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Biomedical subjects

D Hess

Publications and source records attributed to D Hess.

At least 127 records · Page 7Linked to original sources
PubMed1995

Weekly ventilator circuit changes. A strategy to reduce costs without affecting pneumonia rates.

BACKGROUND: Mechanical ventilator circuits are commonly changed at 48-h intervals. This frequency may be unnecessary because ventilator-associated pneumonia often results from aspiration of pharyngeal secretions and not from the ventilator circuit. We compared the ventilator-associated pneumonia rates and costs associated with 48-h and 7-day circuit changes. METHODS: Ventilator circuits were changed at 48-h intervals during the control period (November 1992 to April 1993) and at 7-day intervals during the study period (June 1993 to November 1993). Nosocomial pneumonias were prospectively identified using the criteria of the Centers for Disease Control and Prevention. The annual cost difference of changing circuits at 48-h and 7-day intervals was calculated using the distribution of ventilator days for the control and study periods. RESULTS: There were 1,708 patients, 9,858 ventilator days, and a pneumonia rate of 9.64 per 1,000 ventilator days in the control group (48-h circuit changes). There were 1,715 patients, 9,160 ventilator days, and 8.62 pneumonias per 1,000 ventilator days when circuits were changed at 1-week intervals (study group). Using a logistic regression model, there were significantly greater odds of developing a ventilator-associated pneumonia in surgical patients (odds ratio 1.77, P = 0.02) and patients in critical care units (odds ratio 1.54, P = 0.05), but no significant risk of ventilator-associated pneumonia in patients in whom circuits were changed at 1-week intervals (odds ratio 0.82, P = 0.22). Changing circuits at 7-day intervals resulted in a 76.6% ($111,530) reduction in the annual cost for materials and salaries. CONCLUSIONS: We found no difference in pneumonia rates with ventilator circuit changes at 48-h and 7-day intervals. Ventilator circuits can be safely changed at weekly intervals, resulting in large cost savings.

Adult↗
PubMed1995

Nitrogen dioxide production during mechanical ventilation with nitric oxide in adults. Effects of ventilator internal volume, air versus nitrogen dilution, minute ventilation, and inspired oxygen fraction.

BACKGROUND: Inhaled nitric oxide (NO) may be useful in the treatment of adult respiratory distress syndrome and other diseases characterized by pulmonary hypertension and hypoxemia. NO is rapidly converted to nitrogen dioxide (NO2) in oxygen (O2) environments. We hypothesized that in patients whose lungs are mechanically ventilated and in those with a long residence time for NO in the lungs, a clinically important [NO2] may be present. We therefore determined the rate constants for NO conversion in adult mechanical ventilators and in a test lung simulating prolonged intrapulmonary residence of NO. METHODS: NO (800 ppm) was blended with nitrogen (N2), delivered to the high-pressure air inlet of a Puritan-Bennett 7200ae or Siemens Servo 900C ventilator, and used to ventilate a test lung. The ventilator settings were varied: minute ventilation (VE) from 5 to 25 l/min, inspired O2 fraction (FIO2) from 0.24 to 0.87, and [NO] from 10 to 80 ppm. The experiment was then repeated with air instead of N2 as the dilution gas. The effect of pulmonary residence time on NO2 production was examined at test lung volumes of 0.5-4.0 l, VE of 5-25 l/min, FIO2 of 0.24-0.87, and [NO] of 10-80 ppm. The inspiratory gas mixture was sampled 20 cm from the Y-piece and from within the test lung. NO and NO2 were measured by chemiluminescence. The rate constant (k) for the conversion of NO to NO2 was determined from the relation 1/[NO]t-1/[NO]o = k x [O2] x t, where t = residence time. RESULTS: No NO2 was detected during any trial with VE 20 or 25 l/min. With N2 dilution and the Puritan-Bennett 7200ae, NO2 (< or = 1 ppm) was detected only at a VE of 5 l/min with an FIO2 of 0.87 and [NO] > or = 70 ppm. In contrast, [NO2] values were greater with the Servo 900C ventilator than with the Puritan-Bennett 7200ae at similar settings. When NO was diluted with air, clinically important [NO2] values were measured with both ventilators at high [NO] and FIO2. Rate constants were 1.46 x 10(-9) ppm-2.min-1 when NO was mixed with N2, 1.17 x 10(-8) ppm-2.min-1 when NO was blended with air, and 1.44 x 10(-9) ppm-2.min-1 in the test lung. CONCLUSIONS: [NO2] increased with increased FIO2 and [NO], decreased VE, blending with air, and increased lung volumes. Higher [NO2] was produced with the Servo 900C ventilator than the Puritan-Bennett 7200ae because of the greater residence time. With long intrapulmonary residence times for NO, there is a potential for NO2 production within the lungs. The rate constants determined can be used to estimate [NO2] in adult mechanical ventilation systems.

Adult↗
PubMed1995

The response of flow-triggered infant ventilators.

Patient-triggered ventilation (PTV) has not been feasible for infants because of large trigger pressures and long delay times with pressure-triggered systems. Recently, four infant ventilators with flow triggering have become available. We questioned if delay times, trigger pressures, and trigger work with these ventilators would be acceptable for PTV in infants. All ventilators were attached via 3-, 4-, and 5-mm endotracheal tubes to a spontaneously breathing infant lung model. The lung simulator was set at an inspiratory time of 0.65 s, tidal volume of 15, 30, and 45 ml, and 0 and 5 cm H2O positive end-expiratory pressure (PEEP). Delay time, trigger pressure, and trigger work were determined from pressure measured at the proximal airway, trachea, and alveolus. There were significant differences between the endotracheal tube sizes, sites of measurement, ventilatory demand and ventilator brand at each PEEP level for delay time, trigger pressure, and trigger work (p < 0.001). Delay time was greatest with the 3-mm endotracheal tube at high ventilatory drive (maximum 138.2 +/- 2.1 ms). Both trigger pressure (minimum 0.23 +/- 0.02 cm H2O) and trigger work (minimum 0.05 +/- 0.01 g.ml) increased with decreasing endotracheal tube size, increasing ventilatory demand, use of PEEP, and site of measurement: alveolus > trachea > airway (maximum: trigger pressure 5.04 +/- 0.02 cm H2O; trigger work 114.48 +/- 0.88 g.ml). PTV may not be appropriate under conditions of increased ventilatory drive and small endotracheal tube size in infants.

Age Factors↗
PubMed1995

Aerosol therapy.

Aerosols are commonly used in the treatment of patients with pulmonary disease. The clinician must choose the appropriate aerosol delivery device. For both spontaneously breathing and mechanically ventilated patients, the first choice of device is usually the metered-dose inhaler. There are important differences among devices in the dosage delivered to the lungs. For the typical prescription, nebulizers deliver more drug to the lungs than metered-dose inhalers, which may be particularly important for acutely ill patients.

Administration, Inhalation↗
PubMed1994

Unique structural features and differential phosphorylation of the 280-kDa component (isozyme) of rat liver acetyl-CoA carboxylase.

Rat liver acetyl-CoA carboxylase (ACC, EC 6.4.1.2) exhibits major and minor subunits (M(r) of 265,000 and 280,000 respectively), the structure and function of which are compared in this study. The two subunits copurified and each contained biotin as demonstrated by avidin reactivity and direct determination of biocytin. In agreement with previous studies, the ACC subunits could be distinguished with specific monoclonal antibodies and differential tissue expression. We now report extensive differences in primary structure revealed by peptide mapping, mass spectrometric analysis of peptides following reverse phase high performance liquid chromatography, and microsequencing of selected peptides. Four peptides derived from the 265-kDa subunit were sequenced and matched sequences within the predicted structure of rat 265-kDa ACC. Although one identical peptide sequence was detected within both subunits (residues 2009-2024 of the 265-kDa subunit), 12 peptides derived from the 280-kDa subunit exhibited entirely novel sequences or matched partially (average 70% identity) with sequences within the 265-kDa subunit. The 280-kDa subunit may also exhibit distinct functional properties, since the initial rate of phosphorylation was at least 10-fold greater than that of the 265-kDa subunit in the presence of cAMP-dependent protein kinase. Two-dimensional mapping demonstrated that the tryptic phosphopeptides released from the two ACC subunits are distinct. These structural studies suggest that the 265- and 280-kDa components (isozymes) of ACC are so distinct they may be encoded by separate genes, while the differential phosphorylation observed in vitro suggests a key role for the 280-kDa subunit in regulating enzyme activity within intact cells.

Acetyl-CoA Carboxylase↗
PubMed1994

Imposed work and oxygen delivery during spontaneous breathing with adult disposable manual ventilators.

BACKGROUND: Manual ventilators (resuscitators) are used primarily to ventilate the lungs of patients lacking spontaneous ventilatory effort. However, in many settings patients are allowed to breathe through the manual ventilator. Although many aspects of manual ventilator function have been studied, very little has been reported on the use of manual ventilators during spontaneous breathing. The purpose of this study was to evaluate inspiratory and expiratory imposed work of breathing and oxygen delivery during spontaneous breathing through disposable manual ventilators. METHODS: Simulated spontaneous breathing was established with a two-chambered test lung, with one chamber serving as the test chamber and the other as the driving chamber. Imposed work of breathing was evaluated with decelerating inspiratory flow at a rate of 20 breaths/min at tidal volume (VT) 0.25 1 and peak flow 40 l/min, at VT 0.5 l and peak flow 80 l/min, and VT 0.81 and peak flow 120 l/min. Flow (integrated to volume) and pressure were measured between the manual ventilator and test lung, and inspiratory and expiratory imposed work of breathing were calculated by integration of the volume-pressure curve. Oxygen concentration was measured with an oxygen analyzer placed between the manual ventilator and the test lung at 20 breaths/min, VT 0.5 l, and flow 45 l/min. An oxygen flow of 15 l/min was added to the device for all evaluations. Two of the manual ventilators had built-in positive end-expiratory pressure valves, and imposed work was evaluated at 10 cmH2O with these. RESULTS: There were significant differences in imposed work between inspiration and expiration (P < 0.001) and among the three levels of ventilatory demand (P < 0.001). For each ventilatory demand, there was a significant difference in work between manual ventilator brands for inspiratory work and expiratory work (P < 0.001). At a VT of 0.5 l and peak flow of 80 l/min, the pooled inspiratory imposed work for all manual ventilators was 0.44 +/- 0.12 J/l, and the pooled expiratory imposed work was 0.29 +/- 0.05 J/l. With 10 cmH2O positive end-expiratory pressure, the inspiratory imposed work was very high (> 1 J/l). Four of the devices were unable to deliver more than 0.85 oxygen concentration at the spontaneous ventilatory pattern evaluated. CONCLUSIONS: Adult disposable manual ventilators produce a substantial imposed work of spontaneous breathing, which is increased with the addition of positive end-expiratory pressure. With some manual ventilators, a high oxygen concentration may not be delivered during spontaneous breathing. We recommend that patients not be allowed to spontaneously breathe through disposable manual ventilators.

Adult↗
PubMed1994

Postdischarge survival and functional status following in-hospital cardiopulmonary resuscitation.

Outcome from cardiopulmonary resuscitation (CPR) at community hospitals is seldom reported in the literature. Data regarding long-term functional status of CPR survivors are virtually nonexistent. We retrospectively reviewed the medical records of all patients receiving CPR during 1989 at a community teaching hospital to determine survival to hospital discharge from CPR. Long-term functional status was determined by contacting primary care physicians in January 1992. We found 24 of 83 (29 percent) patients survived in-hospital CPR and were discharged. Follow-up of these 24 patients showed 13 (54 percent) were alive a mean of 31 months postdischarge with 10 of the 13 (77 percent) reported to be living independently. We believe survival from CPR at community teaching hospitals is comparable to university hospitals. Additionally, patients who survive in-hospital CPR to hospital discharge have a 54 percent chance of being alive a mean of 31 months postdischarge with most being able to live independently. Further work is needed to validate these long-term functional status results.

Activities of Daily Living↗
PubMed1994

Inhaled bronchodilators during mechanical ventilation: delivery techniques, evaluation of response, and cost-effectiveness.

Inhaled beta 2 agonists can be administered by SVN or MDI during mechanical ventilation. MDI is an effective administration technique, it avoids the problems related to SVN, and it may be less expensive than SVN. A variety of techniques can be used to evaluate bronchodilator response during mechanical ventilation. Low-tech methods are also low cost, but may lack sensitivity. High-tech approaches to evaluate bronchodilator responsiveness may be more sensitive but are also more expensive. More work is needed to determine the most appropriate and cost-effective methods to evaluate bronchodilator response in mechanically ventilated patients.

Administration, Inhalation↗
PubMed1993

Molecular characterization of the transcription termination factor from human mitochondria.

The transcription termination factor (mTERF), which plays a central role in the control of mitochondrial rRNA and mRNA synthesis in mammalian mitochondria, has been previously identified and purified by DNA affinity chromatography from a human mitochondrial lysate (Kruse, B., Narasimhan, N., and Attardi, G. (1989) Cell 58, 391-397). In the present work, this factor has been characterized as to its protein composition and the activities of the protein components. Three polypeptides, two of approximately 34-kDa molecular mass and one of approximately 31 kDa, were shown to be associated with the specific DNA binding and footprinting activity of the factor, with the 31-kDa component having a much lower affinity for the recognition sequence than the 34-kDa components. On the other hand, the transcription termination activity, as assayed in an in vitro system, was found to be associated exclusively with the two 34-kDa polypeptides. Mass spectroscopic analysis of tryptic peptides derived from highly purified polypeptides indicated that all three polypeptides share regions with common sequences. The evidence obtained suggests that differential phosphorylation is not responsible for the difference in electrophoretic mobility of the three polypeptides.

Base Sequence↗
PubMed1993

Analytical and micropreparative peptide mapping by high performance liquid chromatography/electrospray mass spectrometry of proteins purified by gel electrophoresis.

We report the use of microbore reverse-phase high performance liquid chromatography connected on-line to an electrospray mass spectrometer for the separation/detection of peptides derived by proteolytic digestion of proteins separated by polyacrylamide gel electrophoresis. A small fraction (typically 10% of the total) of the peptides eluting from the column was diverted through a flow-splitting device into the ion source of the mass spectrometer, whereas the majority of the peptide samples was collected for further analyses. We demonstrate the feasibility of obtaining reproducible peptide maps from submicrogram amounts of protein applied to the gel and good correlation of the signal detected by the mass spectrometer with peptide detection by UV absorbance. Furthermore, independently verifiable peptide masses were determined from subpicomole amounts of peptides directed into the mass spectrometer. The method was used to analyze the 265-kDa and the 280-kDa isoforms of the enzyme acetyl-CoA carboxylase isolated from rat liver. The results provide compelling evidence that the two enzyme isoforms are translation products of different genes and suggest that these approaches may be of general utility in the definitive comparison of protein isoforms. We furthermore illustrate that knowledge of peptide masses as determined by this technique provides a major advantage for error-free data interpretation in chemical high-sensitivity peptide sequence analysis.

Acetyl-CoA Carboxylase↗
PubMed1993

Comparison of six methods to calculate airway resistance during mechanical ventilation in adults.

OBJECTIVE: A variety of methods are used to calculate indices of lung mechanics. We conducted this study to compare 6 methods of calculating airway resistance. METHODS: Data were recorded from 20 adult mechanically ventilated patients. All were relaxed and breathing in synchrony with the ventilator, and an end-inspiratory pause sufficient to produce a pressure plateau (0.5-1.5 s) was used. Pressure and flow rate were measured at the proximal airway using a calibrated lung mechanics analyzer (VenTrak, Med Science, St Louis, MO). Flow rate, pressure, and volume were printed simultaneously. Airway resistance was calculated using 6 methods: Suter, Krieger, Neergard, Bergman, Comroe, and Jonson. RESULTS: Mean calculated resistances (+/- SD) (cm H2O/L/s) were 11.7 +/- 4.8 (Suter method), 13.3 +/- 5.0 (Krieger method), 14.9 +/- 5.3 (Neergard method), 25.0 +/- 6.6 (Bergman method), 24.7 +/- 6.4 (Comroe method), and 26.9 +/- 4.8 (Jonson method). By repeated measures analysis of variance, these differences were significant (p < 0.001). Using Scheffe analysis, no difference was found between the calculations using the Bergman, Comroe, and Jonson methods; these were significantly greater than the other 3 methods (p < 0.05). CONCLUSIONS: Methods that evaluate expiratory resistance (Comroe, Bergman, and Jonson) produce higher values than methods that evaluate inspiratory resistance (Suter and Neergard) or a combination of inspiratory and expiratory resistance (Krieger). Because of these differences, investigators should clearly describe their calculations when reporting airway resistance values.

Adult↗
PubMed1993

Left ventricular dynamics during strenuous isometric exercise in marathon runners, weight lifters and healthy sedentary men: comparative echocardiographic study.

Global and segmental left ventricular dynamics during strenuous large-muscle isometric exercise were compared between endurance and static type professional athletes and sedentary men. Using a trunk dynamometer and supine echocardiography, only the weight lifters manifested increased (p < 0.01) wall thickness during both diastole and systole, resulting in decreased left ventricular volume at end systole. These group-related differences would suggest a causal relationship between chronic intensive weight-lifting training and efficient myocardial dynamics at the time of strenuous isometric exercise.

Adult↗