Biomedical subjects

Michael Quintel

Publications and source records attributed to Michael Quintel.

26 records · Page 2Linked to original sources

PubMed2003

Measurements of alveolar pO2 using 19F-MRI in partial liquid ventilation.

RATIONALE AND OBJECTIVES: Partial liquid ventilation using Perfluorcarbon (PFC) is an innovative treatment of acute respiratory distress syndrome. However, the underlying mechanisms are not totally clear. The aim was to investigate the distribution of oxygen partial pressure within the PFC-filled lung (ppO2). METHODS: Nine pigs underwent partial liquid ventilation, receiving 20 mL PFC/kg bodyweight (bw). Measurements were obtained by a chemical shift selective TurboFLASH sequence at different axial lung levels. ppO2 was calculated from 19F-MRI by nonlinear curve T1-fitting technique after noise correction. RESULTS: Quantification and distribution of ppO2 was performed successfully. A narrow relationship of the inspiratory O2 fraction and ppO2, as well as a significant ventral-to-dorsal gradient of ppO2 (ventral:dependent lung = 1.9:1) were detected in all subjects and slice positions. CONCLUSIONS: In vivo measurement of local ppO2 gains new and clinical important insights into the physiology of PLV. The previously unknown ppO2 gradient within PFC fits to distribution of perfusion. Dependent lung regions appear to have limited access to O2 from central airways.

Animals↗

PubMed2002

Extracellular ubiquitin inhibits the TNF-alpha response to endotoxin in peripheral blood mononuclear cells and regulates endotoxin hyporesponsiveness in critical illness.

Ubiquitin is suggested to play a key role in essential intracellular functions, such as heat shock response, protein breakdown, and regulation of immune responses. Ubiquitin has also been detected in the extracellular space, but the function and biologic significance is unclear. We describe a new function of extracellular ubiquitin and show that extracellular ubiquitin specifically inhibits ex vivo secretion of tumor necrosis factor-alpha (TNF-alpha) and TNF-alpha mRNA expression from peripheral blood mononuclear cells (PBMNCs) in response to endotoxin in a dose-dependent manner. In contrast, the TNF-alpha response to zymosan or Staphylococcus aureus as well as the interleukin-6 (IL-6) and IL-8 responses to endotoxin were unaffected by ubiquitin. Measurement of serum ubiquitin levels showed a significant 5- to 7-fold increase in sepsis and trauma patients, to the level required for inhibition of the PBMNC TNF-alpha response to endotoxin by ubiquitin. Elevated ubiquitin levels in serum were significantly correlated with a reduced TNF-alpha production. Antibodies to ubiquitin were able to (1) significantly increase (2- to 5-fold) the TNF-alpha response to endotoxin in whole blood from trauma and sepsis patients, (2) completely neutralize the inhibitory effect of trauma patients' serum on healthy donors' TNF-alpha production, and (3) partially neutralize the inhibitory effect of sepsis patients' serum on healthy donors' TNF-alpha production. Ubiquitin-depleted serum from trauma patients lost the inhibitory activity for TNF-alpha production, whereas extracted endogenous ubiquitin exerts the inhibitory activity. The results demonstrate that extracellular ubiquitin acts as a cytokinelike protein with anti-inflammatory properties and indicate that extracellular ubiquitin is involved in the regulation of immunodepression in critical illness.

Adult↗

PubMed2002

19F-MRI of perflubron for measurement of oxygen partial pressure in porcine lungs during partial liquid ventilation.

A method for in vivo measurement of oxygen partial pressure (pO2) in porcine lungs during partial liquid ventilation (PLV) with perflubron (PFOB) was developed. A pulse sequence for high-resolution MRI of the distribution of PFOB in the lung after intratracheal administration was developed as well. Moreover, quantitative measurements of longitudinal relaxation time T(1) of (19)F resonances for assessment of regional pO2 are described. Due to the need to acquire data during a single expiratory breathhold, only low SNRs were achieved in vivo. Therefore, simulations were performed to investigate the influence of background noise on T(1) values calculated from data with low SNR. Based on these simulations, a postprocessing strategy was developed to correct for systematic errors by background noise prior to quantitative analysis. Results of a pilot study in pigs under conditions of PLV are presented.

Animals↗

PubMed2002

Regional lung perfusion as determined by electrical impedance tomography in comparison with electron beam CT imaging.

The aim of the experiments was to check the feasibility of pulmonary perfusion imaging by functional electrical impedance tomography (EIT) and to compare the EIT findings with electron beam computed tomography (EBCT) scans. In three pigs, a Swan-Ganz catheter was positioned in a pulmonary artery branch and hypertonic saline solution or a radiographic contrast agent were administered as boli through the distal or proximal openings of the catheter. During the administration through the proximal opening, the balloon at the tip of the catheter was either deflated or inflated. The latter case represented a perfusion defect. The series of EIT scans of the momentary distribution of electrical impedance within the chest were obtained during each saline bolus administration at a rate of 13/s. EBCT scans were acquired at a rate of 3.3/s during bolus administrations of the radiopaque contrast material under the same steady-state conditions. The EIT data were used to generate local time-impedance curves and functional EIT images showing the perfusion of a small lung region, both lungs with a perfusion defect and complete both lungs during bolus administration through the distal and proximal catheter opening with an inflated or deflated balloon, respectively. The results indicate that EIT imaging of lung perfusion is feasible when an electrical impedance contrast agent is used.

Animals↗

PubMed2002

Detection of local lung air content by electrical impedance tomography compared with electron beam CT.

The aim of the study was to validate the ability of electrical impedance tomography (EIT) to detect local changes in air content, resulting from modified ventilator settings, by comparing EIT findings with electron beam computed tomography (EBCT) scans obtained under identical steady-state conditions. The experiments were carried out on six anesthetized supine pigs ventilated with five tidal volumes (VT) at three positive end-expiratory pressure (PEEP) levels. The lung air content changes were determined both by EIT (Goe-MF1 system) and EBCT (Imatron C-150XP scanner) in six regions of interest, located in the ventral, middle, and dorsal areas of each lung, with respect to the reference air content at the lowest VT and PEEP, as a change in either local electrical impedance or lung tissue density. An increase in local air content with VT and PEEP was identified by both methods at all regions studied. A good correlation between the changes in lung air content determined by EIT and EBCT was revealed. Mean correlation coefficients in the ventral, middle, and dorsal regions were 0.81, 0.87, and 0.93, respectively. The study confirms that EIT is a suitable, noninvasive method for detecting regional changes in air content and monitoring local effects of artificial ventilation.

Animals↗

PubMed2002

Pancreatic phospholipase A2 activity in acute pancreatitis: a prognostic marker for early identification of patients at risk.

Remarkably elevated levels of phospholipase A2 (PLA2) are measurable in human blood samples in cases of acute pancreatitis. The source of the enzyme was first thought to be exclusively the pancreas, but now it is generally accepted that two isoenzymes--the pancreatic PLA2, group I, and the extrapancreatic PLA2, group II--contribute to the raised activity. In contrast to the group II-PLA2, the pancreatic PLA2 is heat-resistant for 1 hour at 60 degrees C. The catalytically inactive proenzyme of the pancreatic PLA2 can be activated by trypsin. The aim of our study was to evaluate the diagnostic value of PLA2 isoenzyme activity measurements to identify patients with severe complications in acute pancreatitis. Blood samples from patients suffering from acute pancreatitis were analyzed for catalytically active pancreatic PLA2 on day 1 and 2 of hospitalization with a modified radiometric Escherichia coli-based PLA2 assay. In 10 of 41 patients clearly elevated values of catalytically active, heat-resistant pancreatic PLA2 (7.2 to 81.2 U/l) were observed. This group of patients was characterized by severe complications (necrotizing pancreatitis, shock, sepsis, respiratory problems) of which two patients subsequently died. Patients with low or undetectable activity (<7 U/l) of pancreatic PLA2 recovered rapidly. According to these results the presence of catalytically active pancreatic PLA2 in serum is associated with severe complications of acute pancreatitis. In contrast to total serum-PLA2, the catalytic concentration of pancreatic PLA2 can serve as a prognostic marker in acute pancreatitis.

Adult↗

PubMedDate not supplied

Comparison of static airway pressures during total liquid ventilation while applying different expiratory modes and time patterns.

To compare pump driven (active) and gravity-siphon (passive) expiration modes during perfluorocarbon total liquid ventilation (TLV), a liquid ventilator was developed capable of providing either expiration mode. In a prospective, controlled laboratory study, 90 rabbits (3.2 +/- 0.1 kg) were anesthetized, tracheotomized, killed. After prefill with 12 ml/kg perflubron and TLV for 90 minutes (tidal volume 12 ml/kg, I:E ratio 1:2), randomly using passive (height 40 or 80 cm) or active expiration, respiratory rates were 4, 8, or 12/min. Static peak inspiratory and end-expiratory intratracheal pressures were measured at 5 minute intervals. Peak inspiratory and end-expiratory were constant in active groups, and increases in all 40 cm and 80 cm passive groups were significant. Differences between groups were significant for expiratory mode but not for respiratory rates. Only passive groups showed significant increases in body weight after TLV. Percentage of fluorothoraces was 10% using active and 85% using passive expiration. Based upon the stability of intrapulmonary pressures and volumes and a reduced rate of fluorothoraces, active expiration is more efficient than passive drainage during TLV.

Animals↗

PubMedDate not supplied

Comparison of different inhalational perfluorocarbons in a rabbit model of acute lung injury.

The purpose of this study was to investigate the influence of different inhaled perfluorocarbons (PFC) upon pulmonary mechanics and gas exchange in a saline lavage model of acute lung injury. A randomized, controlled animal trial was conducted at the university hospital laboratory. Pulmonary gas exchange (pGE), static compliance (Cst), and basic hemodynamics (heart rate [HR], arterial [AP] and central venous pressures [CVP]) were compared. After induction of lung injury by repeated pulmonary lavage with saline solution, 35 New Zealand rabbits (3 +/- 0.2 kg) were randomized into five groups with seven animals each: 1) conventional ventilated control, 2) perfluorooctane (octane), 3) Perflubron (perfluorooctylbromide [PFOB]), 4) Perfluoro-1,3,5-trimethylcyclohexane (PP 4), and 5) perfluorohexane (hexane). Consecutively, PFC groups were subjected to a 120 minute study period applying mechanical ventilation (tidal volume of 7 ml/kg) in conjunction with PFC performed by a modified halothane vaporizer. Amount of vaporization was controlled by weighing the vaporizer at approximately 25 ml/h/kg body-weight PFC. Controls remained gas ventilated. After injury, PaO2 was control = 53 +/- 13 mbar, octane = 55 +/- 24 mbar, perflubron = 57 +/- 18 mbar, PP4 = 68 +/- 25 mbar, and hexane = 51 +/- 16 mbar. Within the 120 minute period, PaO2 was control = 51 +/- 19 mbar, octane = 42 +/- 6 mbar, perflubron = 40 +/- 11 mbar, PP4 = 47 +/- 10 mbar, and hexane = 60 +/- 8 mbar, respectively. At baseline, after injury, and throughout the study period, pGE and Cst, as well as HR, AP, and CVP, did not significantly differ when compared with octane, PP4, PFOB, and controls (p > 0.05), whereas hexane significantly improved pGE and Cst (p < 0.05). From four different inhaled perfluorocarbons, only perfluorohexane has measureable impact upon gas exchange and lung mechanics when compared with a conventional lung protective ventilation mode.

Administration, Inhalation↗