Airway collapse

The therapy for IRDS includes mechanical ventilation with continuous positive airway pressure. This maintains adequate ventilation and prevents airway collapse between breaths with the formation of atelectasis. Therapy also includes administration of exogenous pulmonary surfactant. Two types of surfactants are used to prevent and treat IRDS in the U.S. These include surfactants prepared from animal sources as well as synthetic surfactants. Exogenous pulmonary surfactants are administered as a suspension (in saline) through the endotracheal tube used for mechanical ventilation. 

Figure 17.3 Airway obstruction, (a) Normal, patent airway with radial traction offered to it by surrounding airways. Resistance in this airway is low and air flows through it freely, (b) The airway is obstructed by the presence of excess mucus and airway resistance is increased. Airflow is reduced, (c) Thickening of the airway wall due to inflammation or edema narrows the lumen of the airway. The decrease in airway radius increases airway resistance and decreases airflow, (d) Destruction of surrounding airways results in the loss of interdependence, or radial traction. Without the structural support offered by surrounding airways, the central airway collapses and airflow through it is reduced.

The 5-HT2a/2c receptor agonist [ ]-2,5-dimethoxy-4-iodoaminophentamine improved upper airway collapsibility in Zucker rats, but had complex other effects, including increasing upstream airways resistance, while maintaining unchanged maximal airflow [51]. Studies in humans are not available at this time. 

Kirkness JP, Madronio M, Stavrinou R, Wheatley JR, Amis TC (2003) Relationship between surface tension of upper airway lining liquid and upper airway collapsibility during sleep in obstructive sleep apnea hypopnea syndrome. J Appl Physiol 95 1761— 1766... 

Schwartz AR, Gold AR, Schubert N, Stryzak A, Wise RA, Permutt S, Smith PL (1991) Effect of weight loss on upper airway collapsibility in obstructive sleep apnea. Am Rev Resp Dis 144(3 Pt 1) 494-498... 

Currently, three indices of airway collapse and air trapping are used. One... 

Airway resistance during inspiration is increased in patients with asthma, bronchitis, and upper respiratory tract infections. Expiratory resistance is elevated in patients with emphysema, since the causes of increased expiratory airway resistance are decreased driving pressures and the airway collapse. Airway resistance also may be used to determine the response of obstructed patients to bronchodilator medications. 

Hautmann H, Huber RM (1996) Stent flexibility an essential feature in the treatment of dynamic airway collapse. Eur Respir J 9 609-611... 

Baroni RH, Feller-Kopman D, Nishino M et al. (2005) Tracheobronchomalacia comparison between end-expiratory and dynamic expiratory CT for evatotion of central airway collapse. Radiology 235 635-641 Berger P, Laurent F, Begueret H etal. (2003) Structure and function of small airways in smokers relationship between air trapping at CT and airway inflammation. Radiology 228 85-94... 

The variable controlled during the expiratory phase is known as the baseline variable, most commonly, pressure, typically expressed as EPAP or PEEP. It is necessary to have a positive baseline pressure in bi-level devices to assure CO2 washout. Bi-level devices have also been shown to be effective in managing upper airway collapse, in patients with obstructive sleep apnea and overlap (14). Einally, a positive baseline pressure has been shown to decrease the work of breathing associated with intrinsic PEEP and improve... 

Fig. 3.3.11. Pressure-dependent airways collapse in a patient with smoking-related emphysema. The flow cuts off abruptly after peak flow. The volume contained in the expiratory limb is far less than during inspiration, where the negative intrathoracic pressure keeps the airways open. (Flow in liters/second, expiration upwards, inspiration downwards, volume in liters)...

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