gms | German Medical Science

Objective: Blood samples are often taken before and after exercise testing to investigate reactions to physical activity. However, dehydration during exercise decreases plasma volume and may bias the blood analyses taken after exercise [1]. Dill and Costill therefore introduced a correction factor to adjust the blood values to the decreased plasma volume based on changes in haematocrit (Hct) and haemoglobin (Hb) [2]. Nevertheless, this plasma volume correction (PVC) is not consistently validated in practice. Therefore, metabolic parameters and leucocytes with and without PVC were analysed in a study on four exercise tests within 8 hrs.

Material/Methods: 16 healthy subjects (8 females, 8 males; 27±5 years, 67±7 kg, 173±6 cm, VO2_max 54±11 ml/min/kg) performed four maximal incremental cycling tests with 1.5 h of passive recovery. Fluids and carbohydrates were substituted in a standardized manner after each test. Venous blood samples were taken before and immediately after each test. Hct, Hb, glucose, triglycerides and leucocytes were analysed. Blood values before the first test were used as reference. For all following values plasma volume correction (PVC) factors were calculated according to Dill and Costill: PVC=Hb_before / Hb_after x (100–Hct_after) / (100–Hct_before) [2]. Changes over time (between and within tests) were analyzed by using a repeated measures ANOVA with Bonferroni post-hoc tests. Differences between the non-corrected and corrected values were compared by means of paired t-tests.

Results: Hb and Hct changed significantly from reference to the end of the first and the second test (p<0.05) as well as within each test (p<0.05). PVC led to changes in the outcome measures of -12.5 to+4.7% on average (range: -20.5 to 33.7%). Comparisons between the non-corrected and corrected values for glucose, triglycerides and leucocytes revealed statistically significant differences after the first and the second test (p<0.05; Table 1 [Tab. 1]). Non-corrected and corrected values were also significantly different at the beginning of the third test (p<0.05) but not at the beginning of the second test. Thereafter, comparisons between non-corrected and corrected values showed inconsistent differences. Non-corrected and corrected blood values of test 1 and 2 are given in Table 1 [Tab. 1].

Conclusion: This study showed that PVC is reasonable when analysing blood parameters of incremental cycling tests. Differences between non-corrected and corrected values appear relevant in glucose and leucocytes for both clinical and research questions. However, differences in triglycerides were irrelevantly small which might be attributable to the short duration of exercise.