Regional Distribution of Pulmonary Ventilation and Perfusion in Obesity

Five women and three men, all obese and weighing 95 to 140 kg, were studied by routine pulmonary function tests and by a radioactive xenon technique, while seated upright at rest, to measure the regional ventilation and perfusion distribution in the lung.In four subjects in whom the expiratory reserve volume averaged 49% of predicted normal, the ventilation distribution as measured with (133)xenon was normal. In the remaining four subjects, in whom the expiratory reserve volume was reduced to less than 0.4 L and averaged only 21% of predicted values, the distribution of a normal tidal breath was predominantly to the upper zones.In all subjects the perfusion distribution was predominantly to the lower lung zones but was slightly more uniform than in normal nonobese subjects. During tidal-volume breathing, therefore, in four subjects the ventilation and perfusion distribution was substantially normal, whereas in the remaining four perfusion was maximal in the lower zones, to which ventilation was significantly reduced.These findings show that there may be significant ventilation/perfusion abnormality on a regional basis in obese subjects, this abnormality bearing a close relationship to the reduction in expiratory reserve volume, a finding predictable from recently published data on normal nonobese subjects (1). The abnormalities of ventilation/perfusion relationships that were demonstrated in four of the eight obese subjects could cause a reduction in arterial oxygen tension during resting tidal ventilation.     

Effect of lower body negative pressure and gravity on regional lung ventilation determined by EIT

The aim of our study was to check the effect of varying blood volume in the chest and gravity on the distribution of ventilation and aeration in the lungs. The change in intrathoracic blood volume was elicited by application of lower body negative pressure (LBNP) of -50 cmH2O. The variation of gravity in terms of hypogravity (approximately 0g) and hypergravity (approximately 2g) was induced by changes in vertical acceleration achieved during parabolic flights. Local ventilation magnitude and end-expiratory lung volume were determined in eight human subjects in the ventral and dorsal lung regions within a transverse cross-section of the lower chest by electrical impedance tomography. The subjects were studied in a 20 degrees head-down tilted supine body position during tidal breathing and full forced expirations. During tidal breathing, a significant effect of gravity on local magnitude of ventilation and end-expiratory lung volume was detected in the dorsal lung regions both with and without LBNP. In the ventral regions, this gravity dependency was only observed during LBNP. During forced expiration, LBNP had almost no effect on local ventilation and end-expiratory lung volume in either lung region. Gravity significantly influenced the end-expiratory lung volumes in dorsal lung regions. The results indicate that exposure to LBNP exerts a less appreciable effect on regional lung ventilation than the acute changes in gravity.     

The effect of breathing exercises with body positioning on regional lung ventilation

This review discusses the distribution of ventilation in the normal adult lung and includes the influence of quiet and deep breathing on regional ventilation. The effects of breathing at low lung volumes; inspiratory flow rate; posture; age; and body weight on ventilation are also described. A selection of breathing exercises are examined with regard to their ability to influence regional ventilation. There is no evidence that breathing control (diaphragmatic breathing exercises) improves regional ventilation to the dependent zones of the lungs. Limited evidence does suggest that thoracic expansion exercises, whereby respiratory muscles are voluntarily contracted to alter regional chest wall expansion, can improve underlying ventilation. However, there remains a paucity of evidence regarding the effects of breathing exercises on regional ventilation.     

Studies on the Regulation of Secretion in Clara Cells with Evidence for Chemical Nonautonomic Mediation of the Secretory Response to Increased Ventilation in Rat Lungs

Using electron microscopy and morphometric methods to assess secretion, we previously found that two times tidal volume ventilation of isolated perfused rat lung stimulates secretion by bronchiolar Clara cells; this effect is not prevented by β-adrenergic blockade (J. Clin. Invest. 1981. 67: 345-351.). In this study we used the isolated perfused rat lung and the anesthetized mechanically ventilated rat, to further study the mechanism by which large tidal volumes stimulate secretion by Clara cells. With the perfused lung we found (a) α-adrenergic inhibition did not block the secretory effect of ventilation at two times normal tidal volume; (b) indomethacin completely blocked the secretory action of two times tidal volume ventilation; (c) medium previously used to perfuse lungs ventilated at two times tidal volume, but not medium previously used to ventilate lungs at normal tidal volume, stimulated secretion by Clara cells when used to perfuse fresh lungs ventilated at tidal volume; (d) addition of prostacyclin to the fresh perfusate increased secretion by Clara cells of lungs ventilated at normal tidal volume. In anesthetized mechanically ventilated rats, sighs stimulated secretion by Clara cells; this increased secretion was inhibited by indomethacin but not by cholinergic blockade (bilateral vagotomy). These studies indicate that increased volume ventilation stimulates secretion by Clara cells in vivo and in vitro; they provide evidence that chemical nonadrenergic, noncholinergic mechanisms are involved in this secretion, and that prostaglandins may be the chemical messenger coupling the mechanico-secretory events.     

Regional lung function in patients with hepatic cirrhosis

The lung volume at which the dependent lung zones begin to trap gas as a result of airway closure (i.e., the "closing volume") was measured with (133)Xe in 10 seated patients with hepatic cirrhosis. In all of them the closing volume was increased above normal, and in eight it was greater than the functional residual capacity, indicating the presence of airway closure and gas trapping during resting tidal volume breathing. Direct measurements made with (133)Xe in five cirrhotic patients (a) confirmed the presence of increased gas trapping in the lower lung zones both at residual volume and at functional residual capacity, and (b) indicated that in liver cirrhosis the ventilation-perfusion ratio of the dependent lung zones may be very low, primarily as a result of decreased ventilation due to airway closure. It is concluded that in hepatic cirrhosis, gas trapping in the dependent lung zones may be an important cause of impaired gas exchange within the lungs. It is suggested that the premature airway closure observed in this disease may be due to mechanical compression of small airways by dilated blood vessels and/or interstitial pulmonary edema.     

Alveolar edema dispersion and alveolar protein permeability during high volume ventilation: effect of positive end-expiratory pressure

Objectives To evaluate whether PEEP affects intrapulmonary alveolar edema liquid movement and alveolar permeability to proteins during high volume ventilation. Design and setting Experimental study in an animal research laboratory. Subjects 46 male Wistar rats. Interventions A ^99mTc-labeled albumin solution was instilled in a distal airway to produce a zone of alveolar flooding. Conventional ventilation (CV) was applied for 30 min followed by various ventilation strategies for 3 h: CV, spontaneous breathing, and high volume ventilation with different PEEP levels (0, 6, and 8 cmH₂O) and different tidal volumes. Dispersion of the instilled liquid and systemic leakage of ^99mTc-albumin from the lungs were studied by scintigraphy. Measurements and results The instillation protocol produced a zone of alveolar flooding that stayed localized during CV or spontaneous breathing. High volume ventilation dispersed alveolar liquid in the lungs. This dispersion was prevented by PEEP even when tidal volume was the same and thus end-inspiratory pressure higher. High volume ventilation resulted in the leakage of instilled ^99mTc-albumin from the lungs. This increase in alveolar albumin permeability was reduced by PEEP. Albumin permeability was more affected by the amplitude of tidal excursions than by overall lung distension. Conclusions PEEP prevents the dispersion of alveolar edema liquid in the lungs and lessens the increase in alveolar albumin permeability due to high volume ventilation. This research was supported by a grant from the French Académie Nationale de Médecine     

Ventilatory responses to exercise and to carbon dioxide in mitral stenosis before and after valvulotomy: causes of tachypnoea

1. The ventilation and cardiac frequency during progressive exercise and the respiratory responses to breathing carbon dioxide have been measured in 33 female patients with mitral stenosis and in 31 control subjects. Compared with the control subjects, the patients' exercise ventilation and cardiac frequency were increased; the exercise tidal volume at standard minute volume, the vital capacity and the ventilatory response to carbon dioxide were reduced. The extent to which the standardized tidal volume was lower during exercise than during breathing carbon dioxide was correlated with the severity of the stenosis, as gauged by the increase in exercise cardiac frequency above the level predicted from anthropometric measurements. 2. Twenty patients were studied postoperatively. In the 12 who showed clinical improvement the exercise ventilation and cardiac frequency were reduced and the exercise tidal volume at a given minute ventilation was increased. The latter change occurred despite a reduction in vital capacity, which was probably a residual effect of thoractomy. There was no significant change in the response to breathing carbon dioxide. No material change in function was observed in the patients whose condition was not improved by the operation. 3. It is suggested that in mitral stenosis the tachypnoea which occurs during exercise, whilst mainly a mechanical consequence of the reduced vital capacity, is also partly due to pulmonary congestion stimulating intrapulmonary receptors.     

重度肥胖对肺功能及运动试验中呼吸模式的影响

目的：研究重度肥胖对肺胖对肺功能及运动试验中呼吸模式的影响。方法：４２名女性受试者,正常体重组２０名,重度肥胖组２２名,进行肺功能及功率车运动试验测定。结果：肥胖组补呼气量、功能残气量、残气量及肺总量均比对照组显著降低（Ｐ〈０．０５）。肥胖组静息状态、无氧阈状态和极量运动状态的氧耗量均比对照组显著增高（Ｐ〈０．０５）,而公斤氧耗量比对照组显著降低（Ｐ〈０．０１）。无氧阈状态和极量运动状态时,肥胖组     

The value of electrical impedance tomography in assessing the effect of body position and positive airway pressures on regional lung ventilation in spontaneously breathing subjects

Objective Functional electrical impedance tomography (EIT) measures relative impedance changes in lung tissue during tidal breathing and creates images of local ventilation distribution. A novel approach to analyse the effect of body position and positive pressure ventilation on intrapulmonary tidal volume distribution was evaluated in healthy adult subjects.Design and setting Prospective experimental study in healthy adult subjects in the intensive care unit at university hospital.Subjects Ten healthy male adults.Interventions Change in body position from supine to prone, left and right lateral during spontaneous breathing and positive pressure support ventilation.Measurements and results EIT measurements and multiple-breath sulphur hexafluoride (SF₆) washout were performed. Profiles of average relative impedance change in regional lung areas were calculated. Relative impedance time course analysis and Lissajous figure loop analysis were used to calculate phase angles between dependent or independent lung and total lung (). EIT data were compared to SF₆ data washout measuring the lung clearance index (LCI). Proposed EIT profiles allowed inter-individual comparison of EIT data and identified areas with reduced regional tidal volume using pressure support ventilation. Phase angle of dependent lung in supine position was 11.7±1.4°, in prone 5.3±0.5°, in right lateral 11.0±1.3° and in left lateral position 10.8±1.0°. LCI increased in supine position from 5.63±0.43 to 7.13±0.64 in prone position. Measured showed inverse relationship to LCI in the four different body positions.Conclusions EIT profiles and of functional EIT are new methods to describe regional ventilation distribution with EIT allowing inter-individual comparison.This article refers to the editorial The study was supported by the Preston James Foundation and SensorMedics, The Netherlands     

The assessment of regional lung mechanics with electrical impedance tomography: a pilot study during recruitment manoeuvres

Objective  The purpose of lung recruitment manoeuvres is to open collapsed lung regions, improve gas exchange and optimise regional lung mechanics. This study investigates the efficacy of recruitment manoeuvres for improving regional ventilation distribution as characterised using electrical impedance tomography (EIT). Design, subjects, interventions  A ventilated ovine smoke inhalation lung injury model was used. Respiratory mechanics and regional filling capacity of the lung were measured using EIT pre- and post- recruitment and compared to a control group. Measurements  EIT, expressed as the time course relation of the regional versus the global impedance change, measured the regional filling capacities of the lung. Main results  After smoke inhalation injury, the dependent lung showed a significantly larger area of collapse and a reduced filling capacity compared to the non-dependent lung. After recruitment the ventilated volume increased and the dependent lung showed improved respiratory mechanics, whereas the non-dependent lung was more likely to be hyper-inflated during tidal breathing. Conclusions  Lung recruitment manoeuvres have a significant impact on regional lung mechanics and individual measurement of ventilation distribution using EIT may assist to improve ventilatory management. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Pursed lips breathing improves ventilation in myotonic muscular dystrophy

OBJECTIVE: To determine the effects of pursed lips breathing on ventilation, chest wall mechanics, and abdominal muscle recruitment in myotonic muscular dystrophy (MMD). DESIGN: Before-after trial. SETTING: University hospital pulmonary function laboratory. PARTICIPANTS: Eleven subjects with MMD and 13 normal controls. INTERVENTION: Pursed lips breathing. OUTCOME MEASURES: Electromyographic (EMG) activity of the transversus abdominis, external oblique, internal oblique, and rectus abdominis was recorded with simultaneous measures of gastric pressure, abdominal plethysmography, and oxygen saturation. Self-reported sensations of dyspnea, respiratory effort, and fatigue were recorded at the end of each trial. RESULTS: Pursed lips breathing and deep breathing led to increased tidal volume, increased minute ventilation, increased oxygen saturation, reduced respiratory rate, and reduced endexpiratory lung volume. Dyspnea, respiratory effort, and fatigue increased slightly with pursed lips breathing. EMG activity of the transversus abdominis and internal oblique muscles increased in MMD only and was associated with an increase in gastric pressure. CONCLUSIONS: Pursed lips breathing and deep breathing are effective and easily employed strategies that significantly improve tidal volume and oxygen saturation in subjects with MMD. Abdominal muscle recruitment does not explain the ventilatory improvements, but reduced end-expiratory lung volume may increase the elastic recoil of the chest wall. Further clinical studies are needed to ascertain if the ventilatory improvements with pursed lips breathing and deep breathing improve pulmonary outcomes in MMD.     

Elastic properties of the centrilobular emphysematous space

Bronchograms were performed using finely particulate lead on emphysematous lungs obtained at necropsy. X-ray films were taken of these lungs at distending pressures of 0, 5, 10, and 20 cm H(2)O. The volumes of individual centrilobular emphysematous spaces were calculated at each distending pressure from measurements made on these bronchograms and pressure-volume curves were constructed for each space. The pressure-volume characteristics of seven normal lungs and one lung with centrilobular emphysema was also measured. The normal lungs, the lung with centrilobular emphysema, and the centrilobular emphysematous spaces were compared by expressing the volume of air contained in them at each distending pressure as a per cent of the volume contained at 20 cm H(2)O distending pressure. We conclude that centrilobular emphysematous spaces have a high residual volume, are less compliant than normal lung tissue, and are much less compliant than the emphysematous lungs which contain them. Furthermore, these spaces undergo little volume change in the tidal breathing range and probably add a relatively nondistensible series dead space to the surrounding lung parenchyma.     

Dissociation between respiratory effort and dyspnoea in a subset of patients with stroke

Dyspnoea is not a prominent complaint of resting patients with recent hemispheric stroke (RHS). We hypothesized that, in patients with RHS presenting abnormalities in respiratory mechanics, increased respiratory motor output could translate into an increased perception of dyspnoea. We studied eight wheelchair-bound patients with RHS (mean age 62.4 years), previously evaluated by computerized tomography scanning, and a control group of normal subjects, matched for age and sex. We assessed routine spirometry, inspiratory and expiratory muscle pressures, breathing pattern and dyspnoea using a modified Borg scale. In six patients, we also measured oesophageal pressure during the maximal sniff manoeuvre and tidal inspiratory swing, and mechanical characteristics of the lung in terms of dynamic elastance during both quiet breathing and a hypercapnic/hyperoxic rebreathing test. During room air breathing, ventilation and tidal volume were similar in patients and controls, while tidal inspiratory swings of oesophageal pressure, an index of inspiratory motor output, were greater in patients ( P =0.005). Patients also exhibited a greater dynamic elastance ( P =0.013). During rebreathing, dynamic elastance remained higher ( P =0.01) and a greater than normal inspiratory motor output was found ( P =0.03). Responses of ventilation and tidal volume to carbon dioxide tension were normal, and in all patients but one a lower Borg score for the unit change in carbon dioxide tension and ventilation was found. In conclusion, a higher than normal inspiratory motor output was unexpectedly associated with a blunted perception of dyspnoea in this subset of RHS patients. This is likely to be due to the modulation of the integration process of respiratory sensation.     

Regional pulmonary blood flow in sitting and supine man during and after acute hypoxia

Regional pulmonary blood flow was measured by external counting of intravenously injected (133)Xe during 20 min of breathing 14.2% oxygen and during 20 min of recovery from hypoxia. 16 normal human volunteers were studied, nine sitting and seven supine. During hypoxia there was a slight but significant increase in relative perfusion of the upper portions of the lungs in both the sitting and supine subjects. During recovery from hypoxia, blood flow distribution differed significantly from the control. The erect subjects showed increased relative perfusion of the lung bases and the supine subjects showed increased relative perfusion of the upper zones.Comparison of the distribution of inhaled and intravenously injected isotope showed that in the sitting subjects the altered distribution during hypoxia tended to make alveolar oxygen tension more uniform. In the supine subjects, however, the shift in blood flow increased the perfusion of the regions with the lowest ventilation/perfusion, tending to accentuate uneven alveolar oxygen tension. Therefore it does not seem that the altered blood flow distribution during hypoxia was due to selective vasoconstriction in the regions of lowest alveolar oxygen tension, but rather that vasoconstriction was greatest in the lower lung zones because the vessels there are more responsive to hypoxia. During mild acute hypoxia, vasoconstrictor tone does not seem to effectively match ventilation and perfusion.The altered distribution of pulmonary blood flow during recovery from hypoxia suggests the occurrence of posthypoxic vasodilation. Failure to consider this possibility may lead to erroneous interpretation of pulmonary hemodynamic measurements made after the inspired oxygen concentration has been changed.     

How to set positive end-expiratory pressure

Application of positive end-expiratory pressure (PEEP) in acute lung injury patients under mechanical ventilation improves oxygenation and increases lung volume. The effect of PEEP is to recruit lung tissue in patients with diffuse lung edema. This effect is particularly important in patients ventilated with low tidal volumes. Measurement of respiratory system mechanics in patients with acute respiratory distress syndrome is important to assess the status of the disease and to choose appropriate ventilator settings that provide maximum alveolar recruitment while avoiding overdistention. In patients with acute respiratory distress syndrome in whom the lungs have been near-optimally recruited by PEEP and tidal volume, the use of recruitment maneuvers as adjuncts to mechanical ventilation remains controversial. The application of PEEP in patients with unilateral lung disease may be detrimental if PEEP hyperinflates normal lung regions, thus directing blood flow to diseased lung regions. In patients with air flow limitation and lung hyperinflation, the application of additional external PEEP to compensate for intrinsic PEEP and flow limitation frequently decreases the inspiratory effort to initiate an assisted breath, thus decreasing breathing work load.     

Regional lung function in patients with bronchial asthma

The regional distribution of pulmonary ventilation and perfusion and regional alveolar ventilation/perfusion ratios were measured with radioactive xenon ((133)xenon) in 10 patients with asthma in remission. Four subjects had normal ventilation distribution, four had hypoventilation in some regions and normal ventilation in others, and two patients had abnormal ventilation in almost all lung regions. The lung bases were involved most frequently and the middle zones least frequently. Correlation was good between the degree of over-all ventilatory impairment calculated from (133)xenon values and measurement of the maximal midexpiratory flow rate the same day.Regions which were hypoventilated had low ventilation/perfusion ratios and also tended to be hypoperfused. In the eight subjects who had been studied similarly 5 yr previously, changes in regional function correlated in general with changes in over-all function.     

Electrical impedance tomography: a method for monitoring regional lung aeration and tidal volume distribution?

Objective To demonstrate the monitoring capacity of modern electrical impedance tomography (EIT) as an indicator of regional lung aeration and tidal volume distribution.Design and setting Short-term ventilation experiment in an animal research laboratory.Patients and participants One newborn piglet (body weight: 2 kg).Interventions Surfactant depletion by repeated bronchoalveolar lavage, surfactant administration.Measurements and results EIT scanning was performed at an acquisition rate of 13 images/s during two ventilatory manoeuvres performed before and after surfactant administration. During the scanning periods of 120 s the piglet was ventilated with a tidal volume of 10 ml/kg at positive end-expiratory pressures (PEEP) in the range of 0–30 cmH₂O, increasing and decreasing in 5 cmH₂O steps. Local changes in aeration and ventilation with PEEP were visualised by EIT scans showing the regional shifts in end-expiratory lung volume and distribution of tidal volume, respectively. In selected regions of interest EIT clearly identified the changes in local aeration and tidal volume distribution over time and after surfactant treatment as well as the differences between stepwise inflation and deflation.Conclusions Our data indicate that modern EIT devices provide an assessment of regional lung aeration and tidal volume and allow evaluation of immediate effects of a change in ventilation or other therapeutic intervention. Future use of EIT in a clinical setting is expected to optimise the selection of appropriate ventilation strategies.     

Comparison of high-frequency negative-pressure oscillation with conventional mechanical ventilation in normal and saline-lavaged cats

We modified a negative-pressure respirator to produce high-frequency, subatmospheric pressure oscillations around the chest. The effects of negative-pressure oscillation (NPO) on gas exchange, lung volume, compliance and cardiovascular variables were compared to those of conventional intermittent positive-pressure ventilation (IPPV) at 30 breath/min, using cats with normal and surfactant-depleted lungs. For frequencies in both normal lungs (1, 3, 4, 5, and 7 Hz) and saline-lavaged lungs (3, 5, and 7 Hz), peak inflating pressures were lower during NPO. Oxygenation was similar for both modes of ventilation. In cats with normal lungs, PaCO2 was significantly lower during NPO at 3 and 4 Hz (mean 24 torr) than during IPPV (mean 30 torr); normocapnia was maintained at the other frequencies. In damaged lungs, NPO and IPPV at 3 and 5 Hz resulted in similar CO2 removal, but PaCO2 was significantly higher during NPO at 7 Hz. Oscillatory tidal volumes decreased with increasing frequencies: in normal lungs, mean oscillatory tidal volume was 4.4 ml/kg at 1 Hz and 2.3 ml/kg at 7 Hz; in damaged lungs it was 6.5 ml/kg at 3 Hz and 3.2 ml/kg at 7 Hz. At 3 Hz and above, NPO was associated with a larger functional residual capacity than during sequences of IPPV matched for end-expiratory transthoracic pressure. There were no significant differences in respiratory system compliance, cardiac output, and pulmonary vascular resistance between both modes of ventilation. Further studies are warranted to investigate the potential clinical usefulness of NPO.     

Influence of an end inspiratory pause on pulmonary ventilation, gas distribution, and lung perfusion during artificial ventilation

Using a constant tidal volume and ventilatory frequency, anesthetized piglets were ventilated with a new tidal volume ventilator. A short inspiratory time without a pause (10% of breathing cycle) was compared with a longer inspiratory time with a pause (33%) both with and without bronchial obstruction. Mechanics of ventilation, pulmonary ventilation, gas exchange, gas distribution, and lung perfusion were measured. The longer inspiratory time with a pause resulted in lower peak airway and end inspiratory pressures and a higher total compliance. Dead space/tidal volume ratio was reduced and the RQ was increased. While the cranial pulmonary fields were less well ventilated, the right caudal field was better ventilated. In the presence of bronchial obstruction, better alveolar ventilation was achieved when an end inspiratory pause was added. The results emphasize the importance of static end inspiratory tracheal conditions although the tidal volumes were kept unchanged.     

Variations of regional lung function in acute respiratory failure and during anaesthesia

Acute respiratory failure and anaesthesia impede ventilation of dependent lung units and perfusion of non-dependent ones, creating considerable ventilation-perfusion mismatch. General PEEP can improve but it cannot restore it to normal. To improve matching, ventilation must be distributed in proportion to regional blood flow. This can be accomplished by (1) placing the subject in the lateral position, (2) ventilating each lung in proportion to its blood flow (differential ventilation), and (3) applying PEEP solely to the dependent lung to ensure even distribution of inspired gas within that lung (selective PEEP). Differential ventilation with equal distribution of the tidal volume between the lungs and a selective PEEP of 10 cm H₂O to the dependent lung resulted in equal distribution of perfusion between the lungs in anaesthetized healthy subjects, suggesting “optimum” lung disease, arterial oxygen tension was improved by an average of 45% compared with that during general PEEP, with no reduction in cardiac output. It is concluded that differential ventilation with selective PEEP can offer considerable improvement in gas exchange in acute, bilateral lung disease. However, long-term studies are required before a final evaluation can be made.