Physiologic control. Anatomy and physiology of the airway circulation

Mimicking a Dog's Nose: Scrolling Graphene Nanosheets

Inspired by the densely covered capillary structure inside a dog's nose, we report an artificial nanostructure, i. e., poly(sodium p-styrenesulfonate)-functionalized reduced graphene oxide nanoscrolls (PGNS), with high structural perfection and efficient gas sensing applications. A facile supramolecular assembly is introduced to functionalize graphene with the functional polymer, combined with the lyophilization technique to massively transform the planar graphene-based nanosheets to nanoscrolls. Detailed characterizations reveal that the bioinspired nanoscrolls exhibit a wide-open tubular morphology with uniform dimensions that is structurally distinct from the previously reported ones. The detailed morphologies of the graphene-based nanosheets in each scrolling stage during lyophilization are monitored by cryo-SEM. This unravels an asymmetric polymer-induced graphene scrolling mechanism including the corresponding scrolling process, which is directly presented by molecular dynamics simulations. The fabricated PGNS sensors exhibit superior gas sensing performance with reliable repeatability, excellent linear sensibility, and, especially, an ultrahigh response ( R_a/ R_g = 5.39, 10 ppm) toward NO₂. The supramolecular assembly combined with the lyophilization technique to fabricate PGNS provides a strategy to design biomimetic materials for gas sensors and chemical trace detectors.

Fluid replacement and respiratory function: comparison of whole blood with colloid and crystalloid: A randomised animal study

BACKGROUND

Fluid replacement with blood products, colloids and crystalloids is associated with morbidity and mortality. Despite this, the consequences of fluid administration on airway and respiratory tissue properties are not fully understood.

OBJECTIVE

Comparison of respiratory effects of fluid replacement with autologous blood (Group B), colloid (HES 6% 130/0.4, Group CO) or crystalloid solution (NaCl 0.9%, Group CR) after haemorrhage with separate assessments of airway resistance and respiratory tissue mechanics.

DESIGN

A randomised study.

SETTING

An experimental model of surgical haemorrhage and fluid replacement in rats.

PARTICIPANTS

Anaesthetised, ventilated rats randomly allocated into three groups (Group B: n = 8, Group CO: n = 8, Group CR: n = 9).

INTERVENTION

Animals were bled in six sequential steps, each manoeuvre targeting a loss of 5% of total blood volume. The blood loss was then replaced stepwise in a 1 : 1 ratio with one of the three fluids.

MAIN OUTCOME MEASURE

After each step, airway resistance (Raw), tissue damping and elastance (H) were determined by forced oscillations. Oedema indices from lung weights and histology were also measured.

RESULTS

Raw (mean ± SD) decreased in all groups following blood loss (-20.3 ± 9.5% vs. baseline, P < 0.05), and remained low following blood replacement (-21.7 ± 14.5% vs. baseline, P < 0.05), but was normalised by colloid (5.5 ± 10.7%, NS). Crystalloid administration exhibited an intermediate reversal effect (-8.4 ± 14.7%, NS). Tissue viscoelasticity increased following both blood loss and replacement, with no evidence of a significant difference in H between Groups CO and CR. More severe oedema was observed in Groups CR and CO than in Group B (P < 0.05), with no difference between the colloid and crystalloid solutions.

CONCLUSION

This model, which mimics surgical haemorrhage, yields no evidence of a difference between colloids and crystalloids with regard to the pulmonary consequences of blood volume restoration. Functional changes in the lung should not be a key concern when choosing fluid replacement therapy with these solutions.

Asthma is not only an airway disease, but also a vascular disease

Multiple studies have identified an expansion and morphological dysregulation of the bronchial vascular network in the airways of asthmatics. Increased number, size and density of blood vessels, as well as vascular leakage and plasma engorgement, have been reported in the airways of patients with all grades of asthma from mild to fatal. This neovascularisation is an increasingly commonly reported feature of airway remodelling; however, the pathophysiological impact of the increased vasculature in the bronchial wall and its significance to pulmonary function in asthma are unrecognised at this time. Multiple factors capable of influencing the development and persistence of the vascular network exist within asthmatic airway tissue. These include structural components of the altered extracellular matrix (ECM), imbalance of proteases and their endogenous inhibitors, release of active matrikines and the dysregulated levels of both soluble and matrix sequestered growth factors. This review will explore the features of the asthmatic airway which influence the development and persistence of the increased vascular network, as well as the effect of enhanced tissue perfusion on chronic inflammation and airway dynamics. The response of cells of the airways to the altered vascular profile and the subsequent influence on the features of airway remodelling will also be highlighted. We will explore the failure of current asthma therapeutics in "normalising" this vascular remodelling. Finally, we will summarize the outcomes of recent clinical trials which provide hope that anti-angiogenic therapies may be a potent asthma-resolving class of drugs and provide a new approach to asthma management in the future.

Greater nasal nitric oxide output during inhalation: effects on air temperature and water content

The nose conditions the temperature and humidity of nasal air, and the nasal mucosal vasculature supplies heat and water for these processes. We hypothesize that nitric oxide (NO) modulates these processes through vasoactive effects on nasal mucosal vasculature. We measured the temperature, humidity and NO concentrations of nasal air during inhalation and exhalation across the nose and calculated net heat, water and NO output before (controls, n=7) and after inhibition of NO synthase by topical l-NAME (N=5) in healthy humans. We found that calculated NO output across the nasal passages is approximately three-fold greater during inhalation (503+/-105 nL/min) compared with exhalation (162+/-56 nL/min). Moreover, topical administration of l-NAME decreased nasal air temperature and humidity conditioning and NO output, but these effects were limited to inhalation. We conclude that nasal NO output is greater during inhalation than exhalation in humans. Our findings also support a role of nasal NO in temperature and humidity conditioning of nasal air.

Angiogenesis in paediatric airway disease

A number of characteristic changes occur in the bronchial wall in paediatric airway diseases. The process of remodelling is usually associated with specific changes to the vasculature, resulting in an increase in vessel numbers, vasodilatation, vessel leakage and cellular margination with transmigration to target tissues. This combined action in conditions such as asthma, cystic fibrosis and bronchiolitis lead to airway wall thickening and reduced airflow. Each component of the vascular response has been shown to be controlled by a range of inflammatory mediators and growth factors. These factors are regulated by a complex process involving gene expression, transcription and translation at the molecular level, protein release, binding to matrix elements and receptors on endothelial cells, then the endothelial response itself. A number of commonly used airway medications are potentially capable of modulating the vascular response to inflammatory stimuli. New therapies may be able to improve airflow through better regulation of vessel growth, dilatation and leakage in the airway wall.

Responsiveness of canine bronchial vasculature to excitatory stimuli and to cooling

Changes in bronchial vascular tone, in part due to cooling during ventilation, may contribute to altered control of airflow during airway inflammation, asthma, and exercise-induced bronchoconstriction. We investigated the responses of canine bronchial vasculature to excitatory stimuli and cooling. Electrical stimulation evoked contractions in only some (8 of 88) tissues; these were phentolamine sensitive and augmented by N(omega)-nitro-L-arginine. However, sustained contractions were evoked in all tissues by phenylephrine [concentration evoking a half-maximal response (EC(50)) approximately 2 microM] or the thromboxane A(2) mimetic U-46619 (EC(50) approximately 5 nM) and less so by beta,gamma-methylene-ATP or histamine. Cooling to room temperature markedly suppressed ( approximately 75%) adrenergic responses but had no significant effect against U-46619 responses. Adrenergic responses, but not those to U-46619, were accompanied by an increase in intracellular Ca(2+) concentration. Chelerythrine (protein kinase C antagonist) markedly antagonized adrenergic responses (mean maxima reduced 39% in artery and 86% in vein) but had no significant effect against U-46619, whereas genistein (a nonspecific tyrosine kinase inhibitor) essentially abolished responses to both agonists. We conclude that cooling of the airway wall dramatically interferes with adrenergic control of bronchial perfusion but has little effect on thromboxane-mediated vasoconstriction.

Temperature conditioning of nasal air: effects of vasoactive agents and involvement of nitric oxide

Nitric oxide (NO) is released into nasal air, but its function is unknown. We hypothesized that nasal vascular tone and/or flow influences temperature conditioning of nasal air and that NO participates in this process. We measured nasal air temperature (via a thermocouple) and exhaled nasal NO release (by chemiluminescence) in five humans and examined the effects of an aerosolized vasoconstrictor (oxymetazoline), a vasodilator (papaverine), N(G)-nitro-L-arginine methyl ester, an inhibitor of NO synthase, or saline (control). Compared with saline (which caused no changes in nasal air temperature or exhaled NO release), oxymetazoline (0.05%) reduced nasal air temperature and NO release (130.8 +/- 15.1 to 81.3 +/- 12.8 nl. min(-1). m(-2); P < 0.01). Papaverine (0.01 M) increased nasal air temperature and NO release (131.8 +/- 13.1 to 157.2 +/- 17.4 nl. min(-1). m(-2); P < 0.03). N(G)-nitro-L-arginine methyl ester reduced nasal air temperature and NO release (123.7 +/- 14.2 to 44.2 +/- 23.7 nl. min(-1). m(-2); P < 0.01). The results suggest that vascular tone and/or flow modulates temperature conditioning and that NO may participate in that function.

Eosinophils in the bronchial mucosa in relation to methacholine dose-response curves in atopic asthma

Asthma is characterized by both local infiltration of eosinophils in the bronchial mucosa and bronchial hyperreactivity (BHR). A detailed characterization of BHR implies analysis of a histamine or methacholine dose-response curve yielding not only the dose at 20% fall of baseline forced expiratory volume in 1 s (FEV1), but also a plateau (P) representing the maximal narrowing response in terms of percent change in FEV1 and reactivity as the steepest slope at 50% of P (%FEV1/doubling dose). In the baseline condition, the specific airway conductance (sGaw) may be considered closely related to airway lumen diameter. In 20 nonsmoking asthmatic patients, methacholine dose-response curves were obtained, and a sigmoid model fit yielded the BHR indexes. Immunohistochemistry with the monoclonal antibodies (EG1 and EG2) was used to recognize the total number of eosinophils and activated eosinophils, respectively. The number of activated eosinophils was significantly correlated to both P (r = 0.62; P < 0.05) and sGaw (r = -0.52; P < 0.05), whereas weaker and nonsignificant correlations were found for dose at 20% fall of baseline FEV1 and the total number of eosinophils. We conclude that the number of activated eosinophils can be considered a marker of the inflammation-induced decrease of airway lumen diameter as represented by the plateau index and sGaw.

Innervation of nasal turbinate blood vessels in rhinitic and nonrhinitic children

An immunohistochemical study of the nasal mucosa was done in pediatric patients attending an otorhinolaringology (ORL) clinic. The goal was a comparison between vascular innervation in patients with or without symptoms of chronic rhinitis. All patients had an indication for tonsillectomy prior to their inclusion in this study. Samples were obtained under general anesthesia at the time of programmed surgery and fixed in a paraformaldehyde-picric acid mixture. Cryostat sections were immunostained for the following neuronal markers: protein-gene product 9.5 (PGP), calcitonin gene- related peptide (CGRP), substance P (SP), and C-terminal peptide of neuropeptide Y (CPON). The following classes of vessels were identified: arteries, sinusoids, veins, and arteriovenous anastomoses (AVAs). As shown by immunostaining with the general neuronal marker PGP, each vessel type had a characteristic innervation pattern, differing in the amount of fibers and their distribution within the adventitial and muscle layers. Evaluation of PGP, CPON, and CGRP immunoreactivity patterns indicated that rhinitic arteries and AVAs displayed a richer innervation than did nonrhinitic blood vessels. Quantification of vascular PGP immunostaining confirmed the difference of vascular innervation between nonrhinitic and rhinitic patients. Fibers immunostained by CPON partially accounted for the rhinitic arterial hyperinnervation.

Comparison of the effects of salbutamol and adrenaline on airway smooth muscle contractility in vitro and on bronchial reactivity in vivo

BACKGROUND

The effect of adrenergic agonists in asthma depends on their net effect on microvascular leakage, mucosal oedema, vascular clearance of spasmogens, inhibition of cholinergic neurotransmission, and airway smooth muscle contractility. It has been postulated that adrenaline, by virtue of its alpha effects on the vasculature and cholinergic neurotransmission, may have additional useful properties in asthma compared with selective beta agonists such as salbutamol.

METHODS

The airway effects of adrenaline (a non-selective adrenoreceptor agonist) were compared with the selective beta 2 agonist salbutamol. Their airway smooth muscle relaxant potencies and effect on histamine contraction in human bronchi in vitro were compared with their effects on airway calibre and histamine reactivity in asthmatic subjects in vivo. For the in vitro studies changes in tension were measured in response to these agents in thoracotomy specimens of human airways. In vivo the effects of adrenaline and salbutamol on airway calibre and histamine reactivity were measured in eight subjects with mild to moderate asthma in a randomised crossover study.

RESULTS

Salbutamol and adrenaline had approximately equivalent airway smooth muscle relaxant potencies in vitro and bronchodilator potency in vivo. However, their effects on histamine induced contraction in vitro were significantly different from their effects on histamine reactivity in vivo. Salbutamol was less potent in vitro producing a mean (SE) 2.4 (0.15) doubling dose increase in the histamine EC20 and adrenaline a 5.2 (0.18) doubling dose increase (mean difference between salbutamol and adrenaline 2.8 doubling doses; 95% CI 1.1 to 4.5). Salbutamol had no effect on the maximal response to histamine whereas adrenaline reduced it by 54%. In contrast, salbutamol was more potent in vivo producing a mean (SE) increase in PD20 histamine of 1.84 (0.5) doubling doses whereas adrenaline was without effect increasing PD20 by only 0.06 (0.47) doubling doses (mean difference between adrenaline and salbutamol 1.78, 95% CI 0.26 to 3.29 doubling doses).

CONCLUSIONS

These findings suggest that the alpha adrenergic airway effects of non-selective adrenoreceptor agonists such as adrenaline offer no additional protection against histamine-induced broncho-constriction in vivo than beta 2 selective drugs such as salbutamol, despite adrenaline providing greater protection against histamine-induced contraction in vitro. The differences between the effects of these agents in vitro and in vivo may be related to their opposing vascular effects in vivo.

Studies of human airways in vitro: a review of the methodology

The pathophysiology of human airway narrowing is only partly understood. In order to gain more insight in the mechanisms of human lung diseases and potential beneficial therapeutic agents, adequate models are needed. Animal airway models are of limited value since lung diseases such as asthma and chronic obstructive pulmonary disease (COPD) are unique to humans and because the mechanisms of airway narrowing differ between species. Therefore, it is important to perform studies on human isolated airways. We describe the models that have been developed to study airway function in vitro, emphasizing human airway preparations. The easily prepared airway strip and ring preparations are described first. The potential damage during preparation and the interference with airway structure are important drawbacks in these preparations. Lung parenchymal strips, described next, were designed in order to study responsiveness of small airways. However, parenchymal strips are anatomically complex, and responsiveness is determined by the relative amounts of airway and vascular smooth muscle. The lack of reproducibility between species and even within one animal limits their usefulness. Airway tube preparations, in which luminal and serosal stimulation can be separated, enable us to study the modulatory role of the airways epithelium in vitro. Furthermore, airway compliance can be measured. In the isolated perfused lung preparation, relationships between the airways and the vascular system are preserved and the interaction between these two systems can be studied. Weight gain due to fluid extravasation is a problem in this model which has not been used yet to study human lungs in vitro. Next, methodological aspects such as tissue handling and storage, recording of responses, removal of the epithelium, and electrical field stimulation are discussed in some detail. Although animal airways tissue can be studied immediately after removal, human tissue is often obtained with some delay. However, this seems tenable since electron microscopy of lung tissue obtained at autopsy showed that recovery of the preparation occurs during incubation of carbogenated Krebs-Henseleit (K-H) buffer. Dissected airways can be stored overnight in cooled K-H buffer until up to 55 hr after resection without losing viability. Commonly used physiological salt solutions which bath the tissue contain osmotic molecules, ions important for contractility, glucose as a substrate, and a bicarbonate-carbon dioxide buffer.(ABSTRACT TRUNCATED AT 400 WORDS)