Short-range airborne transmission of expiratory droplets between two people.

The occurrence of close proximity infection for many respiratory diseases is often cited as evidence of large droplet and/or close contact transmission. We explored interpersonal exposure of exhaled droplets and droplet nuclei of two standing thermal manikins as affected by distance, humidity, ventilation, and breathing mode. Under the specific set of conditions studied, we found a substantial increase in airborne exposure to droplet nuclei exhaled by the source manikin when a susceptible manikin is within about 1.5 m of the source manikin, referred to as the proximity effect. The threshold distance of about 1.5 m distinguishes the two basic transmission processes of droplets and droplet nuclei, that is, short-range modes and the long-range airborne route. The short-range modes include both the conventional large droplet route and the newly defined short-range airborne transmission. We thus reveal that transmission occurring in close proximity to the source patient includes both droplet-borne (large droplet) and short-range airborne routes, in addition to the direct deposition of large droplets on other body surfaces. The mechanisms of the droplet-borne and short-range airborne routes are different; their effective control methods also differ. Neither the current droplet precautions nor dilution ventilation prevents short-range airborne transmission, so new control methods are needed.

Measuring the exhaled breath of a manikin and human subjects.

Due to scarcity of accurate information and available data of actual human breathing, this investigation focuses on characterizing the breathing dynamic process based on the measurement of healthy human subjects. The similarities and differences between one breathing thermal manikin and the human subjects, including geometry and breathing functions, were thoroughly studied. As expected, actual human breathing is more complicated than that of the manikin in terms of airflow fluctuations, individual differences, and exhaled flow directions. The simplification of manikin mouth structure could result in overestimated exhaled velocity and contaminant concentration. Furthermore, actual human breathing appears to be relatively stable and reproducible for an individual person in several conditions and is also accompanied by some uncertainties simultaneously. The averaged values are used to analyze the overall characteristics of actual human breathing. There are different characteristics of the exhaled breath between male and female subjects with or without wearing a nose clip. The experimental results obtained from the measurement of human subjects may be helpful for manikin specification or validation and accuracy assessment of CFD simulations.

Influence of air stability and metabolic rate on exhaled flow.

The characteristics of contaminant transport and dispersion of exhaled flow from a manikin are thoroughly studied in this article with respect to the influence of two important factors: air stability conditions and metabolic rates. Four cases with the combinations of stable and neutral conditions as well as lower (1.2 met) and higher (2 met) metabolic rates for a breathing thermal manikin are employed. The exhaled contaminant is simulated by smoke and N2 O to visualize and measure the contaminant distribution both around and in front of the manikin. The results show that the microenvironment around the manikin body can be affected by different air distribution patterns and metabolic heating. Under stable conditions, the exhaled contaminant from mouth or nose is locked and stratified at certain heights, causing potentially high contaminant exposure to others. In addition, velocity profiles of the pulsating exhaled flow, which are normalized by mean peak velocities, present similar shapes to a steady jet. The outlet velocity close to the mouth shows decrement with both exhalation temperature and body plume. The velocity decay and concentration decay also show significant dependence on air stability and metabolic level.

Protected zone ventilation and reduced personal exposure to airborne cross-infection.

The main objective of this study was to examine the performance of protected zone ventilation (PZV) and hybrid protected zone ventilation (HPZV) to reduce the direct exposure to exhaled air from others' breathing. Experimental measurements are carried out to test the performance of PZV in a full-scale office room with two breathing thermal manikins. The measurements were performed under three configurations, including two standing manikins at different distances: 0.35, 0.5, and 1.1 m. When the supply air velocity is increased to 4 m/s in the downward plane jet, the dimensionless concentration is 40% lower than for fully mixed ventilation, which can be considered as a measure of protection from the zoning condition. The measurement results showed that in both the PZV and the HPZV system it is possible to decrease the transmission of tracer gas from one manikin to the opposite manikin; therefore, it probably would reduce the risk of air borne cross-infection between two people at the same relative positions. The results suggest that PZV and HPZV may be used to reduce the exposure of people in a protected zone from indoor pollutants emitted in a source zone.

Predictors for PaO2 and hypoxemic respiratory failure in COPD-A three-year follow-up.

BACKGROUND: Knowledge about predictors for developing hypoxemia in the course of chronic obstructive pulmonary disease (COPD) progression is limited. The objective of the present study was to investigate predictors for overall PaO2, for a potential change in PaO2 over time, and for first occurrence of hypoxemia. METHODS: 419 patients aged 40-76 years with COPD GOLD stages II-IV underwent clinical and pulmonary function measurements, including repeated arterial blood gases over three years. Airway obstruction, lung hyperinflation, markers of systemic inflammation and cardiovascular health, exacerbation frequency, smoking habits, and body composition were tested as possible predictors of PaO2 and first episode of hypoxemia. RESULTS: In multivariate adjusted longitudinal analyses, forced expiratory volume in 1 second, total lung capacity and functional residual capacity (all in% predicted), resting heart rate and fat mass index were all associated with overall PaO2 (all P < 0.005). We found no change in PaO2 over time (ρ = 0.33), nor did we find evidence that any of the tested variables predicted change in PaO2 over time. In multivariate adjusted survival analyses, functional residual capacity and resting heart rate were predictors of episodic hypoxemia (both ρ < 0.005). CONCLUSIONS: This longitudinal study identified pulmonary, cardiac and metabolic risk factors for overall PaO2 and episodic hypoxemia, but detected no change in PaO2 over time.

The risk of airborne cross-infection in a room with vertical low-velocity ventilation.

UNLABELLED: Downward flow ventilation systems are one of the most recommended ventilation strategies when contaminants in rooms must be removed and people must be protected from the risk of airborne cross-infection. This study is based on experimental tests carried out in a room with downward flow ventilation. Two breathing thermal manikins are placed in a room face to face. One manikin's breathing is considered to be the contaminated source to simulate a risky situation with airborne cross-infection. The position of the manikins in relation to the diffuser and the location of diffuser in the room as well as the distance between the manikins are being changed to observe the influence of these factors on the personal exposure of the target manikin. The results show that the DWF in different situations often is unable to penetrate the microenvironment generated by the manikins. The downward ventilation system can give an unexpected high level of contaminant exposure of the target manikin, when the distance between the manikins is reduced. PRACTICAL IMPLICATIONS: Several guidelines recommend the downward ventilation system to reduce the risk of cross-infection between people in hospital rooms. This study shows that this recommendation should be taken into careful consideration. It is important to be aware of people position, position to other thermal loads in the room, and especially be aware of the distance between people if the exposure to the exhaled contaminants wants to be reduced.

Effects of stroke resistance on rowing economy in club rowers post-season.

In the sport of rowing, increasing the impulse applied to the oar handle during the stroke can result in greater boat velocities; this may be facilitated by increasing the surface area of the oar blade and/or increasing the length of the oars. The purpose of this study was to compare the effects of different rowing resistances on the physiological response to rowing. 5 male and 7 female club rowers completed progressive, incremental exercise tests on an air-braked rowing ergometer, using either low (LO; 100) or high (HI; 150) resistance (values are according to the adjustable "drag factor" setting on the ergometer). Expired air, blood lactate concentration, heart rate, rowing cadence, and ergometer power output were monitored during the tests. LO rowing elicited significantly greater cadences (P<0.01) and heart rates (P<0.05), whereas rowing economy (J · L O(2) equivalents(-1)) was significantly greater during HI rowing (P<0.05). These results suggest that economically, rowing with a greater resistance may be advantageous for performance. Moreover, biomechanical analysis of ergometer rowing support the notion that the impulse generated during the stroke increases positively as a function of rowing resistance. We conclude that an aerobic advantage associated with greater resistance parallels the empirical trend toward larger oar blades in competitive rowing. This may be explained by a greater stroke impulse at the higher resistance.

Dietary antioxidants and forced expiratory volume in 1 s decline: the Health, Aging and Body Composition study.

Increased antioxidant defences are hypothesised to decrease age- and smoking-related decline in lung function. The relationship between dietary antioxidants, smoking and forced expiratory volume in 1 s (FEV(1)) was investigated in community-dwelling older adults in the Health, Aging and Body Composition study. 1,443 participants completed a food frequency questionnaire, self-reported smoking history and had measurements taken of FEV(1) at both baseline and after 4 yrs of follow-up. The association of dietary intake of nutrients and foods with antioxidant properties and rate of FEV(1) decline was investigated using hierarchical linear regression models. In continuing smokers (current smokers at both time-points), higher vitamin C intake and higher intake of fruit and vegetables were associated with an 18 and 24 mL · yr(-1) slower rate of FEV(1) decline compared with a lower intake (p < 0.0001 and p = 0.003, respectively). In quitters (a current smoker at study baseline who had quit during follow-up), higher intake was associated with an attenuated rate of decline for each nutrient studied (p ≤ 0.003 for all models). In nonsmoking participants, there was little or no association of diet and rate of decline in FEV(1). The intake of nutrients with antioxidant properties may modulate lung function decline in older adults exposed to cigarette smoke.

Distribution of exhaled contaminants and personal exposure in a room using three different air distribution strategies.

UNLABELLED: The level of exposure to human exhaled contaminants in a room depends not only on the air distribution system but also on people's different positions, the distance between them, people's activity level and height, direction of exhalation, and the surrounding temperature and temperature gradient. Human exhalation is studied in detail for different distribution systems: displacement and mixing ventilation as well as a system without mechanical ventilation. Two thermal manikins breathing through the mouth are used to simulate the exposure to human exhaled contaminants. The position and distance between the manikins are changed to study the influence on the level of exposure. The results show that the air exhaled by a manikin flows a longer distance with a higher concentration in case of displacement ventilation than in the other two cases, indicating a significant exposure to the contaminants for one person positioned in front of another. However, in all three cases, the exhalation flow of the source penetrates the thermal plume, causing an increase in the concentration of contaminants in front of the target person. The results are significantly dependent on the distance and position between the two manikins in all three cases. PRACTICAL IMPLICATIONS: Indoor environments are susceptible to contaminant exposure, as contaminants can easily spread in the air. Human breathing is one of the most important biological contaminant sources, as the exhaled air can contain different pathogens such as viruses and bacteria. This paper addresses the human exhalation flow and its behavior in connection with different ventilation strategies, as well as the interaction between two people in a room. This is a key factor for studying the airborne infection risk when the room is occupied by several persons. The paper only takes into account the airborne part of the infection risk.

FACT-MNG: tumor site specific web-based outcome instrument for meningioma patients.

To formulate Functional Assessment of Cancer Therapy-Meningioma (FACT-MNG), a web-based tumor site-specific outcome instrument for assessing intracranial meningioma patients following surgical resection or stereotactic radiosurgery. We surveyed the relevant literature available on intracranial meningioma surgery and subsequent outcomes (38 papers), making note of which, if any, QOL/outcome instruments were utilized. None of the surgveyed papers included QOL assessment specific to tumor site. We subsequently developed questions that were relevant to the signs and symptoms that characterize each of 11 intracranial meningioma sites, and incorporated them into a modified combination of the Functional Assessment of Cancer Therapy-Brain (FACT-BR) and SF36 outcome instruments, thereby creating a new tumor site-specific outcome instrument, FACT-MNG. With outcomes analysis of surgical and radiosurgical treatments becoming more important, measures of the adequacy and success of treatment are needed. FACT-MNG represents a first effort to formalize such an instrument for meningioma patients. Questions specific to tumor site will allow surgeons to better assess specific quality of life issues not addressed in the past by more general questionnaires.

Using the lower limit of normal for the FEV1/FVC ratio reduces the misclassification of airway obstruction.

AIM: The prevalence of airway obstruction varies widely with the definition used. OBJECTIVES: To study differences in the prevalence of airway obstruction when applying four international guidelines to three population samples using four regression equations. METHODS: We collected predicted values for forced expiratory volume in 1 s/forced vital capacity (FEV(1)/FVC) and its lower limit of normal (LLN) from the literature. FEV(1)/FVC from 40 646 adults (including 13 136 asymptomatic never smokers) aged 17-90+years were available from American, English and Dutch population based surveys. The prevalence of airway obstruction was determined by the LLN for FEV(1)/FVC, and by using the Global Initiative for Chronic Obstructive Lung Disease (GOLD), American Thoracic Society/European Respiratory Society (ATS/ERS) or British Thoracic Society (BTS) guidelines, initially in the healthy subgroup and then in the entire population. RESULTS: The LLN for FEV(1)/FVC varied between prediction equations (57 available for men and 55 for women), and demonstrated marked negative age dependency. Median age at which the LLN fell below 0.70 in healthy subjects was 42 and 48 years in men and women, respectively. When applying the reference equations (Health Survey for England 1995-1996, National Health and Nutrition Examination Survey (NHANES) III, European Community for Coal and Steel (ECCS)/ERS and a Dutch population study) to the selected population samples, the prevalence of airway obstruction in healthy never smokers aged over 60 years varied for each guideline: 17-45% of men and 7-26% of women for GOLD; 0-18% of men and 0-16% of women for ATS/ERS; and 0-9% of men and 0-11% of women for BTS. GOLD guidelines caused false positive rates of up to 60% when applied to entire populations. CONCLUSIONS: Airway obstruction should be defined by FEV(1)/FVC and FEV(1) being below the LLN using appropriate reference equations.

Physician-guided treatment compared with a heparin protocol for deep vein thrombosis.

BACKGROUND: Effective heparin therapy, defined by therapeutic prolongation of the activated partial thromboplastin time (APTT), decreases the risk of recurrent venous thromboembolism. Achieving therapeutic prolongation of the APTT within 24 hours of the start of heparin therapy has proved difficult. We hypothesized that a protocol that delivered high initial heparin infusions to patients without identifiable risk for bleeding complications would decrease the time to achieve a therapeutic anticoagulant effect without increasing the incidence of major bleeding complications. METHODS: To test this hypothesis, we studied concurrent patient cohorts. We defined a therapeutic anticoagulant effect (APTT > 55 seconds) to be an APTT more than 1.5 times the upper limit of normal. Twenty patients with acute symptomatic deep vein thrombosis received a 5000-U heparin bolus, followed by 1680 U/h (low risk to bleed) or 1240 U/h (high risk to bleed), adjusted by protocol-directed response to APTT results. Forty-eight patients with deep vein thrombosis were treated by their physicians. The Kaplan-Meier method was used to examine the proportion of patients who achieved an APTT greater than 55 seconds as a function of time. RESULTS: The two study cohorts did not differ with respect to age, weight, or risk factors for venous thromboembolism. Analysis of Kaplan-Meier curves showed that the heparin protocol decreased the time to achieve a therapeutic anticoagulant effect (P = .025). Ten (91%) of 11 patients (95% confidence interval, 59% to 100%) without risks to bleed who were treated by the heparin protocol and 29 (60%) of 48 patients (95% confidence interval, 45% to 74%) not treated by the protocol had an initial therapeutic APTT (P = .006). CONCLUSION: A protocol that delivers higher initial heparin infusions to patients without identifiable risks for bleeding decreases the time needed to achieve therapeutic prolongation of APTT, when compared with nonprotocol physician management.

Method for estimating confidence levels for measurements by blood glucose monitoring systems.

A joint conference on self-monitoring of blood glucose (SMBG) has proposed that all glucose monitoring systems generate values that are within 10% of the actual blood glucose level 100% of the time. To estimate the confidence limits of blood glucose measurements made in a typical university ambulatory care setting and to ascertain whether they met the proposed standard, we performed duplicate determinations of blood glucose using a reflectance meter and applied to the measurements a method for calculating the closeness of measured values to a "true" mean. Based on paired measurements in 100 consecutive diabetic subjects, we were able to show that one measurement would be within 11.9% of a true mean value 95% of the time and within 8.4% of the mean 90% of the time. The 95 and 90% confidence limits for the average of two repeated measurements were calculated to be 8.4 and 5.9%, respectively. Our methodology can be applied to any set of SMBG values to calculate their confidence limits and to determine whether the measurements meet recommended standards.

Influence of leisure time physical activity and television watching on atherosclerosis risk factors in the NHLBI Family Heart Study.

Physical activity favorably influences atherosclerosis risk factors but only a few studies in adults considered the time watching television (TV) as a measure of physical inactivity. We therefore determined in a population-based sample of 1778 subjects from the NHLBI Family Heart Study (FHS) whether leisure time physical activity and TV watching have independent or interactive associations with cardiovascular disease risk factors and carotid artery intima-media wall thickness (IMT). Subjects were free from diabetes mellitus and clinically-ascertained coronary artery disease and did not take lipid-lowering or antihypertensive drugs. Only 0.7 and 1.3% of the variance in leisure time physical activity in women and men, respectively, was explained by the amount of TV watching. Leisure time physical activity had a clearly favorable, and TV watching an unfavorable association with anthropometric measurements (BMI (body mass index), waist girth, waist-hip ratio, subscapular and triceps skinfold thickness). The odds ratio (95% CI) of being overweight was 0.41 (0.28-0.62) in women and 0.69 (0.46-1.04) in men in the highest quartile of leisure time physical activity compared to the lowest quartile. The odds ratio increased for increasing quartiles of TV watching to 2.12 (1.45-3.10) in women and 1.61 (1.07-2.43) in men. Watching TV only 1 h per day in women with a BMI of 30 kg/m2 and doing about 75 min of moderate exercise per week was associated with a BMI 1.8 kg/m2 lower than in women watching TV 3 h per day and doing the same amount of exercise. Those with twice the amount of moderate exercise and watching TV 1 h per day had a BMI 0.45 kg/m2 lower. Furthermore, leisure time physical activity was negatively associated with concentrations of triglycerides and positively with HDL cholesterol in both genders. TV watching was significantly positively associated with triglycerides and slightly negatively with HDL cholesterol in men. The observed associations of leisure time physical activity and TV watching with atherosclerosis risk factors were independent from each other. Finally, we analyzed the relation between leisure time physical activity, TV watching and the degree of IMT of the carotid arteries. Neither of these two measures was significantly associated with IMT. In summary, TV watching, in addition to leisure time physical activity, shows an independent association with obesity-related anthropometric measurements, HDL and triglycerides. Decreasing the amount of TV watching might be effective as a first step in reducing atherosclerosis risk factors, especially overweight.

Intraindividual peak flow variability.

OBJECTIVES: To quantify intraindividual variability in peak expiratory flow (PEF) measured with peak flow-meters and to define factors affecting PEF variability. METHODS: Three hundred one healthy subjects (aged 4 to 84 years) were recruited from sites at sea level (n = 220) and at 1,400 m altitude (n = 81). All testing was done with the same model peak flowmeter. Each subject was actively coached through five to eight successive PEF maneuvers. Three meters of the same model were tested using a mechanical waveform simulator at three different flows at both testing altitudes (sea level and at 1,400 m). RESULTS: Excluding outliers, the mean PEF was 523 L/min, mean standard deviation (SD) was 22 L/min, and mean coefficient of variation (CV) was 4.6%. The upper 95th percentile for CV was 8% for adults and 10% for youths. Analyzing only the three highest peak flows for each subject, the mean PEF was 539 L/min, mean SD was 12 L/min, and mean CV was 2.4%. The upper 95th percentile for CV was 6% for adults and 9% for youths. Linear regression analysis revealed a small but statistically significant correlation (p < 0.01) between mean peak flow and CV. In adults, SD correlated with sex (p < 0.01) but neither CV nor SD was correlated with age, height, weight, or altitude. Meter variability defined with the mechanical waveform simulator was small. Standard deviation varied from 1.5 to 4.2 L/min and CV from 0.4 to 1.6%. When the three largest peak flows for each subject were used, 5.5% of intraindividual variance was explained by meter variance. CONCLUSIONS: These estimates of intraindividual variability in healthy subjects are generally lower than those previously reported. Meter variability accounts for only a small part of total intraindividual variability. The 95th percentile data suggest that a fall in PEF of 6 to 8% in adults and 9 to 10% in youths would be statistically significant.

Effect of altitude on hand-held peak flowmeters.

OBJECTIVE: To quantify the effect of altitude on the operational characteristics of hand-held peak flowmeters. DESIGN: Altitude simulation within a hypobaric chamber combined with five constant simulated peak flows delivered from a computerized pump were used to test commercially available peak flowmeters. SETTING: F.G. Hall Hyperbaric/Hypobaric facilities located at Duke University School of Medicine. MEASUREMENTS: Two each of nine models of commercially available hand-held peak flowmeters and a volume spirometer were tested at six simulated altitudes (100, 500, 1,000, 1,500, 2,000, and 3,000 m) using five target peak flows. Each peak flow was injected into each meter twice. Forward stepwise regression was used to check for nonlinear relationships between altitude and peak expiratory flowmeter readings. Linear regression equations were fit to the data at each target flow across altitude. Effect of absolute peak flow was tested by analysis of covariance. RESULTS: For these altitudes, linear relationships were found between altitude and measured peak flow. For all meters tested, the average decrease in peak flow ranged from -8.7% at the lowest target flow (123 L/min) to -6.5% at the highest target flow (702 L/min) for each 100 mm Hg decrease in barometric pressure (PB). Individual meters ranged from -12.3% at the lowest target flow to -4.4% at the highest target flow for 100 mm Hg decrease in PB. The spirometer had no significant changes associated with changes in PB. In all cases, the magnitude of the altitude effect, measured by percent change, decreased with increasing peak flow. CONCLUSIONS: Peak expiratory flowmeters underread PEF as a function of both increasing altitude and increasing target peak flow.

Relationship between graft patency, postoperative work status, and symptomatic relief.

In 405 men under the age of 65 requiring coronary bypass, in whom 6 month postoperative arteriograms were performed, we compared graft patency to postoperative work status and recurrent symptoms. We divided the population into subgroups of patients with varying degrees of patency. When these subgroups were tested, no significant dependence was found between the degree of graft patency and the percentages of patients who were working after operation, unless certain subgroups were removed from the population. When relief of angina was examined in the same manner as the postoperative work, we found a significant dependence between the graft patency and the percentage of patients who reported either short or long-term relief of angina in all groups. Because the rate of rehabilitation was high, even in patients with occluded grafts, and because older patients were less likely to return to work than younger patients despite successful revascularization, we conclude that physician emphasis on work rehabilitation and patient age, as well as graft patency, are all important factors which influence postoperative work status.

Longitudinal pulmonary function changes in pigeon breeders.

We studied 15 subjects (14 men and one woman; seven symptomatic and eight asymptomatic) at three- to four-year intervals from 1967 through 1985 (18 years) to determine if continued pigeon antigen exposure in these groups was associated with a decline in pulmonary function greater than expected in healthy individuals. We collected immunologic studies at the initial visit, performed sequential pulmonary function studies and obtained chest radiographs. After compensating for the normal changes expected with increasing age, we found the declines in FVC, FEV1, and Dsb in the symptomatic group were nearly four times greater than expected. There was no significant difference in the decline of pulmonary function between asymptomatic subjects and the normal predicted declines with increasing age. We conclude that, if an individual has episodes of acute hypersensitivity pneumonitis, long-term exposure to pigeon antigens will result in an accelerated decline in pulmonary function.

Ear oximetry to detect apnea and differentiate rapid eye movement (REM) and non-REM (NREM) sleep. Screening for the sleep apnea syndrome.

Ear oximetry is commonly employed in screening patients for the sleep apnea syndrome, but the lack of objective information regarding the duration of sleep, including the presence of rapid-eye-movement (REM) sleep, is a major limitation. Based on the premise that both apnea and sleep-state-dependent changes in ventilation give rise to distinctive patterns in the arterial oxygen saturation, we developed a systematic technique to analyze ear oximetric tracings for wakefulness, REM sleep, and non-REM (NREM) sleep. Fifty-four patients were studied by both all-night polysomnography and ear oximetry. A careful comparison of ear oximetric data for sleep states and apnea was then made, using polysomnography as the correct classification to determine sensitivity, specificity, predictive value positive, and predictive value negative of the ear oximetric tracings. When classification of sleep state was compared, ear oximetry correctly classified 280.5 (82 percent) of 340.9 hours of sleep that was either REM or NREM sleep. The sensitivity for classifying NREM sleep was 0.85, for REM sleep was 0.70, and for wakefulness was 0.49. The sensitivity by ear oximetry for apnea was 0.80, with a predictive value negative of 0.87. We conclude that although polysomnography must be performed for definitive evaluation, ear oximetry is a valuable screening test for sleep apnea because the presence or absence of apnea can be determined, total duration of sleep can be estimated, and NREM vs REM sleep can be differentiated.