Investigation of changes in electrocardiography before and after free diving

Aim: To evaluate the electrocardiographic (ECG) parameters and hemodynamic parameters in predicting the development of arrhythmias after free diving static apnea performance and maximum breath hold. Material and Methods: Twenty-four volunteer athletes participating in the free diving competition in 2015 (19 males (79.2%) and 5 females (20.8%)) were included in the study. Peripheral O2 saturation (SpO2), heart rate (HR), ECG parameters (PR interval, QRS time, T wave amplitude, corrected QT time, presence of bandle branch block and new bandle branch block development, atrial premature beats, ventricular premature beats) were analyzed. Results: There was no statistically significant difference between before static apnea measurements (systolic blood pressure (SBP) 124.7 ± 10.8 mmHg, diastolic blood pressure (DBP) 76.5 ± 6.7 mmHg, heart rate (HR) 80.2 ± 13.4 beats / min, SpO2 97.1 ± 0.9%) and after performance (SBP 128.8 ± 13.6 mmHg DBP 78.0 ± 5.9 mmHg, HR 85.8, ± 16.5 beats / min and SpO2 96.7 ± 2.3%)(p = 0.175; p = 0.334; p = 0.104; p = 0.336, respectively). Conclusion: No significant changes were observed in ECG parameters, heart rate, saturation and blood pressure values evaluated after static apnea performance. These findings can be used to support that the risk of arrhythmia during static apnea does not persist after apnea has ended.


Introduction
Free diving is a water sports area that has a long history, a livelihood for people in the past and started with a deep breath.
Performance trials are conducted in different branches of free diving sports. Static apnea is one of the free diving sports. It' s a kind of official apnea diving disciplines. In this kind of diving, athletes hold their breath as long as possible. Subjects noses and mounths are submerged and their body floats motionless in a shallow water pool. In speed endurance apnea athlete aims at covering a fixed distance at the least possible time. The usual distance is: for speed 2X50meters (m) in pools of 25m or 50m, and for durability 8X50m and 16X50m. In dynamic apnea the athlete aims at covering the maximum horizontal distance. The athlete keeps his/her body below the surface of the water either with or without fins.
The risk of syncope might be increased by cardiac arrhythmias when the athlete is submerged and this leads to drowning, as a result. The incidence of clinical complications in breath hold competitions in shallow water is well documented: approximately 10% of the static apnea performances resulted in loss of motor control and 1% of loss of consciousness. [1] This study tested the hypothesis that maximum breath-holding performance after static apnea competition may be associated with cardiac arrhythmias, electrocardiographic changes (bradycardia, prolongation of PR interval, QT prolongation etc.). Thus, we investigated the electrocardiogram ( ECG) and peripheral oxygen saturation ( SpO2) was assessed using a finger pulse oximeter.

Material and Methods
Twenty-four volunteer athletes who participated in the free diving competition in 2015 (19 (79.2%) males and 5 (20.8%) females) were included in the study (Table 1).   (Table 3).

Discussion
The development of diving-related arrhythmias has been studied in several studies. The first ECG recording taken during shallow dives in 1963 and the researcher Irving didn't mention presence of any arrhythmias. [2] Abnormal P waves and periods of junctional rhythm were seen in Korean Ama more often especially in winter (incidence was 73% versus 43% during summer) [3]. Also periods of sinus arrest with KAFES at al. Static apnea and changes in electrocardiography junctional escape beats, A-V nodal block, and idioventricular rhythms were noted. [4] These findings resolved immediately upon surfacing. T waves became more peaked, but there was no change in corrected QT interval. In another study, ECG was investigated during the maximal apnea performances with the face submerged but any arrhythmias were not reported. [5] While no arrhythmia was observed in our study, there was no significant change in PR interval, P wave morphology, cQT, T wave, QRS duration and bandle branch block development.
Breath-holding (apnea) triggers a series of known as the diving reflex which collectively lower oxygen utilization and in turn, prolong apneic durations. Breath holding starts many physiological modifications that are known as diving reflex. Many reasons such as an initial parasympathetically induced bradycardial response [6] and decreased cardiac output starts diving reflex. It is followed blood redistribution by a sympathetically induced peripheral vasoconstriction of extremities and non-vital organs [7], As a result of diving reflex the oxygenated blood is preferentially redistributed from non vital organs to the vital organs. [8] Human brain is extremely oxygen-dependent. An interruption in oxygen supply lasting more than a few seconds leads to loss of consciousness, and more than a few minutes leads to irreversible damage. [9] The heart tolerates ischemia better than the brain but there is a risk of conduction block and arrhythmias. Peripheral vasoconstriction activated by diving decreaces blood flow selectively to the more anoxia-tolerant tissues that can maintain substantial anaerobic metabolism.
The diving reflex is triggered by stimulation of the trigeminal nerve on the face, which then causes an increase in vagal tonus, strengthened by cooling of the facial region [10].
Immersion leads to a little to moderate raise in arterial blood pressure. [11] In another study, an important change in blood pressure was not observed despite a decrease in heart rate. [13] In our study, the duration of static apnea was shorter than the arrhythmia observed studies.
Ferrigno et al. showed that bradycardic response was more pronounced in hypothermic water ( 25 C) and developed faster than thermoneutral temperature in diving [14]. Diving bradycardia usually occurred in 10 s of submersion, and plateaus was at minimum heart rate approximately 30 to 60s. [11] Heart rates recovered rapidly after cessation of apnea. IN the present study free diving performance was performed in thermoneutral temperature pools and ECG recordings were taken 5 minutes after the end of the competition, we could not be able to determine the development of bradycardic response due to rapid HR recovery after diving. On the other hand several studies shown that arrhythmias are common in deeper breath-hold dives. [12][13][14] It was observed that the hydrostatic pressure was also impotant concerning the effects of submersion on diving bradycardia, Immersion is holding the body underwater, and this leads to external hydrostatic pressure. The pooled blood in the lower extremities is directed to the intrathoracic area with the increase of external hydrostatic pressure and decreased gravity, and the central blood volume increases with the contribution of peripheral vasoconstriction. High central blood volume increases cardiac chamber stretch and preload.
This increases cardiac force of contraction and stroke volume (SV) by the Frank-Starling law of the heart. More frequently, increase may be explaned by greater stroke volume from increased cardiac contractile forces. During contraction there is no significant change in heart rate. [15] Immersion, hypoxia, cold stimulus and extreme bradycardia can trigger arrhythmia. Increased vagal tone causes bradycardia, but increased sympathetic tone leads to ectopy.
[16] Apart from static apnea, increased metabolic activity and oxygen consumption in muscles related to the use of extremities during dive performances such as dynamic apnea have been found to cause more hypoxemic stress in the body. The degree of hypoxemia is also associated with the development of arrhythmia. Arrhythmias were more frequent underwater than on the surface. [11] Diving in shallow waters, such as the pool where our study is performed, the development of arrhythmia could be less likely than in deep water and no decrease in SpO2 levels after performance may be one of the reasons failure to detect arrhythmias.

Conclusion
As a result, no significant changes were observed in ECG parameters, heart rate, saturation and blood pressure values after static apnea performance. In our study, normal findings after apnea can be used to show that the risk of arrhythmia secondary to hypoxemia associated with increased vagal tonus and bradycardia, which has been shown in various studies during apnea, does not persist after the end of diving. 59 Volume 11 Number 2 p: 56-60