Perceptual & Motor Skills: Physical Development & Measurement 2014, 118, 3, 890-896. © Perceptual & Motor Skills 2014

HEART RATE VARIABILITY DIFFERS BETWEEN RIGHTAND LEFT-HANDED INDIVIDUALS1, 2 RAMAZAN YÜKSEL Gulhane Military Medical Academy, Ankara, Turkey MUZEYYEN ARSLAN AND ŞENOL DANE Turgut Özal University, Ankara, Turkey Summary.—Previous studies reported reduced longevity in left-handers with the suggestion that it may be associated with different heart diseases. Therefore, differences in heart rate variability (HRV), an index of autonomic cardiac activity, were examined for right- and left-handed individuals. 120 healthy young university students (75 women, 45 men; M age = 20.4 yr., SD = 1.5) volunteered. Handedness was assessed with the Edinburgh Handedness Inventory and HRV was measured via electrocardiography. The results suggest that the left-handers' HRV was significantly different from that of right-handers on several parameters. The atypical cerebral organization of left-handers may be related to an imbalanced autonomic system that results in higher frequencies of heart irregularities.

Several studies have shown that in the general population, the frequency of left-handedness decreases with increasing age (Fleminger, Dalton, & Standage, 1977; Porac, Coren, & Duncan, 1980; Beukelar & Kroonenberg, 1986; Coren & Halpern, 1991; Aggleton, Kentridge, & Neave, 1993; Hughdal, Satz, Mitrushina, & Miller, 1993; Suar, Mandal, Misra, & Suman, 2007). Coren and Halpern (1991) suggested that the apparent decreased longevity of left-handed people might be due to their high accident susceptibility, birth stress factors such as neuropathy, developmental delays and irregularities, intrauterine hormonal factors, or deficiencies in the immune system. This hypothesis is in line with findings of greater health problems in left-handers. For instance, Fudin, Renninger, Lembessis, and Hirshon (1993) reported a longevity advantage for right-handers, or disadvantage for left-handers, among baseball players. Also, Fritschi, Divitini, TalbotSmith, and Knuiman (2007) reported a higher risk for breast cancer in lefthanders compared to right-handers. Choudhary and O'Carroll (2007) reported a higher frequency of posttraumatic stress disorder in left-handers. Address correspondence to Ramazan Yüksel, Gulhane Military Medical Academy, Department of Physiology, Etlik, Ankara, Turkey or e-mail ([email protected]). 2 The authors wish to thank the third-year students of the Faculty of Medicine, Fatmanur Acabay, Selma Yildirim, and Merve Guler, for their contributions to the recruitment of subjects for this study and recording of ECG. 1

DOI 10.2466/19.10.PMS.118k24w5

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Canakci, Akgul, Akgul, and Canakci (2003) reported a higher risk of dental trauma for left-handers. An alternative hypothesis, that the rarity of older left-handers is due to a more frequent switching to right-handedness, was rejected in a statistical analysis designed to test this possibility (Coren, 1994). Hughes, Dorner, and Wind (2008) reported a higher prevalence of lefthandedness in a Cardiac Rehabilitation Unit. They suggested that heart disease might be one reason for a reduced longevity among left-handers. Lane, Caruso, Brown, Axelrod, Schwartz, Sechrest, et al. (1994) compared the handedness ratios in patients with ventricular tachycardia-ventricular fibrillation (VT-VF) and controls, and found that the ratios of left-handedness and non-right-handedness in the patient group were significantly higher than those of similarly aged adults in the general population. These authors suggested that left-handedness (or non-right-handedness) might be considered as a risk factor for sudden death in the context of coronary artery disease. Heart rate variability (HRV), i.e., the fluctuations in cardiac rate or rhythm, is associated with the equilibrium between activities of the sympathetic and parasympathetic (autonomic) nervous systems (Kristal-Boneh, Raifel, Froom, & Ribak, 1995). These fluctuations in heart rate can be measured with a noninvasive electrocardiography (ECG). Increasing numbers of studies are using this method (HRV) to detect sympathovagal imbalances and their related health issues such as sudden death, coronary artery disease, congestive heart failure, or cardiovascular risk factors such as smoking, diabetes, hyperlipidemia, and hypertension (Naver, Blomstrand, & Wallin, 1996; Schwartz, 1998; Bertoia, Triche, Michaud, Baylin, Hogan, Neuhouser, et al., 2013; Turker, Aslantas, Aydin, Demirin, Kutlucan, Tibilli, et al., 2013). These diseases or pathologies can affect and/or be affected by the autonomic nervous system, and analyses of HRV parameters have been proposed as part of the clinical evaluation for different heart diseases (Sztajzel, 2004). Hypothesis. Heart rate variability (HRV) differs between right-handers and left-handers. METHOD Participants One hundred twenty healthy young university students (75 women, 45 men; M age = 20.4 yr., SD = 1.5) participated in this study. Exclusion criteria were the following health problems: autonomic nervous system, psychiatric, metabolic, respiratory, or cardiac diseases that might affect the heart rate. Exclusion criteria were questioned for all participants before starting the study. They had no complaints regarding health.

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There were 60 left-handers (27 men, 33 women) and 60 right-handers (18 men, 42 women) among the participants. There was no difference between the right- and left-handers on age or gender. The purpose of the study was explained verbally to all students and they provided signed informed consent. All students had volunteered to participate in this study. The Ethical Committee of the Faculty of Medicine of the University of Fatih approved this study. Measures Handedness was assessed with the Edinburgh Handedness Inventory (Oldfield, 1971; Tan, 1988). This inventory generates handedness scores from −100 to 100. Participants having handedness scores from −100 to 0 were considered to be left-handed, and those with scores from 0 to 100 were considered to be right-handed. ECG was recorded using PowerLab 26T data acquisition system (ADInstruments, Australia), a device for multimodal monitoring of biosignals. The digital signals were transferred to a laptop and analyzed using LabChart® software (MLS310/7 HRV Module). A full continuous ECG could be viewed and saved for later analysis, and software-based filters were used to exclude noise, movement artifacts, and ectopic beats prior to HRV analyses. Procedure HRV can be affected by age, physical activity, body position, ambient conditions, and circadian rhythm. So ECG was recorded from 10 am to 12 am in all participants. Before the heart rate measurements were taken, all participants rested for 10 min. to stabilize autonomic parameters before the ECG recording began. Three self-adhesive ECG electrodes were applied to the right wrist and right and left legs, respectively. Then ECG was recorded for 15 min., in the supine position. The noise was reduced to a minimum and the laboratory was darkened to facilitate relaxation. Analysis Means and standard deviations were calculated. Statistical analysis was performed using SPSS for Windows Version 16.0 (SPSS, Inc., Chicago, IL). All variables were normally distributed. Independent samples t test was used to compare groups. A p value lower than .05 was considered significant. RESULTS As can be seen in Table 1, left-handers had significantly lower values, compared to right-handers, in the following parameters: (a) maximal NN (beat to beat) intervals (max NN); (b) minimal NN intervals (min NN); (c) mean NN intervals (mean NN); (d) standard deviation of NNs calculat-

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LEFT-HANDEDNESS, HEART RATE VARIABILITY TABLE 1 HRV PARAMETERS AND HANDEDNESS Right-handers (Mean ± SD)

Left-handers (Mean ± SD)

t

P

Effect Size

Max. NN (ms)

1104.2 ± 174.4

985.2 ± 139.9

4.11

0.00

0.75

Min. NN (ms)

652.6 ± 73.8

613.4 ± 72.8

2.95

0.01

0.54

Mean NN (ms)

846.4 ± 126.2

778.5 ± 118.2

3.04

0.01

0.56

Pulse rate (1/min)

72.3 ± 9.6

78.7 ± 11.1

3.42

0.01

0.63

SDNN (ms)

65.9 ± 24.2

57.5 ± 17.3

2.18

0.03

0.4

SDANN (ms)

65.0 ± 32.8

48.1 ± 22.3

3.29

0.01

0.6

RMSSD (ms)

64.9 ± 32.7

48.1 ± 22.3

3.29

0.01

0.6

pNN50 (%)

37.8 ± 20.4

24 ± 19.5

3.78

0.00

0.69 0.36

HRV parameter

Total power (ms2)

4470.1 ± 3607.3

3430.5 ± 2057.2

1.94

0.05

VLF (ms2)

1349.4 ± 1178.6

1369.3 ± 768.8

0.11

0.91

0.02

LF (ms2)

1071.1 ± 877.8

831.1 ± 663.7

1.69

0.09

0.31

HF (ms2)

1820.5 ± 1633.6

1085.4 ± 922.3

3.04

0.01

0.56

LF/HF 0.8 ± 0.5 1 ± 0.6 1.91 0.06 0.35 Note.—HRV, heart rate variability; NN, beat-to-beat intervals; SDNN, standard deviation of NNs calculated in the entire recording session; SDANN, standard deviation of NNs calculated on 5-minute segments; RMSSD, square root of the mean squared difference of successive NNs; pNN50, percentage of adjacent NNs that differ by more than 50 ms; VLF, very low frequency range (0.003-0.04 Hz); LF, low frequency range (0.04–0.15 Hz); HF, high frequency range (0.15–0.4 Hz).

ed either on the entire recording session (SDNN) or on 5-min., segments (SDANN); (e) square root of the mean squared difference of successive NNs (RMSSD); (f) percentage of adjacent NNs that differ by more than 50 msec. (pNN50); and (g) power in the high frequency range (0.15–0.4 Hz) (HF). Another HRV parameter, the number of pulses in a minute (pulse rate), was higher in left-handers. Other HRV parameters such as (a) variance in all NN intervals ≤ 0.4 Hz (total power), (b) power in the very low frequency range (0.003–0.04 Hz; VLF), (c) power in the low frequency range (0.04–0.15 Hz; LF) and LF/HF were not different statistically significantly. Overall, the hypothesis was supported; there were significant differences in HRV between right-handers and left-handers. In this context, many HRV parameters were lower in left-handers. Thus, HRV decreased in left-handers and cardiac autonomic balance has shifted toward the sympathetic nervous system. This finding supports the hypothesis and also supports more frequent cardiac rhythm disorders in left-handers.

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DISCUSSION In the present study, several HRV parameters were significantly lower in left-handed healthy young university students compared to their righthanded counterparts. These results suggest that the right-handers had, in general, a better cardiac autonomic rhythm than the left-handers. That is, the atypical cerebral dominance or left-handedness seems to be related to the imbalanced functioning of the autonomic nervous system and its effects on the heart rate variability. HRV can be evaluated in two main methods in a continuous ECG recording: time domain analysis (SDNN, SDANN, RMSSD, pNN50) and frequency domain analysis (total power, VLF, LF, HF, LF/HF). One of the time domain measurements, SDNN is a global sign which reflects the components associated with the circadian rhythm of the recording period. SDANN provides long-term information of overall cardiac autonomic activity. RMSSD and pNN50 parameters show mostly autonomic tone changes reflecting the vagal system (Scholz, Bianchi, Cerutti, & Kubicki, 1997; Sztajzel, 2004). In frequency domain measurements, the VLF component is thought to be an important determinant of physical activity and is expressed as an index of sympathetic activity. LF is controversial on cardiac autonomic function, but most authors suggest that LF is an indicator of sympathetic activity. HF is suggested as a marker of vagal tone and respiration. The ratio of LF and HF (LF/HF) is important because it reflects sympatho-vagal balance. A higher LF/HF ratio shows that sympathetic activity is dominant. In the present study, LF/HF was higher in left-handers compared to righthanders, but the difference was not statistically significant, probably due to higher sympathetic activity in left-handers. Finally, the total power is the sum of the all frequency parameters (Scholz, et al., 1997; Sztajzel, 2004). These results support the hypotheses of previous reports of higher prevalence of left-handers with cardiac irregularities and problems (Lane, et al., 1994; Hughes, et al., 2008). In addition, Jaju, Dikshit, Purandare, and Raje (2004) reported different heart rate and blood pressure responses to autonomic stressors in left- and right-handers. Together, these studies suggest different autonomic control on the cardiovascular system and irregular heart functioning in left-handers compared to right-handers. Previous studies have found that postictal heart rates after bilateral and right unilateral electroconvulsive therapy in patients with different psychiatric disorders were higher compared to left unilateral electroconvulsive therapy (Lane, Zeitin, Abrams, & Swartz, 1989; Swartz, Abrams, Lane, DuBois, & Srinivasaraghavan, 1994). These studies suggest asymmetric sympathetic cardiac control where the right cerebral hemisphere has a greater dominance in the control of heart rate activity in healthy persons (Fang & Wang, 1962; Henry & Calaresu, 1974; Rogers, Battit, McPeek,

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& Todd, 1978). Thus, it could be speculated that the atypical cerebral dominance associated with left-handedness is related to an imbalance in the functioning of the autonomic nervous system, which is reflected in the different HRV found in left-handers. This typical cerebral organization associated with left-handedness could be the reason for the higher frequency of heart diseases and lower longevity of left-handers. The limitation of this study was the small number of volunteers, especially left-handers. In addition to this, ambient conditions must be standardized for all participants. Otherwise, the ambient environment can affect the heart rhythm, a very dynamic process, throughout ECG recording. Further studies are needed to follow up these initial intriguing results. REFERENCES

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Heart rate variability differs between right- and left-handed individuals.

Previous studies reported reduced longevity in left-handers with the suggestion that it may be associated with different heart diseases. Therefore, di...
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