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Men ran to a voluntary end point under the following conditions listed in increasing order to resistance, expressed as inspiratory/expiratory in mmH2O at a flow of 4 l-s-1: 1) bare-headed 0/0; 2) face mask 0/0; 3) face mask -6/14; 4) mouthpiece and valves -25/29; 5) face mask -96/62; and 6) face mask -148/60. Average endurance was 545, 490, 434, 392, 343, and 338 s, respectively. Despite the diverse features of the equipment in conditions 2-6, there seemed to be a rather smooth relation between resistance and endurance. There was no indication of a threshold below which endurance would be indifferent to resistance. The duration of the phases of the respiratory cycle was measured by means of a fine thermocouple in the airway. The variability in the duration of the expiratory phase at the end of the run seemed to weaken the concept that the attainment of a critically short expiratory time might be related to the subject's decision to halt running.

Techniques are presented which provide direct measurement of both free cyanide (CN-) in plasma and total CN- in whole blood. Loss of total CN- from blood is prevented by conversion to cyanmethemoglobin. Both free and total CN- are assayed by a completely automated method providing readout 17 minutes after sampling. No prior isolation technique is required and sensitivity is adjustable to cover a broad range of CN- concentrations from 1 to 4000 uM. Precision of blood CN- values from 2 to 2500 uM is within +/- 2.3%. No interference results from thiocyanate or thiosulfate at a concentration of approximately 1 mM.