PHYSIOLOGIC DIAGNOSIS AND FUNCTION IN ASTHMA

Horses With Pasture Asthma Have Airway Remodeling That Is Characteristic of Human Asthma

Severe equine asthma, formerly recurrent airway obstruction (RAO), is the horse counterpart of human asthma, affecting horses maintained indoors in continental climates. Equine pasture asthma, formerly summer pasture RAO, is clinically similar but affects grazing horses during hot, humid conditions in the southeastern United States and United Kingdom. To advance translational relevance of equine pasture asthma to human asthma, histologic features of airway remodeling in human asthma were scored in lung lobes from 15 pasture asthma-affected and 9 control horses of mixed breeds. All noncartilaginous airways were scored using a standardized grading rubric (0-3) in hematoxylin and eosin (HE) and Movat's pentachrome-stained sections; 15 airways were chosen randomly from each lobe for analysis. Logistic regression identified disease, age, and lobe effects on probability of histologic outcomes. Airway smooth muscle (odds ratio [OR] = 2.5, P < .001), goblet cell hyperplasia/metaplasia (OR = 37.6, P < .0001), peribronchiolar elastic system fibers (OR = 4.2, P < .001), peribronchiolar fibrosis (OR = 3.8, P = .01), airway occlusion by mucus/inflammation (OR = 4.2, P = .04), and airway adventitial inflammation (OR = 3.0, P = .01) were significantly greater in diseased airways. A novel complex tissue disorganization, designated terminal bronchiolar remodeling, was overrepresented in diseased airways (OR = 3.7, P < .0001). Distribution of terminal bronchiolar remodeling corresponded to putative sites of air trapping in human asthma, at secondary pulmonary lobules. Age (>15 years) was an independent risk factor for increased peribronchiolar fibrosis, elastic system fibers, and terminal bronchiolar remodeling. Remodeling differed significantly between lung lobes, congruent with nonhomogeneous remodeling in human asthma. Equine pasture asthma recapitulates airway remodeling in human asthma in a manner not achieved in induced animal asthma models, endorsing its translational relevance for human asthma investigation.

Mechanically Ventilating the Severe Asthmatic

The management of the critically ill patients with asthma can be rather challenging. Potentially devastating complications relating to this presentation include hypoxemia, worsening bronchospasm, pulmonary aspiration, tension pneumothorax, dynamic hyperinflation, hypotension, dysrhythmias, and seizures. In contrast to various other pathologies requiring mechanical ventilation, acute asthma is generally associated with better outcomes. This review serves as a practical guide to the physician managing patients with severe acute asthma requiring mechanical ventilation. In addition to specifics relating to endotracheal intubation, we also discuss the interpretation of ventilator graphics, the recommended mode of ventilation, dynamic hyperinflation, permissive hypercapnia, as well as the role of extracorporeal membrane oxygenation and noninvasive mechanical ventilation.

Musculoskeletal dysfunction and pain in adults with asthma

BACKGROUND

The mechanical alterations related to the overload of respiratory muscles observed in adults with persistent asthma might lead to the development of chronic alterations in posture, musculoskeletal dysfunction and pain; however, these changes remain poorly understood.

OBJECTIVE

This study aimed to assess postural alignment, muscle shortening and chronic pain in adults with persistent asthma.

METHODS

This cross-sectional and controlled study enrolled 30 patients with mild (n = 17) and severe (n = 13) persistent asthma. Fifteen non-asthmatic volunteers were also assessed. Asthma was classified by the Global Initiative for Asthma (GINA) guidelines. Postural alignment and muscle shortening were evaluated by head and shoulder positions, chest wall mobility, and posterior (trunk and lower limb) muscle flexibility. In addition, the measures used were previously tested for their reproducibility. Pain complaints were also assessed.

RESULTS

In comparison with non-asthmatic subjects, patients with mild or severe persistent asthma held their head and shoulders more forward and had lower chest wall expansion, decreased shoulder internal rotation, and decreased thoracic spine flexibility. Chronic lower thoracic, cervical, and shoulder pain was significantly increased in patients with mild or severe asthma compared with non-asthmatic subjects (p < 0.05).

CONCLUSION

Adults with persistent asthma have musculoskeletal dysfunction and chronic pain that is independent of the severity of their disease but that might be related to their age at the onset of disease symptoms.

The structural basis of airways hyperresponsiveness in asthma

We hypothesized that structural airway remodeling contributes to airways hyperresponsiveness (AHR) in asthma. Small, medium, and large airways were analyzed by computed tomography in 21 asthmatic volunteers under baseline conditions (FEV1= 64% predicted) and after maximum response to albuterol (FEV1= 76% predicted). The difference in pulmonary function between baseline and albuterol was an estimate of AHR to the baseline smooth muscle tone (BSMT). BSMT caused an increase in residual volume (RV) that was threefold greater than the decrease in forced vital capacity (FVC) because of a simultaneous increase in total lung capacity (TLC). The decrease in FVC with BSMT was the major determinant of the baseline FEV1( P < 0.0001). The increase in RV correlated inversely with the relaxed luminal diameter of the medium airways ( P = 0.009) and directly with the wall thickness of the large airways ( P = 0.001). The effect of BSMT on functional residual capacity (FRC) controlled the change in TLC relative to the change in RV. When the FRC increased with RV, TLC increased and FVC was preserved. When the relaxed large airways were critically narrowed, FRC and TLC did not increase and FVC fell. With critical large airways narrowing, the FRC was already elevated from dynamic hyperinflation before BSMT and did not increase further with BSMT. FEV1/FVC in the absence of BSMT correlated directly with large airway luminal diameter and inversely with the fall in FVC with BSMT. These findings suggest that dynamic hyperinflation caused by narrowing of large airways is a major determinant of AHR in asthma.

Inspiratory flow rates and volumes with the Aerolizer dry powder inhaler in asthmatic children and adults

OBJECTIVE

To assess the peak inspiratory flow rate (PIFR) and forced inspiratory vital capacity (FIVC) through the formoterol (Foradil*) Aerolizer* in patients with mild, moderate and severe asthma.

RESEARCH DESIGN AND METHODS

PIFR and FIVC were assessed in 33 adults and 32 children using a spirometer alone (baseline), a spirometer with an adaptor, and a spirometer with an adaptor and the Aerolizer inhaler (placebo loaded).

RESULTS

Of adult patients using the Aerolizer inhaler, 73% had PIFR values of >100 l/min and 91% had values of >60 l/min. PIFR in adults was reduced from a mean baseline of 283 l/min to 118 l/min through the loaded Aerolizer inhaler. Similarly, 75% of children using the Aerolizer inhaler had PIFR values >80 l/min and 91% had values of > 60 l/min. The mean PIFR in children was reduced from a baseline of 154 l/min to 100 l/min through the loaded Aerolizer inhaler. Only small mean decreases from baseline were observed in FIVC through the loaded Aerolizer inhaler: 8.4% in adults and 3.8% in children. FIVC values of > 2.0 litre were achieved in 82% of adults, and 81% of children achieved FIVC values of >1.5 litre.

CONCLUSIONS

This study, albeit in a relatively small patient population, suggests that most children and adults with asthma can generate PIFRs of > 60 l/min and FIVCs of > 1.5 litre through the Aerolizer inhaler regardless of their disease severity. Such findings compare extremely favourably with other dry powder inhalers.

The ventilatory effects of auto-positive end-expiratory pressure development during cardiopulmonary resuscitation

OBJECTIVE

Auto-positive end-expiratory pressure (auto-PEEP) is a physiologic phenomenon defined as the positive alveolar pressure that exists at the end of expiration. Normally, the alveolar pressure is near zero at the end of expiration. However, certain ventilatory and/or physiologic paradigms can cause the development of auto-PEEP during cardiopulmonary resuscitation (CPR). Auto-PEEP has a detrimental cardiovascular effect similar to that of positive end-expiratory pressure that is intentionally applied to the ventilatory circuit in a mechanically ventilated patient. The connection between auto-PEEP and its cardiovascular effects, however, may go undetected. In this study, the effect that ventilatory factors have on auto-PEEP in a simulation of patients with lung disease undergoing CPR was delineated.

DESIGN

A case control study.

SETTING

Laboratory of a university hospital anesthesia department.

SUBJECTS

A baseline quantification of breathing patterns that occur during CPR was obtained by recording observed respiratory rate and relative tidal volume during treatment of in-hospital cardiac arrests.

MEASUREMENTS AND MAIN RESULTS

A test lung was set up to mimic a series of different airway resistances and lung compliances as would be seen in different types of pulmonary pathology. A sensitivity analysis was performed on each of the factors of respiratory rate, tidal volume, and inspiratory/expiratory ratio as to the effect each of these factors has on the development of auto-PEEP. Our study suggests that in various combinations of airway resistances and lung compliances, auto-PEEP can be generated to substantial levels depending on the methods of ventilation performed.

CONCLUSION

We conclude from our findings that ventilation techniques during CPR may need to be altered to avoid the development of what may be a hemodynamically significant level of auto-PEEP.