Why can't I adjust the perfusion rate by varying the pump driving pressure (the pressure applied to the perfusate reservoir)?

This can be done, but only over a narrow range. If the pump driving pressure is set below 10 psi/67 kpa, measurement accuracy is unacceptably impaired. At 10 psi/67 kpa, a 0.6ml/min resistor delivers 0.4ml/min, still at least 6 times higher than is appropriate for the micro-manometric recording channels used mainly in children and infants.

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