Physiologically acceptable resistance of an air purifying respirator

Abstract

Physiologically acceptable limits of inspiratory impediment for air purifying respirators (APRs) were sought. Measurements on 30 subjects included pressure in, and flow through, an APR, and respiratory and cardiovascular variables. Exercise with and without APR included ladder climbing, load lift and transfer, incremental running and endurance running, with endurance at 85% peak oxygen uptake. Resistance that did not alter minute ventilation () was judged acceptable long-term. Acceptable short-term impediments were deduced from end exercise conditions. Proposed long-term limits are inspiratory work of breathing per tidal volume (WOB _i/V _T) ≤ 0.9 kPa and peak inspiratory pressure (P _{i peak}) ≤ 1.2 kPa. Proposed short-term limits are: for  ≤ 110 L min⁻¹, WOB _i/V _T ≤ 1.3 kPa and P _{i peak} ≤ 1.8 kPa; and for  > 130 L min⁻¹, WOB _i/V _T ≤ 1.6 kPa. A design relation among , pressure–flow coefficients of an APR, and WOB _i/V _T is proposed.

Statement of Relevance: This work generalises results from one APR by considering the altered physiological parameters related to factors inhibiting exercise. Simple expressions are proposed to connect bench-test parameters to the relation between ventilation and work of breathing. Population-based recommendations recognise that those who need more air flow can also generate higher pressures.

Keywords:

• work of breathing
• resistance
• respirator
• respiratory protective device
• testing standards

Acknowledgements

This work was sponsored by the Joint Science and Technology Office (JSTO) of the US Defense Threat Reduction Agency (DTRA) as part of a project at Navy Surface Warfare Center Panama City. It would have been impossible without the committed sailors of NEDU, and difficult without the involvement of our task leaders HM1 Donika Winters and HM1 Charissa Duff.