Objective To investigate the relationship between Near-infrared spectroscopy (NIRS)-derived muscle oxygen saturation (SmO2) and Cardiopulmonary indexes at the Ventilatory threshold (VT1 and VT2) during Cardiopulmonary exercise test (CPET) ofyoung cyclists.
Methods 12 young cyclists performed a maximal incremental exercise test to exhaustion on a friction-braked cycle ergometer (Monark 839E, Sweden).Heart rate (Polar RS400, Finland) and respiratory gas exchange were measured during the Resting and exercise phases using a breath-by-breath system. SmO2 of active muscles during cycling was measured by NIRS monitors (Fortiori Design LLC, USA), and three of the monitors were placed on both vastus lateralis (VLL & VLR) and left gastrocnemius lateralis (GLL) of left leg. The resting value of the SmO2 of the GLL (SmO2-GLL), the left vastus lateralis (SmO2-VLL), and the right vastus lateralis (SmO2-VLR) was recorded as a baseline. Then after VT1 and VT2 of each subject were measured by the V-slope method during a CPET, values of muscle oxygen corresponding to the three lower limb sites at two ventilation thresholds was recorded to reflect the muscle oxygenation level at the anaerobic threshold; And the change of muscle oxygen relative to the baseline was calculated to reflect the degree of muscle deoxygenation, which is termed as deoxygenation indexes(ΔSmO2-GLL, ΔSmO2-VLL, ΔSmO2-VLR); As well, Cardiopulmonary indexes including Heart rate (HR), Minute ventilation (VE), Relative oxygen uptake (VO2R), Carbon dioxide production (VCO2) and Respiratory exchange rate (RER) at the Ventilatory threshold were measured. All Results were expressed as mean ± standard deviation. Finally, Pearson correlation analysis was used to determine the relationship between multi-site muscle oxygen saturation of lower extremities and Cardiopulmonary indexes (HR, VE, VO2R, VCO2, RER). The significance level was defined as p<0.05.
Results Each subject performed their best to complete the aerobic capacity test. The average VO2peak of the 12 subjects was 42.77 ± 9.69 ml/kg/min (Male: 47.38 ± 9.41 ml/kg/min; Female: 36.31 ± 3.33 ml/kg/min). At rest, the calf and thigh SmO2 were 67.92%± 6.84% (SmO2-GLL), 61.42% ± 13.77% (SmO2-VLL), 64.83% ± 10.62% (SmO2-VLR)respectively; HR, VE, VO2, VO2R, VCO2 and RER were 112.08 ± 14.38, 25.96 ± 8.74 L / min 0.94 ± 0.32 L/min, 15.82 ± 4.30 ml/kg/min, 0.81 ± 0.24 L/min,0.88 ± 0.12 L/min, and 0.38 ± 0.07, respectively. Correlation analysis shows that when adolescent athletes reached the anaerobic threshold level, there was a significant correlation between muscle oxygen and cardiopulmonary: At the time of VT1, for Oxygenation index, SmO2 of GLL was highly negatively correlated with HR (r=-0.69,p<0.05), VE (r=-0.71, p<0.01), VO2R (r=-0.65, p<0.05), VCO2 (r=-0.66, p<0.05) and RER (r=-0.58, p<0.05); SmO2-VLL was also highly negatively correlated with VE (r=-0.70, p<0.05), VO2R (r=-0.70, p<0.05), VCO2 (r=-0.66, p<0.05); Additionally, there is also high inverse correlation between SmO2-VLR and HR (r=-0.66, p<0.05), VE (r=-0.70, p<0.05), VO2R (r=-0.66, p<0.05), VCO2 (r=-0.68, p<0.05), RER (r=-0.60, p<0.05). In terms of deoxygenation indexes, ΔSmO2-GLL was highly negatively correlated with VE (r=-0.61, p<0.05), VO2R (r=-0.64, p<0.05) and VCO2 (r=-0.59, p<0.05); While, ΔSmO2-VLL was highly negatively correlated with HR (r=-0.62, p<0.05), VE (r=-0.72, p<0.01),VO2R (r=-0.80, p<0.01) and VCO2(r=-0.84, p<0.01); ΔSmO2-VLR was correlated with HR (r=-0.75, p<0.01), VE (r=-0.62, p<0.05), VO2R (r=-0.58, p<0.05) and RER (r=-0.74, p<0.01), and it also shows highly negative correlation. When VT2 occurred, only SmO2 of the GLL in the oxygenation indexes was highly positively correlated with HR (r=0.65, p<0.05), there was no correlation between GLL-SmO2 and any other gas exchange indexes. In terms of muscle deoxygenation indexes, only ΔSmO2 in the thigh VLR was significantly negatively correlated with RER (r=-0.75, p<0.01).
Conclusions Based on these results, there is a high correlation between NIRS-derived regional muscle oxygen saturation (Oxygenation and Deoxygenation indexes) of lower extremities and cardiopulmonary index (HR, VE, VO2R, VCO2, RER) during CPET of young cyclists at first Ventilatory threshold, however, it is still unclear whether there is a significant correlation between muscle oxygen saturation of lower extremities and other cardiopulmonary indexes when second Ventilatory threshold occurs except Heart rate or Minute ventilation.
Influence of acute haemodynamic changes on the oxygen saturation during electro-convulsive therapy