Arterial hypoxemia has been reported in horses during heavy exercise, but its mechanism has not been determined. With the use of the multiple inert gas elimination technique, we studied five horses, each on two separate occasions, to determine the physiological basis of the hypoxemia that developed during horizontal treadmill exercise at speeds of 4, 10, 12, and 13-14 m/s. Mean, blood temperature-corrected, arterial PO2 fell from 89.4 Torr at rest to 80.7 and 72.1 Torr at 12 and 13-14 m/s, respectively, whereas corresponding PaCO2 values were 40.3, 40.3, and 39.2 Torr. Alveolar-arterial PO2 differences (AaDO2) thus increased from 11.4 Torr at rest to 24.9 and 30.7 Torr at 12 and 13-14 m/s. In 8 of the 10 studies there was no change in ventilation-perfusion (VA/Q) relationships with exercise (despite bronchoscopic evidence of airway bleeding in 3) and total shunt was always less than 1% of the cardiac output. Below 10 m/s, the AaDO2 was due only to VA/Q mismatch, but at higher speeds, diffusion limitation of O2 uptake was increasingly evident, accounting for 76% of the AaDO2 at 13-14 m/s. Most of the exercise-induced hypoxemia is thus the result of diffusion limitation with a smaller contribution from VA/Q inequality and essentially none from shunting.

Infectious disease outbreaks and epidemics such as those due to SARS, influenza, measles, tuberculosis, and Middle East respiratory syndrome coronavirus have raised concern about the airborne transmission of pathogens in indoor environments. Significant gaps in knowledge still exist regarding the role of mechanical ventilation in airborne pathogen transmission. This review, prepared by a multidisciplinary group of researchers, focuses on summarizing the strengths and limitations of epidemiologic studies that specifically addressed the association of at least one heating, ventilating and/or air-conditioning (HVAC) system-related parameter with airborne disease transmission in buildings. The purpose of this literature review was to assess the quality and quantity of available data and to identify research needs. This review suggests that there is a need for well-designed observational and intervention studies in buildings with better HVAC system characterization and measurements of both airborne exposures and disease outcomes. Studies should also be designed so that they may be used in future quantitative meta-analyses.

When microcapsules of phase change materials (PCMS) are added to textiles, they absorb heat energy as they change from a solid to a liquid state and release heat as they return to a solid state. This project quantifies the effect of PCMS in clothing on heat flow from the body during temperature transients. One- and two-layer body suits are constructed of a fabric/foam laminate produced with and without PCMS, and heat loss from a thermal manikin is measured as it is moved from a warm chamber to a cold chamber and back again. The results indicate that the heating and cooling effects last approximately 15 minutes. Heat released by PCMS in a cold environment decreases body heat loss by an average of 6.5 W for a one-layer suit and 13.2 W for a two-layer suit compared with non-PCM counterparts. PCM cooling effects increase body heat loss in a similar manner; therefore, PCMS in clothing provide a small, temporary heating/cooling effect during environmental transients.

Nearly 600 papers were located in citation and keyword searches regarding the effects of humidity on comfort, health, and indoor environmental quality (IEQ). Of these, around 70 papers reported the effects of low humidity (RH≤40%) and were analyzed in detail. Information in some categories was well chronicled, while other categories had significant knowledge gaps.Low humidity decreased house dust mite allergens. Due to different envelopes, generalizations could not be made for all bacteria and viruses. However, lower humidity increased virus survival for influenza. For comfort, low humidity had little effect on thermal comfort, but skin dryness, eye irritation, and static electricity increased as humidity decreased. For IEQ, low humidity had non-uniform effects on volatile organic compound (VOC) emissions and perceived indoor air quality. Across many low humidity studies, ventilation rates and exposure times were noted as confounding variables. A majority of studies that used human subjects utilized exposure times of three hours or less with adult subjects; few studies used children, adolescents, or elderly subjects.

Billions of people travel on airplanes every year, making the aircraft cabin a critical environment to understand with regard to public health. The main control over indoor environmental quality in the cabin is ventilation; therefore, maintaining sufficient ventilation rates on-board is essential for creating healthy and comfortable cabin environments. We measured real-time CO2 concentrations, an indicator of ventilation rates, and cabin pressure in the passenger cabins of 179 US domestic flights from boarding through deplaning. The average CO2 concentrations were 1353 ± 290 ppmv (mean ± SD) and the estimated outside airflow rates were 5.77 ± 2.09 L/s/p across all flights. The results indicated that 96% of observations met the minimum recommended outside airflow rates for acceptable air quality (3.5 L/s/p), but only 73% met the rate required in FAA design requirements (4.7 L/s/p), during flying phases. The CO2 levels on all flights were well below the occupational exposure limit of 5000 ppmv. Statistical analysis indicated that the ventilation rates during boarding phases were significantly lower than the others. The findings are of particular interest because low ventilation in other settings has been associated with increased rates of disease transmission, increased upper respiratory symptoms, and worse performance on cognitive function tests. Verification of ventilation performance rather than reliance on design estimates for determining compliance with ventilation standards is recommended.