CPAP has been proposed as an e f f e c t i v e treatment f o r the apnea o f prematurity. I t s mechanism o f a c t i o n i s unknown. Twentyfour preterm i n f a n t s receiving CPAP f o r the treatment o f r e s p i r a t o r y d i s t r e s s were studied a t 0,5,and lOcm H20 CPAP. These i n f a n t s were allowed t o breathe 2%,5%,and 8% C02 f o r 3 minutes each. During the 3rd minute, recordings o f t i d a l volume,respiratory r a t e , and esophageal pressure were made. From these recordings, minute volume,inspiratory time (Ti),expiratory time (Te), compliance, duty cycle ( T i l T t o t ) , t i d a l volume/inspiratory time r a t i o (VtfTi) and C02 s e n s i t i v i t y were calculatpd. A1 though C02 s e n s i t i v i t y rose from 3.9t6.8 cc/min x m m Hg-a t 0 cm HZ0 o f CPAP t o 4.8*8.0 a t 10 cm H20, t h i s d i f f e r e n c e was not s t a t i s t i c a l l y s i g n i f i c a n t . S i g n i f i c a n t differences i n r e s p i r a t o r y rate, T i , Te, Vt/Ti , and T i / T t o t were not observed when values f o r a l l 3 l e v e l s o f CPAP were compared. Measurements o f intraesophageal pressure indicated t h a t 62% o f the applied airway pressure was transmitted t o the mediastinal structures a t 5 cm H20 and 54% o f applied pressure a t 10 cm H20. These r e s u l t s suggest t h a t i n a group of premature i n f a n t s w i t h poor C02 s e n s i t i v i t y t h a t CPAP does not e i t h e r improve C02 s e n s i t i v i t y o r the d r i v e t o breathe, and t h a t other explanations, such as improvement i n a r t e r i a l blood gases o r s t a b i l i z a t i o n o f the chest wall must account f o r the r e l i e f o f apnea i n i n f a n t s receiving CPAP therapy. Functional anatomy of 0.87 gestation (inmature) rabbit fetal lungs was studied by direct stereomicroscopic observation as the first air volume-pressure (VP) diagrams were recorded. Lungs were airless, but contained normal volume of fetal pulmanary fluid (FPF) prior to air-inflation. Volume was recorded 0, 15 and 120 sec after stepwise changes of 5 cm Hz0 pressure. Inflation pressures up to 25 cm H20 (P25) produced large, time-dependent, volume changes in which the conducting aimays were distended and FPF moved to the periphery of the parent airway before lateral branches were inflated. Characteristically, there was rr> saccular aeration below P25. At pressures greater than P25, but below h x , subpleural saccules were the first to aerate; repeated inflation-deflation cycles in this pressure range produced preferential aeration of the same saccules, which thereby became vulnerable to rupture. As pressure was raised from -P25 to hx (i.e., P35-Pt+0), saccules were recruited by both time-and pressure-dependent processes and recruitment contjnued, but at a s l m rate, during early deflation. Time-dependent changes pre dominated at h i~h pressures and were related to FPF flow through terminal ducts, formation of transient labile bubbles, and progressive enlargement of saccules. hriniilation from P25, derecruitment of saccules w...
To determine the effects of continuous positive airway pressure (CPAP) on ventilatory response to CO2 and inspiratory and expiratory duration in preterm infants, 24 preterm infants with an average birth weight of 1220 g were studied at a mean age of 10.6 days. CPAP was applied via an uncuffed endotracheal tube. Testings were performed between ambient pressure and a positive airway pressure of 10 cm H2O. Approximately 2/3 of the applied pressure was transmitted to the esophagus. All infants demonstrated a ventilatory response to carbon dioxide of less than 50 ml/min per mm Hg Pco2 at ambient pressure, and no infant showed significant improvement at increasing levels of CPAP. Drive to breathe, as reflected in the inspiratory flow rate (Vt/Ti) also failed to change significantly. It may be concluded that in the apparent absence of significant changes in lung volume, CPAP fails to increase sensitivity to CO2 in preterm infants recovering from hyaline membrane disease.
Aspiration of AF is con sidered many to be a cause of respiratory distress. We investiqated the effect of aspiration of human AF on the newborn rabbit. 85 cesarean delivered pups (30-31 days gest) were qiven 0.4 ml (ll ml/kg mean) AF, saline or 10% meconium solution transtracheal puncture prior to the first breath. Controls were sham-injected. Tc99 added to the aspiration fluids demonstrated thorough distribution on lung scan. All mecontim animals died in <15 min. Chest radiographs at <2 hrs age revealed abnormalities in 4/13 AF, 4/10 saline, Respiratory Rates
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