Association of dyspnoea, mortality and resource use in hospitalised patients.

As many as one in 10 patients experience dyspnoea at hospital admission but the relationship between dyspnoea and patient outcomes is unknown. We sought to determine whether dyspnoea on admission predicts outcomes.We conducted a retrospective cohort study in a single, academic medical centre. We analysed 67 362 consecutive hospital admissions with available data on dyspnoea, pain and outcomes. As part of the Initial Patient Assessment by nurses, patients rated "breathing discomfort" using a 0 to 10 scale (10="unbearable"). Patients reported dyspnoea at the time of admission and recalled dyspnoea experienced in the 24 h prior to admission. Outcomes included in-hospital mortality, 2-year mortality, length of stay, need for rapid response system activation, transfer to the intensive care unit, discharge to extended care, and 7- and 30-day all-cause readmission to the same institution.Patients who reported any dyspnoea were at an increased risk of death during that hospital stay; the greater the dyspnoea, the greater the risk of death (dyspnoea 0: 0.8% in-hospital mortality; dyspnoea 1-3: 2.5% in-hospital mortality; dyspnoea ≥4: 3.7% in-hospital mortality; p<0.001). After adjustment for patient comorbidities, demographics and severity of illness, increasing dyspnoea remained associated with inpatient mortality (dyspnoea 1-3: adjusted OR 2.1, 95% CI 1.7-2.6; dyspnoea ≥4: adjusted OR 3.1, 95% CI 2.4-3.9). Pain did not predict increased mortality. Patients reporting dyspnoea also used more hospital resources, were more likely to be readmitted and were at increased risk of death within 2 years (dyspnoea 1-3: adjusted hazard ratio 1.5, 95% CI 1.3-1.6; dyspnoea ≥4: adjusted hazard ratio 1.7, 95% CI 1.5-1.8).We found that dyspnoea of any rating was associated with an increased risk of death. Dyspnoea ratings can be rapidly collected by nursing staff, which may allow for better monitoring or interventions that could reduce mortality and morbidity.

Controlled Delivery of 80 mg Aerosol Furosemide Does Not Achieve Consistent Dyspnea Relief in Patients.

PURPOSE: Aerosol furosemide may be an option to treat refractory dyspnea, though doses, methods of delivery, and outcomes have been variable. We hypothesized that controlled delivery of high dose aerosol furosemide would reduce variability of dyspnea relief in patients with underlying pulmonary disease. METHODS: Seventeen patients with chronic exertional dyspnea were recruited. Patients rated recently recalled breathing discomfort on a numerical rating scale (NRS) and the multidimensional dyspnea profile (MDP). They then performed graded exercise using an arm-ergometer. The NRS was completed following each exercise grade, and the MDP was repeated after a pre-defined dyspnea threshold was reached. During separate visits, patients received either aerosol saline or 80 mg of aerosol furosemide in a randomized, double-blind, crossover design. After treatment, graded exercise to the pre-treatment level was repeated, followed by completion of the NRS and MDP. Treatment effect was defined as the difference between pre- and post-treatment NRS at end exercise, expressed in absolute terms as % Full Scale. "Responders" were defined as those showing treatment effect ≥ 20% of full scale. RESULTS: Final analysis included 15 patients. Neither treatment produced a statistically significant change in NRS and there was no significant difference between treatments (p = 0.45). There were four "responders" and one patient whose dyspnea worsened with furosemide; two patients were responders with saline, of whom one also responded to furosemide. No adverse events were reported. CONCLUSIONS: High dose controlled delivery aerosol furosemide was not statistically different from saline placebo at reducing exercise-induced dyspnea. However, a clinically meaningful improvement was noted in some patients.

Aerosol furosemide for dyspnea: High-dose controlled delivery does not improve effectiveness.

Published studies have shown great variability in response when aerosolized furosemide has been tested as a palliative treatment for dyspnea. We hypothesized that a higher furosemide dose with controlled aerosol administration would produce consistent dyspnea relief. We optimized deposition by controlling inspiratory flow (300-500mL/s) and tidal volume (15% predicted vital capacity) while delivering 3.4µm aerosol from either saline or 80mg of furosemide. We induced dyspnea in healthy subjects by varying inspired PCO2 while restricting minute ventilation. Subjects rated "Breathing Discomfort" on a Visual Analog Scale (BDVAS, 100% Full Scale≡intolerable). At the PETCO2 producing 60% BDVAS pre-treatment, furosemide produced a clinically meaningful reduction of BDVAS (i.e., >20% FS) in 5/11 subjects; saline reduced dyspnea in 3/11 subjects; neither treatment worsened dyspnea in any subject. Furosemide and saline treatment effects were not statistically different. There were no significant adverse events. Higher furosemide dose and controlled delivery did not improve consistency of treatment effect compared with prior studies.

Aerosol furosemide for dyspnea: Controlled delivery does not improve effectiveness.

Aerosolized furosemide has been shown to relieve dyspnea; nevertheless, all published studies have shown great variability in response. This dyspnea relief is thought to result from the stimulation of slowly adapting pulmonary stretch receptors simulating larger tidal volume. We hypothesized that better control over aerosol administration would produce more consistent dyspnea relief; we used a clinical ventilator to control inspiratory flow and tidal volume. Twelve healthy volunteers inhaled furosemide (40mg) or placebo in a double blind, randomized, crossover study. Breathing Discomfort was induced by hypercapnia during constrained ventilation before and after treatment. Both treatments reduced breathing discomfort by 20% full scale. Effectiveness of aerosol furosemide treatment was weakly correlated with larger tidal volume. Response to inhaled furosemide was inversely correlated to furosemide blood level, suggesting that variation among subjects in the fate of deposited drug may determine effectiveness. We conclude that control of aerosol delivery conditions does not improve consistency of treatment effect; we cannot, however, rule out placebo effect.

Multidimensional Dyspnea Profile: an instrument for clinical and laboratory research.

There is growing awareness that dyspnoea, like pain, is a multidimensional experience, but measurement instruments have not kept pace. The Multidimensional Dyspnea Profile (MDP) assesses overall breathing discomfort, sensory qualities, and emotional responses in laboratory and clinical settings. Here we provide the MDP, review published evidence regarding its measurement properties and discuss its use and interpretation. The MDP assesses dyspnoea during a specific time or a particular activity (focus period) and is designed to examine individual items that are theoretically aligned with separate mechanisms. In contrast, other multidimensional dyspnoea scales assess recalled recent dyspnoea over a period of days using aggregate scores. Previous psychophysical and psychometric studies using the MDP show that: 1) subjects exposed to different laboratory stimuli could discriminate between air hunger and work/effort sensation, and found air hunger more unpleasant; 2) the MDP immediate unpleasantness scale (A1) was convergent with common dyspnoea scales; 3) in emergency department patients, two domains were distinguished (immediate perception, emotional response); 4) test-retest reliability over hours was high; 5) the instrument responded to opioid treatment of experimental dyspnoea and to clinical improvement; 6) convergent validity with common instruments was good; and 7) items responded differently from one another as predicted for multiple dimensions.

Respiratory mechanical effects of surgical pneumoperitoneum in humans.

Pneumoperitoneum for laparoscopic surgery is known to stiffen the chest wall and respiratory system, but its effects on resting pleural pressure in humans are unknown. We hypothesized that pneumoperitoneum would raise abdominal pressure, push the diaphragm into the thorax, raise pleural pressure, and squeeze the lung, which would become stiffer at low volumes as in severe obesity. Nineteen predominantly obese laparoscopic patients without pulmonary disease were studied supine (level), under neuromuscular blockade, before and after insufflation of CO2 to a gas pressure of 20 cmH2O. Esophageal pressure (Pes) and airway pressure (Pao) were measured to estimate pleural pressure and transpulmonary pressure (Pl = Pao - Pes). Changes in relaxation volume (Vrel, at Pao = 0) were estimated from changes in expiratory reserve volume, the volume extracted between Vrel, and the volume at Pao = -25 cmH2O. Inflation pressure-volume (Pao-Vl) curves from Vrel were assessed for evidence of lung compression due to high Pl. Respiratory mechanics were measured during ventilation with a positive end-expiratory pressure of 0 and 7 cmH2O. Pneumoperitoneum stiffened the chest wall and the respiratory system (increased elastance), but did not stiffen the lung, and positive end-expiratory pressure reduced Ecw during pneumoperitoneum. Contrary to our expectations, pneumoperitoneum at Vrel did not significantly change Pes [8.7 (3.4) to 7.6 (3.2) cmH2O; means (SD)] or expiratory reserve volume [183 (142) to 155 (114) ml]. The inflation Pao-Vl curve above Vrel did not show evidence of increased lung compression with pneumoperitoneum. These results in predominantly obese subjects can be explained by the inspiratory effects of abdominal pressure on the rib cage.

Arterial stiffness, oxidative stress, and smoke exposure in wildland firefighters.

OBJECTIVES: To assess the association between exposure, oxidative stress, symptoms, and cardiorespiratory function in wildland firefighters. METHODS: We studied two Interagency Hotshot Crews with questionnaires, pulse wave analysis for arterial stiffness, spirometry, urinary 8-iso-prostaglandin F2α (8-isoprostane) and 8-hydroxy-2'-deoxyguanosine (8-OHdG), and the smoke exposure marker (urinary levoglucosan). Arterial stiffness was assessed by examining levels of the aortic augmentation index, expressed as a percentage. An oxidative stress score comprising the average of z-scores created for 8-OHdG and 8-isoprostane was calculated. RESULTS: Mean augmentation index % was higher for participants with higher oxidative stress scores after adjusting for smoking status. Specifically for every one unit increase in oxidative stress score the augmentation index % increased 10.5% (95% CI: 2.5, 18.5%). Higher mean lower respiratory symptom score was associated with lower percent predicted forced expiratory volume in one second/forced vital capacity. CONCLUSIONS: Biomarkers of oxidative stress may serve as indicators of arterial stiffness in wildland firefighters.

Dynamic expiratory tracheal collapse in morbidly obese COPD patients.

Morbid obesity may influence several aspects of airway function. However, the effect of morbid obesity on expiratory tracheal collapse in COPD patients is unknown. We thus prospectively studied 100 COPD patients who underwent full pulmonary function tests (PFTs), 6-minute walk test (6MWT), Saint George's Respiratory Questionnaire (SGRQ), and low-dose CT at total lung capacity and during dynamic exhalation with spirometric monitoring. We examined correlations between percentage dynamic expiratory tracheal collapse and body mass index (BMI). The association between tracheal collapse and BMI was compared to a control group of 53 volunteers without COPD. Patients included 48 women and 52 men with mean age 65 ± 7 years; BMI 30 ± 6; FEV1 64 ± 22% predicted and percentage expiratory collapse 59 ± 19%. Expiratory collapse was significantly associated with BMI (69 ± 12% tracheal collapse among 20 morbidly obese patients with BMI ≥ 35 compared to 57 ± 19% in others, p = 0.002, t-test). In contrast, there was no significant difference in collapse between healthy volunteers with BMI ≥ 35 and < 35. COPD patients with BMI ≥ 35 also demonstrated shorter 6MWT distances (340 ± 139 m vs. 430 ± 139 m, p = 0.003) and higher (worse) total SGRQ scores (48 ± 19 vs. 36 ± 20, p = 0.013) compared to those with BMI < 35. In light of these results, clinicians should consider evaluating for excessive expiratory tracheal collapse when confronted with a morbidly obese COPD patient with greater quality of life impairment and worse exercise performance than expected based on functional measures.

Dyspnea affective response: comparing COPD patients with healthy volunteers and laboratory model with activities of daily living.

BACKGROUND: Laboratory-induced dyspnea (breathing discomfort) in healthy subjects is widely used to study perceptual mechanisms, yet the relationship between laboratory-induced dyspnea in healthy volunteers and spontaneous dyspnea in patients with chronic lung disease is not well established. We compared affective responses to dyspnea 1) in COPD patients vs. healthy volunteers (HV) undergoing the same laboratory stimulus; 2) in COPD during laboratory dyspnea vs. during activities of daily living (ADL). METHODS: We induced moderate and high dyspnea levels in 13 COPD patients and 12 HV by increasing end-tidal CO2 (PETCO2) during restricted ventilation, evoking air hunger. We used the multidimensional dyspnea profile (MDP) to measure intensity of sensory qualities (e.g., air hunger (AH) and work/effort (W/E)) as well as immediate discomfort (A1) and secondary emotions (A2). Ten of the COPD subjects also completed the MDP outside the laboratory following dyspnea evoked by ADL. RESULTS: COPD patients and HV reported similar levels of immediate discomfort relative to sensory intensity. COPD patients and HV reported anxiety and frustration during laboratory-induced dyspnea; variation among individuals far outweighed the small differences between subject groups. COPD patients reported similar intensities of sensory qualities, discomfort, and emotions during ADL vs. during moderate laboratory dyspnea. Patients with COPD described limiting ADL to avoid greater dyspnea. CONCLUSIONS: In this pilot study, we found no evidence that a history of COPD alters the affective response to laboratory-induced dyspnea, and no difference in affective response between dyspnea evoked by this laboratory model and dyspnea evoked by ADL.

Dynamic expiratory tracheal collapse in COPD: correlation with clinical and physiologic parameters.

BACKGROUND: COPD has been described as a risk factor for excessive expiratory tracheal collapse, but its prevalence and clinical correlates have not been fully determined. The purpose of this study is to prospectively determine the prevalence of excessive expiratory tracheal collapse among patients with COPD and to test the hypothesis that clinical and/or physiologic parameters will correlate with the presence of excessive tracheal collapse. METHODS: We studied 100 adults meeting GOLD (Global Initiative for Obstructive Lung Disease) criteria for COPD, who underwent full pulmonary function tests (PFTs), 6-min walk test (6MWT), St. George's Respiratory Questionnaire (SGRQ), and low-dose CT scan at total lung capacity and during dynamic exhalation with spirometric monitoring. We examined correlations between percentage dynamic expiratory tracheal collapse and PFTs, 6MWT distance, and SGRQ scores. RESULTS: Patients included 48 women and 52 men with mean age 65 ± 7 years, FEV1 64% ± 22% predicted, and percentage expiratory collapse 59% ± 19%. Twenty of 100 participants met study criteria for excessive expiratory collapse. There was no significant correlation between percentage expiratory tracheal collapse and any pulmonary function measure, total SGRQ score, or 6MWT distance. The SGRQ symptom subscale was weakly correlated with percentage collapse of the mid trachea (R = 0.215, P = .03). CONCLUSIONS: Excessive expiratory tracheal collapse is observed in a subset of patients with COPD, but the magnitude of collapse is independent of disease severity and does not correlate significantly with physiologic parameters. Thus, the incidental identification of excessive expiratory tracheal collapse in a general COPD population may not necessarily be clinically significant.

Age and sex dependence of forced expiratory central airway collapse in healthy volunteers.

BACKGROUND: A recent estimate for the normal range of forced expiratory tracheal collapse differs substantially from that in an earlier study performed with comparable measurement methods. Given differences in subject characteristics between the two samples, we hypothesized that these discrepant findings may reflect a heretofore unrecognized association between forced expiratory tracheal collapse and age or sex. METHODS: We enrolled 40 female and 41 male healthy volunteers between 25 and 75 years of age who were without respiratory symptoms or known risk factors for tracheomalacia. Subjects underwent low-dose CT scanning at total lung capacity (TLC) and during forced exhalation (Expdyn) with spirometric monitoring and coaching. Percentage forced expiratory collapse was regressed on age for the total sample and separately within sex. RESULTS: Mean tracheal cross-sectional area (CSA) was 2.54 cm(2) ± 0.57 cm(2) at TLC and 1.15 cm(2) ± 0.53 cm(2) at Expdyn. Mean percentage forced expiratory collapse (%collapse) was 54% ± 20%. Men aged 24 to 31 years (n = 12) had mean %collapse of 36% ± 19%, comparable to results previously reported for similarly aged men (35% ± 18%). Men, but not women, showed a significant positive correlation (R(2) = 0.40, P < .001) between %collapse and age. Older men had both greater CSA at TLC (P = .02) and smaller CSA at Expdyn (P = .001) than younger men. CONCLUSIONS: Men exhibit positive age dependence of forced expiratory tracheal collapse. The influence of age and sex on forced expiratory tracheal collapse should be considered in the diagnostic evaluation of expiratory dynamic airway collapse and/or tracheomalacia.

Tracheobronchomalacia: current concepts and controversies.

Tracheobronchomalacia (TBM) results from weakness of the airway walls and/or supporting cartilage and affects both adult and pediatric populations. Diagnosing TBM is challenging because symptoms are nonspecific and overlap with those of other chronic respiratory disorders. Recent advances in multidetector computed tomography have facilitated the noninvasive diagnosis of TBM, and concurrent advances in management have improved clinical outcomes and created a need for greater awareness of the posttreatment appearance of the airways. This review discusses the physiology, histopathology, epidemiology, and clinical features of TBM; it also describes current methods of diagnosis, available therapies, and postoperative imaging evaluation.

Using laboratory models to test treatment: morphine reduces dyspnea and hypercapnic ventilatory response.

RATIONALE: Opioids are commonly used to relieve dyspnea, but clinical data are mixed and practice varies widely. OBJECTIVES: Evaluate the effect of morphine on dyspnea and ventilatory drive under well-controlled laboratory conditions. METHODS: Six healthy volunteers received morphine (0.07 mg/kg) and placebo intravenously on separate days (randomized, blinded). We measured two responses to a CO(2) stimulus: (1) perceptual response (breathing discomfort; described by subjects as "air hunger") induced by increasing partial pressure of end-tidal carbon dioxide (Pet(CO2)) during restricted ventilation, measured with a visual analog scale (range, "neutral" to "intolerable"); and (2) ventilatory response, measured in separate trials during unrestricted breathing. MEASUREMENTS AND MAIN RESULTS: We determined the Pet(CO2) that produced a 60% breathing discomfort rating in each subject before morphine (median, 8.5 mm Hg above resting Pet(CO2)). At the same Pet(CO2) after morphine administration, median breathing discomfort was reduced by 65% of its pretreatment value; P < 0.001. Ventilation fell 28% at the same Pet(CO2); P < 0.01. The effect of morphine on breathing discomfort was not significantly correlated with the effect on ventilatory response. Placebo had no effect. CONCLUSIONS: (1) A moderate morphine dose produced substantial relief of laboratory dyspnea, with a smaller reduction of ventilation. (2) In contrast to an earlier laboratory model of breathing effort, this laboratory model of air hunger established a highly significant treatment effect consistent in magnitude with clinical studies of opioids. Laboratory studies require fewer subjects and enable physiological measurements that are difficult to make in a clinical setting. Within-subject comparison of the response to carefully controlled laboratory stimuli can be an efficient means to optimize treatments before clinical trials.

Effectiveness of the VOICES/VOCES sexually transmitted disease/human immunodeficiency virus prevention intervention when administered by health department staff: does it work in the "real world"?

BACKGROUND: Prevention providers wonder whether benefits achieved in the original, researcher-led, efficacy trials of interventions are replicated when the intervention is delivered in real-world settings by their agency's staff. METHODS: A replication study was conducted at 2 public sexually transmitted disease (STD) clinics (New York City and San Juan, PR). Using a controlled trial design, intervention (VOICES/VOCES) and comparison conditions (regular clinic services) were assigned in alternating 4-week blocks. Trained agency staff delivered the intervention. Effectiveness was assessed for incident STDs, redemption of coupons for condoms at neighborhood location after the visit, and improved knowledge and attitudes about STDs and condoms. RESULTS: A total of 3365 patients were recruited, completed the protocol, and followed through STD surveillance systems for an average of 17 months. Of 397 with an incident infection, 226 (13.4%) were among those enrolled during comparison blocks; 171 were among those in the intervention condition (10.2%). Controlling for site and gender, participants enrolled during intervention blocks were significantly less likely to have an incident STD reported to the surveillance system (hazard ratio, 0.78; 95% confidence interval, 0.64-0.96). Intervention block participants scored higher on scales of STD knowledge (4.89 vs. 3.87, P < 0.001) and condom knowledge, attitude, and efficacy (10.98 vs. 9.16, P < 0.001). More of those exposed to VOICES/VOCES redeemed condoms (P < 0.05). Positive effects were more consistent in New York, which may be related to fidelity of implementation. CONCLUSIONS: A packaged human immunodeficiency virus prevention intervention can be delivered by agencies, with benefits similar to those achieved in the research setting.

Bronchial collapsibility at forced expiration in healthy volunteers: assessment with multidetector CT.

PURPOSE: To assess forced-expiratory bronchial collapsibility in healthy volunteers by using multidetector computed tomography (CT) and to compare the results with the current diagnostic criterion for bronchomalacia. MATERIALS AND METHODS: The institutional review board approved this HIPAA-compliant study. Following informed consent, 51 healthy volunteers with normal pulmonary function and no history of smoking were imaged by using a 64-detector row scanner with spirometric monitoring at total lung capacity and during forced exhalation. The total study population (in whom both main bronchi were imaged) included 25 men and 26 women (mean age, 50 years). Each scan was analyzed at a workstation by a fellowship-trained thoracic radiologist. Cross-sectional area measurements were obtained from end-inspiratory and forced-expiratory CT images for the right main bronchus (RMB), left main bronchus, (LMB), and bronchus intermedius (BI), and the mean percentage of expiratory collapse was calculated for each bronchus. The number of participants who exceeded the current diagnostic threshold level (>50% expiratory reduction in cross-sectional area) for bronchomalacia was calculated. Comparisons of airway dimensions and airway collapse according to bronchial segment and sex were made by using repeated-measures analysis of variance. RESULTS: Mean percentage of expiratory collapse was 66.9% ± 19.0 (standard deviation) for the RMB and 61.4% ± 16.7 for the LMB. Thirty-seven (73%) of 51 participants exceeded the diagnostic threshold level for bronchomalacia. Significant differences were observed in mean percentage of expiratory collapse between the RMB (66.9% ± 19.0) and LMB (61.4% ± 16.7) (P = .0005). Among a subgroup of 37 participants in whom the BI was also imaged, the mean percentage of expiratory collapse was 61.8% ± 22.8, and 27 (73%) participants exceeded the diagnostic threshold level for bronchomalacia. CONCLUSION: Healthy volunteers demonstrate a wide range of forced-expiratory bronchial collapse, frequently exceeding the current diagnostic threshold level for bronchomalacia.

A novel animal model for hyperdynamic airway collapse.

OBJECTIVE: Tracheobronchomalacia (TBM) is increasingly recognized as a condition associated with significant pulmonary morbidity. However, treatment is invasive and complex, and because there is no appropriate animal model, novel diagnostic and treatment strategies are difficult to evaluate. We endeavored to develop a reliable airway model to simulate hyperdynamic airway collapse in humans. METHODS: Seven 20-kg male sheep were enrolled in this study. Tracheomalacia was created by submucosal resection of > 50% of the circumference of 10 consecutive cervical tracheal cartilage rings through a midline cervical incision. A silicone stent was placed in the trachea to prevent airway collapse during recovery. Tracheal collapsibility was assessed at protocol-specific time points by bronchoscopy and multidetector CT imaging while temporarily removing the stent. Esophageal pressure and flow data were collected to assess flow limitation during spontaneous breathing. RESULTS: All animals tolerated the surgical procedure well and were stented without complications. One sheep died at 2 weeks because of respiratory failure related to stent migration. In all sheep, near-total forced inspiratory airway collapse was observed up to 3 months postprocedure. Esophageal manometry demonstrated flow limitation associated with large negative pleural pressure swings during rapid spontaneous inhalation. CONCLUSIONS: Hyperdynamic airway collapse can reliably be induced with this technique. It may serve as a model for evaluation of novel diagnostic and therapeutic strategies for TBM.

Reproducibility of forced expiratory tracheal collapse: assessment with MDCT in healthy volunteers.

RATIONALE AND OBJECTIVES: To assess the reproducibility of multidetector-row computed tomography (MDCT)-measured forced expiratory tracheal collapse in healthy volunteers. METHODS AND MATERIALS: Fourteen healthy, nonsmoking volunteers (6 males, 8 females, mean age 48.7 +/- 13.8 years) underwent repeat imaging 1 year after baseline imaging of tracheal dynamics employing the same scanner and technique (64-MDCT, 40 mAs, 120 kVp, and 0.625 mm detector collimation) with spirometric monitoring of total lung capacity and forced exhalation. Cross-sectional area (CSA) of the trachea was measured 1 cm above the aortic arch at end-inspiration and dynamic expiration, and percentage (%) expiratory reduction in tracheal lumen was calculated. Measurements were compared between baseline (Yr1) and repeat imaging (Yr2) using correlation coefficients and Bland-Altman plots. RESULTS: Mean end-inspiratory CSA was 255.3 +/- 56 mm(2) at Yr1 and 255.1 +/- 52 mm(2) at Yr2; mean dynamic expiratory CSA was 125.6 +/- 60 mm(2) at Yr1 and 132.1 +/- 58 mm(2) at Yr2; and mean % expiratory reduction was 51.7 +/- 18% at Yr1 and 48.7 +/- 19% at Yr2. Mean differences between Yr1 and Yr2 values were 0.2 mm(2) for end-inspiratory CSA, 6.5 mm(2) for dynamic expiratory CSA, and 3.0% for percentage expiratory reduction. There was excellent correlation between the Yr1 and Yr2 measures of end-inspiratory CSA (r(2) = 0.97, P < .001), dynamic expiratory CSA (r(2) = 0.89, P < .001), and % expiratory reduction (r(2) = 0.86, P < .001). CONCLUSION: MDCT measurements of forced expiratory tracheal collapse in healthy volunteers are highly reproducible over time.

Esophageal pressures in acute lung injury: do they represent artifact or useful information about transpulmonary pressure, chest wall mechanics, and lung stress?

Acute lung injury can be worsened by inappropriate mechanical ventilation, and numerous experimental studies suggest that ventilator-induced lung injury is increased by excessive lung inflation at end inspiration or inadequate lung inflation at end expiration. Lung inflation depends not only on airway pressures from the ventilator but, also, pleural pressure within the chest wall. Although esophageal pressure (Pes) measurements are often used to estimate pleural pressures in healthy subjects and patients, they are widely mistrusted and rarely used in critical illness. To assess the credibility of Pes as an estimate of pleural pressure in critically ill patients, we compared Pes measurements in 48 patients with acute lung injury with simultaneously measured gastric and bladder pressures (Pga and P(blad)). End-expiratory Pes, Pga, and P(blad) were high and varied widely among patients, averaging 18.6 +/- 4.7, 18.4 +/- 5.6, and 19.3 +/- 7.8 cmH(2)O, respectively (mean +/- SD). End-expiratory Pes was correlated with Pga (P = 0.0004) and P(blad) (P = 0.0104) and unrelated to chest wall compliance. Pes-Pga differences were consistent with expected gravitational pressure gradients and transdiaphragmatic pressures. Transpulmonary pressure (airway pressure - Pes) was -2.8 +/- 4.9 cmH(2)O at end exhalation and 8.3 +/- 6.2 cmH(2)O at end inflation, values consistent with effects of mediastinal weight, gravitational gradients in pleural pressure, and airway closure at end exhalation. Lung parenchymal stress measured directly as end-inspiratory transpulmonary pressure was much less than stress inferred from the plateau airway pressures and lung and chest wall compliances. We suggest that Pes can be used to estimate transpulmonary pressures that are consistent with known physiology and can provide meaningful information, otherwise unavailable, in critically ill patients.

Comparison of plethysmographic and helium dilution lung volumes: which is best for COPD?

BACKGROUND: Theoretical considerations and limited scientific evidence suggest that whole-body plethysmography overestimates lung volume in patients with severe airflow obstruction. We sought to compare plethysmography (Pleth)-, helium dilution (He)- and CT scan-derived lung volume measurements in a sample containing many patients with severe airflow obstruction. METHODS: We measured total lung capacity (TLC) in 132 patients at three hospitals, with monitored application of recommended techniques for Pleth and He measurements of lung volume and by thoracic CT scans obtained during breath hold at full inspiration. RESULTS: Average TLC among 132 subjects was 6.18 L (+/- 1.69 L) by Pleth-derived TLC, 5.55 L (+/- 1.39 L) by He-derived TLC, and 5.31 L (+/- 1.47) by CT scan-derived TLC. Pleth-derived TLC was significantly greater than either He-derived TLC or CT scan-derived TLC (P < or = .001), whereas there was no significant difference between He-derived and CT scan-derived values. When examined separately, there were significant within-subject differences in TLC by measurement technique among subjects with airflow obstruction, but not among those without airflow obstruction. Plethysmographic overestimation of TLC was greatest among subjects with FEV(1) < 30% of predicted. CONCLUSIONS: In the setting of airflow obstruction, Pleth systematically overestimates lung volume relative to He or thoracic imaging despite adherence to current recommendations for proper measurement technique.