The compliance of the total respiratory system (CRS) was determined by the occlusion technique during expiration in 19 preterm newborns (NB) over 31 weeks of gestational age (mean, 34 +/- 1.5 SD) and in 20 full-term NB. Postnatal age ranged from 1 to 28 days. No sedation was used during the test. In absolute terms, CRS was significantly greater (P less than 0.01) in full-term than in preterm NB (3.17 +/- 0.71 ml/cm H2O vs 2.37 +/- 0.81 ml/cm H2O). When normalized for body weight, length cubed, [corrected] body surface area, and the Quetelet index (body weight/length squared) [corrected], CRS was similar in preterm and full-term NB. These results suggest that, normalized for biometric data, passive elastic properties of the total respiratory system are similar in full-term and preterm NB, at least in the gestation age range studied.

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C Ca ar rd di io ov va as sc cu ul la ar r c ch ha an ng ge es s d du ur ri in ng g a ac cu ut te e e ep pi is so od di ic c r re ep pe et ti it ti iv ve e h hy yp po ox xi ic c a an nd d h hy yp pe er rc ca ap pn ni ic c b br re ea at th hi in ng g i in n r ra at ts s The aim of this study was to investigate the acute haemodynamic changes observed during the repetitive inhalation of various gas mixtures in rats for HO alone and HO + HC, and to analyse the effects of vigilance and of the stress of gas administration.We studied 6 unanaesthetized Wistar rats chronically instrumented with an aortic catheter. Nitrogen, nitrogen + CO 2 mixtures and compressed air were randomly administered in a Plexiglass chamber for 10 s and then flushed by compressed air for 20 s. Two cycles were repeated every min for 10 to 12 min. The inhaled gas fractions (FI,O 2 , FI,CO 2 ) were monitored by O 2 and CO 2 analysers. Blood pressure (BP) was measured by a P23XL transducer. The blood gases were analysed by a 1306 IL meter.In control experiments, with compressed air alone, there were no significant acute changes in heart rate (HR) and BP. During HO there were no changes in HR or BP at FI,O 2 values from 0.05-0.14, whilst at FI,O 2 values from 0-0.05 systolic blood pressure (SBP) rose significantly (+25.3±25.7 (SD) mmHg) and HR decreased (-93.8±124.1 bpm). During HOHC, SBP rose (+35.1±26.4 mmHg) and HR decreased (-139.3±75.7 bpm), significantly more than in HO alone. SBP was linearly correlated with Pa,O 2 during HO (r=0.53) and also during HOHC (r=0.44) and was not directly related to Pa,CO 2 which has, nevertheless, an additive effect to HO. SBP rose with each challenge significantly more when the rats were awake than when asleep (behavioural sleep).We conclude that in this acute repetitive inhalation model, the rise in SBP is not related to gas stress or to Pa,CO 2 but to a decrease in Pa,O 2 and is enhanced by wakefulness.

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Passive total respiratory system compliance (CRS) and gas exchange measurements were performed in nine newborns during the course of hyaline membrane disease. None of the subjects presented bronchopulmonary dysplasia at follow-up investigations. Gestational age ranged from 29 to 37 weeks. CRS was measured by the multiple occlusion technique. Gas exchange parameters were the fraction of inspired oxygen concentration (FIO2) and the arterial/alveolar ratio for oxygen (a/AO2 ratio). In each subject four tests were performed: test 1 during the first day of life; test 2 during the second day of life; test 3 between the fourth and the seventh days of life; test 4 after extubation. CRS/BW (CRS normalized for body weight) was not statistically different at tests 1-3, but it significantly increased (P less than 0.001) between tests 3 and 4. FIO2 and a/AO2 ratio presented no statistical difference at tests 1-2 but several significant differences were noted thereafter: FIO2 decreased significantly (P less than 0.001) when results from tests 2 and 3 were tabulated. The a/AO2 ratio increased significantly between tests 2 and 3 (P less than 0.001), and a further significant increase (P less than 0.01) was also noted when results obtained during tests 3 and 4 were compared. A significant relationship existed during the evolution of the disease between CRS/BW and gas exchange parameters (FIO2 and a/AO2 ratio) (P less than 0.01), but gas exchange improved earlier than lung mechanics.