Effect of ketosis on respiratory sensitivity to carbon dioxide in obesity.

We investigated whether the respiratory defect in the obesity-hypoventilation syndrome might respond to dietary manipulation. The effects of hypocaloric ketogenic regimens on the ventilatory response to carbon dioxide were studied in a manner excluding changes in weight or thoracic mechanics as factors. Six obese subjects with hyporesponse (less than 1.1 1/min/mm Hg) and 12 with normal response were fasted or given a diet containing 400 kcal per day of protein. During ketosis carbon dioxide response more than doubled in those with hyporesponse (0.8 +/- 0.1 to 1.8 +/- 1/min/mm Hg, P less than 0.05) but was unchanged in those with normal response. This improvement could not be accounted for by changes in weight, pulmonary function, pH or degree of ketosis between the two groups. However, a significant positive (r = 0.70; P less than 0.001) correlation between ketone-body concentrations and carbon dioxide response was observed in subjects with hyporesponse. These results indicate that depressed sensitivity to carbon dioxide in obese patients can be increased by dietary manipulation.