Low-frequency response characteristics of three Grass model 7 polygraphs.

A low-frequency response analysis of three Grass model 7 polygraphs was undertaken. Observed error was generally found to fall within the manufacturer's stated range of +5 to -10% of DC signal height over the frequency range of human respiration (0.1-3 Hz), but this was not the case for frequencies greater than 6 Hz under certain circumstances. The magnitude of error was seen to vary directly with frequency and indirectly with pen-deflection amplitude and paper speed. The pen-oscillograph apparatus was the predominant source of low-frequency error, and this is probably due to pen inertia and pen friction on the writing surface. Two schemes to reduce such error are presented.

Hyperbaric chamber for evaluating hydrostatic pressure effects on tissues and cells.

A chamber system is described for the study of pure hydrostatic pressure effects on tissues and cells. The small chamber has an internal volume of 7.6 liters and is rated for working pressures up to 400 ATA. Sliding doors at each end permit easy access and quick sealing. A cam-driven pump provides constant flow of physiological solution to the tissue bath containing the preparation. Connections to the pump allow a variety of test solutions to be used in the course of an experiment. The tissue bath is designed to prevent chamber gas from diffusing in to the perfusate, thus allowing for pure hydrostatic compression of the bath contents. The bath is coupled to a motorized stage to facilitate placement of recording devices once the bath is placed inside the chamber. Temperature is controlled within 0.05 degrees C of set point by thermoelectric modules coupled to a feedback amplifier. This system has been used for electrical and mechanical studies of cardiac muscle, but its versatility makes it suitable for a wide range of other biomedical applications.