Myoglobin O2 desaturation during exercise. Evidence of limited O2 transport.

Abstract

The assumption that cellular oxygen pressure (Po2) is close to zero in maximally exercising muscle is essential for the hypothesis that 02 transport between blood and mitochondria has a finite conductance that determines maximum 02 consumption.

NIRS Measurement of O2 Dynamics in Contracting Blood and Buffer Perfused Hindlimb Muscle

“…In essence, the O 2 gradient continues to widen with increased work. The present result supports the observation that Mb desaturation continues to deoxygenate with increasing muscle activity and does not reach any plateau [17,19].…”

Estimated contribution of hemoglobin and myoglobin to near infrared spectroscopy

“…On the one hand, it has often been assumed that both the NIRS signal at rest, and changes in the signal during exercise, are derived primarily from Hb (>90%), while Mb is thought to contribute minimally (<10%) to the signal (Mancini et al, 1994, Seiyama et al, 1987. In contrast, other studies suggest that Mb may be the predominant contributor to the NIRS signal , Richardson et al, 1995.…”

“…The shorter distances of 2-2.5 cm in the above studies resulted in predominantly skin blood volume being the major contributor to the NIRS signals. Mancini et al, 1994, Seiyama et al, 1988, Wilson et al, 1989, while others found significant contributions of Mb (e.g., Tran et al, 1999, Richardson et al, 1995. Seiyama et al (1988) measured the contribution of Mb to the NIRS signal by measuring the absorption changes in the rat hindlimb perfused with and without blood.…”

“…1 H-MRS has commonly been used to measure Mb levels in tissue (Mancini et al, 1994, Richardson et al, 1995. Tran et al (1999) found a significant increase in the Mb signal with 1 H-MRS during cuff occlusion and plantar flexion exercise.…”

“…These data suggest that the white vastus of the rat is an inappropriate representation of Mb contribution to the NIRS signal, especially when comparing it to human muscles. Richardson et al (1995) used 1 H-MRS to measure Mb deoxygenation. The maximal deoxy-Mb signal was derived from the average signal during minutes 9 and 10 of vascular cuff occlusion, where it was assumed Mb was completely deoxygenated.…”