Biomedical subjects

J Guttmann

Publications and source records attributed to J Guttmann.

At least 37 records · Page 2Linked to original sources

PubMed2000

Static versus dynamic respiratory mechanics for setting the ventilator.

The lower inflection point (LIP) of the inspiratory limb of a static pressure-volume (PV) loop is assumed to indicate the pressure at which most lung units are recruited. The LIP is determined by a static manoeuvre with a PV-history that is different from the PV-history of the actual ventilation. In nine surfactant-deficient piglets, information to allow setting PEEP and VT was obtained, both from the PV-curve and also during ongoing ventilation from the dynamic compliance relationship. According to LIP, PEEP was set at 20 (95% confidence interval 17-22) cm H2O. Volume-dependent dynamic compliance suggested a PEEP reduction (to 15 (13-18) cm H2O). Pulmonary gas exchange remained satisfactory and this change resulted in reduced mechanical stress on the respiratory system, indirectly indicated by volume-dependent compliance being consistently great during the entire inspiration.

Animals↗

PubMed2000

Continuous calculation of intratracheal pressure in the presence of pediatric endotracheal tubes.

OBJECTIVE: To measure the pressure-flow relationship of pediatric endotracheal tubes (ETTs) in trachea models, to mathematically describe this relationship, and to evaluate in trachea/lung models a method for calculation of pressure at the distal end of the ETT (Ptrach) by subtracting the flow-dependent pressure drop across the ETT from the airway pressure measured at the proximal end of the ETT. DESIGN: Trachea models and trachea/lung models. SETTING: Research laboratory in a university medical center. INTERVENTIONS: The pressure-flow relationship of pediatric ETTs (inner diameter, 2.5-6.5 mm) was determined using a physical model consisting of a tube connector, an anatomically curved ETT, and an artificial trachea. The model was ventilated with sinusoidal gas flow (12-60 cycles/min). The coefficients of an approximation equation considering ETT resistance and inertance were fitted separately to the measured pressure-flow curves for inspiration and expiration. Calculated Ptrach was compared with directly measured Ptrach in mechanically ventilated physical trachea/lung models. MEASUREMENTS AND MAIN RESULTS: The pressure-flow relationship was considerably nonlinear and showed hysteresis around the origin caused by the inertia of accelerated gas. ETT inertance ranged from 0.1 to 0.4 cm H2O/L x sec2 (inner diameter, 6-2.5 mm). The abrupt change in cross-sectional area at the tube connector caused an inspiration-to-expiration asymmetry. Calculated and measured Ptrach were within +/- 1 cm H2O. Correspondence between measured and calculated Ptrach is improved even further when the ETT inertance is taken into account. CONCLUSIONS: Ptrach can continuously be monitored in the presence of pediatric ETT by combining ETT coefficients and the flow and airway pressure continuously measured at the proximal end of the ETT.

Adolescent↗

PubMed2000

Respiratory comfort and breathing pattern during volume proportional assist ventilation and pressure support ventilation: a study on volunteers with artificially reduced compliance.

OBJECTIVE: To assess respiratory comfort and associated breathing pattern during volume assist (VA) as a component of proportional assist ventilation and during pressure support ventilation (PSV). DESIGN: Prospective, double-blind, interventional study. SETTING: Laboratory. SUBJECTS: A total of 15 healthy volunteers (11 females, 4 males) aged 21-31 yrs. INTERVENTIONS: Decreased respiratory system compliance was simulated by banding of the thorax and abdomen. Volunteers breathed via a mouthpiece with VA and PSV each applied at two levels (VA, 8 cm H2O/L and 12 cm H2O/L; PSV, 10 cm H2O and 15 cm H2O) using a positive end-expiratory pressure of 5 cm H2O throughout. The study was subdivided into two parts. In Part 1, volunteers breathed three times with each of the four settings for 2 mins in random order. In Part 2, the first breath effects of multiple, randomly applied mode, and level shifts were studied. MEASUREMENTS AND MAIN RESULTS: In Part 1, the volunteers were asked to estimate respiratory comfort in comparison with normal breathing using a visual analog scale. In Part 2, they were asked to estimate the change of respiratory comfort as increased, decreased, or unchanged immediately after a mode shift. Concomitantly, the respiratory pattern (change) was characterized with continuously measured tidal volume, respiratory rate, pressure, and gas flow. Respiratory comfort during VA was higher than during PSV. The higher support level was less important during VA but had a major negative influence on comfort during PSV. Both modes differed with respect to the associated breathing pattern. Variability of breathing was higher during VA than during PSV (Part 1). Changes in respiratory variables were associated with changes in respiratory comfort (Part 2). CONCLUSIONS: For volunteers breathing with artificially reduced respiratory system compliance, respiratory comfort is higher with VA than with PSV. This is probably caused by a better adaptation of the ventilatory support to the volunteer's need with VA.

Adult↗

PubMed2000

Analysis of nonlinear volume-dependent respiratory system mechanics in pediatric patients.

OBJECTIVE: Analysis of dynamic respiratory system mechanics is generally based on a resistance-compliance model in which nonlinearities of the respiratory mechanics indices are not considered. The recently developed SLICE method analyzing consecutive volume slices of the tidal volume was used for determination of non-linear volume-dependent respiratory system mechanics. Volume-dependent compliance C(Slice) and resistance R(Slice) were compared with C(MLR) and R(MLR) obtained by standard multiple linear regression analysis (MLR). DESIGN: Prospective observational study. SETTING: Pediatric intensive care unit in a university hospital. PATIENTS: Fifteen pediatric patients, aged 24 days to 9.6 yrs, weighing 3-67.5 kg. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: With respect to their pulmonary status, the patients were grouped into three clinical groups: patients with no lung diseases, patients with restrictive lung diseases, and patients with obstructive lung diseases. All patients were mechanically ventilated via a cuffed endotracheal tube in the pressure-controlled mode. Flow and airway pressure were measured at the proximal end of the tube and tracheal pressure was continuously calculated. Respiratory mechanics were determined either with the SLICE method or, as reference, by using standard MLR. In most patients, the pressure-volume relationship was nonlinear, particularly in patients with restrictive and obstructive lung diseases. In the presence of considerable nonlinearity, the volume-dependent respiratory mechanics indices obtained by the SLICE method showed better agreement between recalculated and original pressure-volume loops compared with the MLR results. Furthermore, signs of overdistension of the patient's lung became obvious when using the SLICE method, whereas they were undetected by MLR. CONCLUSIONS: The SLICE method is well suited for the analysis of nonlinear volume-dependent respiratory system mechanics in pediatric patients. The SLICE method may be used as a first step toward an adaptation of ventilator settings with respect to the actual mechanical status of the patient's respiratory system, and, to prevent pulmonary overdistension.

Journal Article↗

PubMed2000

Detection of sleep apnea with the forced oscillation technique compared to three standard polysomnographic signals.

BACKGROUND: The forced oscillation technique (FOT) allows analysis of the upper airway impedance and, hence, detection of obstructive sleep apnea. OBJECTIVE: To evaluate FOT with respect to sensitivity and to specificity in online detection of sleep-disordered breathing patterns and to compare algorithmic onset detection time with manual onset time markers of staff physicians. METHODS: We compared the absolute value mid R:Zmid R: of the impedance with three routinely obtained polysomnographic signals - nasal airflow V(nasal), thoracic excursion Thox and esophageal pressure P(es) - by retrospective analysis of the diagnostic polysomnograms of 51 patients. For each signal we evaluated algorithms for online detection of respiratory events. For each out of five apnea classes, 50 respiratory events marked by staff physicians were drawn randomly from the 51 polysomnograms to optimize the online detection algorithms (learning set). The algorithm analyzes relative changes of signal baseline and amplitude. Again 50 respiratory events were drawn randomly for each apnea class to examine to what extent it is possible to detect event onsets with the algorithms (test set). RESULTS: The sensitivity of the signals varied between 56 and 94% and was on average 74%. The specificity was 96 +/- 1.5% on average. The onset was detected 4-6 s after the initially evaluated onset of the staff physicians. CONCLUSION: We conclude that nasal airflow and FOT are equivalent sensitive measurands for detection of respiratory events.

Adult↗

PubMed2000

Compliance is nonlinear over tidal volume irrespective of positive end-expiratory pressure level in surfactant-depleted piglets.

Between the lower and the upper inflection point of a quasistatic pressure-volume (PV) curve, a segment usually appears in which the PV relationship is steep and linear (i.e., compliance is high, with maximal volume change per pressure change, and is constant). Traditionally it is assumed that when positive end-expiratory pressure (PEEP) and tidal volume (V T) are titrated such that the end-inspiratory volume is positioned at this linear segment of the PV curve, compliance is constant over VT during ongoing ventilation. The validity of this assumption was addressed in this study. In 14 surfactant-deficient piglets, PEEP was increased from 3 cm H(2)O to 24 cm H(2)O, and the compliance associated with 10 consecutive volume increments up to full VT was determined with a modified multiple-occlusion method at the different PEEP levels. With PEEP at approximately the lower inflection point, compliance was minimal in most lungs and decreased markedly over VT, indicating overdistension. Compliance both increased and decreased within the same breath at intermediate PEEP levels. It is concluded that a PEEP that results in constant compliance over the full VT range is difficult to find, and cannot be derived from conventional respiratory-mechanical analyses; nor does this PEEP level coincide with maximal gas exchange.

Animals↗

PubMed2000

Respiratory system inertance: investigation in a physical inertance model.

For analysis of respiratory system mechanics the very complex structure of the respiratory system is strongly simplified to a simple resistance-compliance-model. While for most patients this simplification seems sufficient, in patients with pulmonary disease this model is inappropriate. Additionally, to regional inhomogeneity throughout the lung, large volume accelerations due to the strongly decreased respiratory system compliance together with a mass increase of the patients' lungs, i.e. an increased respiratory system inertance Irs, result in a significant inertive pressure contribution. The aim of this study was to develop a physical inertance model, and its description by conventional methods of respiratory monitoring. Its parameters are adjustable within the physiological range, with Irs between 0.06 and 0.2 mbar.s2.l-1. The model proved well with static and dynamic analysis of respiratory system parameters. Using our physical model it is possible to evaluate new methods of respiratory monitoring and to investigate experimentally the interrelationship of respiratory system parameters.

Airway Resistance↗

PubMed1999

Additional inspiratory work of breathing imposed by tracheostomy tubes and non-ideal ventilator properties in critically ill patients.

OBJECTIVE: To determine the tracheostomy tube-related additional work of breathing (WOBadd) in critically ill patients and to show its reduction by different ventilatory modes. DESIGN: Prospective, clinical study. SETTING: Medical ICU of a university teaching hospital. INTERVENTION: Standard tracheostomy due to prolonged respiratory failure. MEASUREMENTS AND RESULTS: Ten tracheostomized, spontaneously breathing patients were investigated. As the tube resistance depends on gas flow, patients were subdivided according to minute ventilation into a low ventilation group (= 10 l/min; n = 5) and a high ventilation group (> 10 l/min; n = 5). The WOBadd due to tube resistance and non-ideal ventilator properties was calculated on the basis of the tracheal pressure measured. Ventilatory modes investigated were: continuous positive airway pressure (CPAP), inspiratory pressure support (IPS) of 5, 10, and 15 cm H2O above PEEP, and automatic tube compensation (ATC). In the low ventilation group, WOBadd during CPAP was 0.382+/-0.106 J/l. It was reduced to below 15% of that value by ATC or IPS more than 5 cm H2O. In the high ventilation group WOBadd during CPAP increased to 0.908+/-0.142 J/l. In this group, however, only ATC was able to reduce WOBadd below 15% of the value observed in the CPAP mode. CONCLUSIONS: The results indicate that, depending on respiratory flow rate, (1) tracheostomy tubes can cause a considerable amount of WOBadd, and (2) ATC, in contrast to IPS, is a suitable mode to compensate for WOBadd at any ventilatory effort of the patient.

Aged↗

PubMed1999

Volume-dependent compliance in ARDS: proposal of a new diagnostic concept.

OBJECTIVE: Adaptation of ventilator settings to the individual's respiratory system mechanics requires information about the pressure-volume relationship and the change of compliance which is dependent on inflated volume. Unfortunately, established methods of obtaining this information are invasive and time-consuming, and, therefore, not well suited for clinical routine. We propose a new standardized diagnostic concept based on the recently developed slice method. This multiple linear regression method (MLR) determines volume-dependent respiratory system compliance (C(SLICE)) within the tidal volume (V(T)) during ongoing mechanical ventilation. The impact of a ventilator strategy, recommended by a consensus conference, on the course of compliance within V(T) was investigated in patients with the acute respiratory distress syndrome (ARDS) or acute lung injury (ALI). DESIGN: Prospective observational study. SETTING: Intensive care unit of a university hospital. PATIENTS: 14 ARDS patients, 2 patients with ALI. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: After measurement of flow and airway pressure and calculation of tracheal pressure, C(SLICE) was determined. The resulting course of C(SLICE) within V(T) was estimated using a mathematical algorithm. C(SLICE) data were compared to those obtained by standard MLR. We found decreasing C(SLICE) mainly in the upper part of V(T) in all patients. In 7 patients, we found an additional increasing C(SLICE) mainly in the lower part of V(T). CONCLUSIONS: C(SLICE) was not constant in patients with ARDS/ALI whose lungs were ventilated according to consensus conference recommendations. The proposed diagnostic concept may serve as a new tool to obtain a standardized estimation of respiratory system compliance within V(T) non-invasively without interfering with ongoing mechanical ventilation.

Adolescent↗

PubMed1999

Early detection of upper airway obstructions by analysis of acoustical respiratory input impedance.

Repetitive occurrence of partial or total upper airway obstruction characterizes several respiratory dysfunctions such as the obstructive sleep apnea syndrome (OSAS). In OSAS patients, pharyngeal collapses are linked to a decrease in upper airway muscle activity during sleep which causes decreased upper airway wall stiffness. Continuous positive airway pressure (CPAP) is recommended as the treatment of choice. Advancements in CPAP therapy require early detection of respiratory events in real time to adapt the level of the applied pressure to airway collapsibility. The forced oscillation technique (FOT) is a noninvasive method which reflects patients' airway patency by measuring respiratory impedance. The aim of this study was to evaluate by a mathematical model of the respiratory system if FOT can provide an early detection index of total or partial upper airway obstruction. Furthermore, the simulation should suggest which characteristic features are relevant for early apnea detection in measured clinical data. The respiratory system has been treated as a series of cylindrical segments. The oropharynx analog of the model allows simulation of upper airway collapse, mimicking the situation in patients with OSAS. We calculated the input impedance for different degrees of upper airway obstruction ranging from unobstructed airways to total occlusion. Furthermore, we simulated different upper airway wall compliances. We compared the simulation with real data. The results of the study suggest that FOT is a valuable tool for assessing the degree of upper airway obstruction in patients with OSAS. Especially, the phase angle of the impedance seems to be a potentially useful tool for early apnea detection by assessing the upper airway wall collapsibility.

Humans↗

PubMed1999

Variables used to set PEEP in the lung lavage model are poorly related.

Setting an appropriate positive end-expiratory pressure (PEEP) value is determined by respiratory mechanics, gas exchange and oxygen transport. As these variables may be optimal at different PEEP values, a unique PEEP value may not exist which satisfies both the demands of minimizing mechanical stress and optimizing oxygen transport. In 15 surfactant-deficient piglets, PEEP was increased progressively. Arterial oxygenation and functional residual capacity (FRC) increased, while specific compliance of the respiratory system decreased. Static compliance increased up to a threshold value of PEEP of 8 cm H2O, after which it decreased. This threshold PEEP did not coincide with the lower inflection point of the inspiratory limb of the pressure-volume (PV) loop. Oxygen transport did not correlate with respiratory mechanics or FRC. In the lavage model, the lower inflection point of the PV curve may reflect opening pressure rather than the pressure required to keep the recruited lung open. Recruitment takes place together with a change in the elastic properties of the already open parts of the lung. No single PEEP level is optimal for both oxygen transport and reduction of mechanical stress.

Animals↗

PubMed1999

Interrupter airway and tissue resistance: errors caused by valve properties and respiratory system compliance.

The interrupter technique is used to determine airway and tissue resistance. Their accuracy is influenced by the technical properties of the interrupter device and the compliance of the respiratory system. We investigated the influence of valve characteristics and respiratory system compliance on the accuracy of determining airway and tissue resistance by means of a computer simulation. With decreasing compliance we found increasing errors in both airway and tissue resistance determination of up to 34 and 71%, respectively. On this basis we developed a new occlusion valve, with special emphasis on rapid closing time and tightness in the closed state to improve the accuracy of resistance determination. The newly developed occlusion device greatly improves the accuracy of airway and tissue resistance determination. We conclude that respiratory system compliance is a limiting factor for the accuracy of the interrupter technique. To apply the interrupter technique in patients with extremely low respiratory system compliances, we need sophisticated technical devices.

Airway Resistance↗

PubMed1999

In vivo evaluation of a new method for chemical analysis of volatile components in the respiratory gas of mechanically ventilated patients.

Using the volatile anaesthetic isoflurane as a marker substance a gas chromatographic method for analysis of exhaled gas in mechanically ventilated patients was evaluated. Twelve patients with and 10 patients without preceding isoflurane exposure and seven blank respiratory circuits were investigated. Respiratory gas was sampled at four different sites in the respiratory tubing system. Analysis of volatile components was based upon adsorption onto activated charcoal, desorption by means of microwave energy, gas chromatographic separation and flame ionisation or mass spectrometric detection. Isoflurane concentrations in the blank respiratory circuits, in the control group, and in the inspiratory limb of patients with preceding isoflurane inhalation were at the limit of detection (<10(-12) mol/l). In the isoflurane group, isoflurane concentrations in the inspiratory and expiratory limb differed considerably. Using the method described, substances at very low concentrations could be identified as originating in the patient or as coming from the gas delivery system.

Adult↗

PubMed1999

Dynamic delay time compensation for sampling capillaries used in respiratory mass spectrometry.

In intensive care patients who receive ventilatory support or full mechanical ventilation, valuable information can be drawn from gas exchange measurements. In this setting, the most favorable method for gas exchange measurement is by simultaneous recording of gas concentrations and gas flow, and by time resolved multiplication and accumulation. This paper presents a new method to compensate for the signal delay time which occurs when a sampling capillary is used for measuring gas concentrations with a respiratory mass spectrometer or some equivalent sidestream gas analyzer. The signal delay of gas concentrations must be accurately compensated to avoid error accumulation in gas exchange calculation. A delay time can be easily measured with a test gas in a laboratory setup and be readily compensated for during the measurements in a ventilated patient. This is a standard procedure which gives reasonable results under normal conditions. Special attention is however required in cases where the gas viscosity changes due to large changes in gas composition, e.g., those used for diagnostic breathing or ventilatory maneuvers. Such changes of viscosity will influence the delay time of the capillary, because they affect its flow resistance. As a consequence they will degrade the quality of measurements when done with a simple fixed delay compensation. The method described here consists of an algorithm which enables compensation for such a temporally changing delay time due to changes in gas composition.

Algorithms↗

PubMed1999

The Traveling Shutter Wave analyses non-linear compliance during mechanical ventilation.

Mechanical ventilation is an important, often life-saving component of modern intensive care medicine. However, it may further aggravate pulmonary pathology by endinspiratory overdistension of the alveoli or by their endexpiratory collapse. To prevent both the ventilator may be adjusted based on the slope of the pressure-volume curve, named as compliance, which is often determined by a stepwise inflation of the lungs. This maneuver gained no widespread clinical acceptance because of being cumbersome and invasive. Therefore, we developed a modification of the well known interrupter technique - the Traveling Shutter Wave. A wave of short-term (300 ms) occlusions "travels" over the tidal volume range. Differential compliance is calculated by division of volume and pressure differences between two adjacent occlusion maneuvers. The technique is well suited for the clinical setting because the ventilatory pattern does not need to be changed. This manuscript describes the realization of the Traveling Shutter Wave as well as its application in two patients.

Feasibility Studies↗

PubMed1999

Reduction of the bacterial load by the silver-coated endotracheal tube (SCET), a laboratory investigation.

Microaspiration enabled by high-volume-low-pressure cuffed endotracheal tubes is the most likely explanation for ventilator-associated pneumonia. To decontaminate the secretion at the proximal end of the cuff we developed a silver-coated endotracheal tube (SCET). In an in vitro model we investigated the efficacy of SCET to lower the bacterial load of secretion and aspirate. We developed a continuously contaminated and mechanically ventilated oropharynx-larynx-lung model to investigate the reduction of the bacterial count by SCET compared to controls. The model was continuously contaminated via the oropharynx-larynx with Pseudomonas aeruginosa ATCC 27853. During the investigation period of 50 hours the bacterial count of oropharynx-larynx and lung was measured as colony-forming-units/ml. In addition, the characteristic curve of silver ion release of SCET was determined. SCET significantly reduced the bacterial count in oropharynx-larynx at all timepoints (p < 0.05). In lung the bacterial count was significantly lower beginning with the 36th hour of recording (p < 0.05). A reduction of greater than 2 log was found from 28 hours on in oropharynx-larynx and from 50 hours on in lung. The release of silver ions was very rapid and was described by a mono-exponential function with a time-constant tau of about 60 minutes and a saturation concentration of 200 +/- 80 microg/l. SCET showed a significant inhibition of growth of P. aeruginosa in the continuously contaminated and mechanically ventilated oropharynx-larynx-lung model. SCET by thus might be helpful in reducing ventilator-associated pneumonia.

Bacterial Infections↗

PubMed1998

Detection of endotracheal tube obstruction by analysis of the expiratory flow signal.

OBJECTIVE: Acute obstruction of endotracheal tubes (ETT) increases airway pressure, decreases tidal volume, increases the risk of dynamic hyperinflation by prolonging the duration of passive expiration, and prevents reliable calculation of tracheal pressure. We propose a computer-assisted method for detecting ETT obstruction during controlled mechanical ventilation. The method only requires measurement of the expiratory flow. DESIGN: Computer simulation; prospective study in two cases; retrospective study in one case and in seven patients with the adult respiratory distress syndrome (ARDS). SETTING: Laboratory of the Section of Experimental Anaesthesiology (University of Freiburg); surgical adult intensive care units in a university hospital (University of Basel) and in a university affiliated hospital (Zentralklinikum Augsburg). PATIENTS: 3 patients with partial ETT or bronchial obstructions and 7 ARDS patients. MEASUREMENTS AND RESULTS: Expiratory flow was measured using a pneumotachograph and integrated to obtain expiratory volume. The time-constant of passive expiration (tauE) as a function of expired volume [tauE(V(E)) function] was calculated from the expiratory volume/flow curve. We investigated the tauE(V(E)) function of data obtained from: (1) computer simulation of mechanically ventilated homogeneous and inhomogeneous lungs intubated with ETTs of different sizes; (2) one patient with an artificial ETT obstruction of 7.5 and 25% of the cross-sectional area of the ETT (case 1); (3) one patient with ETT obstruction due to secretions (case 2); (4) one patient with acute bronchial constriction (case 3); (5) seven ARDS patients who showed an increase in airway resistance of more than 2 cm H2O x s/l. It was found that an ETT obstruction caused an increase in tauE in early expiration (at high flow), whereas tauE in late expiration was virtually unchanged. The reason for this is the flow dependency of the increase in ETT resistance produced by ETT obstruction. Unlike ETT obstruction, an increase in pure airway resistance produced an increase in tauE throughout expiration. CONCLUSIONS: An ETT obstruction can be reliably distinguished from an increase in pure airway resistance by a characteristic pattern change in the tauE(V(E)) function, which can be detected easily even by an automated pattern recognition system.

Aged↗

PubMed1998

Effects of mechanical unloading/loading on respiratory loop gain and periodic breathing in man.

We investigated the effect of mechanical unloading and loading on Cheyne-Stokes respiration (CSR) in seven intubated patients with preexisting CSR. For mechanical loading patients had to breathe against the resistance of the endotracheal tube. For mechanical unloading patients were supported with a volume-proportional pressure support in the proportional assist ventilation (PAV) mode whilst the flow-dependent (nonlinear) endotracheal tube resistance was continuously compensated for by means of the automatic tube compensation (ATC) mode. Mechanical unloading aggravated CSR as revealed by a prolongation of apnea time and by an increase in the so-called strength index whereas mechanical loading shortened apnea time and decreased strength index. To test whether the observed changes are caused by the effect of mechanical unloading/loading on respiratory loop gain (relationship between minute ventilation and arterial CO2 tension), the response of respiratory loop gain on mechanical unloading/loading was determined in five healthy subjects (without CSR). In each subject, mechanical unloading increased respiratory loop gain whereas mechanical loading decreased it.

Adult↗