Respiratory mechanics during mechanical ventilation: A model study on the effects of leak around a tracheal tube

Air leak around a tracheal tube (TT) during mechanical ventilation is likely to occur during the inspiratory phase because airway pressure is high for a prolonged period. The presence of a leak may introduce errors in measurements of respiratory mechanics made at the airway opening. If so, respiratory mechanics can be measured more accurately when data are collected during the expiratory phase of ventilation. We examined this phenomenon in a lung model. When a leak was introduced into the model, simulating a leak around the TT, the leak occurred predominantly during the inspiratory phase of respiration. As the magnitude of the leak increased, the overestimation of resistance progressively increased, when calculated from pressure and flow measured at the airway opening. A large leak (38%) resulted in an overestimation of respiratory system resistance by 51% and an underestimation of elastance (Ers) by 23% when calculated from the entire ventilatory cycle. However, there was no under- or overestimation in Rrs when calculated from the expiratory phase only, and ERS was overestimated by only 6.1%. Varying peak inspiratory pressure, end-expiratory pressure, and expiratory time did influence the effect of leak, however, respiratory mechanics could still be calculated accurately from the expiratory phase under these conditions. We conclude that measurements of lung mechanics from the expiratory phase is a promising approach to dealing with the problem of measuring respiratory mechanics in mechanically ventilated infants with leaks around the tracheal tube. Pediatr. Pulmonol. 1997; 24:423–428. © 1997 Wiley-Liss, Inc.     

Influence of negative pressure applied to the upper airway on the breathing pattern in unanesthetized awake dogs

We examined the influence of changes in upper airway pressure on the breathing pattern in 5 unanesthetized awake dogs. The dogs breathed through an endotracheal tube or through a comfortably fitting fiberglass snout mask. With matched resistances and volume of the dead space, the inspiratory duration, tidal volume, and minute ventilation were higher during nasal breathing compared to tracheal breathing. Nasal and tracheal occlusion produced prolongation of inspiration in the first occluded breathing attempt, but the prolongation was more marked in nasal occlusion tests. Augmentation of genioglossus muscle activity occurred on the first occluded breath in nasal but not tracheal occlusion. In another series of experiments, negative pressure was applied to the isolated upper airway while the dog breathed through a tracheostomy tube. Negative pressure caused a prolongation of inspiratory duration which was proportional to the level of the applied pressure. However, the prolongation of inspiratory duration was significantly more marked when application of negative pressure was timed simultaneously with tracheal occlusion. Our results demonstrate that the upper airway has a powerful effect on the control of breathing, which becomes more evident during tracheal occlusion.     

A comparison of proximal and distal high-frequency jet ventilation in an experimental animal model

High-frequency jet ventilation using either a proximal or a distal endotracheal injection site through a triple-lumen endotracheal tube was studied in 10 adult cats. The comparative effects on pulmonary gas exchange, tracheal pressure, heart rate, and blood pressure were examined for each injection site at both high (8-12 pounds per square inch [PSI] and low (5-8 PSI) jet-driving pressures in normal and lung-injured cats. Lung injury was created by modification of a surfactant washout technique previously demonstrated in rabbits. Alveolar ventilation (PaCO2) was found to be significantly better with distal than with proximal jet injection under all experimental conditions. At high jet-driving pressures, peak inspiratory pressure was higher in both normal (p = 0.03) and lung-injured cats (p = 0.002) with distal high-frequency jet ventilation. In addition, lung-injured animals were observed to have higher distal mean airway pressures at high jet-driving pressures (p less than 0.01). No differences in oxygenation were found in any circumstances. The results of this animal study suggest that distal high-frequency jet ventilation may be more effective in those situations in which improvement in alveolar ventilation is the major goal and that during proximal high-frequency jet ventilation airway pressures should be monitored as far distally as possible.     

Intracuff pressures in endotracheal and tracheostomy tubes. Related cuff physical characteristics

This study compared intracuff pressure (ICP) during mechanical ventilation in a variety of currently used endotracheal (ET) and tracheostomy (trach) tube cuffs and related cuff physical characteristics. Tracheostomy tube physical characteristics were also measured. Variation was observed to exist between "just-seal" inspiratory and end-expiratory intracuff pressure during mechanical ventilation. Cuff diameter, thickness, compliance, geometry (shape), resting volume, and just-seal volume also varied. ICP varied with cuff diameter, thickness, compliance, geometry (shape), and trachea size, as well as tube curve and cuff position in the trachea. Thin, large-diameter, compliant cuffs generally "just seal" with relatively low ICPs. We recommend use of tracheal airways (endotracheal and tracheostomy) fitted with cuffs that seal in patients with low intracuff pressures. We also recommend nonrigid (soft) thermolabile tracheostomy tubes.     

Reflex influences from the extrathoracic trachea during airway occlusion.

We have performed experiments in 26 dogs anesthetized with pentobarbital and fitted with an endotracheal tube. The inflatable cuff of this tube was positioned either at the level of the cricoid cartilage or at the thoracic inlet. In this latter situation the extrathoracic trachea (E.T.T.) is not subjected to any change in transmural pressure both during breathing and airway occlusion. We have compared the inspiratory output in term of the integrated phrenic discharge during airway occlusion at FRC with the tracheal tube positioned at either one of the two levels. In most of the experiments (16 out of 26) the inspiratory output during airway occlusion is significantly greater (157%) when the E.T.T. is not by-passed and this difference disappears after bilateral vagotomy. We interpret these results by the asymmetrical response of the tracheal stretch receptors to positive and negative transmural pressure (Pt); most of these receptors are active at FRC and decrease their activity at low negative Pt, as that attained in the first occluded breath. These results seem to suggest that the reflex influences from the extrathoracic tracheal receptors on the inspiratory output are similar to those originating from the intrathoracic airway stretch receptors.     

Reduction in tracheal lumen due to endotracheal intubation and its calculated clinical significance

BACKGROUND: The flow in the human trachea is turbulent. Thus, the tracheal resistance (R) and the pressure gradient (DeltaP) required to maintain a given flow across the trachea is inversely related to its radius raised to the fifth power. If the caliber reduction ratio (X) after endotracheal intubation is calculated as X = radius of the endotracheal tube (rETT)/radius of the trachea (rT), then DeltaP and/or R will be increased by (1/X)(5). STUDY OBJECTIVES: To measure the actual ratio between rETT and rT following endotracheal intubation of pediatric patients with respiratory failure and to calculate the resulting increase in the tracheal R and DeltaP for a given inspiratory flow rate. DESIGN: Retrospective chart review. SETTING: Pediatric ICU in a tertiary-care teaching children's medical center. PATIENT ENROLLMENT: Twenty consecutive pediatric patients (mean [+/- SD] age, 6.4 +/- 7.2 years) whose tracheas had been intubated for various causes of respiratory failure, and who had received a CT scan, were included in our study. All patients received an endotracheal tube the size of which was derived from the following formula: (age in years/4) + 4. MEASUREMENTS AND MAIN RESULTS: rT and rETT were measured from CT scan sections at and around the level of the thoracic inlet, and the average values were used to calculate X. These values ranged from 0.33 to 0.65 (mean, 0. 55 +/- 0.8). The factor (1/X)(5) was calculated for each patient and then was multiplied by the known normal value for tracheal R for adolescents and adults (0.07 cm H(2)O/L/s) to obtain the value of R resulting from the artificial airway, (1/X)(5) x 0.07. Our results showed that tracheal R increased due to caliber reduction of the trachea after endotracheal intubation by 33.9 +/- 52.5-fold (range, 8.6- to 255.5-fold). In order to maintain an inspiratory flow of 1 L/s, the value of P for the intubated trachea would increase from 0. 07 cm H(2)O to a mean of 2.4 +/- 3.7 cm H(2)O (range, 0.6 to 18 cm H(2)O). In two of our patients, the rT/rETT ratios were < 0.5 (0.33 and 0.44, respectively); this translated into a more significant increase in the calculated DeltaPs, 18 and 4.2 cm H(2)O, respectively. CONCLUSIONS:: The common value of X due to endotracheal intubation is between 0.5 and 0.6, which in and of itself results in an increase in R across the intubated trachea up to 32-fold. The calculated increase in P as a result of this is between 2 and 3 cm H(2)O for adolescents or young adults. The addition of pressure support of at least 3 cm H(2)O during spontaneous ventilation via an endotracheal tube, which is common practice in pediatric critical care, should alleviate any respiratory distress emanating from the increased R. However, a value for X < 0.5, which was found in 10% of our patients (2 of 20 patients), results in a much higher calculated increase in the pressure gradient and, therefore, a higher level of pressure support is required to overcome this increase.     

Accurate, noninvasive quantitation of expiratory gas leak from uncuffed infant endotracheal tubes

Accurate measurement of expiratory gas leak from uncuffed infant endotracheal tubes is an important requirement for evaluating the rates of metabolic gas exchange by indirect calorimetry in neonates receiving mechanical ventilation. The present study reports a new, noninvasive technique for the efficient collection and analysis of expiratory gases leaked from a closed-circuit metabolic monitoring system recently described. A loose-fitting face mask is placed over the infant's endotracheal appliance and air is entrained from the mask cavity at 100 mL/min for CO2 analysis by infrared capnometry. In vitro calibration of this apparatus demonstrates a relative error of less than 5% of simulated endotracheal tube leak. In vivo application to metabolic rate assessment (using the MGM Jr. metabolic cart) in 12 intubated, ventilated infants ranging from 1.56 to 4.07 kg study weight demonstrated endotracheal tube leaks from 0.49 to 7.40% of net CO2 production, which ranged 10.67 to 70.91 mL/min (or mean 8.22 +/- 0.93 SEM mL/kg/min). The magnitude of tube leakage of mixed expiratory gases could not be predicted from endotracheal tube diameter, ventilator settings, or infant activity or posture. As new instrumentation becomes available to measure the rates of metabolic gas exchange in intubated infants, systematic evaluation of uncuffed endotracheal tube gas leaks becomes critical.     

Influence of the upper airway on breathing pattern and expiratory time constant in unanesthetized dog pups

Unanesthetized dog pups (2 to 31 days old) respond to sudden opening of a tracheal cannula to atmospheric pressure with a marked increase in breathing frequency. This response is achieved with a 25% decrease in inspiratory and 40% decrease in expiratory times. Expiratory thyroarytenoid muscle activity increased concomitantly, while inspiratory diaphragmatic and posterior cricoarytenoid muscle activities were reduced. These responses are interpreted as a compensatory mechanism for maintenance of an elevated end-expiratory lung volume with functional loss of the upper airway. The changes in expiratory time and thyroarytenoid muscle activity were not observed when positive pressure was applied at the trachea. The expiratory time constant was assessed during spontaneous breathing. The mean value was twice as long during nasal breathing than during tracheal breathing. The nasal value was substantially increased when the thyroarytenoid muscle was active during expiration.     

Functional diagnosis in surgery of the large airways

The main indications for surgery of the airways are (1) non-tumorous airway stenosis and (2) tumors of the large airways with and without relevant stenoses. The aim of the following study was to find out which degree of stenosis is an absolute indication for resection and to what extent the functional disturbances are reversible following surgery. We investigated various groups of patients (stenosis of the trachea, lobectomy with sleeve resection, extended pneumectomy with resection of the distal trachea, pneumectomy with resection of the bifurcation, resection of the main bronchus and lobectomy, rupture of the main bronchus) from 1978 to 1982, before and up to 3 years after surgery. Body-plethysmography (one second forced expiratory volume = FEV1; one second forced inspiratory volume = FIV1; Residual volume = RV; total lung capacity = TLC; airway resistance = Raw; specific airway conductance = sGaw), flow volume relation measurements (maximal inspiratory flow = Vmax insp; maximal expiratory flow = Vmax exp; and flow at various lung volumes), blood gas analysis and an endoscopic estimation of the tracheal diameter were performed. Tracheal resection with end-to-end anastomosis in patients with non-tumerous tracheal stenosis improved the tracheal diameter from 6.0 to 11.7 mm, the sGaw from 0.04 to 0.08 (cmH2O s)-1 and the severity of dyspnea significantly. There was no measurable change in airway caliber following administration of beta 2-adrenergics. The most sensitive parameters for describing the tracheal stenosis are the resistance and flow volume values. A tracheal diameter smaller than 6.5 mm corresponding to a sGaw smaller than 0.03 (cmH2O s)-1 procedured severe dyspnea, which is incompatibly with normal life.(ABSTRACT TRUNCATED AT 250 WORDS)     

常规密闭机械通气在全麻下支气管镜介入治疗中的应用研究

目的 通过经气管插管对常规密闭机械通气的健康犬施行支气管镜模拟介入治疗,观察气管镜插入前后呼吸机参数及动脉血气分析的变化情况,以期寻求在常规密闭机械通气的条件下实施支气管镜介入治疗时所需要的适宜的气管通道及呼吸机参数.方法 健康杂种犬10只,全麻和肌松状态下气管插管、常规密闭机械通气,稳定后将直径6.0 mm的支气管镜...     

Evaluation of bronchodilator responsiveness in mechanically ventilated patients

Airway pressure, flow, and volume were measured before and after administration of aerosolized metaproterenol during controlled mechanical inflation and stepwise deflation of the relaxed respiratory system in 13 mechanically ventilated patients. An increase in passive expiratory flow at constant respiratory system recoil pressure was considered evidence of bronchodilatation. In 10 patients, at a respiratory system recoil pressure of 6 cm H2O (VP6), expiratory flow increased 21 to 500% above prebronchodilator level. In these 10 dynamically hyperinflated patients, an increase in VP6 was associated with a decrease in peak inspiratory pressure (Ppeak) (mean delta = -4.7 cm H2O) and a decrease in intrinsic positive end-expiratory pressure (Peepi) (mean delta = -2.4 cm H2O). The elastance of the respiratory system was not affected by metaproterenol, and the delta Peepi corresponded to a mean decrease in end-expiratory lung volume of 0.20 L. The results are consistent with predictions based on a single-compartment model. When mean expiratory flow is determined only by the tidal volume and expiratory time, a decrease in airway resistance results in a decrease in lung volume at which patients are ventilated. Therefore, the decrease in Ppeak is caused not only by a decrease in the resistive pressure cost but also by a decrease in the elastic pressure cost of inflating the respiratory system. It is emphasized that Ppeak and Peepi provide valuable information about bronchodilator-induced changes in lung function during controlled mechanical ventilation.     

Effects of expiratory flow resistance on inspiratory work of breathing

To minimize work of breathing, airway pressure should not fluctuate during spontaneous breathing with continuous positive airway pressure (CPAP). However, flow resistance in the inspiratory limb of the breathing circuit and an inadequate continuous gas flow rate result in airway pressure fluctuation and increased work of breathing. Flow resistance of the expiratory pressure/exhalation valve also directly affects the level of airway pressure during spontaneous inhalation with CPAP (the greater the resistance of the valve, the greater the decrease in airway pressure and work of breathing). We compared this effect with three types of expiratory pressure valves: a threshold resistor with low resistance to flow, an inflatable balloon (mushroom) valve with moderate resistance to flow, and a variable-orifice flow resistor with a high resistance to flow. Work increased up to threefold with the balloon valve and more than tenfold with the flow resistor compared with the threshold resistor. To apply CPAP, expiratory pressure valves with low resistance to flow should be used to minimize fluctuations in airway pressure and, thus, in the work of spontaneous breathing.     

气管内吹气对急性高碳酸血症家兔血气及呼吸力学的影响

目的　探讨气管内吹气（ Ｔ Ｇ Ｉ） 对急性高碳酸血症（ Ｈ Ｃ） 家兔二氧化碳清除的效果及其对通气效率的改善作用。方法　用自行设计的 Ｔ Ｇ Ｉ装置对常规正常机械通气（ Ｃ Ｍ Ｖ） 和低通气致 Ｈ Ｃ 家兔行 Ｔ Ｇ Ｉ,分别观察两组动物在不同吹气流量（０２ Ｌ·ｍｉｎ１ 和０４ Ｌ·ｍｉｎ１） 时呼气末二氧化碳分压（ Ｐｅｔ Ｃ Ｏ２） 、血气与呼吸力学等指标的变化。结果　（１） Ｔ Ｇ Ｉ可明显降低两组动物的动脉血二氧化碳分压（ Ｐａ Ｃ Ｏ２） 水平,并能在潮气量（ Ｖ Ｔ） 降低３０ ％ 的情况下维持 Ｐａ Ｃ Ｏ２ 在正常范围, Ｔ Ｇ Ｉ降低 Ｐａ Ｃ Ｏ２ 的作用呈流量依赖性;（２） Ｔ Ｇ Ｉ使两组动物的气道压力明显增高,但 Ｈ Ｃ 组气道峰压（ Ｐｐｅａｋ） 、平台压（ Ｐｐａｕｓｅ） 水平均显著低于 Ｃ Ｍ Ｖ 组;（３） Ｔ Ｇ Ｉ使 Ｐｅｔ Ｃ Ｏ２ 明显降低,呼气阻力（ Ｒｅ） 及呼气潮气量（ Ｖ Ｅ） 显著增高,而对肺顺应性（ Ｃｓｔ） 无明显影响;（４） Ｔ Ｇ Ｉ对平均动脉压及心率无显著影响。结论　 Ｔ Ｇ Ｉ是一种简便实用的机械通气的辅助手段,它能有效地降低 Ｐａ Ｃ Ｏ２ ,并使气道压力维持在低水平。     

Elevated lung volume and alveolar pressure during jet ventilation of rabbits

We measured lung volume, tidal volume, and pressures at the airway opening, trachea, and alveoli during jet ventilation of rabbits at frequencies from 2 to 15 Hz when inspiratory time was varied from 10 to 50% of the ventilator cycle. Lung volume was determined dynamically and was dependent on tidal volume, expiratory duration, and the expiratory time constant of the respiratory system. Tidal volume decreased with increasing frequency and lung volume, and was greater than estimated dead-space volume over most of the frequency range studied. Pressure at the airway opening was not a good estimate of either mean pressure or pressure swings in the alveoli. Tracheal pressure corresponded fairly well to alveolar pressure. Alveolar pressure swings diminished with increasing frequency and decreasing inspiratory duration. In the clinical setting these results mean that measurement of pressures at the airway opening is not an adequate way to monitor patients during jet ventilation. In addition, the clinician must be aware that substantial increases in functional residual capacity may occur during jet ventilation, thereby placing the patient at risk of pneumothorax.     

Demand and continuous flow intermittent mandatory ventilation systems

A mechanical lung was used to evaluate the pressure and flow characteristics of four demand and two continuous flow intermittent mandatory ventilation (IMV) systems. The amount of negative pressure required to initiate inspiratory flow and peak expiratory resistance were measured. The inspiratory pressure required to initiate flow in the demand mode was also compared to pressures generated in the assist mode. In addition, the peak expiratory resistance was measured with four commercially available exhalation valves. Results showed that the ventilator manometer measuring internal machine pressures significantly underestimated the amount of negative pressure required to open the demand valve (p less than 0.01). There are major differences in the flow and pressure characteristics among demand and continuous flow IMV systems. Systems that impose high inspiratory elastic threshold loads and expiratory flow resistive loads may have a deleterious effect on the mechanics of breathing, and thereby limit weaning success and eventually impair the recovery of certain patients in respiratory failure. The basic methodology, especially the simple technique of inserting an aneroid manometer in line next to a patient's ET tube, for measuring proximal negative inspiratory force (NIF test) can be easily applied to any and all ventilators at any practitioner's individual institution.     

Tracheal pressure ventilator control

Tracheal pressure ventilator control (TPVC) is a ventilator mode that relies on tracheal pressure at the carinal end of the endotracheal tube for triggering the ventilator ;;on,' controlling pressure, and cycling the ventilator ;;off.' TPVC automatically nullifies imposed resistive work of the breathing apparatus (endotracheal tube plus ventilator) by providing automatic and variable levels of pressure assist. TPVC improves ventilator responsiveness for a spontaneously breathing patient by providing significantly higher peak inspiratory flow rates much closer to that demanded by a patient. TPVC also provides higher assist pressures and flow rates earlier in the breath and thus better-match ventilator-supplied flow to patient-demanded flow than an equivalent level of pressure support ventilation. Matching patient demand for flow to ventilator supply of flow, early in the breath, promotes patient-ventilator synchrony and minimizes work of breathing. We recommend moving the pressure-triggering and control site to the carinal end of the endotracheal tube to provide TPVC.     

Percutaneous transtracheal jet ventilation: a safe, quick, and temporary way to provide oxygenation and ventilation when conventional methods are unsuccessful

INTRODUCTION: Percutaneous transtracheal jet ventilation (PTJV) with a large-bore angiocath that is inserted through the cricothyroid membrane can provide immediate oxygenation from a high-pressure (50 lb per square inch) oxygen wall outlet, as well as ventilation by means of manual triggering. The objective of this retrospective study is to highlight the potential benefit of PTJV as a temporary lifesaving procedure during difficult situations when oral endotracheal intubation is unsuccessful and bag-valve-mask ventilation is ineffective for oxygenation during acute respiratory failure. METHODS: The medical records of 29 consecutive patients who required emergent PTJV within the past 4 years were reviewed. PTJV was required because the pulse O(2) saturation could not be maintained at > 90% with bag-mask-valve ventilation and because the airway could not be secured quickly with direct laryngoscopy. RESULTS: The cricothyroid membrane was cannulated successfully in 23 patients. In these patients, pulse O(2) saturation was raised to > 90% and was maintained with PTJV until the airway was secured. All but 3 of the 23 patients were subsequently intubated orally. In one patient, PTJV maintained adequate gas exchange until an emergent tracheostomy was performed. In two patients, airway exchange catheters were inserted into the trachea due to a small glottic aperture. The endotracheal tube was slid over the catheter. In 6 of the 29 patients, there was difficulty inserting a catheter through the cricothyroid membrane or there was inability to insufflate the oxygen with a jet ventilator. There were no immediate fatalities from the use of PTJV. CONCLUSION: Based on the subsequent insertion of an endotracheal tube into the trachea, there were two important benefits in the patients who underwent PTJV successfully. First, PTJV provided effective oxygenation, while allowing adequate time for upper airway visualization and possible suctioning of oropharyngeal secretions. Second, tracheal intubation was subsequently easier, possibly because the high tracheal pressure from the gas insufflation opened the collapsed glottis, making visualization of the glottic aperture better. PTJV is safe and quick in providing immediate oxygenation, and therefore should be considered as an alternative to insistent, multiple intubation attempts, when neither bag-mask-valve ventilation nor endotracheal intubation is feasible in providing adequate gas exchange.     

Ventilator autocycling due to an endotracheal tube cuff leak

Ventilator autocycling can occur with any ventilator if the sensitivity is improperly set or if a gas leak exists in the respiratory system which creates a negative change in proximal airway pressure. We report a case of ventilator autocycling in a paralyzed patient secondary to an endotracheal cuff leak which was misconstrued as assisted ventilation. We believe this is the first report of autocycling due to a cuff leak.     

The delivery of therapeutic aerosols through endotracheal tubes

We used an in vitro model system to examine the sites of deposition of aqueous therapeutic aerosols administered through 3-mm, 6-mm, and 9-mm endotracheal tubes (commonly used in infants, children, and adults) at clinically relevant inspiratory flow rates. Aerosol was delivered to the endotracheal tube via a "T" piece and a 90 degree elbow. Aerosol exiting the endotracheal tube passed through an appropriately sized Plexiglas model of the trachea and mainstem bronchi, and then into an 80-liter bag. Aerosol deposited in the "T" and elbow, endotracheal tube, large airway model, and collection bag was quantitated separately using 0.1% uranine as a tracer. Study of a conventional aerosol typical of those in common clinical use (aerodynamic mass median diameter = 3.95 microns) showed that most of the aerosol delivered into each endotracheal tube was deposited before leaving the mainstem bronchi. Substitution of an alternative nebulizer that produced a much smaller aerosol particle size (aerodynamic mass median diameter = 0.54 micron) dramatically decreased aerosol deposition in the "T" and elbow, endotracheal tube, and large airway model, and increased the quantity of aerosol penetrating beyond the mainstem bronchi up to ninefold. The mass median particle diameter of the conventional aerosol was reduced during endotracheal tube and large airway passage by poorly defined aerodynamic mechanisms that selectively removed larger particles. The smaller submicron aerosol was not similarly affected. Thus, conventional therapeutic aerosols appear to penetrate poorly through endotracheal tubes. Use of smaller particle size aerosols in treatment of intubated patients may be an effective way to circumvent this problem.     

Airway anesthesia during positive and negative inspiratory pressure breathing in man.

We have measured the effects of airway anesthesia (aerosolized 5% lidocaine) on the respiratory pattern during positive or negative inspiratory pressure in 8 resting subjects. The subjects breathed through a 600 ml dead space (peak inspiratory airway pressure, Paw = -2 cmH2O) without or with negative (approx. -5 or -10 cmH2O) or positive (approx. +5 or +10 cmH2O) inspiratory pressure, provided by a laminar flow resistance or a positive pressure source, respectively. Control measurements were performed before and after measurements with airway anesthesia. Measurements included tidal volume, respiratory frequency, ventilation, inspiratory and expiratory duration, occlusion pressure (P0.1) and end-tidal PCO2. None of the parameters measured was significantly altered by airway anesthesia, which was effective in suppressing the cough reflex. We conclude that information from lung afferents that are suppressed with the elimination of the cough reflex is not important for the breathing pattern during resting ventilation with elevated tidal volume (dead space load) and with positive or negative inspiratory pressure.