Isovolume pressure/flow curves of rapid thoracoabdominal compressions in infants without respiratory disease.

To assess whether flow limitation can be achieved during rapid thoracoabdominal compressions (RTC), we performed esophageal pressure measurements in 11 healthy infants less than 3 months of age. Recordings of esophageal pressure were obtained with an esophageal balloon placed in the lower esophagus. RTCs were started at 20 cm H2O and increased to 140 cm H2O or until the infant responded with glottic closure to the compression. Flow limitation was assessed from isovolume pressure flow curves at peak flow and flow at FRC (V'max, FRC). The transmission of jacket pressure was higher at peak flow than at FRC for pressures below 60 cm H2O, due to active inspiration during the compression. Active inspiration was not observed at compression pressures above 80 cm H2O, as reflected by a plateau in the esophageal pressure tracing. Esophageal pressure increased parallel to the compression pressure at jacket pressures below 60 cm H2O. The relationship between jacket pressure and esophageal pressure became curvilinear at high compression pressures and plateaued at compressions above 100 cm H2O, so that further increases in jacket pressure did not increase esophageal pressure. Flow limitation was seen in all infants studied, as indicated by a lack of increase in flow with increasing esophageal pressures for V'max, FRC. Jacket compression pressures of 60 cm H2O and esophageal pressures of 20 cm H2O were sufficient to reach maximal expiratory flow. These data indicate that jacket pressure is a poor indicator of pleural pressure at high compression pressures in young healthy infants, and high pressures are not needed, as flow limitation is seen during RTCs at moderate compression pressures.

Carbon dioxide chemosensitivity and exercise ventilation in healthy children and in children with cystic fibrosis.

This two-part study sought to determine the relationship between arterial PCO2, CO2 chemoresponsiveness, and ventilation during exercise in healthy children and children with cystic fibrosis (CF). In the first part, we measured the hypercapnic ventilatory response (HCVR) in 16 healthy children and 16 patients with CF, and compared HCVR with the ventilatory response to progressive exercise (delta VE/delta VCO2). In the second part, we assessed the relation between age, the ventilatory equivalent for CO2 (VE/VCO2), and arterialized capillary PCO2 (PaCO2), during exercise in 28 healthy children and 23 children with CF. The HCVR showed an age-related decline in both healthy controls and CF subjects. In addition, there was a correlation between forced expiratory flow from 25 to 75% of forced vital capacity and the HCVR, regardless of age. In controls, but not in CF, there was also a decline in delta VE/delta VCO2 with increasing age; and there was a significant correlation between delta VE/delta VCO2 and HCVR. Findings in the second part were similar, with a significant inverse correlation between age and VE/VCO2 during steady state exercise only in healthy controls. However, when physiologic dead space was taken into account, both CF and healthy control children showed a significant decline in VA/VCO2 with age. When all subjects were grouped together, there was a statistically significant correlation between PaCO2 and age, such that younger subjects had lower PaCO2 than older subjects. Age and PaCO2 together accounted for 71% of the variance in VA/VCO2. We conclude that younger children ventilate proportionately more on exercise than older children because they regulate PaCO2 about a lower set point. As the ventilatory response to exercise is significantly correlated with the HCVR, and the latter can be reduced in the presence of airways obstruction, an innately low HCVR could permit the development of exertional hypercapnia in some CF patients with advancing pulmonary disease.

Effect of racemic epinephrine and salbutamol on clinical score and pulmonary mechanics in infants with bronchiolitis.

To test the efficacy of a combined alpha- and beta-receptor agonist in acute bronchiolitis, we compared inhaled racemic epinephrine with salbutamol in a double-blind, crossover, randomized protocol. Twenty-four infants, 4.6 +/- 0.5 (mean +/- SEM) months of age, with their first episode of bronchiolitis were tested. After sedation with chloral hydrate, a clinical score and pulmonary mechanics measurements using simultaneous signals of airflow volume and transpulmonary pressure were recorded. After baseline measurements, infants received either nebulized salbutamol, 0.03 ml/kg, or racemic epinephrine, 0.1 ml/kg. Thirty minutes later, there was a significant decrease in clinical score after treatment with racemic epinephrine compared with the baseline score (p < 0.001); this difference was not present after salbutamol inhalation (p = 0.42). Only 13 patients had a decrease in clinical score after salbutamol therapy, in comparison with 20 infants treated with racemic epinephrine (p < 0.01). Both drug decreased respiratory rate, but the decrease was greater after the use of racemic epinephrine (p < 0.001). There was a significant decrease in inspiratory, expiratory, and total pulmonary resistance after treatment with racemic epinephrine compared with baseline values (p < 0.01) but no significant change after salbutamol inhalation. There was no significant correlation between the clinical score and pulmonary mechanics either at baseline or after drug treatment. We conclude that racemic epinephrine is superior to salbutamol in the treatment of infants with their first episode of acute bronchiolitis.