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Biomedical subjects

J Guttmann

Publications and source records attributed to J Guttmann.

At least 55 records · Page 3Linked to original sources
PubMed1998

Effect of different doses of inhaled nitric oxide on pulmonary capillary pressure and on longitudinal distribution of pulmonary vascular resistance in ARDS.

Inhaled nitric oxide lowers pulmonary capillary pressure (PCP) in animals and in patients with acute respiratory distress syndrome (ARDS). A dose-response relationship in patients with ARDS has not yet been established. Therefore, we studied the effects of four concentrations of nitric oxide (1, 10, 20 and 40 volumes per million (vpm)) in random order, on PCP in 19 patients with ARDS. PCP was estimated by visual analysis of the pressure decay curve after balloon inflation of the pulmonary artery catheter. Haemodynamic and gas exchange variables were measured at each nitric oxide concentration. Patients were classified as responders when PCP decreased by at least 2 mm Hg after nitric oxide 20 vpm. In responders (n = 8), nitric oxide decreased PCP and post-capillary vascular resistance dose-dependently and changed longitudinal distribution of pulmonary vascular resistance with a maximum effect at 20 vpm. In non-responders (n = 11), PCP did not change. In both groups, the nitric oxide-induced decrease in pre-capillary vascular resistance was small with a maximum effect at 1 vpm. In ARDS, vasodilatation of pre-capillary vessels is achieved at low concentrations of nitric oxide, whereas the effect of nitric oxide on postcapillary vessels is variable. Higher concentrations may be required for optimal post-capillary vasodilatation in a subgroup of ARDS patients.

Adolescent↗
PubMed1998

Analysis of respiratory mechanics during artificial ventilation.

Mechanical or artificial ventilation is the most important life-saving therapeutic instrument in modern intensive care medicine. The ventilator takes on the convective transport of the respiratory gas, i.e. delivery of oxygen and removal of carbon dioxide. The technical gas delivery system (ventilator, respiratory tubing system, gas humidifier) and the respiratory system (lungs and thorax) of the patients form a connected pneumatic system of high complexity. The respiratory system produces a mechanical impedance to ventilator output. Impedance is composed of an elastic, a non-elastic, i.e. resistive, and an inertive part. The corresponding indices describing respiratory mechanics are compliance, flow resistance and inertance. Based on the equation of motion of the respiratory system, several methods of analysing respiratory mechanics during mechanical ventilation are described. Quantitative analysis of respiratory system mechanics (a) is a prerequisite for the understanding of the complex patient-ventilator interaction, (b) provides important clinical information on pulmonary function and the course of disease, and (c) allows the physician at the bedside to adjust the ventilatory settings to the needs of the individual patient.

Biomechanical Phenomena↗
PubMed1998

Evaluation of forced oscillation technique for early detection of airway obstruction in sleep apnea: a model study.

The forced oscillation technique (FOT) is a non-invasive method which may be suitable for assessing upper airway obstruction in obstructive sleep apnea/hypopnea syndrome (OSAS) patients. The aim of this study was to determine in vitro if FOT can provide an early detection index of total or partial upper airway occlusion. A respiratory system analog was developed which includes an upper airway analog that allows simulation of upper airway collapse (thus mimicking the situation in patients with OSAS). We simulated different degrees of upper airway obstructions ranging from 0 (unobstructed airways) to 1 (total occlusion). Furthermore, we imitated the collapsible upper airway wall by means of elastic membranes with ten different wall compliances ranging from 3.3 x 10(-4) to 1 1/mbar. For the two stiffest rubber membranes (Cwall = 0.01 and 3.3 x 10(-4) l/mbar) the absolute value of the impedance (¿Z¿) showed a marked increase for obstructions greater than 0.6. For the two membranes with the highest wall compliances (Cwall = 0.03 and 1 1/mbar) obstructions with an increase in ¿Z¿ could not be detected before the obstruction reached 0.8. For degrees of obstruction less than 0.6 the phase angle of collapsible membranes with low compliance (stiff airway wall) were about 1.5pi which significantly differed from phase angles of 1.77pi measured in membranes with high compliance (elastic airway wall); p < 0.01. We hypothesized that stiffness of upper airway walls corresponds with their muscle tone, i.e., stiff airway walls are related with high muscle tone and vice versa. Thus, a decrease in upper airway muscle activity would cause an increase of upper airway wall elasticity that enables upper airway collapse. As a consequence the phase angle phi could be expected to change from values characterizing stiff membranes to values characterizing more elastic membranes which could be used as early indicator for obstructive respiratory events. We have frequently observed such changes in morphology of phi(t) data obtained from patients with OSAS.

Airway Obstruction↗
PubMed1997

Breathing pattern and additional work of breathing in spontaneously breathing patients with different ventilatory demands during inspiratory pressure support and automatic tube compensation.

OBJECTIVE: We designed a new ventilatory mode to support spontaneously breathing, intubated patients and to improve weaning from mechanical ventilation. This mode, named Automatic Tube Compensation (ATC), compensates for the flow-dependent pressure drop across the endotracheal tube (ETT) and controls tracheal pressure to a constant value. In this study, we compared ATC with conventional patient-triggered inspiratory pressure support (IPS). DESIGN: A prospective, interventional study. SETTING: A medical intensive care unit (ICU) and an ICU for heart and thoracic surgery in a university hospital. PATIENTS: We investigated two groups of intubated, spontaneously breathing patients: ten postoperative patients without lung injury, who had a normal minute ventilation (VE) of 7.6 +/- 1.7 l/min, and six critically ill patients who showed increased ventilatory demand (VE = 16.8 +/- 3.0 l/ min). INTERVENTIONS: We measured the breathing pattern [VE, tidal volume (VT), and respiratory rate (RR)] and additional work of breathing (WOBadd) due to ETT resistance and demand valve resistance. Measurements were performed under IPS of 5, 10, and 15 mbar and under ATC. RESULTS: The response of VT, RR, and WOBadd to different ventilatory modes was different in both patient groups, whereas VE remained unchanged. In postoperative patients, ATC, IPS of 10 mbar, and IPS of 15 mbar were sufficient to compensate for WOBadd. In contrast, WOBadd under IPS was greatly increased in patients with increased ventilatory demand, and only ATC was able to compensate for WOBadd. CONCLUSIONS: The breathing pattern response to IPS and ATC is different in patients with differing ventilatory demand. ATC, in contrast to IPS, is a suitable mode to compensate for WOBadd in patients with increased ventilatory demand. When WOBadd was avoided using ATC, the patients did not need additional pressure support.

Adult↗
PubMed1997

Respiratory comfort of automatic tube compensation and inspiratory pressure support in conscious humans.

OBJECTIVE: To compare the new mode of ventilatory support, which we call automatic tube compensation (ATC), with inspiratory pressure support (IPS) with respect to perception of respiratory comfort. ATC unloads the resistance of the endotracheal tube (ETT) in inspiration by increasing the airway pressure, and in expiration by decreasing the airway pressure according to the non-linear pressure-flow relationship of the ETT. DESIGN: Prospective randomized single blind cross-over study. SETTING: Laboratory of the Section of Experimental Anaesthesiology (Clinic of Anaesthesiology; University of Freiburg). SUBJECTS: Ten healthy volunteers. INTERVENTIONS: The subjects breathed spontaneously through an ETT of 7.5 mm i.d. Three different ventilatory modes, each with a PEEP of 5 cmH2O, were presented in random order using the Dräger Evita 2 ventilator with prototype software: (1) IPS (10 cmH2O, 1 s ramp), (2) inspiratory ATC (ATC-in), (3) inspiratory and expiratory ATC (ATC-in-ex). MEASUREMENTS AND MAIN RESULTS: Immediately following a mode transition, the volunteers answered with a hand sign to show how they perceived the new mode compared with the preceding mode in terms of gain or loss in subjective respiratory comfort: "better", "unchanged" or "worse". Inspiration and expiration were investigated separately analyzing 60 mode transitions each. Flow rates were continuously measured. The transition from IPS to either type of ATC was perceived positively, i.e. as increased comfort, whereas the opposite transition from ATC to IPS was perceived negatively, i.e. as decreased comfort. The transition from ATC-in to ATC-in-ex was perceived positively whereas the opposite mode transition was perceived negatively in expiration only. Tidal volume was 1220 +/- 404 ml during IPS and 1017 +/- 362 ml during ATC. The inspiratory peak flow rate was 959 +/- 78 ml/s during IPS and 1048 +/- 197 ml/s during ATC. CONCLUSIONS: ATC provides an increase in respiratory comfort compared with IPS. The predominant cause for respiratory discomfort in the IPS mode seems to be lung over-inflation.

Adult↗
PubMed1997

Delayed derecruitment after removal of PEEP in patients with acute lung injury.

BACKGROUND: A step decrease in positive end-expiratory airway pressure (PEEP) is not followed by an instantaneous loss of the PEEP-induced increase in end-expiratory lung volume (EELV). Rather, the reduction of EELV is delayed, while adverse PEEP effects on hemodynamics are immediately attenuated upon the drop in airway pressure. Step PEEP increments were applied to the lungs of patients with acute lung injury. It was investigated retrospectively whether enlargement of end-expiratory lung volume and changes in lung mechanics persist 45 min after removal of the PEEP increment. METHODS: In 14 patients with acute lung injury (LIS score 2.7) EELV and volume-dependent dynamic compliance of the respiratory system (Cdyn,rs) were determined 45 min after removal of an additional PEEP increment (0.64 kPa added to baseline PEEP of 1.0 kPa). RESULTS: Nine patients kept an EELV gain of 13% (SD 7) and showed improved Cdyn,rs. In 5 patients, EELV was reduced (by 9% (SD 6)) and Cdyn,rs unchanged after removal of the PEEP increment compared to baseline. CONCLUSION: A subgroup of patients with acute lung injury, the characteristics of which remain to be defined, benefit from prolonged recruitment effects up to 45 min after removal of a PEEP increment, while sequelae of continuously increased airway pressures are minimised.

Adult↗
PubMed1995

Time constant/volume relationship of passive expiration in mechanically ventilated ARDS patients.

Since the adult respiratory distress syndrome (ARDS) lung is known to be inhomogeneous, one could expect an uneven distribution of expiratory time constant during uninterrupted mechanical ventilation. We investigated the time constant/volume relationship of passive expiration, and their modification by external resistive elements. In 12 paralysed intubated ARDS patients, we determined the expiratory time constant (tau E) as a function of the expired volume (VE) during uninterrupted mechanical ventilation. Mean expiratory time was 2.9 +/- 0.3 s (+/- SD). VE was divided into five equal volume slices (portions) and a mean tau E calculated from the expiratory tidal volume/flow curve for each slice. The mean values of tau E for each volume slice did not differ significantly throughout expiration, averaging 690 +/- 218 ms (mean +/- SD of five slices and 12 patients). We show that the flow-dependent resistance of the endotracheal tube (RETT) is mainly responsible for the observed time constant homogeneity. We conclude that in ARDS patients during uninterrupted mechanical ventilation the time constants of passive expiration are markedly modified by the flow-dependent resistance of the endotracheal tube (RETT), and also by the external resistance of tubing and ventilator (REX). RETT and REX render tau E about three times larger than the time constant of the patient's respiratory system alone.

Adult↗
PubMed1995

An analysis of desynchronization between the spontaneously breathing patient and ventilator during inspiratory pressure support.

It is common practice to convert patients with acute respiratory insufficiency (ARI) from controlled mechanical ventilation to some form of assisted spontaneous breathing as early as possible. A widely used mode of assisted spontaneous breathing is patient-triggered inspiratory pressure support (IPS). We investigated 11 patients with ARI during weaning from mechanical ventilation using IPS and found that in 9 of these patients, desynchronization between patient and ventilator occurred, ie, that the ventilator did not detect and support all the patients' breathing efforts. Five of these 9 patients displayed severe desynchronization lasting at least 5 min and with less than half of all breathing efforts being supported by the ventilator. We present the analysis of gas flow, volume, esophageal pressure, airway pressure, and tracheal pressure of 1 patient with ARI displaying desynchronization under IPS. Our results imply that desynchronization can occur due to the following: (1) inspiratory response delays caused by the inspiratory triggering mechanisms and the demand flow characteristics of the ventilator; (2) a mismatch between the patient's completion of the inspiration effort and the ventilator's criterion for terminating pressure support; and (3) restriction of expiration due to resistance from patient's airways, endotracheal tube, and expiratory valve. From our analysis, we have made proposals for reducing desynchronization in clinical practice.

Aged↗
PubMed1993

Continuous calculation of intratracheal pressure in tracheally intubated patients.

BACKGROUND: Intratracheal pressure (Ptrach) should be the basis for analysis of lung mechanics. If measured at all, Ptrach is usually assessed by introducing a catheter into the trachea via the lumen of the endotracheal tube (ETT). The authors propose a computer-assisted method for calculating Ptrach on a point-by-point basis by subtracting the flow-dependent pressure drop delta PETT(V) across the ETT from the airway pressure (P(aw)), continuously measured at the proximal end of the ETT. METHODS: The authors measured the pressure-flow relationship of adult endotracheal tubes with different diameters (ID, 7-9 mm) at different lengths and of tracheostomy tubes (ID, 8-10 mm) in the laboratory. The coefficients of an approximation equation were fitted to the measured pressure-flow curves separately for inspiration and expiration. In 15 tracheally intubated patients under volume-controlled ventilation and spontaneous breathing, the calculated Ptrach was compared with the measured Ptrach. RESULTS: The authors present the coefficients of the "nonlinear approximation": delta PETT = K1.VK2, with delta PETT being the pressure drop across the ETT and K1 and K2 being the coefficients relating V to delta PETT. An important result was an inspiration/expiration asymmetry: the pressure drop caused by the inspiratory flow exceeds that of the expiratory flow. A complete description of the pressure-flow relationship of an ETT, therefore, requires a set of four coefficients: K1I, K2I, K1E, and K2E. The reason for this asymmetry is the abrupt sectional change between ETT and trachea and the asymmetric shape of the swivel connector. Comparison of calculated and measured Ptrach in patients gives a correspondence within +/- 1 cmH2O (mean limits of agreement). The mean root-mean-square (rms) deviation is 0.55 cmH2O. CONCLUSIONS: Ptrach can be monitored by combining our ETT coefficients and the flow and airway pressure continuously measured at the proximal end of the ETT.

Adult↗
PubMed1992

Intrinsic PEEP monitored in the ventilated ARDS patient with a mathematical method.

Under mechanical volume-controlled ventilation, the intensive care patient can develop intrinsic positive end-expiratory pressure (iPEEP); that is, the passive expiration is terminated by the following inspiration before the alveolar pressure comes to its physical equilibrium value. We present a mathematical method to estimate this alveolar dynamic iPEEP breath by breath, without the need of a maneuver. We tested it in paralyzed patients ventilated for adult respiratory distress syndrome after multiple trauma and/or sepsis, and we compared the results obtained with the new mathematical method with those from the occlusion method introduced by Pepe and Marini. The results agreed well (median difference of 0.8 mbar in 201 investigations in 12 patients). However, the mathematically determined values, representing dynamic iPEEP, are systematically slightly smaller than those measured by the occlusion maneuver. A variation of expiratory time suggests that this difference might be due to mechanical time-constant inhomogeneity, viscoelastic processes, or other mechanisms showing time dependence.

Adult↗
PubMed1992

Maneuver-free determination of compliance and resistance in ventilated ARDS patients.

At present, most methods of lung mechanics analysis do not take nonlinearities of compliance and resistance into account. Nevertheless, nonlinearity of compliance is an inherent property of the respiratory system in ARDS and nonlinearity of resistance is an inherent property of the endotracheal tube. Herein we describe a computer-assisted multipoint method (LOOP) for breath-by-breath calculation of total respiratory system compliance (Ctrs) and total respiratory system resistance (Rtrs). Unlike our previously published method, LOOP excludes nonlinearities of compliance and resistance by confining the data used from the P/V/V loop to sequences with constant flow in inspiration and with steadily decreasing flow in expiration. LOOP was applied to five patients ventilated after open heart surgery (HEART group) and 12 patients ventilated for ARDS (ARDS group). The compliance results from LOOP were compared with the semistatic reference values corrected for intrinsic PEEP (CsST,IP). In the ARDS patients the compliance values from LOOP (46 ml/mbar) corresponded well with the semistatic compliance (CsST,IP = 42 ml/mbar). Despite the fact that there is no reference method for resistance known to date, we also determined the semistatic resistance (RsST) at end-inspiratory pause. The resistance values determined with LOOP were 8.5 mbar/L/s (RsST = 7.3 mbar/L/s) in the HEART group and 11.1 mbar/L/s (RsST = 8.6 mbar/L/s) in the ARDS group. LOOP gives a good correspondence between the linear RC model and the measured data in ARDS patients. In conclusion, LOOP requires neither an end-inspiratory pause (EIP) nor additional determination of intrinsic PEEP and gives Ctrs, automatically corrected for IPEEP, as well as Rtrs breath by breath at the bedside.

Adult↗