Mental stress is a growing problem in our society. In order to deal with this, it is important to understand the underlying stress mechanisms. In this study, we aim to determine how the cardiorespiratory interactions are affected by mental arithmetic stress and attention. We conduct cross time-frequency (TF) analyses to assess the cardiorespiratory coupling. In addition, we introduce partial TF spectra to separate variations in the RR interval series that are linearly related to respiration from RR interval variations (RRV) that are not related to respiration. The performance of partial spectra is evaluated in two simulation studies. Time-varying parameters, such as instantaneous powers and frequencies, are derived from the computed spectra. Statistical analysis is carried out continuously in time to evaluate the dynamic response to mental stress and attention. The results show an increased heart and respiratory rate during stress and attention, compared to a resting condition. Also a fast reduction in vagal activity is noted. The partial TF analysis reveals a faster reduction of RRV power related to (3？s) than unrelated to (30？s) respiration, demonstrating that the autonomic response to mental stress is driven by mechanisms characterized by different temporal scales. 1. Introduction Stress research has gained growing interest in the last decades. Results from the European Working Conditions Survey in 2000 suggested that 28% of all work-related health problems can be attributed to stress. Work absence associated with stress not only brings along highcosts; for example, in The Netherlands, they estimate a cost of 3 billion € per year [1], but it is also linked with serious health problems such as cardiovascular diseases [2, 3] and musculoskeletal disorders [1, 4, 5]. It is therefore important to identify the mechanisms underlying stress, such as physiological mechanisms. The autonomic nervous system (ANS) dynamically coordinates, among others, cardiovascular variables (such as heart rate and contractility, blood pressure, and peripheral resistance), respiration, and complex interactions between them. The impact of stress on the cardiovascular system has been investigated extensively via the variability of the RR interval variation (RRV) series [6–10]. RRV analysis is widely used to assess the functioning of the ANS. Starting from the RR interval series, several RRV indices that quantify the activity of the ANS have been proposed [11]. In the power spectrum of RRV, a low-frequency (LF) band (0.04–0.15？Hz) and a high-frequency (HF) band (0.15–0.40？Hz) are
References
[1]
I. L. D. Houtman, “Work-related stress,” European Foundation for the Improvement of Living and Working Conditions, February, 2005, http://www.eurofound.europa.eu/ewco/.
[2]
J. E. Dimsdale, “Psychological stress and cardiovascular disease,” Journal of the American College of Cardiology, vol. 51, no. 13, pp. 1237–1246, 2008.
[3]
M. Kivim？ki, P. Leino-Arjas, R. Luukkonen, H. Riihim？ki, J. Vahtera, and J. Kirjonen, “Work stress and risk of cardiovascular mortality: prospective cohort study of industrial employees,” British Medical Journal, vol. 325, no. 7369, pp. 857–860, 2002.
[4]
“Commission asks workers and employers what action should be taken to combat musculoskeletal disorders,” IP/04/1358, Brussels, Belgium, November 2004.
[5]
L. M. Schleifer, R. Ley, and T. W. Spalding, “A hyperventilation theory of job stress and musculoskeletal disorders,” American Journal of Industrial Medicine, vol. 41, no. 5, pp. 420–432, 2002.
[6]
L. Bernardi, J. Wdowczyk-Szulc, C. Valenti et al., “Effects of controlled breathing, mental activity and mental stress with or without verbalization on heart rate variability,” Journal of the American College of Cardiology, vol. 35, no. 6, pp. 1462–1469, 2000.
[7]
N. Hjortskov, D. Rissén, A. K. Blangsted, N. Fallentin, U. Lundberg, and K. S？gaard, “The effect of mental stress on heart rate variability and blood pressure during computer work,” European Journal of Applied Physiology, vol. 92, no. 1-2, pp. 84–89, 2004.
[8]
R. P. Sloan, P. A. Shapiro, E. Bagiella et al., “Effect of mental stress throughout the day on cardiac autonomic control,” Biological Psychology, vol. 37, no. 2, pp. 89–99, 1994.
[9]
J. Taelman, S. Vandeput, E. Vlemincx, A. Spaepen, and S. van Huffel, “Instantaneous changes in heart rate regulation due to mental load in simulated office work,” European Journal of Applied Physiology, vol. 111, no. 7, pp. 1497–1505, 2011.
[10]
T. G. M. Vrijkotte, L. J. P. van Doornen, and E. J. C. de Geus, “Effects of work stress on ambulatory blood pressure, heart rate, and heart rate variability,” Hypertension, vol. 35, no. 4, pp. 880–886, 2000.
[11]
Task Force of The European Society of Cardiology and The North American Society of Pacing and Electrophysiology, “Heart rate variability: standards of measurement, physiological interpretation, and clinical use,” European Heart Journal, vol. 17, no. 3, pp. 354–381, 1996.
[12]
Y. Masaoka and I. Homma, “Anxiety and respiratory patterns: their relationship during mental stress and physical load,” International Journal of Psychophysiology, vol. 27, no. 2, pp. 153–159, 1997.
[13]
W. M. Suess, A. B. Alexander, D. D. Smith, H. W. Sweeney, and R. J. Marion, “The effects of psychological stress on respiration: a preliminary study of anxiety and hyperventilation,” Psychophysiology, vol. 17, no. 6, pp. 535–540, 1980.
[14]
E. Vlemincx, J. Taelman, S. de Peuter, I. van Diest, and O. van den Bergh, “Sigh rate and respiratory variability during mental load and sustained attention,” Psychophysiology, vol. 48, no. 1, pp. 117–120, 2011.
[15]
J. A. Hirsch and B. Bishop, “Respiratory sinus arrhythmia in humans: how breathing pattern modulates heart rate,” The American journal of physiology, vol. 241, no. 4, pp. H620–H629, 1981.
[16]
G. G. Berntson, J. T. Cacioppo, and K. S. Quigley, “Respiratory sinus arrhythmia: autonomic origins, physiological mechanisms, and psychophysiological implications,” Psychophysiology, vol. 30, no. 2, pp. 183–196, 1993.
[17]
D. L. Eckberg, “The human respiratory gate,” The Journal of Physiology, vol. 548, no. 2, pp. 339–352, 2003.
[18]
P. G. Katona and F. Jih, “Respiratory sinus arrhythmia: noninvasive measure of parasympathetic cardiac control,” Journal of Applied Physiology, vol. 39, no. 5, pp. 801–805, 1975.
[19]
J. W. Denver, S. F. Reed, and S. W. Porges, “Methodological issues in the quantification of respiratory sinus arrhythmia,” Biological Psychology, vol. 74, no. 2, pp. 286–294, 2007.
[20]
P. Grossman and E. W. Taylor, “Toward understanding respiratory sinus arrhythmia: relations to cardiac vagal tone, evolution and biobehavioral functions,” Biological Psychology, vol. 74, no. 2, pp. 263–285, 2007.
[21]
T. Ritz, “Studying noninvasive indices of vagal control: the need for respiratory control and the problem of target specificity,” Biological Psychology, vol. 80, no. 2, pp. 158–168, 2009.
[22]
T. Ritz and B. Dahme, “Implementation and interpretation of respiratory sinus arrhythmia measures in psychosomatic medicine: practice against better evidence?” Psychosomatic Medicine, vol. 68, no. 4, pp. 617–627, 2006.
[23]
N. Pattyn, P.-F. Migeotte, X. Neyt, A. V. den Nest, and R. Cluydts, “Comparing real-life and laboratory-induced stress reactivity on cardio-respiratory parameters: differentiation of a tonic and a phasic component,” Physiology and Behavior, vol. 101, no. 2, pp. 218–223, 2010.
[24]
J. Zhang, X. Yu, and D. Xie, “Effects of mental tasks on the cardiorespiratory synchronization,” Respiratory Physiology and Neurobiology, vol. 170, no. 1, pp. 91–95, 2010.
[25]
M. Orini, R. Bailon, L. T. Mainardi, P. Laguna, and P. Flandrin, “Characterization of dynamic interactions between cardiovascular signals by time-frequency coherence,” IEEE Transactions on Biomedical Engineering, vol. 59, no. 3, pp. 663–673, 2012.
[26]
M. Orini, P. Laguna, L. T. Mainardi, and R. Bailón, “Assessment of the dynamic interactions between heart rate and arterial pressure by the cross time-frequency analysis,” Physiological Measurement, vol. 33, no. 3, pp. 315–331, 2012.
[27]
J. S. Bendat and A. G. Piersol, Random Data: Analysis and Measurement Procedures, John Wiley & Sons, New York, NY, USA, 2010.
[28]
L. J. Badra, W. H. Cooke, J. B. Hoag et al., “Respiratory modulation of human autonomic rhythms,” American Journal of Physiology—Heart and Circulatory Physiology, vol. 280, no. 6, pp. H2674–H2688, 2001.
[29]
D. Widjaja, E. Vlemincx, and S. van Huffel, “Stress classification by separation of respiratory modulations in heart rate variability using orthogonal subspace projection,” in Proceedings of the 35th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, pp. 6123–6126, IEEE, 2013.
[30]
J. Pan and W. J. Tompkins, “A real-time QRS detection algorithm,” IEEE Transactions on Biomedical Engineering, vol. 32, no. 3, pp. 230–236, 1985.
[31]
D. Widjaja, S. Vandeput, J. Taelman et al., “Accurate R peak detection and advanced preprocessing of normal ECG for heart rate variability analysis,” in Computing in Cardiology, pp. 533–536, IEEE, 2010.
[32]
M. Orini, R. Bailón, P. Laguna, L. T. Mainardi, and R. Barbieri, “A multivariate time-frequency method to characterize the influence of respiration over heart period and arterial pressure,” EURASIP Journal on Advances in Signal Processing, vol. 2012, no. 1, pp. 1–17, 2012.
[33]
M. Orini, R. Bailón, L. Mainardi, and P. Laguna, “Synthesis of HRV signals characterized by predetermined time-frequency structure by means of time-varying ARMA models,” Biomedical Signal Processing and Control, vol. 7, no. 2, pp. 141–150, 2012.
[34]
L. A. Baccalá and K. Sameshima, “Comments on ‘Is partial coherence a viable technique for identifying generators of neural oscillations?’,” Biological Cybernetics, vol. 95, no. 2, pp. 135–141, 2006.
[35]
M. Yildiz and Y. Z. Ider, “Model based and experimental investigation of respiratory effect on the HRV power spectrum,” Physiological Measurement, vol. 27, no. 10, pp. 973–988, 2006.
