Muscle O₂ diffusion capacity by NIRS: A new approach in the air

Reply to the letter from Manferdelli et al.: ‘Muscle O2 diffusion capacity by NIRS: a new approach in the air’

“…We thank Dr Manferdelli and colleagues for their Letter to the Editor (Manferdelli et al, 2022) regarding our recent work (Pilotto et al, 2022). We described the use of serial arterial occlusions to assess muscle VO 2 (m VO 2 ) recovery kinetics at two different levels of muscle oxygenation by near-infrared spectroscopy (NIRS), in order to estimate muscle O 2 diffusing capacity (DmO 2 ).…”

“…We described the use of serial arterial occlusions to assess muscle VO 2 (m VO 2 ) recovery kinetics at two different levels of muscle oxygenation by near-infrared spectroscopy (NIRS), in order to estimate muscle O 2 diffusing capacity (DmO 2 ). Manferdelli et al (2022) suggested the use of hypoxic gas breathing as an alternative method to alter muscle oxygenation with the same goal.…”

“…Therefore, we concluded that the NIRS-based protocol represents a cost-effective and non-invasive means of assessing in vivo both muscle oxidative capacity and muscle O 2 diffusive capacity. Manferdelli et al (2022) suggested that the outcomes of our proposed experimental protocol might be influenced by the 'low' number of serial arterial occlusions used (we used a minimum of 12). First, we would like to highlight that others have demonstrated that six repeated arterial occlusions leads to reliable measurement of k for muscle oxidative capacity estimation and similar to those obtained with 22 occlusions (Sumner et al, 2020) using a superior inferential approach than traditional null hypothesis significance testing (Mazzolari et al, 2022).…”

“…Thus, even though we do recommend a minimum of 12 occlusions being performed, administering 10 or 20 intermittent arterial occlusions should make only a small difference in measurement of k, while fewer ischaemic occlusions require less time, and it may increase the acceptability of the procedure from the participants. Nevertheless, we would like to thank Manferdelli et al (2022) for commenting on the design of our test, because it gives us the opportunity to provide further clarifications in support of its validity and reliability. Indeed, it is possible that differences in the frequency and duration of the arterial occlusions could introduce differences in capillary distention and capillary haematrocrit, which have the potential to influence muscle O 2 diffusion.…”

“…Thus, we anticipate that use of hypoxic gases would be more variable, not less. Finally, Manferdelli et al (2022) pointed out the that use of hypoxia would allow a wider applicability in fragile patient populations. We disagree with this suggestion, as we think the use of hypoxic gases is unquestionably less amenable for application in clinical populations and would alter the true physiological condition we seek to measure with our new protocol.…”