The reason why John was instructed to avoid high altitude and fly in non-pressurized aircraft.
The main reason for the doctor to guide John this was so as to help prevent the rupture of the blobs again. From the case study, we have found out that John is undergoing spontaneous pneumothorax and the risks of developing it during flying or places of high altitude are much greater. This can only be explained by the changes in air pressure onto the lung cavities or blebs (blisters) in the weaken areas of the lungs. From the case study already this is a problem the doctor has established Hence John is more danger in case he is to find himself in high altitude areas or on a non-pressurized aircraft.
Pneumothorax, as discussed in the case study by the doctor to John, is the presence of air in the pleural cavity which causes the lungs to collapse. In most cases, the air pressure between the pleural is lower than that pressure being experienced in the lungs. This leads to the partial or complete collapse of the lungs.
There are also some effects of high altitude on the respiratory system of a human being and first being on the inhalation of oxygen in the body. The level of oxygen in high altitude area is less accessible which can cause a cluster of symptoms which are referred to as altitude sickness. Although the human body has mechanisms to adapt to different environmental features such as high altitudes for a person who has suffered spontaneous pneumothorax does not need to expose themselves to high-pressure conditions since their respiratory system is more prone to the attack once more. Hence this is the main reason why the doctor told him to avoid high altitude area also non-pressurized aircraft.