Variable ventilation decreases airway responsiveness and improves ventilation efficiency in a rat model of asthma

The protective effect of inhaled corticosteroid on lung inflammation and breathing pattern complexity in a rat model of asthma

Asthma is a heterogeneous disease in which the complexity of the breathing pattern reduces as the severity of the disease increases. Since the pathophysiological basis of reduced breathing pattern complexity in asthma is unclear, in this study, we investigated the effect of reducing inflammation using an inhaled corticosteroid (fluticasone propionate) on the breathing pattern of a rat model of asthma. Detrended fluctuation analysis, sample entropy, and cross-sample entropy analysis of both inter-breath interval and respiratory volume time series showed that early treatment with inhaled corticosteroids not only diminishes lung inflammation and airway hyper-responsiveness, but also has a protective effect against the reduction of breathing pattern complexity due to asthma. However, late treatment had a partial effect on asthma-induced respiratory pattern changes. Since inflammation is a key factor in shifting breathing dynamics away from normal fluctuations, these findings further emphasize the importance of early treatment of asthma with corticosteroids.

Corticosteroid treatment attenuates anxiety and mPFC-amygdala circuit dysfunction in allergic asthma

AIMS

Allergic asthma is associated with anxiety-related behaviors, leading to poor quality of life. Previous studies mainly described the neuropathophysiology of asthma-induced anxiety. However, the effects of corticosteroids, the most common anti-inflammatory agents for asthma treatment, on the neurophysiological foundations of allergic asthma-induced anxiety are unexplored.

MAIN METHODS

Here, we evaluated lung and brain inflammation as well as anxiety in an animal model of allergic asthma pretreated with inhaled fluticasone propionate. Furthermore, to define the neurophysiological bases of these conditions, we studied the medial prefrontal cortex (mPFC)-amygdala circuit, which is previously shown to accompany asthma-induced anxiety.

KEY FINDINGS

Our data showed that allergen induces anxiety, mPFC and amygdala inflammation, as well as disruptions in the local and long-range oscillatory activities within the mPFC-amygdala circuit. Interestingly, we observed a roughly consistent trend of changes with inhaled fluticasone pretreatment. Namely, the asthma-induced behavioral, inflammatory, and neurophysiological changes were partly, but not totally, prevented by inhaled fluticasone pretreatment.

SIGNIFICANCE

We suggest that early treatment of asthmatic patients with inhaled corticosteroids improves mPFC-amygdala circuit function by attenuating neuroinflammation leading to reduced anxiety. These findings could lead clinical guidelines of asthma to consider the neuropsychiatric disorders of patients in treatment recommendations.

ACC-BLA functional connectivity disruption in allergic inflammation is associated with anxiety

Allergic asthma is a chronic inflammatory respiratory disease. Psychiatric disorders, including anxiety are associated with poorer treatment response and disease control in asthmatic patients. To date, there is no experimental evidence describing the role of peripheral inflammation on the oscillatory activities in the anterior cingulate cortex (ACC) and basolateral amygdala (BLA), two major brain structures modulating anxiety. In the present work we evaluated lung and brain inflammatory responses, anxiety-like behavior, in association with oscillatory features of the ACC-BLA circuit in an animal model of allergic inflammation. Our data showed that allergic inflammation induced anxiety-like behavior and reactivation of microglia and astrocytes in ACC and BLA. Allergic inflammation also enhanced neuronal activities and functional connectivity of the ACC-BLA circuit which were correlated with the level of anxiety. Together, we suggest that disruption in the dynamic oscillatory activities of the ACC-BLA circuit, maybe due to regional inflammation, is an underlying mechanism of allergic asthma-induced anxiety-like behavior. Our findings could pave the way for better understanding the neuro-pathophysiology of the psychiatric disorders observed in asthmatic patients, possibly leading to develop novel treatment strategies.

Paternal preconception exposure to chronic morphine alters respiratory pattern in response to morphine in male offspring

The clinical use of opioids is restricted by its deleterious impacts on respiratory system. Gaining a better understanding of an individual's susceptibility to adverse opioid effects is important to recognize patients at risk. Ancestral drug addiction has been shown to be associated with alterations in drug responsiveness in the progenies. In the current study, we sought to evaluate the effects of preconception paternal morphine consumption on respiratory parameters in response to acute morphine in male offspring during adulthood, using plethysmography technique. Male Wistar rats administered 10 days of increasing doses of morphine in the period of adolescence. Thereafter, following a 30-day abstinence time, adult males copulated with naïve females. The adult male offspring were examined for breathing response to morphine. Our results indicated that sires who introduce chronic morphine during adolescence leads to increase irregularity of respiratory pattern and asynchronization between inter-breath interval (IBI) and respiratory volume (RV) time series in male offspring. These findings provide evidence that chronic morphine use by parents even before pregnancy can affect respiratory pattern and response to morphine in the offspring.

Rhythmic air-puff into nasal cavity modulates activity across multiple brain areas: A non-invasive brain stimulation method to reduce ventilator-induced memory impairment

Mechanical ventilation (MV) can result in long-term brain impairments that are resistant to treatment. The mechanisms underlying MV-induced brain function impairment remain unclear. Since nasal airflow modulates brain activity, here we evaluated whether reinstating airflow during MV could influence the memory performance of rats after recovery. Rats were allocated into two study groups: one group received rhythmic air-puff into the nasal cavity during MV and a control group that underwent ventilation without air-puff. During MV, air-puffs induced time-locked event potentials in OB, mPFC and vHPC and significantly increased the oscillatory activity at the air-puff frequency. Furthermore, in mPFC and vHPC, (but not in OB), delta and theta oscillations were more prominent during air-puff application. After recovery, working memory performance was significantly higher in the air-puff group compared to control. Our study thus suggests a promising non-invasive brain stimulation approach to alleviate the neurological complications of prolonged mechanical ventilation.

Physiologically variable ventilation in a rabbit model of asthma exacerbation

BACKGROUND

Mechanical ventilation during status asthmaticus is challenging and increases the risk of severe complications. We recently reported the value of physiologically variable ventilation (PVV) in healthy and acutely injured lungs. We investigated whether PVV provides benefits compared with pressure-controlled ventilation (PCV) in an experimental model of severe acute asthma.

METHODS

Allergen-sensitised rabbits were anaesthetised and randomised to either PCV (n=10) or PVV (n=12) during sustained bronchoconstriction induced by allergen and cholinergic stimuli for 6 h. The PVV pattern was generated from pre-recorded spontaneous breathing. Ventilation parameters, oxygenation index (PaO₂/FiO₂), and respiratory mechanics were measured hourly. Histological injury and inflammation were quantified after 6 h of ventilation.

RESULTS

PVV resulted in lower driving pressures (13.7 cm H₂O [12.5-14.9], mean [95% confidence interval]), compared with pressure-controlled ventilation (17.6 cm H₂O [15.4-19.8]; P=0.002). PVV improved PaO₂/FiO₂ (PVV: 55.1 kPa [52-58.2]; PCV: 45.6 kPa [39.3-51.9]; P=0.018) and maintained tissue elastance (PVV: +8.7% [-0.6 to 18]; PCV: -11.2% [-17.3 to -5.1]; P=0.03). PVV resulted in less lung injury as assessed by lower histological injury score (PVV: 0.65 [0.62-0.65]; PCV: 0.71 [0.69-0.73]; P=0.003), cell count (PVV: 247 10⁴ ml^-1 [189-305]; PCV: 447 10⁴ ml^-1 [324-570]; P=0.005), and protein concentration in bronchoalveolar lavage fluid (PVV: 0.14 μg ml^-1 [0.10-0.18]; PCV: 0.21 μg ml^-1 [0.15-0.27]; P=0.035).

CONCLUSIONS

Applying physiological variable ventilation in a model of asthma exacerbation led to improvements in gas exchange, ventilatory pressures, and respiratory tissue mechanics, and reduced lung injury. A global reduction in lung shear stress and recruitment effects may explain the benefits of PVV in status asthmaticus.

Allergen-induced anxiety-like behavior is associated with disruption of medial prefrontal cortex - amygdala circuit

Anxiety is prevalent in asthma, and is associated with disease severity and poor quality of life. However, no study to date provides direct experimental evidence for the effect of allergic inflammation on the structure and function of medial prefrontal cortex (mPFC) and amygdala, which are essential regions for modulating anxiety and its behavioral expression. We assessed the impact of ovalbumin (OVA)-induced allergic inflammation on the appearance of anxiety-like behavior, mPFC and amygdala volumes using MRI, and the mPFC-amygdala circuit activity in sensitized rats. Our findings exhibited that the OVA challenge in sensitized rats induced anxiety-like behavior, and led to more activated microglia and astrocytes in the mPFC and amygdala. We also found a negative correlation between anxiety-like behavior and amygdala volume. Moreover, OVA challenge in sensitized rats was associated with increases in mPFC and amygdala activity, elevation of amygdala delta-gamma coupling, and the enhancement of functional connectivity within mPFC-amygdala circuit – accompanied by an inverted direction of information transferred from the amygdala to the mPFC. We indicated that disrupting the dynamic interactions of the mPFC-amygdala circuit may contribute to the induction of anxiety-related behaviors with asthma. These findings could provide new insight to clarify the underlying mechanisms of allergic inflammation-induced psychiatric disorders related to asthma.

The effect of fractal-like mechanical ventilation on vital signs in a rat model of acute-on-chronic liver failure

OBJECTIVE

The network of interactions between different organs is impaired in liver cirrhosis. Liver cirrhosis is associated with multi-system involvement, which eventually leads to multiple organ failure. This process is accelerated by a precipitating factor such as bacterial infection, which leads to respiratory distress, circulatory shock, neural dysfunction and very high mortality. Cirrhotic patients often have blunted respiratory sinus arrhythmia and impaired cardio-respiratory variability. Fractal-like mechanical ventilation is reported to enhance respiratory sinus arrhythmia and attenuate respiratory distress in experimental models. In the present study we hypothesise that fractal-like mechanical ventilation may improve the outcome of cirrhotic rats with multiple organ failure.

APPROACH

Cirrhosis was induced by chronic biliary obstruction in rats. Acute multiple organ failure was induced by intraperitoneal injection of bacterial endotoxin in cirrhotic rats. The effect of conventional mechanical ventilation (with constant tidal volume and respiratory rate) or fractal-like ventilation (with the same average but variable tidal volume and respiratory rate) were assessed on vital signs, oxygen saturation and plasma alanine aminotransferase in anaesthetised cirrhotic rats.

MAIN RESULTS

We demonstrated that fractal-like mechanical ventilation was accompanied by improved oxygen saturation, reduced heart rate and decreased liver injury following injection of bacterial endotoxin. Moreover, variable mechanical ventilation in cirrhotic rats reduced mortality and prevented a fall in short-term heart rate variability following endotoxin challenge in comparison with rats with constant mechanical ventilation.

SIGNIFICANCE

We suggest further investigations into the beneficial effects of fractal-like ventilation strategy in critically ill patients with liver failure requiring organ support and mechanical ventilation.