Acceptable levels for the breathing resistance of respiratory apparatus: results for men over the age of 45.

Tolerance of additional external resistance to inspiration has been investigated in a group of coalworkers older than 45 years. Peak inspiratory pressure, external respiratory work rate, ventilation, and gas exchange were measured, during periods with and without one of four inspiratory resistances, on 41 subjects walking on a treadmill. Minute volume was reduced, breathing frequency was unchanged and oxygen uptake and carbon dioxide elimination were reduced by the presence of resistance. It was established that, at the workload studied, older men were able to tolerate inspiratory resistance to at least the same extent as younger men, when the respiratory work was expressed in terms of unit ventilation. It is suggested that the acceptable level of breathing resistance established for younger men can also be applied to older workers.