Cargo racks for use with all terrain vehicles are disclosed. The additional control loop cooperates with the LDO regulator’s amplifier stage and output stage to maintain at least a minimum desired voltage drop across the output stage from the power supply to the load. A tubular porous membrane having a porous wall with an inner surface that defines an inner space is located along the distal end portion of the elongated body. The design of the probe enables correct orientation of the transducers with respect to a blood vessel under measurements.