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  • 1
    ISSN: 1432-055X
    Keywords: Schlüsselwörter: Messung der Sauerstoffaufnahme – Methodenvergleichsstudie – Inverses Ficksches Prinzip – Indirekte Kalorimetrie – Intrapulmonaler Sauerstoffverbrauch ; Key words: Measurement of oxygen uptake – Method comparison study – Reversed Fick principle – Indirect calorimetry – Intrapulmonary oxygen consumption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Abstract. Automated measurements of respiratory gas exchange recently became available for the determination of oxygen uptake (V˙O2) in critically ill patients. Whereas these metabolic gas monitoring systems (MBM) are assumed to measure total body V˙O2, the reversed Fick method in principle excludes intrapulmonary V˙O2. Previous clinical reports comparing V˙O2 measured by the reversed Fick principle (V˙O2  Fick) with V˙O2 measured by MBM (V˙O2  MBM) found that V˙O2  MBM was significantly greater than V˙O2  Fick. It was suggested that these differences between methods represent V˙O2 of pulmonary and bronchial tissue, as intrapulmonary V˙O2 had been estimated to account for 15% of total body V˙O2 in dogs with experimental pneumonia. The objective of this study was to compare V˙O2  Fick with V˙O2  MBM in patients with and without pneumonia and to assess the reproducibility of both methods in critically ill patients. Method. With institutional approval nine critically ill patients with acute pneumonia were studied under controlled mechanical ventilation. The diagnosis of pneumonia was based on respective changes of chest X-rays, body temperature 〉38 °C, and WBC counts 〉12,000/mm3. Inspiratory oxygen fractions (FIO2) ranged from 0.3 to 0.6; all patients routinely received opioids and hypnotics. Complete muscle relaxation was achieved during the periods of measurement to avoid sudden changes in V˙O2 due to shivering or involuntary movements. Arterial and pulmonary-arterial blood samples were drawn simultaneously after aspiration of the sevenfold catheter dead space. Measurements of haemoglobin concentration (Hb), fractional oxygen saturation (SO2), and O2 partial pressure (PO2) were performed by use of a calibrated haemoximeter and blood gas analyser, respectively; 2×5 thermodilution measurements of cardiac output (CO) were spread randomly over the respiratory cycle for each determination of V˙O2  Fick. To minimise systematic errors of CO measurements, the CO computer was calibrated in an extracorporeal model using an electromagnetic flowmeter. Calculations of V˙O2  Fick were based on an oxygen binding capacity of 1.39 ml/g Hb. Simultaneous measurements of V˙O2  MBM were obtained by use of a Datex Deltatrac MBM that had been validated in vitro with a gas dilution model of respiratory gas exchange. Calibration of the MBM was performed prior to each measurement. Gas supply of the respirator was provided by an external high-precision mixing device to reduce errors in V˙O2 measurements that may arise from short-term oscillations in FIO2. All patients with pneumonia were studied on three consecutive days; thus, measurements from 27 days could be analysed. On each day two sets of measurements were performed at an interval of 60 min to assess the reproducibility of differences between methods. During each set of measurements duplicate blood samples were drawn twice, before and after thermodilution measurements of CO, to evaluate the short-term repeatability of V˙O2  Fick. The beginning and the end of each set of measurements were marked in the computer record of the MBM to assess the respective repeatability of V˙O2  MBM. Fifty control measurements were performed in ten patients undergoing major neurosurgical procedures. None of these patients exhibited signs of pulmonary infection. Except for the number of repeated measures, all V˙O2 measurements were obtained in the same way as in the study group. Descriptive statistical analysis was performed according to Bland and Altman; comparisons between methods were done by multivariate analysis of variance for repeated measures. Results. Neither in the study group nor in the control group could a significant difference between methods be demonstrated. In patients with pneumonia the mean difference between methods (V˙O2  Fick−V˙O2  MBM) was 15.2 ml/min (4.2%); the double standard deviation of differences (2 SD) was 59.2 ml/min (19.2%). Control patients exhibited a mean difference of 7.2 ml/min (3.1%); 2 SD was 41.1 ml/min (20.4%). Duplicate determinations of V˙O2  Fick and V˙O2  MBM within one set of measurements showed a repeatability coefficient (2 SD of differences between repeated measures) of 43.8 ml/min (13.2%) and 15.3 ml/min (5.1%), respectively. The large variation of duplicate measurements of V˙O2  Fick was caused rather by the variability of arteriovenous O2 content determinations than by the variability of CO measurements. Discussion. These results are in contrast to previous method comparison studies, which suggested that in infected lungs V˙O2 of pulmonary and bronchial tissue represents up to 15% of total body V˙O2. Since the mean differences between V˙O2  Fick and V˙O2  MBM did not differ between the two groups of patients, pulmonary infection did not seem to cause a considerable increase in intrapulmonary V˙O2. A minor effect of intrapulmonary V˙O2 on differences between methods cannot be excluded because of the variability of data. The poor repeatability of V˙O2  Fick measurements, however, seems to limit the use of method comparison studies for estimation of intrapulmonary V˙O2.
    Notes: Zusammenfassung. Automatisierte metabolische Monitorsysteme (MBM) ermöglichen nahezu kontinuierliche Messungen der Sauerstoffaufnahme (V˙O2) aus respiratorischen Gasen. Das inverse Ficksche Prinzip unterscheidet sich bei der Bestimmung der Gesamt-V˙O2 von diesen Verfahren insofern, als die intrapulmonale V˙O2 durch Lungen- und Bronchialgewebe nicht mit erfaßt wird. In der vorliegenden Untersuchung wurde daher unter besonderer Berücksichtigung der Methodenreproduzierbarkeit das inverse Ficksche Prinzip (V˙O2 Fick) mit V˙O2-Messungen aus respiratorischen Gasen (V˙O2  MBM) verglichen. Unter der Annahme, daß akute entzündliche Lungenerkrankungen zur Steigerung des intrapulmonalen Anteils der V˙O2 führen, wurden Vergleichsmessungen sowohl bei kritisch kranken Patienten mit akuter Pneumonie (n=9) als auch bei lungengesunden Kontrollpatienten (n=10) durchgeführt. Weder in der Studien- noch in der Kontrollgruppe fand sich eine signifikante Differenz zwischen den untersuchten Meßverfahren. Die mittlere relative Methodendifferenz V˙O2  Fick−V˙O2  MBM betrug +4,2% (2 SD=19,2%) in der Studiengruppe und +3,1% (2 SD=20,4%) in der Kontrollgruppe. V˙O2  Fick-Bestimmungen wiesen in Abhängigkeit von der Anzahl der gemittelten Blutanalysen eine zwei- bis dreifach schlechtere Reproduzierbarkeit auf als simultane V˙O2  MBM-Messungen. Die vorliegenden Befunde widersprechen der Hypothese, daß die intrapulmonale O2-Aufnahme bei Patienten mit pulmonalen Infektionen bis zu 15% der Gesamtkörper-V˙O2 repräsentiert. Ferner ist aufgrund der engen Übereinstimmung der systematischen Methodendifferenzen von Studien- und Kontrollpatienten nicht von einer klinisch bedeutsamen Steigerung der intrapulmonalen V˙O2 infolge von Pneumonien auszugehen.
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  • 2
    ISSN: 1432-055X
    Keywords: Schlüsselwörter: HZV-Messung – Pulmonaler Blutfluß– Thermodilutionsmethode – Intrakardialer Links-Rechts-Shunt ; Key words: Cardiac output measurement – Pulmonary blood flow – Thermodilution method – Intracardiac left-to-right shunt
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Abstract. Thermodilution measurements of cardiac output (CO) by means of Swan-Ganz catheters, in a strict sense, represent pulmonary arterial blood flow (PBF). In principle, this is also true in the presence of intracardiac left-to-right shunts due to atrial or ventricular septal defects. However, early recirculation of indicator may give rise to serious methodological problems in these cases. We sought to determine the influence of intracardiac left-to-right shunts on different devices for thermodilution measurements of CO using an extracorporeal flow model. Methods. Blood flow was regulated by means of a centrifugal pump that at the same time enabled complete mixing of the indicator after injection (Fig. 1). Pulmonary and systemic parts of the circulation were simulated using two membrane oxygenators and a systemic-venous reservoir to delay systemic recirculation of indicator. Control measurements of PBF (Qp) and systemic (Qs) blood flow were performed by calibrated electromagnetic flow-meters (EMF). Blood temperature was kept constant using a heat exchanger without altering the indicator mass balance in the pulmonary circulation. Left-to-right shunt was varied at different systemic flow levels applying a Qp:Qs ratio ranging from 1:1 to 2.5:1. Thermodilution measurements of PBF were performed using two different thermodilution catheters that were connected to commercially available CO computers. Additionally, thermodilution curves were recorded on a microcomputer and analysed with custom-made software that enabled iterative regression analyses of the initial decay to determine that part of the downslope that best fits a monoexponentially declining function. Extrapolation of the thermodilution curve was then based on the respective curve segment in order to eliminate indicator recirculation due to shunt flow. Results. At moderate left-to-right shunts (Qp:Qs〈2:1) all thermodilution measurements showed close agreement with control measurements. At higher shunt flows (Qp:Qs≥2:1), however, conventional extrapolation procedures of CO computers considerably underestimated PBF (Fig. 2). This was particularly true when a slow-response thermistor catheter was used (Fig. 3). The reason for this underestimation of Qp was an overestimation of the area under curve because of inadequate mathematical elimination of indicator recirculation by standard truncation methods (Fig. 4). However, curve-alert messages of the commercially implemented software did not occur. A high level of agreement could be consistently obtained using a fast-response thermistor together with individual definition of extrapolation limits according to logarithmic regression analyses. Discussion and conclusion. Under varying levels of left-to-right shunt, both the reponse time of thermodilution catheters and the algorithms for calculation of flow considerably influenced the validity of thermodilution measurements of PBF in an extracorporeal flow model. The use of computer-based regression analyses to define the optimal segment for monoexponential extrapolation could effectively eliminate indicator recirculation from the initial portion of the declining thermodilution curve and showed the closest agreement with EMF measurements of Qp. The quality of thermodilution curves with respect to recirculation peaks in the flow model was slightly better than in clinical routine. Nevertheless, the clinical applicability of the modified extrapolation algorithm could be illustrated during pulmonary thermodilution measurements in an exemplary patient with a ventricular septal defect (Fig. 5). PBF at extremely high shunt ratios, however, cannot be assessed by monoexponential extrapolation in principle (Fig. 6). Insufficient elimination of indicator recirculation resulted in flow values that closely resembled systemic rather than PBF. This finding is in accordance with a mathematical analysis of the underlying Steward-Hamilton equation if an infinite number of recirculations would be included in the area under curve.
    Notes: Zusammenfassung. Thermodilutionsmessungen des HZV mittels pulmonal-arterieller Einschwemmkatheter repräsentieren im engeren Sinne den pulmonalen Blutfluß (Qp). Bei Vorliegen eines Vorhof- oder Ventrikelseptumdefekts können jedoch unphysiologisch frühe Rezirkulationen des injizierten Indikators zu methodischen Problemen führen. In der vorliegenden Untersuchung wurde daher in einem Kreislaufmodell der Einfluß eines Links-Rechts-Shunts auf 2 unterschiedliche HZV-Meßsysteme überprüft. Die Flußmessungen erfolgten bei 37 °C in zirkulierendem Blut unter Variation des Qp:Qs-Verhältnisses von 1:1 bis 2,5:1, eine Zentrifugalpumpe diente als Flußgenerator und als Mischkammer für den injizierten Indikator. Referenzmessungen des pulmonalen und des systemischen Stromzeitvolumens (Qs) wurden mittels elektromagnetischer Flowmeter durchgeführt. Hohe Shuntvolumina führten aufgrund einer mangelhaften Diskriminierung der Shunt-bedingten Kälterezirkulation zu einer erheblichen Unterschätzung des aktuellen Qp. Abweichungen von den Referenzflußmessungen fanden sich insbesondere bei einer vergleichsweise hohen Zeitkonstante des verwendeten Thermistors sowie bei Verwendung konventioneller Auswertungsalgorithmen, die eine monoexponentielle Extrapolation auf der Basis eines schematisch definierten Kurvenintervalls beinhalten. Die mangelnde Abgrenzung rezirkulierender Indikatoranteile führte zur Ermittlung eines Stromzeitvolumens, das an Stelle von Qp näherungsweise Qs repräsentierte. Eine bessere Übereinstimmung mit Qp-Referenzmessungen konnte durch ein dem Einzelfall angepaßtes Extrapolationsverfahren erzielt werden, das mittels Regressionsanalysen denjenigen Kurvenabschnitt ermittelt, der einem monoexponentiellen Abfall tatsächlich am nächsten kommt.
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  • 3
    ISSN: 1432-1238
    Keywords: Oxygen consumption ; Carbon dioxide ; Pediatric ; Indirect calorimetry ; Energy expenditure ; Mechanical ventilation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objective A paediatric option for the measurement of $$\dot VO_2$$ and $$\dot VCO_2$$ (20 to 150 ml/min) has recently been introduced for the adult Deltatrac metabolic monitor (Datex Instrumentarium, Finland) to use in ventilated and spontaneously breathing children. This paper describes a laboratory validation of the paediatric option for ventilated children with regard to the influence of respiratory variables. Design Respiratory variables were varied within the following ranges: FIO2 0.21–0.8, $$\overline {FEO_2 }$$ (DFO2) 0.01–0.05, $$\overline {FECO_2 } 0.01 - 0.05,\dot V_E 300 - 6000ml/\min$$ , VT 8–300 ml, RR 10–50/min, Paw 10–60 mbar, relative humidity 10% and 60%, and resulted in 107 test situations. Setting Gas exchange was simulated by injection of nitrogen and CO2 at a RQ close to 1. Patients or participants Different situations of paediatric patients ventilated in controlled mode were simulated on a gas injection model. Interventions Respiratory and metabolic variables were varied independently to result in a range of 8 to 210 ml/min of $$\dot VO_2$$ and $$\dot VCO_2$$ . Measurements and results Reference measurements were carried out by mass spectrometry and wet gas spirometry. The mean $$\dot VCO_2$$ difference for all tests ranging from 20 ml/min to 210 ml/min was −2.4% (2SD=±12%). The respective $$\dot VO_2$$ difference was −3.2% (2SD=±23%). Measurement agreement for $$\dot VO_2$$ in neonatal respirator treatment (20–50 ml/min) compared to older children (50–210 ml/min) showed a mean difference of −3.9% (2SD=±26%) versus −2.8% (2SD=±20%). The respective differences for $$\dot VCO_2$$ were −7.1% (2SD=±7%) versus +0.4% (2SD=±10%). The mean difference for $$\dot VO_2$$ as well as $$\dot VCO_2$$ indicated a high systematic agreement of both methods. The variability (±2SD) in $$\dot VCO_2$$ measurement is acceptable for all applications. The overall variability in $$\dot VO_2$$ measurement (2SD=±23%) can be reduced by exclusion of all tests with a $${FECO_2 }$$ and DFO2 below 0.03. This results in a mean difference of −3.2% (2SD=±13.7%). Conclusion Within this limitation the paediatric measurement option seems to introduce a valuable method for clinical application in paediatric intensive care medicine.
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  • 4
    ISSN: 1432-1238
    Keywords: Oxygen consumption ; Ventilation, mechanical ; Ventilator weaning ; Post-operative period ; Chronic obstructive pulmonary disease ; Work of breathing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objective We investigated the effects of continuous positive airway pressure (CPAP) and pressure support ventilation (PSV) on the oxygen cost of breathing ( $$\dot V$$ O2resp) for different states of pulmonary function. Additionally $$\dot V$$ O2resp was measured during spontaneous breathing. Design This was done in a controlled and prospective study. Ventilatory modes were applied randomly. Setting Measurements were performed in a quiet room on volunteers (VOL) and inpatients treated for chronic obstructive pulmonary disease (COPD). Post-operative patients after aortocoronary bypass surgery (ACB) were studied on the cardio-thoracic intensive care unit just before and after extubation. Patients Healthy volunteers (n=14), postoperative patients after aorto-coronary bypass surgery (n=15) and patients with COPD (n=9), xFEV1 47.7%) were the objects of study. Interventions Demand flow CPAP (5 mbar) and PSV (7 mbar, PEEP 5 mbar), using the Hamilton Veolar ventilator, were investigated in comparison to spontaneous breathing. Measurements and results $$\dot V$$ O2 measured by a Datex Deltatrac metabolic monitor. $$\dot V$$ O2resp was calculated by subtraction of total oxygen uptake $$\dot V$$ O2tot) in controlled mode ventilation (CMV) from that in the respective spontaneous breathing mode. For VOL and COPD patients who were not intubated, a CPAP facemask connected to a short 7.5 mm tube was used as connection to the ventilator. Breathing spontaneously under a canopy system VOL showed a VO2resp of 4.5±4.0% compared to 9.2±3.5% for ACB and 15.4±7.7% for COPD. CPAP changed the VO2resp to 7.8±3.9%, 12.0±4.0% and 9.1±3.6% respectively. PSV reduced the $$\dot V$$ O2resp to 7.9±3.8% in ACB and 7.7±5.5% in COPD. Conclusions This investigation confirms findings that postoperative patients have a mild increase in $$\dot V$$ O2resp. COPD exhibit the highest increase in VO2resp. Tracheal tubes, masks and CPAP on a demand flow apparatus increases $$\dot V$$ O2resp in volunteers and postoperative patients after cardiac surgery. The same amount of CPAP in contrary reduces $$\dot V$$ O2resp in patients with COPD. Pressure support ventilation can offset the additional $$\dot V$$ O2resp induced by CPAP but at the same level does not further reduce $$\dot V$$ O2resp in COPD patients.
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  • 5
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    German Medical Science GMS Publishing House; Düsseldorf
    In:  Learning through Inquiry in Higher Education: Current Research and Future Challenges (INHERE 2018); 20180308-20180309; München; DOC31 /20180301/
    Publication Date: 2018-03-02
    Keywords: ddc: 610
    Language: English
    Type: conferenceObject
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  • 6
    ISSN: 0273-1177
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 7
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters A 15 (1965), S. 240-241 
    ISSN: 0375-9601
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    ISSN: 0378-4371
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters A 93 (1982), S. 81-82 
    ISSN: 0375-9601
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters A 70 (1979), S. 323-325 
    ISSN: 0375-9601
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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