Can pursed lip breathing reduce the symptoms of an asthma attack?

Yes: But not enough. Need rescue inhalers and possibly emergency care.

Yes.: It helps to keep the airways open. It's not a very effective technique. Open physical measures that you can try (1) stay calm (2) breathe slowly from diaphragm (3) sit up and lean a little forward (4) meditate. These techniques augment but do not replace the use of effective medications including bronchodilators and controller drugs like inhaled corticosteroids.

Obstruction...: In an asthma attack, there is airway obstruction so expiration becomes difficult and, eventually, there is an increase in carbon dioxide since it can't be expired. Pursed lip breathing prolongs the expiratory phase of respiration so that, potentially, more air and carbon dioxide can be exhaled. That way, there is more room for oxygen to be inhaled.