Test system was likely a Fleisch Metabometer. From: Survey of Current Cardiovascular and Respiratory Examination Methods in Medical Selection and Control of Aircrew by A. Scano, NATO Agardograph No. 196, published December 1974, page 58.
Tidal volume was monitored with a heated Fleisch pneumotachograph that was mounted downstream of a Hans Rudolph two-way high velocity valve. Exhaled air was collected in plastic and neoprene bags, the volume subsequently measured with precision gas meters. Gas concentrations were measured with a gas chromatograph. The bicycle eergometer used friction resistance to maintain and steady workload and the subject pedealed to a metronome. Taken from the “The inhalation of the photochemical smog compound peroxyacetyl nitrate” by Leon E. Smith EdD in AJPH volume 55, no 9, Sept 1965, page 1460.
Jaeger Exercise bike with mixing box. Photo courtesy of Felip Burgos, MSC, RPFT, RN. Barcelona, Spain.