Subcutaneous and muscular (cranial tibial) tissue PO₂ and PCO₂ in CO₂ vapour bath were measured on rabbit by means of Medical Mass Spectrometry, MEDSPECT II, Chemetron, U. S. A.
Subcutaneous PO₂ increased by 30% during CO₂ vapour bath of 5L/min at 37°C and muscular PO₂ increased by 50% after CO₂ vapour bath, keeping the level at least for 2 hours.
Ideal elevation of PO₂ level was observed in vapour bath of 1L/min at 37°C for 30min.
A number of factors causing an elevation of PO₂ in tissue by topically applied CO₂ are to be thought, such as a vasodilating effect, pH-lowering, shift to right of oxygen dissociation curve and so on.
It is assumed that the PO₂ elevation together with an improved tissue perfusion could ameliorate complains of patients suffering from degenerative pathology and peripheral arterial insufficiency by stimulating patients' own potential curability.

Tissue partial pressure of O₂ (PO₂) and CO₂ (PCO₂) in CO₂ vapour bath were measured on rabbit by means of Medical Mass Spectrometry, MEDSPECT II, Chemetron, U. S. A.
Topical absorption of CO₂ through the skin exposed to CO₂ gas was confirmed by comparing the subcutaneous tissue PO₂ and PCO₂ in CO₂ vapour bath with those of CO₂ free head area; subcutaneous tissue PO₂ and PCO₂ were elevated by 92% and 48% respectively in the former, whereas subcutaneous tissue PO₂ and PCO₂ in the latter were found no change. Lowering of subcutaneous pH was found simultaneously with the elevation of PCO₂ in CO₂ vapour bath, contributing largely to the elevation of PO₂ in response to CO₂ accumulation.
Subcutaneous tissue PCO₂ reaches a saturated level in about 30 minutes regardless of each CO₂ flow rate varying from 1 to 5 liters per minute. Too much application of CO₂ gas is not always so effective as expected. Changes of PCO₂ and PO₂ were not in proportion to a rise in temperature from 33.4°C to 41.5°C on the same rabbit. It is, therefore, suggested that the optimal application of CO₂ gas on rabbits is at their indifferent temperature of around 37°C.
The optimal conditions for rabbits would be suggested as 1 liter of CO₂ gas per minute at 37°C for 30 minutes in consideration of the side effects on both circulatory and respiratory systems.
Based on the experimental data, conditions of 30 liters per minute at 40°C for 30 minutes would be recommended in clinical application of CO₂ gas cabin.

We examined Tissue Partial Pressure of O₂ (PO₂) and CO₂ (PCO₂), changes of Pulse Rate (P. R.) and Blood Pressure (B. P.) in a bath at different temperature using rabbit. Expeilmental method;
A rabbit about 2kg body weight is taken a bath at each temperature of 37°C, 40°C, and 43°C for 30 minutes by means of constant-temperature water bath method under the anesthesia of venous drip of NEMBUTAL® (Pentobarbital Sodium).
Teflon catheters for tissue gas analyses are inserted to the Cranial tibial muscle and the over-lying subcutaneous tissue. Tissue PO₂ and PCO₂ in a bath are measured by Medical Mass Spectrometry (MEDSPECT II, Chemetron, U. S. A.). The changes of B. P. and P. R. are recorded simultaneously.
Results and Discussion;
1, In a bath at 37°C, there are no changes on both B. P. and P. R., but the elevation of PO₂ is a little, leading to an insignificant effect.
2, In a bath at 40°C, subcutaneous tissue PO₂ and muscular tissue PO₂ are found elevated by 74% and 53% respectively. P. R. is found increased by 34%, and B. P. is found reduced by 8%. This reduce of B. P. is due possibly to the peripheral vasodilatation. From the standpoint of a peripheral circulation, bath temperature of 40°C is thought to be efficient in washing out metabolites, leading to recovery from fatigue.
3, In a bath at 43°C, subcutaneous tissue PO₂ and muscular tissue PO₂ are found elevated by 74% and by 53% respectively. And tissue PCO₂ are found elevated by 65% in subcutaneous tissue and by 64% in muscular one; 13% up from those found in a bath at 40°C, leading to some fatigue. B. P. is elevated by 16% and P. R. is increased by 69% respectively in a bath at 43°C. Arrhythmia occurs sometimes. It is, therefore, assumed that the man who has a handicap on the circulation system and the elder who has arteriosclerosis in his base should not take a bath at high temperature and/or for a long time.

Actual changes in tissue partial pressures of each gas and tissue perfusion with serial artificial CO₂ bathing were evaluated by means of medical mass spectrometry using 5 rabbits.
An artificial CO₂ bath was prepared by adding “BUB”-KAO, a 50g sodium hydrogencarbonate and succinic acid tablet producing fine CO₂ bubbles in water of constant temperature 20-litre tub at 36-37°C.
Regional tissue perfusion volume was determined on the basis of a clearance curve for Argon tissue partial pressure which was monitored by an on-line computer system with mass spectrometry.
Increase in subcutaneous tissue PCO₂ changed from 27% to 10%, and in PO₂ from 12% to 5% on average by serial bathing every day for 4 weeks, on the other hand tissue perfusion volume was increased in 3 out of 5 cases; from 20.85±3.56 (X±SE) ml/100g/min, SD=6.71, p<0.05 to 25.23±8.00 (X±SE) ml/100g/min, SD=6.96, p<0.05.
CO₂ has been shown to be locally absorbed through the skin resulting in the elevation of subcutaneous tissue CO₂ partial pessure which decreases depending on the tissue perfusion irrespective of metabolic processes. It is, therefore, assumed that the elimination of absorbed constituents by serial bathings is not caused by a decrease in the percutaneous absorption rate but an increase in washing out rate by the improved tissue perfusion.

Artificial CO₂-bath was prepared with a tablet (50g): made from sodium bicarbonate and succinic acid, putting simply in plain water bath tub of 100-200 litre at 40C.
The effect of artificial CO₂-bath was studied in relation to the change in blood lactic acid which is thought to be indicative of the physical fatigue.
It has been clearly demonstrated experimentally using rats that the blood lactic acid after exercise is significantly reduced as compared both to a plain and an artificial Na₂ SO₄-NaHCO₃ bathing.
A favorable effect of the artificial CO₂-bath was also confirmed clinically by a relief from the stiff pain following maximal abdominal muscle exercise.

Sodium succinate is remained behind following artificial CO₂ bathing, prepared with a 50g sodium hydrogencarbonate and succinic acid tablet producing fine bubbles in water.
2NaHCO₂+(CH₂)₂→(COOH)₂→(CH₂)₂(COONa)₂+H₂O+CO₂
Na₂CO₃+(CH₂)₂(COOH)₂→(CH₂)₂(COONa)₂+H₂O+CO₂
Balneotherapeutic effect of sodium succinate was evaluated experimentally using 10 rabbits by means of medical mass spectrometry.
Subcutaneous PO₂ and PCO₂ did not change during the bathing and tissue perfusion of 21.30±3.48ml/100g/min (mean±standard error), SD=4.94, p<0.05 was evaluated at 36-37°C, demonstrating no significant difference compared with that of 20.85±3.56ml/100g/min, SD=6.71, p<0.05 by plain water bathing.
These data showed clearly that the balneotherapeutic effects of an artificial CO₂ bathing prepared with a CO₂-tablet, “BUB”-KAO, was not from organic salt of sodium succinate but from CO₂.

Increase in dermal blood flow by the artificial CO₂-bathing was confirmed by means of a Thermocouple flow meter and by a Laser doppler velocimeter.
The artificial CO₂-bath was prepared with 50g tablet, made from sodium bicarbonate and succinic acid, putting simply in plain water at 38°C.
Dermal blood flow was increased nearly 5-fold by the simple bathing, and was further enhanced 1.3-fold by the artificial CO₂-bathing.
It has been definitely shown by the artificial CO₂-bathing that an increase in oral, finger tip, and forehead temperature and transepidermal water loss is significant compared to the plain bathing, so that the thermal effect equivalent to carbon-dioxated spring will be obtained.

It was found that no effect of increase in dermal blood flow depended solely on HCO₃^- or CO₃^2-, but on CO₂ gas dissolved in water.
The artificial CO₂ bath was prepared with sodium bicarbonate and citric acid, mixing simply in plain water at 38-40°C.
Thermal efficacy was confirmed by a rise in temperature of oral, finger tip and forehead respectively, and by a high transepidermal water loss (TWL) in consequence of increase in dermal blood flow, compared to a plain bathing.
A remarkable effect in artificial CO₂ bathing of 400-800ppm has been well-known clinically, however, a substantial increase in dermal blood flow has observed with artificial CO₂-bathing of 59.8ppm or greater in this study, so that a CO₂-bathing using the preparation would be popularized.

It has been well recognized that no known method can produce as strong or as effective a bath as can be given with natural waters.
The method of bubbling gas through the bath water is thought to be almost entirely ineffective; the solubility of CO₂-gas in water at 40°C is about 10%, but is much further enhanced about 50% by bubbling through an airstone, making fine bubbles.
Tablet form of the CO₂-bath preparation, made from bicarbonate and succinic acid, produces fine CO₂ bubbles so that about 80% of water solubility at 40°C can be obtained.
A CO₂-bath preparation, 50g tablet, can produce 100ppm in maximum concentration in a bath of 150 liter at 40°C, maintaining the level of more than 60ppm for 2 hours.
In order for the safety to estimate the escaped CO₂, a large quantity of the CO₂-bath preparation, 20 and 50 tablets, was used in a relatively air tight room; CO₂ concentration reached the maximum level of 1.9 and 6.6% respectively with a tendency of rapid falling, so that the critical complications could rarely be happened.