Respiratory performance of humans exposed to moderate levels of carbon dioxide

Abstract

In a business-as-usual scenario, atmospheric carbon dioxide concentration (CO2) could reach 950 parts per million (ppm) by 2100. Indoor CO2 concentrations will rise consequently, given its dependence on atmospheric CO2 levels. If buildings are ventilated following current standards in 2100, indoor CO2 concentration could be over 1,300 ppm, depending on specific ventilation codes. Such exposure to CO2 could have physiological and psychological effects on building occupants. We conducted a randomized, within-subject study, examining the physiological effects on the respiratory functions of 15 persons. We examined three exposures, each 150 minutes long, with CO2 of: 900 ppm (reference), 1,450 ppm (decreased ventilation), and 1,450 ppm (reference condition with added pure CO2). We measured respiratory parameters with capnometry and forced vital capacity (FVC) tests. End-tidal CO2 and respiration rates did not significantly differ across the three exposures. Parameters measured using FVC decreased significantly from the start to the end of exposure only at the reduced ventilation condition (p<0.04, large effect size). Hence poor ventilation likely affects respiratory parameters. This effect is probably not caused by increased CO2 alone and rather by other pollutantspredominantly human bioeffluents in this work -whose concentrations increased as a result. Practical implicationsRising atmospheric CO2 levels have raised concerns regarding the negative effects on humans and consequently the future of building ventilation. It has been discussed whether it would still be possible to guide ventilation requirements by a difference between outdoor and indoor CO2 levels or if absolute CO2 levels should be used. We use this study to show that an increase in the CO2 level with no change to ventilation, did not affect human respiration parameters. However, poor ventilation was shown to affect lung capacity demonstrated in the form of an obstructive breathing pattern most likely caused by an increase in the concentration of other pollutants, primarily bioeffluents, and not only CO2. This result provides additional confirmation for the health effects in ill-ventilated spaces.

Emission rate of carbon dioxide while sleeping

“…Probably, the respiratory pattern of subjects during sleep did not change between conditions in the present study. Previous studies of subjects who were awake have documented reduced respiration in a polluted environment 52,53 and at high temperature 54 . Further studies are required to monitor the respiratory pattern during sleep at different temperatures and levels of IAQ.…”

The effects of warmth and CO 2 concentration, with and without bioeffluents, on the emission of CO 2 by occupants and physiological responses

“…As heart rate and minute ventilation are strongly correlated, 24 they inferred that changes in respiration rate and tidal volume could have affected ETCO 2 but the former did not change and the latter was not measured. Moreover, Mishra et al 20 showed that ETCO 2 and respiration rate did not differ significantly across three exposure conditions of CO 2 with bioeffluent: 900 ppm, 1,450 ppm (increase caused by reduced ventilation rate), and 1,450 ppm (pure CO 2 added, ventilation rate same as 900 ppm), although Forced Expiratory Volume flow in 1 second (FEV1) and Forced Vital Capacity (FVC) decreased with reduced ventilation. The studies mentioned above suggest that increased air pollution caused by increasing the levels of CO 2 , bioeffluents, or other pollutants to the levels that are typically observed indoors may reduce the rate of elimination of CO 2 from the lungs.…”

“…For example, in spirometry tests under different exposure conditions, Shriram et al 19 suggested that the exposure to high levels of CO2 and bioeffluents that is associated with low ventilation levels may reduce lung capacity. Additionally, Mishra et al 20 showed that exposure to bioeffluents but not CO 2 can affect pulmonary function.…”

Evaluation of indoor environmental quality and health concerns among employees of a public elementary school.

“…As the level of CO 2 increases, the level of indoor contaminants may also be increasing. Recent studies have shown that the health effects associated with elevated CO 2 levels are varied and may be associated with other factors [Fisk et al 2019;Mishra et al 2021;Persily and de Jonge 2017].…”