Background: Carbon dioxide (CO2) re‐breathing has been recognised as a key concern regarding
respirator use and is related to increased respiration, heart rate, breathing discomfort, anxiety,
headache, impaired cognitive function, and in higher amounts asphyxia or death. Several studies
have examined CO2 levels in respiratory protective devices (RPDs), however no previous
investigations have evaluated the relationship between CO2 inhalation and phonic respiration
(breathing during speech).
Methods and Approach: A total of 22 participants (8 females) volunteered for the pilot study.
Participants performed a graded exercise test on a cycle ergometer that increased in resistance
every 5 minutes. During the third minute of each stage participants read aloud a prepared text.
Measures of expired (PECO2) and inspired CO2 (PICO2), heart rate (HR), peak inspiratory air flow
(PIAF) and dyspnoea (breathing discomfort) were monitored.
Results and Discussion: A paired sample t‐test was performed to compare PICO2 within the two
breathing conditions (normal and phonic respiration). The variables were calculated across all six
workloads (rest, 75W, 100W, 125W, 150W and 175W) (alpha was set at 0.05). Significant
differences between the two breathing conditions, at rest and each exercise workload were found
(see Table 1). During normal respiration, PICO2 was generally below 2%, however was present at
higher levels during phonic respiration. The highest PICO2 was obtained at rest, and was observed
to decrease during increased oxygen uptake (workload) suggesting that the breathing frequency
and flow rates are a decisive factor in CO2 re‐breathing in RPDs.
Preliminary Conclusions: The results showed that phonic respiration in respirators contributed to
significantly higher levels of CO2 re‐breathing that was often beyond the design standards
recommended by Standards Australia (1%). Further research into the occurrence of CO2 rebreathing in RPDs and its impact on workers who inevitably wear them for prolonged periods is in