Oxygen-haemoglobin dissociation curve is used to study the percentage saturation of oxygen to hemoglobin. A right shift indicates decreased oxygen affinity of haemoglobin allowing more oxygen to be available to the tissues. It may be due to following reasons: increased temperature, increased hydrogen ion concentration. A left shift indicates increased oxygen affinity of haemoglobin allowing less oxygen to be available to the tissues. It is due to the following reasons: decreased temperature, decreased hydrogen ion concentration.