The role of neuronal excitation and inhibition in the pre-Bötzinger complex on the cough reflex in the cat.

Brainstem respiratory neuronal network significantly contributes to cough motor pattern generation. Neuronal populations in the pre-Bötzinger complex (PreBötC) represent a substantial component for respiratory rhythmogenesis. We studied the role of PreBötC neuronal excitation and inhibition on mechanically induced tracheobronchial cough in 15 spontaneously breathing, pentobarbital anesthetized adult cats (35 mg/kg, iv initially). Neuronal excitation by unilateral microinjection of glutamate analog d,l-homocysteic acid resulted in mild reduction of cough abdominal electromyogram (EMG) amplitudes and very limited temporal changes of cough compared with effects on breathing (very high respiratory rate, high amplitude inspiratory bursts with a short inspiratory phase, and tonic inspiratory motor component). Mean arterial blood pressure temporarily decreased. Blocking glutamate-related neuronal excitation by bilateral microinjections of nonspecific glutamate receptor antagonist kynurenic acid reduced cough inspiratory and expiratory EMG amplitude and shortened most cough temporal characteristics similarly to breathing temporal characteristics. Respiratory rate decreased and blood pressure temporarily increased. Limiting active neuronal inhibition by unilateral and bilateral microinjections of GABAA receptor antagonist gabazine resulted in lower cough number, reduced expiratory cough efforts, and prolongation of cough temporal features and breathing phases (with lower respiratory rate). The PreBötC is important for cough motor pattern generation. Excitatory glutamatergic neurotransmission in the PreBötC is involved in control of cough intensity and patterning. GABAA receptor-related inhibition in the PreBötC strongly affects breathing and coughing phase durations in the same manner, as well as cough expiratory efforts. In conclusion, differences in effects on cough and breathing are consistent with separate control of these behaviors.NEW & NOTEWORTHY This study is the first to explore the role of the inspiratory rhythm and pattern generator, the pre-Bötzinger complex (PreBötC), in cough motor pattern formation. In the PreBötC, excitatory glutamatergic neurotransmission affects cough intensity and patterning but not rhythm, and GABAA receptor-related inhibition affects coughing and breathing phase durations similarly to each other. Our data show that the PreBötC is important for cough motor pattern generation, but cough rhythmogenesis appears to be controlled elsewhere.

Phasic inhibition as a mechanism for generation of rapid respiratory rhythms.

Central neural networks operate continuously throughout life to control respiration, yet mechanisms regulating ventilatory frequency are poorly understood. Inspiration is generated by the pre-Bötzinger complex of the ventrolateral medulla, where it is thought that excitation increases inspiratory frequency and inhibition causes apnea. To test this model, we used an in vitro optogenetic approach to stimulate select populations of hindbrain neurons and characterize how they modulate frequency. Unexpectedly, we found that inhibition was required for increases in frequency caused by stimulation of Phox2b-lineage, putative CO2-chemosensitive neurons. As a mechanistic explanation for inhibition-dependent increases in frequency, we found that phasic stimulation of inhibitory neurons can increase inspiratory frequency via postinhibitory rebound. We present evidence that Phox2b-mediated increases in frequency are caused by rebound excitation following an inhibitory synaptic volley relayed by expiration. Thus, although it is widely thought that inhibition between inspiration and expiration simply prevents activity in the antagonistic phase, we instead propose a model whereby inhibitory coupling via postinhibitory rebound excitation actually generates fast modes of inspiration.

The effect of erector spinae plane block on respiratory and analgesic outcomes in multiple rib fractures: a retrospective cohort study.

Regional anaesthesia is often helpful in improving respiratory function and analgesia following multiple rib fractures. The erector spinae plane block has become the technique of choice in our institution due to its relative simplicity and purported safety. The aim of this retrospective cohort study was to determine its effectiveness in improving respiratory and analgesic outcomes. We reviewed electronic medical records of patients with traumatic rib fractures admitted to a level-one trauma centre between January 2016 and July 2017, who also received erector spinae plane blocks. We analysed the following outcomes before and up to 72 h after erector spinae plane blockade: incentive spirometry volume; maximum numerical rating scale static pain scores; and 12-h opioid consumption. Pre- and post-block data were compared. We included 79 patients, 77% of whom received continuous erector spinae plane block for a mean (SD) of 3.7 (1.9) days. The majority (85%) had other associated injuries. Incentive spirometry volumes improved from 784 (694) to 1375 (667) ml (p < 0.01) during the first 24 h following erector spinae plane blockade. Pain scores were reduced from 7.7 (2.5) to 4.7 (3.2) in the first three hours (p < 0.01). Reductions in opioid consumption were observed but did not achieve statistical significance. These improvements were largely sustained for up to 72 h. Mean arterial blood pressure remained unchanged from baseline. In conclusion, erector spinae plane blocks were associated with improved inspiratory capacity and analgesic outcomes following rib fracture, without haemodynamic instability. We propose that it should be considered to be a viable alternative to other regional analgesic techniques when these are not feasible.

Influence of xenon on pulmonary mechanics and lung aeration in patients with healthy lungs.

BACKGROUND: The anaesthetic xenon shows potent organ-protective properties. Due to high density and dynamic viscosity, peak inspiratory pressure (Pmax) increases during xenon application. Thus, barotrauma may counteract organ protection. Accordingly, we investigated the influence of xenon on lung mechanics and lung aeration in patients with normal and reduced thoracic wall compliance. METHODS: After registration and ethical approval, 20 patients free of pulmonary disease undergoing routine xenon-based anaesthesia were mechanically ventilated. The primary outcome variable transpulmonary pressure (Ptp) was determined from plateau pressure and intraoesophageal pressure before and after xenon wash-in. We recorded Pmax, and calculated airway resistance (RAW), and static (Cstat) and dynamic (Cdyn) respiratory compliances. Finally, lung aeration was quantified by electrical impedance tomography-derived centre of ventilation index (CVI) and global inhomogeneity index (GI) in the awake state, before and during xenon. RESULTS: Xenon increased Pmax [20.8 (SD 3) vs 22.6 (3) cm H2O, P<0.001] and RAW [0.9 (0.2) vs 1.4 (0.3) cm H2O litre-1 s, P<0.001], without affecting Ptp [1.5 (4) vs 2.0 (4) cm H2O, P=0.15]. While Cstat remained unchanged, Cdyn was reduced [33.9 (7) vs 31.2 (6) ml (cm H2O)-1, P<0.001). A ventral tidal volume shift after anaesthesia induction [CVI 0.53 (0.03) vs 0.59 (0.04), P<0.001] was unaltered during xenon [CVI 0.59 (0.04), P=0.29]. Homogeneity of lung aeration was also unchanged during xenon [GI 0.37 (0.03) vs 0.37 (0.03), P=0.99]. There were no clinically meaningful differential BMI-related effects. CONCLUSIONS: Xenon increases calculated airway resistance and peak inspiratory pressure without affecting transpulmonary pressure, independent of BMI. CLINICAL TRIAL REGISTRATION: NCT02682758.

Development of an inhalation reference concentration for diethanolamine.

An inhalation reference concentration (RfC) was developed for diethanolamine (DEA), based principally on evaluation of three animal studies (Gamer et al., 1993, 1996, 2008). The RfC (25 µg/m3) was based on statistically significantly increased relative liver weight in female rats in Gamer et al. (2008) as the critical effect. The lower confidence limit on the benchmark dose (BMDL10 of 5.5 mg/m3) was adjusted to a human equivalent concentration and to continuous exposure before dividing the final point of departure (2.3 mg/m3) by a total factor of 90 that considered standard key areas of uncertainty (intrahuman variability, potential interspecies toxicodynamic differences, database limitations). While laryngeal effects observed in Gamer et al. (2008) were also considered as candidate critical effects, evaluation of the adversity and human relevance of rat laryngeal squamous metaplasia and concomitant effects at the various exposure levels resulted in identifying a LOAEL for laryngeal squamous hyperplasia and chronic inflammation that was much higher than the liver weight LOAEL identified. The RfC of 25 µg/m3 is considered health protective for the general population and can be used to evaluate the potential health effects of long-term environmental exposure of the general public (i.e., long-term, ambient air dispersion modelling or monitoring data).

BDNF effects on functional recovery across motor behaviors after cervical spinal cord injury.

Unilateral C2 cervical spinal cord hemisection (SH) disrupts descending excitatory drive to phrenic motor neurons, thereby paralyzing the ipsilateral diaphragm muscle (DIAm) during ventilatory behaviors. Recovery of rhythmic DIAm activity ipsilateral to injury occurs over time, consistent with neuroplasticity and strengthening of spared synaptic inputs to phrenic motor neurons. Localized intrathecal delivery of brain-derived neurotrophic factor (BDNF) to phrenic motor neurons after SH enhances recovery of eupneic DIAm activity. However, the impact of SH and BDNF treatment on the full range of DIAm motor behaviors has not been fully characterized. We hypothesized that all DIAm motor behaviors are affected by SH and that intrathecal BDNF enhances the recovery of both ventilatory and higher force, nonventilatory motor behaviors. An intrathecal catheter was placed in adult, male Sprague-Dawley rats at C4 to chronically infuse artificial cerebrospinal fluid (aCSF) or BDNF. DIAm electromyography (EMG) electrodes were implanted bilaterally to record activity across motor behaviors, i.e., eupnea, hypoxia-hypercapnia (10% O2 and 5% CO2), sighs, airway occlusion, and sneezing. After SH, ipsilateral DIAm EMG activity was evident in only 43% of aCSF-treated rats during eupnea, and activity was restored in all rats after BDNF treatment. The amplitude of DIAm EMG (root mean square, RMS) was reduced following SH during eupnea and hypoxia-hypercapnia in aCSF-treated rats, and BDNF treatment promoted recovery in both conditions. The amplitude of DIAm RMS EMG during sighs, airway occlusion, and sneezing was not affected by SH or BDNF treatment. We conclude that the effects of SH and BDNF treatment on DIAm activity depend on motor behavior. NEW & NOTEWORTHY: This study demonstrates that after unilateral C2 spinal cord hemisection (SH), there are differences in the spontaneous recovery of diaphragm (DIAm) electromyographic activity during ventilatory compared with more forceful, nonventilatory motor behaviors. Furthermore, we show that intrathecal delivery of brain-derived neurotrophic factor (BDNF) at the level of the phrenic motor neuron pool enhances recovery of ipsilateral DIAm activity following SH, exerting main effects on recovery of ventilatory but not higher force, nonventilatory behaviors.

The role of Src & ERK1/2 kinases in inspiratory resistive breathing induced acute lung injury and inflammation.

BACKGROUND: Inspiratory resistive breathing (IRB), a hallmark of obstructive airway diseases, is associated with large negative intrathoracic pressures, due to strenuous contractions of the inspiratory muscles. IRB is shown to induce lung injury in previously healthy animals. Src is a multifunctional kinase that is activated in the lung by mechanical stress. ERK1/2 kinase is a downstream target of Src. We hypothesized that Src is activated in the lung during IRB, mediates ERK1/2 activation and IRB-induced lung injury. METHODS: Anaesthetized, tracheostomized adult rats breathed spontaneously through a 2-way non-rebreathing valve. Resistance was added to the inspiratory port to provide a peak tidal inspiratory pressure of 50% of maximum (inspiratory resistive breathing). Activation of Src and ERK1/2 in the lung was estimated during IRB. Following 6 h of IRB, respiratory system mechanics were measured by the forced oscillation technique and bronchoalveolar lavage (BAL) was performed to measure total and differential cell count and total protein levels. IL-1b and MIP-2a protein levels were measured in lung tissue samples. Wet lung weight to total body weight was measured and Evans blue dye extravasation was estimated to measure lung permeability. Lung injury was evaluated by histology. The Src inhibitor, PP-2 or the inhibitor of ERK1/2 activation, PD98059 was administrated 30 min prior to IRB. RESULTS: Src kinase was activated 30 min after the initiation of IRB. Src inhibition ameliorated the increase in BAL cellularity after 6 h IRB, but not the increase of IL-1ß and MIP-2a in the lung. The increase in BAL total protein and lung injury score were not affected. The increase in tissue elasticity was partly inhibited. Src inhibition blocked ERK1/2 activation at 3 but not at 6 h of IRB. ERK1/2 inhibition ameliorated the increase in BAL cellularity after 6 h of IRB, blocked the increase of IL-1ß and returned Evans blue extravasation and wet lung weight to control values. BAL total protein and the increase in elasticity were partially affected. ERK1/2 inhibition did not significantly change total lung injury score compared to 6 h IRB. CONCLUSIONS: Src and ERK1/2 are activated in the lung following IRB and participate in IRB-induced lung injury.

Evaluation of the effects of olodaterol on exercise endurance in patients with chronic obstructive pulmonary disease: results from two 6-week crossover studies.

BACKGROUND: Two replicate, double-blind, placebo-controlled, 6-week crossover studies assessed the effect of the once-daily long-acting ß2-agonist olodaterol 5 µg and 10 µg on constant work-rate cycle endurance in patients with moderate to very severe chronic obstructive pulmonary disease. METHODS: Patients received placebo, olodaterol 5 µg once daily (QD) and olodaterol 10 µg QD in a randomised order for 6 weeks each, with a 2-week washout period in between. The primary end point was change in endurance time during constant work-rate cycle ergometry to symptom limitation at 75 % maximal work capacity after 6 weeks of treatment (2 h post-dose), based on log10-transformed data. Key secondary end points were inspiratory capacity at isotime and intensity of breathing discomfort at isotime. RESULTS: 151 and 157 patients were randomised and treated in Studies 1222.37 and 1222.38, respectively, with 147 and 154 being included in the full analysis sets. Mean endurance time at week 6 was increased compared to placebo by 14.0 % (Study 1222.37; p < 0.001) and 11.8 % (Study 1222.38; p < 0.01) with olodaterol 5 µg, and by 13.8 % (Study 1222.37; p < 0.001) and 10.5 % (Study 1222.38; p < 0.01) with olodaterol 10 µg. Inspiratory capacity at isotime increased with olodaterol 5 µg (Study 1222.37, 0.182 L, p < 0.0001; Study 1222.38, 0.084 L, p < 0.05) and 10 µg (Study 1222.37, 0.174 L; Study 1222.38, 0.166 L; both studies, p < 0.0001), and breathing discomfort was significantly reduced in Study 1222.37 (olodaterol 5 µg, 0.77 Borg units, p < 0.001; olodaterol 10 µg, 0.63 Borg units, p < 0.01) but not Study 1222.38. CONCLUSIONS: These studies provide further characterisation of the efficacy of olodaterol, showing that improvements in airflow (forced expiratory volume in 1 s) are associated with increases in inspiratory capacity and improvements in exercise endurance time. TRIAL REGISTRATIONS: NCT01040130 (1222.37) and NCT01040793 (1222.38).

A phase IV, single-center, crossover evaluation of the efficacy of an external nasal dilator strip in children with nasal congestion.

BACKGROUND: In the United States and other countries, external nasal dilator strips have been marketed for use by adults and by children ages 5-12 years to improve nasal airflow and provide temporary relief from nasal congestion and stuffiness. OBJECTIVE: The objectives of this exploratory analysis were to assess and correlate objective and subjective measures of efficacy of two nasal strips variants, Kids and adult small/medium (Regular), in children with nasal congestion. The correlation of efficacy for each variant to nose dimensions and age was also explored. METHODS: In a single-center, crossover study, peak nasal inspiratory flow (PNIF) was measured in 40 children with nasal congestion ages 5-12 years before and after application of the nasal strips. Spearman correlations were calculated between objective and subjective measures of efficacy and between efficacy measures, nose dimensions, and age. RESULTS: In the 40 patients who completed the study, both the Kids and the Regular nasal strips worked well and improved the PNIF by 15% (supine position) to 22% (seated position) over baseline. No statistically significant differences in efficacy were found between the two variants of nasal dilator strips. CONCLUSIONS: Use of both the Kids and Regular nasal strips significantly improved the PNIF from baseline in children with nasal congestion, and no new safety signals were observed. There was a slight subjective preference for the Kids nasal strips by the younger children, which indicated that children with smaller noses preferred the Kids nasal strips instead of the larger Regular nasal strips. Clinical trial NCT02113449, www.clinicaltrials.gov.

Dynamic variables and fluid responsiveness in patients for aortic stenosis surgery.

BACKGROUND: Aortic stenosis is the most common valvular disease in developed countries, but it carries an increased mortality during non-cardiac surgery underscoring the importance of adequate hemodynamic management. Further, haemodynamic management of patients immediately after surgery for aortic stenosis can be challenging. Prediction of fluid responsiveness using dynamic variables has not been sufficiently studied in patients for aortic stenosis surgery. METHODS: Observational study evaluating fluid responsiveness on 32 (31 analysed) patients scheduled for aortic valve replacement due to aortic stenosis on mechanical ventilation before and after valve replacement. Increase in stroke volume (oesophagus Doppler) ≥ 15% to a fluid challenge defined fluid responders. RESULTS: Before surgery (31 fluid loads performed in 31 patients), areas under receiver operating characteristics curves (95% confidence intervals) were stroke volume variation (from arterial pulse contour analysis) 0.77 (0.58-0.90), pulse pressure variation 0.75 (0.54-0.90) and Pleth variability index 0.51 (0.31-0.69). After aortic valve replacement (31 fluid loads performed in 23 patients) the values were stroke volume variation 0.90 (0.74-0.98), pulse pressure variation 0.95 (0.80-1.0) and Pleth variability index 0.72 (0.52-0.87). CONCLUSIONS: The arterial pressure-based variables had moderate predictive values before valve replacement, but it predicted fluid responsiveness well postoperatively. Pleth variability index did not predict fluid responsiveness preoperatively, and it had a moderate predictive value postoperatively. These results indicate that arterial pressure-based dynamic variables have limited potential to guide fluid therapy in patients with aortic stenosis. Their ability to guide fluid therapy after aortic valve replacement seems better.

Dopamine receptor 1 modulates the discharge activities of inspiratory and biphasic expiratory neurons via cAMP-dependent pathways.

Dopamine receptor 1 (D(1)R) plays an essential role in regulating respiratory activity in mammals, however, little is known about how this receptor acts to modulate the basic respiratory rhythmogenesis. Here, by simultaneously recording the discharge activities of biphasic expiratory (biphasic E) neurons/inspiratory (I) neurons and the XII nerve rootlets from brainstem slices, we found that the application of D(1)R agonist cis-(±)-1-(aminomethyl)-3,4-dihydro-3-phenyl-1H-2-benzopyran-5,6-diolhydrochloride (A68930, 5 µM), or forskolin, an intracellular cAMP-increasing agent, substantially decreased respiratory cycle and expiratory time of both types of neurons, and elevated the integral amplitude and frequency of XII nerve rootlets discharge. These changes were reversed by subsequent application of their antagonists SCH-23390 and Rp-Adenosine 3',5'-cyclic monophosphorothioate triethylammonium salt hydrate (Rp-cAMPS), respectively. Importantly, after pretreatment with Rp-cAMPS, the effects of A68930 in both types of neurons were blocked, suggestive of a cAMP-dependent action of A68930. Thus, the current study indicates that D(1)R may modulate basic breathing rhythmogenesis via cAMP-dependent mechanisms.

Phosphodiesterase V inhibition reduces airway responsiveness, but does not improve the beneficial effect of deep inspiration.

BACKGROUND: Deep inspirations (DIs) can prevent (bronchoprotection; BP) and reverse (bronchodilation; BD) methacholine (Mch)-induced bronchoconstriction, but this effect is reduced or absent in people with asthma or airways hyperresponsiveness (AHR). The mechanisms of this defect are unknown. OBJECTIVE: To indirectly examine the role of guanosine 3',5'-cyclic monophosphate (cGMP) by testing the hypothesis that the phosphodiesterase (PDE) V inhibitor, sildenafil, would improve DI-induced BP in individuals with AHR. METHODS: Thirty-two individuals were screened and 15 met all the inclusion/exclusion criteria (7 subjects with AHR and 8 healthy subjects). A single-dose Mch challenge inducing a 20% reduction in FEV1 in the absence of DIs was first identified. Thereafter, every study participant had 4 pairs of visits, each pair testing DI-induced BP and BD against the single-dose Mch, with no drug, or pretreatment with 25, 50 and 100 mg of sildenafil, respectively, in consecutive order. RESULTS: Sildenafil did not influence baseline lung function. However, in the absence of DIs, the drug caused a dose-dependent attenuation of the Mch-induced decrease in FEV1 by 17% (median value; 25th percentile: 1, 75th percentile: 16), 35% (-3, 61) and 37% (13, 79) for the 25-, 50- and 100-mg doses, respectively (p = 0.0004). No differences between the two participant groups were found. There were no effects of sildenafil on DI-induced BP or BD. CONCLUSION: We infer from these results that the mechanism responsible for the defective ability of DIs to protect the airways from bronchoconstriction is unlikely to be due to dysregulation of cGMP. Of importance, a potential role for PDE V inhibition as a bronchoprotector treatment needs to be explored.

Rho-kinase inhibition attenuates airway responsiveness, inflammation, matrix remodeling, and oxidative stress activation induced by chronic inflammation.

Several studies have demonstrated the importance of Rho-kinase in the modulation of smooth muscle contraction, airway hyperresponsiveness, and inflammation. However, the effects of repeated treatment with a specific inhibitor of this pathway have not been previously investigated. We evaluated the effects of repeated treatment with Y-27632, a highly selective Rho-kinase inhibitor, on airway hyperresponsiveness, oxidative stress activation, extracellular matrix remodeling, eosinophilic inflammation, and cytokine expression in an animal model of chronic airway inflammation. Guinea pigs were subjected to seven ovalbumin or saline exposures. The treatment with Y-27632 (1 mM) started at the fifth inhalation. Seventy-two hours after the seventh inhalation, the animals' pulmonary mechanics were evaluated, and exhaled nitric oxide (E(NO)) was collected. The lungs were removed, and histological analysis was performed using morphometry. Treatment with Y-27632 in sensitized animals reduced E(NO) concentrations, maximal responses of resistance, elastance of the respiratory system, eosinophil counts, collagen and elastic fiber contents, the numbers of cells positive for IL-2, IL-4, IL-5, IL-13, inducible nitric oxide synthase, matrix metalloproteinase-9, tissue inhibitor of metalloproteinase-1, transforming growth factor-ß, NF-κB, IFN-γ, and 8-iso-prostaglandin F2α contents compared with the untreated group (P < 0.05). We observed positive correlations among the functional responses and inflammation, remodeling, and oxidative stress pathway activation markers evaluated. In conclusion, Rho-kinase pathway activation contributes to the potentiation of the hyperresponsiveness, inflammation, the extracellular matrix remodeling process, and oxidative stress activation. These results suggest that Rho-kinase inhibitors represent potential pharmacological tools for the control of asthma.

The airflow resistance sensing threshold during tidal breathing rises in old age in patients with asthma.

BACKGROUND: in a previous study, we showed that the ability to detect a rise in airflow resistance at rest was reduced in some non-asthmatic subjects in old age. OBJECTIVE: to determine whether airflow resistance detection is attenuated in elderly subjects with asthma. METHODS: we studied 60 adult subjects with stable asthma (age range 20-88). Progressive external airflow resistance loading was used to measure the inspiratory load detection threshold (LDT) during tidal breathing at rest. RESULTS: the mean inspiratory LDT was 5.57 (4.33 SD) kPa.s/l in the 20-64 age group (n=32) and 15.6 (10.1 SD) kPa.s/l in those aged 65 and above (n=28) (P<0.0001). The inspiratory LDT was significantly correlated with age (r=0.5246, P<0.00008), mainly due to the effect of higher LDTs in about half of the subjects above the age of 65 years. Expiratory LDT values and correlations were very similar to inspiratory values. CONCLUSIONS: the threshold for detecting external resistive loads during tidal breathing rises in old age in some, but not all, asthmatic patients as was observed in non-asthmatic subjects. The finding has implications for treatment guidelines because some elderly subjects are likely to have reduced awareness of worsening airflow obstruction, and consequently delay their use of rescue treatments.

Glia contribute to the purinergic modulation of inspiratory rhythm-generating networks.

Glia modulate neuronal activity by releasing transmitters in a process called gliotransmission. The role of this process in controlling the activity of neuronal networks underlying motor behavior is unknown. ATP features prominently in gliotransmission; it also contributes to the homeostatic ventilatory response evoked by low oxygen through mechanisms that likely include excitation of preBötzinger complex (preBötC) neural networks, brainstem centers critical for breathing. We therefore inhibited glial function in rhythmically active inspiratory networks in vitro to determine whether glia contribute to preBötC ATP sensitivity. Glial toxins markedly reduced preBötC responses to ATP, but not other modulators. Furthermore, since preBötC glia responded to ATP with increased intracellular Ca(2+) and glutamate release, we conclude that glia contribute to the ATP sensitivity of preBötC networks, and possibly the hypoxic ventilatory response. Data reveal a role for glia in signal processing within brainstem motor networks that may be relevant to similar networks throughout the neuraxis.

Purinergic modulation of preBötzinger complex inspiratory rhythm in rodents: the interaction between ATP and adenosine.

ATP signalling in the CNS is mediated by a three-part system comprising the actions of ATP (and ADP) at P2 receptors (P2Rs), adenosine (ADO) at P1 receptors (P1Rs), and ectonucleotidases that degrade ATP into ADO. ATP excites preBötzinger complex (preBötC) inspiratory rhythm-generating networks where its release attenuates the hypoxic depression of breathing. Its metabolite, ADO, inhibits breathing through unknown mechanisms that may involve the preBötC. Our objective is to understand the dynamics of this signalling system and its influence on preBötC networks. We show that the preBötC of mouse and rat is sensitive to P2Y(1) purinoceptor (P2Y(1)R) activation, responding with a >2-fold increase in frequency. Remarkably, the mouse preBötC is insensitive to ATP. Only after block of A(1) ADORs is the ATP-evoked, P2Y(1)R-mediated frequency increase observed. This demonstrates that ATP is rapidly degraded to ADO, which activates inhibitory A(1)Rs, counteracting the P2Y(1)R-mediated excitation. ADO sensitivity of mouse preBötC was confirmed by a frequency decrease that was absent in rat. Differential ectonucleotidase activities are likely to contribute to the negligible ATP sensitivity of mouse preBötC. Real-time PCR analysis of ectonucleotidase isoforms in preBötC punches revealed TNAP (degrades ATP to ADO) or ENTPDase2 (favours production of excitatory ADP) as the primary constituent in mouse and rat, respectively. These data further establish the sensitivity of this vital network to P2Y(1)R-mediated excitation, emphasizing that individual components of the three-part signalling system dramatically alter network responses to ATP. Data also suggest therapeutic potential may derive from methods that alter the ATP-ADO balance to favour the excitatory actions of ATP.

Airway resistance at maximum inhalation as a marker of asthma and airway hyperresponsiveness.

BACKGROUND: Asthmatics exhibit reduced airway dilation at maximal inspiration, likely due to structural differences in airway walls and/or functional differences in airway smooth muscle, factors that may also increase airway responsiveness to bronchoconstricting stimuli. The goal of this study was to test the hypothesis that the minimal airway resistance achievable during a maximal inspiration (R(min)) is abnormally elevated in subjects with airway hyperresponsiveness. METHODS: The R(min) was measured in 34 nonasthmatic and 35 asthmatic subjects using forced oscillations at 8 Hz. R(min) and spirometric indices were measured before and after bronchodilation (albuterol) and bronchoconstriction (methacholine). A preliminary study of 84 healthy subjects first established height dependence of baseline R(min) values. RESULTS: Asthmatics had a higher baseline R(min) % predicted than nonasthmatic subjects (134 ± 33 vs. 109 ± 19 % predicted, p = 0.0004). Sensitivity-specificity analysis using receiver operating characteristic curves indicated that baseline R(min) was able to identify subjects with airway hyperresponsiveness (PC20 < 16 mg/mL) better than most spirometric indices (Area under curve = 0.85, 0.78, and 0.87 for R(min) % predicted, FEV1 % predicted, and FEF25-75 % predicted, respectively). Also, 80% of the subjects with baseline R(min) < 100% predicted did not have airway hyperresponsiveness while 100% of subjects with R(min) > 145% predicted had hyperresponsive airways, regardless of clinical classification as asthmatic or nonasthmatic. CONCLUSIONS: These findings suggest that baseline R(min), a measurement that is easier to perform than spirometry, performs as well as or better than standard spirometric indices in distinguishing subjects with airway hyperresponsiveness from those without hyperresponsive airways. The relationship of baseline R(min) to asthma and airway hyperresponsiveness likely reflects a causal relation between conditions that stiffen airway walls and hyperresponsiveness. In conjunction with symptom history, R(min) could provide a clinically useful tool for assessing asthma and monitoring response to treatment.

Effect of heliox on heart rate kinetics and dynamic hyperinflation during high-intensity exercise in COPD.

Respiratory mechanical abnormalities in patients with chronic obstructive pulmonary disease (COPD) may impair cardiodynamic responses and slow down heart rate (HR) kinetics compared with normal resulting in reduced convective oxygen delivery during exercise. We reasoned that heliox breathing (79% helium-21% oxygen) and the attendant reduction of operating lung volumes should accelerate HR kinetics in the transition from rest to high-intensity exercise. Eleven male ambulatory patients with clinically stable COPD undertook constant work-rate cycle testing at 80% of each individuals' maximum work capacity while breathing room air (RA) or heliox (HX), randomly. Mean response time (MRT) for HR and dynamic end-expiratory lung volume (EELV) were measured. Resting EELV was not affected by HX breathing, while exercise EELV decreased significantly by 0.23 L at isotime during HX breathing compared with RA. During HX breathing, MRT for HR significantly accelerated (p = 0.002) by an average of 20 s (i.e., 17%). Speeded MRT for HR correlated with indices of reduced lung hyperinflation, such as EELV at isotime (r = 0.88, p = 0.03), and with improved exercise endurance time (r = -0.64, p = 0.03). The results confirm that HX-induced reduction of dynamic lung hyperinflation is associated with consistent improvement in indices of cardio-circulatory function such as HR kinetics in the rest-to-exercise transition in COPD patients.

A quantitative method for estimating dermal benzene absorption from benzene-containing hydrocarbon liquids.

This study examines a method for estimating the dermal absorption of benzene contained in hydrocarbon liquids that contact the skin. This method applies to crude oil, gasoline, organic solvents, penetrants, and oils. The flux of benzene through occluded skin as a function of the percent vol/vol benzene in the liquid is derived by fitting a curve to experimental data; the function is supralinear at benzene concentrations < or = 5% vol/vol. When a liquid other than pure benzene is on nonoccluded skin, benzene may preferentially evaporate from the liquid, which thereby decreases the benzene flux. We present a time-averaging method here for estimating the reduced dermal flux during evaporation. Example calculations are presented for benzene at 2% vol/vol in gasoline, and for benzene at 0.1% vol/vol in a less volatile liquid. We also discuss other factors affecting dermal absorption.

A method for measuring the molecular ratio of inhalation to exhalation and effect of inspired oxygen levels on oxygen consumption.

Using a new method for measuring the molecular ratio (R) of inhalation to exhalation, we investigated the effect of high fraction of inspired oxygen (FIO2) on oxygen consumption (VO2), carbon dioxide generation (VCO2), and respiratory quotient (RQ) in mechanically ventilated rats. Twelve rats were equally assigned into two groups by anesthetics: intravenous midazolam/fentanyl vs. inhaled isoflurane. R, VO2, VCO2, and RQ were measured at FIO2 0.3 or 1.0. R error was ± 0.003. R was 1.0099 ± 0.0023 with isoflurane and 1.0074 ± 0.0018 with midazolam/fentanyl. R was 1.0081 ± 0.0017 at an FIO2 of 0.3 and 1.0092 ± 0.0029 at an FIO2 of 1.0. There were no differences in VCO2 among the groups. VO2 increased at FIO2 1.0, which was more notable when midazolam/fentanyl was used (isoflurane-FIO2 0.3: 15.4 ± 1.1; isoflurane-FIO2 1.0: 17.2 ± 1.8; midazolam/fentanyl-FIO2 0.3: 15.4 ± 1.1; midazolam/fentanyl-FIO2 1.0: 21.0 ± 2.2 mL/kg/min at STP). The RQ was lower at FIO2 1.0 than FIO2 0.3 (isoflurane-FIO2 0.3: 0.80 ± 0.07; isoflurane-FIO2 1.0: 0.71 ± 0.05; midazolam/fentanyl-FIO2 0.3: 0.79 ± 0.03; midazolam/fentanyl-FIO2 1.0: 0.59 ± 0.04). R was not affected by either anesthetics or FIO2. Inspired 100% O2 increased VO2 and decreased RQ, which might be more remarkable when midazolam/fentanyl was used.