What typically regulates the second pressure in a differential pressure-based flow cytometer?

In a differential pressure-based flow cytometer, the second pressure is primarily regulated by a constant pressure source. This pressure source is critical in creating and maintaining a controlled flow environment that ensures the cells or particles being analyzed are transported uniformly through the optical detection system.

A constant pressure source helps to stabilize the sample flow rate, which is essential for obtaining reliable and reproducible data during cytometric analysis. This controlled pressure contributes to the efficiency of the sheath fluid that surrounds the sample stream, allowing for laminar flow and preventing turbulence that could disrupt the analysis.

While sample thickness, investigator control, and environmental conditions can have roles in the overall operation of a flow cytometer, their influence is not as direct or critical in regulating the second pressure compared to the use of a constant pressure source. Maintaining constant pressure ensures that the hydrodynamic focusing required for accurate measurements is achieved, thereby facilitating precise cytometric assessments.