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Cardiac autonomic modulation before parachute descent.

Introduction

Chronic psychological stress increases permanent cardiac electric activity that is controlled by the autonomic nervous system (ANS) (1). It is considered as a risk factor that increases cardiovascular morbidity and mortality (2). However, psychological stress linked with high-risk sports has a completely different role. Uncomfortable emotions are suppressed by excitation and they can also be handled better (3). Psychological and physical stress have been shown to act concurrently to increase the levels of beta-endorphins and ACTH (4). Endorphins production counters the negative effects of stress (5) and can even lead to a positive addiction.

Parachuting is one of the traditional risk sports. The psychological state before the parachute descent causes some physiological changes and reactions associated with the expectation and preparation for the parachute descent. Previously, only the anticipatory effect of an acute highly stressful event such as a parachute jump had been evaluated by the comparison of HRV parameters between the night and the orthostatic test in the morning preceding the jump and the control night and the orthostatic test on a separate day (6). Hynynen et al. and Roth et al. (6), (7) also studied the HR response to the stress induced by the upcoming parachute descent. However, monitoring of the heart rate variability (HRV) hasn't been used in such a situation yet. So we expected our study to produce additional information regarding changes of the cardiac autonomic modulation during the preparation for the jump and immediately before the jump. It was predicted that the monitoring of HRV parameters is a sensitive enough method to describe expected changes in autonomic cardiac modulation.

As it was hypothesized, the level of changes in cardiac autonomic modulation depends on physical, mental and technical preparation, and especially on previous experiences. Because of that it is possible to expect significant differences in the changes of the evaluated parameters between beginning and advanced parachutists.

The aim of the study was to analyze if preparation for parachute descent can influence cardiac autonomic modulation of persons undergoing their first parachute descent, how preparation for parachute descent influenced cardiac autonomic modulation of advanced parachutists (more than 200 descents), and if there is a difference in cardiac autonomic modulation during preparation for parachute descent between persons undergoing their first parachute descent and for advanced parachutists.

Methods

Participants

All participants felt healthy (without acute disease) and were asked to abstain from heavy exercise and alcohol for 24 hours before testing, and refrain from smoking the morning of the testing.

Procedure

The cardiac autonomic modulation was monitored by spectral analysis (SA) of heart rate variability at rest and during preparation for parachute descent on land and immediately before leaving the airplane.

The standard position for HRV testing is most frequently lying down. Because of the impossibility to lie down during testing in airplanes, the parachutists were tested in a sitting position. Measurements of the cardiac autonomic modulation were taken in three situations:

* Measurement Ml: out of the landing area, more than 3 hours before drop.

* Measurement M2: in the landing area approximately 20 minutes before boarding.

* Measurement M3: in the airplane between take-off and parachute descent.

All measurements took 10 minutes. The first 5 minutes were used as a time for standardization. The analysis of SA HRV from the start of the 6th minute till the end of the 10th minute was performed and evaluated.

The parachutists were divided into two groups. Participants of basic training, who were prepared for the first parachute descent, entered the first group (BT). Sport parachutists with more than 200 drops were placed into the second group (SP). The parachutists jumped out from the airplane at an altitude of 800 to 4000 meters.

Participants in the BT group took part in all three planned measurements. Measurement M2 was skipped in the SP group because of technical reasons. The starting number of participants was 37. The records of 14 participants contained abnormalities and couldn't be evaluated. Finally, the records of 23 participants were evaluated. Three females and twelve males in the beginners group (BT group) and one female and seven males in the advanced group (SP group) participated in this study. The age of the participants was from 18 to 45 years; the average age of all participants was 26,23 [+ or -] 6,98 years (24,10 [+ or -] 5,93 years in the BT group; 30,5 [+ or -] 6,87 years in the SP group).

The HR was continuously monitored and stored each R-R period (Polar S 810, Finland). The parameters of the spectral analysis of heart rate variability were set by Polar Precision Performance 3.0 software. The limits for frequency components were set to values [P.sub.T]: 0,01--0,40 Hz; [P.sub.VLF]: 0,01--0,04 Hz; [P.sub.LF]: 0,04--0,15 Hz; [P.sub.HF]: 0,15--0,40 Hz. We evaluated total spectral power [(P.sub.T]) [[ms.sup.2]], spectral powers of separate frequency components [P.sub.VLF], [P.sub.LF] a [P.sub.HF] [[ms.sup.2]], and the ratio between [P.sub.LF] a [P.sub.HF] (LF/HF ratio).

Statistical analysis

Statistical analysis was performed with StatSoft, Inc. (2011), STATISTICA (data analysis software system, www.statsoft.com), version 10. Due to the data not having a normal distribution even after logarithm transformation, we used solely nonparametric tests for statistical analysis. The Friedman ANOVA was used to analyze the differences between the situations M1, M2, M3 in the BT group. The nonparametric Wilcoxon ranks test was used to analyze the differences between the situations M1 and M3 for the SP and for the BT group. To analyze the differences between the groups (BT vs. SP) in the different situations (M1 vs. M3), the Mann-Whitney test was used. P-values < 0.05 were considered statistically significant.

Results

Influence of experimental situations on SA HRV parameters in groups

All spectral power parameters ([P.sub.T], [P.sub.VLF], [P.sub.LF] and [P.sub.HF]) were higher in the situation M1 than in M2 and M3 in the BT group. The statistical analysis showed statistically significant differences between all tested situations. On the contrary, the LF/HF ratios were lower in the situation M1 than in M2 and M3 and these differences were not statistically significant (Table 1).
Table 1. Comparison of the SA HRVparameters under the conditions
Ml, M2, and M3 in basic training leavers (BT, n = 15)

                 Ml        M2       M3       P

[P.sub.T]       5055.0    2655.7    581.4      <
([ms.sup.2])  (3971.7)  (2497.0)  (789.0)  0,001

[P.sub.vlf]     1496.0    1136.1    254.5      <
([ms.sup.2])  (1305.6)  (1298.4)  (317.0)  0,001

[P.sub.LF]      2521.2    1238.4    269.0      <
([ms.sup.2])  (1773.0)  (1042.8)  (401.9)  0,001

[P.sub.HF]      1037.8     281.2     57.8      <
([ms.sup.2])  (1202.3)   (300.7)  (101.3)  0,001

LF/HF             6.07      7.34     9.10  0.819
                (5.56)    (5.84)   (7.74)

Data are means (SD)


Similar, statistically significant differences were also found while comparing the results of all the spectral power parameters only in the M1 vs. M3 in the BP group. Despite these results, the differences were smaller and statistically significant only for [P.sub.T] a [P.sub.LF] in the SP group. The LH/HF ratios were higher in the situation M3 than in M1, but the difference wasn't statistically significant in both evaluated groups (Table 2).
Table 2. Comparison of the SA HRVparameters under the conditions Ml,
and M3 in sport parachutists (SP, n = 8) and basic training leavers
(BT, n = 15). Comparison of the influence of experimental situations
between the BT and SP groups

                              (SP, n = 8)

Parameter           Ml             M3         P          M1

[P.sub.T]     2863.6(1761.0)  941.2(815.6)  0.012  5055.0(3971.7)
([ms.sup.2])

[P.sub.VLF]     879.3(482.1)  415.5(323.6)   0.05  1496.0(1305.6)
([ms.sup.2])

[P.sub.LF]     1603.0(976.6)  379.3(319.4)  0.012  2521.2(1773.0)
([ms.sup.2])

[P.sub.HF]      381.2(426.3)  146.3(330.7)  0.208  1037.8(1202.3)
([ms.sup.2])

LF/HF           11.16(14.84)  12.05(11.70)  0.779      6.07(5.56)
              (BT, n = 15)         BT x SP

Parameter          M3         P       P

[P.sub.T]     581.4(789.0)      <    0.049
([ms.sup.2])                0.001

[P.sub.VLF]   254.5(317.0)  0.009    0.087
([ms.sup.2])

[P.sub.LF]    269.0(401.9)      <    0.087
([ms.sup.2])                0.001

[P.sub.HF]     57.8(101.3)  0.002    0.100
([ms.sup.2])

LF/HF           9.10(7.74)  0.423     0.77

Data are means (SD)


Comparison of the influence of experimental situations in the BT and SP groups

The spectral power parameters (except LF/HF ration) were higher in the BT group than in the SP group in the situation M1, however, any statistical significant differences in the parameters were not ascertained by comparing values between the groups. The spectral parameters decreased and the LF/HF ratios increased in both groups in the airplane before parachute descent (M3) (compare Table 2). Whereas the changes were higher in the BT group than in the SP group, in all evaluated parameters the statistical analysis showed significant difference only in the change of PT. We assume the differences between groups in other parameters are not statistically significant mainly because of a small number of participants in the groups (Table 2).

Discussion

Total spectral power of HRV is primarily conditioned by the parasympathetic activity that is significantly reduced during situations of mental stress (8). Whereas a majority of earlier studies used lab-induced stress to study the cardiac autonomic response, our paper is focused on HRV response to a real-life stressful situation.

The design of our experiment was set in such a way that mental stress was gradually increased. The arrival at the landing area, getting dressed and equipped with a parachute, and other necessary materials preparation and the sensation of being at the airport itself caused a significant reduction of cardiac autonomic modulation in inexperienced participants. Our results are in line with the previous study (9) focused on the evaluation of the influence of mental stress on people preparing for their fist parachute descent. The algorithms of both experiments were almost identical even though they evaluated mental stress by biochemical markers such as salivary alfa-amylase and cortisol, testosterone, PRL, LH, and GH in plasma and saliva. These findings appropriately complement the results of Hynynen et al. (6) who did not find any differences in HR, HRV, or stress hormones during the night or the orthostatic test in the morning preceding the jump and concluded that there is not an anticipatory effect on autonomic modulation of the heart caused by the acute highly stressful event of the parachute jump. Our results add new information regarding changes in HRV parameters and cardiac autonomic modulation hours and minutes before the jump and are in line with the other part of Hynynen et al. (6) study focused on evaluation of the HR values before and during the jump.

In addition, the results of our study focused on the differences in cardiac autonomic response between the groups of beginners (BT) and advanced parachutists (SP) are in line with the previous findings (6), (9). Our study found differences between the changes of HRV parameters in evaluated situations between the groups; however, not all of them were statistically significant. Reduction of the PT and power of separate components was smaller in the group of sport parachutists than in the BT group, but the difference was statistically significant only in PT. However, it is difficult to estimate to what extent the changes of cardiac autonomic modulation were caused by physical stress (e.g. discomfort elicited by a relatively narrow space on the airplane, the weight and size of parachutist's equipment, etc.) and to what extent by mental stress. Complete spectral power is primarily influenced by the vagal activity during mentally-neutral conditions at rest. Under the conditions of mental stress or during anxiety, cardiac vagal activity and also HRV are reduced, indicating higher sympathetic activation (10). The extent of this reduction is dependent on the intensity of stress. It is likely that differences in activity of the ANS between both groups were caused by different intensities of mental stress since the outside conditions were identical (identical physical stress). A decreased reaction of the ANS associated with repeated exposure to specific stressful situations in the group of sport parachutists can be considered as proof of a specific adaptation of the ANS during stressful conditions.

We assume that differences between groups in other parameters are not statistically significant mainly because of the small number of participants in the groups.

As the conditions needed for such type of study are very specific, it is not easy to maintain the integrity of the study with a higher amount of participants. However, we found it necessary to increase the amount of participants in future studies to confirm our present findings. On the one hand, ANS stress resistance depends on the number of stressful situations, but on the other hand, it is determined by genetic inheritance. Some authors, moreover, suggest that acute mental stress resistance and its impact on cardiac autonomic modulation are influenced by aerobic training and physical fitness (11), (12).

These papers support that the significance of regular physical activity (particularly aerobic types) can decrease the negative influence of chronically-occurring mental stress. Because of that the questions about whether or not the tolerance effect induced by repeated emotions can have a synergistic action still remain unanswered.

As it was mentioned above there are some limitations in the present study. The jumpers in the SP group were older than the jumpers in the BT group as it is difficult to find younger, but experienced enough (more than 200 jumps) parachutists. There were also a smaller number of females among participants and we can also expect differences in the fitness levels among the participants. Although the changes in the parameters of SA HRV monitored in the situations M1, M2, and M3 were primarily evaluated, we are aware of the limitations caused by the influences of the mentioned factors.

Conclusion

The results of our study showed that preparation for a parachute descent can act as mental stressor that reduces cardiac autonomic modulation. In both studied groups (beginners and experienced jumpers) we found changes in HRV parameters indicating higher sympathetic activation immediately before the jump. Contrary to expectations, the differences that were found in the reaction to acute stress between the groups were not statistically significant. Whereas it seems that monitoring of SA HRV could be also used for a quantification of mental stress, it is necessary to carry out the same experiment with a higher number of participants and with repeatedly monitored cardiac autonomic modulation at rest and in conditions of laboratory psychological stress to confirm the preliminary conclusions of this study.

Acknowledgement

The study has been supported by the research grant from the Ministry of Education, Youth and Sports of the Czech Republic (No. MSM 6198959221) "Physical Activity and Inactivity of the Inhabitants of the Czech Republic in the Context of Behavioral Changes".

Special thanks to colleague Donald N. Roberson, Jr., Ph.D. and Anthony Clementi for assistance in editing and RNDr. Milan Elfmark for assistance in statistical expertise.

Declaration of interest

The authors report no conflicts of interest.

References

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(2.) Rosengren A, Tibblin G, Wilhelmsen L. Self-perceived psychological stress and incidence of coronary artery disease in middle-aged men. Am J Cardiol 1991; 68: 1171-5.

(3.) Rougemont-Buecking A, Rougemont E, Toth R et al. "Epinephrine-addiction" and risk-seeking behavior in athletes: what realities? Rev Med de la Suisse Romande 2007; 3: 1536-40.

(4.) Oltras CM, Mora F, Vives F. Beta-endorphin and ACTH in plasma: effects of physical and psychological stress. Life Sci 1987; 40: 1683-6.

(5.) Carrasco L, Villaverde C, Oltras CM. Endorphin responses to stress induced by competitive swimming event. J Sports Med Phys Fit 2007; 47: 239-45.

(6.) Hynynen E, Konttinen N, Rusko H. Heart rate variability and stress hormones in novice and experienced parachutists anticipating a jump. Aviat Space Environ Med 2009; 80: 976-80.

(7.) Roth WT, Breivik G, Jorgensen PE, Hofmann S. Activation in novice and expert parachutists while jumping. Psychophysiology 1996: 33: 63-72.

(8.) Tonhajzerova I. Mental activity and Heart Rate Variability In: Javorka K., ed. Heart Rate Variability. Mechanisms, evaluation and clinical application. Martin, Slovakia: Osveta, 2008: 96-99.

(9.) Chatternon RT jr, Vogelsong KM, Yu-Cai L, et al. Hormonal response to psychological stress in men preparing for skydiving. J Clin Endocrinol Metab 1997; 82: 2503-9.

(10.) Friedman BH. An autonomic flexibility-neurovisceral integration model of anxiety and cardiac vagal tone. Biol Psych 2007; 74: 185-99.

(11.) Boutcher SH, Nugent FW, McLaren PF et al. Heart period variability of trained and untrained men at rest and during mental challenge. Psychophysiol 1998; 35: 16-22.

(12.) Hamer M, Steptoe A. Association between physical fitness, parasympathetic control, and proinflammatory responses to mental stress. Psychosom Med 2007; 69: 660-6.

Accepted: November 30, 2012

Published: December 21, 2012

Adrress for correspondence:

Radim Slachta

Center for Sports and Preventive Medicine AGEL

Stredomoravska nemocnicni a.s.

Clen skupiny AGEL

Mathonova 291/1, 796 04 Prostejov

Czech republic

mobil: +420 725 761 066

e-mail: radim.slachta@nemsne.cz

Slachta Radim (A), (C-G), Stejskal Pavel (D), (F), Kutalek Libor (B)

Faculty of Physical Culture, Palacky University, Olomouc, Czech Republic

Authors' contribution

A--Study Design

B--Data Collection

C--Statistical Analysis

D--Data Interpretation

E--Manuscript Preparation

F--Literature Search

G--Funds Collection

Stejskal Pavel: stejpa@volny.cz

Libor Kutalek: libor.kutalek@seznam.cz

DOI: 10.5604/17342260.1024767
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Title Annotation:ORIGINAL RESEARCH
Author:Radim, Slachta; Pavel, Stejskal; Libor, Kutalek
Publication:Medicina Sportiva
Article Type:Report
Date:Dec 1, 2012
Words:2983
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