External high frequency oscillation--concept and practice.
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Equipment Design↗
Biomedical subjects
Z Hayek
Publications and source records attributed to Z Hayek.
The effects of positive and negative extrathoracic pressure ventilation on pulmonary blood flow after the total cavopulmonary shunt procedure.
Pulmonary blood flow patterns were studied during the application of varying extrathoracic pressure in 2 patients after total cavopulmonary anastomosis. The application of negative extrathoracic pressure was associated with large increases in pulmonary blood flow, while positive extrathoracic pressure, caused retrograde flow away from the lungs. These preliminary observations suggest that negative extrathoracic pressure may be useful as a means of respiratory support in patients after right heart bypass procedures.
Adolescent↗
Comparison of high-frequency chest wall compression with conventional mechanical ventilation in cats.
Six anesthetized paralyzed cats with normal lungs were ventilated by high-frequency chest wall compression (HFCWC) at 5 Hz using a single-chamber circumferential cuff enclosing the thorax from the axillae to the xiphisternum. PaCO2 during HFCWC + PEEP (3 cm H2O) was significantly (p less than .0005) lower compared with conventional mechanical ventilation (CMV). End-expiratory lung volume (VL) during HFCWC + PEEP was significantly (p less than .001) lower than VL during CMV + PEEP but was higher than VL during CMV without PEEP. After the cats' lungs were stiffened by repeated saline lavage, CMV + PEEP at a mean airway pressure (Paw) of 10 cm H2O was compared with HFCWC + continuous positive airway pressure (CPAP) at an equal or lower Paw. A significant decrease in PaCO2 (p less than .02) during HFCWC occurred but no significant differences were observed in PaO2, VL, or compliance. Arterial BP and cardiac output were similar between CMV + PEEP and HFCWC + CPAP. In cats with normal lungs, VL can be maintained by applying CPAP during HFCWC, and in those with injured lungs, HFCWC + CPAP produces comparable gas exchange at a Paw equal to or lower than that used during CMV + PEEP.
Animals↗
High frequency chest wall compression in cats with normal lungs.
Ten anesthetized, paralyzed adult cats were ventilated by high frequency chest wall compression (HFCWC) at 3, 5, 7, and 9 Hz by means of a single chamber cuff enclosing the thorax from the axillae to the xyphisternum. The effects of HFCWC in terms of gas exchange, end-expiratory lung volume, and respiratory system compliance were compared to conventional intermittent positive pressure ventilation (IPPV) (30 breaths/mn). HFCWC and IPPV were compared at three levels of matched end-expiratory airway pressure [continuous positive airway pressure (CPAP)/positive end-expiratory pressure/(PEEP) of 0, 2, and 5 cm H2O]. In the absence of CPAP, HFCWC resulted in a marked decrease (up to 50%) in end-expiratory lung volume with significantly lower PaO2, lower compliance, and higher alveolar-arterial oxygen gradient than during IPPV. No differences in PaO2 and a-ADO2 were observed when HFCWC was combined to CPAP greater than or equal to 2 cm H2O. At frequencies below 9 Hz, PaCO2 became significantly lower during HFCWC + CPAP than during IPPV. During HFCWC + 2 cm H2O CPAP, lung volume was lower than during IPPV + 2 cm H2O and similar to the volumes observed during IPPV + 0 positive end-expiratory pressure. Additional studies in six cats at HFCWC + 3 cm H2O confirmed that CPAP greater than 2 cm H2O more than adequately compensated the decrease in lung volume associated with HFCWC alone. Peak cuff pressures between 14 and 17 cm H2O generated oscillary tidal volumes between 4.5 and 2.1 ml/kg. The size of the oscillatory volume was significantly affected by increasing frequencies (decrease in tidal volume) and increasing levels of positive airway pressure (increase in tidal volume). We conclude that in cats with normal lungs, HFCWC can provide for normal gas exchange, provided that it is combined with low level CPAP in order to prevent the occurrence of airway closure associated with HFCWC alone.
Animals↗
Comparison of high-frequency negative-pressure oscillation with conventional mechanical ventilation in normal and saline-lavaged cats.
We modified a negative-pressure respirator to produce high-frequency, subatmospheric pressure oscillations around the chest. The effects of negative-pressure oscillation (NPO) on gas exchange, lung volume, compliance and cardiovascular variables were compared to those of conventional intermittent positive-pressure ventilation (IPPV) at 30 breath/min, using cats with normal and surfactant-depleted lungs. For frequencies in both normal lungs (1, 3, 4, 5, and 7 Hz) and saline-lavaged lungs (3, 5, and 7 Hz), peak inflating pressures were lower during NPO. Oxygenation was similar for both modes of ventilation. In cats with normal lungs, PaCO2 was significantly lower during NPO at 3 and 4 Hz (mean 24 torr) than during IPPV (mean 30 torr); normocapnia was maintained at the other frequencies. In damaged lungs, NPO and IPPV at 3 and 5 Hz resulted in similar CO2 removal, but PaCO2 was significantly higher during NPO at 7 Hz. Oscillatory tidal volumes decreased with increasing frequencies: in normal lungs, mean oscillatory tidal volume was 4.4 ml/kg at 1 Hz and 2.3 ml/kg at 7 Hz; in damaged lungs it was 6.5 ml/kg at 3 Hz and 3.2 ml/kg at 7 Hz. At 3 Hz and above, NPO was associated with a larger functional residual capacity than during sequences of IPPV matched for end-expiratory transthoracic pressure. There were no significant differences in respiratory system compliance, cardiac output, and pulmonary vascular resistance between both modes of ventilation. Further studies are warranted to investigate the potential clinical usefulness of NPO.
Animals↗
External high frequency oscillation in cats. Experience in the normal lung and after saline lung lavage.
In an effort to develop a method of assisted ventilation that would avoid endotracheal intubation, 11 anesthetized, paralyzed, nonintubated adult mongrel cats with normal lungs were externally oscillated by means of a thoracoabdominal chamber connected to a vacuum source and a high frequency oscillator. Chamber pressure was adjusted to the desired negative pressure using the vacuum source, and the animal was then oscillated above and below this pressure. The lowest PaCO2 and AaPO2 were observed at 3 Hz. Tidal volume (VT) fell (p less than 0.001) with increases in frequency, and lung volume (VL) rose with increased negative chamber pressure (p less than 0.001). In 11 additional tracheostomized cats, a stiff lung was created by repeated saline lung lavage. External high frequency oscillation (EHFO), using pressures comparable to those used for conventional mechanical ventilation (CMV), was associated with a significant increase in PaO2 (p less than 0.001), and a significant fall in AaPO2 (p less than 0.01) compared with that during CMV. Lung volume was significantly higher during EHFO (p less than 0.001) and, as in the normal lung, VT fell with increasing frequencies to 15 Hz (p less than 0.001). There were no significant frequency-dependent variations in gas exchange or VL. An increasingly negative mean chamber pressure was associated with a significant increase in PaO2 (p less than 0.05) and VL(p less than 0.005) and a significant decrease in PaCO2 (p less than 0.025).(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Vitamin E and necrotizing enterocolitis.
Although vitamin E has been shown to reduce the incidence of severe sequelae from retrolental fibroplasia, there have been recent suggestions that its use may be associated with an increased incidence of necrotizing enterocolitis (NEC). A review was made of experience with vitamin E, both intramuscular and oral, and NEC over a 4 1/2-year period. Of 418 infants of birth weight less than 1,500 g admitted during this period, 28/209 infants who had received vitamin E had definite NEC (13.4%) compared with 12/209 who had not received vitamin E (5.74%, chi 2 = 7.07, P = .008). For infants of birth weight less than 1,250 g, 16/103 infants who received vitamin E developed NEC v 1/159 who had not (chi 2 = 21.1, P less than .001); the incidence of NEC was not significantly different between the two groups for infants with birth weight between 1,250 to 1,500 g. The early mortality (less than seven days) for infants with birth weight of 1,500 g or less was significantly greater for those who had not received vitamin E (43.5% v 13.8%, chi 2 = 44.9, P less than .001), most probably a reflection of the omission of this drug for the most critically ill infants in this retrospective review. The incidence of NEC was not different for infants with birth weight of 1,500 g or less who received intramuscular vitamin E compared with control infants from the same period. For those infants for whom serum tocopherol levels were available, no infant who developed NEC and who had received only oral vitamin E had a serum tocopherol levels of greater than 3.5 mg/100 mL.(ABSTRACT TRUNCATED AT 250 WORDS)
Administration, Oral↗
Systolic time intervals in adolescents. Normal standards for clinical use and comparison with children and adults.
Systolic time intervals were measured in 147 healthy 13-19-year-old adolescents to derive regression equations for clinical use in this age group and to determine to what extent they differ from those of children and adults. Stepwise regression analysis showed that heart rate was the only variable consistently and significantly related to electromechanical systole (QS2), left ventricular ejection time (LVET) and preejection period (PEP). None of the other variables tested (age, height, weight, body surface area, blood pressure, hemoglobin, hematocrit and serum electrolytes), when used alone, were relevant variables in relation to QS2, LVET or PEP. The PEP/LVET ratio in adolescents was essentially independent of heart rate, as in children and adults. The regression lines for QS2, LVET and PEP in adolescents fall between those for children and adults, indicating that there is a distinct tendency toward lengthening of all the systolic time intervals with age, independent of changes in heart rate. The PEP lengthens proportionately more than the LVET, resulting in a progressive increase in the mean PEP/LVET ratio from childhood (0.30) to adolescence (0.32) and to adulthood (0.345). The precise hemodynamic factors underlying these changes with increasing age remain to be determined.
Adolescent↗