# Heart Rate and Rhythm Changes in Dogs Treated in a Hyperbaric Oxygen Chamber
###### Abstract  
In veterinary medicine, hyperbaric oxygen chamber treatment (HBOT) is gaining popularity. Therefore, an increasing number of patients referred for this therapy are being recorded, mainly due to ischemic events, wound healing support, and a high risk of reperfusion damage. During the HBOT procedure, several changes occur in the body's micro- and macroenvironments. This study involved 34 dogs of various ages and health statuses. The atmospheric conditions in the test hyperbaric chamber included a pressure of 1.5 atmosphere absolute (ATA) at 100% oxygenation. The individuals were divided into three groups: (1) individuals with degenerative mitral valve disease (DMVD), (2) individuals with diseases other than cardiac issues, and (3) healthy individuals who qualified for the HBOT procedure. The period of measurement using the Holter apparatus was divided into four stages: 30 min before the subject's placement in the hyperbaric chamber; a 4-min compression period (setting chamber conditions); a 90 min HBOT period; and a 1 min decompression period of the hyperbaric chamber. During the HBOT, there was a statistically significant decrease in heart rate in groups 2 and 3 compared to group 1. The heart rate in group 1 remained unchanged through every period of the study. In addition, some of the dogs developed respiratory arrhythmia; in two dogs, premature ventricle beats occurred. The changes observed during the ventricular period indicate that the HBOT procedure causes a significant change in heart rate in dogs without cardiac diseases.  
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dia occurs with a decrease in cardiac output [15]. These mechanisms have been described in a number of papers on the physiology and pathophysiology of the cardiovascular system under hyperbaric chamber conditions [5]. However, apart from a composite human patient group [16], these changes have not been described in dogs under veterinary care. It is indicated that heart rate reductions are largely dependent on oxygen; so, pressure conditions should not have as strong an effect as that of high oxygen saturation [17]. Nevertheless, it is known that acquired heart disease and the changes it causes, especially those associated with degenerative mitral valve disease, lead to hyperactivation of the sympathetic nervous system, with a decrease in vagus nerve tone [18]. This leads to an increased heart rate, often resulting in tachycardia, as noted particularly in mitral valve degenerative disease [18]. In addition, available studies in dogs subjected to HBOT describe repeated sessions at different intervals. One of these described one or at least two targeted therapies within a 24 h period in dogs with acute clinical signs [11]. In contrast, another study indicated the tolerability of the chamber and its effect on wound healing in dogs subjected to a single HBOT for 7 consecutive days [14]. However, in nervous system diseases, the number of treatments can reach more than 70 sessions, making the procedure associated with high safety and tolerability [12]. Furthermore, HBOT did not show any negative effects on females after neutering 6 and 18 h after surgery [13]. All procedures from the mentioned studies took place under 100% oxygen saturation with different atmospheric pressures. This varied between 1.5 and 3 ATA, depending on the case being undertaken. Apart from studies on laboratory animals including healthy dogs, no studies of heart rate variability using veterinary patients of different health statuses have been carried out to date. It has not yet been described how dogs with degenerative diseases of the spine, joints, or acquired heart disease respond to changes associated with hyperbaric chamber conditions. Furthermore, the risks associated with potential arrhythmias that could be generated by HBOT have not been described.  
Therefore, the present study aimed to evaluate the effect of a single hyperbaric chamber treatment at 1.5 ATA under 100% oxygenation on the heart rate and rhythm in dogs of different health statuses.