[Exercise-induced asthma and arterial hypoxemia]. / Anstrengungs-induziertes Asthma und arterielle Hypoxämie.

ABSTRACT

40 young asthmatic patients performed submaximal work on a treadmill ergometer for 6 minutes. In 20 cases the PaO2 was found to be below 77.5 mm Hg (arterial hypoxemia) at the 10th or the 20th minute of post-exercise recovery time. A first subgroup A of 9 asthmatics presented hypoxemia together with a fall of FEV1 below 90% of control at the first to the 20th minute post-exercise recovery phase. A second subgroup B of 11 asthmatics showed hypoxemia with FEV1's higher than 90%, often higher than 100% of the control value. The following features of the recovery period were observed 1. 10 minutes delay of onset of hypoxemia in relation to the FEV1 drop in group A. 2. Progressive hypoxemia despite a clear return of FEV1 versus the control value during the late recovery phase of group A. 3. Appearance of arterial hypoxemia despite unchanged normal FEV1's in group B. These three observations suggest that there are 2 kinds of post-exercise bronchoconstrictions. The first may be situated in the large bronchi (FEV1-drop), the second in the small peripheral airways (PaO2-drop), from the first to the 20th and from the 20th to the 40th minute respectively after the end of submaximal work load. It is concluded that there must be 2 sequential bronchoconstrictions due to cooling of the airways and these constrictions may guarantee alveolar homeostasis for body temperature and full saturation with water vapour. However, the first barrier in the large airways can be abolished by high blood levels of adrenaline. In such cases the second barrier in the small airways becomes important and may protect the alveoli from cooling and dry air.