A plethysmograph for long-term measurements of ventilation in unrestrained animals

An apparatus for quantitative measurement of ventilation in unrestrained small animals is described. The subject rests in an environmental chamber, and respiration is indicated by barometric pressure oscillations proportional to tidal volume. The chamber is purged continuously at a relatively high flow rate during studies. Thus, CO2 does not accumulate and long-term measurement can proceed without interruption. Respiratory control studies are especially facilitated since different gas mixtures can be rapidly passed through the chamber. An electronic device also is described which automatically calculates expired minute volumes (VE) from the pressure signal obtained from the plethysmograph.