## 4 Discussion
included 22 patients with diabetes who immersed their feet in CO\({}_{2}\)-enriched water at 37 degrees for 30 min each day for 15 days [37]. The sensation of the area was evaluated on a scale from one (normal sensation) to five (no sensation) using a pressure pin. Results showed improved sensation from 4.36 before CO\({}_{2}\) therapy to 3.45 after therapy. There was no control group, and statistical evaluation is not presented. Three years later, [PERSON] et al. used the same application mode as [PERSON] [38]. One hundred patients with diabetes and chronic wounds immersed their feet in CO\({}_{2}\)-enriched water, only this time the treatment protocol was somewhat modified--their feet were immersed for 30 min three times a week for 12 weeks. The control group received standard treatment for chronic wounds. Sensation was evaluated similarly to [PERSON]'s method, using a pressure pin. The results showed significant improvement in sensation in the CO\({}_{2}\)-treated group after the therapies compared to pretreatment values and compared to the values of the control group (\(p<0.01\)). Duration of treatment and repetition of the CO\({}_{2}\) applications seems to be of importance. [PERSON] achieved statistically significant improvement in sensation as he increased the number of therapies compared to [PERSON]. In previously mentioned publications, the duration of the therapy is 30 min [37, 38]. We decided to extend the exposure time considering our previous experiences. In healthy subjects, the temperature of the skin reached a plateau in 30 min [19]. In patients with diabetes where circulation is impaired, we added 15 min to ensure the desired effect. The number of repetitions was 20 (4 weeks, 5 times a week), which was enough to heal most of the wounds and achieve improvement in the microcirculation [16, 19, 36]. Considering previous results, we maintained the same protocol to evaluate treatment results for DSPN. Another non-pharmacological treatment approach, which has been investigated to treat DSPN, is a monochromatic infrared energy therapy. The first publications were promising, but additional research findings did not corroborate previous results [11, 12, 13, 14]. A possible explanation stated that patients treated with monochromatic infrared energy therapy also had foot infections that could aggravate the neuropathy [13]. The recovered sensations could have been falsely attributed to monochromatic infrared energy therapy as the infection was treated. To overcome possible bias, we included only patients with a single unilateral chronic wound with no signs of progressive or systemic infections (no elevated inflammatory parameters) to separately evaluate the monofilament and vibration sensation on wound-affected and unaffected legs. In the PVR System, transcutaneous gaseous CO\({}_{2}\) therapy is performed on the entire lower part of the body, meaning that the affected and unaffected legs were equally treated. Results showed comparable improvements in sensation in both legs in patients treated with gaseous CO\({}_{2}\) (Figures 1 and 2). Another limitation of our study is the subjectivity of the methods for sensory evaluation since they are based on patients' responses. The vibration sensation and monofilament tests are recommended for screening and evaluating peripheral neuropathy in diabetic patients [23, 24, 25]. To overcome this limitation, the study was designed as a double-blind, randomized trial in which neither the patient nor the doctor evaluating the results did not know the patient's group. The results of both subjective outcomes--monofilamenttest and vibration sensation test were following results of the temperature of the great toe, which was objectively evaluated with an infrared thermometer. Previously confirmed improved microcirculation [36] could represent the underlying mechanism that improves skin temperature and blood supply to the nerves and, therefore, sensory improvement.