A 6 months old baby coming with /o increasing difficulty in breathing of 2 days duration and on examination baby is afebrile & B/L wheeze & CXR shows B/L hyperinflation of the lungs with normal WBC count, the diagnosis is –
Clinical manifestations of bronchiolitis 

The usual course of the disease is 1-2 days of → Fever, Rhinorrhea, Cough
This is followed by -
Wheezing  
Cyanosis  
Tachypnea 
Nasal flaring     
The breathing pattern is shallow
Rales, crepitation and Ronchi 

Respiratory distress → retraction of intercostal space & suprasternal notch.

Liver and spleen are pushed downward because the hyperinflated emphysematous lungs push the diaphragm downward.
Anteroposterior diameter of the chest is increased and hyper-resonance is noted on percussion.
The leukocyte count is normal or slightly elevated.

Chest X-ray

Hyperinflation of the lung
The diaphragm is pushed down                 
Lung fields are abnormally translucent.
Bronchiolitis
Asthma
Ch. Bronchitis
Pneumonia