Pulmonary Hypertension (PH) is a progressive disease affecting the pulmonary vessels and
leading to an increased pulmonary vascular resistance (PVR) and thus right heart strain. The
result is an increase in mean pulmonary arterial pressure (mPAP) and with time dilation of
the right heart chambers as well as hypertrophy of the right ventricular myocardium. As the
increase in PVR progresses further, the right ventricle struggles to cope with the rising
afterload and starts to fail. Before this worst case scenario occurs, most individuals
suffering from PH notice dyspnea on exertion as the first sign of their underlying disease.
The increased proliferation and the resulting rise in PVR lead to a slower blood flow through
the pulmonary vessels and thus sometimes result in in situ thrombosis. Furthermore the
thickening of the capillary vessel bed increases the diffusion barrier for oxygen and herby
results ventilation-perfusion mismatch and leads to hypoxia first during exercise, and later
even at rest, making long term oxygen therapy (LTOT) necessary. Today's specific
pulmonary-vasoactive therapy helps individuals suffering from PH to live a "normal" life. For
most people this also means going on vacation
The latter however
bares risks for patients suffering from PH:
While the average traveling altitude of passenger planes is between 9.150
- - 12.200m (30.000 -
40.000ft) where the atmospheric pressure is less than 30% compared to that at sea level,
reducing the pressure of inspired oxygen (PIO2) from 143mmHg to less than 40mmHg.
In other
words the air contains less than 6% oxygen compared to 21% at sea level. Since this is not
compatible with human life airplane cabins are pressurized to maintain a pressure equally to
a height between 1520
- - 2440m (5.000 - 8.000ft) which contains about 15% of oxygen.
However,
even the National Research Council (NRC) stated that passengers with cardiovascular problems
might experience discomfort within this cabin environment. These conditions of hypobaric
hypoxia, even in the pulmonary vasculature of a healthy individual, lead to a generalized
hypoxic pulmonary vasoconstriction (HPV). These changes, in healthy individual lead to a rise
in PVR and thus right ventricular systolic pressure (RVSP). Healthy individuals are able to
compensate the resulting increase in right ventricular afterload. It however is easily
imaginable that the heart of a patient with right heart insufficiency may struggle or even
fail under these circumstances. Increasing the PIO2 through supplemental oxygen (O2) is known
to prevent these changes, which is why it is recommended to be used by patients with world
health organization functional class (WHO-FC) III and IV as well as patients with arterial
blood O2 pressure consistently <, 60mmHg (8 kPa) by the current guidelines. This general
advice is given by the American Aerospace Medical Association and the British Thoracic
Society as well. There is however a problem with most of these recommendations: There's a
lack of studies concerning the effects of commercial air travel on patients with PH, which is
why many recommendations are made by transferring data from surveys about more common lung
diseases. There are however some studies on the effects of (simulated) air travel in patients
with PH:
In 2012 a survey was conducted where hypoxic challenge test (HCT) was performed on 36
individuals suffering from PH and compared the acquired data of HCT and WHO-FC with the
actual need of in flight oxygen. The latter information was gained through a questionnaire
handed out to the before named individuals that focused on in flight symptoms and events that
lead to the use of in flight oxygen prior to and after diagnosis of PH. It was found that 25
out of the examined 36 individuals according to the current recommendations would need in
flight oxygen judging by their WHO-FC, but only 10 failed HCT. Out of all 36 patients, 14
traveled by plane after being diagnosed with PH. Of these, nine subjects should have had
in-flight oxygen based on WHO-FC but were asymptomatic without. Furthermore 1 individual that
passed the HCT had developed symptoms during the flight and 3 who failed the HCT were
asymptomatic flying without oxygen. In other words: HCT did not identify one patient who
developed symptoms during a flight.
In the same year another study was published with data of a prospective survey from 34
individuals of which data was collected during flight. Cabin pressure, peripheral oxygen
saturation (SpO2), heart rate and symptoms were assessed. Desaturation was defined as SpO2 <
85%. It was found that nine individuals experienced significant desaturation. Furthermore
only five out of the 13 patients that reported symptoms presented desaturation during their
flight. Furthermore no predictive factor to predict possible desaturation during the time
being airborne (neither resting SpO2 at sea level nor maximal estimated cabin altitude was
predictive) were found.
In 2011 a retrospective analysis during which patients with diagnosed PH, who had traveled by
airplane, were asked to complete a questionnaire containing general information (group of PH,
WHO-FC, current medication, usage of LTOT, etc.) as well as possible symptoms conceived
(dyspnea, chest pain, peripheral edema, etc.) was released. Out of 179 patients who had
traveled by plane 57 were under LTOT and 29 used supplemental oxygen during the flight. In
total 20 adverse events were reported (mainly mild to moderate in severity) and 7 needed
medical assistance. In total 159 out of 179 patients didn't experience any discomfort during
or shortly after their travel.
In summary of the scarce data available hitherto there is no sufficient test available to
predict in flight complications in patients with pulmonary hypertension. It could however be
shown that using WHO-FC as the only surrogate is not useful to determine which patient might
be in need of additional oxygen during air travel. Furthermore even HCT is not capable of
detecting patients at risk. Even the British Thoracic Society marks their recommendations on
the use of supplemental oxygen for patients with PH with "evidence level D".
It is this absence of sufficient data and the thereby resulting uncertainty of patients,
physicians, pneumologist and cardiologists as well as specialists in the field of PH on this
topic that lead to the concept of this study. By this prospective survey on patients
suffering from all forms of PH, under all different types of available treatments and in all
WHO-FCs the investigators hope to gain further insight in possible markers to predict in
flight adverse events and thus make flying safer for individuals struggling with PH. This
study therefore aims to include a total of 1000 patients suffering from all forms of PH
which, after providing written and informed consent, will be asked to fill out a
questionnaire prior to and after air traveling as well as assessing vital parameters (SpO2,
pulse and respiration rate) prior to, during and shortly after their flight. In addition all
clinical data available will be collected and analyzed. The aim of this study is to find
possible parameters in echocardiography, right heart catheterization, laboratory findings,
spiroergometry as well as six minute walk test to produce a risk assessment for possible
expected in flight adverse events as well as a recommendation concerning the need of
supplemental oxygen for each individual patient.
All data collected will be anonymised to prevent possible identification of each
participating individual. Examinations conducted during this survey would have been necessary
anyway in the course of regular clinical visits. So there will be no additional health risk
for patients participating in the study.
