PREFLIGHT MEDICAL ASSESSMENT IN A HYPOBARIC CHAMBER TO STAGE THE RISK OF PULMONARY THROMBOEMBOLISM (PTE) IN AVIATION  

> BACKGROUND

The Medical Aviation Literature contains a number of studies stating out that long flights are associated with PTE. But it was only after the death of the young English athlete Cristoferson in London Airport that a big controversy arose regarding this association worldwide. Consequently, the WHO proposed a research program aiming to clarifying this issue through a study program called WRIGHT, which has already resulted in concrete outcomes on the incidence of such pathology that amounted to near 10 percent. 

> STUDY REPORT IN 10 VOLUNTEERS

REPORT OF 2 CASES OF PTE

We conducted this study in an attempt to gain knowledge regarding the relationship between height (cruise level of an international flight), the time period of staying at that height level in cabin, and O2 desaturation, to activate clotting cascade, the main cause for PTE. In the Hypobaric Chamber installed at the Aeronautics Medicine Institute (Instituto de Medicina Aeronáutica; IMA), Sanatorio Modelo Quilmes, a study was conducted on a group of healthy volunteers with ages ranging from 26 to 52 years (6 female and 4 male subjects), who have been duly informed of the study characteristics, the scope and possible adverse events, and who granted their written informed consent. Additionally, the effect of planned exercises, localized at the level of lower extremities, was evaluated, and exercising was performed at a duly designed device, with a similar design of an airplane seat (MSG or Multiple System Gym, HEALTHY FLIGHT). 

Prior to the study, clinical examination, lab, radiology and cardiology tests were performed; and all of the values were found normal. Hemostasis was particularly studied by means of clotting markers and fibrinolysis. No abnormalities were detected, and blood vessel system in lower extremities was assessed by means of an echo-Doppler and radioisotope phlebography. 

Procedure consisted of a rise in a Height Chamber (Hypobaric Chamber), in basal conditions; sit in an airplane seat, with a vertical rise rhythm similar to the one of a commercial line air jet. Neither signs nor symptoms of intolerance were detected. Hypobaric Chamber was stabilized at a cruise height level (2400 msnm), and remained at that altitude for over 3 hours. In the meantime, cardiovascular and pulmonary functions were monitored (pulse, blood pressure, respiratory rate, ECG), which were not affected; gas saturation in blood showed a decrease, which was consistent with the altitude reached, 90%/88%); blood samples were withdrawn to weigh blood coagulation activation markers, which were added a Peripheral Muscle Blood Flow in lower extremities in full resting condition. That study was conducted under exercising condition at lower-extremity muscle level, by walking for 10 minutes, and using the MES for an identical period of time. At the end, new measurements were performed, and no symptomatic signs were detected; a descent to 0 mnm was applied, and a new venous ultrasonography was conducted on lower extremities, which was completed with a radioisotope phlebography.  

Results revealed a significant increase in TAT and D.Dimer markers in three cases (1/3); no changes were observed in other three cases, and in the remaining 3, an increase in both markers was observed that required specific information on medication consumption, which revealed a contraceptive intake. After exercising with Multiple System Gym-HEALTHY FLIGHT, a significant Peripheral Muscle Blood Flow increase was observed in lower extremities versus the blood flow observed under resting conditions or walking. Furthermore, a lower O 2 desaturation was observed with MSG -HEALTHY FLIGHT Commpared to just walking.

Additionally, it has been shown that throughout resting period, surface venous system as well as color changes in the skin surface of distal section in the leg were more evident. Likewise, 2 of the subjects developed a significant increase in foot blood pressure.

Three of the volunteers developed a higher TAT and D.Dimer increase even when they were asymptomatic, and in view of the possible lung involvement, a new study in the Height Chamber was performed but under full resting conditions (3 hours sit, without any exercise or walk). These individuals revealed hypocapture of the radionucleotide administered (MAA Tc99m, administered by IV intrachamber) in the imaging obtained by lung scintiscan, with a significant expression at the level of the periphery of both lung sections. In view of this finding, and even when they were asymptomatic, adequate medication was prescribed, and were monitored on a daily basis with a scintiscan performed on the Day 8, when the pulmonary perfusion image remitted “ad integrum” (being the scintiscan categorized as normal.) 
 
 
 

Conclusions

Virchoff triad is well-known as part of the etiology of VT, situation mimicked by passengers under immobility conditions and at a cabin altitude in long flights, where lower extremities edema and circulation slowing down are observed, which gives place to changes in blood reology, promoting coagulation cascade activation increased by the hypoxia experienced at passengers’ cabin environment.

This study shows that planned and localized muscle exercise at lower-extremity level is more effective for counterbalancing blood flow slowing down and lower-extremity edema, by promoting a O2 saturation improvement in those lower extremities, thus positively impacting on the three core symptoms in Virchoff triad, and we have obtained these results by using MSG.

Implementation of this easy and friendly gym plan, which may be easily understood and performed by passengers, will result in a great benefit for the latter, and for passengers’ cabin operational functionality, and it will also imply an advantage for overall transportation safety. 
 

Authors: 

Dr.Pedro Oliveri, Dr.Jaime A German, Dr.Natalio Hupert, Dr.Di Giovani, Dra.Mabel Buzzurro, Dr.Vicente Ciancio, Julio Bralo, Engineer.

Dr Anibal Thompson(+), D.I.Noberto Baldoni(+)   

INSTITUTO DE MEDICINA AERONAUTICA Y MEDICINA DE LA ALTURA. 

POSTGRADUATE DEGREE IN AERONAUTIC MEDICINE.  UNIVERSITY OF LA PLATA.