Abstract
Two experiments were performed to study the cardiac output (Q̇) vs. hemoglobin concentration (Hb) relationship during constant load submaximum exercise. The first experiment examined the relationship between submaximum exercise Q̇. and Hb in 28 females. A correlation of (r = -0.83 (P < 0.05) was observed between Q̇ and Hb during exercise at 88 W (X̄ Q̇ = 11.04 I·min-1) and 118 W (X̄Q̇ = 13.10 I·min-1) (X̄ steady rate V̇O2 = 1.40 I·min-1 and 1.79 I·min-1, respectively). By removing the influence of stroke volume (SV) from Q̇ (part correlation analyses), the relationship between Q̇ and Hb is compromised (r = -0.29, P > 0.05, 88 W and r = -0.33, P > 0.05, 118 W). The second experiment compared the V̇O max and submaximum exercise (118 W) Q̇ responses in six males before and after blood donation. Experimentally reducing Hb 18.6% (P < 0.05) caused a 6.2% decrease (P < 0.05) in V̇O2 max. Additionally, submaximum exercise Q̇ increased 12% (P < 0.05) 6 days following hemodilution. The Q̇ remained elevated 11 days (10% higher, (P < 0.05) and 16 days (9% higher, (P < 0.05) post-blood donation and progressively returned to pre-donation levels by 21 days post-withdrawal. The higher Q̇'s during submaximum exercise were ascribed primarily to an 8% (P < 0.05) higher SV in comparison to pre-donation levels. Collectively, the data from the two experiments indicate that individual differences in submaximum exercise Q̇ are due, in part, to individual differences in Hb concentration. Furthermore, it is suggested that the stimulus for the SV-induced Q̇ vs. Hb association is related to maintaining maximal myocardial efficiency.
Key words
cardiac output - submaximum exercise - hemoglobin - 2 - 3 DPG - stroke volume - V̇O2
- blood donation
