salbutamol bronchodilatorcentrilobular emphysema treatmentpulmonary emphysema treatmentsympathomimetic bronchodilatorsemphysema managementanticholinergic bronchodilatorsubcutaneous emphysema treatmentantimuscarinic bronchodilatorsalbuterol bronchodilatorepinephrine bronchodilatormediastinal emphysema treatmentterbutaline bronchodilator