Which of the following is a false statement about Type I respiratory failure:

A-a Gradient is the difference between the Alveolar PO2 (A) and aerial PO2 (a). The a-a gradient indicates how well O2 is equilibrating across the blood air barrier. Acute respiratory failure is defined as a lung disorder, wherein adequate functioning of lung, to meet the necessary demands of an individual is not met. It is unable to maintain normal levels of aerial gas in the blood. Respiratory failure is of 3 types, namely Type 1 respiratory failure or Oxygenation Failure Type 2 respiratory failure or Ventilation Failure Type 3 respiratory failure or Combined Respiratory Failure Ref: NMS Medicine By Susan. D. Wolfsthal, Page 63 ; High-Yield Physiology, Pa 845, Volume 2008, By Ronald W. Dudek, Page 59 ; Clinical Llaboratory Medicine By Kenneth D. McClatchey, 2202, Page 375