Derivation of cardiac output and alveolar ventilation rate based on energy expenditure measurements in healthy males and females

Modeling the impact of heat stress on the toxicokinetics of toluene and acetone

Many workers can be exposed simultaneously to heat and volatile chemicals. In a controlled human exposure study, it was observed that an increase in ambient temperature was associated with increased blood concentrations for acetone and toluene. Based on the expected changes in physiological parameters that occur with an increase in ambient temperature, we aimed to develop a PBPK model for acetone and toluene that could account for the impact of temperature on the kinetics of these solvents. Changes in temperature-dependent physiological parameters (i.e. blood flows, cardiac output, alveolar ventilation) based on recent measurements in volunteers were introduced in the PBPK models to simulate observed blood concentrations for different temperature exposure conditions. Because initial simulations did not adequately predict solvent kinetics at any temperature, the most sensitive parameter (alveolar ventilation; Qp) was, therefore, optimized on experimental acetone blood concentrations to obtain a relationship with temperature. The new temperature-dependent Qp relationship gave Qp values consistent with the literature and estimated a mean increase of 19% at 30 °C (wet bulb globe temperature) compared to 21 °C. The integration of a new temperature-dependent Qp relationship in the PBPK toluene model yielded adequate simulations of the experimental data for toluene in blood, exhaled air and urine. With further validation with other solvents, the temperature-dependant PBPK model could be a useful tool to better assess the risks of simultaneous exposure to volatile chemicals and heat stress and interpret biomonitoring data in workers as well as in the general population. TRN: NCT02659410, Registration date: January 15, 2016.

Changes in the negative logarithm of end-tidal hydrogen partial pressure indicate the variation of electrode potential in healthy Japanese subjects

Molecular hydrogen (H2) is produced by human colon microbiomes and exhaled. End-tidal H2 sampling is a simple method of measuring alveolar H2. The logarithm of the hydrogen ion (H+)/H2 ratio suggests the electrode potential in the solution according to the Nernst equation. As pH is defined as the negative logarithm of the H+ concentration, pH2 is defined as the negative logarithm of the H2 effective pressure in this study. We investigated whether changes in pH2 indicated the variation of electrode potential in the solution and whether changes in end-tidal pH2 could be measured using a portable breath H2 sensor. Changes in the electrode potential were proportional to ([Formula: see text]) in phosphate-buffered solution (pH = 7.1). End-tidal H2 was measured in the morning (baseline) and at noon (after daily activities) in 149 healthy Japanese subjects using a handheld H2 sensor. The median pH2 at the baseline was 4.89, and it increased by 0.15 after daily activities. The variation of electrode potential was obtained by multiplying the pH2 difference, which suggested approximately + 4.6 mV oxidation after daily activities. These data suggested that changes in end-tidal pH2 indicate the variation of electrode potential during daily activities in healthy human subjects.

Cardiopulmonary parameters and organ blood flows for workers expressed in terms of VO2 for use in physiologically based toxicokinetic modeling

Minute ventilation rates (VE), alveolar ventilation rates (VA), cardiac outputs (Q), liver blood flow (LBF) and kidneys blood flows (KBF) for physiologically based toxicokinetic modeling and occupational health risk assessment in active workers have apparently not been determined. Minute energy expenditure rates (E) and oxygen consumption rates (VO₂) in workers during exertions and their aggregate daytime activities are obtained by using open-circuit wearable devices for indirect calorimetry measurements and the doubly labeled water method respectively. Hundreds of E (in kcal/min) and VO₂ (in L of O₂/min) were previously reported for workers. The oxygen uptake factors of 0.2059 ± 0.0019 and 0.2057 ± 0.0018 L of O₂/kcal during postprandial and fasting phases respectively enabled conversion of E into VO₂. Equations determined in this study based upon more than 25 000 published measurements enable the calculation of 15 parameters in the same worker only by using the VO₂ reflecting workload. These parameters, notably VE, VA, VE/VO₂ VA/Q, Q, LBF and KBF were found to be interrelated. Altering one of these changes the order of magnitude of the others. Q, LBF and KBF decrease when supine adults at rest switch to an upright position. This effect of gravity diminished when VO₂ increased. The fall in LBF and KBF during exertion might enhance muscle blood flow as reported previously. Taken together these equations and data may improve the accuracy of physiologically based toxicokinetic modeling as well as occupational health assessment studies in active workers exposed to xenobiotics.List of main abbreviations: AVOD: arterioveinous oxygen content difference.BMI: body mass index (in kg/m²).BSA: body surface area (in m²).BTPS: body temperature and saturated with water vapor.Bw: body weight (in kg).E: minute energy expenditure rate (in kcal/min).F_GE: organ blood flow factor for the gravitational effect on blood circulation.H: oxygen uptake factor, volume of oxygen (at STPD) consumed to produce 1 kcal of energy expended.KBF: kidneys blood flow (in ml/min).LBF: liver blood flow (in ml/min).P_BF: liver or kidneys blood flows expressed in terms of percentages (in %) of Q_{sup C} values: namely P_BF = (LBF or KBF/Q_{sup C}) x 100.Q: cardiac output (in L/min or ml/min).Q_{sup C:} cardiac output for the cohort of males or females in supination (in ml/min).STPD: standard temperature and pressure, dry air.sup: values measured when adults are in the supine position.up: values measured when adults are in the upright position.VDphys: physiological dead space at BTPS (in L).VT: tidal volume at BTPS (in L).VA: alveolar ventilation rate at BTPS (in L/min).VA/Q: ventilation-perfusion ratio (unitless).VE: minute ventilation rate at BTPS (in L/min).VO₂: oxygen consumption rate (i.e. the oxygen uptake) at STPD (in L/min).VQ: ventilatory equivalent for VO₂ (VE at BTPS /VO₂ at STPD).

Cardiopulmonary values and organ blood flows before and during heat stress: data in nine subjects at rest in the upright position

Physiological changes associated with thermoregulation can influence the kinetics of chemicals in the human body, such as alveolar ventilation (VA) and redistribution of blood flow to organs. In this study, the influence of heat stress on various physiological parameters was evaluated in nine male volunteers during sessions of exposure to wet blub globe temperatures (WBGT) of 21, 25 and 30°C for four hours. Skin and core temperatures and more than twenty cardiopulmonary parameters were measured. Liver, kidneys, brain, skin and muscles blood flows were also determined based on published measurements. Results show that most subjects (8 out of 9) have been affected by the inhalation of hot and dry air at the WBGT of 30°C. High respiratory rates, superficial tidal volumes and low VA values were notably observed. The skin blood flow has increased by 2.16-fold, whereas the renal blood flow and liver blood flow have decreased by about by 11 and 18% respectively. A complete set of key cardiopulmonary parameters in healthy male adults before and during heat stress was generated for use in PBPK modeling. A toxicokinetic studies are ongoing to evaluate the impact of heat stress on the absorption, biotransformation and excretion rates of volatile xenobiotics.

Factors Contributing to CO Uptake and Elimination in the Body: A Critical Review

BACKGROUND

Carbon monoxide (CO) poisoning is an important public health issue around the world. Research indicates that many factors may be related to the rate of CO uptake and elimination in the human body. However, some factors related to CO uptake and elimination are considered controversial. Relatively little attention has been devoted to review and synthesis of factors affecting CO uptake and elimination.

PURPOSE

This paper provides a critical scoping review of the factors and divides them into four aspects, including environmental, demographic, physiological and treatment factors.

METHODS

We searched the scientific databases for research that has proposed a mathematical equation as a synthesis of quantities related to CO poisoning, CO elimination, CO uptake, CO half-life, CO uptake and elimination and their relationships. After excluding the studies that did not meet the study criteria, there were 39 studies included in the review and the search was completed before 16 December 2019.

RESULTS AND CONCLUSION

This review discusses most of the factors that impact the rate of CO uptake and elimination. Several factors may be related to CO uptake and elimination, such as CO concentration, the duration of exposure to CO, age, sex, exercise, minute ventilation, alveolar ventilation, total haemoglobin mass and different treatments for CO poisoning. Although some potential factors were not included in the review, the findings are useful by presenting an overview for discussing factors affecting CO uptake and elimination and provide a starting point for further study regarding strategies for CO poisoning and the environmental standard of CO.

The Impact of Scaling Factor Variability on Risk-Relevant Pharmacokinetic Outcomes in Children: A Case Study Using Bromodichloromethane (BDCM)

Biotransformation rates extrapolated from in vitro data are used increasingly in human physiologically based pharmacokinetic (PBPK) models. This practice requires use of scaling factors, including microsomal content (mg of microsomal protein/g liver, MPPGL), enzyme specific content, and liver mass as a fraction of body weight (FVL). Previous analyses indicated that scaling factor variability impacts pharmacokinetic (PK) outcomes used in adult population dose-response studies. This analysis was extended to pediatric populations because large inter-individual differences in enzyme ontogeny likely would further contribute to scaling factor variability. An adult bromodichloromethane (BDCM) model (Kenyon, E. M., Eklund, C., Leavens, T. L., and Pegram, R. A. (2016a). Development and application of a human PBPK model for bromodichloromethane (BDCM) to investigate impacts of multi-route exposure. J. Appl. Toxicol. 36, 1095-1111) was re-parameterized for neonates, infants, and toddlers. Monte Carlo analysis was used to assess the impact of pediatric scaling factor variation on model-derived PK outcomes compared with adult findings. BDCM dose metrics were estimated following a single 0.05-liter drink of water or a 20-min bath, under typical (5 µg/l) and plausible higher (20 µg/l) BDCM concentrations. MPPGL, CYP2E1, and FVL values reflected the distribution of reported pediatric population values. The impact of scaling factor variability on PK outcome variation was different for each exposure scenario, but similar for each BDCM water concentration. The higher CYP2E1 expression variability during early childhood was reflected in greater variability in predicted PK outcomes in younger age groups, particularly for the oral exposure route. Sensitivity analysis confirmed the most influential parameter for this variability was CYP2E1, particularly in neonates. These findings demonstrate the importance of age-dependent scaling factor variation used for in vitro to in vivo extrapolation of biotransformation rates.

Physiological daily inhalation rates for health risk assessment in overweight/obese children, adults, and elderly

Physiological daily inhalation rates reported in our previous study for normal-weight subjects 2.6-96 years old were compared to inhalation data determined in free-living overweight/obese individuals (n = 661) aged 5-96 years. Inhalation rates were also calculated in normal-weight (n = 408), overweight (n = 225), and obese classes 1, 2, and 3 adults (n = 134) aged 20-96 years. These inhalation values were based on published indirect calorimetry measurements (n = 1,069) and disappearance rates of oral doses of water isotopes (i.e., (2)H2 O and H2 (18)O) monitored by gas isotope ratio mass spectrometry usually in urine samples for an aggregate period of over 16,000 days. Ventilatory equivalents for overweight/obese subjects at rest and during their aggregate daytime activities (28.99 ± 6.03 L to 34.82 ± 8.22 L of air inhaled/L of oxygen consumed; mean ± SD) were determined and used for calculations of inhalation rates. The interindividual variability factor calculated as the ratio of the highest 99th percentile to the lowest 1st percentile of daily inhalation rates is higher for absolute data expressed in m3 /day (26.7) compared to those of data in m3/kg-day (12.2) and m3/m2-day (5.9). Higher absolute rates generally found in overweight/obese individuals compared to their normal-weight counterparts suggest higher intakes of air pollutants (in μg/day) for the former compared to the latter during identical exposure concentrations and conditions. Highest absolute mean (24.57 m3/day) and 99th percentile (55.55 m3 /day) values were found in obese class 2 adults. They inhale on average 8.21 m3 more air per day than normal-weight adults.