Table 2 Summary of lowest levels of carboxyhemoglobin (COHb) for which health outcomes have been described, by health status

 Exercise-induced arrhythmias [44]

5 [44]

1000–3000 ppm for 4–6 min

No effect.

 Exercise duration [31, 32, 40, 50]

3.95 (SD: 0.49) [31]

100 ppm for 1 h

Decrease in mean exercise duration from 698 to 663 s (p < 0.001).

 Cardiovascular effects (cardiac output, heart rate, artery diameter, electrocardiogram changes) [25, 29, 33, 49, 89, 90]

2.4 [33]

15 ppm for 10 days (continuous exposure)

Electrocardiogram changes, specifically to p-waves, observed among three out of 15 subjects.

 Respiratory effects [22, 25, 36, 45, 46, 89, 91]

3.95 (SD: 1.87) [25]

5000 ppm for 2.5–3.5 min

Decrease in mean (sd) inspiratory capacity from 3655 (415) ml to 3380 (419) ml (p < 0.05), and total lung capacity from 7705 (1083) ml to 7545 (993) ml (p < 0.02).

 Cognitive function [24, 26, 28, 34, 37, 38, 43, 47]

5.1 (SD: 0.57) [34]

74.1 ppm for 4 h

Decreases in performance of visual tracking exercises among high exposure group, compared with low exposure and control groups (p < 0.01).

 Cytokine production [48]

7 (95% CI: 6.5,7.7) [48]

500 ppm for 1 h

No effect.

 Visual function [39]

17.06 (SD: 1.38) [39]

11,569 ppm for 4–5 min, followed by 141 ppm for 2 h

No effect.

 Exercise-induced angina [53,54,55, 58,59,60,61,62,63, 66, 70]

2.0 (SD: 0.05) [61]

117 ppm for 50–70 min

Decrease in mean (sd) time to onset of angina from 501 (25) seconds to 482 (22) seconds (p = 0.054).

 Exercise-induced arrhythmias [54, 61, 64, 65, 67,68,69]

5.91 (SD: 0.07) [65]

200 ppm for 1 h

Higher frequency of single premature ventricular contractions per hour during exercise among subjects (p = 0.03).

 Other cardiovascular effects [51, 52, 61, 66, 69]

2.0 (SD: 0.05) [61]

117 ppm for 50–70 min

Decrease in mean (sd) length of time to a threshold ischemic ST-segment change from 576 (27) seconds to 510 (26) seconds (p < 0.0001).

 Cognitive function [57]

3.90 [57]

100 ppm, duration not reported

Decrease in mean performance of visualization test (p < 0.001), but no effects on performance of speed, flexibility, digit symbol, time perception, or reaction time tests.

 Exercise-induced claudication (impairment, pain discomfort in legs) [56]

2.77 [56]

50 ppm for 2 h

Decrease in mean (sd) exercise time until onset of intermittent claudication from 174 (49) to 144 (38) seconds.

 Exercise performance [71]

4.08 [71]

100 ppm for 1 h

Decrease in mean (sd) exercise duration from 219 (48) to 147 (28) seconds (p < 0.001).

 Exercise performance [72]

3.38 (SD: 0.83) [72]

50 ppm for 1 h

Decrease in mean (sd) exercise duration from 221 (72) to 217 (73) seconds (p < 0.0001).

 Cognitive function [73]

5.0 [73]

200 ppm for 1 h and 50 ppm for 2 h

No effect.