ABSTRACT
Resumen La variabilidad de la frecuencia cardiaca (VFC) se utiliza como una señal fisiológica para evaluar la reactividad psicofisiológica al estrés. El análisis en el dominio de la frecuencia de esta señal se ha usado para describir el papel del sistema nervioso autónomo en los procesos de adaptación al estrés. Sin embargo, el uso de medidas de tendencia central para reportar los resultados de distintas poblaciones desestima las diferencias individuales en la reacción frente al estrés. El objetivo de esta investigación fue caracterizar la reactividad cardiaca ante la evocación de eventos estresantes en población universitaria. Participaron 94 estudiantes de nuevo ingreso a la carrera de psicología, de dos universidades de México. Los resultados indican un decremento consistente en la banda de alta frecuencia ante la evocación de eventos estresantes, en comparación con la banda de baja frecuencia. La caracterización de la respuesta autonómica al estrés presenta dos subgrupos acoplados (co-activación y co-inhibición); y uno desacoplado. Nuestros hallazgos, ratifican la viabilidad de la banda de frecuencia alta de la VFC como un indicador estable de reactividad al estrés, y resaltan la importancia de las diferencias específicas de la actividad autonómica en la caracterización de la respuesta fisiológica al estrés.
Abstract Heart rate variability (HRV) is used as a reliable physiological signal to assess psychophysiological reactivity to stress. Frequency-domain mathematical analysis of the HRV signal provides metrics that are associated with the performance of the autonomic nervous system. However, the use of measures of central tendency to report global results in different populations underestimates individual differences in the way people react to stress and the clinical importance of this response. The objective of this research was to characterize cardiac reactivity to the evocation of stressful events in a university population. The participants were 94 new psychology students from two universities in Mexico. A psychophysiological stress assessment was performed to estimate cardiac reactivity; the evaluation consisted of the following conditions: 1) Baseline; 2) Evocation of stress; and 3) Recovery. The participants were sitting with their eyes closed and without moving during every single one of the conditions. Four subgroups were created depending on the type of cardiac reactivity to stress. The results indicate a significant consistent decrease in the high-frequency band when evoking stressful events, compared to the low-frequency band. Similar responses were observed between the low-frequency band and the high-frequency band in 60.6% of the cases, suggesting that the antagonistic autonomic balance between the two divisions of the ANS was scarce. According to the autonomic space model and the type of stress reactivity of each student, there were two subgroups characterized by co-activation and co-inhibition modes; and one subgroup characterized by uncoupled response mode. Our findings confirm the viability of the high-frequency band of HRV as a stable indicator of stress reactivity. Likewise, evidence is generated in favor of using evocative stress stimuli to assess physiological reactivity like more personal stressors. Lastly, the importance of specific differences in autonomic activity to characterize the physiological response to stress and its possible clinical utility to propose interventions and select techniques that most effectively benefit vulnerable populations are highlighted.
ABSTRACT
BACKGROUND AND OBJECTIVES: Insomnia is the most prevalent sleep disorder in the general population and is considered to be a disorder of hyperarousal. The aim of this study was to measure the psychophysiological responses in insomnia patients using a biofeedback system, and to compare them with results from normal healthy subjects. MATERIALS AND MATHODS: Eighty patients with primary insomnia (35 males and 45 females, average age 49.71 +/- 12.91 years) and 101 normal healthy controls (64 males and 37 females, average age 27.65 +/- 2.77) participated in this study. Electromyography (EMG), heart rate (HR), skin conductance (SC), skin temperature (ST), and respiratory rate (RR) were recorded using a biofeedback system during 5 phases (baseline, stress 1, recovery 1, stress 2, recovery 2) of a stress reactivity test, and average values were calculated. Difference in values between the two groups in each corresponding phase was analyzed with independent t-test, and change in values across phases of the stress reactivity test was analyzed with paired t-test (all two-tailed, p<0.05). RESULTS: Compared to normal controls, insomnia patients had higher EMG in all 5 phases (baseline : 7.72 +/- 3.88 microV vs. 4.89 +/- 1.73 microV, t = -6.06, p<0.001 ; stress 1 : 10.29 +/- 5.16 microV vs. 6.63 +/- 2.48 microV, t = -5.84, p<0.001 ; recovery 1 : 7.87 +/- 3.86 microV vs. 5.17 +/- 2.17 microV, t = -5.61, p<0.001 ; stress 2 : 10.22 +/- 6.07 microV vs. 6.98 +/- 2.98 microV, t = -4.37, p<0.001 ; recovery 2 : 7.88 +/- 4.25 microV vs. 5.17 +/- 1.99 microV, t = -5.27, p<0.001). Change in heart rate across phases of the stress reactivity test were higher in normal controls than in insomnia patients (stress 1-baseline : 6.48 +/- 0.59 vs. 3.77 +/- 0.59, t = 3.22, p = 0.002 ; recovery 1- stress 1 : -5.36 +/- 0.0.59 vs. -3.16 +/- 0.47, t = 2.91, p = 0.004 ; stress 2-recovery 1 : 8.45 +/- 0.61 vs. 4.03 +/- 0.47, t = 5.72, p<0.001 ; recovery 2-stress 2 : -8.56 +/- 0.65 vs. 4.02 +/- 0.51, t = -5.31, p<0.001). CONCLUSION: Psychophysiological profiles of insomnia patients in a stress reactivity test were different from those of normal healthy controls. These results suggest that the sympathetic nervous system is more highly activated in insomnia patients.