The American review of respiratory disease
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Am. Rev. Respir. Dis. · Jul 1989
Comparative StudyIn vitro versus in vivo comparison of endotracheal tube airflow resistance.
The mechanics of gas flow in endotracheal (ET) tubes have been evaluated extensively in vitro under static and dynamic conditions. Previous bedside determinations of respiratory system mechanics in patients with acute respiratory failure have been based on assumptions derived from in vitro measurements without direct measurement of in vivo ET tube resistance (RET). We hypothesized that the RET measured in vivo would be greater than those values obtained in vitro when peak flow rates and ET tube size were held constant. ⋯ Although there was considerable individual variation, values of RET measured in vivo were generally higher than those derived from in vitro measurements at both peak flow rates tested, perhaps because of secretions, head or neck position, tube deformation, or increased turbulence. We conclude that ET tubes contribute significantly to total airflow resistance and that RET is often significantly greater than indicated by in vitro studies. Estimates of work of breathing in critically ill patients must take into consideration the contribution of in vivo RET on total pulmonary system resistance.
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Am. Rev. Respir. Dis. · Jul 1989
Detrimental effects of positive end-expiratory pressure during controlled mechanical ventilation of patients with severe airflow obstruction.
Positive end-expiratory pressure (PEEP) in treatment of asthma may be beneficial by dilating airways or detrimental by increasing hyperinflation. Several studies have reported beneficial results but with conflicting effects on lung volume. We studied the effects of PEEP on pulmonary hyperinflation, gas exchange, and circulation in six patients (59 +/- 19 yr, four men, two women) with severe airflow obstruction requiring mechanical ventilation (four with asthma, two with an exacerbation of chronic airflow obstruction). ⋯ Two patients were not studied at 15 cm H2O PEEP because of hypotension. Without PEEP, all patients showed gas trapping above FRC that increased progressively as R was increased (i.e., expiratory time decreased). At each R, increases in PEEP progressively increased FRC up to 1.42 +/- 0.43 L (mean +/- SD) at 15 cm H2O PEEP (n = 4) and progressively reduced the degree of gas trapping above the PEEP FRC.(ABSTRACT TRUNCATED AT 250 WORDS)
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Am. Rev. Respir. Dis. · Jun 1989
Hypoxic, hypercapnic acidosis decreases tension and increases fatigue in hamster diaphragm muscle in vitro.
Hypoxia and hypercapnic acidosis have been shown to have a negative inotropic effect on diaphragmatic contractility. The effect of combined hypercapnia and hypoxia was studied in vitro using hamster diaphragm strips. A 12% CO2, 21% O2, and 67% N2 gas mixture was used to produce hypoxic, hypercapnic acidosis. ⋯ With repeated contractions, tension declined at a faster rate than in control, hypoxia alone, or hypercapnia alone. In the combined hypoxic, hypercapnic solution, the time constant of relaxation (tau) was increased prior to the start of the fatigue run compared to the control (tau = 35 +/- 6 versus 45 +/- 5 ms; p less than 0.001), and the tau increased at a faster rate than in control. These studies suggest that hypoxic, hypercapnic acidosis has a greater detrimental effect on the muscle than either abnormality alone and makes the muscle more susceptible to fatigue.
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Am. Rev. Respir. Dis. · May 1989
Comparative StudyThe role of airflow resistance in patients with the adult respiratory distress syndrome.
Although reduced lung compliance is a hallmark of the adult respiratory distress syndrome (ARDS), the role of increased airflow resistance in this disorder has not been well studied. Because animal models of ARDS show marked increases in airflow resistance and because mediators known to participate in lung parenchymal injury have also been implicated in models of increased airway reactivity, we hypothesized that increased airflow resistance is a major contributor to altered lung mechanics in human ARDS. We studied 10 mechanically ventilated patients with ARDS (criteria: PaO2 less than or equal to 70 mm Hg breathing FIO2 greater than or equal to 0.4; bilateral pulmonary roentgenographic infiltrates; Ppaw less than or equal to 18 mm Hg) measuring dynamic (Cdyn) and static (Cstat) compliance, airflow resistance across the lungs (RL), shunt fraction (QS/QT breathing FIO2 = 1.0), minute ventilation (VE), (a/A)PO2, dead space to tidal volume ratio (VD/VT), airflow (pneumotachograph), transpulmonary pressure (intratracheal pressure minus esophageal pressure) and volume (integrated from flow) at 50 L/min peak flow rate. ⋯ RL correlated with peak pressure, but did not correlate with VE, shunt, (a/A)PO2, or VD/VT. We conclude that increased pulmonary airflow resistance contributes significantly to the altered lung mechanics in ARDS. These data are consistent with studies of animal models of ARDS and long-term survivors of ARDS and may be secondary to tissue factors, airway hyperreactivity, or airway inflammation.
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Am. Rev. Respir. Dis. · Apr 1989
Preoperative assessment as a predictor of mortality and morbidity after lung resection.
To refine the functional guidelines for operability for lung resection, we prospectively studied 55 consecutive patients with suspected lung malignancy thought to be surgically resectable. Lung function and exercise capacity were measured preoperatively and at 3 and 12 months postoperatively. Preoperative pulmonary scintigraphy was used to calculate the contribution to overall function by the affected lung or lobe and to predict postoperative lung function. ⋯ In patients who underwent pneumonectomy, the best predictor of death was FEV1-ppo. The predictions were enhanced by expressing the value as a percentage of the predicted normal value (% pred) rather than in absolute units. For the entire surgical group a FEV1-ppo greater than or equal to 40% pred was associated with no postoperative mortality (n = 47), whereas a value less than 40% pred was associated with a 50% mortality (n = 6), suggesting that resection is feasible when FEV1-ppo is greater than or equal to 40% pred.(ABSTRACT TRUNCATED AT 250 WORDS)