Steady-Rate Exercise Cardiac Output: Influence of Hemoglobin.

Four experiments were conducted to examine the relationship between hemoglobin concentration (Hb) and cardiac output (Q) during submaximum exercise: (1) EXPERIMENT ONE: four submaximum exercise bicycle tests (180, 360, 540 and 720 kgm) were completed on two separate occasions by six males (X age = 23.33 years). Individual differences in steady-rate oxygen consumption (VO(,2)) were small (test-retest r = .05 - .49) while individual differences in Q were substantial (r = .60 - .91). (2) EXPERIMENT TWO: Twenty-eight females (X age = 27.61 years) completed the four submaximum exercise tests. The correlations between Q and Hb were r = -.13 (180 kgm) (p > .05), r = -.52 (360 kgm) (p .05). Dividing subjects into a low Hb group (X Hb (+OR-) SD = 12.62 (+OR-) 0.95 gm(.)100 m1('-1)) and a high Hb group (X Hb (+OR-) SD = 14.68 + 0.88 gm(.)100 m1('-1)) revealed significantly higher Q's for the low Hb group at 540 kgm (21 percent higher) and 720 kgm (18.6 percent higher). (3) EXPERIMENT THREE: Six males completed a bicycle VO(,2) max test before and after a 19 percent reduction in Hb concentration (via blood donation). Two submaximum bicycle tests (360 and 720 kgm) were performed once before and four times following the blood donation (6, 11, 16 and 21 days post-donation). VO(,2) max decreased 6 percent (p .05) between the groups. Data from the four experiments indicate that Hb levels (oxygen carrying capacity) influence Q during steady-rate exercise ranging between 360 and 720 kgm. These results suggest that during exercise below 360 kgm min('-1), Q is low, which permits adequate oxygen (O(,2)) extraction to maintain VO(,2) at a constant rate in a reduced Hb state. 2,3 diphosphoglycerate (2,3 DPG) was also postulated to enhance O(,2) unloading during low levels of exercise. Collectively, the data from this study support the hypothesis that an exercise intensity threshold exists above which Hb levels account for the greatest portion of individual difference variance in Q during submaximum exercise.PhDPhysical educationUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/157739/1/8017263.pd