Capillary recruitment and flow velocity in skeletal muscle after contractions

Hudlická, O; Zweifach, Benjamin W.; Tyler, K. R.

doi:10.1016/0026-2862(82)90065-6

Cited by 61 publications

(38 citation statements)

References 29 publications

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“…The exchange capacity of a capillary is determined principally by whether it is flowing (recruited) or not rather than its rate of flow. As seen in Figure 6 increased exchange capacity purported to result from capillary recruitment can be explained by increased flow and substrate delivery through already-recruited capillaries (Hargreaves et al 1990; Hudlicka et al 1982; Kindig et al 2002). This latter notion is in accord with the enormous increase in RBC flux and O 2 delivery seen from rest to exercise within already flowing capillaries and also the established wisdom that free fatty acids and glucose are taken up by muscle in proportion to their delivery (i.e., plasma flow × concentration).…”

Section: Presumptions Arising From “Capillary Recruitment”mentioning

confidence: 95%

Dynamics of muscle microcirculatory and blood–myocyte O₂ flux during contractions

et al. 2011

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The O2 requirements of contracting skeletal muscle may increase 100-fold above rest. In 1919 August Krogh’s brilliant insights recognized the capillary as the principal site for this increased blood-myocyte O2 flux. Based on the premise that most capillaries did not sustain RBC flux at rest Krogh proposed that capillary recruitment (i.e., initiation of red blood cell (RBC) flux in previously non-flowing capillaries) increased the capillary surface area available for O2 flux and reduced mean capillary-to-mitochondrial diffusion distances. More modern experimental approaches reveal that most muscle capillaries may support RBC flux at rest. Thus, rather than contraction-induced capillary recruitment per se, increased RBC flux and hematocrit within already-flowing capillaries likely elevate perfusive and diffusive O2 conductances and hence blood-myocyte O2 flux. Additional surface area for O2 exchange is recruited but, crucially, this may occur along the length of already-flowing capillaries (i.e. longitudinal recruitment). Today, the capillary is still considered the principal site for O2 and substrate delivery to contracting skeletal muscle. Indeed, the presence of very low intramyocyte O2 partial pressures (PO2’s) and the absence of PO2 gradients, whilst refuting the relevance of diffusion distances, place an even greater importance on capillary hemodynamics. This emergent picture calls for a paradigm-shift in our understanding of the function of capillaries by de-emphasizing de novo ‘capillary recruitment.’ Diseases such as heart failure impair blood-myocyte O2 flux, in part, by decreasing the proportion of RBC-flowing capillaries. Knowledge of capillary function in healthy muscle is requisite for identification of pathology and efficient design of therapeutic treatments.

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Section: Presumptions Arising From “Capillary Recruitment”mentioning

confidence: 95%

Dynamics of muscle microcirculatory and blood–myocyte O₂ flux during contractions

et al. 2011

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“…20, 28). Accepting a mean value for capillary density and length of 300/mm 2 and 1,000 m, respectively, if 80% of the 8.9 ϫ 10 9 capillaries support RBC flow at rest, as in the rat (14,17, 24), this would be ϳ12 RBCs per capillary per second-very close to the 15-20 RBCs per capillary/s actually measured in rat muscle (17). Whereas such calculations are certainly not proof that most skeletal muscle capillaries have RBC flow in humans at rest, they support that it is feasible.…”

mentioning

confidence: 85%

“…In resting muscle, intravital light microscopy shows that over 80% of capillaries support RBC flow, e.g., in rat spinotrapezius (14,17,24), diaphragm (15), and extensor digitorum longus (1), hamster cremaster and sartorius (8), cat sartorius (6), rabbit tenuissimus (30). However, animals in these experiments were anesthetized to facilitate muscle exteriorization and viewing of the capillary beds.…”

mentioning

confidence: 99%

“…However, neither observation of contracting (17) nor vasodilated (16) muscles revealed a significant number of such vessels (see also Refs. 8,14). The technical requirements necessary to observe capillaries within living muscle restrict the procedure to a limited selection of animal muscles so that one question to ask is: How representative of other muscles in the animals' body and in humans are these?…”

mentioning

confidence: 99%

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Counterpoint: There is not capillary recruitment in active skeletal muscle during exercise

Poole

Brown²,

Hudlická³

2008

Journal of Applied Physiology

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COUNTERPOINT: THERE IS NOT CAPILLARY RECRUITMENT IN ACTIVE SKELETAL MUSCLE DURING EXERCISEThe notion that a substantial proportion of capillaries do not contain moving red blood cells (RBCs) in muscle at rest but are "recruited," i.e., begin flowing with RBCs during contractions, is one basis for our present understanding of blood-muscle exchange during exercise (20, 28). This concept emanates, in part, from August Krogh, who showed that many capillaries in resting muscle did not contain India ink after high pressure perfusion (19). Despite Krogh himself recognizing that India ink particles clumped together, more likely to prevent complete perfusion of the capillary bed at rest than during exercise, these experiments, and Krogh's O 2 diffusion model based on them, are still cited by researchers invoking capillary recruitment (e.g., Refs. 22). Today capillary recruitment during exercise is accepted by many to explain important physiological phenomena, including: 1) greater blood-muscle delivery and extraction of O 2 , free fatty acids, and glucose and 2) reduced capillaryto-mitochondrial diffusion distances. It makes great sense that, if there were a reserve of capillaries at rest, during exercise when the muscle demands for O 2 may increase up to 100-fold, all-or at least most-capillaries would contribute to meet that demand.Why, therefore, choose to oppose the concept of capillary recruitment during exercise? In Britain, the motto of The Royal Society is "Nullius in Verba" (Take nobody's word for it, see it for yourself). However, the majority of research papers invoking capillary recruitment have not visualized the capillary bed (e.g., Refs. 3, 7, 25). In his letter to the editor of The American Journal of Physiology, the eminent microcirculation expert, Professor Eugene Renkin (26) criticized Dr. Bentzer for entitling his paper "Capillary filtration coefficient is independent of number of perfused capillaries in skeletal muscle"(4) on the basis that ". . . its title is misleading. No direct measurements of [RBC-flowing] capillary number were made. . . ." The same criticism could be leveled at almost all papers that include the words capillary recruitment in their titles. Evidence that most capillaries already sustain flow in resting muscle would preclude the possibility that recruitment of previously nonperfused capillaries occurs to any great extent during contractions.Direct evidence for RBC flow in most capillaries in resting muscle. In resting muscle, intravital light microscopy shows that over 80% of capillaries support RBC flow, e.g., in rat spinotrapezius (14,17, 24), diaphragm (15), and extensor digitorum longus (1), hamster cremaster and sartorius (8), cat sartorius (6), rabbit tenuissimus (30). However, animals in these experiments were anesthetized to facilitate muscle exteriorization and viewing of the capillary beds. To address this, Bailey and colleagues (2) employed minimally invasive techniques to measure blood flow (radioactive microspheres) and microvascular oxygen partial pressure in muscle...

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“…There was an inverse correlation between heart weight and PS-Na and PS-Rb, which is in agreement with previous findings of an inverse correlation between capillary density and heart weight. Capillary flow velocities have previously been measured in mixed muscles either during (Gorczynski, Klitzman & Duling, 1978) or immediately after contractions (Hudlicka, Zweifach & Tyler, 1982). Since the total blood flow in fast muscles is usually lower at rest than in slow muscles and increases more during contractions, (Hudlicka, 1975), it was of interest to find out whether this is reflected in flow velocities supplying individual slow and fast muscle fibres.…”

Section: Pmentioning

confidence: 99%

Proceedings of the Physiological Society, 20‐21 December 1982, Birmingham Meeting: Demonstrations

1983

The Journal of Physiology

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Capillary recruitment and flow velocity in skeletal muscle after contractions

Cited by 61 publications

References 29 publications

Dynamics of muscle microcirculatory and blood–myocyte O₂ flux during contractions

Dynamics of muscle microcirculatory and blood–myocyte O₂ flux during contractions

Counterpoint: There is not capillary recruitment in active skeletal muscle during exercise

Proceedings of the Physiological Society, 20‐21 December 1982, Birmingham Meeting: Demonstrations

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Capillary recruitment and flow velocity in skeletal muscle after contractions

Cited by 61 publications

References 29 publications

Dynamics of muscle microcirculatory and blood–myocyte O2 flux during contractions

Dynamics of muscle microcirculatory and blood–myocyte O2 flux during contractions

Counterpoint: There is not capillary recruitment in active skeletal muscle during exercise

Proceedings of the Physiological Society, 20‐21 December 1982, Birmingham Meeting: Demonstrations

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Dynamics of muscle microcirculatory and blood–myocyte O₂ flux during contractions

Dynamics of muscle microcirculatory and blood–myocyte O₂ flux during contractions