Rare broncho-pulmonary arterial fistula in a healthy 9-year-old girl

A 9-year-old previously well girl presented with multiple episodes of large volume haemoptysis and right sided consolidation. She continued to have haemoptysis despite intravenous antibiotics. CT chest suggested a right mainstem endobronchial lesion; this was not seen on bronchoscopy where an extensive blood clot was removed. Distal flexible bronchoscopy could not identify the source of bleeding. CT angiogram revealed a broncho-pulmonary arterial fistula, a rare cause of haemoptysis in children. Endovascular embolisation resulted in short-term symptom resolution; however, haemoptysis recurred months later, leading to re-embolisation. This case highlights a stepwise approach to the workup of large volume haemoptysis.

[The surgical treatment of the pleural empyem]

The treatment results of the 286 patients with pleural empyem after thoracic injuries (n=107) and closed trauma of the pleural cavity (n=179) were retrospectively analyzed. The frequency of pleural empyem was 1.39% by injuries and 1.34% by the closed thoracic trauma. 15 (14%) patients of the first group developed the bronchopleural fistula, whereas the complication was observed in 32 (17.9%) patients of the second group. The adequate pleural drainage with intrapleural enzyme therapy in acute inflammation period allowed recovery in 78% and 71.9% of patients, respectively. Early videothoracoscopic sanation of the pleural cavity shortened the recovery time in more then 1.5 times. The chronization of the empyem was more often observed after the closed thoracic trauma - 14.5% rather than 6.5% after the open thoracic injury. The lethality rate by pleural empyem was 14% after the open injuries and 15.6% after the closed trauma.

Repeated lung lavage with extracorporeal membrane oxygenation treating severe acute respiratory distress syndrome due to nasogastric tube malposition for enternal nutrition: a case report

Enternal nutritional support, a frequently applied technique for providing nutrition and energy, played a pivotal role in the treatment of high risk patients. However, severe complications induced by malposition of nasogastric tube caused great danger and even death to the patients. In this case report, we present a patient with severe acute respiratory distress syndrome (ARDS) induced by bronchopleural fistula (BPF) due to malposition of nasogastric tube. Repeated lung lavage combined with extracorporeal membrane oxygenation (ECMO) was performed after transferring to the ICU of our hospital. Finally, the patient recovered and discharged 7 days after admission.

[A CASE OF ESOPHAGOGASTRIC FISTULA CURE IN A PATIENT WITH COMPLICATED TUBERCULOSIS OF INTRATHORACIC LYMPH NODES]

The authors describe a successful case of esophageal fistula being cured in a patient with complicated tuberculosis of intrathoracic lymph nodes. They show it possible to medically cure the fistula via temporary esophageal stenting, which in combination with therapeutic bronchoscopies enables prompt fistula healing, without resorting to surgical treatment.

[Congenital bronchoesophageal fistula in an adult; an undiscribed mechanism of symptom tolerance]

We present a case of a congenital bronchoesophageal fistula in a 61-year-old woman. She was referred to hospital because of postprandial heart burn. Three-dimensional (3D) computed tomography (CT) demonstrated an anastomosis between her right intermediate bronchus and esophagus. In spite of direct communication between her bronchus and esophagus, she has never suffered severe infection. We visualized the orifice of fistula closed with mucosal flap in swallowing by means of a bronchofiberscope. The delay of a diagnosis was explained by symptom tolerance. Some theories as to the symptom tolerance are found in literatures, but we supposed to find an undiscribed mechanism; closure of the orifice in swallowing. The fistula was surgically closed.

Use of a Modified Dumon Stent for Postoperative Bronchopleural Fistula

This report describes a case of a postoperative bronchopleural fistula successfully managed with a modified Dumon stent. Surgical interventions for the bronchopleural fistula with empyema were subsequently avoided. Dumon stent is an acceptable option for the treatment of postoperative bronchopleural fistulas.

[Aortobronchial fistulas]

INTRODUCTION

Aortobronchial fistulas are uncommon but generally fatal if not treated surgically. Haemoptysis is the main symptom of this pathology. STATES OF ART AND PERSPECTIVES: Aortobronchial fistulas occur most commonly in patients with thoracic aneurysms (atherosclerosis, mycotic, aortic surgery's complication...). Main investigation is CT angiography with 2 D and 3 D reconstructions.

CONCLUSION

Endovascular exclusion can be efficient treatment option.

Natural history of bronchopleural fistula after pneumonectomy: a review of 96 cases

BACKGROUND

Various therapeutic approaches to bronchopleural fistula have been reported. Its natural history, which may be key to the best therapeutic management, early detection, and possibly, prevention of fistula formation, has received little attention.

METHODS

The cases of 96 patients with bronchopleural fistula after pneumonectomy seen over a 13-year period (1982 to 1995) were retrospectively analyzed. Cancer, TNM stage and histology, age, sex, side and size of the fistula at primary bronchoscopic diagnosis, time of occurrence after operation (days), cause of death, and survival after fistula formation (days) were analyzed. Management consisted of bronchoscopic closure with fibrin sealant or decalcified spongy calf bone or both, repeat thoracotomy with resection of the bronchial stump, thoracoplasty, or open window thoracostomy.

RESULTS

Except for one instance, all total stump dehiscences occurred within 90 days after operation. Sixty-four patients (67%) died during the observation period; in 25, the cause of death was aspiration pneumonia. Only 2 patients who died of aspiration pneumonia had development of a fistula after 90 postoperative days. The aspiration rate dropped with increasing interval between operation and fistula occurrence (p = 0.000). Patient survival after fistula formation was positively correlated to this interval (p = 0.002). Successful fistula closure was achieved by surgical intervention in 21 patients and endoscopically in 11 patients. The overall postoperative mortality rate irrespective of treatment method was 31%.

CONCLUSIONS

The incidence of aspiration pneumonia declines sharply if bronchopleural fistula occurs more than 3 months after operation. Formation of fibrothorax apparently represents a natural protection against fistula formation and subsequent fatal aspiration pneumonia. Close follow-up during the first 3 postoperative months should detect bronchopleural fistula before aspiration occurs.

Independent lung ventilation

Situations in which independent lung ventilation may be of use include massive hemoptysis, pulmonary alveolar proteinosis, risk of interbronchial aspiration, unilateral lung injury, single lung transplant, and BPF. Any decision to attempt independent lung ventilation should take into consideration the many technical difficulties associated with the procedure. They include difficulties in the placement of DLTs and monitoring tube position, the risk of tube displacement, and the risk of airway trauma. The clinician also must consider the costs in terms of available manpower and resources. Maintaining a patient on independent lung ventilation requires highly skilled nursing care, specialized monitoring devices, and readily available FOB. Even with these limitations, independent lung ventilation may be of use in certain clinical situations when standard methods have failed.

Broncho-mediastinal fistula following perforation of the oesophagus

We present a 63-year old female with mediastinitis following an esophageal perforation, possibly favoured by an oesophageal motility-disorder and the use of non-steroidal anti-inflammatory drugs, who developed a broncho-mediastinal fistula in the left main bronchus. She was successfully treated with intravenous antibiotics, a cervical oesophagostomy and secondary isoperistaltic coloplasty.

Treatment of tuberculous empyema with multiple fistulae by reexpansion of the affected lung and restoration of its function: report of a case

We report herein the case of a patient in whom a calcified tuberculous empyema with multiple fistulae was successfully treated by a new surgical approach. Reexpansion of the affected lung which had calcified over 30 years was achieved by covering the multiple bronchial fistulae using the omentum without obliterating the empyema cavity. Although the patient presented with severe aspiration pneumonia, he made a complete recovery and is now leading a better quality of life than before. This new operative method is less invasive and can therefore be performed much more easily on critically ill patients than conventional methods.

Management of bronchopleural fistula in the adult respiratory distress syndrome

Bronchopleural fistula occurring as a complication in patients with the adult respiratory distress syndrome typically appears after 1 to 2 wks of illness, and is associated with a poor prognosis. Whether the bronchopleural fistula per se worsens outcome is not known because of the lack of studies on its natural history. There are several potential adverse effects of bronchopleural fistula in adult respiratory distress syndrome (e.g., incomplete lung expansion, loss of effective tidal volume or positive end-expiratory pressure, inability to remove CO2, etc.), but the actual frequency of these problems among patients with this complication appears to be low, and their magnitude and clinical impact remain uncertain. Most of the literature consists of anecdotal reports of innovative measures for reducing the leak, such as manipulation of chest tube suction, high-frequency jet ventilation, independent lung ventilation, and various maneuvers using the fiberoptic bronchoscope. Controlled studies are lacking, however, and the application of sound, general management principles is of primary importance. The great majority of patients can be managed satisfactorily without resort to unfamiliar, labor-intensive, potentially hazardous measures.

Optimal application of high-frequency ventilation in infants: a theoretical study

A recent multicenter study of preterm infants concluded that high-frequency ventilation (HFV) applied at 15 Hz, in comparison with conventional mechanical ventilation (CMV), did not lead to reduced incidence of barotrauma, contrary to previous expectations. The primary goal of the present theoretical study was to determine whether computed estimates of lung pressures during HFV and CMV are consistent with these findings. An existing theoretical model of lung mechanics and gas transport in HFV was modified for applicability to neonates. New features, such as expiratory flow limitation and pulmonary air leak, were also incorporated. Simulations with the model were conducted assuming combinations of frequency and tidal volume that maintained a constant level of eucapnia. We found that peak alveolar pressures and the magnitude of alveolar pressure swings resulting from HFV at 15 Hz were in general comparable to those produced by CMV in healthy neonates and infants with bronchopulmonary dysplasia; peak alveolar pressures in the latter group tended to be higher with HFV than in CMV. Application of HFV at 15 Hz was even less advantageous than CMV when pulmonary air leak was also present in the infants with bronchopulmonary dysplasia. However, the model predicted the existence of an optimal range of frequencies between 2 and 4 Hz in which alveolar pressure swings and peak alveolar pressures could be minimized, and in some cases, reduced below the levels produced by CMV.

Pulmonary function tests in bronchopleural fistula

A 53-year-old white man underwent a left pneumonectomy for alveolar cell carcinoma. His postoperative course was complicated by pneumonia. At a follow-up clinic visit, the patient complained of a "roaring sound" during respiration. A follow-up PFT did not show the expected loss of volume (nitrogen washout) from a preoperative PFT, suggesting a bronchopleural fistula. A chest x-ray film and xenon lung scan confirmed the diagnosis. The fistula was surgically repaired.

Management of malignant air leak in a child with a neonatal high-frequency oscillatory ventilator

A 10-year-old, 36-kg child with a malignant air leak who failed conventional mechanical ventilation and high-frequency jet ventilation was successfully treated with a neonatal high-frequency oscillatory ventilator for 31 days. Since the air leak resolved with minimal hemodynamic compromise, this technique may have application in the management of respiratory failure and air leak in the older and larger child for prolonged periods of time.

Bronchocutaneous fistula in dogs: influence of fistula size and ventilatory mode on airleak

Bronchocutaneous fistula (BCF) can originate at different levels, from the major airways to the peripheral lung. Little is published on the influence of the fistula origin or the ventilatory effect of the airleak. This study evaluates relative CO2 elimination via fistulas of various size and how different ventilatory modes influence both the quantity and quality, i.e., oxygen and CO2 content, of the airleak. We created BCF with five polyethylene tubings of different diameters (tube 1, 3.0 mm; tube 2, 4.0 mm; tube 3, 5.1 mm; tube 4, 6.4 mm; tube 5, 9.8 mm) in nine dogs. Six modes of ventilation were used with each tubing: spontaneous breathing (SB), pressure support (PS), high frequency (HF), assisted controlled with inspiration set at 20% (AC20) and at 67% (AC67) of the respiratory cycle, and AC20 with an end-expiratory pressure of +10 cm H2O (PEEP). For each ventilatory mode, the fistula air flow (Vf), CO2, and oxygen partial pressure of fistula air (PfCO2 and PfO2) and arterial blood were measured. Vf was measured for all tubes, while gas analysis was done for tubes 1, 3, and 5 only. As expected, Vf increased with tubing size. Vf was higher with AC67 and PEEP than with the other ventilatory modes. PfCO2 was not significantly influenced by the tube size and Vf. Fistula air alveolization was increased only with HF ventilation. Air leaked via the fistula contributed significantly to gas exchange; even when expiration was totally via the fistula, the arterial gases remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Determinants of gas flow through a bronchopleural fistula

To assess the determinants of bronchopleural fistula (BPF) flow, we used a surgically created BPF to study 15 anesthetized intubated mechanically ventilated New Zealand White rabbits. Mean airway pressure and intrathoracic pressure were evaluated independently. Mean airway pressure was varied (8, 10, or 12 cmH2O) by independent manipulations of either peak inspiratory pressure, positive end-expiratory pressure, or inspiratory time. Intrathoracic pressure was varied from 0 to -40 cmH2O. BPF flow varied directly with mean airway pressure (P less than 0.001). However, at constant mean airway pressure, BPF flow was not influenced independently by changes in peak inspiratory pressure, positive end-expiratory pressure, or inspiratory time. Resistance of the BPF increased as intrathoracic pressure became more negative. Despite increased resistance, BPF flow also increased. BPF resistance was constant over the range of mean airway (P less than 0.01) pressures investigated. Our data document the influence of mean airway pressure and intrathoracic pressure on BPF flow and suggest that manipulations which reduce transpulmonary pressure will decrease BPF flow.

Pressure-flow behavior of a bronchopleural fistula during mechanical ventilation with positive pressure

We examined the mechanical behavior of a bronchopleural fistula created by sectioning a small subpleural bronchus in seven anesthetized lambs. The pressure across the fistula was measured as the difference between the pressure recorded by a retrograde bronchial catheter inserted in the vicinity of the fistula and the outflow pressure at the fistula exit. The effective resistance of the fistula (Rf) was computed by dividing this pressure difference by the gas flow through the fistula measured at the outlet of an intrapleural tube adjacent to the fistula. Rf increased by 114 +/- 25% (SE) when we inflated the lungs in a stepwise manner from a tracheal pressure of 2-20 cmH2O. Rf also increased when inflation pressure varied continuously; this increase, however, was less evident when we decreased the inflation time from 1.0 to 0.2 s. The relationship between Rf and lung volume was similar during the stepwise inflations and deflations but showed marked hysteresis during the continuous inflation-deflation maneuvers, when Rf was greater during deflation than inflation. Our results suggest that the fistula behaves as a compliant pathway whose relevant transmural pressure is the transmural pressure at or near the fistula's exit. We attribute the increase in Rf during inflation to decreases in transmural pressure caused by convective and dissipative losses inside the fistula and by the stress applied by the chest wall on the outer surface of the fistula.

Changes in pneumonectomy-space gas tensions

The development of a simple and reliable method for measurement of the partial pressures of the atmospheric gases offers the possibility of both basic and clinical examination of the air in natural as well as pathological or iatrogenic cavities. From measurements in nine patients a plot of the changes in pO2 and pCO2 in the pneumonectomy space from the end of the thoracotomy to the establishment of equilibrium with the blood gases was made. pCO2 equilibrated faster than pO2 (6- and 50 h respectively). The equilibrium difference between arterial pO2 and pneumonectomy space pO2 was 6.5 kPa (2.5-12.3 kPa) and we propose that measuring this difference may be a sensitive method for the diagnosis of bronchopleural fistula. During the study period one of the patients developed a bronchopleural fistula. The suspicion was based on X-ray findings and was supported by gas analysis from the pneumonectomy space, and conclusively confirmed by bronchoscopy.

Ultra-high-frequency jet ventilation in a bronchopleural fistula model

High-frequency ventilation techniques have been demonstrated to be useful in decreasing gas loss from bronchopleural fistulas. We performed the present study to evaluate the impact of a new jet ventilator design and ventilatory frequency on hemodynamics, gas exchange, and bronchialstump gas flow in an animal model of bronchopleural fistula. Ten pigs underwent a right-sided thoracotomy and right-sided upper pulmonary lobectomy with cannulation of the upper lobe bronchus for measurement of bronchial fistula flow rate. Animals underwent a random sequence of conventional ventilation (12 to 20 breaths per minute), conventional high-frequency jet ventilation (120 breaths per minute), and ultra-high-frequency jet ventilation (UHFJV; 450 breaths per minute). Hemodynamic measurements were similar in the three ventilatory modes, but oxygenation was best with UHFJV. Bronchial fistula flow was lowest with UHFJV and greatest with conventional ventilation. Ultra-high-frequency jet ventilation demonstrated superior oxygen loading, adequate carbon dioxide elimination, and the least flow through the fistula, suggesting that both ventilator design and frequency are important therapeutic variables in the management of major airway disruption.

Gas flow through a bronchopleural fistula. Measuring the effects of high-frequency jet ventilation and chest-tube suction

High-frequency jet ventilation (HFJV) is FDA-approved for ventilating patients with bronchopleural fistulae (BPF), yet little is known about its effect on the fistula airleak. We quantitated a patient's BPF airleak during both conventional volume-cycled ventilation and HFJV. The effect of chest-tube suction (CTS) on BPF flow was also studied. Despite a significant reduction in peak airway pressure, the HFJV resulted in a 50-70 percent increase in BPF flow. CTS also significantly increased the airleak. HFJV may not always be the preferential method for ventilating patients with BPF and we recommend measuring the fistula airleak when attempting to optimize a patient's ventilatory parameters.

The maintenance of total ventilatory requirements through a chronic bronchopleural cutaneous fistula

In patient with a chronic post-tuberculous bronchopleural cutaneous fistula (BPCF), minute ventilation, dead space, flow rates, arterial blood gas tensions, and oxygen consumption were measured during mouth breathing and after 30 min of steady-state breathing solely through the BPCF. Despite a 390-ml (18%) decrease in dead space when breathing took place through the BPCF, there were no significant changes in minute ventilation or respiratory rate. BPCF breathing was also associated with an increase in airways resistance as reflected by a 300-ml (35%) decrease in the FEV1 and a 16% decrease in the FEV1/FVC ratio. The increased resistance resulted in a 20 ml/min (18%) increase in oxygen consumption. Arterial blood gas tensions remained constant. We conclude that although ventilatory efficiency was not improved, this patient was able to satisfy his total minute ventilatory requirements, for the 30-min period, solely through BPCF breathing.

Artificial ventilation of a canine model of bronchopleural fistula

The authors studied the abnormalities of gas exchange and lung mechanics in a canine model of bronchopleural fistula during intermittent positive pressure ventilation (IPPV) and high-frequency oscillatory ventilation (HFOV). The left lower lobe bronchus was opened to atmosphere and it was determined that end expired volume was best maintained at frequencies of 45-50 breaths/min. during IPPV. Comparing alternating periods of IPPV and HFOV in six dogs (Group I) at matched airway opening pressure (Pao), we found that Pao2 decreased significantly to 68 +/- 14 mmHg and 69 +/- 24 mmHg, respectively, on opening the fistula. In a second group of six dogs (Group 2), when Pao was increased by additional bias flow into the ventilatory circuit during both IPPV and HFOV, Pao2 increased significantly to 89 +/- 12 mmHg and 87 +/- 8 mmHg, respectively. Repeating Group 2 studies after induction of oleic acid low-pressure pulmonary edema demonstrated that conventional IPPV was associated with large intrapulmonary shunts. HFOV, however, maintained gas exchange at near baseline values. For both Group 1 and Group 2, the calculated gas flow through the fistula was significantly less at all levels of airway pressure during HFOV. The authors conclude that HFOV offers advantages over conventional IPPV in the maintenance of oxygenation and in the reduction of gas leak through the fistula.

Conventional and high-frequency ventilation in dogs with bronchopleural fistula

Seven anesthetized dogs with bronchopleural fistulas were subjected to a sequence of continuous positive-pressure ventilation (CPPV), volume-controlled high-frequency positive-pressure ventilation (HFPPV), and high-frequency vibratory ventilation (HFVV). Adequate short-term ventilation and oxygenation were possible with all three ventilatory modes. During HFPPV and HFVV, PaCO2 was unchanged, but hypercarbia developed during CPPV. PaO2 decreased during each mode of ventilation, but HFPPV maintained PaO2 at a sufficient and constant level during the 30-min test period. HFPPV was the most efficient technique with respect to delivery of minute ventilation, the relation between fistula flow and delivered ventilation, and maintenance of both ventilation and oxygenation.

Differential mechanical ventilation in respiratory failure due to severe unilateral lung disease

Severe unilateral lung disease that produces respiratory failure may necessitate mechanical ventilatory support to sustain gas exchange. This article describes the successful use of differential lung ventilation in the management of one patient with diffuse unilateral pneumonia and another with a postoperative bronchopleural fistula after standard methods of mechanical ventilation failed to provide adequate gas exchange for these patients.

Pneumatic-to-electrical analog for high-frequency jet ventilation of disrupted airways

A pneumatic-to-electrical circuit analog is used to describe 2 separate mechanisms by which high-frequency jet ventilators sustain ventilation and oxygenation in the presence of large airway disruptions. The frequency-dependent mechanism is based on variations in the pneumatic equivalent to capacitive reactance. The pressure-dependent mechanism models lung defects on a voltage-controlled resistor. The electrical circuit model is also used to explain the factors leading to gas trapping and inadvertent positive end-expiratory pressure during high-frequency jet ventilation.

Ventilatory management of life-threatening bronchopleural fistulae. A summary

The loss of a substantial portion of a critically ill patient's inspired tidal volume through a bronchopleural fistula (BPF) may significantly alter the intrapulmonary distribution of ventilation, ventilation-perfusion matching and arterial blood gases. If surgical closure of the fistulous tract is not possible, modifications of traditional ventilatory methods may be necessary to preserve adequate gas exchange. The effect of the methods summarized later in this paper upon the patient's mortality and morbidity has not been rigorously analyzed in a large numbers of patients but has been presented in the case studies referenced. Although these techniques might be considered investigational, they can be justified: (1) in the presence of profound hypoxemia and hypercarbia caused by a large BPF, and (2) when reduced gas loss through the fistula is considered an important part of therapy. All the methods discussed below apply in patients requiring endotracheal intubation and mechanical ventilation, whereas some (as indicated in the text) can be used during spontaneous breathing.

The relationship between peak inspiratory pressure and positive end expiratory pressure on the volume of air lost through a bronchopleural fistula

A bronchopleural fistula (BPF) may complicate the management of patients with major pulmonary disease or thoracic surgery. Neonates with idiopathic respiratory distress syndrome and requiring ventilation are especially susceptible to pulmonary barotrauma, which may result in a BPF. Morbidity and mortality are consistently high. In ventilating patients with BPF, the effects of peak inspiratory pressure (PIP) and positive and expiratory pressure (PEEP) on air leak have not been documented. These relationships were studied in rabbits prepared by thoracotomy and creation of a standardized BPF. Randomized trials of various levels of PIP and PEEP were applied, and the percent of inspired tidal volume lost through the BPF calculated. The percent of inspired volume lost does not increase significantly from 10 to 30 cm H2O PIP (p greater than 0.05). Percent leak does increase significantly when increasing PEEP frm 0 to 16 cm H2O (p less than 0.001). Any PEEP greater than 6 cm H2O results in more air loss through the BPF than any level of PIP (p less than 0.01). Linear regressions through a common origin were calculated to illustrate the relationship of PIP versus leak and PEEP versus leak. The slopes of these lines (0.572 and 3.97, respectively) are significantly different (p less than 0.001). When using equal increments of PIP and PEEP, PEEP will have over a sixfold greater effect on air leak than doses PIP. These data suggests that PIP should be increased preferentially when ventilating patients with BPF in order to minimize air leak. PEEP less than 6 cm H2O can be used without any significant increase in the volume of air lost.

Intermittent inspiratory chest tube occlusion to limit bronchopleural cutaneous airleaks

A significant bronchopleural cutaneous fistula (BPCF) developed in a 36-year-old female who required mechanical ventilation for acute respiratory failure. Progressive increase in arterial PCO2 to 75 torr occurred because of inability to effect satisfactory alveolar ventilation. Insertion of unidirectional values into the chest tube drainage apparatus, which were closed synchronously each time the ventilator cycled to the inspiratory phase, allowed effective alveolar ventilation to be achieved with subsequent reduction of arterial CO2 to previous levels. Both high inspiratory (120 torr) and expiratory (23 torr) positive pressures were employed with intermittent mandatory ventilation (IMV). Deleterious effects on cardiopulmonary function were not observed, and the patient was weaned successfully from mechanical support with spontaneous closure of the BPCFs.

Horizontal gradient in ventilation distribution due to a localized chest wall abnormality

Horizontal gradients in the distribution of ventilation and of regional vital capacities, as well as a reversed vertical, esophageal pressure gradient, were observed in a patient with a unilateral painful chest wall lesion. The distribution abnormalities disappeared after surgical treatment. These findings suggest that the interdependency between chest wall and lungs, and within the latter, between lobes, is an important factor determining the regional distribution of ventilation and the pleural pressure gradient in man.