Respiratory Mechanics and Plasma Levels of Tumor Necrosis Factor Alpha and Interleukin 6 Are Affected by Gas Humidification during Mechanical Ventilation in Dogs

The use of dry gases during mechanical ventilation has been associated with the risk of serious airway complications. The goal of the present study was to quantify the plasma levels of TNF-alpha and IL-6 and to determine the radiological, hemodynamic, gasometric, and microscopic changes in lung mechanics in dogs subjected to short-term mechanical ventilation with and without humidification of the inhaled gas. The experiment was conducted for 24 hours in 10 dogs divided into two groups: Group I (n = 5), mechanical ventilation with dry oxygen dispensation, and Group II (n = 5), mechanical ventilation with oxygen dispensation using a moisture chamber. Variance analysis was used. No changes in physiological, hemodynamic, or gasometric, and radiographic constants were observed. Plasma TNF-alpha levels increased in group I, reaching a maximum 24 hours after mechanical ventilation was initiated (ANOVA p = 0.77). This increase was correlated to changes in mechanical ventilation. Plasma IL-6 levels decreased at 12 hours and increased again towards the end of the study (ANOVA p>0.05). Both groups exhibited a decrease in lung compliance and functional residual capacity values, but this was more pronounced in group I. Pplat increased in group I (ANOVA p = 0.02). Inhalation of dry gas caused histological lesions in the entire respiratory tract, including pulmonary parenchyma, to a greater extent than humidified gas. Humidification of inspired gases can attenuate damage associated with mechanical ventilation.     

ALI/ARDS患者使用保护性通气策略对于肺部损伤的影响

急性肺损伤(ALI)和急性呼吸窘迫综合征(ARDS)是常见的临床综合征,绝大多数ALI/ARDS患者需机械通气治疗,机械通气在提供可接受的肺部气体交换的同时治疗基础疾病,但机械通气本身也会引起肺部损伤,即机械通气性肺损伤(VILI)。而通过调整机械通气参数的设置,使用保护性通气策略可显著减低ALI/ARDS患者机械通气性肺损伤程度,从而减少肺部感染,缩短机械通气时间和住院时间,降低28天死亡率,明显改善ALI/ARDS患者的生存质量,起到最大程度地肺保护作用。本文从气道平台压,通气容积,呼气末正压等几个不同通气参数方面分别进行综述,讨论ALI/ARDS患者机械通气时使用保护性通气策略对于肺部损伤的影响。     

Deciding about mechanical ventilation in end-stage chronic obstructive pulmonary disease: how respirologists perceive their role

OBJECTIVE: To determine when respirologists approach patients with end-stage chronic obstructive pulmonary disease (COPD) to decide about the use of mechanical ventilation, what information they provide to patients and how they provide it. DESIGN: Self-administered national survey. PARTICIPANTS: All Canadian specialists in respiratory medicine; of 401 eligible respirologists, 279 (69.6%) returned a completed questionnaire. OUTCOME MEASURES: Timing and content of doctor-patient discussions regarding mechanical ventilation; physicians'' perception of their level of involvement in the decision-making process; and patient and physician characteristics that may influence decisions. RESULTS: Discussions were reported to occur most often at advanced stages of COPD: when the patient''s dyspnea was severe (reported by 235 [84.2%] of the respondents) or when the patient''s forced expiratory volume in the first second was 30% or less than predicted value (reported by 210 [75.3%]). A total of 120 respondents (43.0%) stated that they discuss mechanical ventilation with 40% or less of their COPD patients before an exacerbation necessitates ventilatory support. Most (154 [55.2%]) described the decision-making process as a collaboration between patient and physician; 83 (29.7%) reported that the patient decides after he or she has considered the physician''s opinion. Over half (148 [53.0%]) of the respondents indicated that they occasionally, often or always modify the information provided to patients in order to influence their decision about mechanical ventilation. CONCLUSIONS: Discussions with COPD patients concerning end-of-life decisions about mechanical ventilation are reported to occur in advanced stages of the disease or not at all, with patients'' input where possible. Information presented to patients is often modified in order to influence the decision. Future studies should explore ways to involve patients further in the decision-making process and to improve the process for both patients and physicians.     

机械通气患者呼吸机相关性肺炎临床分析与护理

目的探讨呼吸机相关性肺炎的临床相关因素及病原学特点,以指导临床防治。方法对100例呼吸机患者的呼吸机管路、下呼吸道感染病菌的菌种种类、呼吸机时间进行统计,分析与呼吸机相关性肺炎发病的因素。结果呼吸机管路和下呼吸道病原菌构成比具有同源性表现,呼吸机相关性肺炎发生率为36%,使用呼吸机时间长短与呼吸机相关性肺炎发生率呈正相关(P0.01)。结论呼吸机相关性肺炎与多种临床因素有关,使用时间越长,发病率越高。     

Noninvasive positive-pressure ventilation in acute respiratory failure

Noninvasive positive-pressure ventilation is a type of mechanical ventilation that does not require an artificial airway. Studies published in the 1990s that evaluated the efficacy of this technique for the treatment of diseases as chronic obstructive pulmonary disease, congestive heart failure and acute respiratory failure have generalized its use in recent years. Important issues include the selection of the ventilation interface and the type of ventilator. Currently available interfaces include nasal, oronasal and facial masks, mouthpieces and helmets. Comparisons of the available interfaces have not shown one to be clearly superior. Both critical care ventilators and portable ventilators can be used for noninvasive positive-pressure ventilation; however, the choice of ventilator type depends on the patient''s condition and therapeutic requirements and on the expertise of the attending staff and the location of care. The best results (decreased need for intubation and decreased mortality) have been reported among patients with exacerbations of chronic obstructive pulmonary disease and cardiogenic pulmonary edema.Noninvasive positive-pressure ventilation is the delivery of mechanical ventilation to patients with respiratory failure without the requirement of an artificial airway. The key change that led to the recent increase in the use of this technique occurred in the early 1980s with the introduction of the nasal continuous positive airway pressure mask for the treatment of obstructive sleep apnea. Studies published in the 1990s that evaluated the efficacy of noninvasive positive-pressure ventilation for treatment of diseases such as chronic obstructive pulmonary disease, congestive heart failure and acute respiratory failure have generalized its use in recent years.¹ In 1998, an international study on the use of mechanical ventilation found that 5% of patients admitted to intensive care units received noninvasive positive-pressure ventilation.²Noninvasive positive-pressure ventilation includes various techniques for augmenting alveolar ventilation without an endotracheal airway. The clinical application of noninvasive ventilation by use of continuous positive airway pressure alone is referred to as “mask CPAP,” and noninvasive ventilation by use of intermittent positive-pressure ventilation with or without continuous positive airway pressure is called noninvasive positive-pressure ventilation.     

Severe hypophosphataemia during recovery from acute respiratory acidosis.

Three elderly patients with established chronic obstructive airways disease were admitted with a short history of increasing dyspnoea and tiredness and (in two cases) a deterioration in mental state. Acute respiratory acidosis was diagnosed and mechanical ventilation instituted. Two hours after beginning mechanical ventilation the mean arterial pH had risen to 7.40, but all patients showed a dramatic fall in the serum phosphate concentration (lowest value 0.3 mmol/l (0.9 mg/100 ml] accompanied by a low urinary excretion of phosphate. No patient could tolerate withdrawal of mechanical ventilation until the serum and urinary concentrations of phosphate had returned to normal. Recovery from acute respiratory acidosis should be added to the list of conditions associated with severe hypophosphataemia.     

COVID-19 and dys-regulation of pulmonary endothelium: implications for vascular remodeling

Coronavirus disease-2019 (COVID-19), the disease caused by severe acute respiratory syndrome-coronavirus-2, has claimed more than 4.4 million lives worldwide (as of 20 August 2021). Severe cases of the disease often result in respiratory distress due to cytokine storm, and mechanical ventilation is required. Although, the lungs are the primary organs affected by the disease, more evidence on damage to the heart, kidney, and liver is emerging. A common link in these connections is the cardiovascular network. Inner lining of the blood vessels, called endothelium, is formed by a single layer of endothelial cells. Several clinical manifestations involving the endothelium have been reported, such as its activation via immunomodulation, endotheliitis, thrombosis, vasoconstriction, and distinct intussusceptive angiogenesis (IA), a unique and rapid process of blood-vessel formation by splitting a vessel into two lumens. In fact, the virus directly infects the endothelium via TMPRSS2 spike glycoprotein priming to facilitate ACE-2-mediated viral entry. Recent studies have indicated a significant increase in remodeling of the pulmonary vascular bed via intussusception in patients with COVID-19. However, the lack of circulatory biomarkers for IA limits its detection in COVID-19 pathogenesis. In this review, we describe the implications of angiogenesis in COVID-19, unique features of the pulmonary vascular bed and its remodeling, and a rapid and non-invasive assessment of IA to overcome the technical limitations in patients with COVID-19.     

伴下呼吸道多重耐药菌感染的 慢性阻塞性肺病患者病原菌分布及危险因素分析

目的 探讨伴下呼吸道多重耐药菌感染的慢性阻塞性肺病(COPD)患者病原菌分布及其危险因素。方法 选取2017年1月至2018年6月我院收治的138例COPD伴下呼吸道感染患者作为研究对象,根据下呼吸道分泌物是否分离出多重耐药菌将患者分为多重耐药组(MDR组,71例)和非多重耐药组(NMDR组,67例)。采用全自动细菌鉴定仪对菌种进行鉴定,采用K-B纸片法进行药敏试验,并分析多重耐药菌感染的危险因素。结果 多重耐药组患者共分离出84株病原菌,其中革兰阴性菌所占比例最高,为58.33%;革兰阳性菌与真菌分别占22.62%和19.05%。MDR组与NMDR组患者在COPD分级、住院时间、机械通气治疗、侵入性操作、长期使用糖皮质激素、长期使用抗菌药物及糖尿病史方面差异均有统计学意义(P0.05)。多因素Logistic回归分析显示机械通气治疗、侵入性操作、使用糖皮质激素、长期使用抗菌药物及糖尿病史是多重耐药菌感染的独立危险因素(P0.05)。结论 COPD伴下呼吸道多重耐药菌感染病原菌以革兰阴性菌为主,机械通气治疗、侵入性操作、长期使用糖皮质激素、长期使用抗菌药物及糖尿病史是发生感染的独立危险因素。建议根据病原菌种类选择相应的敏感药物,并采取针对危险因素的有效措施。     

Estradiol improves pulmonary hemodynamics and vascular remodeling in perinatal pulmonary hypertension

Partial ligation of the ductus arteriosus (DA) in the fetal lamb causes sustained elevation of pulmonary vascular resistance (PVR) and hypertensive structural changes in small pulmonary arteries, providing an animal model for persistent pulmonary hypertension of the newborn. Based on its vasodilator and antimitogenic properties in other experimental studies, we hypothesized that estradiol (E(2)) would attenuate the pulmonary vascular structural and hemodynamic changes caused by pulmonary hypertension in utero. To test our hypothesis, we treated chronically instrumented fetal lambs (128 days, term = 147 days) with daily infusions of E(2) (10 microg; E(2) group, n = 6) or saline (control group, n = 5) after partial ligation of the DA. We measured intrauterine pulmonary and systemic artery pressures in both groups throughout the study period. After 8 days, we delivered the study animals by cesarean section to measure their hemodynamic responses to birth-related stimuli. Although pulmonary and systemic arterial pressures were not different in utero, fetal PVR immediately before ventilation was reduced in the E(2)-treated group (2.43 +/- 0.79 vs. 1.48 +/- 0.26 mmHg. ml(-1). min, control vs. E(2), P < 0.05). During the subsequent delivery study, PVR was lower in the E(2)-treated group in response to ventilation with hypoxic gas but was not different between groups with ventilation with 100% O(2). During mechanical ventilation after delivery, arterial partial O(2) pressure was higher in E(2) animals than controls (41 +/- 11 vs. 80 +/- 35 Torr, control vs. E(2), P < 0. 05). Morphometric studies of hypertensive vascular changes revealed that E(2) treatment decreased wall thickness of small pulmonary arteries (59 +/- 1 vs. 48 +/- 1%, control vs. E(2), P < 0.01). We conclude that chronic E(2) treatment in utero attenuates the pulmonary hemodynamic and histological changes caused by DA ligation in fetal lambs.     

A two-component simulation model to teach respiratory mechanics

Interactive learning has been proven instrumental for the understanding of complex systems where the interaction of interdependent components is hard to envision. Due to the mechanical properties and mutual coupling of the lung and thorax, respiratory mechanics represent such a complex system, yet their understanding is essential for the diagnosis, prognosis, and treatment of various respiratory disorders. Here, we present a new mechanical model that allows for the simulation of respiratory pressure and volume changes in different ventilation modes. A bellow reflecting the "lung" is positioned within the inverted glass cylinder of a bell spirometer, which is sealed by a water lock and reflects the "thorax." A counterweight attached to springs representing the elastic properties of the chest wall lifts the glass cylinder, thus creating negative "pleural" pressure inside the cylinder and inflating the bellow. Lung volume changes as well as pleural and intrapulmonary pressures are monitored during simulations of spontaneous ventilation, forced expiration, and mechanical ventilation, allowing for construction of respiratory pressure-volume curves. The mechanical model allows for simulation of respiratory pressure changes during different ventilation modes. Individual relaxation curves constructed for the lung and thorax reflect the basic physiological characteristics of the respiratory system. In self-assessment, 232 medical students passing the physiology laboratory course rated that interactive teaching at the simulation model increased their understanding of respiratory mechanics by 70% despite extensive prior didactic teaching. Hence, the newly developed simulation model fosters students' comprehension of complex mechanical interactions and may advance the understanding of respiratory physiology.     

Non-invasive mechanical ventilation for acute respiratory failure.

The value of mechanical ventilation using intermittent positive pressure ventilation delivered non-invasively by nasal mask was assessed in six patients with life threatening exacerbations of chronic respiratory disease. Median (range) arterial oxygen and carbon dioxide tensions were 4.4 (3.5-7.2) kPa and 8.7 (5.5-10.9) kPa respectively, with four patients breathing air and two controlled concentrations of oxygen. The arterial oxygen tension increased with mechanical ventilation to a median (range) of 8.7 (8.0-12.6) kPa and the carbon dioxide tension fell to 8.2 (6.5-9.2) kPa. Four patients discharged after a median of 10 (8-17) days in hospital were well five to 22 months later. One died at four days of worsening sputum retention and another after five weeks using the ventilator for 12-16 hours each day while awaiting heart-lung transplantation. This technique of mechanical ventilation avoids endotracheal intubation and can be used intermittently. Hypercapnic respiratory failure can be relieved in patients with either restrictive or obstructive lung disease in whom controlled oxygen treatment results in unacceptable hypercapnia. Respiratory assistance can be tailored to individual need and undertaken without conventional intensive care facilities.     

Efficacy of high-frequency ventilation in presence of extensive ventilation-perfusion mismatch

Ten anesthetized normal dogs were each given two methacholine inhalational challenges to produce large amounts of low ventilation-perfusion (VA/Q) regions but little shunt. After one challenge, high-frequency ventilation (HFV) was applied, whereas after the other conventional mechanical ventilation (MV) was used, the order being randomized. Levels of both ventilatory modes were selected prior to challenge so as to result in similar and normal mean airway pressures and arterial PCO2 levels during control conditions. Gas exchange was assessed by both respiratory and multiple inert-gas transfer. Comparing the effect of HFV and MV, no statistically significant differences were found for lung resistance, pulmonary hemodynamic indices, arterial and mixed venous PO2, expired-arterial PO2 differences, or inert-gas data expressed as retention-excretion differences. The only variables that were different were mean airway pressure (2 cm higher during HFV, P less than 0.04) and arterial PCO2 (10 Torr higher during HFV, P less than 0.002). These results suggest that in this canine model of lung disease characterized by large amounts of low VA/Q regions, HFV is no more effective in delivering fresh gas to such regions than is MV.     

Ontogeny of respiratory control and pulmonary mechanics in newborn rabbits

Maturation of the respiratory pattern and the active and passive mechanical properties of the respiratory system were assessed in 19 tracheotomized rabbits (postnatal age range: 1-26 days) placed in a body plethysmograph. With maturation both minute ventilation and tidal volume significantly increased, whereas respiratory frequency decreased. When normalized for body weight (kg) both the passive (Rrs X kg) and active (R'rs X kg) resistances of the respiratory system significantly increased with age, whereas the corresponding passive (Crs X kg-1) and active (C'rs X kg-1) compliances significantly decreased. At any given age R'rs X kg only slightly exceeded Rrs X kg, whereas C'rs X kg-1 was significantly lower than Crs X kg-1. Moreover, the maturational increases in Rrs X kg and R'rs X kg exceeded the corresponding decreases in Crs X kg-1 and C'rs X kg-1, resulting in significant age-related increases in both the passive (tau rs) and active (tau'rs) time constants of the respiratory system. Due to the age-related increases in tau'rs, producing a delayed volume response to any given inspiratory driving pressure, the relative volume loss obtained at any time during inspiration was greater in the maturing rabbit. On the other hand, because of concomitant compensatory changes in respiratory pattern, evidenced by increases in inspiratory duration with age, the end-inspiratory tidal volume loss in the maturing animal was maintained generally less than 10% at all postnatal ages. Thus maturational changes in respiratory pattern appear coupled to changes in the active mechanical properties of the respiratory system. The latter coupling serves to optimize the transduction of inspiratory pressure into volume change in a manner consistent with establishing the minimum inspiratory work of breathing during postnatal development.     

Congenital pulmonary lymphangiectasia

Congenital pulmonary lymphangiectasia (PL) is a rare developmental disorder involving the lung, and characterized by pulmonary subpleural, interlobar, perivascular and peribronchial lymphatic dilatation. The prevalence is unknown. PL presents at birth with severe respiratory distress, tachypnea and cyanosis, with a very high mortality rate at or within a few hours of birth. Most reported cases are sporadic and the etiology is not completely understood. It has been suggested that PL lymphatic channels of the fetal lung do not undergo the normal regression process at 20 weeks of gestation. Secondary PL may be caused by a cardiac lesion. The diagnostic approach includes complete family and obstetric history, conventional radiologic studies, ultrasound and magnetic resonance studies, lymphoscintigraphy, lung functionality tests, lung biopsy, bronchoscopy, and pleural effusion examination. During the prenatal period, all causes leading to hydrops fetalis should be considered in the diagnosis of PL. Fetal ultrasound evaluation plays a key role in the antenatal diagnosis of PL. At birth, mechanical ventilation and pleural drainage are nearly always necessary to obtain a favorable outcome of respiratory distress. Home supplemental oxygen therapy and symptomatic treatment of recurrent cough and wheeze are often necessary during childhood, sometimes associated with prolonged pleural drainage. Recent advances in intensive neonatal care have changed the previously nearly fatal outcome of PL at birth. Patients affected by PL who survive infancy, present medical problems which are characteristic of chronic lung disease.     

Positive outcome of average volume-assured pressure support mode of a Respironics V60 Ventilator in acute exacerbation of chronic obstructive pulmonary disease: a case report

ABSTRACT: INTRODUCTION: We were able to treat a patient with acute exacerbation of chronic obstructive pulmonary disease who also suffered from sleep-disordered breathing by using the average volume-assured pressure support mode of a Respironics V60 Ventilator (Philips Respironics: United States). This allows a target tidal volume to be set based on automatic changes in inspiratory positive airway pressure. This removed the need to change the noninvasive positive pressure ventilation settings during the day and during sleep. The Respironics V60 Ventilator, in the average volume-assured pressure support mode, was attached to our patient and improved and stabilized his sleep-related hypoventilation by automatically adjusting force to within an acceptable range. CASE PRESENTATION: Our patient was a 74-year-old Japanese man who was hospitalized for treatment due to worsening of dyspnea and hypoxemia. He was diagnosed with acute exacerbation of chronic obstructive pulmonary disease and full-time biphasic positive airway pressure support ventilation was initiated. Our patient was temporarily provided with portable noninvasive positive pressure ventilation at night-time following an improvement in his condition, but his chronic obstructive pulmonary disease again worsened due to the recurrence of a respiratory infection. During the initial exacerbation, his tidal volume was significantly lower during sleep (378.9 +/- 72.9mL) than while awake (446.5 +/- 63.3mL). A ventilator that allows ventilation to be maintained by automatically adjusting the inspiratory force to within an acceptable range was attached in average volume-assured pressure support mode, improving his sleep-related hypoventilation, which is often associated with the use of the Respironics V60 Ventilator. Polysomnography performed while our patient was on noninvasive positive pressure ventilation revealed obstructive sleep apnea syndrome (apnea-hypopnea index = 14), suggesting that his chronic obstructive pulmonary disease was complicated by obstructive sleep apnea syndrome. CONCLUSION: In cases such as this, in which patients with severe acute respiratory failure requiring full-time noninvasive positive pressure ventilation therapy also show sleep-disordered breathing, different ventilator settings must be used for waking and sleeping. On such occasions, the Respironics V60 Ventilator, which is equipped with an average volume-assured pressure support mode, may be useful in improving gas exchange and may achieve good patient compliance, because that mode allows ventilation to be maintained by automatically adjusting the inspiratory force to within an acceptable range whenever ventilation falls below target levels.     

A mathematical model of pulmonary gas exchange under inflammatory stress

During a severe local or systemic inflammatory response, immune mediators target lung tissue. This process may lead to acute lung injury and impaired diffusion of gas molecules. Although several mathematical models of gas exchange have been described, none simulate acute lung injury following inflammatory stress. In view of recent laboratory and clinical progress in the understanding of the pathophysiology of acute lung injury, such a mathematical model would be useful. We first derived a partial differential equations model of gas exchange on a small physiological unit of the lung (≈25 alveoli), which we refer to as a respiratory unit (RU). We next developed a simple model of the acute inflammatory response and implemented its effects within a RU, creating a single RU model. Linking multiple RUs with various ventilation/perfusion ratios and taking into account pulmonary venous blood remixing yielded our lung-scale model. Using the lung-scale model, we explored the predicted effects of inflammation on ventilation/perfusion distribution and the resulting pulmonary venous partial pressure oxygen level during systemic inflammatory stresses. This model represents a first step towards the development of anatomically faithful models of gas exchange and ventilation under a broad range of local and systemic inflammatory stimuli resulting in acute lung injury, such as infection and mechanical strain of lung tissue.     

PEEP对骨肿瘤手术患者全身麻醉期呼吸功能和血流动力学的影响

目的:探讨呼气末正压通气(PEEP)对骨肿瘤手术患者全身麻醉期呼吸功能和血流动力学的影响。方法:选取2014年1月-2015年12月期间我院收治的60例骨肿瘤患者,所有患者给予常规麻醉诱导后连接呼吸机行机械通气,观察并记录不同PEEP通气(0cm H_2O,5cm H_2O和10cm H_2O)下呼吸功能及血流动力学指标。结果:PEEP 10cm H_2O通气水平的气道峰压(Peak)、气道平台压(Plat)显著高于PEEP 5cm H_2O和PEEP 0cm H_2O通气,PEEP 5cm H_2O通气水平的Ppeak和Pplat显著高于PEEP 0cm H_2O通气,差异均有统计学意义(P0.05);不同PEEP通气水平的心率(HR)、平均动脉压(MAP)和中心静脉压(CVP)比较差异无统计学意义(P0.05);不同PEEP通气水平的心脏指数(CI)、每搏指数(SVI)、全心射血分数(GEF)、心脏功能指数(CFI)、每搏变异度(SVV)、脉压变异率(PPV)、胸腔内血容量指数(ITBI)、血管外肺水指数(ELWI)和肺血管通透性指数(PVPI)比较差异无统计学意义(P0.05)。结论:增加PEEP通气值能够显著改善吸功能的Ppeak和Ppla指标,但不影响血流动力学指标,值得临床推广应用。     

An ultrasound imaging method for in vivo tracheal bulk and Young's moduli of elasticity

Alterations in neonatal airway mechanical properties resulting from ventilatory therapies such as mechanical ventilation have been implicated in airway collapse and chronic disease. Advances in ultrasound (US) technology allow for real-time imaging and accurate measurement of tracheal dimensions in vivo; thus, changes in mechanical properties can be tracked longitudinally. In this report we introduce an adaptation of engineering concepts using US imaging data to study airway mechanics in vivo. In this protocol, tracheal segments are isolated in a spontaneously breathing newborn lamb model and the segments are exposed to time-cycled, pressure-limited mechanical ventilation. Serially, tracheal segments are filled with saline and pressure-volume relationships are recorded with stepwise volume infusions. US dimensional measurements of the segments are made while static (no distending pressure) and at pressure limits during dynamic ventilator cycling. US measurements are used to normalize pressure-volume data for resting volume, calculation of bulk modulus, stress-strain relationships and the adapted Young's modulus associated with tangential wall stress. Temporal changes in bulk and Young's moduli demonstrate the time dependence of alterations in conducting airway mechanical properties in vivo during the course of mechanical ventilation. This methodology will provide a means to evaluate respiratory therapies with respect to airway mechanics.     

Self-controlled artificial respiration

We compared respiratory parameters during natural and self-controlled mechanical breathing to investigate mechanisms of respiratory control in alert humans. The self-control of mechanical breathing is realised manually: duration and velocity of air flow are controlled by left and right hands, resp. In this case, the respiratory afferent information is used to control activity of hand muscles but not of breathing muscles. The findings show that lung ventilation during self-controlled mechanical breathing increases by 7.5 l/min. at resting, by 6.3 l/min. during an exercise, as compared with the natural breathing. The increase in the lung ventilation occurs on account of an increase in the tidal volume but the frequency of the self-controlled mechanical breathing tends to be lesser at resting and was statistically significantly lower in exercise that at natural breathing. The exercise increases the lung ventilation by 13.0 l/min. at natural breathing and by 11.8 l/min. during self-controlled mechanical breathing. The findings suggest that the increased lung ventilation during self-controlled mechanical breathing is connected with creation of a new movement skill, and the modified pattern of self-controlled mechanical breathing is caused by a process of cortical transformation of respiratory afferents signals to efferent signals towards the hand muscles.     

Factors influencing mechanical performance of neonatal high-frequency ventilators

Factors influencing the mechanical performance of neonatal high-frequency ventilators of diverse design were assessed under controlled conditions. Each of eight ventilators was coupled to in vitro models of the neonatal respiratory system simulating disease of varying severity. The principal performance characteristics examined were frequency dependence and load dependence of tidal volume delivered, peak inspiratory flow rate, and waveforms of pressure at either end of the endotracheal tube. Despite wide diversity of ventilator designs, including jets, flow interrupters, and oscillators, common features emerged. In almost all devices tidal volume increased with endotracheal tube size, was invariant with respiratory system compliance, and decreased with frequency of oscillation. Peak inspiratory flow rates for a given tidal volume and frequency were smallest in the group of oscillators compared with jets and flow interrupters. Proximal pressure was a poor indicator of distal pressure. These findings suggest that delivered tidal volume may be sensitive to endotracheal tube size and airway patency but relatively insensitive to changes in lung tissue or chest wall mechanical properties. In these regards high-frequency ventilation differs from pressure-limited conventional mechanical ventilation. Comparison of data obtained at different clinical centers using high-frequency ventilators of varying design may be possible by taking these factors into account.