Optimal hematocrit for canine skeletal muscle during rhythmic isotonic exercise

Abstract

Contractile power, blood flow, O2-uptake, and O2-extraction during isotonic, rhythmic exercise were determined in the isolated canine gastrocnemius muscle during perfusion with blood with hematocrits between 0.21 and 0.81. The results obtained in 36 measurements on nine muscles showed that maximal O2-delivery to the muscle if found at hematocrits between 0.5 and 0.6. Both in the range of hemodilution, and in the range of extreme hemoconcentration, O2-delivery decreases significantly. O2-consumption and contractile power of the muscles are almost unaffected in the hematocrit range between 0.4 and 0.7; beyond and below this hematocrit range both parameters decrease. O2-extraction is virtually constant in the hematocrit range between 0.3 and 0.6, but increase both below and above these hematocrit levels. It is concluded that due to reduced vasodilatory reserve in working skeletal muscle compared to resting muscle the optimal hematocrit is shifted to higher values.

Optimal hematocrit for maximal exercise performance in acute and chronic erythropoietin-treated mice

“…It should be noted, however, that this may vary under different circumstances because of the blood's non-Newtonian behavior (13). Factors affecting this variation include the species, the organs involved, and whether the organism is in resting or exercising conditions (11,12,(14)(15)(16). Thus, the above mentioned observations do not always reflect the general situation in exercising mammals and humans.…”

“…Because of these counteracting effects, it was suggested that the optimal Htc may be lower than expected because of limitations induced by a higher blood viscosity (8,(10)(11)(12). Although the role of Htc on exercise performance seems obvious, there is only one ex vivo study available addressing the above hypothesis in isolated higher vertebrate muscles (11). It should be noted, however, that this may vary under different circumstances because of the blood's non-Newtonian behavior (13).…”

“…Accordingly, the exercise capacity of polycythemic patients with chronic obstructive pulmonary disease (COPD) is improved after hemodilution (9). Because of these counteracting effects, it was suggested that the optimal Htc may be lower than expected because of limitations induced by a higher blood viscosity (8,(10)(11)(12). Although the role of Htc on exercise performance seems obvious, there is only one ex vivo study available addressing the above hypothesis in isolated higher vertebrate muscles (11).…”

Redistribution of red blood cell flow in microcirculatory networks by hemodilution.

“…HD was then derived from HT by using literature data of the Fahraeus effect in vitro. 2 When capillaries were seen to form meshes creating divergent bifurcations downstream of a convergent bifurcation, only the initial capillary branch connected to the arteriolar tree was included in the analysis; less than 1% of all capillaries was seen to form such meshes. One network of the CTRL group and two networks of the HES group consisted of two arteriolar trees that could be analyzed independently.…”

The Effect of Dobutamine and Bolus Crystalloid Fluids on the Cardiovascular Function of Isoflurane Anaesthetised Horses

“…Haemodilution and a reduction in blood viscosity were associated with a significant increase in the mean partial pressure of oxygen in the tissues of organs studied. Results of a number of similar studies prompted further research to determine the optimal PCV, at which overall oxygen delivery to the tissues via hemoglobin transport is maximized, in veterinary patients undergoing general anaesthesia (Gaehtgens et al 1979, Fan et al 1980. However to date, the results of these studies have been variable and an optimal PCV has not yet been determined …”