Charles W. Sargent

Furosemide acutely decreases airways resistance in chronic bronchopulmonary dysplasia

We studied the effects of furosemide on pulmonary mechanics in 10 infants with bronchopulmonary dysplasia aged 41 +/- 1 (SE) weeks post-conception, gestational age at birth 30 +/- 1 wk, birth weight 1370 +/- 200 gm. Thoracic gas volume, airways resistance, and specific airway conductance were measured in an infant body pressure plethysmograph during quiet breathing. Dynamic pulmonary compliance was measured using an esophageal balloon. Infants with BPD had greater Raw, lower SGaw, and lower Cdyn than did 16 normal control infants. Within one hour after administration of furosemide 1 mg/kg IV to infants with BPD, Raw fell 36 +/- 13%, SGaw increased 84 +/- 22%, and Cdyn increased 54 +/- 13%; TGV did not change. Diuretic treatment of BPD in infants is associated with rapid, short-term improvement in Raw and Cdyn.

Developmental Pattern of Maximal Transdiaphragmatic Pressure in Infants during Crying

Summary: Diaphragm strength was measured as maximal transdiaphragmatic pressure (Pdi) during airway occlusion in 38 infants aged 11.6 ± 0.5 (S.E.) months postconception (mpc), range 8–21 mpc. All infants were asymptomatic at the time of study and required no mechanical ventilatory assistance. Ten infants had previous surgical correction of abdominal wall defects (gastroschisis/omphalocele); 10 infants had previous surgical correction of congenital diaphragmatic hernia; and 18 infants had no thoracic or abdominal surgery. The mean maximal Pdi for all infants was 72 ± 3 cmH2O. There were no significant differences between the three groups. All infants with a maximal Pdi of less than 60 cmH2O were aged less than 10 mpc. After 13 mpc there was no significant increase in maximal Pdi. Between the ages 8–13 mpc there was a significant positive correlation between maximal Pdi and age postconception (r = 0.87, P < 0.0005), reflecting a developmental pattern of increasing maximal transdiaphragmatic pressure in infants during crying.

Abnormal control of ventilation in adolescents with myelodysplasia

Infants with myelomeningocele have abnormalities in ventilatory control. To determine whether these persist into later life, we studied 14 patients with myelomeningocele and Arnold-Chiari malformation (age 18.0 +/- 0.8 (SE) years), and compared them with 14 control subjects (age 24.0 +/- 0.9 years). Pulmonary function and ventilatory muscle strength did not differ between patients with myelomeningocele and control subjects. Hypercapnic ventilatory responses were significantly lower in the group with myelomeningocele (1.98 L/min/mm Hg) compared with control values (3.33 L/min/mm Hg; p less than 0.01). Hypoxic ventilatory responses (-1.4 L/min/%oxygen saturation of hemoglobin in arterial blood) were not significantly different from control values (-2.14 L/min/%oxygen saturation). In control subjects the hypercapnic and hypoxic ventilatory responses were highly correlated with each other within subjects (r = 0.84; p less than 0.002) but not in those with myelomeningocele (r = 0.34; not significant). We concluded that adolescents and young adults with myelomeningocele have abnormalities in control of ventilation during sleep and wakefulness. We speculate that the Arnold-Chiari malformation interferes with central chemosensitivity (hypercapnic ventilatory response) and central integration of chemoreceptor output.

1721 DEVELOPMENTAL PATTERN OF DIAPHRAGM STRENGTH IN INFANCY

Diaphragm strength was measured as maximal transdiaphragmatic pressure (Pdi) during airway occlusion in 33 infants aged 11.3 ± 0.6 (SE) months post-conception (mpc), range 8-21 mpc. All infants were asymptomatic at the time of study and required no ventilatory support. 9 infants had previous surgical correction of abdominal wall defects (gastroschisis/omphalocele), 9 infants had previous surgical correction of congenital diaphragmatic hernia, and 15 infants had no thoracic or abdominal surgery. The mean maximal Pdi for all infants was 69.7 ± 3.5 cm H2O. There were no significant differences between the 3 groups (P = 0.20). In the entire group, there was a significant correlation between maximal Pdi and age {Pdi (cm H20) = Age (mpc) x 3.4 + 30.9; r = 0.598; P = 0.0005}. In contrast, maximal Pdi in 3 ventilator dependent infants was less than 30 cm H2O. Subsequently, Pdi increased to above 40 cm H2O in these 3 infants following the ability to wean from mechanical ventilatory assistance. We conclude that diaphragm strength increases during the first year of life. Since respiratory failure may be viewed as inadequate ventilatory muscle power to overcome increased work of breathing, young infants may be at increased risk for respiratory failure relative to older infants due to decreased diaphragm strength.