A device for electrically isolating pulmonary veins in atrial fibrillation for treatment thereof by ablation of a circumferential zone of tissue. Each of the tubes provides a closure plate at one end with one or more apertures in it. The invention is demonstrated using deposited columnvoid network materials as examples of large surface to volume ratio materials. The pump cavity can include a mechanism for automating the rapid interchangeability of the pump source. Each cask rests on four rotating wheels which are disposed on the vertices of the framework of the carriage. A comparison is made between the relative values of the outputs of the different sensors to identify sensor drift or potentially significant changes in flow conditions.