S. Duschek et al., Autonomic control in chronic hypotension
exposure to a mental challenge. This procedure also allowed for evaluation of the magnitude of cardiovascular reactivity during stress conditions, where previous research suggested blunted reactivity in chronic hypotension and thus poorer short-term autonomic cardiovascular adjustment to situational requirements (Covassin et al., 2013; Duschek, Dietel, et al., 2008; Duschek, Matthias, & Schandry, 2005). The following main hypotheses were tested in the study: Hypothesis 1 (H1): Taking into account the research delineated above, reduced beta-adrenergic cardiac tone in chronic low blood pressure was postulated. This was expected to be expressed in lower SV and CO, and in a longer PEP in hypotensive versus normotensive individuals. Hypothesis 2 (H2): Though the available research remains inconsistent, augmented parasympathetic influences on heart rate, indicated by higher expressions of RMSSD, were predicted in hypotension. Hypothesis 3 (H3): Based on our pilot data, greater BRS in hypotensive versus normotensive participants was also predicted. Hypothesis 4 (H4): Finally, reduced autonomic stress reactivity, in terms of smaller modulations in the assessed parameters during mental challenge, was postulated.
Methods Participants Forty subjects with hypotension, according to WHO (1978) criteria, and 40 normotensive control persons participated (35 women and 5 men in each group). None of the subjects suffered from a relevant physical disease or mental disorder. Health status was assessed by means of an anamnestic interview and a questionnaire covering diseases of the cardiovascular, respiratory, gastrointestinal, and urogenital systems, and of the thyroid and the liver, as well as metabolic diseases and psychiatric disorders. None of the participants used any kind of medication affecting the cardiovascular or central/ peripheral nervous system. In total, 67 of the participants were university students (34 in the hypotensive sample, 33 in the control group); the remaining subjects were in the workforce. Table 1 provides information about blood pressure, as recorded at the beginning of the experimental procedure, as well as age and body mass index (BMI). Sample size was determined based on previous studies comparing parameters of autonomic control between Ó 2017 Hogrefe Publishing
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Table 1. Means (M) and standard deviations (SD) of systolic blood pressure, diastolic blood pressure, age, and body mass index in both samples Hypotensive group
Normotensive group
M
SD
M
SD
Systolic blood pressure (mmHg)
95.41
6.69
119.18
3.82
Diastolic blood pressure (mmHg)
64.59
6.30
77.05
5.48
Age (years)
24.70
4.90
23.98
4.28
Body mass index (kg/m2)
20.15
1.85
21.95
2.78
hypotensive and normotensive individuals (c.f. Introduction), which revealed effect sizes (Cohen’s d) generally between .3 and .5. Assuming an effect size of .4, an α level of 5%, and a β error of 20%, power analysis revealed a required total sample size of 39 per group. The study was part of a larger project investigating psychophysiological aspects of chronic hypotension. Further results obtained in this sample are presented in Duschek, Hoffmann, and Reyes del Paso (2017) and Duschek, Hoffmann, Reyes del Paso, and Ettinger (2017).
Hemodynamic Recordings For impedance cardiography recording, a CardioScreen 1000 (Medis Inc., Ilmenau, Germany) device was employed (c.f. Berntson et al., 2016; Moshkovitz, Kaluski, Milo, Vered, & Cotter, 2004; Raaijmakers, Faes, Scholten, Goovaerts, & Heethaar, 1999 for technical framework and discussion of method reliability and validity). The impedance signal was acquired using four spot electrodes positioned at the lateral neck and the lateral chest (left side) with alternating current of 1.5 mA and 85 kHz. The ECG was recorded at a sampling rate of 1,000 Hz from two electrodes placed at the left mid-clavicle and lowest right rib using a Biopac system (MP 150, Biopac Systems Inc., Goleta, CA). The back of the left hand served as a ground. Blood pressure was monitored continuously with a Finometer Model-2 (Finapres Medical Systems, Amsterdam, The Netherlands). The cuff of the device was applied to the left index finger and that hand was positioned at the level of the heart. For periodic recalibration, the device’s “Physiocal” feature (Wesseling, De Wit, Van der Hoeven, Van Goudoever, & Settels, 1995) was in operation. Data were recorded by means of the Biopac system (sampling rate 1,000 Hz).
Procedure Assignment of subjects to the two study groups was carried out on the basis of blood pressure readings taken in a Journal of Psychophysiology (2019), 33(1), 39–53