An unusual tone-modulated signal was received on the Salyut-6 121.75 MHz FM voice link on 9 April 1979 in Fort Worth, Texas and again on 11 May 1979 in Stockholm, Sweden. The signal received was basically a quickly varying high-pitched tone with short and regularly spaced higher pitched segments. The signal was quickly identified as a signal channel of FM/FM telemetry using the voice transmitter as the radio link. By counting the high-pitched spikes it was found that they occurred about 60 times a minute which prompted speculation that the signal was actually some type of heartbeat monitor channel. the signal received on 11 May 1979 was therefore fed through a frequency meter, the output of which was allowed to deflect the galvo pen of a strip-chart recorder. With the advent of audio processing software in our time the signals can be shown as a software-generated image (see below) and they can clearly be seen to be an electrocardiogram. (Ordinate is frequency in Hz, abscissa is time in seconds).
A careful analysis of the recording made in Fort Worth shows that the ECG signals came from an onboard cassette recording played back through the voice link. the start of the cassette recording clearly identified the source of the ECG as being cosmonaut Ryumin. ECG telemetry was again received from Salyut-6 by Dieter Oslender in Bonn, Germany on 19 June 1979, and then became a regular feature of the Salyut-6 mission.
Soviet sources at the time more or less confirmed that such ECG recordings have been made. In a Tass statement issued at mid-day on 11 May 1979 we can read:
"...today the cosmonauts are also working with the onboard documentation and doing physical exercises on the veloergometer and the trainer. According to the results fo the medical checks, Vladimir Lyakhov and Valery Ryumin are in good health. the commander's pulse rate is 65 beats per minute and the flight engineer's 62 beats. their blood pressure is respectively 130 by 65 and 130 by 70 mm of the mercury column.."
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