Among patients with sickle cell disease, the acute chest syndrome is commonly precipitated by fat embolism and infection, especially community-acquired pneumonia. Among older patients and those with neurologic symptoms, the syndrome often progresses to respiratory failure. Treatment with transfusions and bronchodilators improves oxygenation, and with aggressive treatment, most patients who have respiratory failure recover.

Acute chest syndrome (ACS) is an important cause of morbidity and mortality in sickle cell disease (SCD). Previous studies reported conflicting pictures of ACS making therapeutic interventions difficult. The Cooperative Study of Sickle Cell Disease prospectively followed 3,751 patients enrolled from birth to 66 years of age for ACS. Data on presenting signs and symptoms, laboratory findings, and hospital course were collected. There were 1,722 ACS episodes in 939 patients. Young children (age 2 to 4 years) presented with fever and cough, a negative physical exam, and rarely had pain. Adults were often afebrile and complained of shortness of breath, chills, and severe pain. Upper lobe disease was more common in children; multilobe and lower lobe disease affected adults more often. Severe hypoxia occurred in 18% of adults tested and could not be predicted by examination or laboratory findings. Bacteremia was documented in 3.5% of episodes, but was strongly influenced by age (14% of infants and 1.8% of patients <10 years). ACS was most common in winter with children having the most striking increase. Transfusion was used less frequently, but earlier in children. Young children were hospitalized for 5.4 days versus 9 days for adults. Fifty percent of adults had a pain event in the 2 weeks preceding ACS and children were more likely to have febrile events. The death rate was four times higher in adults than in children. Fatal cases generally developed rapid pulmonary failure and one third were associated with bacteremia. Age has a striking effect on the clinical picture of ACS. In children, ACS was milder and more likely due to infection, whereas in adults ACS was severe, associated with pain and had a higher mortality rate.

We have devised a method for measuring ventilatory muscle endurance as the sustainable inspiratory pressure (SIP), which is the highest pressure a subject can generate in each breath for 10 min. We used a weighted plunger as an inspiratory valve. This both ensures that a constant pressure is generated with each breath and allows the subject to vary his tidal volume freely. Fifteen normal subjects, ages 5--75 yr, had SIP of 82 +/- 6 (SE) cmH2O or 68 +/- 3% of their maximum inspiratory pressure. The respiratory rate was 13 +/- 1 breaths/min with 52 +/- 4% of the respiratory cycle spent in inspiration; end-tidal CO2 pressure increased by 3.3 +/- 1.0 Torr during runs at SIP. Oxygen consumption measured in two subjects rose with increasing pressure below SIP. There was no further increase in oxygen consumption when these subjects breathed with inspiratory pressures above SIP. Our method allows reproducible measurement of ventilatory muscle endurance without dependence on the subject's flow rates or the resistance chosen.

Background: Aggregate hospital encounters for asthma (admissions or emergency department visits) have been associated with daily regional air pollution. There are fewer data on relationships between repeated hospital encounters and traffic-related air pollution near the home.Objective: To estimate the association of local traffic-generated air pollution with repeated hospital encounters for asthma in children.Methods: Hospital records for 2,768 children aged 0 to 18 years (697 of whom had Ն2 encounters) were obtained for a catchment area of 2 hospitals in northern Orange County, California. Residential addresses were geocoded. A line source dispersion model was used to estimate individual seasonal exposures to local traffic-generated pollutants (nitrogen oxides and carbon monoxide) longitudinally beginning with the first hospital encounter. Recurrent proportional hazards analysis was used to estimate risk of exposure to air pollution adjusting for sex, age, health insurance, census-derived poverty, race/ethnicity, residence distance to hospital, and season. The adjustment variables and census-derived median household income were tested for effect modification.Results: Adjusted hazard ratios for interquartile range increases in nitrogen oxides (4.00 ppb) and carbon monoxide (0.056 ppm) were 1.10 (95% confidence interval, 1.03-1.16) and 1.07 (1.01-1.14), respectively. Associations were strongest for girls and infants but were not significantly different from other groups. Stronger associations in children from higher-income block groups (P Ͻ .09 for trend) may have been due to more accurate data.Conclusions: Associations for repeated hospital encounters suggest that locally generated air pollution near the home affects asthma severity in children. Risk may begin during infancy and continue in later childhood, when asthma diagnoses are clearer.

Results suggest exposure to traffic-related air pollution increases asthma severity as indicated by hospital utilisation. The finding in infants suggests this is an especially vulnerable population, although the validity of asthma diagnosis at this age is unknown. Females and children who do not have private insurance may also be more vulnerable to air pollution from traffic.