Non-invasive measurement of total respiratory compliance and resistance in cats

We adapted non-invasive techniques developed for human infants to measure total respiratory system compliance (Crs) and resistance (Rrs) in 21 healthy cats. The animals breathed through a face mask attached to a respiratory circuit and measurements were taken of changes in lung volume and airway pressure during brief occlusions of the airway at different lung volumes. The slope of the plot of change in volume against airway pressure yielded the multiple occlusion Crs with a mean (+/-95%CI) value of 6.8 (6.3-7.3) ml/cm H2O. In 12 animals measurements were made by the single breath technique in which occlusion was made early in expiration and on release, a plot of the subsequent relaxed expiratory flow and volume yielded the time constant (taurs), Crs and Rrs with mean (+/-95%CI) values of 0.27 (0.22-0.31) s, 7.0 (6.1-7.8) ml/cm H2O, and 38.7 (33.7-43.6) cm H2O/l/s, respectively. Rrs was significantly correlated inversely with forced expiratory flow at resting lung volume (V'maxFRC).     

无创通气下应用强迫振荡技术检测呼吸阻力

目的 构建强迫振荡测量系统,在无创正压通气(NPPV)条件下检测人呼吸系统阻抗(Rrs)和电抗(Xrs),用于评估肺阻力(RL)和弹件阻力(EL).方法 基于现有的强迫振荡技术,构建包括振荡发生器和信号分析软件在内的新强迫振荡测量系统,采用呼吸系统一阶线性力学模型(R-I-E模型)验证新系统测量的准确性和可靠性.8例健康正常人为研究对象,分别经鼻罩给予不同水平的双水平气道止压(BiPAP)和持续气道正压(CPAP)通气,探讨在不同通气模式和压力水平下利用Rrs无创评价R,的可行性.结果 (1)振荡压力和振荡流量的相干函数系数值r2=0.98,强迫振荡测量可靠.5 Hz强迫振荡测定的模型阻抗与模型的粘性阻力接近,两者平均相差(1.26±0.44)cm H2O·s·L-1,一敛性范嗣在(0.36～2.14)cm H2O·s·L-1.(2)8例在不同通气模式及压力条件下测定的Rrs值大小接近,与RL平均相差(0.16±1.58)cm H2O·s·L-1.RL的预计方程式为RL=1.40+0.77Rrs,[决定系数(r2)=0.43,P<0.01].(3)强迫振荡弹性阻力EFOT(EFOT=-2πfXrs)显著大于实际值EL,(P<0.01).两者存在低水平的相关(r=0.40,P<0.01).结论 新强迫振荡系统测量准确、可靠.Rrs近似地反映了RL的大小,RL预测值可用于优化NPPV的压力支持水平,使呼吸机提供的压力支持能有效地克服肺阻力.     

Vagal influence on respiratory mechanics in newborn kittens

The aim of this study was to investigate the effects of pulmonary vagal innervation on respiratory mechanics of the newborn kitten. To this end, eight kittens in the first week of life were anaesthetized, tracheostomized and measurements of breathing pattern and respiratory mechanics compared between the intact and post-vagotomy condition. Airflow (V) and changes in lung volume (V) were measured with a pneumotachograph attached to the tracheal cannula; tracheal pressure (Ptr) was measured from a side-port of the cannula. Pressure in the oesophagus (Pes), representing the mean pleural pressure (Ppl), was recorded using a liquid filled catheter. By occluding the airway at end-inspiration, static respiratory system compliance (Crs), chest wall (Cw), and lung compliance (CL) were computed as the ratio of V over, respectively, Ptr, Pes and Ptr-Pes. The slope of the relationship between V and V during expiration represented the respiratory system time constant (tau rs), from which the resistance of the respiratory system was obtained (Rrs = tau rs/Crs). Dynamic lung compliance (Cdyn) and total pulmonary resistance (TPR) were obtained from the V, V and Ppl values during spontaneous breathing. After bilateral cervical vagotomy, most of the variables pertinent to respiratory mechanics did not change significantly, but Cw increased (35%) and TPR decreased (12%). The former probably resulted mainly from the deeper post-vagotomy breathing pattern, the latter from a loss in bronchomotor tone. Both the work per breath and the work per minute, computed as proposed by OTIS et al., tended to increase after vagotomy because of the deeper tidal volume, more than offsetting the changes in pulmonary mechanics.(ABSTRACT TRUNCATED AT 250 WORDS)     

Procedures to improve the repeatability of forced oscillation measurements in school-aged children

Forced oscillation technique (FOT) parameters are less repeatable than spirometry, and the impact of technical factors, such as data acquisition and data filtering, are unknown. FOT was performed, in triplicate, on 48 children (8-11 years) and repeated two weeks later. We examined the separate effects of monitoring tidal volume (V(T)) prior to measurement and length of data acquisition on measurement repeatability. We compared the effects on repeatability of a filtering technique in which complete breaths containing respiratory artefact were rejected and statistical filters in which outlying data points were rejected. Within- and between-session repeatability of respiratory system resistance (Rrs) and reactance (Xrs) were assessed using coefficient of variation (CV) and intra-class correlation coefficient (ICC). Longer data acquisition reduced CV of Rrs and Xrs (60s vs. shorter durations, p ≤ 0.001). Monitoring V(T) reduced CV of Rrs (p = 0.05). Complete breath filtering improved CV and ICC for both Rrs and Xrs. The repeatability of FOT measurements can be improved by optimising data acquisition and filtering.     

Volume Dependence of High-Frequency Respiratory Mechanics in Healthy Adults

Respiratory system input impedance (Zrs) at low to medium frequencies below 100 Hz, and study of its volume dependence, have been used extensively to quantify airway and tissue mechanics. Zrs at high oscillation frequencies including the first antiresonant frequency (far,1) may contain important information about airway mechanics. Changes in high-frequency Zrs with lung volume have not been studied. The volume-dependent behavior of high-frequency Zrs, specifically far,1 and respiratory system resistance at first antiresonance (Rrs(far,1)), was characterized in 16 healthy adults. Zrs was measured with a forced oscillation signal (5–302.5 Hz) through a wavetube setup. To track Zrs, subjects performed slow deep inspiratory and expiratory maneuvers over 30-s measurements, during which average impedance was calculated over 0.4-s intervals, with successive overlapping estimates every 0.156 s. Flow was measured using a pneumotachometer and integrated to obtain volume. Transpulmonary pressure dependence (Ptp) of Zrs was separately determined in five subjects. Both far,1 and Rrs(far,1) decreased with increasing lung volume and Ptp, consistent with an increase in airway caliber and decreased airway wall compliance as volume increased. These characterizations provide insight into airway mechanics, and are furthermore a necessary first step toward determining whether volume dependence of the first antiresonance is altered in disease.     

Inhalation of a precursor analogue of vasoactive intestinal polypeptide (Leu17 VIP-Gly-Lys) protects ascaris-induced bronchoconstriction in dog

We studied in vivo the effects of pre-inhalations of vasoactive intestinal polypeptide (VIP) and a precursor analogue of VIP (Leu17 VIP-Gly-Lys: preVIP) in mongrel dogs bronchoconstricted by ascaris. An inhalation of preVIP solution (2 mg/5 ml saline) gave significant protection for 120 min against increases in respiratory resistance (Rrs) and decreases in dynamic compliance (Cdyn) induced by ascaris challenges. An inhalation of VIP solution (2 mg/ml saline) also gave significant protection for 120 min against increases in Rrs induced by ascaris challenges. Protective effect of the inhalation of preVIP against ascaris-induced bronchoconstriction was more potent than that of VIP. The inhalations of preVIP and VIP solution did not change systemic blood pressure or heart rate. These results indicate that inhalations of preVIP or VIP solution would attenuate ascaris-induced bronchoconstriction in dogs without affecting cardiovascular dynamics.     

Continuous monitoring of tracheal pressure including spot-check of endotracheal tube resistance.

During mechanical ventilation, the resistance of the endotracheal and tracheostomy tube (ETT) highly influences analysis of respiratory system mechanics and imposes additional work of breathing for the spontaneously breathing patient which both can be circumvented by applying the automatic tube compensation (ATC) mode. In the ATC mode, tracheal pressure (ptrach) is continuously calculated on the basis of measured flow and airway pressure using predetermined tube specific coefficients. However, as during long-term ventilation the ETT might become partially obstructed by secretions or tube kinking, the predetermined coefficients are no longer valid rendering calculation of ptrach inaccurate. We propose an easy-to-handle maneuver for the bedside determination of current tube coefficients in the tracheally intubated patient. Based on check-spot measurement of ptrach, current tube coefficients are determined by a least-squares fit procedure valid for the partially obstructed ETT with the indwelling pressure-measuring catheter (PMC). To correct for the removal of the PMC, the relationship between tube coefficients with and those without indwelling PMC has been determined in a laboratory investigation. Accuracy of the procedure was determined during artificial ETT obstruction by comparing calculated with measured ptrach. Correspondence between calculated and measured ptrach has been found excellent. We conclude that by adopting this bedside procedure periodically, accurate calculation of ptrach is guaranteed and the advantages of the ATC mode are ensured even in long-term ventilatory support.     

Correction of compliance and resistance altered by endotracheal tube leaks and non-linear pressure/volume-relationships

Measurements of lung compliance (C) and resistance (R) are influenced by endotracheal tube leaks (ETTL) as well as non-linear pressure/volume relationships (P/V relationship). To keep C and R reliable, we developed an algorithm to mathematically correct inspiratory and expiratory volume (V) and flow. In this study, a ventilated lung model for non-linear P/V relationship with adjustment of an increasing ETTL was studied. In addition, the recordings (airway pressure, flow, and volume) of 21 infants (median weight: 1,220 g, range: 640-2,160 g, with a median leak size of 32%, range: 24-56%) were investigated. C and R were calculated continuously from the recordings of flow, volume, and airway pressure over time according to the changing volume. A method especially developed for the analysis of non-linear pressure-volume-relationship (APVNL) was employed. C and R affected by leaks were corrected applying the newly developed mathematical algorithm and compared with measurements without leakage. C could be corrected up to a leak of 80% and R up to 55% leak at half tidal V for the model with non-linear P/V-R. C and R without leak and after leak correction did not differ significantly in all infants where the APVNL method was applied (P > 0.05).     

Design of a new artificial breathing system for simulating the human respiratory activities

The purpose of this work is the conception and implementation of an artificial active respiratory system that allows the simulation of human respiratory activities. The system consists of two modules, mechanical and electronical. The first one represents a cylindrical lung adjustable in resistance and compliance. This lung is located inside a transparent thoracic box, connected to a piston that generates variable respiratory efforts. The parameters of the system, which are pressure, flow and volume, are measured by the second module. A computer application was developed to control the whole system, and enables the display of the parameters. A series of tests were made to evaluate the respiratory efforts, resistances and compliances. The results were compared to the bibliographical studies, allowing the validation of the proposed system.     

New developments in lung function measurements in rodents

There are invasive and noninvasive pulmonary function tests available which are sensitive in detecting bronchoconstriction in rodents. Noninvasively measured midexpiratory flow (EF₅₀) has been shown to be an appropriate parameter to monitor bronchoconstriction in a large number of animals, e.g. for screening purposes.Recently, a novel technique for repetitive lung function measurements in orotracheally intubated, spontaneously breathing mice has been established. Bronchoconstriction is assessed by the “gold standard” parameters airway resistance and dynamic compliance in response to aerosolized methacholine or allergens in anesthetized mice. This measurement technique has been combined with an inhalation technique which has been optimized to allow simultaneous lung function measurement in intubated animals and to obtain high aerosol concentrations. A feedback dose control system has been developed to administer a defined and constant aerosol dose to each individual animal. Using this system a prominent early allergic response and late airway hyperresponsiveness could be demonstrated in intubated mice challenged with Aspergillus fumigatus allergen.We conclude: The noninvasive EF₅₀ method seems particularly appropriate for measurements of respiratory function in large numbers of conscious mice in assembly line fashion. The invasive technology – newly established for the mouse – is more sensitive and specific since true airway resistance and dynamic compliance are determined and allows now the adequate detection of an early allergic response in the mouse and also repetitive measurements e.g. to assess the airway hyperresponsiveness in the same animal or for monitoring purposes in chronic models.     

Indirekte Bestimmung des intrapulmonalen Druckverlaufes am Lungenmodell bei Hochfrequenzbeatmung

Summary One of the determinants of intrapulmonary pressure during machine ventilation at a given time constant of the respiratory system is the duration of expiration. At high frequencies of ventilation with short expiration times substantial gas trapping can occur with end-expiratory increase in transpulmonary pressure (inadvertent PEEP). The occlusion technique allows measurement of the intrapulmonary pressure at the airway opening because of equilibration throughout the respiratory tract. The complete intrapulmonary pressure curve can be obtained, if occlusion takes place at progressively increasing intervals after the beginning of a breath. We present a computer-assisted methode for measuring the occlusion pressure at defined time points throughout the respiratory cycle.A lung simulator is ventilated by a Sechrist ventilator. The tube leading to the simulator is occluded every 5 breaths, the time point of the occlusion being advanced progressively into each breath. Occlusion pressure is compared to intrapulmonary pressure measured directly by an intrapulmonary probe. All of this is controlled by a personal computer. We are able to demonstrate that, at ventilation frequencies of up to 600/min pressure curves measured indirectly correspond sufficiently well with pressures recorded directly in the lung model. An automatic evaluation of the measurements is possible even with a tube leakage of up to 70%.

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Abkürzungen PEEP Positive end-expiratory pressure     

自动导管阻力补偿技术联合压力支持通气对撤机患者呼吸力学参数的影响

目的观察自动导管阻力补偿技术（ATC）联合压力支持通气（PSV）对接受机械通气支持的撤机患者在自主呼吸试验（SBT）时通气参数的影响。方法呼吸衰竭患者16例．其中男性9例,女性7例,年龄（65±6）岁,基础疾病均为慢性阻塞性肺疾病急性加重期（AECOPD）．所有入选患者均为接受气管插管（导管直径7．0～8．0mm）并机械通气支持至少24h以上,在治疗过程中病情稳定进入撤机阶段者。患者随机接受不同辅助通气模式（ATC、PSV或ATC＋PSV）进行SBT,持续时间均为60min。预置持续气道正压（CPAP）／呼气末气道正压（PEEP）为0．49kPa（5cmH2O）,ATC时根据气管导管类型与直径将补偿比例设置为100％,PSV的吸气压力支持（PS）水平则为0．78kPa（8cmH2O）,吸气触发灵敏度为2L／min。结果ATC＋PSV时的气道峰压（PIP）明显高于标准PSV时,且出现在吸气早期;吸气峰流速（PIFR）与呼气峰流速（PEFR）也均显著增高,达峰容积比（VPEFR/VTE）则由PSV时的7．9％±0．4％降至3．7％±0．3％（P〈0．05）;但潮气量（VT）、呼吸频率（RR）、分钟通气量（MV）和浅快呼吸指数（RSBI）等参数差异则无统计学意义（P〈0．05）。ATC时患者的PIP最低,VT与ATC＋PSV相比略减小,但差异无统计学意义;RR和RSBI则明显增高。ATC时的PIFR低于PSV和ATC＋PSV时,PEFR则与ATC＋PSV时相近．而较PSV增高。结论ATC技术与PSV一样均通过提供一定的预置压力,以帮助患者在自主呼吸状态克服人工气道所引起的阻力。但与PSV的固定水平压力补偿所不同．ATC时呼吸机所提供的压力补偿是根据实际气流变化而相应改变,且对呼气也有效。     

A new method of estimating bronchial hyper-responsiveness in younger children

By using the new device, the "Astograph," it is possible to measure the continuous changes of respiratory resistance (Rrs) during bronchial inhalation challenge. This method, however, is not suitable for younger children because of wide variations in Rrs. So we studied a technique using a transcutaneous oxygen pressure (tcPO2) monitoring system. The bronchial reactivity and sensitivity were significantly correlated between Rrs and tcPO2 (P less than .001), and there was no correlation between cardiac output and Rrs. The tcPO2-method is useful for measuring bronchial responsiveness, especially in younger children.     

Detection of partial endotracheal tube obstruction by forced pressure oscillations

Rapid airway occlusions during mechanical ventilation are followed immediately by high-frequency pressure oscillations. To answer the question if the frequency of forced pressure oscillations is an indicator for partial obstruction of the endotracheal tube (ETT) we performed mathematical simulations and studies in a ventilated physical lung model. Model-derived predictions were evaluated in seven healthy volunteers. Partial ETT obstruction was mimicked by decreasing the inner diameter (ID) of the ETT. In the physical model ETTs of different ID were used. In spontaneously breathing volunteers viscous fluid was applied into the ETT's lumen. According to the predictions derived from mathematical simulations, narrowing of the ETT's ID from 9.0 to 7.0mm decreased the frequency of the pressure oscillations by 11% while changes of the respiratory system's compliance had no effect. In volunteers, a similar reduction (10.9%) was found when 5 ml fluid were applied. We conclude that analysis of pressure oscillations after flow interruption offers a tool for non-invasive detection of partial ETT obstruction.     

Day-to-day variability of oscillatory impedance and spirometry in asthma and COPD

Variability in airway function may be a marker of disease activity in COPD and asthma. The aim was to determine the effects of repeatability and airway obstruction on day-to-day variability in respiratory system resistance (Rrs) and reactance (Xrs) measured by forced oscillation technique (FOT). Three groups of 10 subjects; normals, stable asthmatic and stable COPD subjects underwent daily FOT recordings for 7 days. Mean total and inspiratory Rrs and Xrs, and expiratory flow limitation (EFL) Index (inspiratory – expiratory Xrs), were calculated. The ICC's were high for all parameters in all groups. Repeatability, in terms of absolute units, correlated with airway obstruction and was therefore lowest in COPD. Day-to-day variability was due mostly to repeatability, with a small contribution from the mean value for some parameters. FOT measures are highly repeatable in health, stable asthma and COPD in relation to the wide range of measures between subjects. For home monitoring in asthma and COPD, either the coefficient of variation or individualized SDs could be used to define day-to-day variability.     

A microcomputer-based procedure for carrying out rhinomanometry

The determination of nasal airway resistance by the technique of anterior rhinomanometry is made difficult by several factors. Among these are the variability in the breath by breath measurement of airflow and pressure, the effect of under or over breathing, and the ability to produce a smooth transition between inspiration and expiration during which period the measurements are made. To overcome some of these problems a standard procedure has been developed (in our laboratory) for active anterior rhinomanometry. The nasal resistance is calculated from the mean of three sets of three readings with a rest interval between each set. To enable the procedure to be carried out with consistency it has been implemented on a BBC microcomputer. This enables a breathing guide to be provided for the subject, as well as providing a display of each flow pressure curve, a display of the mean curve, plus and minus one standard deviation, and the calculation of left, right and total nasal airway resistance.     

A new approach to mechanical simulation of lung behaviour: Pressure-controlled and time-related piston movement

A mechanical lung simulator is described (an extension of a previous mechanical simulator) which simulates normal breathing and artificial ventilation in patients. The extended integration of hardware and software offers many new possibilities and advantages over the former simulator. The properties of components which simulate elastance and airway resistance of the lung are defined in software rather than by the mechanical properties of the components alone. Therefore, a more flexible simulation of non-linear behaviour and the cross-over effects of lung properties is obtained. Furthermore, the range of lung compliance is extended to simulate patients with emphysema. The dependency of airway resistance on lung recoil pressure and transmural pressure of the airways can also be simulated. The new approach enables one to incorporate time-related mechanics such as the influence of lung viscosity or cardiac oscillation. The different relations defined in the software can be changed from breath to breath. Three simulations are presented: (1) computer-controlled expiration in the artificially ventilated lung; (2) simulation of normal breathing; and (3) simulation of viscoelastance and cardiac influences during artificial ventilation. The mechanical simulator provides a reproducible and flexible environment for testing new software and equipment in the lung function laboratory and in intensive care, and can be used for instruction and training.     

Bronchodilation induced by muscular contraction in spontaneously breathing rabbits: Neural or mechanical?

The respective contribution of mechanical and neural mechanisms to the bronchodilation occurring during exercise is not fully identified in spontaneously breathing animals. The airway response to electrically induced muscular contractions (MC) was studied after vagal cold block in 9 spontaneously breathing rabbits. The forced oscillation respiratory system resistance (Rrs) was measured at vagal nerve temperatures 37°C, 8°C and 4°C. Rrs was found to decrease significantly during MC in all conditions. The occasional occurrence of a deep breath was responsible for a sudden decrease in Rrs. However, when the deep breath was absent - after vagal cooling and in some experiments at 37°C - the bronchodilation was frequently dissociated from the change in breathing pattern, most likely illustrating a neural mechanism. Altogether, while some bronchodilation may be ascribed to the mechanical stretching of the airways, Rrs decreasing with little change in breathing pattern is likely related to a reflex effect, possibly a sympathetic-borne mechanism.     

Effects of histamine on the pressure-volume curve of the respiratory system in the guinea pig

Intravenous infusion of histamine has been shown to constrict smooth muscle of alveolar ducts. In this study, we have assessed the effects of a prolonged infusion of histamine to obtain a steady state response on quasistatic pressure-volume curves (P-V curves) together with the changes in dynamic compliance (Cdyn) and conductance (G) of the respiratory system. Increasing doses of histamine were given in order to obtain the dose-response characteristics of the changes in Cdyn, G and P-V curves. In nine anesthetized guinea-pigs under mechanical ventilation, administration of histamine resulted in a fall in Cdyn and G with a decrease of 50% of initial value approximately for 150 ng X kg-1 X s-1 of histamine. Modifications of the P-V curves were characterized by a decrease in the maximal volume, and an increase in the hysteresis of the P-V loop due to the downward displacement of the inflation limb. With infusion of histamine, there was a large decrease of quasi-static compliance which appeared to account for most of the decrease in dynamic compliance. Such changes in P-V curves can be related both to a closure of alveolar ducts and to an alteration of lung distensibility. Comparison of the dose-response curves for the different parameters indicated that Cdyn and G reflect, at least in part, events occurring in the periphery of the lung.     

Management of detachment of pilot balloon during intraoral repositioning of the submental endotracheal tube

Submental endotracheal intubation for surgery was used as an alternative to nasotracheal intubation in patients with craniomaxillofacial injury. Generally extubation was performed in the operation room by pulling the tube through the submental incision site. When extubation is not indicated, intraoral indwelling is preferred to submental intubation. We report a case of a 35-year-old male patient with multiple facial bone fractures. At the end of the surgery, we noticed the oropharyngeal edema, and so the submental intubation was converted into a standard orotracheal intubation. During that procedure, the pilot balloon was accidentally detached from the endotracheal tube. The situation was managed by cutting a pilot tube from a new, unused endotracheal tube and connecting it to the intubated tube using a needle connector.