Expiratory Positive Airway Pressure Research Articles

Sleep and neuromuscular disease: bilevel positive airway pressure by nasal mask as a treatment for sleep disordered breathing in patients with neuromuscular disease

OBJECTIVEInvestigation of the therapeutic effects of bilevel positive airway pressure delivered by nasal mask in patients with neuromuscular disease.METHODS20 patients with neuromuscular disease were evaluated for symptoms of nocturnal sleep...

Effectiveness of Controlled and Spontaneous Modes in Nasal Two-Level Positive Pressure Ventilation in Awake and Asleep Normal Subjects

The purpose of the present study was to compare in awake and asleep healthy subjects, under nasal intermittent positive pressure ventilation (nIPPV) with a two-level intermittent positive pressure device (two-level nIPPV), the efficacy of the controlled and spontaneous modes, and of different ventilator settings in increasing effective minute ventilation (VE). Eight healthy subjects were studied. In the controlled mode, inspiratory positive airway pressure (IPAP) was kept at 15 cm H2O, expiratory positive airway pressure (EPAP) at 4 cm H2O, and the inspiratory/expiratory (I/E) time ratio at 1. The respirator frequencies were 17 and 25/min. In the spontaneous mode experiment, IPAP was started at 10 cm H2O and progressively increased to 15 and 20 cm H2O; EPAP was kept at 4 cm H2O. We measured breath by breath the effective tidal volume (VT with respiratory inductive plethysmography), actual respiratory frequency (f), and effective VE. Using the controlled mode, effective VE was significantly higher on nIPPV than during spontaneous unassisted breathing, except in stage 2 nonrapid eye movement sleep at 17/min of frequency; increases in f from 17 to 25/min led to a significant decrease in VT reaching the lungs, during wakefulness and sleep; effective VE was higher at 25 than at 17/min of frequency only during sleep; periodic breathing was scarce and apneas were never observed. Using the spontaneous mode, with respect to awake spontaneous unassisted breathing, two-level nIPPV at 10 and 15 cm H2O of IPAP did not result in any significant increase in effective VE either in wakefulness or in sleep; only IPAP levels of 20 cm H2O resulted in a significant increase in effective VE; during sleep, effective VE was significantly lower than during wakefulness; respiratory rhythm instability (ie, periodic breathing and central apneas) were exceedingly common, and in some subjects extremely frequent, leading to surprisingly large falls in arterial oxygen saturation. It appears that two-level nIPPV should be used in the controlled mode rather than in the spontaneous mode, since it seems easier to increase effective VE with a lower IPAP at a high frequency than at a high pressure using the spontaneous mode. We suggest that the initial respirator settings in the controlled mode should be an f around 20/min, an I/E ratio of 1, 15 cm H2O of IPAP, and EPAP as low as possible.

Effect of Bi-Level Positive Airway Pressure (BiPAP) Nasal Ventilation on the Postoperative Pulmonary Restrictive Syndrome in Obese Patients Undergoing Gastroplasty

Upper abdominal surgery results in a postoperative restrictive pulmonary syndrome. Bi-level positive airway pressure (BiPAP System; Respironics Inc; Murrysville, Pa), which combines pressure support ventilation and positive end-expiratory pressure via a nasal mask, could allow alveolar recruitment during inspiration and prevent expiratory alveolar collapse, and therefore limit the postoperative pulmonary restrictive syndrome. This study investigated the effect of BiPAP on postoperative pulmonary function in obese patients after gastroplasty. Prospective controlled randomized study. GI surgical ward in a university hospital. Thirty-three morbidly obese patients scheduled for gastroplasty were studied. The patients were assigned to one of three techniques of ventilatory support during the first 24 h postoperatively: O2 via a face mask, BiPAP System 8/4, with inspiratory and expiratory positive airway pressure set at 8 and 4 cm H2O, respectively, or BiPAP System 12/4 set at 12 and 4 cm H2O. Pulmonary function (FVC, FEV1, and peak expiratory flow rate [PEFR]) were measured the day before surgery, 24 h after surgery, and on days 2 and 3. Oxygen saturation by pulse oximeter (SpO2) was also recorded during room air breathing. Three patients were excluded. After surgery, FVC, FEV1, PEFR, and SpO2 significantly decreased in the three groups. On day 1, FVC and FEV1 were significantly improved in the group BiPAP System 12/4, as compared with no BiPAP; SpO2 was also significantly improved. After removal of BiPAP System 12/4, these benefits were maintained, allowing faster recovery of pulmonary function. No significant effects were observed on PEFR. BiPAP System 8/4 had no significant effect on the postoperative pulmonary restrictive syndrome. Prophylactic use of BiPAP System 12/4 during the first 24 h postoperatively significantly reduces pulmonary dysfunction after gastroplasty in obese patients and accelerates reestablishment of preoperative pulmonary function.

Bi-level positive airway pressure support system use in acute congestive heart failure: preliminary case series.

To describe the use of a noninvasive bi-level positive airway pressure (PAP) support system for ED patients with acute congestive heart failure (CHF). Retrospective case series analysis of ED patients presenting with acute CHF in imminent need of endotracheal intubation (ETI) managed with a bi-level PAP system. The bi-level PAP system was applied at the discretion of the treating emergency physician. Management of the bi-level PAP system, including setting of inspiratory PAP (IPAP) and expiratory PAP (EPAP), weaning, adjunct pharmacologic therapy, and failure of bi-level PAP support, was determined by the treating physician. Only two (9%) of 22 patient presentations necessitated ETI. The mean duration of bi-level PAP therapy was 7.9 hours. The mean maximum IPAP and EPAP settings were 10.8 and 5.8 cm H2O, respectively. Mean intensive care unit length of stay (LOS) was 2.4 days, with a median LOS of only 1 day. There were three deaths in the series; none were attributed to the bi-level PAP system. No technical difficulty with the bi-level PAP system was noted. Noninvasive pressure support ventilation with a bi-level PAP support system may avert ETI in acute CHF patients. This device can be effectively used by ED personnel.

Clinical Application of Nasal Intermittent Positive Pressure Ventilation with Bi-level Positive Airway Pressure(BiPAP)

BACKGROUND: Noninvasive ventilation has been used extensively for the treatment of patients with neuromuscular weakness or restrictive chest wall disorders complicated by hypoventilatory respiratory failure. Recently, noninvasive positive pressure ventilation has been used in patients with alveolar hypoventilation,chronic obstructive pulmonary disease(COPD),and adult respiratory distress syndrome. Sanders and Kern reported treatment of obstructive sleep apnea with a modification of the standard nasal CPAP device to deliver seperate inspiratory positive airway pressure(IPAP) and expiratory positive airway pressure(EPAP).Bi-level positive airway pressure (BiPAP) unlike nasal CPAP, the unit delivers a different pressure during inspiration from that during expiration The device is similar to the positive pressure ventilator or pressure support ventilation. METHOD AND PURPOSE: Bi-level positive airway pressure(BiPAP) system(Respironics, USA) was applied to seven patients with acute respiratory failure and three patients on conventional mechanical ventilation. RESULTS: 1) Two of three patients after extubation were successfully achieved weaning from conventional mechanical ventilation by the use of BiPAP ventilation with nasal mask. Five of seven patients with acute respiratory failure successfully recovered without use of conventional mechanical ventilation. 2) PaO2 lhour after BiPAP ventilation in acute respiratory failure patients significantly improved more than baseline values(p<0.01)). PaCO2 lhour after BiPAP ventilation in acute respiratory failure patients did not change significantly more than baseline values. CONCLUSION: Nasal mask BiPAP ventilation can be one of the possible alternatives of conventional mechanical ventilation in acute respiratory failure and supportive method for weaning from mechanical ventilation.

Severe Exacerbations of Chronic Obstructive Pulmonary Disease Treated with BiPAP&lt;sup&gt;®&lt;/sup&gt; by Nasal Mask

Bi-level pressure support ventilation via a nasal mask (NIPSV) was provided to 28 consecutive unselected patients with acute respiratory failure due to exacerbation of chronic obstructive pulmonary failure (COPD). If NIPSV improved gas exchange within 2 h, it was continued. Otherwise, patients would be promptly intubated. The patients median age was 68 years (minimum 56, maximum 82). The arterial blood gas drawn before initiating NIPSV showed (FiO2 21%) a mean PaO2 of 41.3 +/- 6 mm Hg, a mean PaCO2 of 66 +/- 15 mm Hg and a mean pH of 7.31. Upon admission the mean respiratory rate was 36 breaths/min and the median Apache II score was 20.5 (minimum 13, maximum 32). Despite oxygen administration all patients failed to improve their PaO2 and/or showed a consistent and dangerous hypercapnic response. NIPSV was performed with a median inspiratory positive airway pressure of 14 cm H2O (minimum 10, maximum 20) and a median expiratory positive airway pressure of 4 cm H2O (minimum 3, maximum 6). Eighteen patients (64%) were successfully ventilated with NIPSV, while in 10 (36%) NIPSV failed. A high Apache II score, but not admission blood gas exchange or respiratory rate, seems to be correlated with the failure to ventilate with NIPSV. The results of our preliminary experience suggest the use of NIPSV as an initial approach to acute respiratory failure due to exacerbation of COPD, particularly in patients with an Apache II score of less than 29.

Inhaled β2-Agonist and Positive Expiratory Pressure in Bronchial Asthma: Influence on Airway Resistance and Functional Residual Capacity

<h3>Introduction</h3> Positive expiratory airway pressure seems to dilate narrowed or collapsed airways, but this may be accompanied by a maintained and harmful increase in resting lung volume in obstructive pulmonary disease. <h3>Purpose</h3> To evaluate the influence of inhaled terbutaline and positive expiratory pressure (PEP) on airway resistance (Raw) and functional residual capacity (FRC) in bronchial asthma. <h3>Design</h3> Randomized crossover design, single blind with regard to inhaled medication, open with regard to PEP (PEP can be felt). <h3>Material and Methods</h3> Ten patients with bronchial asthma inhaled placebo and terbutaline in doses of 0.125 mg, 0.5 mg, and 1.5 mg by cone spacer combined with a facemask giving 0, 10, or 15 cm H₂O PEP on separate days. FRC and Raw were measured by body plethysmography before and after inhalations. Data were analyzed by analysis of variance with terbutaline dose and PEP as factor levels. <h3>Results</h3> The effect of terbutaline: Raw decreased significantly (p<0.0001) after 0.125 mg and 1.5 mg. The FRC did not change significantly. The effect of PEP: Raw decreased, but significantly only when the dose of 1.5 mg terbutaline was excluded from the analysis. Raw decreased with PEP 10 and 15 cm H₂O, mean 0.6 (95 percent CI: —1.1, — 0.2) and 0.9 (95 percent CI: —1.3, — 0.4) cm H₂O/L/s. The FRC did not change significantly with the PEP level. <h3>Conclusion</h3> PEP only had influence on Raw when insufficient doses of terbutaline were inhaled, whereas once an efficient dose of terbutaline was administered, significant bronchodilation was achieved with or without PEP. Positive expiratory pressure did not increase FRC.

Treatment of high altitude diseases without drugs.

Treatments other than descent and supplemental oxygen are discussed in this short review. Exercise gives rise to physiologic responses which may enhance acute mountain sickness (AMS), high altitude cerebral edema (HACE) and high altitude pulmonary edema (HAPE). Therefore, physical rest can be considered the principle treatment for moderate AMS and it should always accompany any treatment of severe high altitude illnesses as long as descent is not possible. Therapy with a portable fabric hyperbaric chamber has a beneficial short-term effect in subjects with AMS, HACE and HAPE. However, treatment modalities using this device which result in long-term beneficial effects need yet to be established. New technical solutions practicable under field conditions at extreme altitude are required for the removal of CO2 from the bag. Expiratory positive airway pressure (EPAP) improves arterial oxygen saturation by 10-20% in subjects with HAPE in trials of 10 min duration. Clinical studies examining longterm effects are necessary, before EPAP can be recommended as initial emergency treatment of HAPE.

Effect of reduced expiratory pressure on pharyngeal size during nasal positive airway pressure in patients with sleep apnoea: evaluation by continuous computed tomography.

This study aimed to determine whether reducing the expiratory pressure during nasal positive airway pressure for reasons of comfort causes a substantial decrease in the upper airway calibre. Eight patients with obstructive sleep apnoea were studied. Continuous computed tomography (each run lasting 12 seconds) was used to measure minimum and maximum pharyngeal cross sectional areas at the velopharynx and the hypopharynx. Pharyngeal areas were measured while patients were awake and breathing without assistance, during the application of 12 cm H2O continuous positive airway pressure, and during bi-level positive airway pressure with an inspiratory pressure of 12 cm H2O and an expiratory pressure of 6 cm H2O. Nasal continuous positive airway pressure significantly increased the mean minimum and maximum upper airway areas at both the velopharynx and the hypopharynx compared with normal unassisted breathing. Bi-level positive airway pressure did not show a statistically significant increase in the minimum upper airway area at either level compared with normal unassisted breathing. The minimum areas of the velopharynx and hypopharynx were smaller with bi-level than continuous positive airways pressure in six of eight and eight of eight patients respectively but these were still greater than during unassisted breathing in seven of eight and six of eight patients respectively. Continuous positive airway pressure at 12 cm H2O is more effective in splinting the pharynx open than bi-level positive airway pressure with an inspiratory positive airway pressure of 12 cm H2O and an expiratory pressure of 6 cm H2O in patients with obstructive sleep apnoea during wakefulness, suggesting an important role for expiratory positive airway pressure. The clinical importance of this finding needs to be evaluated during sleep.

Nocturnal ventilatory assistance with bi-level positive airway pressure

Administration of bi-level positive airway pressure (BIPAP) via nasal mask can provide substantial benefit to patients with obstructive sleep apnea (OSA) and nocturnal alveolar hypoventilation. This modality maintains upper airway patency as well as assists patients in maintaining adequate ventilation during sleep without mandating oral/nasal tracheal intubation or tracheostomy. In OSA patients, BIPAP allows greater flexibility than conventional nasal continuous positive airway pressure (CPAP) by permitting independent adjustment of inspiratory and expiratory positive airway pressure (IPAP and EPAP, respectively). Therapy may therefore be achieved with lower expiratory pressure, improved patient comfort, and reduced mechanical impedance to ventilation with less potential for hypoventilation. Additionally, BIPAP allows patients to determine their own tidal volume, respiratory rate, and inspiratory flow. A back-up mode is also available in which the IPAP is delivered if the patient does not spontaneously initiate a breath within a prescribed interval. In this article we describe two representative OSA patients who underwent therapeutic trials of both nasal CPAP and BIPAP. In both patients, effective treatment was achieved at lower expiratory pressure and with greater comfort using BIPAP compared with CPAP. We also describe the effect of nocturnal BIPAP on a representative patient with ventilatory muscle weakness and chronic ventilatory failure. During sleep on BIPAP, there was improved alveolar ventilation and ventilatory muscle rest. On long-term home therapy with nocturnal BIPAP, there was a significant improvement in daytime alertness and performance of daily activities. We conclude that bi-level positive airway pressure therapy is a useful addition to the therapeutic armamentarium for patients with OSA as well as patients with compromised ventilatory muscle function and hypercapnia.

Obstructive Sleep Apnea Treated by Independently Adjusted Inspiratory and Expiratory Positive Airway Pressures via Nasal Mask: Physiologic and Clinical Implications

Treatment of obstructive sleep apnea with nasal continuous positive airway pressure mandates simultaneous increases of both inspiratory and expiratory positive airway pressures to eliminate apneas as well as nonapneic oxyhemoglobin desaturation events. We hypothesized that the forces acting to collapse the upper airway during inspiration and expiration are of different magnitudes and that obstructive sleep-disordered breathing events (including apneas, hypopneas and nonapneic desaturation events) could be eliminated at lower levels of EPAP than IPAP. To test these hypotheses, a device was built that allows the independent adjustment of EPAP and IPAP (nasal BiPAP). Our data support the hypotheses that expiratory phase events are important in the pathogenesis of OSA and that there are differences in the magnitudes of the forces destabilizing the upper airway during inspiration and expiration. Finally, applying these concepts, we have shown that by using a device that permits independent adjustment of EPAP and IPAP, obstructive sleep-disordered breathing can be eliminated at lower levels of expiratory airway pressure compared with conventional nasal CPAP therapy. This may reduce the adverse effects associated with nasal CPAP therapy and improve long-term therapeutic compliance.

Effects of lung volume and positive airway pressure on collateral resistance

Nine mongrel dogs were anesthetized, paralysed, ventilated, and placed in an iron lung. Each animal was transiently connected to a spirometer and the respiratory system compliance measured by applying negative or positive extrathoracic pressures (from −20 cm H 2O to +20 cm H 2O in 5 cm H 2O steps). A sub-lobar bronchus was wedged with a 5.5 mm bronchoscope, and a 5f Swan-Ganz catheter was inserted into the lumen of the bronchoscope; one port served to introduce a 200 ml·min −1 flow of 5% CO 2 in air, the other to measure the pressure in the wedged segment. Rcoll was measured with extrathoracic pressures in the iron lung ranging from 0 to −20 cm H 2O (NEP) and 0 to +20 cm H 2O (PEP) in 5 cm H 2O steps, and under expiratory positive airway pressure (EPAP) of 5, 10, 15, and 20 cm H 2O. The maximal changes in FRC were an increase of 1009±49ml (mean ± SEM) with NEP and a decrease of 397±33 ml with PEP. Increasing FRC decreased Rcoll while decreasing FRC markedly increased it. EPAP induced similar decreases in Rcoll as NEP of equal pressure. This effect of EPAP was inhibited by simultaneously applying PEP of equal pressure. We conclude that resistance to collateral flow is highly dependent on lung volume, and that positive airway pressure decreases Rcoll by its effects on lung volume.

Changes in upper airway resistance with lung inflation and positive airway pressure

The influence of pulmonary inflation and positive airway pressure on nasal and pharyngeal resistance were studied in 10 normal subjects lying in an iron lung. Upper airway pressures were measured with two low-bias flow catheters while the subjects breathed by the nose through a Fleish no. 3 pneumotachograph into a spirometer. Resistances were calculated at isoflow rates in four different conditions: exclusive pulmonary inflation, achieved by applying a negative extra-thoracic pressure (NEP); expiratory positive airway pressure (EPAP), which was created by immersion of the expiratory line; continuous positive airway pressure (CPAP), realized by loading the bell of the spirometer; and CPAP without pulmonary inflation by simultaneously applying the same positive extrathoracic pressure (CPAP + PEP). Resistance measurements were obtained at 5- and 10-cmH2O pressure levels. Pharyngeal resistance (Rph) significantly decreased during each measurement; the decreases in nasal resistance were only significant with CPAP and CPAP + PEP; the deepest fall in Rph occurred with CPAP. It reached 70.8 +/- 5.5 and 54.8 +/- 6.5% (SE) of base-line values at 5 and 10 cmH2O, respectively. The changes in lung volume recorded with CPAP + PEP ranged from -180 to 120 ml at 5 cmH2O and from -240 to 120 ml at 10 cmH2O. Resistances tended to increase with CPAP + PEP compared with CPAP values, but these changes were not significant (Rph = 75.9 +/- 6.1 and 59.9 +/- 6.6% at 5 and 10 cmH2O of CPAP + PEP). We conclude that 1) the upper airway patency increases during pulmonary inflation, 2) the main effect of CPAP is related to pneumatic splinting, and 3) pulmonary inflation contributes little to the decrease in upper airways resistance observed with CPAP.

Continuous Positive Airway Pressure and Expiratory Positive Airway Pressure Increase Functional Residual Capacity Equivalently

The effect of continuous positive airway pressure (CPAP) and expiratory positive airway pressure (EPAP) on functional residual capacity (FRC) of ten healthy, spontaneously breathing, lightly anesthetized intubated mongrel dogs was studied. The CPAP and EPAP at 5, 10, 15, and 20 cm H2O were alternately applied to all animals. Total (lung and chest wall) compliance, esophageal pressure, airway pressure, transpulmonary pressure, control FRC, and the change in FRC (delta FRC) were measured before and after each application of CPAP and EPAP. Neither expiratory transpulmonary pressure nor delta FRC with CPAP differed significantly from that with EPAP at all levels (p greater than 0.05). These data suggest that CPAP and EPAP, when applied at the same expiratory pressure, result in an equivalent increase in FRC due to passive mechanical distention of the lungs.

High Altitude Pulmonary Edema and Exercise at 4, 400 Meters on Mount McKinley: Effect of Expiratory Positive Airway Pressure

Breathing against positive expiratory pressure has been used to improve gas exchange in many forms of pulmonary edema, and forced expiration against resistance during exercise has been advocated for climbing at high altitude as a method to optimize performance. To evaluate the effect of expiratory positive airway pressure (EPAP) on climbers with high altitude pulmonary edema (HAPE) and on exercise at high altitude, we studied four climbers with HAPE at rest and 13 healthy climbers during exercise on a bicycle ergometer at 4400 m. We measured minute ventilation (VI, L/min), arterial oxygen saturation (SaO2 percent), end-tidal carbon dioxide (PACO2, mm Hg), respiratory rate (RR), and heart rate (HR) during the last minute of a five minute interval at rest in the climbers with HAPE, and at rest, 300, and 600 kpm/minute workloads on a bicycle ergometer in the healthy subjects. The HAPE subjects demonstrated an increased SaO2 percent, no change in HR or VI, and a decrease in RR on EPAP as compared to control. In normal subjects, SaO2 percent, VI, and heart rate were significantly higher on EPAP 10 cm H2O than 0 cm H2O control (p less than 0.01, 0.01, and 0.05, respectively). The RR and PaCO2 were not significantly different. In summary, EPAP improves gas exchange in HAPE subjects at rest. The EPAP in normal subjects at high altitude resulted in a higher SaO2 percent at the expense of a higher VI and higher HR. These results suggest that the work of breathing is higher and the stroke volume lower on EPAP. The positive pressure mask may be an effective temporizing measure for victims of HAPE who cannot immediately go to a lower altitude.

POSITIVE AIRWAY PRESSURE FOR HIGH-ALTITUDE PULMONARY OEDEMA

Expiratory positive airway pressure was studied on Mount McKinley, Alaska, at an altitude of 4400 m, in three climbers with high-altitude pulmonary oedema and five climbers without evidence of this disorder. In the subjects with high-altitude pulmonary oedema oxygen saturation improved from 53·3±10·1% to 72·0±5·7% with expiratory positive airway pressure of 10 cm water. Oxygen saturation, heart rate, and respiratory rate did not change in healthy climbers. No adverse effects were noted. Improved oxygen saturation did not persist when expiratory positive airway pressure was discontinued. This procedure may be useful as a temporary first-aid measure in high-altitude pulmonary oedema.

The Effects of Prophylactic Expiratory Positive Airway Pressure on the Resolution of Oleic Acid-Induced Lung Injury in Dogs

LUCE, J. M.; HUANG, T. W.; ROBERTSON, H. T.; COLLEY, P. S.; GRONKA, R.; NESSLY, M. L.; CHENEY, F. W.; Modell, Jerome H. M.D. Author Information

The effects of prophylactic expiratory positive airway pressure on the resolution of oleic acid-induced lung injury in dogs.

It is not known whether positive end-expiratory airway pressure (PEEP) merely improves gas exchange in patients with the adult respiratory distress syndrome (ARDS) or if it also affects the resolution of their lung injury. The present investigation was performed to determine whether expiratory positive airway pressure (EPAP), a form of PEEP, is prophylactic in preventing the lung injury induced by oleic acid in dogs or in enhancing its resolution. Arterial and mixed venous blood gases and functional residual capacity (FRC) were measured in 14 pairs of mongrel dogs with indwelling catheters and permanent tracheostomies. One member of each pair was treated with 10 cm H2O EPAP through a valve attached to the tracheostomy tube. Both dogs received 0.06 ml/kg oleic acid intravenously at hour 0. Measurements were made at three, 12, and 24 hours, when EPAP was discontinued, and over the next six days. Five dog pairs were sacrificed at 72 hours; the other surviving animals were sacrificed at 168 hours. FRC was higher at three, 12, and 24 hours in dogs receiving EPAP than in the untreated dogs. The arterial oxygen tension (PaO2) was higher and the venous admixture (Qva/Qt) was lower at three and 12 hours in the dogs receiving EPAP than in the untreated dogs. However, after 24 hours, no differences were noted between the two groups in FRC, PaO2, Qav/Qt, mortality, final lung compliance to initial lung compliance differences, lung water to dry lung weight ratios, or histology. It is concluded that EPAP improves gas exchange during its administration, but has no demonstrable prophylactic effect on the resolution of lung injury in the oleic acid model of human ARDS.

The effects of expiratory positive airway pressure on the resolution of oleic acid-induced lung injury in dogs.

It is not known whether positive end-expiratory pressure (PEEP) merely improves gas exchange in patients with the adult respiratory distress syndrome or also affects the resolution of their lung injury. We examined the effects of expiratory positive airway pressure (EPAP), a form of PEEP, on 13 pairs of spontaneously breathing mongrel dogs with permanent tracheostomies that were subjected to acute lung injury from oleic acid. One member of each pair was treated with 10 cm H2O EPAP by means of a special valve attached to its tracheostomy tube; the other member breathed through the tracheostomy tube alone. The EPAP was applied 3 h after an intravenous injection of 0.06 ml/kg oleic acid and continued for a total of 21 h. Functional residual capacity (FRC) was increased to preinjury values in the EPAP-treated dogs at 3, 12, and 24 h compared with that in the untreated dogs. The PaO2 was higher and the venous admixture (Qva/QT) was lower in the EPAP-treated dogs compared with that in the untreated dogs at 3 and at 12 h. However, over the 7 days after removal of EPAP no significant differences were noted between the 2 groups in FRC, PaO2, Qva/QT, inert gas elimination profiles, mortality, final lung compliance to initial lung compliance differences, lung water to dry lung weight ratios, or histologic features. We conclude that EPAP improves gas exchange during its administration but has no demonstrable effect on the resolution of lung injury induced by oleic acid in dogs.

Cardiovascular effects of ventilation with positive expiratory airway pressure.

The broad clinical application of positive and expiratory pressure (PEEP) in the treatment of a variety of respiratory disorders has led to the observation that positive airway pressure can result in cardiac dysfunction. Recent attempts to integrate and extend the results of past research have led to diverse explanations of the overall cardiopulmonary effects of PEEP. This review summarizes previous work in the field and attempts to explain the basis of the divergent conclusions of previous investigators. Data are presented from several experimental models, as well as studies in postoperative patients to formulate an overall analysis of the influence of airway pressure on the central circulation. It appears that the effects of PEEP are primarily mechanical and are mediated through a combination of right ventricular preload limitation and outflow obstruction. Both effects are additive in limiting left ventricular preload and can be ameliorated by volume loading in the absence of significant right ventricular or pulmonary vascular disease. Neural, humoral and ventricular interactive forces appear to be insignificant under most circumstances. The clinical implications of these advances in the current understanding of PEEP are reviewed.