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The Lancet 2007; 370:566

DOI:10.1016/S0140-6736(07)61292-6
Correspondence

Zero G in a patient with advanced amyotrophic lateral sclerosis

I Mackenzie a, E Viirre b, JM Vanderploeg c and ER Chilvers a

The ability to generate gravity-free (zero G) conditions during parabolic flight has existed for several decades. To date, this experience has been restricted to healthy adults. We report the physiological effects of zero G and high G in a patient with advanced amyotrophic lateral sclerosis requiring nocturnal ventilation via an end tracheostomy and supplementary enteral feeding.

The patient's additional medical conditions include hypertension, recurrent sigmoid volvulus, low body-mass index, and severe osteoporosis. His usual blood pressure is 140/93 mmHg, with an arterial PaCO2 and pH when self-ventilating on room air of 4·3 kPa and 7·49, respectively.

A modified Boeing 727-200 was used to fly parabolas between 7315 m and 9754 m, generating eight 15–20 s periods of weightlessness preceded and followed by equivalent periods of high G to 1·5 G. The cabin was pressurised to the equivalent of 1067 m above sea level throughout the flight.

The patient received glycopyrrolate 200 μg, dexamethasone 8 mg, and ondansetron 4 mg intravenously 1 h before flight. Monitoring consisted of non-invasive blood pressure measurement every 2 min with continuous three-lead electrocardiography, and respiratory rate (Fukuda Denshi SDS-7100, Old Woking, UK), and transcutaneous SaO2 and PcapCO2 measurement (SenTec Digital Monitoring System, Therwell, Switzerland). Supplemental oxygen was available at 2 or 4 L/min, delivered via a standard tracheostomy mask. In-flight communication was limited to facial gestures. The patient was maintained supine with a cushioned head support during the horizontal and high G periods and guided by two flight coaches throughout the zero G phases. A training flight was undertaken on the previous day with a healthy 14-year-old height-matched and weight-matched individual. Facilities for intubation and cardiorespiratory support were available.

The periods of zero G and high G were tolerated extremely well, with no significant fluctuation in pulse rate, blood pressure, or ventilatory function (figure). SaO2 values were maintained above 90% throughout, and oxygen supplementation at 2 L/min was used only briefly (figure). We saw a single episode of transient asymptomatic hypotension (systolic pressure 54 mmHg) in the healthy individual during zero G but did not capture a blood pressure measurement during these periods in our patient. Six of the periods of zero G were accompanied by transient dips in the SaO2 concentration and four by brief dips in PcapCO2, consistent with brief periods of hypotension at the onset of weightlessness. There was no reported motion sickness.


Click to enlarge imageFigure. Profile of the physiological responses during zero G parabolic flight
Periods of zero G are marked by longitudinal grey bars and period of oxygen supplementation (2 L/min) by horizontal black bar.

“It was amazing…I could have gone on and on…Space here I come!” were the first responses communicated after landing. This offers the prospect of zero G and high G travel to a much wider group of individuals.

EV is a medical consultant for ZERO-G and the X-PRIZE Foundation. JMV is a medical consultant for Virgin Galactic.

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