Measurement of ventilatory flow during pulmonary function maneuvers and in severe exercise by the pneumotachograph flow transducer in dense atmospheres is handicapped by the inverse relationship between the linear range of such transducers and gas density. This limitation in the usefulness of the pneumotachograph can be overcome by mounting such flow transducers in parallel and taking into account the reduction in peak ventilatory flow transducers in parallel and taking into account the reduction in peak ventilatory flow which occurs with increasing density. The design of such assemblies, their static performance characteristics, and a drift subtractor, constructed to stabilize the output of the pneumotachograph pressure transducer, are described.