Muscle microvascular hemoglobin concentration and oxygenation within the contraction–relaxation cycle

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Abstract

Inability to directly measure microvascular oxygen distribution and extraction in striated muscle during a contraction/relaxation cycle limits our understanding of oxygen transport to and utilization by contracting muscle. We examined muscle microvascular hemoglobin concentration (total [Hb/Mb]) and oxygenation within the contraction–relaxation cycle to determine if microvascular RBC volume would be preserved and if oxygen extraction continued during the actual contraction phase. Eight subjects performed dynamic knee extension exercise (40 contractions/min) at moderate (∼30% of peak work rate) and heavy (∼80% of peak) work rates. Total hemoglobin/myoglobin (total [Hb/Mb]) and deoxy-hemoglobin/myoglobin (deoxy-[Hb/Mb]) were measured in the rectus femoris using NIRS to determine if microvascular total [Hb/Mb] would be preserved during the contraction, and to estimate microvascular oxygen extraction, respectively. Mean values during the relaxation (RP) and contractile phases and the peak values during the contractile phase for both moderate and heavy exercise were calculated. Total [Hb/Mb] increased from rest to steady-state exercise (6.36 ± 5.08 μM moderate; 5.72 ± 4.46 μM heavy exercise, both P < 0.05), but did not change significantly within the contraction/relaxation cycle. Muscle contractions were associated with a significant (1.29 ± 0.98 μM moderate; 2.16 ± 2.12 μM heavy exercise, P < 0.05) increase in deoxy-[Hb/Mb] relative to RP. We conclude that (a) microvascular RBC volume is preserved during muscle contractions (i.e., RBCs are present in the capillaries), and (b) the cyclical pattern of deoxygenation/oxygenation during the respective contraction/relaxation phases of the contraction cycle suggests that oxygen extraction is not restricted to the relaxation phase but continues to occur during muscle contractions.

Introduction

Rhythmic muscle contractions cause oscillations of inflowing arterial (Barcroft and Dornhorst, 1949, Lutjemeier et al., 2005, Walloe and Wesche, 1988) and outflowing venous (Grassi et al., 1996, Richardson and Saltin, 1998) blood flow. However, technological constraints have precluded analysis of any oscillatory patterns in microvascular blood volume and their effects on blood-myocyte gas exchange within the contraction cycle in human muscle. Even with analysis of muscle blood flow and V˙O2 kinetics, the tacit assumption has been that O2 exchange proceeds unimpeded and uniformly across the contraction–relaxation cycle (Grassi et al., 1996).

Notwithstanding the above, contraction-induced increases in intramuscular pressure have been considered to at least partially evacuate the muscle vascular bed (Vedsted et al., 2006) which would account for the retrograde arterial (Hoelting et al., 2001, Lutjemeier et al., 2005, Walloe and Wesche, 1988) and anterograde venous (Ameredes and Provenzano, 1997, Vedsted et al., 2006) blood “spurts.” If the source of these blood spurts was the microcirculation, in addition to intervening large arteriolar and venular sites, the reduction in microvascular red blood cell (RBC) volume during contraction would reduce or abolish the potential for blood-myocyte O2 delivery and relegate that delivery to the following relaxation phase. Such behavior would reduce the effective mean capillary RBC transit time and mandate a higher O2 flux density from each RBC during relaxation. In addition, because intramyocyte phosphocreatine concentration falls and those of phosphagen-linked mitochondrial controllers (e.g., free ADP, inorganic phosphate) rise rapidly during the contractile phase of the contraction cycle (Chung et al., 1998), the O2 supply would be decreasing at the very instant that O2 demand were rising.

In marked contrast to the notion that the microvascular bed is emptied of RBCs during contraction, Gray et al. (1967) demonstrated that maximal tetanic contractions did not cause microvascular collapse in the rat spinotrapezius muscle, while Poole et al. (1992) observed RBCs in myocardial capillaries during barium-induced hypersystole. These latter findings suggest that during the muscle contractile phase RBCs would be present in the capillaries – albeit at a reduced flux – to facilitate continued myocyte O2 delivery. Resolution of this issue in human muscle(s) during exercise is crucial for construction of O2 transport models that have physiological validity (Pittman, 2000).

Near infrared spectroscopy (NIRS) technology can track changes in muscle total hemoglobin/myoglobin concentration (total [Hb/Mb]) as well as that of oxygenated and deoxygenated (Hb/Mb) (as oxy-[Hb/Mb] and deoxy-[Hb/Mb], respectively) (DeLorey et al., 2004, Grassi et al., 2003, Kowalchuk et al., 2002). Recent advances in NIRS technology now allow for very rapid sampling (Gratton et al., 1997), providing the temporal resolution necessary to dynamically examine muscle microvascular hemoglobin concentration and oxygenation dynamically within the contraction–relaxation cycle. We conducted the experiment described herein to test the following hypotheses: (1) Microvascular total [Hb/Mb] would be preserved during contraction, and (2) there would be a cyclical pattern of deoxygenation/oxygenation that corresponded with the contraction/relaxation phases of the contraction cycle.

Section snippets

Subjects

Seven male and one female volunteer participated in the study. The physical characteristics of the subjects were (mean ± standard deviation): age 23 ± 2 years, height 175 ± 9 cm, and weight 71 ± 13 kg. Experimental procedures and all possible risks and discomforts associated with the experiment protocol were explained to each subject prior to their providing written consent. This study was approved by the Institutional Review Board for Research Involving Human Subjects at Kansas State University, where

Validation protocol

The responses of one subject during the validation protocol are shown in Fig. 1. Note that the level of noise or variability in each of the NIRS channels did not change from rest to passive movement. Further note that, in this subject, both the deoxy-[Hb/Mb] and oxy-[Hb/Mb] signals showed a progressive emergence of oscillations in concert with active contractions (Exercise), with deoxy-[Hb/Mb] increasing and oxy-[Hb/Mb] decreasing in approximate symmetry, such that total [Hb/Mb] did not change

Discussion

Two principal new findings arise from the present study. First, microvascular RBC volume was preserved during muscle contractions. Thus, RBCs are present in the capillaries – albeit at a reduced flux – which could facilitate continued oxygen delivery to the myocyte. Second, there was a cyclical pattern of deoxygenation/oxygenation that corresponded with the contraction/relaxation phases of the contraction cycle, with deoxy-[Hb/Mb] increasing significantly during the contractile phase. This

References (47)

  • K.K. Kalliokoski et al.

    Blood transit time heterogeneity is associated to oxygen extraction in exercising human skeletal muscle

    Microvasc. Res.

    (2004)
  • J. Piiper et al.

    Modeling oxygen availability to exercising muscle

    Respir. Physiol.

    (1999)
  • R.S. Richardson et al.

    Red blood cell transit time in man: theoretical effects of capillary density

    Adv. Exp. Med. Biol.

    (1994)
  • B.T. Ameredes et al.

    Regional intramuscular pressure development and fatigue in the canine gastrocnemius muscle in situ

    J. Appl. Physiol.

    (1997)
  • P. Andersen et al.

    Maximal perfusion of skeletal muscle in man

    J. Physiol.

    (1985)
  • H. Barcroft et al.

    The blood flow through the human calf during rhythmic exercise

    J. Physiol.

    (1949)
  • R. Boushel et al.

    Monitoring tissue oxygen availability with near infrared spectroscopy (NIRS) in health and disease

    Scand. J. Med. Sci. Sports

    (2001)
  • M.J. Buono et al.

    Skin blood flow affects in vivo near-infrared spectroscopy measurements in human skeletal muscle

    Jpn. J. Physiol.

    (2005)
  • Y. Chung et al.

    Control of respiration and bioenergetics during muscle contraction

    Am. J. Physiol. Cell Physiol.

    (2005)
  • Y. Chung et al.

    Metabolic fluctuation during a muscle contraction cycle

    Am. J. Physiol.

    (1998)
  • S.L. Davis et al.

    Skin blood flow influences near-infrared spectroscopy-derived measurements of tissue oxygenation during heat stress

    J. Appl. Physiol.

    (2006)
  • R.A. De Blasi et al.

    Noninvasive measurement of human forearm oxygen consumption by near infrared spectroscopy

    Eur. J. Appl. Physiol. Occup. Physiol.

    (1993)
  • R.A. De Blasi et al.

    Noninvasive measurement of forearm blood flow and oxygen consumption by near-infrared spectroscopy

    J. Appl. Physiol.

    (1994)
  • D.S. DeLorey et al.

    Effects of prior heavy-intensity exercise on pulmonary O2 uptake and muscle deoxygenation kinetics in young and older adult humans

    J. Appl. Physiol.

    (2004)
  • D.S. DeLorey et al.

    Relationship between pulmonary O2 uptake kinetics and muscle deoxygenation during moderate-intensity exercise

    J. Appl. Physiol.

    (2003)
  • M. Ferrari et al.

    Oxidative metabolism in muscle

    Philos. Trans. R Soc. Lond. B Biol. Sci.

    (1997)
  • L.F. Ferreira et al.

    Effects of pedal frequency on estimated muscle microvascular O2 extraction

    Eur. J. Appl. Physiol.

    (2006)
  • L.F. Ferreira et al.

    Temporal profile of rat skeletal muscle capillary haemodynamics during recovery from contractions

    J. Physiol.

    (2006)
  • L.F. Ferreira et al.

    Muscle capillary blood flow kinetics estimated from pulmonary O2 uptake and near-infrared spectroscopy

    J. Appl. Physiol.

    (2005)
  • B. Grassi et al.

    Muscle oxygenation and pulmonary gas exchange kinetics during cycling exercise on-transitions in humans

    J. Appl. Physiol.

    (2003)
  • B. Grassi et al.

    Muscle O2 uptake kinetics in humans: implications for metabolic control

    J. Appl. Physiol.

    (1996)
  • E. Gratton et al.

    Measurements of scattering and absorption changes in muscle and brain

    Philos. Trans. R Soc. Lond. B Biol. Sci.

    (1997)
  • S.D. Gray et al.

    Site of increased vascular resistance during isometric muscle contraction

    Am. J. Physiol.

    (1967)
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      Based on this, the calculated relative concentration of [Mb] in the rat hindlimb would be 30% and [Hb] 70%. Table 1 shows in human subjects the change in total[Hb + Mb] of the rectus femoris during constant work rate knee extension exercise (Lutjemeier et al., 2008) and of the vastus lateralis during incremental cycling exercise (Ferreira et al., 2006). During knee extension exercise the change in total[Hb + Mb] from rest ranged from 6.9 to 34.5% (mean of 20%).

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