Marvin D. Lough

Decrease in airway pressure during high-frequency jet ventilation in infants with respiratory distress syndrome

Using a crossover study design, we compared a system of high-frequency jet ventilation with appropriate humidification to pressure-limited conventional ventilation in 12 preterm infants with a birth weight of 1.9 +/- 0.6 kg and gestational age of 32 +/- 2 weeks who had severe respiratory distress syndrome. After a control period of conventional ventilation, high-frequency jet ventilation was administered for 1 to 3 hours at a constant rate (250/min) and inspiratory to expiratory time (1:3 or 1:4) in the same fraction of inspired oxygen as during conventional ventilation. Average peak inspiratory pressure decreased from 29 +/- 3 cm H2O during conventional ventilation to 20 +/- 4 cm H2O during high-frequency jet ventilation (P less than 0.001), whereas positive end expiratory pressure was unchanged, resulting in a reduction in mean airway pressure from 14 +/- 3 to 10 +/- 2 cm H2O (P less than 0.001). There was a simultaneous decrease in PaCO2 (39 +/- 4 to 34 +/- 4 mm Hg, P less than 0.01), but PaO2 did not change. These data indicate that short-term high-frequency jet ventilation maintains gas exchange in infants with respiratory distress syndrome despite a lower PIP and Paw, and results in smaller airway pressure swings than during conventional ventilation. Thus, high-frequency jet ventilation may offer hope for reducing barotrauma in this population.

A Method for Ventilatory Measurements in Subjects 1 Month-5 Years of Age: Normal Results and Observations in Disease

Extract: Using the total body plethysmograph, a method for the measurement of lung volume and airway resistance was developed for infants and young children of 1 month-5 years of age. The subjects were studied in a supine position using a reproducible method of sedation. The procedure providing the most consistent results involved use of a Rendell-Baker mask directly controlled by the operator while the subjects were breathing through the nose. Availability of an oscilloscope permitted immediate detection of pressure leaks, artifacts, and abnormal patterns during each determination and minimized potential errors during the study of each subject. Care was required to avoid pressure on the tip of the nose because an abnormally high airway resistance resulted.The logarithmic relation of thoracic gas volume (TGV) at functional residual capacity (FRC) to body length for 52 normal subjects compared well with results obtained on newborn infants and with those obtained on older subjects. The equation was: TGV at FRC, litters = 1.57 × 10-5 × length, cm2.238 (correlation coefficient = 0.948). The logarithmic relation of airway conductance to TGV was: conductance, liters/sec/cm H2O = 0.1431 TGV, liters0.6441 (correlation coefficient = 0.835). Comparison with older subjects was limited by the difference in airflow rates at which the airway conductance was determined (0.06-0.28 liters/sec versus about 0.5 liters/sec for adults) and by the use of sedation and nasal breathing in this study; adults are studied a wake and during mouth breathing. Comparison of our conductance values with those obtained on unsedated newborns suggests that either sedation alters the airway resistance or that some change occurs in the airway size-lung volume relation during the first weeks of life.Examples of the application of this method to patients with asthmatic bronchitis and cystic fibrosis of the pancreas are provided.Speculation: It is possible that an airflow-lung voliume-airway resistance relation exists throughout life; however, the results presented in this study, combined with those previously presented on newborns for airway resistance, suggest that a change may occur in the relation of the size of the airways to lung volume during early infancy, or that sedation alters airway resistance. Development of this and other methodology should permit more adequate studies of the early changes in pulmonary physiology associated with growth and the acute and chronic pulmonary conditions seen during the first 5 years of life.

Optimal temperature for the measurement of transcutaneous carbon dioxide tension in the neonate

cemic for the first 72 hours. In hypocalcemic IDM, serum PTH concentrations did not rise in response to the low serum calcium concentration. In normocalcemic IDM, in association with a small fall in the iCa concentrations after birth, serum PTH concentrations rose significantly, a finding similar to that reported for term well infants? In this study, even though hypocalcemic IDM were less mature, the sluggish response of serum PTH appeared to be inappropriately low for gestational age, as assessed by covariance analysis. Thus, maternal diabetes may be an independent factor related to suppressed neonatal parathyroid function in addition to the possible effects of prematurity. The lack of increase of serum PTH concentrations in hypocalcemic IDM theoretically may be due to increased catabolism of circulating PTH by the kidney, liver, or bone. No data are available at present regarding catabolism of PTH in the neonatal period. Alternatively, parathyroid function may be suppressed by high intrauterine calcium concentrations in utero. Although serum ionized Ca concentrations in the umbilical vein were high, and appeared higher in hypocalcemic infants when compared with those in normocalcemic infants, there actually was no significant difference between the groups; further study will be needed to test this possibility. Serum Mg concentrations were lower in hypocalcemic [DM compared with those in normocalcemic IDM, at 48 and 72 hours of age. In a previous study we demonstrated that maternal diabetes was associated with a significant incidence of hypomagnesemia in the infants and that neonatal hypomagnesemia was correlated with the severity of maternal diabetes and with maternal hypomagnesemia. 7 Since diabetes mellitus is associated With significant magnesium loss in the urine, and magnesium depletion, s it is possible that diabetes during pregnancy is indeed associated with magnesium deficiency. Magnesium deficiency is a well-known cause of decreased parathyroid hormone secretion? Thus we speculate that hypocalcemia in IDM is related to decreased parathyroid function, possibly related to maternal and fetal magnesium deficiency.

Effect of head position on distribution of nasal airflow in preterm infants

Supine preterm infants characteristically adopt a lateral head position; however, it is not known whether this influences the distribution of nasal airflow. Ventilation was measured in 12 healthy preterm infants (postconceptional age 34 +/- 2 weeks) by employing a nasal mask pneumotachygraph that separated airflow between the left and right nasal passages. In the midline supine position, the percent of total tidal volume (%VT) through the right nasal passage ranged from 31% to 64% and varied by less than 5% between active and quiet sleep in any infant. Lateral positioning of the head caused %VT to increase on the dependent side and decrease through the upper nasal passage. When the right side was dependent, mean %VT on that side increased from 52 +/- 9% to 67 +/- 14% (P less than 0.01) and decreased to 43 +/- 10% (P less than 0.05) when the right side was up. In the midline position, the presence of a nasogastric tube caused %VT through the nasal passage with the tube to fall from 54 +/- 8% to 39 +/- 8% (P less than 0.01). The %VT fell farther, to 25 +/- 10% (P less than 0.01), when the nasal passage with the nasogastric tube was up. Despite these changes in VT distribution, total VT remained constant during these maneuvers. We speculate that when supine preterm infants adopt a lateral head position, the decrease in airflow through the upper nasal passage results from partial obstruction of the oropharyngeal or nasopharyngeal airway on that side.

Mist Tent Therapy of Cystic Fibrosis

Cystic fibrosis is a hereditary disease of children, adolescents, and young adults. Until recently this disease, which involves the exocrine glands of the body, caused death at an early age. Now, thanks to early diagnosis1 and treatment: some children with cystic fibrosis may lead almost normal lives.3 A primary reason for the improved outlook for patients with cystic fibrosis has been improved methods for preventing and treating the pulmonary aspect of this disease. The pulmonary involvement is due to abnormal secretions which the mucus glands of the respiratory tract produce. These mucous secretions accumulate in the tracheobronchial tree. Airways are obstructed and air trapping results. Infection occurs in the stagnant mucus and may produce damage to the lining of the tracheobronchial tree. Progressive infection causes destruction of the bronchial walls and adjacent lung tissue. About 95 per cent of the overall problems in children with cystic fibrosis are due to the pulmonary involvement. One of the most effective therapeutic measures for preventing and treating the obstructive pulmonary lesion of cystic fibrosis is mist tent therapy used during sleeping ho~rs.~ The objective of such therapy is to wet and thin the bronchial secretions to facilitate their clearance from the respiratory tract. This is accomplished by the addition of small particles of water or of water containing mucolytic substances to the secretions at the site of their production or accumulation. Since the obstructive lesion starts in the smaller bronchi and bronchioles and progresses toward the larger bronchi, effective therapy requires use of a nebulizer which provides small mist particles which will deposit in the peripheral bronchial tree. This can be accomplished with both jet-type and ultrasonic nebulizers5 Of equal importance is the density of the mist inhaled. The surface area of the tracheobronchial tree at any age is measured in square meters. To wet and thin secretions covering such a large area requires deposition of a large amount of water, and this can only be accomplished by inhalation of a dense mist over a long (8-10 hour) period of time. Use of a mist tent during sleeping hours permits such therapy with a minimum of inconvenience for the patient. Many factors influence the water content of the air in a mist tent and the effectiveness of mist tent therapy (Table I). Condensation, rain-out and impaction of particles on the tent walls all reduce the water content of the air

Computer analysis of slow vital capacity spirograms

We have developed a digital computer program which evaluates the vital capacity and its subdivisions, expiratory reserve volume and inspiratory capacity. The algorithm examines the multibreath spirogram, a continuous record of quiet breathing interspersed among repeated slow, large volume maneuvers. Quiet breaths are recognized by comparing features of each breath to the respective average and variation of these features for all breaths. A self-scaling, iterative procedure is used to identify those end-tidal points that most likely represent the subjects functional residual capacity. A least-squared error baseline is then fit through these points to partition the vital capacity. Twenty-three spirograms from patients with documented pulmonary disease were independently analyzed by the computer, a pulmonary function technician, and the laboratory supervisor. No practical differences were found among the results. However, the computers values, in contrast to those of the technician, were reproducible on repeated trials and free of computational and transcriptional errors.

ASSOCIATION OF CHILDHOOD OBESITY-HYPOVENTILATION SYNDROME AND FAMILIAL DECREASED VENTILATORY RESPONSE TO HYPERCAPNIA

Subnormal ventilatory response to hypercapnia is accepted as part of the obesity-hypoventilation syndrome in adults, but ventilatory control has not been studied in children with the obesity-hypoventilation syndrome. We studied ventilatory response to hypercapnia in the families of 2 obese 13-year-old girls with the Prader-Willi Syndrome, one of whom had recovered from the obesity hypoventilation syndrome, and one of whom had never hypoventilated. Siblings and parents were not obese.The response to hypercapnia, measured as the slope (S) of ventilation (L/min) vs. alveolar carbon dioxide tension (mmHg) during rebreathing, was decreased in the patient with the obesity-hypoventilation syndrome (S=1.0) and in 3 family members (mean S=1.1, range .7-1.4). The other Prader-Willi patient (S=3.6) and her family (mean S=2.2, range 1.6-3.6) had considerably greater responses. Young adult controls (mean S=3.3, range 2.8-4.2) fell within published normal ranges (S=1.5 - 5.0).Respiratory failure in the child with the obesity-hypoventilation syndrome is probably related to two independent factors: obesity and a familial diminished response to hypercapnia. The familial factor may explain why only a small percentage of obese patients develop the obesity-hypoventilation syndrome.