Plethysmographic measurement of lung volume in chronic obstructive pulmonary disease. Influence of the panting pattern

In 9 healthy subjects and 22 patients with chronic obstructive disease, we computed total lung capacity (TLC) using an integrated flow pressure-corrected body plethysmograph. During panting manoeuvre, TLC derived from oesophageal pressure (TLCes) was compared to TLC derived from mouth pressure (TLCm). In healthy subjects, TLCm was identical to TLCes. Patients with obstructive disease exhibited different behaviours according to experimental conditions: a) in free frequency panting with mouth occlusion close to functional residual capacity (FRC) (9 patients), TLCm appeared to be significantly higher than TLCes (mean difference: 0.25 1; p less than 0.05); b) in panting with both low (less than 1 Hz) and high (2 Hz) frequencies and mouth occlusion close to FRC (7 patients), TLCm appeared to be significantly higher than TLCes only at a high frequency (p less than 0.05); c) in panting with both low and high frequencies and mouth occlusion close to TLC (6 patients), no significant difference was observed between TLCm and TLCes. These results suggest that in patients with chronic obstructive disease plethysmographic lung volume measurements are subject to error, due to the influence of extrathoracic airways. During occlusion at FRC, panting frequency was found to influence the results obtained, the error being minimized with low frequencies. In contrast, by occluding at TLC, we found that panting frequency was less likely to influence the results. However, potential sources of error still exist: for instance, the influence of abdominal gas or the panting pattern.     

Effects of ischemia on pressure-velocity and pressure-volume relationships in the isolated rabbit left ventricle

The pressure-velocity and pressure-volume relationships were determined in the isolated rabbit left ventricle in order to evaluate ventricular function during global ischemia (low pressure perfusion) and under reperfusion after a 10 min complete coronary occlusion (reperfusion after coronary occlusion). Reducing coronary perfusion pressure, the maximum isovolumic pressure (P0) decreased, but the maximum ejection velocity (Vmax) did not. The slope of the end-systolic pressure-volume relationship (Emax) decreased without any significant change in the volume-axis intercept. On the other hand, under reperfusion after coronary occlusion, both P0 and Vmax were depressed considerably, but Emax quickly recovered to the control level. Thus, Vmax and Emax show different behavior depending on the ischemic conditions. To analyze the relaxation process under low pressure perfusion and reperfusion after coronary occlusion, the pressure-velocity relations during the relaxation phase were determined by the isovelocity method. Similar to the relation for contraction phase, the relation obtained here could be adequately approximated by a hyperbolic equation. Under the control condition, the relaxation velocity was always lower than the contraction velocity at the corresponding pressure level, and the ratio of the maximum filling velocity (Rmax) to Vmax was relatively constant. Although both Rmax and Rmax/Vmax were little affected by the low pressure perfusion, Vmax and Rmax, especially Vmax, decreased when the ventricle was reperfused after coronary occlusion, resulting in an increased Rmax/Vmax.     

Assessment of the catheter tip pressure transducer for use in infant lung function tests

A catheter tip pressure transducer was testedin vitro to determine its stability, linearity and frequency response. It was then compared simultaneously with an oesophageal balloon in two trained adult subjects, using measurements of end-expiratory oesophageal pressure and the ratio of oesophageal pressure to mouth pressure changes during airway occlusion. This ratio should be unity, since during airway occlusion there is no flow and pressure changes should be evenly distributed throughout the closed system. The catheter tip pressure transducer was used in 13 infants, who were all studied initially with an oesophageal balloon, during the course of routine lung function tests. Measurements of pulmonary resistance, compliance, end-expiratory oesophageal pressure and the ratio of oesophageal pressure change to mouth pressure change were made with both instruments. The ratio of oesophageal to mouth pressure change and pulmonary resistance were elevated and dynamic compliance reduced when measured with the catheter tip pressure transducer, showing that the catheter tip pressure transducer was overestimating the size of pressure swings within the oesophagus. The absolute value of end-expiratory oesophageal pressure was always more positive when measured with the catheter tip pressure transducer than with the balloon, suggesting that absolute pressure was also incorrectly monitored. It is recommended that the catheter tip pressure transducer should not be used in studies of infant lung mechanics until these problems have been resolved.     

A sigmoidal fit for pressure-volume curves of idiopathic pulmonary fibrosis patients on mechanical ventilation: clinical implications

OBJECTIVE:

Respiratory pressure-volume curves fitted to exponential equations have been used to assess disease severity and prognosis in spontaneously breathing patients with idiopathic pulmonary fibrosis. Sigmoidal equations have been used to fit pressure-volume curves for mechanically ventilated patients but not for idiopathic pulmonary fibrosis patients. We compared a sigmoidal model and an exponential model to fit pressure-volume curves from mechanically ventilated patients with idiopathic pulmonary fibrosis.

METHODS:

Six idiopathic pulmonary fibrosis patients and five controls underwent inflation pressure-volume curves using the constant-flow technique during general anesthesia prior to open lung biopsy or thymectomy. We identified the lower and upper inflection points and fit the curves with an exponential equation, V = A-B.e^-k.P, and a sigmoid equation, V = a+b/(1+e^-(P-c)/d).

RESULTS:

The mean lower inflection point for idiopathic pulmonary fibrosis patients was significantly higher (10.5±5.7 cm H₂O) than that of controls (3.6±2.4 cm H₂O). The sigmoidal equation fit the pressure-volume curves of the fibrotic and control patients well, but the exponential equation fit the data well only when points below 50% of the inspiratory capacity were excluded.

CONCLUSION:

The elevated lower inflection point and the sigmoidal shape of the pressure-volume curves suggest that respiratory system compliance is decreased close to end-expiratory lung volume in idiopathic pulmonary fibrosis patients under general anesthesia and mechanical ventilation. The sigmoidal fit was superior to the exponential fit for inflation pressure-volume curves of anesthetized patients with idiopathic pulmonary fibrosis and could be useful for guiding mechanical ventilation during general anesthesia in this condition.     

Effect of lung inhomogeneity on partial flow-volume manoeuvres

We evaluated the effects of inhomogeneous lung emptying on the relationship of partial to maximal complete expiratory flow by obtaining pre- and post-metaproterenol maximal (MEFV) and partial flow-volume curves in normal subjects and asthmatics. Partial curves were initiated between 65-70% of vital capacity after inspiration from functional residual capacity (PEFV curve) or after deflation from total lung capacity (PEFVDI curve). Since PEFVDI curves were initiated at lower lung volumes than MEFV manoeuvres (but with a similar volume history), non-homogeneous emptying should cause higher flow on PEFVDI than on MEFV manoeuvres. Expiratory flow (Vmax) was highest on MEFV manoeuvres in normals and PEFV curves in asthmatics. Pre- and post-metaproterenol Vmax was very similar on MEFV and PEFVDI manoeuvres in both groups, although Vmax(MEFV) slightly but significantly exceeded Vmax(PEFVDI) in normals and the reverse was true in asthmatics. Lung elastic recoil did not differ significantly on MEFV and PEFVDI manoeuvres in either group. We conclude that asthmatics demonstrate inhomogeneous emptying. However, because flow-volume curves are relatively insensitive to sequences of lung emptying, inhomogeneous emptying during forced expiration only has minor effects on the relationship of partial to maximal expiratory flow.     

Effect of lung volume reduction surgery for emphysema on diaphragm function

Preoperative prediction of a successful outcome following lung volume reduction surgery (LVRS) for emphysema is imperfect. One mechanism could be improvement in respiratory muscle function yet controversy exists regarding the magnitude and mechanism of such an improvement. Therefore, we measured diaphragm strength in 18 patients before and after LVRS. Mean (S.D.) FRC fell from 6.53 to 5.40 l (p = 0.0001). Mean sniff transdiaphragmatic pressure increased from 76 to 87 cm H2O (14%, p < 0.03) and mean twitch transdiaphragmatic pressure (Tw Pdi) increased by 2.5 cm H2O at 3 months (12%, p = 0.03). There was a highly significant increase in twitch esophageal pressure (Tw Pes) (60%, p < 0.0001), which was maintained at 12 months (46% increase, p = 0.0004). No change was observed in quadriceps twitch tension in nine subjects in whom it was measured. After LVRS the ratio Tw Pes:Tw Pdi increased from 0.24 to 0.37 at 3 months (p = 0.0003) and 0.36 at 12 months (p = 008). Low values of Sn Pdi, Sn Pes, Tw Pes and a high RV/TLC ratio were the preoperative variables most predictive of improvement in shuttle walking distance. We conclude that LVRS improves diaphragm function primarily by alteration of lung volume. Patients with poor diaphragm function and high RV/TLC ratio preoperatively are most likely to benefit from the procedure.     

Small airway function in acromegaly

Small airway function was studied in 21 acromegalic patients (13 females, 8 males) and quantitated as the maximal expiratory flow at 25 and 50% of vital capacity (VEmax25, VEmax50) breathing room air, as the difference of flow at 50% of VC breathing air and 80% helium 20% O2 (delta Vmax50) and as the volume of equal flows (VisoV). In addition, lung volumes were investigated by spirometry and body plethysmography. Static lung volumes were statistically significantly increased in both male and female acromegalic patients (p less than 0.05), but RV/TLC and FEV1/FVC did not change (p greater than 0.1). VEmax25, delta Vmax50 and VisoV showed an abnormal function of small airways in nonsmoking acromegalic patients. However, smoking acromegalics did not differ significantly from 'normal' smoking subjects, suggesting that the dysfunction of small airways is not a contributory factor to mortality from the disease. Maximal expiratory flows, when related to lung volume, were reduced in acromegalic women. Abnormal small airway function in acromegaly could either be due to obstruction or, more likely, to an exaggeration of dysanaptic lung growth.     

Transhiatal oesophagectomy--its role for tumours of the middle third of the intrathoracic oesophagus

All patients presenting to a regional unit with oesophageal carcinoma over a twelve month period are reviewed and the role of transhiatal oesophagectomy for tumours of the middle third of the intrathoracic oesophagus is evaluated. Of the 28 cases of oesophageal carcinoma, 22 (78%) were resected by blunt transhiatal oesophagectomy, the remaining six (22%) has various forms of palliative treatment. In the resected group post-operative morbidity was compared in patients with tumours of the middle third to those with lower and upper third tumours combined. There was one post-operative death in each group giving an overall operative mortality of 9%. Resection for carcinoma of the middle third (N = 7) resulted in a complication rate of 50% and a mean ICU stay of 19.5 days as opposed to a complication rate of 35% and a mean ICU stay of ten days (P = 0.050) for tumours of upper and lower third combined (N = 15). On the basis of these figures we question whether transhiatal oesophagectomy, despite its many advantages, can be applied safely to tumours of the middle third of the intrathoracic oesophagus.     

Combined pH and pressure measurement device for oesophageal investigations

A combined pH- and pressure-measurement device for oesophageal investigations has been designed using monocrystalline antimony pH electrodes and perfused polyvinyl catheters. The combined device facilitates pressure measurements simultaneously with pH recording, both distal and proximal to the pH electrode. The device is easier to pass through the nose to the oesophagus than the conventional glass pH electrode. pH and pressure measurements in the oesophagus are therefore simplified and valuable information about the function of the region of the lower oesophageal sphincter is added owing to the simultaneous recording of the two parameters.     

Chest pain and oesophageal pressure relationships in man following an intravenous bolus of adenosine

After titration of maximum tolerable i.v. bolus dose of adenosine, this dose was given to seven volunteers (20-42 years), instrumented with a three-lumen oesophageal pressure catheter with recording sites at the levels of the stomach, the lower oesophageal sphincter (LOS) and the oesophagus. In addition to continuous pressure recordings, chest pain was estimated continuously by a 10-graded category-ratio scale. Baseline resting pressures were 8.4 (1.9) mmHg in the stomach, 1.6 (1.7) mmHg in the oesophagus and 20 (2.6) mmHg in the LOS resulting in a net LOS pressure of 11 (+/- 1.3) mmHg. Following injection of adenosine which provoked transient chest pain with a rated maximum of 5.4 (1.0), resting oesophageal pressure did not change while net LOS pressure decreased to -1.3 (1.9) mmHg (P less than 0.0001). Adenosine injection did not affect swallowing-induced peristaltic contractions of the oesophagus and LOS although the peristaltic wave was delayed (P less than 0.05). Thus, chest pain evoked by adenosine cannot be caused by spastic oesophageal contractions. Adenosine may have a relaxing effect on the LOS but does not block its normal reactions to swallowing.     

Oesophageal mesenchymal tumours: clinicopathological features and absence of Epstein-Barr virus

BACKGROUND: Recent studies have suggested that the Epstein-Barr virus (EBV) is associated with smooth muscle tumours (leiomyoma and leiomyosarcoma) in patients with human immunodeficiency virus and in organ transplant recipients. Leiomyoma is the most common mensenchymal tumour found in the oesophagus. AIM: To report a single institution experience on oesophageal mesenchymal tumours and to determine whether EBV is associated with these tumours. METHODS: 40 sporadic oesophageal mesenchymal tumours were studied and their diagnosis confirmed on pathological review and immunohistochemical studies. Formalin fixed, paraffin was embedded tissues from these tumours were analysed for EBV using in situ hybridisation for two messenger RNA (mRNA) probes, EBER and BamH1 W. RESULTS: The oesophageal mesenchymal tumours comprised 36 leiomyomas, two undifferentiated stromal tumours, and two gastrointestinal autonomic nerve tumours (GANTs). Median age of the patients with leiomyoma (26 men, 10 women) was 62 years (range 30 to 85) and 81% of them had an asymptomatic lesion. The median longitudinal size was 1.2 cm. Multiple leiomyomas were seen in 11% of the patients and calcification was noted in one tumour. Coexisting squamous cell carcinoma was found in one third of cases. The stromal tumours were small, asymptomatic, and located in the lower third of the oesophagus, while the GANTs were large, symptomatic, and found in the upper third of the oesophagus. EBV mRNAs were not detected in all these tumours. CONCLUSIONS: The clinicopathological features of oesophageal leiomyoma, undifferentiated stromal tumour, and GANT were different. Some oesophageal leiomyomas were associated with oesophageal squamous cell carcinomas. EBV is not associated with sporadic oesophageal mesenchymal tumours.     

Esophageal pressure as an estimate of average pleural pressure with lung or chest distortion in rats

Pressure–volume curves of the lungs and chest wall require knowledge of an effective ‘average’ pleural pressure (Ppl_av), and are usually estimated using esophageal pressure as Pl_es–V and Pw_es–V curves. Such estimates could be misleading when Ppl becomes spatially non-uniform with lung lavage or shape distortion of the chest. We therefore measured Pl_es–V and Pw_es–V curves in conditions causing spatial non-uniformity of Ppl in rats. Pl_es–V curves of normal lungs were unchanged by chest removal. Lung lavage depressed PL_es–V but not Pw_es–V curves to lower volumes, and chest removal after lavage increased volumes at PL ≥ 15 cmH₂O by relieving distortion of the mechanically heterogeneous lungs. Chest wall distortion by ribcage compression or abdominal distension depressed Pw_es–V curves and Pl_es–V curves of normal lungs only at Pl ≥ 3 cmH₂O. In conclusion, Pes reflects Ppl_av with normal and mechanically heterogeneous lungs. With chest wall distortion and dependent deformation of the normal lung, changes of Pl_es–V curves are qualitatively consistent with greater work of inflation.     

Online calculation of lung volumes by digital computer from a plethysmographic measurement of ventilatory flow

The actual gas contents of lungs can be measured by a total plethysmographic technique. A classical way of obtaining thoracic gas volume (t.g.v.) is by fitting a straight line to the thoracic volume (V_t) and mouth pressure (P_m) changes occurring during a panting manoeuvre with airway occlusion at the mouth. In our lung-function laboratory, a minicomputer has been connected to a pressure-compensated flow body plethysmograph. We describe here both the plethysmographic technique of measuring thoracic flow (V′_t) and the computerised system developed to calculate on-line lung volumes in patients. By replacing V_t and P_m by their time derivatives, V′_t and P′_m, in the linear regression procedure, we significantly improve the correlation coefficient, namely the confidence which can be attributed to calculated t.g.v. The within-subject reproducibility of lung volumes is thus improved, and a closer comparison is found between the computer-derived and hand-calculated volumes, both in normal subjects and patients.     

Site distribution of oesophagogastric cancer

AIMS: It has been suggested that adenocarcinomas of the lower oesophagus and gastric cardia should be reclassified as oesophagogastric junction (OGJ) cancers. This study aimed to define the frequency of OGJ cancers in a geographically defined population of 4.3 million people. METHODS: All cases of oesophageal and gastric cancer occurring in 1993 were identified by the North Western Regional Cancer Registry. A total of 1192 hospital case notes were reviewed and a study group of 1067 patients was defined. Tumour involvement was documented at individual subsites in the oesophagus and stomach, allowing for tumour presence in more than one oesophageal/gastric subsite. RESULTS: There were 627 tumours in men and 440 in women. The tumour was confined to the oesophagus in 281 (26.3%) cases and to the stomach in 454 (42.6%) cases. The tumour encroached upon or crossed the OGJ in 332 (31.1%) cases. Overall, tumours involved the cardia, OGJ, or lower oesophagus in 633 (59.3%) cases; in 179 (18.5%) cases the tumour involved the lower oesophagus but not the OGJ, and in another 122 (11.4%) cases the cardia was involved but not the OGJ. CONCLUSIONS: Oesophagogastric cancers in this population predominantly involve the OGJ, lower oesophagus, and/or cardia.     

The total compliance of the respiratory system during the first year of life

Respiratory system compliance (Crs) was measured in 34 spontaneously breathing infants during the first year of life. An occlusion technique was used whereby several expiratory occlusions were performed at different lung volumes within the tidal range. The airway opening pressure generated during a plateau after occlusion was related to the volume included above the end-tidal level by a regression equation. The slope of this equation represented the compliance of the infant's respiratory system; the intercept was significantly different for preterm (-0.5 ml) and post-term (-5.5 ml) infants and may represent the difference between end-expiratory lung volume during tidal breathing and the relaxed functional residual capacity. The values for respiratory system compliance were similar to those previously reported for infants during muscle relaxation. As a function of body length, Crs = 1.58 X length3.13 X 10(-4) ml . kPa-1. The technique described is simple to apply and is independent of oesophageal pressure measurements.     

Lung volumes measured by helium dilution and by body plethysmography with mouth and oesophageal pressures: a comparative study in patients with lung disease

A comparison was made between the helium dilution technique and body plethysmography--using both mouth pressure and oesophageal pressure against box pressure--for measuring functional residual capacity (FRC). In patients with restrictive lung disease (n = 9) no major differences in FRC were noted between the techniques. In patients with obstructive lung disease (n = 17), helium dilution underestimated FRC by a mean of 0.9 l and conventional body plethysmography (mouth-box pressure) overestimated it by 0.4 l in comparison with FRC obtained by oesophageal pressure against box pressure. The difference between the techniques increased with increasing lung volumes. It is concluded that conventional body plethysmography measures FRC more accurately than the helium dilution technique in patients with obstructive lung disease.     

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)     

Melanocytes and melanosis of the oesophagus in Japanese subjects — analysis of factors effecting their increase

Summary Normal oesophagus specimens taken from 65 autopsy cases and surgical specimens from 127 oesophageal carcinoma cases were examined histopathologically to determine melanocyte incidence and distribution. Melanocytes were found in the epithelio-stromal junction in 7.7% of normal oesophagus specimens examined at autopsy, and in 29.9% of surgical cases with oesophageal carcinoma. Positive specimens in the latter groups, especially from pre-operatively irradiated individuals, showed a more remarkable increase of melanocytes than was evident in any of the normal oesophageal samples. There were no significant differences in incidence between males and females, or between age groups. In cases where the cancer invaded into deeper stroma, the melanocytes were mainly observed in the normal epithelium around the carcinomas. Epithelial and stromal elements of the melanotic mucosa commonly showed hyperplastic changes such as acanthosis or basal cell hyperplasia, and chronic oesophagitis. Melanocytes were observed most commonly in the lower part of the oesophagus, the site where malignant melanoma of the oesophagus, most often originates. These results strongly suggest that the melanocyte increase observed in areas of hyperplastic epithelium and chronic oesophagitis may play an important role as a precursor lesion for malignant melanoma in the oesophagus.     

Distribution of laminins in the basement membranes of the upper gastrointestinal tract and Barrett's oesophagus

Barrett's oesophagus predisposes to oesophageal adenocarcinoma. In vitro, laminin, a component of the epithelial basement membrane (BM), is important in regulation of cell differentiation. There is limited information on the distribution of laminin chains in the upper gastrointestinal tract (GIT) and none in Barrett's oesophagus. This study aimed to investigate qualitatively the distribution of laminins in the normal upper GIT mucosa and Barrett's oesophagus in order to understand the role of laminins in metaplasia. Immunoperoxidase staining for laminin chains alpha1, alpha2, alpha3, alpha5, beta1, beta2, beta3, gamma1, and gamma2 was performed on frozen endoscopic squamous and Barrett's oesophageal biopsies and surgical resection specimens from squamous oesophagus (in resection specimens for oesophageal cancer), and in oesophageal and gastric biopsies from control subjects. alpha1 laminin was expressed in the BM of submucosal glands and ducts in squamous oesophagus and Brunner's glands in the duodenum, but not in Barrett's oesophagus or elsewhere in the upper GIT. alpha2 laminin chain was expressed in a granular distribution in the BM of squamous epithelium. In columnar epithelium, including Barrett's oesophagus, alpha2 laminin chain was expressed continuously in the BM of glands and deeper pits, but expression was reduced and granular in the surface epithelial BM. beta2 laminin was continuous in squamous epithelial BM, but in Barrett's and cardia, gastric body, and duodenum, it was expressed faintly in the surface but continuously in the BM of glands and deeper pits. The constituents of laminin-5 were continuously expressed in the BM of squamous epithelium, but in the cardia, gastric body, duodenum, and Barrett's, they were expressed only in the BM of surface epithelium, with a sharp decline in the glandular and deeper pit BM. Site-specific distribution of the alpha2 and beta2 laminin chains may therefore have an important role in Barrett's metaplasia. However, the absence of alpha1 laminin in Barrett's mucosa suggests that this is unlikely to play an important role in columnar metaplasia.     

Localization of pulmonary stretch receptors in the airways of the dog

1. During respiratory efforts against a closed airway, the afferent activity of vagal fibres from pulmonary stretch receptors does not appreciably increase during the inspiratory phase because the lung is prevented from expanding.2. Occlusion at different levels of the airways allows the localization of pulmonary stretch receptors in the tracheo-bronchial tree.3. 144 fibres from pulmonary stretch receptors on the left side of the tracheo-bronchial tree have been studied in eleven dogs and their localization was as follows: 17.4% in the upper half of the intrathoracic trachea, 27.1% in the lower half of the intrathoracic trachea and the carina, 11.1% in the main bronchus, 13.9% in the upper lobe and 30.5% in the lower lobe.4. From the surface area of the tracheo-bronchial tree at different levels on the assumption of a total of 2000 stretch receptors on each side, their average concentration was as follows: 34.8% receptors/cm(2) in the upper half of the intrathoracic trachea, 54.2/cm(2) in the lower half of the intrathoracic trachea, 56.8/cm(2) in the main bronchus, 0.37/cm(2) in the intrapulmonary airways.5. Occlusion of the main bronchus caused an increase of the eupnoeic oesophageal pressure swing by about 75% whereas occlusion of the inferior lobar bronchus led to an increase of only 20%. Therefore the reflex effects induced on the respiratory activity by occluding the airways at various levels show the greatest importance of the hilar portions of the airways where the concentration of pulmonary stretch receptors has been found to be greater.