Isao Nishi

Simultaneous continuous 13C, 12C analysis of expired gas in the 13C breath test

The 13C breath test is a method of clarifying the metabolism of loaded substances by administering 13C‐labelled materials and calculating the 13CO2 and 12CO2 ratio (13C/12C isotope ratio) in the expired gas. The materials are metabolized and expelled in the expired gas. Because simultaneous continuous measurement of 13CO2 and 12CO2 in expired gas has been difficult up to the present, respective expired gases, including dead space before and after administration, have been sampled to separate sampling bags and 13C/12C has been measured in the bags and changed fraction of 13C/12C after administration (δ) has been used to judge the metabolic process. This method is affected by the contamination of the dead space gas. In the present study, in order to exclude the dead space effect, simultaneous continuous analysis of 12CO2 and 13CO2 of expired gas identifying alveolar gas was applied to the 13C‐urea breath test in addition to the conventional sampling bag method. Both isotope detectors were attached to a mass spectrometer. Fifty‐six cases receiving stomach health check‐ups for Helicobacter pylori were examined. δ was calculated in the bag or in phase III of continuous gas measurement. Because the bag contains dead space, δ was reduced and sensitivity and specificity with reference to gastric fluoroscopy or Helicobacter pylori IgG antibody were reduced. Decreasing the dead space contamination is important in reducing the measurement error in the 13C breath test and simultaneous continuous measurement is a good tool for this purpose.

Pulmonary tissue volume measured by acetylene rebreathing under artificial ventilation.

In order to evaluate the pulmonary congestive state of patients being mechanically ventilated, an acetylene rebreathing method was employed. Measurement of pulmonary tissue volume by the acetylene (C2H2) rebreathing method was performed in 15 patients under artificial ventilation including four congestive heart failure cases, one renal failure case, and 12 healthy controls.

Measurement Method of Carbohydrate Metabolism during Prolonged Exercise by Monitoring 13CO2 as Tracer.

The discriminative measurement method of the dynamic metabolic change of an administered glucose and a pre-reserved carbohydrate is clearly demonstrated during the prolonged exercise (75 W bicycle ergometer work). The administered glucose is an ordinary commercial available medical use. The isotopic abundance difference ratio of the glucose is as high as 20‰ comparing to that of the expired CO2 before the administration. This paper proposed the discriminative measurement method and showed a trail measurement for inspecting the method.

Mass spectrometric measurement of distribution of ventilation-perfusion ratio in lung by using the concept of Multiple compartment transfer function.

Distribution of ventilation-perfusion ratio (VA/QC distribution) is one of the most important functional parameters of the lung. A new method for noninvasive measurement of VA/QC distribution is described. Based on a multiple compartment model which simulates the lung as an electric RC network, a concept of multiple compartment transfer function (MCTF) is proposed. A system of algebraic equations is derived from MCTF and the VAZQC distribution can be obtained by solving these equations according to the frequency response of the lung which is measured by continuous analysis of respiratory gas during the inspiration of the gas with sinusoidally varied halothane concentration.Simultaneous and instantaneous analysis of physiological and inert gases is essential in this measurement. By employing an improved multicollector mass spectrometer, such measurement was accomplished with comparatively satisfactory sensitivity and stability. Another technical problem was to produce the air flow containing sinusoidally varied halothane concentration with a wider range of frequency components. It was achieved by using a commercially available flow controller combining with computer-controlled frequency modulation and synthesis technique.Experimental results of normal subjects and patients with lung diseases gave physiologically reasonable results of VA/QC distributions. It is demonstrated that the method is useful in physiological studies and clinical diagnoses.

Continuous measurements of respiratory gas analysis in hyperbaric heliox environment.

An N2 washout measurement was applied in the hyperbaric heliox environment to estimate lung ventilation distribution. In this procedure, N2 lung content was flushed by the inhalation of an N2 free gas. The purpose of the measurement was to investigate change in ventilation distribution in a hyperbaric environment which was created by the use of a deep diving simulator. Physiological parameters measured were respiratory gas concentrations (FN2, FAr, FCO2, FO2, FHe and FH2O), respiratory flow rate and temperature.The respiratory gas concentrations, flow, and temperature were simultaneously measured in a breath-by-breath fashion in the full pattern and digitally recorded with high accuracy and response. Concentration and flow of each breath were examined on a CRT and corrected as required prior to recording on a data base system. The corrections were made to compensate for gas leakage to and from the gas circuit, the electronic drift and noise.In this experiment, a mass spectrometer to analyze respiratory gas concentrations and an amplifier to enhance readings, were placed outside the hyperbaric chamber for reading of a Fleish pheumotachometer and thermistor sensors.In order to be analyzed, it was necessary to introduce the respiratory gas sample through the large pressure difference. Concentrations of physiological gases were decreased with the increased ambient pressure of He balance.Other technical points to be resolved were mass spectrometer and flow meter calibrations under hyperbaric conditions. The computer-assisted measurement was also used to conduct the complex procedure. The technical problems which were encountered are discussed in this study.The experimental results obtained at 12, 18 and 31 ATA (equivalent to depths of 110, 170 and 300m) are shown in comparison with results in the atmospheric environment.

Multidimensional measuring system of respiratory and circulatory functions by mass spectrometer.

A method for non-invasive measurement and multidimensional analyses of respiration and circulation was developed by using the respiratory mass spectrometer by combining a C2H2 mixture rebreathing method with a bag in box technique, various respiratory and circulatory factors are simultaneously obtained from continuous gas concentrations and respiratory flow rates. Respiratory and circulatory functions can be evaluated from relevant physiological aspects including ventilation, perfusion, gas exchange, ventilation perfusion ratio and the correlations between them. By applying microcomputer and special algorithms developed, an automatic system for real time measurement was constructed. Results show that the proposed system has the possibility of practical use in physiological research and clinical diagnoses.