can be set individually. A deep breath is usually induced every 5 to 20 min.
Constant Flow Perfusion
The constant flow rate of perfusate into the pulmonary artery is determined by a roller pump. The perfusate is stored in a water-jacketed container to maintain constant temperature. Aeration is provided to keep the pH constant. A heat exchanger and a bubble trap are placed next to the pulmonary artery connection for exact adjustment of the perfusate temperature just before the thorax chamber and to prevent air bubbles entering the lung.
Different perfusates can be provided in turn by transferring the suction tube from one reservoir to another; there is no need for prior aeration or temperature control. The use of oxygen-sensitive test substances raises few problems since the contact time with the high oxygen concentration is minimized. It is also possible to vary the gas mixture rapidly during the study.
A Constant Pressure Perfusion System is optionally available. Please call for details.
Lung Mechanics
The pressure inside the thoracic chamber is measured with a MPX pressure transducer. Air flow is determined with the pneumotachometer connected to a Validyne differential pressure transducer DP 45-14. The volume is derived from the air flow by integration. The calculation of pulmonary compliance and resistance needs a computer controlled data acquisition system (HSE-HA Pulmodyn).