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PubMed2006

High-frequency oscillatory ventilation in pediatric patients with acute respiratory failure.

OBJECTIVE: To evaluate the effectiveness of high-frequency oscillatory ventilation (HFOV) in pediatric patients with acute respiratory failure, failing conventional ventilation. DESIGN: A prospective, clinical study. SETTING: Tertiary care pediatric intensive care unit. PATIENTS: Twenty pediatric patients (ages 12 days to 5 yrs) with acute respiratory failure (pneumonia, 14; sepsis with acute respiratory distress syndrome, 3; pulmonary edema as a complication of upper airway obstruction, 2; salicylate intoxication with acute respiratory distress syndrome, 1), failing conventional ventilation (median alveolar-arterial oxygen difference [P(A-a)O2] 578 [489-624] torr, median oxygenation index 26 [21-32]. INTERVENTIONS: HFOV was instituted after a median length of conventional ventilation of 15.5 (3.3-43.5) hrs. MEASUREMENTS AND MAIN RESULTS: Ventilator settings, arterial blood gases, oxygenation index, and P(A-a)O2 were recorded before HFOV (0 hrs) and at predetermined intervals during HFOV and compared using the one-way Friedman rank-sum procedure and a two-tailed Wilcoxon matched-pairs test. Initiation of HFOV caused a significant decrease in FiO2 at 1 hr that continued to 24 hrs (p <or= .04). In all patients, target ventilation was achieved, and 19 had improved oxygenation. After 1 hr, PaCO2 significantly decreased (p = .002) and remained within the target range thereafter. There were significant decreases in P(A-a)O2 and oxygenation index at 1 and 4 hrs, respectively, that were sustained up to 12 hrs (p <or= .04). No significant complications associated with HFOV were detected. Fifteen patients (75%) survived to hospital discharge. Only one patient died from respiratory failure. CONCLUSIONS: In pediatric patients with acute respiratory failure, failing conventional ventilation, HFOV improves gas exchange in a rapid and sustained fashion. However, randomized controlled trials are needed to identify its benefits over conventional modes of mechanical ventilation.

Acute Disease↗
PubMed2006

Keuskamp and the Amsterdam Infant Ventilator.

At the First International Symposium on the History of Modern Anaesthesia (1982), Professor Keuskamp mentioned that the introduction of breathing machines for lung ventilation during operations had taken over 'the tiresome handwork of ventilation'. This paper traces some aspects of Keuskamp's professional career and his role in the development of the Amsterdam Infant Ventilator. In 1974, Urban and Weitzner from the State University of New York reported that the ventilator was a reliable and effective constant-volume paediatric ventilator. Other clinicians from the United States and Europe echoed this satisfactory clinical evaluation. At present, this paediatric ventilator is still in use for the initial ventilation of small infants and for the mechanical ventilation of different animal species in a variety of experimental settings.

Anesthesia, General↗
PubMed1976

The effect of respiratory frequency on pulmonary function during artificial ventilation. A review.

This is a review of previous studies on the effects of variations between 12 and 24 breaths per minute in ventilation frequency during artificial ventilation, minute ventilation being constant. The total material consisted of 66 healthy subjects investigated under anaesthesia with artificial ventilation and 43 patients investigated during prolonged respiratory treatment. An increase in ventilation frequency resulted in an increased ratio of dead space to tidal volume (VD/VT) and in diminished alveolar ventilation with a subsequent elevation of Paco2. The pressures in airways and alveoli were lowered. The dynamic compliance both of the lungs and of the chest wall was diminished and inspiratory resistance was slightly reduced. Intrapulmonary gas distribution was unaffected. Cardiac output was increased, as was venous admixture. Pao2 was slightly reduced. The more efficient gas exchange occurring at a low ventilation frequency makes this setting preferable in the treatment of patients with chronic obstructive lung disease, whereas a high ventilation frequency, by improving cardiac output, may be advantageous in patients with circulatory failure.

Adult↗
PubMedDate not supplied

Volume-targeted ventilation and arterial carbon dioxide in neonates.

OBJECTIVES: To review the arterial carbon dioxide tensions (PaCO(2)) in newborn infants ventilated using synchronized intermittent mandatory ventilation (SIMV) in volume guarantee mode (using the Dräger Babylog 8000+) with a unit policy targeting tidal volumes of approximately 4 mL/kg. METHODS: Data on ventilator settings and arterial PaCO(2) levels were collected on all arterial blood gases (ABG; n = 288) from 50 neonates (<33 weeks gestational age) ventilated using the Dräger Babylog 8000+ ventilator (Dräger Medizintechnik GmbH, Lübeck, Germany) in SIMV plus volume guarantee mode. Data were analysed for all blood gases done on the entire cohort in the first 48 h of life and a subanalysis was done on the first gas for each infant (n = 38) ventilated using volume guarantee from admission to the nursery. The number of ABG showing severe hypocapnoea (PaCO(2) < 25 mmHg) and/or severe hypercapnoea (PaCO(2) > 65 mmHg) were determined. RESULTS: The mean (SD) PaCO(2) during the first 48 h was 46.6 (9.0) mmHg. The mean (SD) PaCO(2) on the first blood gas of those infants commenced on volume guarantee from admission was 45.1 (12.5) mmHg. Severe hypo- or hypercapnoea occurred in 8% of infants at the time of their first blood gas measurement, and in <4% of blood gas measurements in the first 48 h. CONCLUSIONS: Infants ventilated with volume guarantee ventilation targeting approximately 4 mL/kg (range: 2.9-5.1) have acceptable PaCO(2) levels at the first blood gas measurement and during the first 48 h of life; and avoid severe hypo- or hypercapnoea over 90% of the time.

Arteries↗
PubMed1995

Ventilation-perfusion inequality in nocturnal hypoxaemia due to chronic obstructive lung disease (COLD).

Nocturnal hypoxaemia is often noted in COLD patients with a daytime PaO2 above 8.0 kPa. It has been assumed that ventilation-perfusion inequality contributes to nocturnal hypoxaemia. 10 patients with advanced COLD [median FEV1 0.73 (range 0.50-1.32)l], but without daytime hypoxaemia [median PaO2 8.35 (range 8.0-12.2) kPa] were investigated with regard to possible nocturnal hypoxaemia using polysomnography. Daytime lung function was assessed by spirometry and carbon monoxide diffusion capacity (DLCO). Daytime ventilation-perfusion (VA/Q) relationships were measured by the multiple inert gas elimination technique. Dispersion of perfusion and ventilation distributions was increased [log SDQ 1.01 (range 0.80-1.35) and log SDV 0.91 (range 0.69-1.86) resp.]. Around 8% of the ventilation was directed towards high VA/Q areas (10 < VA/Q < 100). All subjects reached all sleep stages, and all but one had a nadir nocturnal oxygen saturation (SaO2) of below 90%. Their median lowest nocturnal SaO2 was 84.0 (range 70-93)% and their mean oxygen saturation in the course of desaturation episodes (MminSaO2) was 86.4 (range 83.6-91.5)%. An increased mean VA/Q ratio of ventilation distribution was associated with a reduced DLCO. Increased nocturnal episodes of wakefulness and of stage I sleep correlated with increased dead space ventilation and dispersion of the ventilation distribution. Patients with deep nocturnal desaturations had a low mean VA/Q ratio of the perfusion distribution (Q mean) (r = 0.87, P < 0.01) and increased perfusion of inferior VA/Q areas (0.1 VA/Q < 0.3). Low MminSaO2 was associated with low morning PaO2 and a low Q mean. COLD patient with solely nocturnal hypoxaemia have a high degree of pulmonary hyperinflation and emphysema. Increased sleep disruption is associated with more severe small airway disease. Increased perfusion of sparsely ventilated areas is associated with more pronounced nocturnal desaturations.

Aged↗
PubMed2004

Evidence of inadequate ventilation in portable classrooms: results of a pilot study in Los Angeles County.

UNLABELLED: The prevalence of prefabricated, portable classrooms (portables) for United States public schools has increased; in California, approximately one of three students learn inside portables. Limited research has been conducted on indoor air and environmental quality in American schools, and almost none in portables. Available reports and conference proceedings suggest problems from insufficient ventilation due to poor design, operation, and/or maintenance of heating, ventilation and air conditioning (HVAC) systems; most portables have one mechanical, wall-mounted HVAC system. A pilot assessment was conducted in Los Angeles County, including measurements of integrated ventilation rates based on a perfluorocarbon tracer gas technique and continuous monitoring of temperature (T) and relative humidity (RH). Measured ventilation rates were low [mean school day integrated average 0.8 per hour (range: 0.1-2.9 per hour)]. Compared with relevant standards, results suggested adequate ventilation and associated conditioning of indoor air for occupant comfort were not always provided to these classrooms. Future school studies should include integrated and continuous measurements of T, RH, and ventilation with appropriate tracer gas methods, and other airflow measures. PRACTICAL IMPLICATIONS: Adequate ventilation has the potential to mitigate concentrations of chemical pollutants, particles, carbon dioxide, and odors in portable and traditional classrooms, which should lead to a reduction in reported health outcomes, e.g., symptoms of 'sick building syndrome', allergies, asthma. Investigations of school indoor air and environmental quality should include continuous temperature and relative humidity data with inexpensive instrumentation as indicators of thermal comfort, and techniques to measure ventilation rates.

Air Conditioning↗
PubMed2004

Reducing the ingress of urban noise through natural ventilation openings.

UNLABELLED: For buildings in busy urban areas affected by high levels of road traffic noise the potential to use natural ventilation can be limited by excessive noise entering through ventilation openings. This paper is concerned with techniques to reduce noise ingress into naturally ventilated buildings while minimizing airflow path resistance. A combined experimental and theoretical approach to the interaction of airflow and sound transmission through ventilators for natural ventilation applications is described. A key element of the investigation has been the development of testing facilities capable of measuring the airflow and sound transmission losses for a range of ventilation noise control strategies. It is demonstrated that a combination of sound reduction mechanisms -- one covering low frequency sound and another covering high frequency sound -- is required to attenuate effectively noise from typical urban sources. A method is proposed for quantifying the acoustic performance of different strategies to enable comparisons and informed decisions to be made leading to the possibility of a design methodology for optimizing the ventilation and acoustic performance of different strategies. PRACTICAL IMPLICATIONS: The need for employing techniques for combating low frequency sound in tandem with techniques for reducing high frequency sound in reducing the ingress of noise from urban sources such as road traffic to acceptable levels is demonstrated. A technique is proposed for enabling the acoustic and airflow performance of apertures for natural ventilation systems to be designed simultaneously.

Acoustics↗
PubMed2005

Volume guarantee ventilation, interrupted expiration, and expiratory braking.

BACKGROUND: In volume guarantee ventilation with the Dräger Babylog 8000 ventilator, inspiratory and expiratory flows are monitored and the expiratory tidal volume calculated following each inflation. The pressure for the next inflation is modified to ensure the expired tidal volume is close to the set value. AIM: To investigate interrupted expiration observed during volume guarantee ventilation of spontaneously breathing, ventilated infants. METHODS: Spontaneously breathing infants, ventilated with volume guarantee, had recordings of gas flow, ventilator pressures, tidal volume waveforms, oximetry, heart rate, and transcutaneous oxygen and carbon dioxide during 10 minute recordings. RESULTS: A total of 6540 inflations were analysed from 10 infants; 62% were triggered. Two different patterns were found: (1) Normal volume guarantee pattern with 97% of triggered and 91% untriggered inflations. It had a normal expiratory curve and a mean expired tidal volume within 3% of the set volume, but a large variation due to the babies' breathing. (2) A pattern of interrupted expiratory flow after approximately 3% of inflations due to a small inspiration (approximately 1.3 ml/kg) during expiration. This led the ventilator to calculate an inappropriate total expired tidal volume for that inflation and an increase in the pressure for the next inflation. CONCLUSIONS: After about 3% of inflations, with volume guarantee ventilation, interruption of the expiration causes an increased pressure for the next inflation of approximately 4.9 cm H2O, compared with normal volume guarantee inflation. The interrupted expiration is most likely to be due to diaphragmatic braking.

Diaphragm↗
PubMed1989

Does mechanical ventilation precipitate gastro-oesophageal reflux during enteral feeding?

The influence of intermittent positive pressure ventilation on gastro-oesophageal reflux in preterm infants is not known. In many neonatal units, however, concern that ventilation may increase gastro-oesophageal reflux (and therefore aspiration) leads to avoidance of enteral feeding during ventilation. We have therefore performed a crossover study of gastrooesophageal reflux by monitoring lower oesophageal pH in a group of nine enterally fed, very low birthweight infants both during assisted ventilation and normal breathing. All infants had less reflux during intermittent positive pressure ventilation (mean (SEM) reflux index 2.3 (0.6%)) than during normal breathing (mean (SEM) reflux index 6.1 (1.1%)). Assisted ventilation was associated with a significant reduction in the gastro-oesophageal pressure gradient, an effect which may be related to the use of positive and end expiratory pressure during ventilation. These data show that fear of gastro-oesophageal reflux should not preclude the use of enteral feeding in preterm infants receiving ventilation.

Enteral Nutrition↗
PubMed2000

A randomised control study of partial liquid ventilation after airway lavage with exogenous surfactant in a meconium aspiration syndrome animal model.

AIMS: To test the hypothesis that lavage with exogenous surfactant before partial liquid ventilation in meconium aspiration syndrome (MAS) would improve debris removal, and therefore the effectiveness of partial liquid ventilation. METHODS: 12 newborn piglets were randomised into 4 groups, partial liquid ventilation or gas ventilation, with and without surfactant lavage. Physiological and blood gas data were compared between groups by analysis of variance. RESULTS: Arterial oxygen pressure (PaO(2)) was improved in the group treated with surfactant lavage when compared with the group not receiving surfactant. PaO(2) in the group receiving surfactant lavage followed by partial liquid ventilation was further improved when compared with the group treated with surfactant lavage followed by gas ventilation and the group receiving partial liquid ventilation alone. CONCLUSION: The effectiveness of partial liquid ventilation in MAS might be enhanced by pretreatment with exogenous surfactant bronchial lavage.

Animals↗
PubMed1991

Effect of negative pressure ventilation on arterial blood gas pressures and inspiratory muscle strength during an exacerbation of chronic obstructive lung disease.

The effects of intermittent negative pressure ventilation have been studied in 20 patients with chronic obstructive pulmonary disease during an exacerbation of their disease. Measurements of arterial blood gas tensions and maximal inspiratory pressure (MIP) were performed before and after six hours of negative pressure ventilation or standard treatment (control day) given in random order on two consecutive days. After negative pressure ventilation the mean (SD) value of MIP increased from 68.1 (21.5) to 74.8 (20) cm H2O;* arterial oxygen tension (PaCO2) fell from 60.6 (12.2) to 50.9 (8.9) mm Hg* but PaO2 changed little (from 48.4 (7.4) to 47.6 (8.2) mm Hg). There were no significant changes on the control day in arterial blood gas tensions (PaO2 47.8 (8.1) and 48.9 (9.4) and Paco2 59.8 (10.9) and 57.5 (8.06) mm Hg) or in MIP (69.4 (22.4) and 70.9 (22.9) cm H2O). Six patients tolerated negative pressure ventilation poorly and these patients showed less improvement after negative pressure ventilation. Our results suggest that intermittent negative pressure ventilation can increase alveolar ventilation in patients with an exacerbation of chronic obstructive lung disease, particularly in those who tolerate the procedure well. Most subjects showed a fall in PaCO2 and an increase in MIP. The fact that PaO2 was unchanged despite the fall in PaCO2 suggests that gas exchange may deteriorate with negative pressure ventilation in these patients.

Aged↗
PubMed1977

Frequency dependence of ventilation distribution in normal and obstructed lungs.

Differences in regional pulmonary time constant may cause ventilation distribution to vary with breathing frequency and frequency-dependent changes in regional ventilation per unit volume might be expected. We measured the regional distribution of inhaled xenon-133 (133Xe) at 10 and 60 breaths/min in normal subjects and in patients with a clinical diagnosis of chornic bronchitis or asthma. Breathing frequency had no siqnificant effect on ventilation distribution in normals but in patients with chronic bronchitis ventilation decreased in the lower lung regions at 60 breaths/min compared with 10 breaths/min. In six asthmatic patients the lung regions demonstrating the greatest frequency-dependent reductions in ventilation, which were assumed to have the greatest time constants, also showed decreased ventilation-perfusion ratios (V/Q) measured by standard 133Xe techniques. Bronchodilator increased ventilation more than perfusion in these regions and thus V/Q ratio increased toward the normal range. These results imply that measurement of the frequency dependence of regional ventilation provides information about the relative distribution of airway obstruction, and that airway function in the most obstructed lung regions in asthmatics is improved following bronchodilator therapy.

Asthma↗
PubMed1987

Effect of high-frequency ventilation on lung mechanics at high transpulmonary pressure.

The different tidal volumes and frequencies of high-frequency ventilation (HFV) compared with conventional mechanical ventilation (CMV) may have different effects on lung mechanics. To test this hypothesis, we compared the effects of 3 h of HFV and CMV on total lung capacity (TLC), functional residual capacity (FRC), the shape of the pressure-volume (PV) curve (%V10), and dynamic compliance (Cdyn), as well as venous admixture and alveolar-arterial O2 gradient. We studied a total of 12 dogs at lung inflations equivalent to 15 cmH2O positive end-expiratory pressure (PEEP) (group I) and 8 dogs at lung inflations equivalent to 0 cmH2O PEEP (group II). For CMV, we used a standard-volume ventilator at a mean tidal volume of 13.8 ml/kg. For HFV, we used an oscillator-type ventilator at 15 Hz and an average tidal volume of 4.3 ml/kg. Our results showed that ventilation with 3 h of PEEP raised lung volume, and lung volumes on HFV were higher than those on CMV in both groups. Specifically, in group I, the volume during ventilation rose on both CMV (150 ml) and HFV (250 ml). These volume changes persisted beyond the ventilation period, such that TLC was unchanged on CMV but had risen 200 ml on HFV. FRC also rose 200 and 300 ml after HFV and CMV, respectively. In group II, the volume during ventilation fell 100 ml on CMV and rose slightly (40 ml) on HFV. TLC and FRC both tended to fall more on CMV.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1998

Pulmonary embolization causes hypoxemia by redistributing regional blood flow without changing ventilation.

To explore mechanisms of hypoxemia after acute pulmonary embolism, we measured regional pulmonary blood flow and alveolar ventilation before and after embolization with 780-micrometers beads in five anesthetized, mechanically ventilated pigs. Regional ventilation and perfusion were determined in approximately 2.0-cm3 lung volumes by using 1-micrometers-diameter aerosolized and 15-micrometers-diameter injected fluorescent microspheres. Hypoxemia after embolization resulted from increased perfusion to regions with low ventilation-to-perfusion ratios. Embolization caused an increase in perfusion heterogeneity and a fall in the correlation between ventilation and perfusion. Correlation between regional ventilation pre- and postembolization was greater than correlation between regional perfusion pre- and postembolization. The majority of regional ventilation-to-perfusion ratio heterogeneity was attributable to changes in regional perfusion. Regional perfusion redistribution without compensatory changes in regional ventilation is responsible for hypoxemia after pulmonary vascular embolization in pigs.

Animals↗
PubMed1980

Distribution of ventilation-perfusion ratios in pneumonectomized dogs.

In this paper, the distribution of ventilation (VA) and of pulmonary perfusion (Q), gas exchanges, and the single breath CO diffusing capacity are measured in 8 dogs before and after left pneumonectomy. During surgery 4 dogs, in which the left pulmonary artery is clamped, and 4 other dogs in which the left mainstem bronchus is clamped, are studied. A minute ventilation (VE) is adjusted during the initial stage in each dog but it is kept constant for the other stages. For the entire group of dogs, the overall VE/Q varies from 0.8 to 3.0 in the baseline study. In the initial study, the perfusion distribution is unimodal and the ventilation distribution is unimodal or bimodal. The percentage of ventilation of the second mode correlates approximately with the overall VA/Q. After clamping the left pulmonary artery, the correlation between overall VA/Q, capillary shunt, and blood gases data is excellent and the ventilation and perfusion distributions are both bimodal. One perfusion mode is situated in the low VA/Q ratios while one ventilation mode is situated in the high VA/Q ratios. After clamping the left mainstem bronchus, the average anatomical shunt is 27%, the ventilation and perfusion are both bimodal, and the mean PaO2 is 55 mm Hg. Ultimately the ventilation and perfusion distributions tend to return to normal after pneumonectomy.

Animals↗
PubMed2001

Efficacy of low tidal volume ventilation in patients with different clinical risk factors for acute lung injury and the acute respiratory distress syndrome.

In patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), a recent ARDS Network randomized controlled trial demonstrated that a low tidal volume (VT) mechanical ventilation strategy (6 ml/kg) reduced mortality by 22% compared with traditional mechanical ventilation (12 ml/kg). In this study, we examined the relative efficacy of low VT mechanical ventilation among 902 patients with different clinical risk factors for ALI/ARDS who participated in ARDS Network randomized controlled trials. The clinical risk factor for ALI/ARDS was associated with substantial variation in mortality. The risk of death (before discharge home with unassisted breathing) was highest in patients with sepsis (43%); intermediate in subjects with pneumonia (36%), aspiration (37%), and other risk factors (35%); and lowest in those with trauma (11%) (p < 0.0001). Despite these differences in mortality, there was no evidence that the efficacy of the low VT strategy varied by clinical risk factor (p = 0.76, for interaction between ventilator group and risk factor). There was also no evidence of differential efficacy of low VT ventilation in the other study outcomes: proportion of patients achieving unassisted breathing (p = 0.59), ventilator-free days (p = 0.58), or development of nonpulmonary organ failure (p = 0.44). Controlling for demographic and clinical covariates did not appreciably affect these results. After reclassifying the clinical risk factors as pulmonary versus nonpulmonary predisposing conditions and infection-related versus non-infection-related conditions, there was still no evidence that the efficacy of low VT ventilation differed among clinical risk factor subgroups. In conclusion, we found no evidence that the efficacy of the low VT ventilation strategy differed among clinical risk factor subgroups for ALI/ARDS.

Adult↗
PubMed1988

Lung volume maintenance prevents lung injury during high frequency oscillatory ventilation in surfactant-deficient rabbits.

Controversy exists whether high frequency oscillatory ventilation with an active expiratory phase (HFO-A) should be used at low ventilator pressures or high alveolar volumes to minimize lung injury in the atelectasis-prone lung. We therefore ventilated 20 anesthetized, tracheostomized rabbits made surfactant-deficient by lung lavage in 1 of 3 ways: HFO-A at a high lung volume (HFO-A/HI), HFO-A at a low lung volume (HFO-A/LO), or conventional mechanical ventilation (CMV); all received 100% oxygen for 7 h. We examined oxygenation, lung mechanics, and lung pathology. Arterial oxygenation in the HFO-A/HI rabbits was kept greater than 350 mm Hg. Mean lung volume above FRC in these animals was 23.4 ml/kg. In rabbits ventilated with HFO-A/LO and CMV, arterial oxygen tensions were 70 to 100 mm Hg. Mean lung volumes were 7.8 and 4.3 ml/kg, respectively. Total respiratory system pressure-volume curves (P-V curves) showed no change from baseline in the HFO-A/HI group after 7 h of ventilation. The low lung volume groups (HFO-A/LO and CMV) showed a diminution in hysteresis of their P-V curves, lower total respiratory system compliance, more hyaline membranes and severe airway epithelial damage. (All changes significant with p less than 0.05). We conclude that maintenance of alveolar volume is a key mechanism in the prevention of lung injury during mechanical ventilation of the atelectasis-prone lung. For optimal outcome using high frequency oscillatory ventilation, alveoli must be actively reexpanded and then kept expanded using appropriate mean airway pressures.

Airway Resistance↗
PubMed1991

Airborne infection. Theoretical limits of protection achievable by building ventilation.

Of 67 office workers 27 (40%) had documented tuberculin skin test conversions after an estimated 4-wk exposure to a coworker with cavitary tuberculosis. Worker complaints for more than 2 yr before the tuberculosis exposure prompted investigations of air quality in the building before and after the tuberculosis exposure. Carbon dioxide concentrations in many parts of the building were found to be above recommended levels, indicating suboptimal ventilation with outdoor air. We applied a mathematical model of airborne transmission to the data to assess the role of building ventilation and other transmission factors. We estimated that ventilation with outside air averaged about 15 feet 3/min (cfm) per occupant, the low end of acceptable ventilation, corresponding to CO2 levels of about 1,000 ppm. The model predicted that at 25 cfm per person 18 workers would have been infected (a 33% reduction) and at 35 cfm, a level considered optimal for comfort, that 13 workers would have been infected (an additional 19% reduction). Further increases in outdoor air ventilation would be impractical and would have resulted in progressively smaller increments in protection. According to the model, the index case added approximately 13 infectious doses (quanta) per hour (qph) to the office air during the exposure period, 10 times the average infectiousness reported in a large series of tuberculosis cases. Further modeling predicted that as infectiousness rises, ventilation would offer progressively less protection. We conclude that outdoor air ventilation that is inadequate for comfort may contribute to airborne infection but that the protection afforded to building occupants by ventilation above comfort levels may be inherently limited, especially when the level of exposure to infection is high.

Adult↗