breathing helps the patient compensate for the decrease in blood pH by increasing the amount of exhaled carbon dioxide, which helps prevent further acid accumulation in the blood. Cheyne–Stokes respiration is a breathing pattern consisting of alternating periods of rapid and slow breathing, which may result from a brain stem injury. Cheyne-Stokes respiration may be observed in newborn babies, but this is occasionally physiological (normal). Chest retractions may be observed in patients with asthma. During a chest retraction, the patient's skin appears to sink into the chest. During supra-sternal retractions, the skin of the neck appears to sink in as the accessory breathing muscles of the neck contract to aid with inspiration. During intercostal retractions, the skin between the ribs appears to sink in as the intercostal muscles (the muscles between the ribs) aid in respiration. These are signs of respiratory distress. The physician then typically inspects the fingers for cyanosis and clubbing. Tracheal deviation is also examined. Palpation Palpation is the use of physical touch during examination. During palpation, the physician checks for areas of tenderness, abnormalities of the skin, respiratory expansion and fremitus. To assess areas of tenderness, palpate areas of pain, bruises, or lesions on the front and back of the chest. Bruises may indicate a fractured rib, and tenderness between the ribs may indicate inflamed pleura. Palpate any abnormal masses or structures on the front and back of the chest. Abnormal masses or sinus tracts may point to infections. To observe chest wall expansion on the back of the chest, place palms on the patient's back with fingers parallel to the ribs and thumbs at the 10th ribs. Move hands towards each other to raise some skin on either side of the spine. Instruct the patient to inhale and observe the movement of the thumbs on the patient's back. Repeat the process with each hand on the lower margin of the ribcage at the front of the chest to further observe chest expansion. Asymmetry in chest expansion may be due to disease of lung or pleura. Place the bony parts of the palm around the borders of the patient's scapulae while he or she says "ninety-nine" or "one one one" to test for fremitus. Repeat the sequence on the front of the chest. A decrease in fremitus may be observed if the patient has a soft voice, obstructed bronchus, COPD, pneumothorax, or other disease or injuries