Sleep is changed by blood sampling through an indwelling venous catheter.

Seven volunteers, four men and three women aged 53-63 years, each had his or her sleep recorded electrophysiologically on twelve baseline nights and on two nights during which a catheter had been inserted into a forearm vein. On the catheter nights, total sleep time and sleep efficiency were both reduced significantly, there was significantly more wakefulness after the first onset of sleep, and there was less rapid eye movement (REM sleep. The effects on REM sleep were attributable almost entirely to a significant reduction in the amount of REM sleep in the second half of each catheter night. Possible explanations of the effect of REM sleep are discussed.