## 4 Discussion
In support of our notion that bathing of feet in CO2-enriched water, several clinical studies have demonstrated an increase in blood flow subsequent to treatment with CO2. In patients with mild, bilateral, peripheral occlusive arterial disease (intermittent claudication,femoral or iliac type) immersion of the lower leg and foot in fresh CO\({}_{2}\)-enriched water (1200 mg CO\({}_{2}\)) for 20 min has shown increases in microcirculation and oxygen tension in the skin of the foot [15]. Interestingly, topical applications of CO\({}_{2}\) have been shown to increase skin blood flow in a concentration-dependent manner, providing additional support for the clinical use of CO\({}_{2}\) bathing in the treatment of disturbances of skin circulation as well as skin ulcers and wounds [50]. It has been suggested that the effects of CO\({}_{2}\)-enriched water on the subcutaneous microcirculation may be due to peripheral vasodilation as evidenced by increased parasympathetic and decreased sympathetic activity and that CO\({}_{2}\) foot bathing is clinically effective on salvage of CLI (Fontaine stage IV) limbs [16]. Recently, patients with PAD risk factors (ABI in the normal range or ABI indicating some or moderate arterial disease, ABI > 0.5) were shown to benefit from CO\({}_{2}\) therapy due to improvements in blood flow [51]. In our study, while data on usage of bespoke footwear, ability to walk barefoot at home, occurrence of amputation and use of antibiotics for the treatment of foot ulcer were collected, no differences were observed between control and treated groups (_data not shown_). It is also pointed out that in 2/7 hemodialysis subjects that were randomized into the treated group there was the occurrence of new pressure type ulcers in different region of the foot. Accordingly, in this North American population of subjects with foot ulcers and undergoing hemodialysis, there is potentially an increase in the risk (by about 28%) of new pressure-type ulcers forming and thus this negative effect from exposure to CO\({}_{2}\) foot bathing is suggestive that foot bathing may be contraindicated in this population (_data not shown_). It should be mentioned that tap water contains various impurities and salts used for its purification. Salts dissolved in water, when exposed to CO\({}_{2}\) can lead to the formation of substances that can cause chemical burns, it is thus possible that the high risk for new ulcer formation observed in some of the hemodialysis patients may be related to this. Therefore, in any follow up especially a large-scale study, use of distilled water may be indicated. Several preclinical studies have examined the potential mechanisms for the beneficial actions of bathing of ischemic limbs in CO\({}_{2}\)-enriched water with respect to improved microcirculation. In this regard, [PERSON] et al. [52] have shown that CO\({}_{2}\) bathing increased small blood vessel count, an index of vascular density. In addition, [PERSON] et al. [53] have reported that CO\({}_{2}\) water bath therapy of the ischemic hind limb of diabetic rat augments blood flow as well as evokes the development of angiogenesis in the skeletal muscle of diabetic ischemic animals. Taken together, such therapy may be some benefit for the treatment of PAD in diabetes that may also be due to a reduction in oxidative stress [54]. In this regard, a reduction of plasma free radical concentration, as well as an increase in antioxidant levels have been reported to be associated with an increase in microcirculation in patients with PAD (Fontaine stage III) [55]. In conclusion, although the sample size is small, the present pilot study is suggestive that foot bathing in CO\({}_{2}\)-enriched water may accelerate the healing of foot ulcers due to an improvement in microcirculation and adequate perfusion of the ischemic wound area. Thus, treatment of foot ulcers by immersing in CO\({}_{2}\)-enriched water may potentially serve as an adjunct to standard therapeutic approaches for diabetic foot wound healing. Conceptualization, P.S.T. and B.R.