Pre mortem analysis of lung injury and lung function in oxygen toxic rabbits.

OBJECTIVES: To determine whether respiratory system mechanics measurements could detect lung injury in oxygen toxic rabbits before clinical deterioration. To determine whether respiratory system mechanics measurements, using a power analysis, have the statistical power to detect significant reductions in hyperoxic lung injury due to an intervention when compared with traditional post mortem measurements of lung injury, extravascular lung water, and bronchoalveolar lavage protein concentration. DESIGN: Prospective, controlled study. SETTING: Institutional animal laboratories. SUBJECTS: Adult New Zealand white rabbits. INTERVENTIONS: Spontaneously breathing adult New Zealand white rabbits were exposed continuously to either > 95% oxygen or room air. MEASUREMENTS AND MAIN RESULTS: We measured arterial pH, blood gas tensions, and respiratory system mechanics in rabbits twice, both before exposure to > 95% oxygen, and after the rabbits developed symptoms of mild lung dysfunction. After the second set of respiratory system mechanics measurements, we measured extravascular lung water and bronchoalveolar lavage protein concentration in the hyperoxia-exposed rabbits and compared the values with those values obtained in animals that breathed room air only. Our hyperoxia-exposed rabbits developed symptoms of mild respiratory impairment at 69 +/- 2 hrs. In these hyperoxia-exposed rabbits, measurements of static compliance, quasi-static compliance and resistance all changed significantly (p < .05) when compared with baseline measurements. Functional residual capacity and arterial blood gas values did not change significantly. Furthermore, assuming that an intervention reduced hyperoxic lung injury by a given amount, we performed a power analysis and found that the measurement of static compliance had at least equivalent power to detect a reduction in lung injury from an intervention when compared with measurement of extravascular lung water and bronchoalveolar lavage protein concentration. CONCLUSIONS: Measurements of respiratory system mechanics can detect lung injury in hyperoxic rabbits before the onset of severe clinical deterioration or death. Furthermore, measurement of static compliance of the respiratory system is likely to be a powerful tool to detect a reduction in lung injury produced by an intervention.

Current issues in Texas neonatology.

Since almost 10% of the births in the United States occur in Texas, issues that affect neonatal care in Texas are important for both the state and the nation. Although overall statistics are similar for the state and nation, closer examination reveals a need for improvement in specific areas, namely prenatal care, black and Hispanic mortality, and low birth-weight rates. Lay midwifery regulation has been an important concern in Texas. Surfactant use and education to prevent birth asphyxia have had a positive impact on perinatal health, contributing to public health efforts to improve perinatal outcome.

A nonlinear regression analysis of nonlinear, passive-deflation flow-volume plots.

When studying lung mechanics of intubated premature infants, by the passive-deflation technique we noted that in many flow-volume plots the descending limb was curvilinear with a convexity toward the volume axis. By conventional linear analysis lung mechanics of these patients did not change after the administration of terbutaline, but Mead's tangent-chord slope ratio method for quantifying the amount of curvature showed that the shape of the flow-volume plots did change. Because of the limitations of this method, we developed a microcomputer-based, reiterative regression algorithm which optimizes a nonlinear function for the best fit to any given set of data. We then studied six very low birth weight infants with clinical evidence of pulmonary gas trapping (weight at study, 1.22 +/- 0.29 kg; age, 26 +/- 16 days). We measured respiratory system resistance (Rrs), compliance (Crs), and expiratory time constants (TCrs) by the passive deflation technique before and after subcutaneous administration of 0.02 mg/kg of terbutaline. No effect of terbutaline in a dose sufficient to increase heart rate > 25 beats/min was observed. The same data analyzed using the nonlinear regression technique with a function based upon a two compartment model of parallel inhomogeneities revealed one compartment with relatively normal Rrs, Crs, and TCrs values, and a second compartment with a very high Rrs. The latter fell by 50% after terbutaline. These data suggest that abnormalities of airway resistance in ventilated preterm infants are not easily identifiable by classic linear analysis of lung mechanics.(ABSTRACT TRUNCATED AT 250 WORDS)

Passive deflation time constant of 7-week-old rabbits.

The purpose of our study was to determine the effects of insufflation time (TI) and of tidal volume (VT) on the passive deflation time constant (tau) of juvenile rabbits. We sedated and paralyzed nine 7-wk-old New Zealand rabbits (wt 1.2 +/- 0.2 SD kg) and placed them on a time-cycled, pressure-limited mechanical ventilator. Measurements of tau and dynamic compliance of the respiratory system were made at nine ventilator settings. TI was adjusted to 0.2, 0.4, and 0.6 s and VT was adjusted to 10, 15, and 20 mL so that the effects of TI and VT on tau could be determined independently. Respiratory system quasi-static and static compliances were also measured and served as a basis for discussing the physiologic explanations for the effects of TI and VT on tau. In general, increases in TI resulted in increases in tau and increases in VT also resulted in increases in tau. Increasing TI from 0.2 to 0.6 s plus increasing VI from 10 to 20 mL resulted in an increase in tau from 0.220 +/- 0.007 to 0.282 +/- 0.010 s (mean +/- SEM) (p less than 0.05, student Newman-Kuels), which is a 28% increase. At a VT of 10 mL, dynamic compliance increased from 1.95 +/- 0.10 to 2.14 +/- 0.10 mL/cm H2O (p less than 0.05) when TI was increased from 0.2 to 0.6 s; however, dynamic compliance decreased 19% as VT was increased from 10 to 20 mL.(ABSTRACT TRUNCATED AT 250 WORDS)