Physiological Daily Inhalation Rates for Free-Living Individuals Aged 2.6 Months to 96 Years Based on Doubly Labeled Water Measurements: Comparison with Time-Activity-Ventilation and Metabolic Energy Conversion Estimates

ABSTRACT

In the first part of this article, a critical review of traditional approaches used to estimate daily inhalation rates as a function of age for health risk assessment purposes shows that such rates are not totally reliable due to various biases introduced by both quantitative and qualitative deficiencies regarding certain input parameters. In the second part, the magnitude of under- and overestimations of published inhalation rates derived from each approach is described by a comparison with new sets of physiological daily inhalation rates and distribution percentile values based on total daily energy expenditures (TDEEs) measured by the doubly labeled water (DLW) method. TDEEs are derived from the analysis of deuterium (²H) and heavy oxygen-18 (¹⁸O) in urine samples by gas-isotope-ratio mass spectrometry during an aggregate period of over 20,000 days for unrestrained free-living normal-weight individuals aged 2.6 months to 96 years (n = 1252). Regarding physiological values based on DLW measurements, opposite tendencies have been observed between two sets of estimates using time-activity patterns both biased by conservative input data assumptions during sleep and light activities: most estimates based on the time-activity-ventilation approach are overestimated, whereas most of those using metabolic equivalent approach are underestimated. Erroneous food intakes have clearly lead to underestimated rates when used in daily food-energy intake (EFD) and Parameter A approaches. With the latter approach, overestimated basal metabolic rates (BMRs) used in EFD/BMR ratios contribute to the underestimation of inhalation values. Few mean daily inhalation rates and Monte Carlo simulation percentiles based on traditional approaches (57 out of 253) are close to physiological values within a gap of ± 5% or less. Aggregate errors in all estimates (in m³/day and m³/kg-day) vary from -52 to +126%. The most accurate daily inhalation rates are those based on DLW measurements with an error of about ± 5%, as calculated in previous studies for free-living males and females aged 1 month to 96 years and pregnant and lactating adolescents and women aged 11 to 55 years during real-life situations in their normal surroundings.

Key Words:

• daily inhalation rates
• distribution percentiles
• probability density functions
• air quality criteria
• standard value
• risk assessment
• doubly labeled water.

ACKNOWLEDGMENTS

The authors thank Mrs. Isabelle Brochu for the linguistic revision of this manuscript. Acknowledgments are also due to Dr. Alain Le Page and Mr. Norman Beauregard for their collaboration in specific statistical calculations. Finally, the authors wish to point out that the views expressed in this article may not reflect the official policy of the Québec Ministry of Sustainable Development, Environment and Parks.

Web tables for this article can be viewed by accessing the publisher's website.

Notes

^a Subjects aged 60 to 96 years.

^b Estimated by Allan and Richardson (1998) using the time-activity-ventilation (TAV) approach and Monte Carlo simulations.

^c DLW = doubly labeled water. Percentiles based on a normal distribution assumption for all age groups. Means and standard deviations are reported in Table 4.

^d Observed p values based on Kolmogorov-Smirnov normality tests.

^e The number of individuals per age group is reported in Table Web-1, which is available on the Québec Ministry of Sustainable Development, Environment and Parks website (MDDEP 2006).

^a Subjects aged 60 to 96 years.

^b Estimated by Finley et al. (1994) based on the Parameter A approach and Monte Carlo simulations.

^c DLW = doubly labeled water. Percentiles based on a normal distribution assumption for all age groups. Means and standard deviations are reported in Table 6.

^d Observed p values based on Kolmogorov-Smirnov normality tests.

^e The number of individuals per age group is reported in Table Web-4, which is available on the Québec Ministry of Sustainable Development, Environment and Parks website (MDDEP 2006).

^a Subjects aged 60 to 96 years.

^b Body weight values are reported in Richardson (1997).

^c Estimated by Allan (1994) and Richardson (1997) and reported in Allan and Richardson (1998) using the time-activity-ventilation approach.

^d Energy expenditure (E) calculated for each minute ventilation assumption used in the time-activity-ventilation approach by Allan and Richardson (1998), based on the equation from Layton (1993): E = V_E / (H*V_E/VO₂), where V_E = minute ventilation rate, H = 0.21 L of O₂/Kcal and V_E/VO₂ = 27.

^e BEE = basal energy expenditure (BMR expressed on a 24-hour basis) based on the energy expenditure corresponding to the minute ventilation assumptions for level 1, as used in the time-activity-ventilation approach by Allan and Richardson (1998).

^f Basal metabolic rate as measured by indirect calorimetry in the doubly labeled water method (IOM 2002).

^g Metabolic equivalent or daily BMR multiplier required at each activity level. n.a. = non available.

^a Subjects aged 60 to 96 years.

^b Total daily energy requirements (TDERs) for normal-weight subjects (in kcal/day and kcal/kg-day) according to body mass index (BMI) cut-offs were converted into physiological daily inhalation rates by the following equation: TDER*H*(V_E/VO₂)*10⁻³. H = 0.21 L of O₂/Kcal and V_E/VO₂ = 27 (Layton 1993). TDER = (TDEE + ECG). TDEE = total daily energy expenditure. ECG = stored daily energy cost for growth (Brochu et al. 2006a). TDEEs were based on ²H₂O and H₂ ¹⁸O disappearance rates from urine monitored by gaz-isotope-ratio mass spectrometry for 1,252 free-living subjects aged between 2.6 months and 96 years during 7- to 21-day periods (IOM 2002). DLW = doubly labeled water.

^c Estimated by Allan (1994) and Richardson (1997) and reported in Allan and Richardson (1998) using the time-activity-ventilation approach and Monte Carlo simulations. Body weight values are reported in Richardson (1997).

^d For both genders.

^e Based on mean values. S.D. = standard deviation. The number of individuals, measured body weights, BMIs, BEEs, TDEEs, ECGs, and TDERs per age group are reported in Table Web-1, which is available on the Québec Ministry of Sustainable Development, Environment and Parks website (MDDEP 2006).

^a Subjects aged 75 to 96 years.

^b Values are reported in Layton (1993). Bw = body weight.

^c Total daily energy requirements (TDERs) for normal-weight individuals (in kcal/day and kcal/kg-day) according to body mass index (BMI) cut-offs were converted into physiological daily inhalation rates by the following equation: TDER*H*(V_E/VO₂)*10⁻³. H = 0.21 L of O₂/Kcal and V_E/VO₂ = 27 (Layton 1993). TDER = (TDEE + ECG). TDEE = total daily energy expenditure. ECG = stored daily energy cost for growth (Brochu et al. 2006a). TDEEs were based on ²H₂O and H₂ ¹⁸O disappearance rates from urine monitored by gaz-isotope-ratio mass spectrometry for 1252 free-living subjects aged between 2.6 months and 96 years during 7 to 21-day periods (IOM 2002). DLW = doubly labeled water.

^d Estimated by Layton (1993) using the daily food-energy intake approach.

^e For both genders. S.D. = standard deviation. The number of individuals, measured body weights, BMIs, BEEs, TDEEs, ECGs, and TDERs per age group are reported in Tables Web-2 and Web-3, which are available on the Québec Ministry of Sustainable Development, Environment and Parks website (MDDEP 2006).

^a Subjects aged 60 to 96 years.

^b Values used by Layton (1993). EFD/BMR ratio = Parameter A.

^c Total daily energy requirements (TDERs) for normal-weight subjects (in kcal/day and kcal/kg-day) according to body mass index (BMI) cut-offs were converted into physiological daily inhalation rates by the following equation: TDER*H*(V_E/VO₂)*10⁻³. H = 0.21 L of O₂/Kcal and V_E/VO₂ = 27 (Layton 1993). TDER = (TDEE + ECG). TDEE = total daily energy expenditure.

^d Values from Layton (1993) based on the Parameter A approach. S.D. = standard deviation.

^a Values are reported in Layton (1993).

^b BEE = basal energy expenditure (BMR expressed on a 24-hour basis).

^c DLW = doubly labeled water.

^d Total daily energy requirements (TDERs) for normal-weight subjects (in kcal/day and kcal/kg-day) according to body mass index (BMI) cut-offs were converted into physiological daily inhalation rates by the following equation: TDER*H*(V_E/VO₂)*10⁻³. H = 0.21 L of O₂/Kcal and V_E/VO₂ = 27 (Layton 1993). TDER = (TDEE + ECG). TDEE = total daily energy expenditure. ECG = stored daily energy cost for growth (Brochu et al. 2006a). TDEEs were based on ²H₂O and H₂ ¹⁸O disappearance rates from urine monitored by gaz-isotope-ratio mass spectrometry for 367 free-living adults aged 20 to less than 75 years during 7 to 21-day periods (IOM 2002).

^e Estimated by Layton (1993) using the metabolic equivalent (MET) approach. S.D. = standard deviation. The number of individuals, measured body weights, BMIs, BEEs, TDEEs, ECGs, and TDERs per age group are reported in Table Web-5, which is available on the Québec Ministry of Sustainable Development, Environment and Parks website (MDDEP 2006).