If there is something true about the butterfly effect, then that it often can be a metaphor for the circumstances that determine our professional life. If it wouldn’t have been for a defect speedometer on a Boing 737 in May 1984 the first author of this obituary and founder of this journal would have never gotten in touch with the field of sleep medicine by flirting during the delay in the airport bar with a medical intern, who wrote her dissertation about a cradle bed for adults to treat insomnia. Regarding our recently deceased teacher and friend Professor Karl Heinz Rühle MD PhD he could be called the butterfly effect of sleep medicine for both us authors and many others. My, Nikolaus Netzer’s, short flirt with sleep medicine was almost over when Professor Rühle reignited it spring 1986 by showing me his 8-channel polygraph and a few meters of paper from a severe OSAS patient in a little bedroom at the pulmonary department of the University Hospital Freiburg. Impressed by these lines on paper, I wrote my first article about sleep apnea in the Frankfurter Allgemeine (Medical) Zeitung and was caught by sleep medicine and in close contact with Karl Heinz Rühle from there on until the onset of his chronic severe disease 10 years ago. 1991 I presented his two-channel Apnoe-Check device with pulseoximeter and thermistor [1]) in a comparison to the Mesam 2 with heart rate measurement and microphone [2] at the ATS (American Thoracic Society) meeting in the Anaheim Convention Center. One year later I continued his work as head of the sleep laboratory at the pulmonary department in Freiburg.

For coauthor Georg Nilius it was the start into pulmonary sleep medicine as a pulmonary and internal medicine fellow under Professor Rühle as then from 1987 on director of the Clinic Hagen Ambrock, a famous German lung medicine clinic on the eastern edge of the Ruhrgebiet, which was the origin of his career in sleep medicine until Georg followed him in the directorial position of this clinic, actually director of the pulmonary department in Dortmund, and was now just a few days ago elected as president of the German Sleep Society. Several Generations of sleep physicians originate from this source. Among many others are names like Winfried Randerath, Cornelius Kellner, Uwe Weber. Antje Büttner, Edmund Schlenker, Bernd Sanner and Martin Hoster. Almost all of Karl Heinz Rühle’s fellows report that he inspired them to perform research in sleep medicine and trained them in scientific writing and giving speeches, which was the key to great careers in the scientific community.

Karl Hein Rühle was born in Tuttlingen, Swabia, Germany, July 12th, 1941, and studied Physics and Mathematics near his home in Tübingen and Frankfurt before continuing with medical school in Heidelberg. After his medical school he joined the famous pulmonary group at the University Hospital Ulm with Heinrich Matthys, Nikolaus Konietzko, Peter Werner and others. The group was the nucleus for several world leading inventions in pulmonary medicine in the late 60s and during the 70s concerning bodyplethysmography, lung diffusion measurement, aerosol research, and lung ventilation measurement. 1971 Karl-Heinz Rühle published his dissertation in Ulm with the title “Measurement of regional lung ventilation and perfusion via xenon 133”. He followed Heinrich Matthys to Freiburg, after this one received the call to lead the pulmonary department at the university hospitals, wrote there his habilitation work on spiroergometry and shortly later became deputy head of the department. He continued work on mucociliary clearance in coworking with Ulrich Costabel, who added famous work with bronchoalveolar lavage in interstitial lung diseases to the portfolio of the department, before he turned his research focus in the early eighties after the publications of Christian Guilleminault and Colin Sullivan towards sleep disordered breathing. In the early 90s he used his physics skills not only for the construction and patenting of different diagnostic devices like the above mentioned Apnoe (Apnea)-Check but for an invention that later revolutionized sleep apnea therapy: The auto CPAP (APAP) based on impedance measurement via forced oscillometry [3,4,5]. Karl-Heinz Rühle, of course, was a motor for establishing the German Sleep Society and the influence of pulmonary medicine within the society. Although he was a very progressive sleep physician and was an early inventor of polygraphy in sleep apnea diagnosis, he fiercely defended the need for PSG in a collegial but hot and well-remembered discussion with Michael Coppola in a larger sleep meeting 1995 in Freiburg, probably to calm down the neurologists in the just founded German Sleep Society. He continued to work on inventions until due to a chronic illness he retreated from work and public almost 10 years ago. His last published paper, on heated air tubes for CPAP with humidifier, was in this journal [6]. We will miss his humor, his smile and his energy and never forget him. If you never met him, maybe you might think of him the next time you prescribe a PG or an auto-CPAP.