## 4 Discussion
Alternatively, the magnitude of perfusion (i.e., peak FBF), termed RH, is largely related to the ability of an individual to vasodilate the microvasculature via various myogenic and local metabolic/endothelial factors within arterioles [7; 9; 10]. Taken together, it remains quite possible that the separate, but linked, factors specifically contributing to reperfusion and re-saturation may not be aligned intra-individually. That is, perhaps the major promoter of the mismatch between NIRS- and strain-gauge-derived measures included inconsistent relationships between discrete factors influencing diffusion capacity and RH. Thus, caution should be used when extending the predictive value of actual microvascular blood flow [2; 9; 10; 43] to measures of microvascular oxygenation. However, it is still important to note that NIRS-parameters have demonstrated value and usefulness, as evidenced by their sensitivity to various chronic conditions such as obesity and CVD [51; 52], as well as sex- and age-specific differences [11; 38; 53; 54; 55; 56; 13]. Ultimately, future work remains needed to fully establish the potential prognostic value of NIRS-based microvascular oxygenation values. Associations among micro- and macrovascular measures. The current results indicated that resting hemodynamics assessed by BABF did not correlate with either FBF or the NIRS measures (O\({}_{2}\)Hb, HHb, tHb, HbDiff) (Table 4). The lack of a clear association of either FBF or the NIRS-derived variables with BABF suggested that the resting macrovascular measures did not track the microvascular blood flow measures. This was particularly interesting given the role of the brachial artery in supplying the downstream micro-vessels (e.g., arterioles). Previously, [PERSON] et al. [58] provided evidence that NIRS (microvascular) appropriately tracked pharmacologically induced changes in blood flow as compared to Doppler ultrasound (macrovascular) measures. Thus, there is some evidence that simultaneous measures from different locations along the vascular tree should be associated. The current results did, however, partially demonstrate this notion. When examining associations separately for the men and women, HHb correlated \"fairly\" with BABF in men (r = 0.303), but not women (r = 0.069), whereas HbDiff exhibited a stronger correlation in women (r = 0.303) than men (r = 0.004) (Table 4). Specifically, HHb is a proxy variable for the degree of deoxygenation in arterial and venous blood (e.g., the perfusive component of the Fick equation) [23]. Related, but distinctly different, HbDiff represents the collective changes in oxygenation in response to supply and demand, and thus, may serve as an index of oxygen delivery [59]. It has previously been advised that these measures should be used in tandem to provide a more comprehensive indicator of metabolic changes [60]. Notably, the NIRS-Doppler ultrasound relation was determined between O\({}_{2}\)Hb and femoral blood flow and from a sample of 10 healthy men [58]. Potential underlying sex differences such as intrinsic respiration, efficiency, oxidative capacity and/or oxygen affinity should likely not be ignored when assessing NIRS-derived values [29; 30; 54]. In support of these intrinsic factors likely promoting the observed sex differences, the men and women did not exhibit any difference in changes of HR or MAP during the experiment. Overall, in conjunction with a previous report [61], the current results suggest using caution when attempting to generalize vascular findings of one specific region to another, and underlying differences between men and women should be considered. Consistency of FBF and NIRS variables at rest. Limited data exist concerning the consistency of consecutive slopes of FBF and NIRS-derived variables induced by venous occlusion during resting conditions. Previous investigations, like the current study, have reported methodology including a calculated resting mean value derived from four recordings [62].