Unilateral high-frequency jet ventilation during one-lung ventilation for thoracotomy

One-lung ventilation is indicated during thoracic operations for bronchopleural fistula, pulmonary abscess, and pulmonary hemorrhage in spite of the possibility of the development of severe hypoxemia. To evaluate methods for improving oxygen transport during one-lung ventilation, we applied high-frequency jet ventilation (HFJV) and continuous positive airway pressure (CPAP) to the nondependent lung following deflation to atmospheric pressure in each procedure, and measured the effects on cardiac output and arterial oxygenation. In each case, the dependent lung was ventilated with conventional intermittent positive pressure ventilation (IPPV).

Eight patients were studied during posterolateral thoracotomy using double-lumen endobronchial tubes. HFJV or CPAP to the nondependent lung improved arterial oxygenation significantly during both closed and open stages of the surgical procedures (p < 0.008). When the chest was open, HFJV maintained satisfactory cardiac output, whereas CPAP usually decreased cardiac output (p < 0.008). There were no significant differences in mean partial pressure of arterial carbon dioxide between HFJV, CPAP, and deflation to atmospheric pressure.

In conclusion, HFJV to the nondependent lung provides not only satisfactory oxygenation but also good cardiac output, thereby maintaining better oxygen transport than CPAP or deflation to atmospheric pressure, while the dependent lung is ventilated with IPPV during one-lung ventilation for thoracotomy.     

Unilateral high-frequency jet ventilation during one-lung ventilation for thoracotomy

One-lung ventilation is indicated during thoracic operations for bronchopleural fistula, pulmonary abscess, and pulmonary hemorrhage in spite of the possibility of the development of severe hypoxemia. To evaluate methods for improving oxygen transport during one-lung ventilation, we applied high-frequency jet ventilation (HFJV) and continuous positive airway pressure (CPAP) to the nondependent lung following deflation to atmospheric pressure in each procedure, and measured the effects on cardiac output and arterial oxygenation. In each case, the dependent lung was ventilated with conventional intermittent positive pressure ventilation (IPPV). Eight patients were studied during posterolateral thoracotomy using double-lumen endobronchial tubes. HFJV or CPAP to the nondependent lung improved arterial oxygenation significantly during both closed and open stages of the surgical procedures (p less than 0.008). When the chest was open, HFJV maintained satisfactory cardiac output, whereas CPAP usually decreased cardiac output (p less than 0.008). There were no significant differences in mean partial pressure of arterial carbon dioxide between HFJV, CPAP, and deflation to atmospheric pressure. In conclusion, HFJV to the nondependent lung provides not only satisfactory oxygenation but also good cardiac output, thereby maintaining better oxygen transport than CPAP or deflation to atmospheric pressure, while the dependent lung is ventilated with IPPV during one-lung ventilation for thoracotomy.     

Comparison of conventional intermittent positive pressure ventilation with high frequency jet ventilation

This study was designed to compare the cardiorespiratory effects of high frequency jet ventilation at 150 breaths/minute with and without added positive and expiratory pressure, with conventional intermittent positive pressure ventilation in 20 patients following aortocoronary bypass graft surgery. On comparison with intermittent positive pressure ventilation, there was a decrease in peak airway pressure during high frequency jet ventilation when positive and expiratory pressure of 0 or 0.5 kPa was applied, but not with 1 kPa, and an increase in mean airway pressure with positive end expiratory pressures of 0.5 and 1 kPa. On changing from intermittent positive pressure to high frequency jet ventilation with no added end expiratory pressure, there was an acute decrease in arterial oxygen tension and increases in cardiac output and total tissue oxygen delivery. On changing from intermittent positive pressure ventilation to high frequency jet ventilation with 1 kPa of positive end expiratory pressure, there was an acute decrease in arterial oxygen tension, cardiac output and oxygen delivery, and increases in pulmonary arterial, right atrial and pulmonary capillary wedge pressures. The addition of positive end expiratory pressure did not prevent the acute decrease in arterial oxygen tension which occurred on transfer to high frequency jet ventilation.     

Differential lung ventilation during thoracotomy

The effect of differential lung ventilation on arterial PO2 and PCO2 was compared to that achieved during one-lung ventilation in 8 patients undergoing thoracotomy. In all patients, OLV of the dependent lung, while collapsing the nondependent lung, was associated with lowering of the arterial PO2. DLV using a special double-lumen tube adaptor was then initiated; the dependent lung was preferentially ventilated by 75-80% of the tidal volume, while the nondependent lung on the operative side was only ventilated by 20-25% of the tidal volume. DLV improved oxygenation and maintained adequate carbon dioxide elimination, with minimal inflation of the nondependent lung into the surgical field. DLV may be used to increase oxygenation whenever conventional OLV is associated with hypoxemia despite the use of 100% oxygen.     

Effects of positive end-expiratory pressure (PEEP) or prolonged inspiration time on lung mechanics, gas exchange and hemodynamics in differential pulmonary ventilation

In the case of patients with unilateral lung disorders one must anticipate a further increase in the intake volume of the more elastic lung and a decrease in intake volume of the less elastic lung when the inspiratory pressure is increased or the inspiratory time is extended within the framework of mechanical ventilation. Therefore, differential pulmonary ventilation lends itself for the treatment of unilateral damage of the lung by enabling the selective application of a positive end-expiratory pressure or an inverse inspiratory time. For a better understanding of the overlapping pathophysiologic reactions, the changes in lung mechanics, haemodynamics and gas exchange were measured on the healthy lung with unilateral application of a positive and expiratory pressure or an increased inspiratory time. Thirteen male and female patients, who had to undergo intracranial surgery were ventilated with two synchronized servoventilators using a Carlens tube. The positive end expiratory pressure varied in the right lung in spans of 6 cm each, 0-12 cm H2O, inspiratory time varied 34-70%. The left lung was ventilated with a 35% inspiratory time and an end expiratory pressure of 0. The respiratory intake volume was divided up into 45% (left lung) and 55% (right lung) based on the physiological difference in size between the left and right lung. Our results show that a directed unilateral application of a positive end expiratory pressure or an increased inspiratory time does not have any relevant damaging effects on the other lung. It can be expected that in the case of non-differentiated mechanical ventilation the ensuing unequal distribution of alveolar ventilation and perfusion with consecutive increase of intrapulmonary shunt volume can be decreased by the discriminate treatment of each lung.     

Comparison of the haemodynamic effects of intermittent positive pressure ventilation with high frequency jet ventilation

The cardiorespiratory effects of intermittent positive pressure ventilation and high frequency jet ventilation with and without positive end expiratory pressure were compared in patients following valvular heart surgery (mitral and/or aortic). Twenty patients received intermittent positive pressure ventilation and high frequency jet ventilation with 0, 0.5 and 1.0 kPa positive end expiratory pressure. High frequency jet ventilation was well tolerated. The addition of 1.0 kPa positive end expiratory pressure was associated with preservation of the arterial oxygen tension without any increase in shunt or significant adverse haemodynamic effect. The results are discussed and compared with a previous study of high frequency jet ventilation following aortocoronary bypass graft surgery.     

The effect of induction of anesthesia and intubation on end-expiratory lung level and regional ventilation distribution in cardiac children

Background: During the induction of anesthesia, changes in functional residual capacity and ventilation distribution (VD) occur. Although these physiological changes are well investigated in adults, little data are available in infants and children. Aim: To describe continuous changes in lung physiology during the induction of anesthesia in infants and children using electrical impedance tomography (EIT). Methods: Lung mechanics and volume changes in 38 infants and children undergoing elective cardiac surgery were assessed using EIT before, during, and after the induction of anesthesia. End‐expiratory level (EEL as an equivalent to FRC) and VD were measured with EIT and referenced to a period of spontaneous breathing prior to induction. Results: EEL changed significantly during induction with the lowest during the intubation phase and normalized with the application of positive end‐expiratory pressures (PEEP) after induction. Ventilation prior to induction was preferentially distributed toward the dependent lung, whereas after induction, the nondependent lung was better ventilated. PEEP during mechanical ventilation did not improve ventilation inhomogeneity. Conclusion: Lung volume and mechanics deteriorate significantly during the induction of anesthesia and remain altered during mechanical ventilation.     

"Closing volume" during high–frequency ventilation in anesthetized dogs

Airway closure, mean airway pressure, gas exchange and different modes of artificial ventilation were investigated in anesthetized and paralyzed dogs with clinically healthy lungs. The animals were ventilated with either intermittent positive pressure ventilation (IPPV), continuous positive pressure ventilation (GPPV, positive end-expiratory pressure (PEEP) = 0.49 kPa) or high-frequency jet ventilation (HFJV, open system) of 2 and 30 Hz with an inspiratory to expiratory (I/E) - ratio of 30/70 and 60/40. Closing volume (CV) was determined by a modified technique, submitting the lung to constant subatmospheric pressure after an inspiratory vital capacity of oxygen. Two different tests for CV were used: the foreign gas bolus (FGB) with helium as nonresident gas and the single breath nitrogen dilution technique (SBO2). During conventional mechanical ventilation, CV decreased significantly (P less than 0.05) after establishing a PEEP of 0.49 kPa. During HFJV, CV increased significantly (P less than 0.01). This effect was predominantly dependent on I/E duration time ratio and to a lesser extent on ventilatory frequency. There were significant differences between CV obtained by the FGB-method (CV(helium] and CV derived from the SBO2-test (CV(SBO2], although both tests revealed the same proportional changes of CV during the different modes of ventilation. The elevated CV was associated with a decreasing Pao2 and increasing Aa-Do2 and Paco2, indicating substantial hypoventilation and mismatching of ventilation and perfusion. Mean airway pressure increased with both CPPV and HFJV, revealing a dissociation between airway pressure and regional FRC distribution during HFJV. It is concluded that certain modes of high-frequency ventilation lead to impaired distribution of inspired gas to dependent lung regions.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of one-lung ventilation upon pulmonary inflammatory responses during lung resection

Purpose  

One-lung ventilation (OLV) is commonly used during thoracic surgery. Clinical studies using bronchoalveolar lavage fluid analysis have demonstrated that OLV induces pulmonary inflammatory reactions in the ventilated dependent lung. However, few clinical studies have investigated such inflammatory reactions in the dependent lung compared with the collapsed nondependent lung. Here we used a bronchoscopic microsampling method to obtain epithelial lining fluid (ELF) from each lung, and then compared the inflammatory reactions in the dependent lung and the nondependent lung during thoracic surgery.     

The effect of positive end-expiratory pressure and continuous positive airway pressure on the oxygenation and shunt fraction during one-lung ventilation with propofol anesthesia.

STUDY OBJECTIVE: To evaluate the effect of positive end-expiratory pressure (PEEP) and continuous positive airway pressure (CPAP) on the oxygenation and shunt fraction during one-lung ventilation (OLV). DESIGN: Prospective clinical study. SETTING: Inpatient thoracic surgery and anesthesia clinic at an University hospital. PATIENTS: 15 patients with esophageal cancer who were scheduled for radical surgery. INTERVENTIONS: Arterial oxygenation, shunt fraction, and hemodynamics were evaluated at 20 min after the start of operation, at 20 minutes after the initiation of OLV under zero end-expiratory pressure (ZEEP), 20 minutes after the application of 4 cm PEEP to the dependent lung, at 20 minutes after OLV under ZEEP, 20 minutes after the application of 4 cm CPAP to the nondependent lung, and again under ZEEP, and after the combined application of PEEP and CPAP to the dependent and nondependent lungs. MEASUREMENTS AND MAIN RESULTS: There were no significant changes in mean pulmonary artery pressure, mean arterial blood pressure, heart rate, mixed venous partial pressure of oxygen, or arterial and mixed venous saturation of oxygen (SVO(2)) during this study. Arterial partial pressure of oxygen (pO(2)) increased and shunt fraction values decreased significantly after the application of PEEP (pO(2); 197.8 +/- 32.9 mmHg, Qs/Qt; 22.9 +/- 5.6%), CPAP (pO(2); 212.6 +/- 15.9 mmHg, Qs/Qt; 22.8 +/- 5.9%), and combination of PEEP and CPAP (pO(2); 222.0 +/- 42.8 mmHg, Qs/Qt; 24.1 +/- 6.4%) compared with ZEEP (pO(2); 128.1 +/- 37.5 mmHg, Qs/Qt; 33.2 +/- 6.8% ). But there were no significant differences regarding oxygenation and shunt fraction during PEEP, CPAP, or the combination of PEEP and CPAP. CONCLUSIONS: The application of PEEP to the dependent lung, CPAP to the nondependent lung, and the combination of PEEP and CPAP, are useful for improving oxygenation and decreasing Qs/Qt.     

Differential Lung Ventilation with Unilateral PEEP Following Unilateral Hydrochloric Acid Aspiration in the Dog

Differential lung ventilation with positive end expiratory pressure (PEEP) improves pulmonary gas exchange when used in the supportive care of patients with severe unilateral or asymmetrical lung disease. Once the provision of selective PEEP to the two lungs is accomplished, the best method of partitioning the tidal volume between the two lungs is unknown. Twelve mongrel dogs were given a unilateral hydrochloric acid (HCl) aspiration injury. A computer controlled differential lung ventilation system was used to ventilate four dogs with equal volumes to each lung, four dogs with equal driving pressure (end inspiratory pressure-PEEP) to each lung, and four dogs with equal end-tidal CO₂ fraction from each lung. The respiratory rate was feedback controlled to maintain Paco₂ at 4.67 kPa. The dogs were kept supine and ventilated with 30% O₂. Following injury, the PEEP was set at 0 kPa for 1 h. The dogs were then given 1.36 kPa and 2.72 kPa PEEP to the injured lung for 2 h in a cross-over fashion. The assignment of the tidal volume controller, the side of injury, and the PEEP sequence was random. Oxygen tension fell and pulmonary venous admixture increased after giving the HCl injury. In all three groups considered simultaneously, unilateral PEEP improved Pao₂ and venous admixture. The equal tidal volume distribution was the only group to show a significant improvement in Pao₂ at both PEEP increments (0 to 1.36 kPa and 2.72 kPa). There was a significant difference in tidal volume allocation between the three groups with the equal end-tidal and equal pause pressure groups only minimally ventilating the injured lung. With differential lung ventilation and unilateral PEEP, equal partitioning of tidal volume provides the highest Pao₂, compared to the other two methods of partitioning tidal volume.     

Pulmonary Blood Flow Redistribution with Low Levels of Positive End-expiratory Pressure

Background: Recent studies have questioned the importance of the gravitational model of pulmonary perfusion. Because low levels of positive end-expiratory pressure (PEEP) are commonly used during anesthesia, the authors studied the distribution of pulmonary blood flow with low levels of PEEP using a high spatial resolution technique. They hypothesized that if hydrostatic factors were important in the distribution of pulmonary blood flow, PEEP would redistribute flow to more dependent lung regions.

Methods: The effects of zero cm H2 O PEEP and 5 cm H2 O PEEP on pulmonary gas exchange were studied using the multiple inert gas elimination technique; the distribution of pulmonary blood flow, using fluorescent-labeled microspheres, was also investigated in mechanically ventilated, pentobarbital-anesthetized dogs. The lungs were removed, cleared of blood, dried at total lung capacity, and then cubed to obtain approximately 1,000 small pieces of lung ([approximately] 1.7 cm3).

Results: Positive end-expiratory pressure increased the partial pressure of oxygen by 6 +/- 2 mmHg (P < 0.05) and reduced all measures of ventilation and perfusion heterogeneity (P < 0.05). By reducing flow to nondependent ventral lung regions and increasing flow to dependent dorsal lung regions, PEEP increased (P < 0.05) the dorsal-to-ventral gradient. Redistribution of blood flow with PEEP accounted for 7 +/- 3%, whereas structural factors accounted for 93 +/- 3% of the total variance in blood flow.     

Postoperative Arterial Oxygen Tension after Peroperative PEEP-Ventilation

Forty otherwise healthy patients (29 women and 11 men), undergoing elective cholecystectomy, were randomly allocated to be ventilated during the operation either with a positive end-expiratory pressure of 1 kPa (10 cmH2O) (PEEP group) or with intermittent positive pressure ventilation without PEEP (control group). During the operation the mean arterial oxygen tension (PaO2) in the PEEP group increased from 14.6 to 16.5 kPa, while no changes occurred in the control group (13.5 and 13.6 kPa). On the first postoperative day, PaO2 decreased by 12% of the preoperative values in the PEEP group; the decrease was 20% in the control group. On the third postoperative day, the PaO2 in the control group was still 9% below the preoperative values, but on the fifth day, both groups had reached their preoperative PaO2 values. In the postoperative period, no statistically significant difference in PaO2 could be demonstrated between the groups. Determinations of the forced vital capacity and forced expiratory volume in the first second showed no difference between the groups pre- or postoperatively. The present study demonstrated no clinically relevant beneficial effect of peroperative PEEP ventilation on the postoperative arterial hypoxaemia after an upper abdominal laparotomy.     

Effect of Selective PEEP on Pulmonary Blood Flow following Unilateral Hydrochloric Acid Aspiration in the Dog

We investigated the effect of unilateral or bilateral positive end-expiratory pressure (PEEP) on pulmonary perfusion in 12 dogs with a hydrochloric acid aspiration injury of the left lung. The lungs were ventilated separately and PEEP was applied to the left lung at 10 cmH2O (1.0 kPa) in six and at 15 cmH2O (1.5 kPa) in six others. Measurements of the right and left pulmonary arterial blood flows (QR and QL) and venous admixture were made before, during and after PEEP. After this study, 5 and 10 cmH2O (0.5 and 1.0 kPa) PEEP were applied to both lungs in six dogs and measurements were repeated. Following the application of PEEP to the left lung, a significant decrease in QL and increase in QR were observed. However, the application of PEEP to both lungs was followed by significant decreases in both QL and QR. The cardiac output decreased slightly during unilateral PEEP and markedly during bilateral PEEP. The venous admixture decreased significantly during PEEP in all the groups. These findings indicate that selective PEEP causes a transfer of pulmonary blood flow from the injured lung to the normal lung, improving ventilation-perfusion inequality, and improves gas exchange without impeding oxygen delivery.     

One lung anaesthesia

Ten patients about to undergo left-sided thoracotomy for carcinoma of the lung were entered into a crossover trial to compare cardiovascular and respiratory function during high frequency jet ventilation and conventional mechanical ventilation for one lung anaesthesia. All patients were anaesthetised with a standard technique using double lumen tubes and placed in the lateral position with the left chest open. The results showed no significant differences with regard to ventilation sequence but one lung high frequency jet ventilation gave higher values than one lung conventional ventilation for shunt (p less than 0.01) and positive end expiratory pressure (p less than 0.05) and lower peak inflation pressure values (p less than 0.01). There were no significant differences in cardiac output, pulmonary capillary wedge pressure, arterial carbon dioxide or available oxygen. Surgical conditions were satisfactory during both methods of ventilation and satisfactory gas exchange occurred. It was, however, more difficult to assess adequacy of ventilation during high frequency jet ventilation and the routine use of this method of ventilation is not recommended during one lung anaesthesia.     

Selective PEEP in Acute Bilateral Lung Disease. Effect on Patients in the Lateral Posture

Seven patients with acute respiratory failure due to diffuse and fairly uniform lung disease were studied during mechanical ventilation in the lateral decubital position with: (a) zero end-expiratory pressure (ZEEP) through a double-lumen oro-bronchial tube to permit a recording of the ventilation to each lung; (b) bilateral positive end-expiratory pressure (PEEP) of 1.2 kPa, with maintenance of ventilation distribution between lungs as observed during ZEEP; (c) selective PEEP of 1.2 kPa, applied to the dependent lung only, with ventilation as during ZEEP; and (d) conventional PEEP of 1.2 kPa applied to both lungs through a single-lumen tube, with free distribution of ventilation between the lungs. During ZEEP, 69% of ventilation was distributed to the non-dependent and 31% to the dependent lung; cardiac output was 6.51 X min-1, venous admixture (QS/QT) 40% and arterial oxygen tension (PaO2) 8.3 kPa. With bilateral PEEP, functional residual capacity (FRC) increased by 0.331, cardiac output was reduced to 5.11 X min-1 and venous admixture to 32%. PaO2 increased to 10.1 kPa. With selective PEEP the dependent lung FRC increased by 0.211 and the FRC of the non-dependent lung decreased by 0.081. Cardiac output increased to 6.11 X min-1, which was no longer significantly different from that during ZEEP. Venous admixture remained at the same level as with bilateral PEEP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of isoflurane on gas exchange and systemic and pulmonary hemodynamics in man during single lung ventilation]

OBJECTIVE. We studied the effect of 1.5% isoflurane end expiratory fraction on arterial oxygenation and on systemic and pulmonary hemodynamics during nonsurgical single lung ventilation. MATERIAL AND METHODS. The study includes 6 patients undergoing surgical thoracotomy. In all cases a double lumen endotracheal tube was inserted and pulmonary ventilation was performed with a FiO2 = 1. Patients were placed on lateral decubitus position. The following variables were measured: mean arterial pressure (MAP), mean pulmonary artery pressure (MPAP), central venous pressure (CVP), capillary pulmonary pressure (CPP), cardiac output (CO), and Qs/Qt. Measurements were taken at three different situations. The first was done under bilateral pulmonary ventilation and intravenous anesthesia with thiopental, fentanyl, and diazepam. The nondependent lung was collapsed by means of a selective ventilation of the dependent lung, and the second series of measurements was done 20 min after intravenous anesthesia. The third block of data was obtained after 15 min of respiratory ventilation with 1.5% isoflurane. RESULTS. Single lung ventilation induced a significant decrease of Pa O2 (379 +/- 96 mmHg vs 208 +/- 93 mmHg) and a significant increase in Qs/Qt (20 +/- 8% vs 30 +/- 10%). However, during isoflurane ventilation there were no significant changes in PaO2 (208 +/- 93 mmHg vs 204 +/- 94 mmHg) nor in Qs/Qt (30 +/- 10 vs 28 +/- 8). Isoflurane elicited a significant decrease of the CO, whereas MPAP, RVS, and PvO2 did not show significant variations. CONCLUSIONS. We conclude that 1.5% isoflurane end expiratory concentrations did not significantly affect pulmonary oxygenation during single lung ventilation.     

The effect of positive end expiratory pressure on the respiratory profile during one-lung ventilation for thoracotomy

Summary In this randomised controlled trial we examined the effects of four different levels of positive end expiratory pressure (PEEP at 0, 5, 8 or 10 cmH(2)O), added to the dependent lung, on respiratory profile and oxygenation during one lung ventilation. Forty-six patients were recruited to receive one of the randomised PEEP levels during one lung ventilation. We did not find significant differences in lung compliance, intra-operative or postoperative oxygenation amongst the four different groups. However, the physiological deadspace to tidal volume ventilation ratio was significantly lower in the 8 cmH(2)O PEEP group compared with the other levels of PEEP (p < 0.0001). We concluded that the use of PEEP (< or =10 cmH(2)O) during one lung ventilation does not clinically improve lung compliance, intra-operative or postoperative oxygenation despite a statistically significant reduction in the physiological deadspace to tidal volume ratio.     

Speed of collapse of the non-ventilated lung during one-lung anaesthesia: the effects of the use of nitrous oxide in sheep

By enhancing gaseous uptake from the non-ventilated lung during procedures performed thoracoscopically, the rapid diffusion properties of nitrous oxide would be expected to speed lung collapse and so facilitate surgery. To assess the effect of nitrous oxide on the speed of absorptive lung collapse, a study was conducted using 11 anaesthetised sheep. Speed of collapse was assessed in an indirect manner by recording the time required in a closed-chest situation for the airway pressure distal to a single lung airway occlusion to decrease to - 1.0 kPa. The influence of nitrous oxide was assessed by comparing the time taken for this decrease in airway pressure when the animal was being mechanically ventilated with 50% nitrous oxide in oxygen with the time taken when using 100% oxygen. In all assessments, it was found that the decrease in airway pressure to - 1.0 kPa occurred in a shorter time when nitrous oxide was used. The findings lend support to the hypothesis that during thoracoscopic surgery, mechanical lung ventilation with an oxygen/nitrous oxide mixture will increase the rate of gaseous uptake from the non-ventilated lung and so hasten its absorptive collapse.     

Changes in ventilatory mechanics and diaphragmatic function after lung volume reduction surgery in patients with COPD

BACKGROUND: Lung volume reduction (LVR) has recently been used to treat severe emphysema. About 25% of the volume of each lung is removed with this method. Little is known about the mechanism of functional improvement so a study was undertaken to investigate the changes in ventilatory mechanics and diaphragmatic function in eight patients after LVR. METHODS: Measurements of work of breathing (WOB), intrinsic positive end expiratory pressure (PEEPi), dynamic compliance (Cdyn), and arterial carbon dioxide tension (PaCO2) were performed on the day before surgery and daily for seven days after surgery, as well as one, three, and six months after surgery. All measurements were performed on spontaneously breathing patients, simultaneously assessing oesophageal pressure via an oesophageal balloon catheter and air flow via a tightly adjusted mask. Diaphragmatic function was evaluated by measuring oesophageal and transdiaphragmatic pressure (Pdi) preoperatively and at one, three, and six months postoperatively. RESULTS: Mean forced expiratory volume in one second (FEV1) was 23 (3.6)% predicted, and all patients were oxygen dependent before the-operation. One day after LVR the mean decrease in WOB was 0.93 (95% confidence interval (CI) 0.46 to 1.40) joule/l, the mean decrease in PEEPi was 0.61 (95% CI 0.35 to 0.87) kPa, and the mean increase in Cdyn was 182.5 (95% CI 80.0 to 284.2) ml/kPa. Similar changes were found seven days and six months after surgery. PaCO2 was higher on the day after the operation but was significantly reduced six months later. Pdi was increased three and six months after surgery. CONCLUSIONS: Ventilatory mechanics improved immediately after LVR, probably by decompression of lung tissue and relief of thoracic distension. An improvement in diaphragmatic function three and six months postoperatively also contributes to improved respiratory function after LVR.