Diurnal variations in serum erythropoietin levels in healthy subjects and sleep apnea patients.

We measured arterial oxygen saturation (SaO2) and serum erythropoietin (EPO) levels in patients with obstructive sleep apnea syndrome (OSAS) and in healthy subjects. SaO2 profile was analyzed as the cumulative distribution of SaO2 over time. OSAS patients spent 25.5 +/- 30.9% (SD) of the time at SaO2 of less than 88% vs. 0.64 +/- 1.6% in healthy subjects (P less than 0.05) and had 59 +/- 25 desaturations (greater than 4%) per hour vs. less than 5 per hour in healthy subjects (P less than 0.05). EPO measurements (radioimmunoassay) were made in blood samples withdrawn every 1 or 2 h over a 24-h period. The mean EPO concentration was higher (P less than 0.05) for OSAS patients (45 +/- 33 mU/ml) than for normal subjects (17 +/- 8 mU/ml). There was a significant variability in EPO values over the 24-h period. To analyze the EPO pattern over 24 h, EPO time series were fit to a general cosine function. Data from normal subjects conformed to a cosine function with an amplitude of 3.5 +/- 2.1 (CV of 60%) and an acrophase of 1,000 +/- 184 min after 0800 (CV of 18%), indicating a zenith about 1 A.M. and a nadir around 1 P.M. Data from OSAS subjects fit a similar cosine function with an amplitude of 19.9 +/- 41.0 (CV of 206%) and acrophase of 582 +/- 408 min (CV of 70%), indicating a greater variability in the magnitude and the timing of peak serum EPO levels.(ABSTRACT TRUNCATED AT 250 WORDS)