Anaerobic threshold in patients with pectus excavatum

Pectus excavatum is a condition characterized by a dent in the chest wall, at
the location of the 4th to the 7th rib, which usually has a funnel-like shape.
Pectus excavatum can be calculated by using the Haller index. The Haller index
is the thorax transversal distance divided by the distance between sternum and
spine. The distances are assessed on an X-ray. Normal Haller index is <2.5, all
values above 2.5 are called pectus excavatum. However, the degree of symptoms
is not determined by the Haller index. Patients with a Haller index of 3.5 may
have more symptoms than patients with an index of 5.5.
The shape of pectus excavatum is not always symmetrical. The deviation can be a
severe deformity of the chest wall. The incidence is not fully known but it is
expected that at least 1 in 1,000 born children has pectus excavatum. Usually
boys are affected (85%) and pectus is more common in families with a member
already familiar with pectus excavatum. If the deviation is seen at all after
birth, then it is often not included in the medical record.
That heredity plays a role in the occurrence of pectus excavatum is known, but
the exact mechanism not entirely clear. However, research shows that pectus
excavatum is more common in hereditary syndromes such as Ehlers danlos-,
marfan- or poland syndrome.
Usually the cosmetic aspect of pectus excavatum plays an important role in a
surgical intervention, however because of the reduced space in the chest
pressure is exerted on the right atrium and the right ventricle of the heart.
This can result in cardio compression.
The chest wall is very flexible when patients are young , therefore the heart
is able to divert, so no complaints arise. However, as the patient gets older,
the chest wall is less flexible and often creates a thoracic kyphosis by the
collapse of the intervertebral discs, which gives even less deflection space.
The resulting symptoms can also give a reason for surgical intervention.
These complaints are difficult to objectify. There are several markers that can
give some information for this purpose, such as the aerobic capacity. The
turning point from aerobic to anaerobic metabolism, also called "anaerobic
threshold" (AT), could possibly give a good indication of physical problems. In
multiple studies the subject of aerobic capacity after performing a Nuss
procedure is discussed, but not the AT.

The objective of this study is to demonstrate the influence of pectus
excavatum on the anaerobic threshold during exercise. This could be an
objective measurement of exercise intolerance. An objective measurement of
exercise intolerance can later help in the decision for surgical treatment of
pectus excavatum. Furthermore, the effect of a thorax correction on the AT can
be examined.

The study design is a prospective design. Differences of the anaerobic
threshold can be checked pre- en postoperatively and the measurement points can
be chosen relatively freely.
Randomization can not be applied, because there is one group of patients with
pre- and post-tests.
Informed consent will be obtained.
Patients have minimally five days to think about participating in this study.
After this period, patients will be included.

All patients, whom qualify for a Nuss procedure, are asked to participate in
this study. These are patients between the ages of 18 and 40. During outpatient
consultation patients receive information about the study, or will be contacted
by phone at least one week before surgery. After the time for consideration
patients will have to decide whether they want to participate or not. The
pectus operations can not be performed immediately so the patients will have
more than five days to consider their participation. All patients will be
planned for the Nuss procedure regardless of their choice to participate in the
study. The preoperative investigations are completed and a bicycle test with
determination of the AT is performed on the day of surgery.
The AT will be measured, in collaboration with the Department for pulmonology,
before thoracic correction. Patients have to do a maximum effort bicycle test
during which the AT can be seen. This test will be done a second time 3 months
after the operation and a third time 1 year after the operation, so patients
have had more time to recover.
Then all values will be compared. The AT is determined by means of the maximal
oxygen uptake (VO2 max). The cut-off value for normal AT is > 40% of the
predicted VO2 max.
All values of the test will be obtained non-invasively. The gold standard for
the AT determination is described as drawing arterial blood and determining the
actual lactate value at different times during the test. However, the AT can be
accurately determined non-invasively (V-slope) in patients with cardiopulmonary
disease. Because the non-invasive AT determination is similar to the gold
standard and an invasive measurement would be an additional burden for the
patient the V-slope method according to Wasserman, which is VO2 versus VCO2, is
used. If the AT is above 40% of the predicted VO2max the AT then can be called
normal.

It is known that the maximal oxygen uptake (VO2max) is lower in people with
pectus excavatum before correction of the chest wall than in people without
pectus excavatum. However, VO2max as a measurement of cardiopulmonary
limitation in pectus patients can have drawbacks. If patients do not perform
the maximum load during a bike test, VO2max may not always reflect the true
clinical status of the patient and in such case AT can give more information
than the VO2max.