ASHRAE Journal - September 2019 - 74

COLUMN PRODUCTIVITY-ASHRAE

FIGURE 3 Associations of CO2 concentrations with physiological outcomes.

Statistically significant effect (P<0.05)

Increased Mental Effort Based on Heart Rate
Variability (HRV)

12
12
15
23
19
22
15
23
19
12
12
15
23
19
12
12
15
23
19
22
12
12

Increased Stress Based on HRV

21

Increased Stress Based on Salivary α-amylase

15
23
19

Sleepiness Measured with
Electroencephalogram (EEG)

22

Increased Respiratory Frequency

Increased Exhaled CO2 Concentration (ETCO2)

Increased Diastolic Blood Pressure

Increased Heart Rate

0

500

1,000

1,500

prior training. The authors of the other paper20 hypothesized that their subjects (submariners) might have been
unaffected by CO2 as a consequence of their prior regular occupational exposure to CO2 at 2,500 ppm or higher
concentrations.
Five of the studies12,14,18,19,23 investigated whether subjects' perceptions of IAQ, e.g., acceptability of indoor air,
was influenced by CO2 concentrations. Only one study12
found that subjects reported air quality as less acceptable with 3,000 ppm, 4,000 ppm, and 5,000 ppm CO2
relative to 600 ppm.
Six studies, reported in eight papers,12,14,15,18,19,21-23
investigated whether the level of CO2 influenced health
symptoms reported on questionnaires or health-related
physiological outcomes such as blood pressure, pulse,
respiration rate, markers of stress, and exhaled concentrations of CO2. Four studies that included questionnaires on acute health symptoms,14,19,22,23 including
fatigue, found that CO2 level had no statistically significant effect on symptoms. One study12 reported that
subjects were significantly more tired with 5,000 ppm
CO2 relative to 600 ppm CO2. This study12 also found
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S E P T E M B E R 2 0 19

2,000

2,500
3,000
3,500
CO2 Concentrations (ppm)

4,000

4,500

5,000

5,500

that blood pressure, respiration rate and volume, and
mental effort (based on heart period variability) were
increased with higher CO2 concentrations. In contrast,
other studies15,19,23 generally found no statistically significant effects of CO2 levels on a broad range of physiological outcomes except for increases in the concentrations of CO2 in exhaled air, called end-tidal CO2, and two
instances of increases in heart rate. In one study,15 heart
rate decreased less during the exposure session with
3,000 ppm CO2 vs. 500 ppm CO2 while another study22
reported a SS increase in heart rate with exposure to
2,680 ppm CO2 relative to 700 ppm CO2. Another study19
found that levels of α-amylase, markers of mental stress,
were higher with 3,000 ppm CO2 compared to 380 ppm
CO2. Other research26 has shown that exposure of mice
to 2,000 and 4,000 ppm CO2 for two hours triggers an
inflammatory response and vascular injury with generation of microparticles by immune system cells. Also, in
human immune system cells, microparticle generation
resulted from increased CO2 exposures.27
Main findings of this research are summarized below.
* There is very limited evidence that CO2 levels below
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