Determination of respiratory point compensation in healthy adults: Can non-invasive near-infrared spectroscopy help?

Abstract Objectives We tested the hypothesis that the respiratory compensation point can be accurately determined in healthy participants during incremental cycling exercise using non-invasive near-infrared spectroscopy-derived measures of deoxygenated hemoglobin ( deoxy Hb). Design Validation study. Methods 118 healthy men (average age 47 ± 19 yrs, range 20–79 yrs) performed an incremental cycling test to exhaustion. Breath-by-breath pulmonary oxygen uptake ( V ˙ O 2 ) and other ventilatory and gas exchange variables were measured and used to determine respiratory compensation point. Vastus lateralis deoxy Hb was monitored using a frequency domain multi-distance system near-infrared spectroscopy device and deoxy Hb data were modeled with a piece-wise double-linear function from which the deoxy Hb deflection point ( deoxy HbDP ) was determined. The absolute (L min−1 ) and relative (% maximal V ˙ O 2 [ V ˙ O 2max ]) V ˙ O 2 values associated with the respiratory compensation point and deoxy HbDP were determined for each individual. Results Deoxy Hb increased as a function of exercise intensity up to a point ( deoxy HbDP ) after which the signal displayed a “near-plateau”. The deoxy HbDP corresponded to a V ˙ O 2 of 2.25 ± 0.69 L min−1 (74 ± 12% V ˙ O 2max ) which was not significantly different from the V ˙ O 2 at respiratory compensation point (2.28 ± 0.70 L min−1 and 74 ± 10% V ˙ O 2max , p < 0.05). Both indices were highly correlated ( r2 = 0.86) and Bland Altman analyses confirmed a non-significant bias for V ˙ O 2 (−0.024 L min−1 ) concomitant with a small imprecision of 0.26 L min−1. Conclusions During incremental cycling exercise, the V ˙ O 2 associated with the onset of a plateau in near-infrared spectroscopy-derived deoxy Hb occurs in coincidence with the V ˙ O 2 at respiratory compensation point suggesting that respiratory compensation point can be accurately estimated, non-invasively, using near-infrared spectroscopy-derived deoxy Hb in alternative to the use of ventilatory-based techniques.