ONLINE POST, commissioned | AMP Student 2016;4
Awarded Research Work at AstraZeneca Foundation Competition, In4Med (19-21 February, Coimbra, Portugal)
Student author and presenter: Vivien SOMOGYI, Department of Pulmonology, Semmelweis University, Hungary
Chronic obstructive pulmonary disease (COPD) is a very common obstructive airway disease. In COPD significant airflow limitation and hyperinflation develops through airway inflammation, emphysema and small airway collapse present due to decrease in alveolar attachments. It leads to relative hypoxia and resultant hypoxaemia in the affected alveoli. It is not fully known how alveolar oxygen tension changes in the lungs of COPD patients and how it might contribute to pulmonary damage.Our aim was to assess the exhaled oxygen levels (PexO2) in COPD patients with normoxaemia and hypoxaemia and its correlation with clinical parameters.
Healthy volunteers (C, n=10), normoxaemic (N, n=11) and hypoxaemic (H, n=10) COPD patients were enrolled into detailed clinical examinations, including lung function test, blood gas analysis and quality of life tests (COPD Assessment Test [CAT], modified Medical Research Council [mMRC], Visual Analog Scale [VAS]). Mass spectrometry (figure) was used to determine PexO2. During measurements each subject performed two different prolonged maneuvers. First, the patients were asked to perform at least 5 breathing maneuvers at rest and then exhaled from functional residual capacity (FRC) to residual volume (RV) at a constant rate. After this period patients repeated the 5 breathing maneuvers at rest, after that inhaled quickly from FRC to total lung capacity (TLC) and exhaled to RV. The PexO2 was measured on the level of FRC and RV after both maneuvers.
FEV1 was similar for both COPD groups (N: 39.90±4.12 vs H: 34.53±5.31 reference%); whereas pO2 showed significant difference (N: 69.33±1.88 vs H: 51.15±1.54 mmHg; P<0.0001). The CAT total score was higher in group H compared to group N (N: 20.90 vs H: 21.40 points). The dyspnoe evaluating mMRC score was higher in group H compared to group N (N: 3.00 vs H: 3.10 points). The VAS score was worse in group H compared to group N (N: 3.85 vs H: 5.65 points). PexO2 did not show difference between the three groups on the level of FRC. PexO2 measured on the level of RV was significantly lower in group H compared to group C (C: 15.32±0.99 vs H: 12.34±1.79 mmHg; P<0.0001) and in group N compared to group C (C: 15.32±0.99 vs N: 13.63±1.03 mmHg, P<0.05), but did not show significant difference between COPD groups. PexO2 correlated positively to airway obstruction (forced expiratory volume in one second [FEV1(%)]: r=0.6846; P<0.0001) and small airway obstruction (forced expiratory flow [FEF25-75(%)]: r=0.6515; P<0.0001).
Based on our results alveolar hypoxia is present in the lungs of COPD patients. The worse overall quality of life test results in H COPD patients reflects more symptomatic subgroup of COPD patients. Decreased PexO2 is related to the severity of lung hyperinflation and associated with worse quality of life indicators. The severity of airway obstruction correlates with PexO2, which may lead to decreased alveolar oxygen tension in COPD patients. Hypoxia may contribute to the worsening of alveolar lung damage and might be an easy measurable non-invasive marker for lung structural deterioration in patients with COPD.