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Biomedical subjects

T H Shaffer

Publications and source records attributed to T H Shaffer.

At least 145 records · Page 8Linked to original sources
PubMed1980

Alterations in bulk modulus of tracheae during development.

Tracheal dimensions, pressure-volume relationships, and bulk moduli, K, were determined in excised tracheae at different developmental ages: 21-, 27-1, and 31-day rabbit fetuses; 7-day pups; and adult rabbits 18 +/- 6 months of age. Alterations in tracheal dimensions paralleled the growth of the animal. At low segmental pressures such as 10 cm H2O, the tracheal segments became stiffer with age (K = 20.4 cm H2O for the 21-day fetus to K = 58.0 cm H2O for the adult). However, at segmental pressures greater than 15 cm H2O, the overdistended immature trachea became stiffer than even those of the adults. Developmental alterations in bulk modulus suggest significant changes in the material and mechanical properties of the wirways as a function of both pressure and developmental age.

Animals↗
PubMed1980

Sequential effects of acute meconium obstruction on pulmonary function.

The relationship between pulmonary function and the migration of meconium to distal airways was determined in 10 rabbits (mean weight 2.6 kg) after insufflation of a meconium-saline mixture (1--2 ml/kg). Animals were anesthetized, cannulated, intubated, and mechanically ventilated with 100% oxygen. Lung mechanical dysfunction was most severe during the early phase of meconium migration, 15 min postinsufflation. Substantial increases in inspiratory lung resistance (RI) and expiratory lung resistance (RE) suggest that the site of obstruction at 15 min was the large airways. A decrease in dynamic lung compliance with unchanged static compliance characterizes the obstruction as partial. At 15 min and throughout the migration process, RE was greater than RI, demonstrating a check-valve effect. This phenomenon was substantiated by an increased functional residual capacity (FRC) in all rabbits, presumably due to gas trapping. Secondary to these changes, marked hypoxemia, hypercapnea, and acidosis developed in spite of assisted ventilation with 100% oxygen. At 60 and 120 min postinsufflation, both RI and RE decreased as compared to 15 min. This suggests that the predominant site of obstruction shifted to medium and small airways concomitant with the migration of meconium. Widespread and uneven distribution of meconium still produced significant frequency dependence of lung compliance. Static compliance remained unchanged, indicating that meconium does not affect surface-active or tissue properties of the lung within 120 min postinsufflation. These data suggest that effective respiratory management after meconium aspiration is dependent on the degree of meconium migration, as reflected by pulmonary mechanics.

Airway Obstruction↗
PubMed1979

Improved oxygenation and lung compliance with prone positioning of neonates.

Fourteen intubated infants recovering from neonatal respiratory disease had arterial blood gases and lung mechanics measured in the supine position and in two variants of the prone position. Prone positioning resulted in significant increases in mean (+/- SEM) arterial oxygen tension (Pa(o2 70.4 +/- 2.5 to 81.1 +/- 4.4mm Hg), dynamic lung compliance (1.7 +/- 0.24 to 2.55 +/- 0.37 ml/cm H2O),and tidal volume (8.6 +/- 1.0 to 10.5 +/- 1.2 ml) when all prone values were compared to supine values. Prone positioning with the abdomen protruding freely, when compared to all supine values, was associated with significantly increased dynamic lung compliance and tidal volume. Values for prone-abdomen free were not significantly different from values for prone-abdomen restricted. This suggests that there are clinical benefits from prone positioning in neonates recovering from respiratory disease.

Acid-Base Equilibrium↗
PubMed1979

Liquid ventilation: cardiovascular adjustments with secondary hyperlactatemia and acidosis.

Cardiovascular adjustments during liquid ventilation were investigated in seven cats. Cardiac output (CO) and regional blood flow were measured with radioactive microspheres during both spontaneous air breathing (control) and ventilation with fluorocarbon liquid, FC-80. CO was found to decrease 48% (P less than 0.05) during liquid breathing as compared to control. This decrease largely reflected a reduced stroke volume. Despite the decreased CO, mean arterial pressure remained unchanged, indicating a 48% increase (P less than 0.002) in total peripheral resistance (TPR). Secondary to the reduced CO and increased TPR, extensive redistribution of blood flow occurred during liquid ventilation. The arterial lactate concentration and lactate-to-pyruvate ratio (L/P) were significantly increased (P less than 0.02). Furthermore, the increase in L/P correlated with the decrease in CO (r = 0.70; P less than 0.01). In turn, the significant decrease in pH during liquid breathing was found to correlate with the increase in L/P (r = 0.85; P less than 0.001). These data clearly demonstrate signficant alterations in cardiovascular dynamics during liquid ventilation with secondary hyperlactatemia and acidosis.

Animals↗
PubMed1979

Effects of endotracheal tube leaks on functional residual capacity determination in intubated neonates.

The present study evaluates a new closed circuit helium (He) dilution technique for determination of endotracheal (ET) tube leakage and functional residual capacity (FRC) in neonates with ET tubes. By analytically relating the fall in He concentration due to mixing with that due to leakage, it is possible to predict the final equilibration concentration of He and, therefore, correct for ET tube leaks. The system (120 ml) contains an air pump, He meter, breathing bag in cyclinder, a strip chart readout, and solenoid valve. Continuous positive airway pressure (CPAP) or ventilator pressure can be applied during testing. FRC measurements were performed on 13 neonates (799--4500 g) on CPAP with ET tubes. Leak rates were significantly higher (P less than 0.001) on 3 cm H2O CPAP compared to O cm H2O CPAP. The mean measured FRC was 53.5 ml at 3 cm H2O and 46.3 ml at 0 cm H2O CPAP. If gas leakage had not been considered in FRC calculations, the error in FRC could have been as high as 39% at 3 cm H2O CPAP and 18% at 0 cm H2O CPAP.

Birth Weight↗
PubMed1979

Cardiopulmonary changes in the crying neonate.

To determine hemodynamic effects of crying, 12 newborn infants recovering from the respiratory distress syndrome (RDS) were studied. When crying, the range of inspiratory esophageal pressure was -18.8 to -32.5 cm H2O and the range of espiratory pressure was +6.2 to 34.4 cm H2O. The esophageal pressure remained positive for a mean value of 66% of the respiratory cycle. There was a mean significant increase in heart rate of 19 beats/min. The systolic and diastolic blood pressures increased significantly at the beginning of strain to 115 and 135% of the respective control values. There was a progressive decrease in systolic and diastolic pressures during the period of strain and the systolic pressures reached values significantly less than control. With the decrease in systolic and diastolic pressures, there were pronounced reductions in pulse pressures. Three infants reached pulse pressure values less than 1% of control when cries were sustained for nine cardiac cycles. There was a significant mean decrease in arterial oxygen tension (PaO2) of 16.8 mm Hg. There were no changes in arterial carbon dioxide tension (PaCO2), pH, or base excess.

Blood Pressure↗
PubMed1979

A new device for diagnosis and treatment of neonatal pneumothorax.

A new closed-system device for the diagnosis and treatment of pneumothorax was evaluated in ten New Zealand white rabbits and compared with and open-system needle. The closed-system device proved to be safe for diagnostic thoracentesis. There were no pneumothoraces as a result of the procedure with the closed-system device as confirmed by chest roentgenograms and pleural pressure measurements. In contrast, 70% of the diagnostic thoracenteses with the open-system needle were associated with pneumothorax documented by x-ray films and a significant increase in mean pleural pressure. The new apparatus was more efficacious for evacuation of pneumothoraces because complete air removal occurred in 90% of the rabbits as compared with 60% of trials with the open-system needle. If the efficacy of the new closed-system device proves to be good in human infants, the pediatrician encountering a tension pneumothorax in the newborn can use a completely assembled system that is safe for diagnosing and treating this acute life-threatening condition.

Animals↗
PubMed1978

Pulmonary physiotherapy in neonates: physiologic changes and respiratory management.

To investigate physiologic alterations in respiratory function associated with chest physiotherapy, arterial blood gases, respiratory patterns, lung mechanics, and functional residual capacity were measured in 13 neonates (weights 1.25 to 3.20 kg) during the control period, after vibration of the chest and suctioning, after hyperventilation, and two hours after suctioning. Compared to control values, mean PO2decreased significantly after suctioning to 43 mm Hg and increased significantly after hyperventilation to 78 mm Hg. There was a significant decrease in inspiratory resistance and a trend toward decrease in expiratory resistance after suctioning, with return to control levels after hyperventilation. Respiratory rate increased significantly after suctioning. Functional residual capacity, dynamic lung compliance, and tidal volume, as well as PCO2 and base excess, were not changed appreciably throughout the protocol. Because of potentially severe hypoxemia, this study suggests that suctioning and hyperventilation are not warranted on a routine basis in infants recovering from respiratory diseases.

Carbon Dioxide↗
PubMed1978

Alterations in pulmonary function of premature lambs due to positive end-expiratory pressure.

These studies compare lung mechanics and volumes of premature lambs delivered at 139 days of gestation by cesarean section and ventilated by either intermittent positive pressure (IPP) or positive end-expiratory pressure (PEEP). During the first few hours of life, sequential determinations of lung compliance, specific lung compliance; lung resistance, specific lung conductance and functional residual capacity were made at half-hour intervals. Measurements in 5 lambs ventilated with PEEP demonstrated that lung compliance (p less than 0.005), specific lung compliance (p less than 0.001) and specific lung conductance (p less than 0.005) decreased; while lung resistance (p less than 0.10) and functional residual capacity (p less than 0.02) increased as compared to 7 lambs ventilated with IPP.

Animals↗
PubMed1978

Positive end expiratory pressure: effects on lung mechanics of premature lambs.

Pulmonary mechanics were determined at 0, 3, 6, and 10 cm H2O positive and expiratory pressure (PEEP) in premature lambs at a mean gestational age of 134 days. Functional residual capacity increased (p less than 0.005) by 7% (1.6 ml/kg) per cm H2O PEEP. Dynamic lung compliance and specific compliance significantly decreased by 10% (0.11 ml/cm H2O/kg) and 9% (0.0051 l/cm H2O) per cm H2O PEEP, respectively, for PEEP above 3 cm H2O level. Inspiratory lung resistance increased significantly (p less than 0.05) only between 0 and 6 cm H2O PEEP while expiratory lung resistance increased (p less than 0.05) between 0 cm H2O PEEP and all higher levels. The data suggest that PEEP in excess of 3 cm H2O produces undesirable effects on lung mechanics in premature lambs. These results may be important in predicting contraindications and potential complications of positive pressure breathing in the newborn.

Animals↗
PubMed1978

Pulmonary lavage in preterm lambs.

Pulmonary function was studied before and after bilateral lung lavage with oxygenated FC-80 fluorocarbon liquid in seven perterm lambs, 134 days of gestation. Measurements of transpulmoary pressure, airflow, tidal volume, and functional residual capacity (FRC) enabled calculation of lung resistance and compliance, specific compliance, and work of breathing. Immediately postlavage, arterial oxygen tension (PaO2) decreased significantly (P less than 0.05) by 41% from control values. In addition, at 1 hr postlavage, lung compliance significantly decreased (P less than 0.01) by 43% from control levels. Lung resistance, FRC work of breathing arterial carbon dioxide tension, and pH postlavage were not significantly different from prelavage values. The mean volume of FC-80 remaining in the lungs at 1 hr postlavage was 32% of the instilled volume. These data indicate that lung lavage with a low surface tension liquid has a relatively small effect on lung mechanics of the premature lung.

Animals↗
PubMed1977

Instrumentation for measuring functional residual capacity in small animals.

A system for measuring functional residual capacity (FRC) by the dilution method was evaluated to determine its suitability for use in neonates and small animals. The system makes use of rapid, automatically triggered valves for precise closure at end expiration. Results of a theoretical error analysis and experimental in vitro tests are presented and indicate that the measuring error in FRC is related to the FRC-to-initial rebreathing bag volume ratio. With a 200-ml bag volume one standard deviation of the calculated error was 16% for a 50-ml, 9.1% for a 100-ml, and 5.8% for a 200-ml FRC.

Animals↗
PubMed1977

Tracheal extubation of the neonate at 2 to 3 cm H2O continuous positive airway pressure.

To investigate the efficacy of extubation at higher levels of continuous positive airway pressure (CPAP), 49 newborns (0.95 to 4.0 kg) were extubated at 2 to 3 cm H2O following 1 to 47 days of CPAP therapy. Pre- and postextubation measurements of Po2, PCO2, pH, FiO2, and CPAP were made in all infants. No significant differences (P less than.05) were found between pre- and post-extubation arterial blood gas values for all patients. Comparison of pre- and post-extubation blood gas data with respect to birthweight (less than 2.0 kg vs greater than 2.0 kg) and intubation time (less than 8 days vs. greater than 8 days) also indicated no statistical differences. Mean alveolar-arterial oxygen differences and FiO2 for 41 infants showed progressive decreases following extubation. Six of the 49 infants required reintubation within 72 hours following extubation. The results of this study indicate that newborns with respiratory disease requiring CPAP may be extubated at 2 to 3 cm H2O with no significant changes in arterial blood gas values, thus preventing prolonged intubation associated with weaning to 0 cm H2O CPAP.

Birth Weight↗
PubMed1976

Pulmonary function in premature lambs during the first few hours of life.

This study establishes the mean values, variations, and trend of pulmonary function during the first few hours of life in premature lambs. Measurements of intraesophaheal and tracheal pressure, air flow, tidal volume, and functional residual capacity enabled calculations of lung compliance, specific lung compliance, and inspiratory and expiratory resistance of the lungs. Arterial carbon dioxide tension and pH were maintained within a physiologic range. Mean arterial oxygen tension (PO2) at elevated inspired oxygen tension, varied in the individual animals from 51 to 185 mm Hg at an inspired oxygen concentration of 46 to 71%. It was found that the lungs of premature lambs delivered by cesarean section were mechanically unstable; the lambs were all ineffectual at breathing and required some form of mechanical ventilation. During the first 6 hours of postnatal life the lungs of premature lambs are characterized by a wide range of mechanical values and blood gas tensions.

Animals↗