Increase In End-expiratory Lung Volume Research Articles

Physiological effects of high-flow nasal cannula oxygen therapy after extubation: a randomized crossover study

BackgroundProphylactic high-flow nasal cannula (HFNC) oxygen therapy can decrease the risk of extubation failure. It is frequently used in the postextubation phase alone or in combination with noninvasive ventilation. However, its physiological effects in this setting have not been thoroughly investigated. The aim of this study was to determine comprehensively the effects of HFNC applied after extubation on respiratory effort, diaphragm activity, gas exchange, ventilation distribution, and cardiovascular biomarkers.MethodsThis was a prospective randomized crossover physiological study in critically ill patients comparing 1 h of HFNC versus 1 h of standard oxygen after extubation. The main inclusion criteria were mechanical ventilation for at least 48 h due to acute respiratory failure, and extubation after a successful spontaneous breathing trial (SBT). We measured respiratory effort through esophageal/transdiaphragmatic pressures, and diaphragm electrical activity (ΔEAdi). Lung volumes and ventilation distribution were estimated by electrical impedance tomography. Arterial and central venous blood gases were analyzed, as well as cardiac stress biomarkers.ResultsWe enrolled 22 patients (age 59 ± 17 years; 9 women) who had been intubated for 8 ± 6 days before extubation. Respiratory effort was significantly lower with HFNC than with standard oxygen therapy, as evidenced by esophageal pressure swings (5.3 [4.2–7.1] vs. 7.2 [5.6–10.3] cmH2O; p < 0.001), pressure–time product (85 [67–140] vs. 156 [114–238] cmH2O*s/min; p < 0.001) and ΔEAdi (10 [7–13] vs. 14 [9–16] µV; p = 0.022). In addition, HFNC induced increases in end-expiratory lung volume and PaO2/FiO2 ratio, decreases in respiratory rate and ventilatory ratio, while no changes were observed in systemic hemodynamics, Troponin T, or in amino-terminal pro-B-type natriuretic peptide.ConclusionsProphylactic application of HFNC after extubation provides substantial respiratory support and unloads respiratory muscles.Trial registration January 15, 2021. NCT04711759.

A new approach for the detection of obesity-related airway obstruction in lung-healthy individuals

BackgroundSubjects with obesity show an increased prevalence of airway obstruction but it is not clear in each case whether this reflects genuine lung disease. Via intentional increase in end-expiratory lung volume we studied the detection of obesity-induced airway obstruction in lung-healthy obese subjects. MethodsThe primary study population comprised 66 lung-healthy obese subjects and 23 normal weight subjects. Measurements were performed in a body plethysmograph allowing for recording and quantification of breathing loops in terms of specific airway resistance at both normal and intentionally elevated end-expiratory lung volume. The change in volume was documented by a shutter maneuver. ResultsThe voluntary increase of lung volume led to a significant reduction of expiratory airway resistance in 11 of the 66 obese subjects. This reduction could be quantified by a change of total expiratory resistance (sRtEX) of >1 kPa*s but was also clearly visible in the breathing loops. sRtEX showed the largest change among all resistance parameters. The loops of normal weight subjects remained virtually unaffected by the change in lung volume. Moreover, those of 5 obese patients with COPD who were measured for comparison partially showed a reduction of resistance but airway obstruction remained. ConclusionThe proposed breathing maneuver was simple to perform and allowed for a quantitative and qualitative detection of obesity-induced airway obstruction. This might help in reducing the likelihood of misdiagnosis and overtreatment of obese patients.

High-Flow Nasal Cannula Reduces Effort of Breathing But Not Consistently via Positive End-Expiratory Pressure

High-flow nasal cannula (HFNC) therapy reduces the effort of breathing in patients with bronchiolitis, but the mechanisms are not understood. Theorized mechanisms include dead space washout and positive end-expiratory pressure (PEEP) application. What are the mechanisms of action of HFNC therapy in patients with bronchiolitis? Prospective, single-center study of children 3 years of age or younger with bronchiolitis from January 2020 through March 2021. Flow was titrated between 0.5 and 2 L/kg/min. Electrical impedance tomography measured end-expiratory lung impedance (EELZ) change as an end-expiratory lung volume (EELV) change surrogate and change in tidal impedance difference (ΔZ) as a tidal volume (VT) surrogate. A subset showed manometry measuring esophageal pressure change (ΔPes; transpulmonary pressure surrogate) and pressure rate product (PRP; effort of breathing metric). We hypothesized that EELV and VT would not change and that effort would reduce via respiratory rate (not ΔPes). Measurements were reported as the difference from 0.5 L/kg/min. We studied 22 patients in total, 10 with esophageal manometry. Median EELZ increased by 0.36 arbitrary unit (AU), 2.42 AU, and 4.8 AU at 1 L/kg/min, 1.5 L/kg/min, and 2 L/kg/min (P= .01, 2 L/kg/min vs0.5 L/kg/min), which corresponded to a median increase in EELV of 1.8mL/kg between 0.5 and 2 L/kg/min. Seven patients showed an increase in EELZ of > 5 AU, 12 showed no change in EELZ (± 5 AU), and three showed a decrease in EELZ of > 5 AU. ΔZ (ie, VT) did not change from 0.5 L/kg/min to 2 L/kg/min (median change, 0.29 AU; P= .48). Median PRP decreased by 78cm H2O/min from 0.5 L/kg/min to 2 L/kg/min (P= .02), with all patients demonstrating a reduction in PRP, with a nonsignificant change in ΔPes (P= .68). Increasing HFNC in children with bronchiolitis reduces the effort of breathing, but no consistent increase occurs in end-expiratory lung volume and no significant change occurs in VT or transpulmonary pressure. This suggests that PEEP application is not the primary mechanism of action of HFNC in children with bronchiolitis.

The Effect of Physical Therapy on Regional Lung Function in Critically Ill Patients.

Early mobilization has become an important aspect of treatment in intensive care medicine, especially in patients with acute pulmonary dysfunction. As its effects on regional lung physiology have not been fully explored, we conceived a prospective observational study (Registration number: DRKS00023076) investigating regional lung function during a 15-min session of early mobilization physiotherapy with a 30-min follow-up period. The study was conducted on 20 spontaneously breathing adult patients with impaired pulmonary gas exchange receiving routine physical therapy during their intensive care unit stay. Electrical impedance tomography (EIT) was applied to continuously monitor ventilation distribution and changes in lung aeration during mobilization and physical therapy. Baseline data was recorded in the supine position, the subjects were then transferred into the seated and partly standing position for physical therapy. Afterward, patients were transferred back into the initial position and followed up with EIT for 30 min. EIT data were analyzed to assess changes in dorsal fraction of ventilation (%dorsal), end-expiratory lung impedance normalized to tidal variation (ΔEELI), center of ventilation (CoV) and global inhomogeneity index (GI index).Follow-up was completed in 19 patients. During exercise, patients exhibited a significant change in ventilation distribution in favor of dorsal lung regions, which did not persist during follow-up. An identical effect was shown by CoV. ΔEELI increased significantly during follow-up. In conclusion, mobilization led to more dorsal ventilation distribution, but this effect subsided after returning to initial position. End-expiratory lung impedance increased during follow-up indicating a slow increase in end-expiratory lung volume following physical therapy.

Predictors of exercise-induced bronchoconstriction in subjects with mild asthma

BackgroundPhysical effort is capable of triggering airway obstruction in asthmatics, the so-called exercise-induced bronchoconstriction in asthma (EIBa). This study was performed in subjects with mild persistent asthma, aiming to find predictors for developing EIBa.MethodsIn 20 subjects with mild asthma, measurements of baseline functional respiratory parameters and airways responsiveness by a methacholine challenge were obtained on the first day. A maximal, symptom-limited incremental cardiopulmonary exercise test (CPExT) was performed the day after, with subsequent, repeated maneuvers of maximal full forced expiration to monitor the FEV1 change at 1,3,5,7,10 and 15 min after the end of the exercise.Results19 subjects completed the two-days protocol. No functional parameters both at rest and during effort were useful to predict EIBa after stopping exercise. In asthmatics with EIBa, mean Inspiratory Capacity (IC) did not increase with increasing ventilatory requirements during CPExT because 6 of them (50%) displayed dynamic pulmonary hyperinflation (DH), as documented by their progressive increase of end-expiratory lung volume. This subgroup, showing earlier post-exercise FEV1 fall, had significantly lower forced mean expiratory flow between 25% and 75% of forced vital capacity (FEF25-75%) at rest (p < 0.05) and higher airways responsiveness, expressed as PD20FEV1 (p < 0.05) as compared with other asthmatics with EIBa.ConclusionsNo functional respiratory parameters seem to predict EIBa in mild asthmatics. However, in those with EIBa, a subgroup developed DH during exercise, and this was associated with a baseline reduced forced expiratory flow rates at lower lung volumes and higher airway hyperresponsiveness, suggesting a prominent small airways impairment.

Flow-controlled ventilation (FCV) improves regional ventilation in obese patients \u2013 a randomized controlled crossover trial

BackgroundIn obese patients, high closing capacity and low functional residual capacity increase the risk for expiratory alveolar collapse. Constant expiratory flow, as provided by the new flow-controlled ventilation (FCV) mode, was shown to improve lung recruitment. We hypothesized that lung aeration and respiratory mechanics improve in obese patients during FCV.MethodsWe compared FCV and volume-controlled (VCV) ventilation in 23 obese patients in a randomized crossover setting. Starting with baseline measurements, ventilation settings were kept identical except for the ventilation mode related differences (VCV: inspiration to expiration ratio 1:2 with passive expiration, FCV: inspiration to expiration ratio 1:1 with active, linearized expiration). Primary endpoint of the study was the change of end-expiratory lung volume compared to baseline ventilation. Secondary endpoints were the change of mean lung volume, respiratory mechanics and hemodynamic variables.ResultsThe loss of end-expiratory lung volume and mean lung volume compared to baseline was lower during FCV compared to VCV (end-expiratory lung volume: FCV, − 126 ± 207 ml; VCV, − 316 ± 254 ml; p < 0.001, mean lung volume: FCV, − 108.2 ± 198.6 ml; VCV, − 315.8 ± 252.1 ml; p < 0.001) and at comparable plateau pressure (baseline, 19.6 ± 3.7; VCV, 20.2 ± 3.4; FCV, 20.2 ± 3.8 cmH2O; p = 0.441), mean tracheal pressure was higher (baseline, 13.1 ± 1.1; VCV, 12.9 ± 1.2; FCV, 14.8 ± 2.2 cmH2O; p < 0.001). All other respiratory and hemodynamic variables were comparable between the ventilation modes.ConclusionsThis study demonstrates that, compared to VCV, FCV improves regional ventilation distribution of the lung at comparable PEEP, tidal volume, PPlat and ventilation frequency. The increase in end-expiratory lung volume during FCV was probably caused by the increased mean tracheal pressure which can be attributed to the linearized expiratory pressure decline.Trial registrationGerman Clinical Trials Register: DRKS00014925. Registered 12 July 2018.

Mechanisms of improved exercise capacity following respiratory muscle training in athletes with cervical spinal cord injury.

Mechanisms of improved exercise capacity following respiratory muscle training in athletes with cervical spinal cord injury.

CON: Persistent Central Sleep Apnea/Hunter-Cheyne-Stokes Breathing, Despite Best Guideline-Based Therapy of Heart Failure With Reduced Ejection Fraction, Is Not a Compensatory Mechanism and Should Be Suppressed.

CON: Persistent Central Sleep Apnea/Hunter-Cheyne-Stokes Breathing, Despite Best Guideline-Based Therapy of Heart Failure With Reduced Ejection Fraction, Is Not a Compensatory Mechanism and Should Be Suppressed.

Low exertional inspiratory capacity is not related to dynamic inspiratory muscle weakness in heart failure

Reduction in inspiratory capacity (IC) during exercise has been reported in chronic heart failure (CHF). Since inspiratory muscle dysfunction may be present to a variable degree, the assumption that IC reduction during exercise represents an increase in end-expiratory lung volume must be made with caution. This interpretation is flawed if patients develop dynamic inspiratory muscle strength reduction, i.e., progressively lower esophageal (Pes) pressures as the IC maneuvers are repeated. Sixteen CHF patients and 9 age-matched controls performed an incremental exercise test with serial IC and respiratory pressure measurements. Regardless whether IC decreased or not with exercise (N = 4 and N = 12, respectively), Pes,IC remained stable. This was confirmed by similar Pes,sniff immediately upon exercise cessation (p > .05). No association was found between changes in IC and related Pes from rest to peak exercise. Owing to the lack of dynamic inspiratory muscle weakness, non-invasive indexes of lung mechanics can be reliably obtained from exercise IC in CHF.

Distinct Patterns of Hyperpnea During Cheyne-Stokes Respiration: Implication for Cardiac Function in Patients With Heart Failure.

In heart failure (HF), we observed two patterns of hyperpnea during Cheyne-Stokes respiration with central sleep apnea (CSR-CSA): a positive pattern where end-expiratory lung volume remains at or above functional residual capacity, and a negative pattern where it falls below functional residual capacity. We hypothesized the negative pattern is associated with worse HF. Patients with HF underwent polysomnography. During CSR-CSA, hyperpnea, apnea-hyperpnea cycle, and lung to finger circulation times (LFCT) were measured. Plasma N-terminal prohormone of brain natriuretic peptide (NT-proBNP) concentration and left ventricular ejection fraction (LVEF) were assessed. Of 33 patients with CSR-CSA (31 men, mean age 68 years), 9 had a negative hyperpnea pattern. There was no difference in age, body mass index, and apnea-hypopnea index between groups. Patients with a negative pattern had longer hyperpnea time (39.5 ± 6.4 versus 25.8 ± 5.9 seconds, P < .01), longer cycle time (67.8 ± 15.9 versus 51.7 ± 9.9 seconds, P < .01), higher NT-proBNP concentrations (2740 [6769] versus 570 [864] pg/ml, P = .01), and worse New York Heart Association class (P = .02) than those with a positive pattern. LFCT and LVEF did not differ between groups. Patients with HF and a negative CSR-CSA pattern have evidence of worse cardiac function than those with a positive pattern. Greater positive expiratory pressure during hyperpnea is likely generated during the negative pattern and might support stroke volume in patients with worse cardiac function. A commentary on this article appears in this issue on page 1227. The trial is registered with Current Controlled Trials (www.controlled-trials.com; ISRCTN67500535) and Clinical Trials (www.clinicaltrials.gov; NCT01128816).

Defining a Ventilation Strategy for Flexible Bronchoscopy on Mechanically Ventilated Patients in the Medical Intensive Care Unit

Flexible bronchoscopy (FB) in intubated patients on mechanical ventilation increases airway resistance. During FB, two ventilatory strategies are possible: maintaining tidal volume (VT) while maintaining baseline CO2 or allowing reduction of VT. The former strategy carries risk of hyperinflation due to expiratory flow limitation with FB. The aim of the authors was too study end expiratory lung volume (EELV) during FB of intubated subjects while limiting VT. We studied 16 subjects who were intubated on mechanical ventilation and required FB. Changes in EELV were measured by respiratory inductance plethysmography. Ventilator mechanics, EELV, and arterial blood gases, were measured. FB insertions decreased EELV in 64% of cases (-325±371 mL) and increased it in 32% of cases (65±59 mL). Suctioning decreased EELV in 76% of cases (-120±104 mL) and increased it in 16% of cases (29±33 mL). Respiratory mechanics were unchanged. Pre-FB and post-FB, PaO2 decreased by 61±96 mm Hg and PaCO2 increased by 15±7 mm Hg. There was no clinically significant increase in EELV in any subject during FB. Decreases in EELV coincided with FB-suctioning maneuvers. Peak pressure limiting ventilation protected the subject against hyperinflation with a consequent, well-tolerated reduction in VT, and hypercapnea. Suctioning should be limited, especially in patients vulnerable to derecruitment effect.

Effect of Minimally Invasive Surfactant Therapy on Lung Volume and Ventilation in Preterm Infants

To assess the changes in (regional) lung volume and gas exchange during minimally invasive surfactant therapy (MIST) in preterm infants with respiratory distress syndrome. In this prospective observational study, infants requiring a fraction of inspired oxygen (FiO2) ≥ 0.30 during nasal continuous positive airway pressure of 6 cmH2O were eligible for MIST. Surfactant (160-240 mg/kg) was administered in supine position in 1-3 minutes via an umbilical catheter placed 2 cm below the vocal cords. Changes in end-expiratory lung volume (EELV), tidal volume, and its distribution were recorded continuously with electrical impedance tomography before and up to 60 minutes after MIST. Changes in transcutaneous oxygen saturation (SpO2) and partial carbon dioxide pressure, FiO2, respiratory rate, and minute ventilation were recorded. A total of 16 preterm infants were included. One patient did not finish study protocol because of severe apnea 10 minutes after MIST. In the remaining infants (gestational age 29.8 ± 2.8 weeks, body weight 1545 ± 481 g) EELV showed a rapid and sustained increase, starting in the dependent lung regions, followed by the nondependent regions approximately 5 minutes later. Oxygenation, expressed as the SpO2/FiO2 ratio, increased from 233 (IQR 206-257) to 418 (IQR 356-446) after 60 minutes (P < .001). This change was significantly correlated with the change in EELV (ρ = 0.70, P < .01). Tidal volume and minute volume decreased significantly after MIST, but transcutaneous partial carbon dioxide pressure was comparable with pre-MIST values. Ventilation distribution remained unchanged. MIST results in a rapid and homogeneous increase in EELV, which is associated with an improvement in oxygenation.

Lung recruitment strategies

Mechanical ventilation in newborns, children and adults leads to lung injury and has been shown to induce the formation of proteinaceous lung oedema causing epithelial disruption and resulting in changes in lung perfusion. Lung injury leads to reduced compliance, worsening of shunt fraction and an inflammatory response that results from high end-inspiratory transpulmonary pressures (Ptp) and inadequate End Expiratory Lung Volume (EELV). Lung injury results if a lung is ventilated from collapsed state with each ventilator cycle. Thus the first concept of treatment in acute hypoxic respiratory failure is: “Open collapsed lung units and keep them open without overdistending them”. The open lung is one in which there is little or no atelectasis and an optimal gas exchange. Lung recruitment strategies transiently increase Ptp to reopen the alveolar units not aerated or poorly aerated but recruitable. Lung recruitment maneuvers may restore EELV resulting in more stable alveoli, and reduce shear stress associated with the alveolar cyclic opening and closing. Lung recruitment can be performed in several ways: in delivery room with a T-piece device, in the NICU setting by using a conventional or high frequency oscillation (HFO) ventilator, and is commonly achieved by increase of end-expiratory lung volume with positive end expiratory pressure (PEEP) or end inspiratory lung volume by inspiratory holds or sustained inflation. Recruitment during both, HFO and CMV (Conventional Mechanical Ventilation), follows similar concepts when using small tidal volume ventilation but is easier to achieve at bedside during HFO. The Sustained Inflation maneuver (SI) applies a high pressure to the lung for a short period (30 sec) before returning to previous mean airway pressures. This volume recruitment strategy has been shown to be as protective as high frequency oscillatory ventilation (HFO) at similar lung volumes. Infants treated with a SI in delivery room had improved short-term respiratory outcomes (reduced need of tracheal intubation and mechanical ventilation), but major outcomes (BPD Bronchopulmonary dysplasia- and/or death) were not improved. Recent reports describe improvements in arterial oxygenation with the use of recruitment maneuvers during CMV and/or HFO. However, the impact of these strategies on patient important outcomes such as survival is still unclear. Further clinical studies are needed to evaluate the efficacy of SI, including selection of patients, setting of SI maneuver in terms of duration and peak pressure, timing of surfactant administration. Further studies are also needed to elucidate the impact of recruitment maneuvers during mechanical ventilation, including survival and BPD.

Lung hyperinflation in COPD: applying physiology to clinical practice

In chronic obstructive pulmonary disease (COPD), worsening expiratory flow limitation together with alteration in the elastic properties of the lung are associated with progressive lung hyperinflation and gradual decline in the resting inspiratory capacity over time. Dynamic hyperinflation (DH) refers to the variable increase in end-expiratory lung volume (EELV) above the relaxation volume (VR) of the respiratory system that occurs when expiratory flow limitation is amplified (e.g., during bronchoconstriction and acute exacerbations) or when ventilation is increased in the setting of expiratory flow limitation. During exercise, the combined factors of worsening expiratory flow limitation, increasing respiratory neural drive and breathing pattern alterations dictate the pattern and extent of DH. Acute-on-chronic hyperinflation increases the intrinsic loads on the inspiratory muscles which become functionally weakened. The combined effects of compromised respiratory and integrated cardio-circulatory function due to lung hyperinflation contribute to exercise limitation. In COPD, the resting inspiratory capacity, which indirectly reflects the extent of lung hyperinflation, dictates the limits of tidal volume expansion and thus, peak ventilatory capacity during activity. Moreover, the growing disparity between increased respiratory neural drive and the blunted respiratory muscular/mechanical response due to lung hyperinflation is mechanistically linked to dyspnea during exercise in COPD. From a clinical standpoint, measurement of lung hyperinflation is integral to the assessment of physiological impairment in individuals with COPD and can effectively be targeted for treatment. Moreover, it is now well established that lung volume reduction (deflation) provides a solid mechanistic rationale for observed improvements in dyspnea and exercise tolerance in patients with COPD following bronchodilator therapy.

Impact of Extraperitoneal Dioxyde Carbon Insufflation on Respiratory Function in Anesthetized Adults: A Preliminary Study Using Electrical Impedance Tomography and Wash-out/Wash-in Technic.

Background:Extraperitoneal laparoscopy has become a common technique for many surgical procedures, especially for inguinal hernia surgery. Investigations of physiological changes occurring during extraperitoneal carbon dioxide (CO2) insufflation mostly focused on blood gas changes. To date, the impact of extraperitoneal CO2 insufflation on respiratory mechanics remains unknown, whereas changes in respiratory mechanics have been extensively studied in intraperitoneal insufflation.Objectives:The aim of this study was to investigate the effects of extraperitoneal CO2 insufflation on respiratory mechanics.Patients and Methods:A prospective and observational study was performed on nine patients undergoing laparoscopic inguinal hernia repair. Anesthetic management and intraoperative care were standardized. All patients were mechanically ventilated with a tidal volume of 8 mL/kg using an Engström Carestation ventilator (GE Healthcare). Ventilation distribution was assessed by electrical impedance tomography (EIT). End-expiratory lung volume (EELV) was measured by a nitrogen wash-out/wash-in method. Ventilation distribution, EELV, ventilator pressures and hemodynamic parameters were assessed before extraperitoneal insufflation, and during insufflation with a PEEP of 0 cmH2O, 5 cmH20 and of 10 cmH20.Results:EELV and thoracopulmonary compliance were significantly decreased after extraperitoneal insufflation. Ventilation distribution was significantly higher in ventral lung regions during general anesthesia and was not modified after insufflation. A 10 cmH20 PEEP application resulted in a significant increase in EELV, and a shift of ventilation toward the dorsal lung regions.Conclusions:Extraperitoneal insufflation decreased EELV and thoracopulmonary compliance. Application of a 10 cmH20 PEEP increased EELV and homogenized ventilation distribution. This preliminary clinical study showed that extraperitoneal insufflation worsened respiratory mechanics, which may justify further investigations to evaluate the clinical impact.

Effects of pleural effusion drainage on oxygenation, respiratory mechanics, and hemodynamics in mechanically ventilated patients.

In mechanically ventilated patients, the effect of draining pleural effusion on oxygenation is controversial. We investigated the effect of large pleural effusion drainage on oxygenation, respiratory function (including lung volumes), and hemodynamics in mechanically ventilated patients after ultrasound-guided drainage. Arterial blood gases, respiratory mechanics (airway, pleural and transpulmonary pressures, end-expiratory lung volume, respiratory system compliance and resistance), and hemodynamics (blood pressure, heart rate, and cardiac output) were recorded before and at 3 and 24 hours (H24) after pleural drainage. The respiratory settings were kept identical during the study period. The mean volume of effusion drained was 1,579 ± 684 ml at H24. Uncomplicated pneumothorax occurred in two patients. Respiratory mechanics significantly improved after drainage, with a decrease in plateau pressure and a large increase in end-expiratory transpulmonary pressure. Respiratory system compliance, end-expiratory lung volume, and PaO2/FiO2 ratio all improved. Hemodynamics were not influenced by drainage. Improvement in the PaO2/FiO2 ratio from baseline to H24 was positively correlated with the increase in end-expiratory lung volume during the same time frame (r = 0.52, P = 0.033), but not with drained volume. A high value of pleural pressure or a highly negative transpulmonary pressure at baseline predicted limited lung expansion following effusion drainage. A lesser improvement in oxygenation occurred in patients with ARDS. Drainage of large (≥500 ml) pleural effusion in mechanically ventilated patients improves oxygenation and end-expiratory lung volume. Oxygenation improvement correlated with an increase in lung volume and a decrease in transpulmonary pressure, but was less so in patients with ARDS.

Physiologic Effect of High-Flow Nasal Cannula in Infants With Bronchiolitis

To assess the effect of delivering high-flow nasal cannula flow on end-expiratory lung volume, continuous distending pressure, and regional ventilation distribution in infants less than 12 months old with bronchiolitis. Prospective observational clinical study. Nineteen bed medical and surgical PICU. Thirteen infants with bronchiolitis on high-flow nasal therapy. The study infants were measured on a flow rate applied at 2 and 8 L/min through the high-flow nasal cannula system. Ventilation distribution was measured with regional electrical impedance amplitudes and end-expiratory lung volume using electrical impedance tomography. Changes in continuous distending pressure were measured from the esophagus via the nasogastric tube. Physiological variables were also recorded. High-flow nasal cannula delivered at 8 L/min resulted in significant increases in global and anterior end-expiratory lung volume (p < 0.01) and improvements in the physiological variables of respiratory rate, SpO2, and FIO2 when compared with flows of 2 L/min. In infants with bronchiolitis, high-flow nasal cannula oxygen/air delivered at 8 L/min resulted in increases in end-expiratory lung volume and improved respiratory rate, FIO2, and SpO2.

Head-of-bed elevation improves end-expiratory lung volumes in mechanically ventilated subjects: a prospective observational study.

Head-of-bed elevation (HOBE) has been shown to assist in reducing respiratory complications associated with mechanical ventilation; however, there is minimal research describing changes in end-expiratory lung volume. This study aims to investigate changes in end-expiratory lung volume in a supine position and 2 levels of HOBE. Twenty postoperative cardiac surgery subjects were examined using electrical impedance tomography. End-expiratory lung impedance (EELI) was recorded as a surrogate measurement of end-expiratory lung volume in a supine position and at 20° and then 30°. Significant increases in end-expiratory lung volume were seen at both 20° and 30° HOBE in all lung regions, except the anterior, with the largest changes from baseline (supine) seen at 30°. From baseline to 30° HOBE, global EELI increased by 1,327 impedance units (95% CI 1,080-1,573, P < .001). EELI increased by 1,007 units (95% CI 880-1,134, P < .001) in the left lung region and by 320 impedance units (95% CI 188-451, P < .001) in the right lung. Posterior increases of 1,544 impedance units (95% CI 1,405-1,682, P < .001) were also seen. EELI decreased anteriorly, with the largest decreases occurring at 30° (-335 impedance units, 95% CI -486 to -183, P < .001). HOBE significantly increases global and regional end-expiratory lung volume; therefore, unless contraindicated, all mechanically ventilated patients should be positioned with HOBE.

B-15 Thematic Poster - Advances in Epidemiology

BACKGROUND: The effect of weight loss on lung function at rest in men and women is well documented. Weight loss also improves breathing mechanics during exercise in obese men. However, the effect of weight loss on breathing mechanics during exercise is unknown in obese women, who have smaller respiratory reserves than obese men. PURPOSE: To investigate the effects of weight loss on breathing mechanics during submaximal exercise in obese women. We hypothesized that weight loss would improve breathing mechanics during submaximal exercise via an increase in end-expiratory lung volume (EELV). METHODS: In 29 obese women (age: 33 ± 8 y, weight: 96.8 ± 14.0 kg, BMI: 36.2 ± 3.5 kg/m2, percent body fat: 45.6 ± 4.5%; Mean ± SD), body composition, fat distribution (MRI), pulmonary function, and breathing mechanics during exercise were studied before and after a 12-week diet and resistance exercise weight loss program. Data were analyzed by paired t-tests. Relationships among variables were investigated by Pearson’s correlations. RESULTS: Subjects lost 7.5 ± 3.1 kg of body weight (P < 0.001). Total lung capacity, functional residual capacity (FRC), and expiratory reserve volume were significantly increased (4.8 ± 0.7 to 4.9 ± 0.8 L, 2.0 ± 0.4 to 2.2 ± 0.5 L, 0.8 ± 0.3 to 1.1 ± 0.5 L respectively; P < 0.05) while inspiratory capacity was decreased (2.8 ± 0.5 to 2.7 ± 0.5 L; P < 0.05) after weight loss. Changes in FRC were moderately associated with changes in body weight, BMI, abdominal fat and total chest fat + abdominal fat (r = -0.58 to -0.65; P < 0.05). EELV increased at rest (42.7 ± 7.5 to 45.7 ± 7.6 %TLC; P = 0.004) and during constant load exercise (40.4 ± 5.1 to 42.5 ± 5.7 %TLC; P = 0.02). There was no significant association between the increase in EELV with weight loss and the magnitude of expiratory flow limitation. There were no meaningful correlations between the changes in EELV during constant load exercise and changes in body composition or pulmonary function. CONCLUSIONS: Moderate weight loss improves breathing mechanics not only at rest but also during submaximal exercise in obese women, which is clinically important since submaximal exercise is a major component in the treatment and prevention of obesity. FUNDING SOURCES: NIH R01 HL096782-01A2, King Charitable Foundation Trust, Texas Health Presbyterian Hospital Dallas

Effect of different seated positions on lung volume and oxygenation in acute respiratory distress syndrome

Lung volume available for ventilation is markedly decreased during acute respiratory distress syndrome. Body positioning may contribute to increase lung volume and partial verticalization is simple to perform. This study evaluated whether verticalization had parallel effects on oxygenation and end expiratory lung volume (EELV). Prospective multicenter study in 40 mechanically ventilated patients with ALI/ARDS in five university hospital MICUs. We evaluated four 45-min successive trunk position epochs (supine slightly elevated at 15°; semi recumbent with trunk elevated at 45°; seated with trunk elevated at 60° and legs down at 45°; back to supine). Arterial blood gases, EELV measured using the nitrogen washin/washout, and static compliance were measured. Responders were defined by a PaO₂/FiO₂ increase >20 % between supine and seated position. Results are median [25th-75th percentiles]. With median PEEP = 10 cmH₂O, verticalization increased lung volume but only responders (13 patients, 32 %) had a significant increase in EELV/PBW (predicted body weight) compared to baseline. This increase persisted at least partially when patients were positioned back to supine. Responders had a lower EELV/PBW supine [14 mL/kg (13-15) vs. 18 mL/kg (15-27) (p = 0.005)] and a lower compliance [30 mL/cmH₂O (22-38) vs. 42 (30-46) (p = 0.01)] than non-responders. Strain decreased with verticalization for responders. EELV/PBW increase and PaO₂/FiO₂ increase were not correlated. Verticalization is easily achieved and improves oxygenation in approximately 32 % of the patients together with an increase in EELV. Nonetheless, effect of verticalization on EELV/PBW is not predictable by PaO₂/FiO₂ increase, its monitoring may be helpful for strain optimization.