Impedance measurement during air and helium-oxygen breathing before and after salbutamol in COPD patients.

1. The forced oscillation technique is an effort-independent method used to characterize the mechanical impedance of the respiratory system. To support the hypothesis that non-invasive partitioning of total pulmonary resistance is possible by this technique, impedance was measured during air breathing and after equilibration with a mixture of 80% helium (He) and 20% oxygen (O2) in 21 chronic obstructive pulmonary disease (COPD) patients by means of a forced pseudo-random noise pressure signal over a frequency spectrum from 4 to 52 Hz. Furthermore, during inhalation of both gas mixtures impedance was determined before and after inhalation of 0.400 mg Salbutamol. 2. He + O2 breathing caused less negative frequency dependence of resistance and a significant decrease in reactance over the range 16-52 Hz. Inhalation of Salbutamol caused a marked increase in reactance values over the range 8-40 Hz. However after equilibration with the He + O2 mixture, Salbutamol caused a significant decrease in resistance and a significant increase in reactance at all frequencies. 3. The results during He + O2 breathing are in accordance with a partitioning of airways resistance into central and peripheral components. The decrease in reactance during He + O2 can be explained by a density dependent decrease in inductive reactance. By comparing the impedance data during air and He + O2 breathing, it can be concluded that a distribution of pulmonary resistance with minimal losses in the larger airways is more sensitive for detecting changes in the peripheral airways in COPD patients.

Density dependence of respiratory input impedance in normal subjects.

1. The forced oscillation technique is a non-invasive and effort-independent test used to characterize the mechanical impedance of the respiratory system. Total respiratory impedance was assessed from 4 to 52 Hz in 15 normal subjects breathing air and a helium-oxygen mixture. 2. Breathing helium-oxygen reduced respiratory resistance and its frequency dependence as well as respiratory reactance very significantly. Resonant frequency during He-O2 breathing was 1.88 times higher than during air breathing. 3. It is concluded that by impedance measurement of the respiratory system in normal subjects a density-dependent decrease of respiratory resistance due to decreased turbulence in the larger airways and a density-dependent decrease in the inductive reactance can be found during breathing of low density gas mixtures.

Forced expiratory flow and oscillometric impedance measurement in evaluating airway obstruction.

The application of forced oscillations has been introduced as a noninvasive method to measure the impedance of the respiratory system. Impedance can be partitioned into a real part or resistance and an imaginary part or reactance. The reactance depends on the elastic and inertial properties of the respiratory system. In the present study, resistance and reactance obtained in a frequency spectrum between 4 and 52 Hz were compared with maximal forced expiratory spirometry in 100 out-patients, aged 18-70 years. Resonant frequency and frequency dependence of resistance correlated significantly with selected parameters of the forced expiratory flow volume curve: correlation coefficient values ranged from 0.492 between frequency dependence and FVC and 0.668 between resonant frequency and FEV1. No correlation between average resistance and spirometric parameters reached a statistically significant level. No marked difference was observed between spirometric parameters depending on the early or effort-dependent portion and those parameters depending on the late or effort independent portion of the maximum forced expiration. It can be concluded that each measurement procedure reveals different but characteristic information about the mechanical behaviour and properties of the respiratory system.

[Snoring as a symptom of severe respiratory obstruction during sleep: causes and results]. / Snurken als uiting van ernstige ademhalingsbelemmering tijdens de slaap: oorzaken en gevolgen.

Snoring is an epiphenomenon of obstructive respiration during sleep, which may be caused by higher airway abnormalities and may result in impaired quality of nocturnal sleep, complaints of fatigue and daytime sleepiness, decreased performance level, psychic complaints and cardiovascular problems. The test results of seven patients complaining of excessive snoring and daytime sleepiness are discussed. The importance of multidisciplinary management of the underlying pathology is stressed.

Impedance measurements of the respiratory system before and after salbutamol in COPD patients.

Impedance measurements of the respiratory system by means of the forced oscillation technique were performed in a group of 20 COPD patients before and after inhalation of 0.400 mg salbutamol. A slight, but statistically non significant decrease of resistance is observed at all frequencies from 12 to 52 Hz. Increase of reactance values reached a statistically significant level at all frequencies except at 24 and 52 Hz. It is hypothesized that the increase of reactance in these patients can be explained by an increase of capacitance due to an increase of airway compliance or a decrease of peripheral resistance according to Mead's analogon of the lungs.

Localization of bronchial response to ipratropium bromide by respiratory impedance measurement in asthmatics.

In 10 asthmatic subjects, the influence of 0.040 mg ipratropium bromide on impedance (Z) of the respiratory system (rs) was determined after cold air challenge. Cold air inhalation caused a significant increase of respiratory resistance (Rrs) at frequencies between 8 and 32 Hz. This increase of Rrs was more pronounced at lower frequencies and, therefore, Rrs became frequency dependent. Respiratory reactance (Xrs) decreased at all frequencies, resulting in an increase of resonant frequency. These changes were compatible with a peripheral airway obstruction and a decrease of airway compliance, according to Mead's analog of the respiratory system. Five min after inhalation of ipratropium bromide, a significant decrease of Rrs between 8 and 28 Hz and a significant increase of Xrs at all frequencies were observed, resulting in a decrease of resonant frequency. Ipratropium bromide significantly reversed the peripheral broncho-constriction induced by cold air challenge.

Response localization of the pharmacological agents histamine and salbutamol along the respiratory system by forced oscillations in asthmatic subjects.

The bronchodilating effect of 1 mg and 0.4 mg salbutamol on the impedance of the respiratory system was studied in 25 asthmatic subjects after histamine-induced bronchoconstriction. Histamine caused an increase of respiratory resistance (Rrs) at lower frequencies and a frequency dependence of Rrs. Respiratory reactance (Xrs) decreased at all frequencies after histamine challenge. These changes can be explained by peripheral airway obstruction. Impedance measurements performed 5 min after inhalation of 1 mg and 0.4 mg salbutamol showed a decrease of Rrs values at lower frequencies, a disappearance of the frequency dependence of Rrs, and a significant increase of Xrs values. No significant differences in absolute changes of Rrs and Xrs are observed between the salbutamol regimens. These changes after inhalation of salbutamol can be explained by supposing a predominant action on the peripheral airways.

Physiological analysis of extended-spectrum oscillometry.

Using a forced oscillation technique, the resistance and reactance of the respiratory system in a frequency range between 4 and 52 Hz were described in a group of healthy subjects and a group of patients with severe chronic obstructive pulmonary disease (COPD). In normal subjects, resistance values increased at higher frequencies. As compared to the results in normal subjects, resistance values were much higher and decreased with frequency in COPD patients. Reactance values were more negative, resulting in an increase of resonant frequency. Using matrix network topography, these findings were analyzed in a modified Mead's model. Compressibility of alveolar gas was incorporated in the model calculations. Resistance and reactance values slightly decreased by adding gas compliance in the model calculations. Our results support Mead's hypothesis that the shunt compliance is formed by the compliance of intrathoracic airway walls. Input impedance measurement by forced oscillation is therefore an easily implemented, non-invasive method to investigate respiratory mechanics not requiring active cooperation from the subject. Analysis of resistance and reactance over an extended frequency range gives information about the distribution of resistance along the bronchial system and about compliance of the intrathoracic airway walls as expanding structures in parallel with the air spaces.

Contribution of impedance measurement of the respiratory system to bronchial challenge tests.

The contribution of impedance measurement of the respiratory system to bronchial challenge tests was studied in 64 asthmatics and 23 control subjects. After histamine challenge, resistance values increased significantly at all frequencies but most markedly at the lower frequencies in the asthmatic group; reactance values significantly decreased at all frequencies. In the control group, resistance significantly increased at 8 and 12 Hz. However, reactance decreased significantly at all frequencies. By multiple logistic model analysis, a simple discriminant score was found with great discriminating power to differentiate asthmatics and nonasthmatics. The discriminating score equals 9 X FEV1 aft - 7 X FEV1 bef. Adding the forced oscillation technique to the equipment for measuring the bronchial response after challenging procedures can give information about the localization of the response to the challenge in the respiratory system.

Gas mixing in the small airways, described by old and new models.

This is a review of models built to explain the inefficiency of intrapulmonary gas mixing observed during multibreath tests, or to explain the slope of the alveolar plateau of the expiratory concentration-volume curve during single breath tests. The question, raised in 1917, whether diffusion was the limiting factor, received a negative answer in 1946. It then became necessary to postulate parallel unequal ventilation in combination with asynchronism. After 1966 diffusion was held responsible for stratification, a form of series inequality. However, a quantitative agreement with experimental data could only be achieved after the introduction of asymmetrical branching into the models.

[Computer measurement of residual volume and alveolar gas distribution parameters in epidemiological studies (author's transl)]. / EDV-gerechte Residualvolumenbestimmung und alveolargas-analytisch Verteilungsanalyse bei epidemiologischen Reihenuntersuchungen

Starting from the quick helium-rebreathing-technique of Kowalski-Visser a method of combined measurement of residual volume and closing volume in one test was developed using automatic data - collection in 3 different variants, that is- automatic control during test- manual control during test and- manual control on the table. A computer program running on minicomputer Cellatron 8205 is described. Experiences using the different program-variants are discussed.

Comparison of the helium rebreathing method and the x-ray film densitometry in epidemiological screening tests of CNSLD (author's transl). / Vergleich des schnellen Heliumrückatmungsverfahrens und der Röntgenfilmdensimetrie im Rahmen epidemiologischere Reihenuntersuchungen

Two methods for the examination of the residual volume were compared under the special conditions of epidemiological studies. The X-ray Photo Densitometry RV/TLC is measured as a quotient of the brightness of the lung radiographs during inspiration and expiration maximums. The Helium Rebreathing method is a gas mixture technique. The correlation between both methods proved to be significant (r = 0,60). The advantages and disadvantages of these methods for epidemiological studies were discussed.

A temporary decrease in the ventilatory function of an urban population during an acute increase in air pollution.

During a short period of increased air pollution in a polluted area in the Netherlands, a majority of the inhabitants showed a lower VC and FEV1 value than during a period of extremely low pollution. This may be due to a temporary decrease in the ventilatory function in response to a temporary increase in air pollution. Persons who showed the greatest "decrease" in the VC and/or FEV1 had a slightly higher prevalence of chronic non-specific lung disease (CNSLD) than did those who had a slight or no decrease in VC and FEV1. The studies will be continued in order to determine whether the groups will show different repiratory disease patterns in the future. In studies on long-term effects of exposure to air pollution, one must consider the possibility that short-term effects may influence the results of the lung function measurements. It is always important, therefore, to include a questionnaire on respiratory symptoms in such studies, since it is unlikely that short periods of air pollution influence the prevalence of chronic respiratory symptoms.