Acceptable breathing resistance of respiratory apparatus

Tolerance of additional external resistance to inspiration has been investigated in 158 mine rescue workers during exercise. Peak inspiratory pressure, minute volume, and respiratory work rates were calculated in order to determine which factor best correlated with subjective tolerance of resistance. A method of defining an acceptable limit for inspiratory resistance is presented, which considers the additional respiratory work load in terms of unit ventilation. St is concluded that excessive pressure exerted during inspiration is a major factor in determining subjective tolerance. It is suggested that 90% of a population breathing through apparatus with low-resistance expiratory valves should experience no discomfort, if the pressure across the apparatus does not exceed 17 cm H2O.