The development of sleep science, sleep medicine, and sleep technology has been codependent on advances in both recording and treatment technology.

It is fascinating to read some of the early information on methodology for recording sleep studies. These recordings were performed on analog equipment, using paper and ink EEG machines with direct current capabilities and limited channel availability. Because of the limitations in the number of recording channels, montages had to be well devised to provide adequate information for proper diagnosis, often sacrificing a recording derivation for one that may be more important, based on the presentation of a particular patient. Recording devices with 8, 10, or 12 channels were commonplace; 16, 18, or 21 channels were a luxury. Sleep technologists had to possess a good understanding of amplifiers and filters as well as expected frequency ranges of the physiologic parameters recorded. Improper use of filters or sensitivity controls could make stage N3 sleep look like wakefulness or make normal breathing appear to be apnea … and there was no return. Once on paper, it was there for good. Sleep technologists had to unclog polygraph pens, change broken galvanometers, fill inkwells, and carefully align and tape together boxes of folded paper to ensure that a single overnight recording was properly acquired. It was extremely awkward to go back and review previous portions of the recording. Scoring was performed manually and data tabulation was done with pencil and paper, sometimes with the assistance of a calculator. It often took longer to generate the requisite sleep report statistics than to identify sleep stages and abnormal events. The recording technologist could hear the sound of sleep spindles, REM sleep, slow-wave sleep, arousals, cardiac dysrhythmias, and periodic limb movements. Each had its own distinct sound generated by the scratching of the pens on the moving paper chart. This was actually quite helpful because it drew the attention of the attending technologist to a particular patient, when concentration may have been focused elsewhere.

The polygraphs were massive, veritable monoliths, with approximate dimensions of 5 to 6 ft height, 4 ft width, and 2.5 to 3 ft depth, each weighing several hundred pounds (see Fig. 1-1). Storage and archival of recorded data was an enormous and expensive problem. The cost of the paper alone for four recordings was over $200 and required about 2.3 ft³ of storage space for a minimum of 7 years (see Fig. 1-2). This is not to say that these behemoths were not wonderful, highly reliable workhorses. They seldom failed in such a way that a recording needed to be rescheduled. Fairly simple
pen or galvanometer replacement, or occasional swapping of an amplifier board “on the fly,” that is, while the recording was still being performed, put you back in business. There are times when many of “the old guard” sleep technologists long for the days of analog recorders with stable amplifiers and filters, in place of nebulous software glitches and corruptions, or the whims and fancies of computer hardware, networks, and interfaces that can put one out of commission for days. Days when a couple of more beds added did not mean several days or weeks of troubleshooting, as often seen today, even when using the same brand of equipment and software.