Effects of pedal frequency on estimated muscle microvascular O2 extraction

Abstract

An increase in muscle contraction frequency could limit muscle blood flow QM compromising the matching of QM and muscle oxygen uptake VO2M. This study examined the effects of pedal cadence on skeletal muscle oxygenation at low, moderate and peak exercise. Nine healthy subjects [24.7+/-6.3 years (SD)] performed incremental cycling exercise at 60 and 100 rpm. Pulmonary VO2(VO2P) was measured breath-by-breath and vastus lateralis oxygenation was determined by near-infrared spectroscopy (NIRS). The deoxyhemoglobin signal ([HHb]) from NIRS was used to estimate microvascular O2 extraction (i.e., [HHb] proportional, variant VO2M/QM). The VO2P and [HHb] for low, moderate and at peak exercise were determined. The VO2P at 60 rpm (low=0.64+/-0.13, moderate=2.03+/-0.38 and peak=3.39+/-0.84 l/min) were lower (P<0.01) than at 100 rpm (1.29+/-0.23, 2.14+/-0.39 and 3.54+/-0.88 l/min, respectively). There was a progressive increase in [HHb] from low to peak exercise. However, there was no significant difference (ANOVA, P=0.94) for the 60 (in microM, low=24.0+/-9.5, moderate=30.5+/-13.8 and peak=36.7+/-16.5) and 100 contractions/min (in microM, low=25.7+/-11.6, moderate=32.1+/-14.0 and peak=35.4+/-16.5). We conclude that vastus lateralis O2 extraction was similar at 60 and 100 cpm, suggesting that the VO2M/QM in the microcirculation was not altered and, presumably, no impairment of QM occurred with the increase in pedal frequency.

Cycling Wheelchair Provides Enjoyable Pedaling Exercises with Increased Physiological Indexes

“…V 4 O 2 , HR, perceived breathlessness, and leg fatigue were measured and all indexes increased substantially, in linear fashion, as pedaling rates increased. Some studies, which have examined the same parameters during exercise with the cycling ERG, showed that V 4 O 2 and HR increased as pedaling rates increased in a constant workload (Chavarren and Calbet 1999;Ferreira et al 2006) or zero workload (Foss and Hallen 2004;Tokui and Hirakoba 2007). Results of the present study were similar to the fi ndings in these former studies, in that each physiological index of pedaling exercise with the CWC also increased with increasing pedaling rates.…”

Estimated contribution of hemoglobin and myoglobin to near infrared spectroscopy

“…Table 4-1 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, 2005). During knee extension exercise the change in total [Hb+Mb] from rest ranged from 6.9-34.5%.…”

“…Using multiple wavelengths also allows for a more accurate correction of the path length variations that occur in tissue due to scattering. Wavelengths in the vicinity of 690-850 nm have commonly been used for measuring changes only in oxy- [Hb+Mb] and deoxy-[Hb+Mb] (Mancini et al, 1994, Chance et al, 1992, Grassi et al, 1999, Ferreira et al, 2005). Mancini et al (1994) attempted to validate NIRS use in humans using a continuous wave dual frequency (760-800nm) spectrometer.…”

“…The first protocol was an incremental ramp cycling exercise test (Ferreira et al, 2005), performed by nine healthy, physically active subjects, seven males and two females (24.7 ± 6.3 yrs, 67.9 ± 12.2 kg). Each subject visited the lab two times for testing with at least 48 hrs between each test day.…”

“…NIRS has been used to try and assess noninvasively changes in tissue (i.e., Hb and Mb) saturation, so as to infer changes in extra-and intracellular PO 2 . Two other examples of the use of NIRS to estimate dynamic physiological processes include the measurement of muscle VO 2 (De Blasi et al, 1994) and the estimation of capillary blood flow (Q cap ) (Ferreira et al, 2005). In both of these methodologies, the assumption is made that the NIRS signal reflects primarily or exclusively Hb saturation status.…”