[Effects of differences in oxygen affinity on circulatory response to hypoxia]

It is well known that tissue hypoxia is an important prognostic predictor in patients with chronic obstructive pulmonary disease (COPD). Compensatory responses to acute hypoxia occur in various organs and the magnitude of such response may also be an important factor in prognosis. P50, (oxygen tension at which the hemoglobin is 50% saturated with oxygen) is recognized as one of the factors affecting oxygen supply to the tissue. These studies were made to determine whether differences of P50 affect the circulatory response to acute hypoxia. Studies were made on nineteen male patients with COPD. They were divided into two groups according to low (less than 26.6 torr) or high (greater than 26.6 torr) P50. Isocapnic hypoxia was induced progressively with the patients being under right cardiac catheterization. The low P50 (25.8 +/- SD 0.6 torr) group included ten patients, and the high P50 (27.4 +/- 0.6 torr) group included nine patients. No differences could be detected in respect of pH, PaCO2, PaO2 or any hemodynamic parameters. Heart rate increased in both low and high P50 groups but the degree of the increase (delta HR/HR ROOM AIR x 100) in the high P50 group (20.7 +/- 9.2%) was significantly greater than in the low P50 group (9.4 +/- 10.9%). An increase in cardiac output was observed in the high P50 group (4.4 +/- 0.8 to 5.3 +/- 0.6 1/min), but not in the low P50 group (4.5 +/- 1.0 to 5.0 +/- 0.9 1/min). There was a significant positive relationship (r = 0.903) between hypoxic circulatory response and oxygen transport (TO2).(ABSTRACT TRUNCATED AT 250 WORDS)