Clinic-Functional Assessment of Hemoglobin Desaturation by Oxygen in 6-Minute Walk Test Among Patients with Bronchial Asthma

   The main purpose of the study is to assess the prevalence and clinical significance of hemoglobin desaturation by oxygen during the 6-minute walk exercise test in patients with bronchial asthma.

   Material and methods: 75 patients with exacerbation of mixed (48 %) and allergic (52 %) bronchial asthma were examined. Research explored following methods: collecting complaints and anamnesis, physical examination, spirometry, CO-metry of exhaled air to determine carboxyhemoglobin, transcutaneous 2-wave pulse oximetry (at rest and during 6-minute walk exercise test) with spectral analysis and correction for COHb. 6-minute walk exercise test was performed after relief of asthma exacerbation (before discharge from the hospital), assessing the desaturation-distance ratio (the ratio of the area of oxygen desaturation of hemoglobin to the 6-minute walk exercise test distance), O₂-GAP index, the dynamics of fatigue and dyspnea before and after 6-minute walk exercise test. In smoking patients (n = 36, 48 %), the smoker index was calculated. Based on oximetry results during the 6-minute walk exercise test, patients were divided into “desaturators” (n = 28, 37 %) and “non-desaturators” (n = 47, 63 %).

   Results. The findings of the research illustrated that hemoglobin desaturation by oxygen, detected by reducing SpO₂ to < 90 % during 6-minute walk exercise test, was associated with the severity of this disease exacerbation, more pronounced impairment of pulmonary ventilation and blood oxygenation, and the demand for longer hospitalization. The prevalence of tobacco smoking and the magnitude of the smoker index in both groups were identical but in “desaturators” we found a higher prevalence of the combination of asthma and COPD compared to “non-desaturators.” The “desaturators” had significantly higher level of desaturation-distance ratio and increased demand for additional oxygen flow to maintain SpO₂ at ≥ 88 % during a 6-minute walk test, which indicates a higher “oxygen price” of physical activity in this group of patients.

   Conclusion. Thus, the high prevalence of the phenomenon of hemoglobin oxygen desaturation during 6-minute walk exercise test in patients with asthma and associated clinic-functional disorders supports the feasibility and clinical significance of conducting a stress test with a 6-minute walk not only in COPD patients, but also in bronchial asthma patients.

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