Design of a chamber for lower body negative pressure with controlled onset rate.

We have designed a lower body negative pressure (LBNP) chamber and control system that makes it possible to apply LBNP either very rapidly (< 300 ms), or more gradually, according to predefined protocols. The capability of the new, high-performance agile aircraft to reach a high-G onset rate makes it highly desirable to be able to study immediate, rapid, and transient cardiovascular responses to simulated gravitational stress. Our new LBNP chamber has been used to study the main cardiovascular variables during onset and release of mild LBNP (-20 mmHg). We have revealed large transient physiological responses during the onset and release of mild LBNP. This new finding was largely made possible by precise control of the onset and release of LBNP during the experiments. The purpose of this paper is therefore to describe some of the technical solutions which made rapid and controlled changes in LBNP possible, focusing on the importance of precise control of the LBNP chamber.