Mechanical dispersion is a superior echocardiographic feature to predict exercise capacity in preclinical and overt heart failure with preserved ejection fraction

BACKGROUND

Heart Failure with Preserved Ejection Fraction (HFpEF) is a syndrome characterized by different degrees of exercise intolerance, which leads to poor quality of life and prognosis. Recently, the European score (HFA-PEFF) was proposed to standardize the diagnosis of HFpEF. Even though Global Longitudinal Strain (GLS) is a component of HFA-PEFF, the role of other strain parameters, such as Mechanical Dispersion (MD), has yet to be studied. In this study, we aimed to compare MD and other features from the HFA-PEFF according to their association with exercise capacity in an outpatient population of subjects at risk or suspected HFpEF.

METHODS

This is a single-center cross-sectional study performed in an outpatient population of 144 subjects with a median age of 57 years, 58% females, referred to the Echocardiography and Cardiopulmonary Exercise Test to investigate HFpEF.

RESULTS

MD had a higher correlation to Peak VO2 (r=-0.43) when compared to GLS (r=-0.26), MD presented a significant correlation to Ventilatory Anaerobic Threshold (VAT) (r=-0.20; p = 0.04), while GLS showed no correlation (r=-0.14; p = 0.15). Neither MD nor GLS showed a correlation with the time to recover VO2 after exercise (T1/2). In Receiver Operator Characteristic (ROC) analysis, MD presented superior performance to GLS to predict Peak VO2 (AUC: 0.77 vs. 0.62), VAT (AUC: 0.61 vs. 0.57), and T1/2 (AUC: 0.64 vs. 0.57). Adding MD to HFA-PEFF improved the model performance (AUC from 0.77 to 0.81).

CONCLUSION

MD presented a higher association with Peak VO2 when compared to GLS and most features from the HFA-PEFF. Adding MD to the HFA-PEFF improved the model performance.

Fasting and prolonged food restriction differentially affect GH secretion independently of GH receptor signaling in AgRP neurons

Growth hormone (GH) receptor (GHR) is abundantly expressed in neurons that co-release the agouti-related protein (AgRP) and neuropeptide Y (NPY) in the arcuate nucleus of the hypothalamus (ARH). Since ARH^AgRP/NPY neurons regulate several hypothalamic-pituitary-endocrine axes, this neuronal population possibly modulates GH secretion via a negative feedback loop, particularly during food restriction, when ARH^AgRP/NPY neurons are highly active. The present study aims to determine the importance of GHR signaling in ARH^AgRP/NPY neurons on the pattern of GH secretion in fed and food-deprived male mice. Additionally, we compared the effect of two distinct situations of food deprivation: 16 h of fasting or four days of food restriction (40% of usual food intake). Overnight fasting strongly suppressed both basal and pulsatile GH secretion. Animals lacking GHR in ARH^AgRP/NPY neurons (AgRP^∆GHR mice) did not exhibit differences in GH secretion either in the fed or fasted state, compared to control mice. In contrast, four days of food restriction increased GH pulse frequency, basal GH secretion, and pulse irregularity/complexity (measured by sample entropy), whereas pulsatile GH secretion was not affected in both control and AgRP^∆GHR mice. Hypothalamic Ghrh mRNA levels were unaffected by fasting or food restriction, but Sst expression increased in acutely fasted mice, but decreased after prolonged food restriction in both control and AgRP^∆GHR mice. Our findings indicate that short-term fasting and prolonged food restriction differentially affect the pattern of GH secretion, independently of GHR signaling in ARH^AgRP/NPY neurons.

Mechanical dispersion of left ventricle and left atrial reservoir strain are both superior to global longitudinal strain to predict exercise capacity in heart failure with preserved ejection fraction

Funding Acknowledgements

Type of funding sources: Public hospital(s). Main funding source(s): Fundação Adib Jatene

Background/Introduction: 

Peak oxygen uptake (peak VO2) measures cardiovascular fitness and is a valuable diagnostic and prognostic marker in patients with heart failure with preserved ejection fraction (HFpEF). Measurement of peak VO2, however, requires specialized equipment and expert supervision, limiting its routine use by practicing clinicians. 

Strain curves obtained by speckle tracking echocardiography (STE) can provide different parameters of myocardial mechanics such as the Global Longitudinal Strain (GLS), which is the most robust STE feature for clinical practice. 

Notwithstanding, there is conflicting data on whether the GLS is associated with peak VO2 in HFpEF subjects.

Moreover, few studies have addressed the relationship between  peak VO2 and other interesting deformation parameters such as the left atrial (LA) reservoir strain or the left ventricular mechanical dispersion (MD).

Purpose

The present study aimed to examine the utility of the myocardial mechanics as assessed by STE in predicting peak VO2 in patients with HFpEF. 

Methods

From an ongoing prospective cohort of 189 subjects, we sampled subjects with different HFpEF stages. All patients underwent cardiopulmonary exercise testing (CPX) and a 2D-STE (LV GLS, MD, LA reservoir strain, LA conduit strain, and LA contraction strain) obtained by a blinded examinator. The missing data was handled by complete case analysis approach. We excluded subjects who had atrial fibrillation/flutter, severe COPD, STE with poor tracking quality, CPX with respiratory exchange rate (RER) < 1. 

The Spearman"s correlation was calculated, and the 95% CI were estimated.

Finally, an estimative of the STE features importance to predict peak VO2 < 20mL/Kg/min was done using the function "xgb.importance()" from machine learning model XGBoost in R software. XGBoost is a variant of Gradient Boosting Method that uses ensembles of decision trees. 

Results

We obtained 74 subjects (23 without evidence of heart disease, 23 with pre-heart failure and 28 with HFpEF). The MD presented the highest correlation with peak VO2 (Rho=-0.48; p-value < 0.001) followed by LA reservoir strain (Rho = 0.40; p-value < 0.001), LA conduit strain (Rho= –0.36; p-value < 0.001) and LA contraction (Rho= –0.30 p-value < 0.004) as shown in Figure 1. However, no correlation was found between GLS and peak VO2 (Rho= –0.07 p-value < 0.5) (Figure 2A). 

The feature importance score (Figure 2B) showed the MD as the best relative contribution for VO2 prediction (gain= 0.34) superior to LA reservoir strain (gain = 0.25).  GLS presented contribution (gain = 20) superior to LA conduit strain (gain =10) and LA contraction strain (gain = 0.08).

Conclusion

Left ventricular mechanical dispersion and left atrial reservoir strain obtained with STE were better predictors of peak VO2 than GLS in patients with different HFpEF stages and may be helpful in risk stratification and diagnosis. Abstract Figure 1  Abstract Figure 2

The impact of isometric handgrip testing in left atrial reservoir function

Funding Acknowledgements

Type of funding sources: Public hospital(s). Main funding source(s): Fundação Adib Jatene

Background

Speckle tracking echocardiography (STE) allows accurate quantification of left atrial (LA) strain, thus allowing assessment of all phases of LA function (reservoir, conduit and contraction). Alterations in LA strain occur before changes in LA volumes, enabling early detection of LA dysfunction. In particular, the peak of LA strain during the reservoir phase (LASr) seems to be of prognostic value in heart failure.

LASr is essential to pool enough blood volume to fill the LV during the subsequent diastole. The main determinants of LA reservoir function include blood volume arriving from the right ventricle, LA relaxation, and LA compliance. Still, changes in atrioventricular plane movement during the ventricular systole have been considered an additional factor influencing LASr. The relative contribution of left ventricular afterload to LASr, however, has yet to be clearly defined.

Purpose

We aimed to study the LA function during changes in LV afterload induced by the handgrip maneuver in subjects without heart disease, applying LASr and strain curve shape analysis.

Material and Methods

We studied 31 subjects (47 ± 15 years) without evidence of heart disease. A comprehensive 2D echocardiography was performed. We recorded 3 beat clips with standard STE views of LV and LA in baseline conditions and then during pressure overload-induced by left handgrip (42 ± 8 kg) combined with simultaneous pneumatic constriction of the right arm and both lower limbs. The LV GLS and LASr were calculated offline by a blinded examinator using commercially available software.

Furthermore, we extracted the raw data of the strain curves and post-processed these signals using custom software. The global curves were split into different cardiac cycle phases using the valve opening and closure times(Figure 1). Quadratic functions estimated strain curves during the ejection phase due to the acceleration involved in the phenomenon. Quadratic function linear coefficients, a component of strain rate, were used to assess the shape of deformation curves.

Results

The handgrip maneuver caused mild reductions in LV strain: GLS baseline –19.07 % (±0.27) vs GLS handgrip -18.58% (±0.26) p = 0.02 (Figure 2A and C). Conversely, the LASr did not present significant changes: LASr baseline 33.82% (±0.84) vs LASr handgrip 32.96% (±0.85)  p= 0.18 (Figure 2B and C).

For the analysis of the shape of strain curves, we obtained data from 29 subjects. We found significant differences in LV ejection linear coefficient (ELC): LV ELC baseline –158.30 (±8.52) vs LV ELC handgrip –144.62 (±8.02) p = 0.02. For LA reservoir linear coefficient (RLC), we also found significant differences: LA RLC baseline 240.30 (±17.19) vs LA RLC handgrip 212.61 (±15.62) p = 0.03 (Figure 2D).

Conclusion(s)

The left atrial reservoir function is affected by changes in LV afterload induced by the handgrip maneuver. Our data suggest that LV pressure overload mainly impact the shape of LA strain curve rather than LASr. Abstract Figure 1  Abstract Figure 2

Signal processing to remove spurious contributions to the assessment of respiratory mechanics

Signal disruptions in small animals during the realization of the Forced Oscillation Technique are a well-known cause of data loss as it leads to non-reliable estimations of the respiratory impedance. In this work, we assessed the effects of removing the disrupted epoch when a 3-seconds input signal composed of one and a half 2-seconds full cycle is used.

We tested our hypothesis in 25 SAMR1 mice under different levels of bronchoconstriction due to methacholine administration by iv bolus injections in different doses (15 animals) and by iv continuous infusion in different infusion rates (10 animals). Signal disruptions were computationally simulated as sharp drops in the pressure signal within a short timescale, and signal processing was performed using own developed algorithms.

We found that the model goodness of fit worsens when averaging techniques to estimate the input respiratory impedance are not used. However, no statistically significant differences were observed in the comparison between Constant Phase Model parameters of the full 3-s signal and the 2-s non disrupted epoch in all doses or infusion rates for both methacholine delivery strategies.

The proposed technique presents reliable outcomes that can reduce animal use in Forced Oscillation Technique realization.

Drug class effects on respiratory mechanics in animal models: access and applications

Assessment of respiratory mechanics extends from basic research and animal modeling to clinical applications in humans. However, to employ the applications in human models, it is desirable and sometimes mandatory to study non-human animals first. To acquire further precise and controlled signals and parameters, the animals studied must be further distant from their spontaneous ventilation. The majority of respiratory mechanics studies use positive pressure ventilation to model the respiratory system. In this scenario, a few drug categories become relevant: anesthetics, muscle blockers, bronchoconstrictors, and bronchodilators. Hence, the main objective of this study is to briefly review and discuss each drug category, and the impact of a drug on the assessment of respiratory mechanics. Before and during the positive pressure ventilation, the experimental animal must be appropriately sedated and anesthetized. The sedation will lower the pain and distress of the studied animal and the plane of anesthesia will prevent the pain. With those drugs, a more controlled procedure is carried out; further, because many anesthetics depress the respiratory system activity, a minimum interference of the animal's respiration efforts are achieved. The latter phenomenon is related to muscle blockers, which aim to minimize respiratory artifacts that may interfere with forced oscillation techniques. Generally, the respiratory mechanics are studied under appropriate anesthesia and muscle blockage. The application of bronchoconstrictors is prevalent in respiratory mechanics studies. To verify the differences among studied groups, it is often necessary to challenge the respiratory system, for example, by pharmacologically inducing bronchoconstriction. However, the selected bronchoconstrictor, doses, and administration can affect the evaluation of respiratory mechanics. Although not prevalent, studies have applied bronchodilators to return (airway resistance) to the basal state after bronchoconstriction. The drug categories can influence the mathematical modeling of the respiratory system, systemic conditions, and respiratory mechanics outcomes.

Pilocarpine-induced status epilepticus reduces chemosensory control of breathing

One of the possible causes of death in epilepsy is breathing disorders, especially apneas, which lead to an increase in CO₂ levels (hypercapnia) and/or a decrease in O₂ levels in arterial blood (hypoxemia). The respiratory neurons located in the ventral brainstem respiratory column are the main groups responsible for controlling breathing. Recent data from our group demonstrated respiratory changes in two experimental models of epilepsy, i.e. audiogenic epilepsy, and amygdala rapid kindling. Here, we aimed to evaluate respiratory changes in the classic model of temporal lobe epilepsy induced by intra-hippocampal injection of pilocarpine. Adult Wistar rats with stainless-steel cannulas implanted in the hippocampus region were used. The animals were submitted to pilocarpine injection (2.4 mg/μL, N = 12-15) or saline (N = 9) into the hippocampus. The respiratory parameters analyzed by whole-body plethysmography were respiratory rate (f_R), tidal volume (V_T) and ventilation (V_E). Respiratory mechanics such as Newtonian airway resistance (R_n), viscance of the pulmonary parenchyma (G) and the elastance of the pulmonary parenchyma (H) were also investigated. No changes in baseline breathing were detected 15 or 30 days after pilocarpine-induced status epilepticus (SE). However, 30 days after pilocarpine-induced SE, a significant reduction in V_E was observed during hypercapnic (7% CO₂) stimulation, without affecting the hypoxia (8% O₂) ventilatory response. We also did not observe changes in respiratory mechanics. The present results suggest that the impairment of the hypercapnia ventilatory response in pilocarpine-induced SE could be related to a presumable degeneration of brainstem respiratory neurons but not to peripheral mechanisms.

Respiratory mechanics evaluation of mice submitted to intravenous methacholine: Bolus vs. continuous infusion

IMPACT STATEMENT

Respiratory mechanics studies are associated with fundamental research and translational studies; the present work thus investigates this particular matter. Our current research describes differences and similarities between two different ways of administrating a very prevalent bronchoconstrictor (methacholine) in an aging process scenario. The core issue of our work is related with troubles we find with the bolus protocol and the application of the mathematical model used to assess the respiratory mechanics. Our findings reveal the continuous infusion as an alternative to these problems and we hope to provide the proper foundations to a more reliable assessment in the respiratory field.

Neurally adjusted ventilatory assist vs. pressure support to deliver protective mechanical ventilation in patients with acute respiratory distress syndrome: a randomized crossover trial

Background

Protective mechanical ventilation is recommended for patients with acute respiratory distress syndrome (ARDS), but it usually requires controlled ventilation and sedation. Using neurally adjusted ventilatory assist (NAVA) or pressure support ventilation (PSV) could have additional benefits, including the use of lower sedative doses, improved patient–ventilator interaction and shortened duration of mechanical ventilation. We designed a pilot study to assess the feasibility of keeping tidal volume (V_T) at protective levels with NAVA and PSV in patients with ARDS.

Methods

We conducted a prospective randomized crossover trial in five ICUs from a university hospital in Brazil and included patients with ARDS transitioning from controlled ventilation to partial ventilatory support. NAVA and PSV were applied in random order, for 15 min each, followed by 3 h in NAVA. Flow, peak airway pressure (Paw) and electrical activity of the diaphragm (EAdi) were captured from the ventilator, and a software (Matlab, Mathworks, USA), automatically detected inspiratory efforts and calculated respiratory rate (RR) and V_T. Asynchrony events detection was based on waveform analysis.

Results

We randomized 20 patients, but the protocol was interrupted for five (25%) patients for whom we were unable to maintain V_T below 6.5 mL/kg in PSV due to strong inspiratory efforts and for one patient for whom we could not detect EAdi signal. For the 14 patients who completed the protocol, V_T was 5.8 ± 1.1 mL/kg for NAVA and 5.6 ± 1.0 mL/kg for PSV (p = 0.455) and there were no differences in RR (24 ± 7 for NAVA and 23 ± 7 for PSV, p = 0.661). Paw was greater in NAVA (21 ± 3 cmH₂O) than in PSV (19 ± 3 cmH₂O, p = 0.001). Most patients were under continuous sedation during the study. NAVA reduced triggering delay compared to PSV (p = 0.020) and the median asynchrony Index was 0.7% (0–2.7) in PSV and 0% (0–2.2) in NAVA (p = 0.6835).

Conclusions

It was feasible to keep V_T in protective levels with NAVA and PSV for 75% of the patients. NAVA resulted in similar V_T, RR and Paw compared to PSV. Our findings suggest that partial ventilatory assistance with NAVA and PSV is feasible as a protective ventilation strategy in selected ARDS patients under continuous sedation.

Trial registration ClinicalTrials.gov (NCT01519258). Registered 26 January 2012, https://clinicaltrials.gov/ct2/show/NCT01519258

Predictors of oronasal breathing among obstructive sleep apnea patients and controls

Oronasal breathing may adversely impact obstructive sleep apnea (OSA) patients either by increasing upper airway collapsibility or by influencing continuous positive airway pressure (CPAP) treatment outcomes. Predicting a preferential breathing route would be helpful to guide CPAP interface prescription. We hypothesized that anthropometric measurements but not self-reported oronasal breathing are predictors of objectively measured oronasal breathing. Seventeen OSA patients and nine healthy subjects underwent overnight polysomnography with an oronasal mask with two sealed compartments attached to independent pneumotacographs. Subjects answered questionnaires about nasal symptoms and perceived breathing route. Oronasal breathing was more common (P = <0.001) among OSA patients than controls while awake (62 ± 44 vs. 5 ± 6%) and during sleep (59 ± 39 vs. 25 ± 21%, respectively). Oronasal breathing was associated with OSA severity (P = 0.009), age (P = 0.005), body mass index (P = 0.044), and neck circumference (P = 0.004). There was no agreement between objective measurement and self-reported breathing route among OSA patients while awake (κ = -0.12) and asleep (κ = -0.02). The breathing route remained unchanged after 92% of obstructive apneas. These results suggest that oronasal breathing is more common among OSA patients than controls during both wakefulness and sleep and is associated with OSA severity and anthropometric measures. Self-reporting is not a reliable predictor of oronasal breathing and should not be considered an indication for oronasal CPAP.NEW & NOTEWORTHY Continuous positive airway pressure (CPAP) interface choice for obstructive sleep apnea (OSA) patients is often guided by nasal symptoms and self-reported breathing route. We showed that oronasal breathing can be predicted by anthropometric measurements and OSA severity but not by self-reported oronasal breathing. Self-reported breathing and nasal symptoms should not be considered for CPAP interface choice.

De-epithelialization of porcine tracheal allografts as an approach for tracheal tissue engineering

Replacement of large tracheal defects remains an unmet clinical need. While recellularization of acellular tracheal grafts appeared to be a viable pathway, evidence from the clinic suggests otherwise. In hindsight, complete removal of chondrocytes and repopulation of the tracheal chondroid matrix to achieve functional tracheal cartilage may have been unrealistic. In contrast, the concept of a hybrid graft whereby the epithelium is removed and the immune-privileged cartilage is preserved is a radically different path with initial reports indicating potential clinical success. Here, we present a novel approach using a double-chamber bioreactor to de-epithelialize tracheal grafts and subsequently repopulate the grafts with exogenous cells. A 3 h treatment with sodium dodecyl sulfate perfused through the inner chamber efficiently removes the majority of the tracheal epithelium while the outer chamber, perfused with growth media, keeps most (68.6 ± 7.3%) of the chondrocyte population viable. De-epithelialized grafts support human bronchial epithelial cell (BEAS-2B) attachment, viability and growth over 7 days. While not without limitations, our approach suggests value in the ultimate use of a chimeric allograft with intact donor cartilage re-epithelialized with recipient-derived epithelium. By adopting a brief and partial decellularization approach, specifically removing the epithelium, we avoid the need for cartilage regeneration.

Transmission of Oral Pressure Compromises Oronasal CPAP Efficacy in the Treatment of OSA

BACKGROUND

An oronasal mask is frequently used to treat OSA. In contrast to nasal CPAP, the effectiveness of oronasal CPAP varies by unknown mechanisms. We hypothesized that oral breathing and pressure transmission through the mouth compromises oronasal CPAP efficacy.

METHODS

Thirteen patients with OSA, well adapted to oronasal CPAP, were monitored by full polysomnography, pharyngeal pressure catheter, and nasoendoscope. Patients slept with low doses of midazolam, using an oronasal mask with sealed nasal and oral compartments. CPAP was titrated during administration by the oronasal and nasal routes, and was then reduced to induce stable flow limitation and abruptly switched to the alternate route. In addition, tape sealing the mouth was used to block pressure transmission to the oral cavity.

RESULTS

Best titrated CPAP was significantly higher by the oronasal route rather than the nasal route (P = .005), and patients with > 25% oral breathing (n = 5) failed to achieve stable breathing during oronasal CPAP. During stable flow limitation, inspiratory peak flow was lower, driving pressure was higher, upper airway inspiratory resistance was higher, and retropalatal and retroglossal area were smaller by the oronasal rather than nasal route (P < .05 for all comparisons). Differences were observed even among patients with no oral flow and were abolished when tape sealing the mouth was used (n = 6).

CONCLUSIONS

Oral breathing and transmission of positive pressure through the mouth compromise oronasal CPAP.

Respiratory disturbances in a mouse model of Parkinson's disease

NEW FINDINGS

What is the central question of this study? Clinical reports have described and suggested central and peripheral respiratory abnormalities in Parkinson's disease (PD) patients; however, these reports have never addressed the occurrence of these abnormalities in an animal model. What is the main finding and its importance? A mouse model of PD has reduced neurokinin-1 receptor immunoreactivity in the pre-Bӧtzinger complex and Phox2b-expressing neurons in the retrotrapezoid nucleus. The PD mouse has impairments of respiratory frequency and the hypercapnic ventilatory response. Lung collagen deposition and ribcage stiffness appear in PD mice.

ABSTRACT

Parkinson's disease (PD) is a neurodegenerative motor disorder characterized by dopaminergic deficits in the brain. Parkinson's disease patients may experience shortness of breath, dyspnoea, breathing difficulties and pneumonia, which can be linked as a cause of morbidity and mortality of those patients. The aim of the present study was to clarify whether a mouse model of PD could develop central brainstem and lung respiratory abnormalities. Adult male C57BL/6 mice received bilateral injections of 6-hydroxydopamine (10 μg μl^-1 ; 0.5 μl) or vehicle into the striatum. Ventilatory parameters were assessed in the 40 days after induction of PD, by whole-body plethysmography. In addition, measurements of respiratory input impedance (closed and opened thorax) were performed. 6-Hydroxydopamine reduced the number of tyrosine hydroxylase neurons in the substantia nigra pars compacta, the density of neurokinin-1 receptor immunoreactivity in the pre-Bӧtzinger complex and the number of Phox2b neurons in the retrotrapezoid nucleus. Physiological experiments revealed a reduction in resting respiratory frequency in PD animals, owing to an increase in expiratory time and a blunted hypercapnic ventilatory response. Measurements of respiratory input impedance showed that only PD animals with the thorax preserved had increased viscance, indicating that the ribcage could be stiff in this animal model of PD. Consistent with stiffened ribcage mechanics, abnormal collagen deposits in alveolar septa and airways were observed in PD animals. Our data showed that our mouse model of PD presented with neurodegeneration in respiratory brainstem centres and disruption of lung mechanical properties, suggesting that both central and peripheral deficiencies contribute to PD-related respiratory pathologies.

Neurally Adjusted Ventilatory Assist (NAVA) or Pressure Support Ventilation (PSV) during spontaneous breathing trials in critically ill patients: a crossover trial

Background

Neurally Adjusted Ventilatory Assist (NAVA) is a proportional ventilatory mode that uses the electrical activity of the diaphragm (EAdi) to offer ventilatory assistance in proportion to patient effort. NAVA has been increasingly used for critically ill patients, but it has not been evaluated during spontaneous breathing trials (SBT). We designed a pilot trial to assess the feasibility of using NAVA during SBTs, and to compare the breathing pattern and patient-ventilator asynchrony of NAVA with Pressure Support (PSV) during SBTs.

Methods

We conducted a crossover trial in the ICU of a university hospital in Brazil and included mechanically ventilated patients considered ready to undergo an SBT on the day of the study. Patients underwent two SBTs in randomized order: 30 min in PSV of 5 cmH₂O or NAVA titrated to generate equivalent peak airway pressure (Paw), with a positive end-expiratory pressure of 5 cmH₂O. The ICU team, blinded to ventilatory mode, evaluated whether patients passed each SBT. We captured flow, Paw and electrical activity of the diaphragm (EAdi) from the ventilator and used it to calculate respiratory rate (RR), tidal volume (VT), and EAdi. Detection of asynchrony events used waveform analysis and we calculated the asynchrony index as the number of asynchrony events divided by the number of neural cycles.

Results

We included 20 patients in the study. All patients passed the SBT in PSV, and three failed the SBT in NAVA. Five patients were reintubated and the extubation failure rate was 25% (95% CI 9–49%). Respiratory parameters were similar in the two modes: VT = 6.1 (5.5–6.5) mL/Kg in NAVA vs. 5.5 (4.8–6.1) mL/Kg in PSV (p = 0.076) and RR = 27 (17–30) rpm in NAVA vs. 26 (20–30) rpm in PSV, p = 0.55. NAVA reduced AI, with a median of 11.5% (4.2–19.7) compared to 24.3% (6.3–34.3) in PSV (p = 0.033).

Conclusions

NAVA reduces patient-ventilator asynchrony index and generates a respiratory pattern similar to PSV during SBTs. Patients considered ready for mechanical ventilation liberation may be submitted to an SBT in NAVA using the same objective criteria used for SBTs in PSV.

Trial registration

ClinicalTrials.gov (NCT01337271), registered April 12, 2011.

Electronic supplementary material

The online version of this article (10.1186/s12890-017-0484-5) contains supplementary material, which is available to authorized users.

Monitoring the electric activity of the diaphragm during noninvasive positive pressure ventilation: a case report

BACKGROUND

In patients with post-extubation respiratory distress, delayed reintubation may worsen clinical outcomes. Objective measures of extubation failure at the bedside are lacking, therefore clinical parameters are currently used to guide the need of reintubation. Electrical activity of the diaphragm (EAdi) provides clinicians with valuable, objective information about respiratory drive and could be used to monitor respiratory effort.

CASE PRESENTATION

We describe the case of a patient with Chronic Obstructive Pulmonary Disease (COPD), from whom we recorded EAdi during four different ventilatory conditions: 1) invasive mechanical ventilation, 2) spontaneous breathing trial (SBT), 3) unassisted spontaneous breathing, and 4) Noninvasive Positive Pressure Ventilation (NPPV). The patient had been intubated due to an exacerbation of COPD, and after four days of mechanical ventilation, she passed the SBT and was extubated. Clinical signs of respiratory distress were present immediately after extubation, and EAdi increased compared to values obtained during mechanical ventilation. As we started NPPV, EAdi decreased substantially, indicating muscle unloading promoted by NPPV, and we used the EAdi signal to monitor respiratory effort during NPPV. Over the next three days, she was on NPPV for most of the time, with short periods of spontaneous breathing. EAdi remained considerably lower during NPPV than during spontaneous breathing, until the third day, when the difference was no longer clinically significant. She was then weaned from NPPV and discharged from the ICU a few days later.

CONCLUSION

EAdi monitoring during NPPV provides an objective parameter of respiratory drive and respiratory muscle unloading and may be a useful tool to guide post-extubation ventilatory support. Clinical studies with continuous EAdi monitoring are necessary to clarify the meaning of its absolute values and changes over time.

Comparison between the phase angle and phase shift parameters to assess thoracoabdominal asynchrony in COPD patients

Determining the presence of thoracoabdominal asynchrony in chronic obstructive pulmonary disease (COPD) patients is clinically relevant, but there is no consensus on the optimal parameters for performing this analysis. We assessed 22 COPD patients (FEV1 40 ± 10% predicted) and 13 healthy controls during rest and exercise with optoelectronic plethysmography (70% maximum workload) on a cycle ergometer. Thoracoabdominal asynchrony was calculated by using phase angle and phase shift parameters following a three-compartment model involving the upper and lower rib cages and abdomen. Patients were classified as having thoracoabdominal asynchrony (TAA+) or not (TAA−) based on control values (mean ± 2 SDs). The chest wall volume and compartmental contribution were also measured. Thoracoabdominal asynchrony was observed in the lower rib cage. The phase angle detected more TAA+ patients at rest (15 vs. 7 patients) and during exercise (14 vs. 8 patients) compared with the phase shift. TAA+ patients also presented a lower chest wall volume, lower rib cage contribution, and higher abdominal contribution to chest wall volume compared with the control and TAA− patients. Thoracoabdominal asynchrony was more detectable during rest and exercise using the phase angle parameter, and it was observed in the lower rib cage compartment, reducing the chest wall volume during exercise in patients with COPD.

NEW & NOTEWORTHY This study contributes to advance the knowledge over the previous lack of consensus on the assessment of thoracoabdominal asynchrony. We rigorously evaluated the related features that interfere in the measurement of the asynchrony (measurement tool, chest wall model and calculation parameter). Our results suggest that phase angle detects more suitably thoracoabdominal asynchrony that occurs on the lower ribcage and leads to a reduction in the chest wall volume during exercise in COPD patients.

Input respiratory impedance in mice: comparison between the flow-based and the wavetube method to perform the forced oscillation technique

Objective and approach: In this study, we estimated the constant phase model (CPM) parameters from the respiratory impedance of male BALB/c mice by performing the forced oscillation technique (FOT) in a control group (n  =  8) and in a murine model of asthma (OVA) (n  =  10). Then, we compared the results obtained by two different methods, using a commercial equipment (flexiVent-flexiWare 7.X; SCIREQ, Montreal, Canada) (FXV) and a wavetube method equipment (Sly et al 2003 J. Appl. Physiol. 94 1460-6) (WVT). We believe that the results from different methods may not be comparable. First, we compared the results performing a two-way analysis of variance (ANOVA) for the resistance, elastance and tissue damping.

MAIN RESULTS

We found statistically significant differences in all CPM parameters, except for resistance, when comparing Control and OVA groups. When comparing devices, we found statistically significant differences in resistance, while differences in elastance were not observed. For tissue damping, the results from WVT were observed to be higher than those from FXV. Finally, when comparing the relative variation between the CPM parameters of the Control and OVA groups in both devices, no significant differences were observed for all parameters.

SIGNIFICANCE

We then conclude that this assessment can compensate the effect of using different cannulas. Furthermore, tissue damping differences between groups can be compensated, since bronchoconstrictors were not used. Therefore, we believe that relative variations in the results between groups can be a comparing parameter when using different equipment without bronchoconstrictor administration.

Different Craniofacial Characteristics Predict Upper Airway Collapsibility in Japanese-Brazilian and White Men

BACKGROUND

OSA pathogenesis is complex and may vary according to ethnicity. The anatomic component predisposing to OSA is the result of the interaction between bony structure and upper airway soft tissues and can be assessed using passive critical closing pressure (Pcrit). We hypothesized that Japanese-Brazilians and whites present different predictors of upper airway collapsibility, suggesting different causal pathways to developing OSA in these two groups.

METHODS

Male Japanese-Brazilians (n = 39) and whites (n = 39) matched for age and OSA severity were evaluated by full polysomnography, Pcrit, and upper airway and abdomen CT scans for determination of upper airway anatomy and abdominal fat, respectively.

RESULTS

Pcrit was similar between the Japanese-Brazilians and the whites (-1.0 ± 3.3 cm H2O vs -0.4 ± 3.1 cm H2O, P = .325). The Japanese-Brazilians presented smaller upper airway bony dimensions (cranial base, maxillary, and mandibular lengths), whereas the whites presented larger upper airway soft tissue (tongue length and volume) and a greater imbalance between tongue and mandible (tongue/mandibular volume ratio). The cranial base angle was associated with Pcrit only among the Japanese-Brazilians (r = -0.535, P < .01). The tongue/mandibular volume ratio was associated with Pcrit only among the whites (r = 0.460, P < .01). Obesity-related variables (visceral fat, BMI, and neck and waist circumferences) showed a similar correlation with Pcrit in the Japanese-Brazilians and the whites.

CONCLUSIONS

Japanese-Brazilians and whites present different predictors of upper airway collapsibility. Although craniofacial bony restriction influenced Pcrit only in the Japanese-Brazilians, an anatomic imbalance between tongue and mandible volume influenced Pcrit among the whites. These findings may have therapeutic implications regarding how to improve the anatomic predisposition to OSA across ethnicities.

Chronic exposure of diesel exhaust particles induces alveolar enlargement in mice

Background

Diesel exhaust particles (DEPs) are deposited into the respiratory tract and are thought to be a risk factor for the development of diseases of the respiratory system. In healthy individuals, the timing and mechanisms of respiratory tract injuries caused by chronic exposure to air pollution remain to be clarified.

Methods

We evaluated the effects of chronic exposure to DEP at doses below those found in a typical bus corridor in Sao Paulo (150 μg/m³). Male BALB/c mice were divided into mice receiving a nasal instillation: saline (saline; n = 30) and 30 μg/10 μL of DEP (DEP; n = 30). Nasal instillations were performed five days a week, over a period of 90 days. Bronchoalveolar lavage (BAL) was performed, and the concentrations of interleukin (IL)-4, IL-10, IL-13 and interferon-gamma (INF-γ) were determined by ELISA-immunoassay. Assessment of respiratory mechanics was performed. The gene expression of Muc5ac in lung was evaluated by RT-PCR. The presence of IL-13, MAC2+ macrophages, CD3+, CD4+, CD8+ T cells and CD20+ B cells in tissues was analysed by immunohistochemistry. Bronchial thickness and the collagen/elastic fibers density were evaluated by morphometry. We measured the mean linear intercept (Lm), a measure of alveolar distension, and the mean airspace diameter (D0) and statistical distribution (D2).

Results

DEP decreased IFN-γ levels in BAL (p = 0.03), but did not significantly alter IL-4, IL-10 and IL-13 levels. MAC2+ macrophage, CD4+ T cell and CD20+ B cell numbers were not altered; however, numbers of CD3+ T cells (p ≤ 0.001) and CD8+ T cells (p ≤ 0.001) increased in the parenchyma. Although IL-13 (p = 0.008) expression decreased in the bronchiolar epithelium, Muc5ac gene expression was not altered in the lung of DEP-exposed animals. Although respiratory mechanics, elastic and collagen density were not modified, the mean linear intercept (Lm) was increased in the DEP-exposed animals (p ≤ 0.001), and the index D2 was statistically different (p = 0.038) from the control animals.

Conclusion

Our data suggest that nasal instillation of low doses of DEP over a period of 90 days results in alveolar enlargement in the pulmonary parenchyma of healthy mice.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-015-0172-z) contains supplementary material, which is available to authorized users.

Upper airway collapsibility is associated with obesity and hyoid position

STUDY OBJECTIVES

Upper airway anatomy plays a major role in obstructive sleep apnea (OSA) pathogenesis. An inferiorly displaced hyoid as measured by the mandibular plane to hyoid distance (MPH) has been consistently associated with OSA. The hyoid is also a common landmark for pharyngeal length, upper airway volume, and tongue base. Tongue dimensions, pharyngeal length, and obesity are associated with OSA severity, although the link between these anatomical variables and pharyngeal collapsibility is less well known. We hypothesized that obesity as measured by body mass index (BMI), neck and waist circumferences, and variables associated with hyoid position (pharyngeal length, upper airway volume, and tongue dimensions) would be associated with passive pharyngeal critical closing pressure (Pcrit).

DESIGN

Cross-sectional.

SETTING

Academic hospital.

PATIENTS

34 Japanese-Brazilian males age 21 to 70 y.

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

We performed computed tomography scans of the upper airway, overnight polysomnography, and Pcrit measurements in all subjects. On average, subjects were overweight (BMI = 28 ± 4 kg/m(2)) and OSA was moderately severe (apnea-hypopnea index = 29 [13-51], range 1-90 events/h). Factor analysis identified two factors among the studied variables: obesity (extracted from BMI, neck and waist circumferences) and hyoid position (MPH, pharyngeal length, tongue length, tongue volume, and upper airway volume). Both obesity and hyoid position correlated with Pcrit (r = 0.470 and 0.630, respectively) (P < 0.01). In addition, tongue volume, tongue length, pharyngeal length, and MPH correlated with waist and neck circumferences (P < 0.05).

CONCLUSIONS

Pharyngeal critical closing pressure is associated with obesity and hyoid position. Tongue dimensions, pharyngeal length, and the mandibular plane to hyoid distance are associated with obesity variables. These findings provide novel insight into the potential factors mediating upper airway collapse in obstructive sleep apnea.

Diaphragmatic breathing training program improves abdominal motion during natural breathing in patients with chronic obstructive pulmonary disease: a randomized controlled trial

OBJECTIVE

To investigate the effects of a diaphragmatic breathing training program (DBTP) on thoracoabdominal motion and functional capacity in patients with chronic obstructive pulmonary disease.

DESIGN

A prospective, randomized controlled trial.

SETTING

Academic medical center.

PARTICIPANTS

Subjects (N=30; forced expiratory volume in 1s, 42%±13% predicted) were randomly allocated to either a training group (TG) or a control group (CG).

INTERVENTIONS

Subjects in the TG completed a 4-week supervised DBTP (3 individualized weekly sessions), while those in the CG received their usual care.

MAIN OUTCOME MEASURES

Effectiveness was assessed by amplitude of the rib cage to abdominal motion ratio (RC/ABD ratio) (primary outcome) and diaphragmatic mobility (secondary outcome). The RC/ABD ratio was measured using respiratory inductive plethysmography during voluntary diaphragmatic breathing and natural breathing. Diaphragmatic mobility was measured by ultrasonography. A 6-minute walk test and health-related quality of life were also evaluated.

RESULTS

Immediately after the 4-week DBTP, the TG showed a greater abdominal motion during natural breathing quantified by a reduction in the RC/ABD ratio when compared with the CG (F=8.66; P<.001). Abdominal motion during voluntary diaphragmatic breathing after the intervention was also greater in the TG than in the CG (F=4.11; P<.05). The TG showed greater diaphragmatic mobility after the 4-week DBTP than did the CG (F=15.08; P<.001). An improvement in the 6-minute walk test and in health-related quality of life was also observed in the TG.

CONCLUSIONS

DBTP for patients with chronic obstructive pulmonary disease induced increased diaphragm participation during natural breathing, resulting in an improvement in functional capacity.

Cigarette smoke dissociates inflammation and lung remodeling in OVA-sensitized and challenged mice

We evaluated the effects of cigarette smoke (CS) on lung inflammation and remodeling in a model of ovalbumin (OVA)-sensitized and OVA-challenged mice. Male BALB/c mice were divided into 4 groups: non-sensitized and air-exposed (control); non-sensitized and exposed to cigarette smoke (CS), sensitized and air-exposed (OVA) (50 μg+OVA 1% 3 times/week for 3 weeks) and sensitized and cigarette smoke exposed mice (OVA+CS). IgE levels were not affected by CS exposure. The increases in total bronchoalveolar fluid cells in the OVA group were attenuated by co-exposure to CS, as were the changes in IL-4, IL-5, and eotaxin levels as well as tissue elastance (p<0.05). In contrast, only the OVA+CS group showed a significant increase in the protein expression of IFN-γ, VEGF, GM-CSF and collagen fiber content (p<0.05). In our study, exposure to cigarette smoke in OVA-challenged mice resulted in an attenuation of pulmonary inflammation but led to an increase in pulmonary remodeling and resulted in the dissociation of airway inflammation from lung remodeling.

Critical closing pressure during midazolam-induced sleep

The critical closing pressure (Pcrit) is the airway pressure at which the airway collapses and reflects the anatomical contribution to the genesis of obstructive sleep apnea. Pcrit is usually determined during non-rapid eye movement sleep at night, but has been determined under midazolam sedation during the day in the absence of sleep stage monitoring. Indeed, little is known about the effects of midazolam on sleep architecture. Moreover, deeper sedation with midazolam can decrease upper airway muscle activity and increase collapsibility compared with natural sleep. Pcrit under sedation has not been systematically compared with the usual method performed during natural sleep. Therefore, this study aimed to test the hypothesis that Pcrit following low doses of midazolam during the day would be comparable to Pcrit measured during natural sleep in the same patient. Fifteen men (age 54 ± 10 yr, body mass index 30 ± 4 kg/m(2)) with obstructive sleep apnea underwent a baseline standard overnight polysomnogram (apnea-hypopnea index 38 ± 22 events/h, range: 8-66 events/h), and Pcrit was determined during natural sleep and following midazolam. Sleep induction was obtained with low doses of midazolam (2.4 mg, range 2.0-4.4 mg), and sleep architecture was comparable to natural sleep. Natural sleep and induced sleep Pcrit were similar (-0.82 ± -3.44 and -0.97 ± 3.21 cmH(2)O, P = 0.663) and closely associated (intraclass correlation coefficient = 0.92; 95% confidence interval, 0.78-0.97, P < 0.001). Natural and midazolam-induced Pcrit correlated with obstructive sleep apnea severity, indicating that both Pcrit measures provided meaningful physiological information. Pcrit determined during the day with sleep induction is similar to natural overnight sleep and is a valid alternative approach in which to determine Pcrit.

Aerobic exercise attenuates pulmonary injury induced by exposure to cigarette smoke

It has recently been suggested that regular exercise reduces lung function decline and risk of chronic obstructive pulmonary disease (COPD) among active smokers; however, the mechanisms involved in this effect remain poorly understood. The present study evaluated the effects of regular exercise training in an experimental mouse model of chronic cigarette smoke exposure. Male C57BL/6 mice were divided into four groups (control, exercise, smoke and smoke+exercise). For 24 weeks, we measured respiratory mechanics, mean linear intercept, inflammatory cells and reactive oxygen species (ROS) in bronchoalveolar lavage (BAL) fluid, collagen deposition in alveolar walls, and the expression of antioxidant enzymes, matrix metalloproteinase 9, tissue inhibitor of metalloproteinase (TIMP)1, interleukin (IL)-10 and 8-isoprostane in alveolar walls. Exercise attenuated the decrease in pulmonary elastance (p<0.01) and the increase in mean linear intercept (p=0.003) induced by cigarette smoke exposure. Exercise substantially inhibited the increase in ROS in BAL fluid and 8-isoprostane expression in lung tissue induced by cigarette smoke. In addition, exercise significantly inhibited the decreases in IL-10, TIMP1 and CuZn superoxide dismutase induced by exposure to cigarette smoke. Exercise also increased the number of cells expressing glutathione peroxidase. Our results suggest that regular aerobic physical training of moderate intensity attenuates the development of pulmonary disease induced by cigarette smoke exposure.

Short-term exposure of mice to cigarette smoke and/or residual oil fly ash produces proximal airspace enlargements and airway epithelium remodeling

Chronic obstructive pulmonary disease (COPD) is associated with inflammatory cell reactions, tissue destruction and lung remodeling. Many signaling pathways for these phenomena are still to be identified. We developed a mouse model of COPD to evaluate some pathophysiological mechanisms acting during the initial stage of the disease. Forty-seven 6- to 8-week-old female C57/BL6 mice (approximately 22 g) were exposed for 2 months to cigarette smoke and/or residual oil fly ash (ROFA), a concentrate of air pollution. We measured lung mechanics, airspace enlargement, airway wall thickness, epithelial cell profile, elastic and collagen fiber deposition, and by immunohistochemistry transforming growth factor-β1 (TGF-β1), macrophage elastase (MMP12), neutrophils and macrophages. We observed regional airspace enlargements near terminal bronchioles associated with the exposure to smoke or ROFA. There were also increases in airway resistance and thickening of airway walls in animals exposed to smoke. In the epithelium, we noted a decrease in the ciliated cell area of animals exposed to smoke and an increase in the total cell area associated with exposure to both smoke and ROFA. There was also an increase in the expression of TGF-β1 both in the airways and parenchyma of animals exposed to smoke. However, we could not detect inflammatory cell recruitment, increases in MMP12 or elastic and collagen fiber deposition. After 2 months of exposure to cigarette smoke and/or ROFA, mice developed regional airspace enlargements and airway epithelium remodeling, although no inflammation or increases in fiber deposition were detected. Some of these phenomena may have been mediated by TGF-β1.

Respiratory mechanics do not always mirror pulmonary histological changes in emphysema

OBJECTIVE

To verify the accordance of functional and morphometric parameters during the development of emphysema.

METHODS

BALB/c mice received a nasal drop of either papain or saline solution and were studied after 1, 3, 15, 28, and 40 days. Functional parameters, such as airway resistance, tissue damping, and tissue elastance, were analyzed. To evaluate the structural changes and possible mechanisms involved in this disease, we measured the mean linear intercept, the volume proportions of elastic and collagen fibers, the number of macrophages, the numbers of cells expressing metalloprotease 12 and 8-isoprostane in lung parenchyma.

RESULTS

We only observed decreases in tissue elastance and tissue damping on the 28th day, with a concomitant increase in the mean linear intercept, indicating the presence of emphysema. However, only the mean linear intercept values remained increased until the 40th day. The volume proportion of collagen fibers was increased from the 15th day to the 40th day, whereas the volume proportion of elastic fibers was only increased on the 40th day. The number of macrophages increased beginning on the 1st day. The expression of metalloproteinase 12 was increased from the 3rd day until the 40th day. However, 8-isoprostane expression was only increased on the 1st and 3rd days.

CONCLUSIONS

In this study, morphometric parameters were found to be more reliable for detecting the presence of emphysema than the functional parameters measured by respiratory mechanics. Further investigations are necessary to understand how the extracellular matrix remodeling observed in the lung parenchyma could be involved in this process.

Exposure to ambient levels of particles emitted by traffic worsens emphysema in mice

OBJECTIVES

We investigated effects of chronic exposure (2 months) to ambient levels of particulate matter (PM) on development of protease-induced emphysema and pulmonary remodeling in mice.

METHODS

Balb/c mice received nasal drop of either papain or normal saline and were kept in two exposure chambers situated in an area with high traffic density. One of them received ambient air and the other had filters for PM.

RESULTS

mean concentration of PM10 was 2.68 +/- 0.38 and 33.86 +/- 2.09 microg/m3, respectively, in the filtered and ambient air chambers (p < 0.001). After 2 months of exposure, lungs from papain-treated mice kept in the chamber with ambient air presented greater values of mean linear intercept, an increase in density of collagen fibers in alveolar septa and in expression of 8-isoprostane (p = 0.002, p < 0.05 and p = 0.002, respectively, compared to papain-treated mice kept in the chamber with filtered air). We did not observe significant differences between these two groups in density of macrophages and in amount of cells expressing matrix metalloproteinase-12. There were no significant differences in saline-treated mice kept in the two chambers.

CONCLUSIONS

We conclude that exposure to urban levels of PM worsens protease-induced emphysema and increases pulmonary remodeling. We suggest that an increase in oxidative stress induced by PM exposure influences this response. These pulmonary effects of PM were observed only in mice with emphysema.

Effects of residual oil fly ash (ROFA) in mice with chronic allergic pulmonary inflammation

Exposure to particulate matter (PM) air pollution is associated with increased asthma morbidity. Residual oil flash ash (ROFA) is rich in water-soluble transition metals, which are involved in the pathological effects of PM. The objective of this study was to investigate the effects of intranasal administration of ROFA on pulmonary inflammation, pulmonary responsiveness, and excess mucus production in a mouse model of chronic pulmonary allergic inflammation. BALB/c mice received intraperitoneal injections of ovalbumin (OVA) solution (days 1 and 14). OVA challenges were performed on days 22, 24, 26, and 28. After the challenge, mice were intranasally instilled with ROFA. After forty-eight hours, pulmonary responsiveness was performed. Mice were sacrificed, and lungs were removed for morphometric analysis. OVA-exposed mice presented eosinophilia in the bronchovascular space (p < .001), increased pulmonary responsiveness (p < .001), and epithelial remodeling (p = .003). ROFA instillation increased pulmonary responsiveness (p = .004) and decreased the area of ciliated cells in the airway epithelium (p = .006). The combined ROFA instillation and OVA exposure induced a further increase in values of pulmonary responsiveness (p = .043) and a decrease in the number of ciliated cells in the airway epithelium (p = .017). PM exposure results in pulmonary effects that are more intense in mice with chronic allergic pulmonary inflammation.

Creatine supplementation exacerbates allergic lung inflammation and airway remodeling in mice

Creatine supplement is the most popular nutritional supplement, and has various metabolic functions and sports medicine applications. Creatine supplementation increases muscle mass and can decrease muscular inflammation. Some studies have also suggested a beneficial role of creatine supplementation on chronic pulmonary diseases such as chronic obstructive pulmonary disease and cystic fibrosis. Among athletes, the prevalence of asthma is high, and many of these individuals may be taking creatine. However, the effects of creatine supplementation on chronic pulmonary diseases of allergic origin have not been investigated. In the present study, we analyzed the effects of creatine supplementation on a model of chronic allergic lung inflammation. Thirty-one Balb/c mice were divided into four groups: control, creatine (Cr), ovalbumin (OVA), and OVA+Cr. OVA and OVA+Cr groups were sensitized with intraperitoneal injections of OVA on Days 0, 14, 28, and 42. OVA challenge (OVA 1%) and Cr treatment (0.5 g/kg/d) were initiated on Day 21 and lasted until Day 53. We determined the index of hyperresponsiveness, the serum levels of OVA-specific immunoglobulin (Ig)E and IgG(1), and the total and differential cell counts in bronchoalveolar lavage fluid. We also quantified airway inflammation, and the airway density of IL-4+, IL-5+, IL-2+, IFN-gamma+, and insulin-like growth factor (IGF)-1+ cells, collagen and elastic fibers, and airway smooth muscle thickness. Our results showed that creatine in OVA-sensitized mice increased hyperresponsiveness; eosinophilic inflammation; airway density of IL-4+, IL-5+, and IGF-1 inflammatory cells; airway collagen and elastin content; and smooth muscle thickness. The results show that creatine supplementation exacerbates the lung allergic response to OVA through a T helper cell type 2 pathway and increased IGF-1 expression.

Oscillation mechanics of the human lung periphery in asthma

To more precisely measure the mechanical properties of the lung periphery in asthma, we have developed a forced oscillation technique that applies a broad-band flow signal through a wedged bronchoscope. We interpreted the data from four healthy and eight mildly asthmatic subjects in terms of an anatomically accurate computer model of the wedged segment. There was substantial overlap in impedance between the two groups, with resistance (R) showing minimal frequency dependence and elastance (E) showing positive and negative frequency dependence across subjects. After direct instillation of methacholine, R rose in both groups, but compared with healthy subjects, the asthmatic subjects displayed upward, parallel shifts in their dose-response curves. The baseline frequency-response patterns of E were enhanced after methacholine. Frequency dependencies of R and E were well reproduced in two normal subjects by a computational model that employed rigid airways connected to constant-phase tissue units but were better reproduced in the other two normal and three asthmatic subjects when the model employed heterogeneous, peripheral airway narrowing and compliant airways. To capture the frequency dependencies of R and E in the remaining five asthmatic subjects, the model was modified by increasing airway wall stiffness. These results indicate that the lung periphery of mildly asthmatic subjects is not well distinguished from that of healthy subjects by measurement of mechanical impedance at baseline, but group differences are seen after challenge with methacholine. Modeling of the response suggests that variable contributions of airway narrowing and wall compliance are operative in determining overall mechanical impedance of the lung periphery in humans with asthma, likely reflecting the functional consequences of airway inflammation and remodeling.

Nonlinear and frequency-dependent mechanical behavior of the mouse respiratory system

The assessment of the mechanical properties of the respiratory system is typically done by oscillating flow into the lungs via the trachea, measuring the resulting pressure generated at the trachea, and relating the two signals to each other in terms of some suitable mathematical model. If the perturbing flow signal is broadband and not too large in amplitude, linear behavior is usually assumed and the input impedance calculated. Alternatively, some researchers have used flow signals that are narrow band but large in amplitude, and invoked nonlinear lumped-parameter models to account for the relationship between flow and pressure. There has been little attempt, however, to deal with respiratory data that are both broadband and reflective of system nonlinearities. In the present study, we collected such data from mice. To interpret these data, we first developed a time-domain approximation to a widely used model of respiratory input impedance. We then extended this model to include nonlinear resistive and elastic terms. We found that the nonlinear elastic term fit the data better than the linear model or the nonlinear resistance model when amplitudes were large. This model may be useful for detecting overinflation of the lung during mechanical ventilation.

Nonlinearity of respiratory mechanics during bronchoconstriction in mice with airway inflammation

Respiratory system resistance (R) and elastance (E) are commonly estimated by fitting the linear equation of motion P = EV + RV + P0 (Eq. 1) to measurements of respiratory pressure (P), lung volume (V), and flow (V). However, the respiratory system is unlikely to behave linearly under many circumstances. We determined the importance of respiratory system nonlinearities in two groups of mechanically ventilated Balb/c mice [controls and mice with allergically inflamed airways (ova/ova)], by assessing the impact of the addition of nonlinear terms (E2V2 and R2V(V)) on the goodness of model fit seen with Eq. 1. Significant improvement in fit (51.85 +/- 4.19%) was only seen in the ova/ova mice during bronchoconstriction when the E2V2 alone was added. An improvement was also observed with addition of the E2V2 term in mice with both low and high lung volumes ventilated at baseline, suggesting a volume-dependent nonlinearity of E. We speculate that airway closure in the constricted ova/ova mice accentuated the volume-dependent nonlinearity by decreasing lung volume and overdistending the remaining lung.