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A real-time microcomputer-based data acquisition and analysis system has been developed to automate the measurement of the ventilatory response to CO2 by the rebreathing method. Previous systems acquire the data on-line and then analyze and display the results off-line. The system described here performs all processing on-line and displays experimental results in real-time. The results of 5 min of data acquisition are available for display only 1.5 sec after completion of the experiment. Immediate interpretation of the results of each experiment enable a series of related studies to be performed on the same patient in a short time period. The microcomputer is Digital Equipment Corporation's LSI-11, a low cost 16 bit machine with the basic instruction set of a PDP-11/40. The system has 16 kbytes of memory, a CRT for data display, and a paper tape reader for program loading. Due to the time constraints of real-time processing and the memory constraints of a small system, the software is written entirely in assembler language. The software includes routines for numeric and character input, line and graphical output, linear curve fitting, start of rise detection and floating point computations.
Biotelem Patient Monit 1978
PMID:A microcomputer-based data acquisition and analysis system for CO2 rebreathing studies. 75 26

New data obtained from treating polymethylmethacrylate (PMMA) with a non-moving cw- 10 watt-CO2 laser-beam focused at 2.5'', 5'', 7.5'' and 15.75'' are presented. . The final equations R(tc) and Z(tc) for each focal length are proposed. A very interesting correlation between the focal lengths in use and the integrated values of R and Z between 0 and 2 sec has been identified and discussed. This result has been used as basis to define a convenient operative protocol to follow during the planning phase of critical osteotomies or bone cement removal operations using a continuous-wave CO2 laser-beam set to any output power and focused by a set of most common, moving or non-moving focal lengths placed on the operating area. With a simple equation, it is possible to compare craters obtained with moving and non-moving laser-beams at different operative conditions between 0 and 2 sec, time interval which covers the majority of cases. A value of 2.3 +/- 0.1 between ablated volumes of PMMA and bone tissue has been identified. Several case studies regarding orthopaedic procedures from Literature are here reported and compared to the present LCA model. The computerized on-line flow of information for the laser-beam optimization and safety control is also described. Finally, a method for the simultaneous data collection from several operating rooms via a Local Area Network (LAN-Industry Standard IEEE) onto a central data base for later consultation is proposed in its general design.
Int J Clin Monit Comput 1992
PMID:Proposal of a computerized algorithm for continuous wave CO2 laser on-line control during orthopaedic surgery. Phase I: theoretical introduction and first in vitro trials. 140 2

We have applied advanced real-time techniques in software, that are intensively used in critical areas like space research and defence applications, to realise an Integrated Real-Time Respiratory Monitoring System at the Thorax Anesthesiology, Academic Hospital Rotterdam. The system is called the 'SERVO WINDOW'--a window to the servo ventilator. The heart of the system is a real-time kernel that uses preemptive scheduling to achieve multitasking on a IBM PC compatible hardware platform. To the clinician this means that he gets all relevant information from one source i.e. the Respiratory Workstation. The waveforms of the airway pressure, airway flow and the expired CO2 curve are displayed continuously on the screen. The Vector Loops like Pressure Volume, Flow Pressure and Flow Volume loops are also available in addition to the lung mechanics parameters like Expiratory and Inspiratory Resistances, Compliances, Peak Pressure, PEEP, etc. The Single Breath Diagram i.e. expired CO2 concentration versus volume and dead space ventilation is also calculated. The blood gas analysis data is plotted in convenient diagrams like the O2-CO2 diagram, Oxygen Chart, etc. The trend of all these parameters are available with a granularity of one minute. An industry standard laser printer is used for report generation to produce reports of the real-time waveforms, parameter values and the trends. User interface is through easy menus with the traditional keyboard, touchscreen including keyboard on screen for data entry and the mouse.
Int J Clin Monit Comput 1992 Oct
PMID:Real-time respiratory monitoring workstation--software and hardware engineering aspects. 144 36

A system has been designed to determine cardiac output noninvasively. The system's main component is a closed breathing circuit and it measures oxygen uptake (VO2), carbon dioxide elimination (VCO2), and end-tidal CO2 partial pressure (PET). As an integral part of the system, periods of CO2 rebreathing can be automatically implemented. The CO2 partial pressure of oxygenated mixed venous blood (Pv) is obtained from the measured exponential rise of the PET value during such a CO2 rebreathing maneuver. A new method is described for estimating the pulmonary blood flow, alveolar ventilation, cardiac output (CO), and mixed venous oxygen saturation (SVO2) from PV, PET, VO2, VCO2, tidal volume, and arterial oxygen saturation. The method was evaluated in 6 anesthetized and mechanically ventilated pigs. A wide range of cardiac output, shunt fractions, and dead space to tidal volume ratios were induced by combinations of bronchoalveolar lavage, hypervolemia, hypovolemia, and variable levels of positive end-expiratory pressure (PEEP). The bias between the CO obtained with the noninvasive technique (CO L/min) and the thermodilution CO (Qt L/min) was 0.13 L/min (SD = 0.78 L/min) and the correlation was N = 64; R = 0.92; CO = 0.95*Qt + 0.38. The bias obtained for double determinations with the noninvasive CO technique was 0.3 L/min (SD = 0.5 L/min). The bias between the noninvasive estimates of Svo2 and the directly measured values was 1.1% (SD = 9.3%). For double determination with the noninvasive technique the bias was -0.9% (SD = 4.7%). It is concluded that in mechanically ventilated pigs the proposed method produces good estimates of CO and SVO2 also in the presence of significant ventilation/perfusion mismatch.
J Clin Monit 1992 Oct
PMID:Noninvasive cardiac output determined with a new method based on gas exchange measurements and carbon dioxide rebreathing: a study in animals/pigs. 145 86

The procedure for weaning a patient with respiratory insufficiency from mechanical ventilation may be complex and requires expertise obtained by long clinical practice. We designed a knowledge-based system for the management of patients receiving respiratory support and implemented a weaning procedure. The system is intended for patients whose spontaneous respiratory activity is assisted by a Hamilton Veolar ventilator delivering a positive pressure plateau during inspiration (Pressure Support Ventilation mode). Our closed-loop real-time system running on a Personal Computer continuously adapts the assistance provided by the ventilator to the patient's evolution, and indicates when the patient can be withdrawn from the ventilator. Three parameters are used to appreciate the 'respiratory comfort' of the patient: breathing frequency, which we consider the most informative index, tidal volume and end-tidal CO2 pressure. A preliminary study of 19 patients was performed to evaluate the ability of our system to adapt the assistance to the patient's needs, with the main objective of facilitating weaning by gradually lowering the level of assistance. In 10 of these patients, considered as good candidates for weaning on the strength of objective criteria, the system maintained the breathing pattern in a zone of comfort for 95% of the period of assisted ventilation and stated that they were 'weanable'. This was consistent with the clinical evolution of all 10 patients. These results show that such a system can provide effective management for mechanically ventilated patients.
Int J Clin Monit Comput 1992 Dec
PMID:A knowledge-based system for assisted ventilation of patients in intensive care units. 148 75

Mixed venous oxygen saturation (SvO2) monitoring has been advocated for some critically ill patients. Patients with end-stage hepatic failure have oxygen consumption rates that are lower than normal. Using the Fick equation, oxygen consumption may be calculated if mixed venous and arterial oxygen tensions (and saturations), hemoglobin, and cardiac output are determined simultaneously. This report describes a unique pattern of changes in SvO2 and oxygen consumption in 7 patients undergoing liver transplantation. A previous study correlated plasma carbohydrate (glucose) levels with early hepatic graft survival. After induction, the 7 patients reported here had low oxygen consumption and high SvO2 values. The oxygen consumption rates decreased to the lowest point during the anhepatic phase and rose above baseline by the end of the case. The SvO2 and oxygen consumption data reported here follow the presence of presumed hepatic metabolic activity (increased CO2 and ionized calcium). Further research must be completed to determine whether these measurements indicate early hepatic nonfunction.
J Clin Monit 1992 Jan
PMID:Oxygen consumption and mixed venous oxygen saturation monitoring during orthotopic liver transplantation. 153 56

To evaluate the potential of trend monitoring of end-tidal PCO2 (PETCO2) to detect pulmonary embolization, the capnograms of 24 mechanically ventilated patients were monitored during simulation of 1-ml pulmonary embolization by inflation of the balloons of their pulmonary artery catheters. Within 1 minute of balloon inflation, PETCO2 showed an exponential decrease to a new equilibrium. This response is characteristic of a CO2 wash-out curve produced by a step increase in dead space. Because of a steady baseline, the depression of the trend line during balloon inflation was apparent to a naive reader repeatedly in 20 of the 24 patients (sensitivity, 85%; specificity, 94%; positive predictive value, 98%; negative predictive value, 89%), despite a small mean decrease in PETCO2 (2 +/- 1.97 mm Hg). The PETCO2 trend curve did not reliably allow detection of balloon inflation in 4 patients whose capnograms were poorly formed. In conclusion, during constant ventilation, PETCO2 trend curve monitoring might provide clinically useful "on line" information regarding pulmonary embolization.
J Clin Monit 1992 Apr
PMID:Capnographic trend curve monitoring can detect 1-ml pulmonary emboli in humans. 158 43

The purposes of this study were to evaluate the clinical utility of a colorimetric end-tidal CO2 (ETCO2) detector in confirming proper endotracheal intubation in patients requiring emergency intubation, to determine if this new device can be used as an adjunct to judge the effectiveness of cardiopulmonary resuscitation (CPR), and to determine whether the device can predict successful resuscitation from cardiopulmonary arrest. We studied prospectively 110 patients requiring emergency intubation for either respiratory distress (53 patients) or cardiopulmonary arrest (57 patients) by recording the color range of the indicator after the initial intubation. In patients who suffered a cardiopulmonary arrest, the color range was also recorded during CPR after the endotracheal tube was confirmed to be in the tracheal position and perfusion optimized, and at the moment CPR was stopped. The ETCO2 detector was 100% specific for correct endotracheal intubation in all patients. It was also highly sensitive (0.98) for correct endotracheal intubation in patients with respiratory distress. However, it was not sensitive (0.62) in patients with cardiopulmonary arrest and low perfusion. The sensitivity improved (0.88) when we used the ETCO2 range obtained after attempts to increase perfusion. A low ETCO2 color range in 19 patients undergoing CPR was interpreted as low cardiac output and prompted the physicians to attempt to increase perfusion. Of the patients who underwent CPR, no patient whose ETCO2 level remained less than 2% was successfully resuscitated. Those patients who had an ETCO2 level greater than or equal to 2% had a significantly higher incidence of successful resuscitation.(ABSTRACT TRUNCATED AT 250 WORDS)
J Clin Monit 1991 Oct
PMID:Clinical utility of a colorimetric end-tidal CO2 detector in cardiopulmonary resuscitation and emergency intubation. 174 72

Anesthetic gases from several patients can be monitored simultaneously with a centrally located mass spectrometer. Such monitoring requires catheters from patient to spectrometer that are several meters long. Scamman (J Clin Monit 1988; 4:227-229) found that when the respiratory frequency is high, as with infants, the CO2 signal from the patient is unacceptably distorted during passage down the catheter. This is due to Taylor dispersion of the input signal. An outline of the theory of Taylor dispersion is given. The equations describe the interaction between the velocity distribution (which, in laminar flow, is parabolic) and the radial diffusion of CO2. This interaction keeps a tracer signal together in a pulse, as it moves down the tube with the mean velocity, spreading somewhat as it proceeds. How much does an initially sharp signal become blurred? The spread of such a signal when it reaches the detector, measured in time, can be expressed in various ways. Measurement is complicated, however, by the fact that the gas pressure may fall by as much as a factor of 10 along the line. The resultant expansion and acceleration of the gas cannot be ignored. A full treatment of this complication is given elsewhere, but the following simple equation is described: delta t = 3.54 x 10(-3) l [(1 + R2)/(1 - R2)]1/2. Typically, the spread time is up to a quarter of a second for catheters of 50 m, such as used by Scamman. This is comparable with the period of CO2 rise and fall for infants and explains the serious distortion in wave form that Scamman+ found.(ABSTRACT TRUNCATED AT 250 WORDS)
J Clin Monit 1991 Jul
PMID:Use of long catheters for multipatient anesthetic monitoring at high respiratory frequencies. 846 13

Spurious readings from a mass spectrometer have been reported following the administration of aerosol bronchodilators. We quantified the response of various respiratory gas analyzers to the aerosol propellant of albuterol inhalant (Proventil). The mass spectrometer systems tested, two Advantage systems, a SARA system, and a Model 6000 Ohmeda system, all displayed artifactual readings in response to the albuterol propellant. Each metered dose of the Proventil brand of albuterol contains 4 ml of Freon 11 (trichloromonofluoromethane) and 11 ml of Freon 12 (dichlorodifluoromethane). The concentration of propellant was expressed in doses/L, where each liter of gas contains 0.4 vol % of Freon 11 and 1.1 vol % of Freon 12 per dose. In proportion to the concentration of albuterol propellant, the two Advantage systems showed substantial readings of isoflurane (%) when no isoflurane was present (13% and 16% per dose/L) and reduced readings of enflurane (-8% and -10% per dose/L) and carbon dioxide (CO2) (-3 and +5 mm Hg per dose/L). The SARA system showed substantial CO2 readings when no CO2 was present (5 mm Hg per dose/L) and displayed small enflurane readings (0.1% per dose/L) when no enflurane was present. The Model 6000 unit showed CO2 readings when no CO2 was present (5 mm Hg per dose/L). Neither the Raman spectrometer, the infrared spectrometers, nor the piezoadsorptive analyzer we tested showed an artifactual effect of albuterol propellant on any of its readings. Simulation and clinical tests demonstrated that a single dose of albuterol propellant into a breathing circuit at the onset of inspiration resulted in concentrations of 0.8 and 0.3 dose/L, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
J Clin Monit 1991 Apr
PMID:The effects of bronchodilator-inhaler aerosol propellants on respiratory gas monitors. 190 29


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