Hospital Anxiety and Depression Scale. Anxiety and depressive symptoms were measured using a well-validated Lithuanian version48,49 of the Hospital Anxiety and Depression Scale (HADS)50. The HADS has 14 self-reported questions that assess the intensity of anxiety and depression symptoms during the last two weeks. It is based on a four-point (0–3) response category. The total score ranges from 0 to 21 for both subscales, with the higher scores indicating more severe symptoms. Scores of eight or more indicate the presence of serious symptoms. In Lithuanian individuals with CAD, the HADS has been shown to have sufficient psychometric characteristics51 and is commonly used in this specific population worldwide52. In our study, the HADS showed adequate internal consistency with HADS-A Cronbach’s α = 0.82 and HADS-D Cronbach’s α = 0.72.
State-Trait Anxiety Inventory. The State-Trait Anxiety Inventory is comprised of two self-reported questionnaires: Trait version (STAI-T) was developed to evaluate a stable tendency of experience anxiety and predispositions to experience stressful situations as threatening, while State version (STAI-S) was created to measure situational anxiety, defining how the participant is feeling at the current moment53. Each questionnaire consist of 20 items that are based on 4-point (1 to 4) Likert scale. The higher score indicates higher level of trait or state anxiety. Scores on each scale that are ≥ 30 points indicate moderate, while scores ≥ 45 determines severe anxiety53. In Lithuanian individual with CAD, the STAI-T and STAI-S has shown adequate psychometric properties54. In the current study, good internal consistency of STAI-T with Cronbach’s α = 0.87, and STAI-S with Cronbach’s α = 0.93 was detected.
Type D Scale-14. The Type D Scale – 14 (DS14)13 was used to evaluate distressed or Type D personality trait and includes two seven-item subscales measuring stable personality traits of negative affectivity (NA) and social inhibition (SI). A score of ten or greater on both subscales indicates Type D personality. Previous studies in CAD population55, as well as our current study report adequate psychometric characteristics of the DS14 with Cronbach’s α = 0.79.
Multidimensional Fatigue Inventory. Fatigue severity was measured by employing subscales from the Multidimensional Fatigue Inventory (MFI-20)49,56,57. The MFI, consisting of 20 items covers five subscales: (1) general fatigue, (2) physical fatigue, (3) mental fatigue, (4) reduced activity, and (5) reduced motivation. Each domain consists of four items with possible answers on a five-point Likert scale (1 = “yes, that is true”; 5 = “no, that is not true”)29. The domain of General fatigue is composed of the general statements about fatigue and reduced functioning, covering physical as well as psychological aspects of fatigue. Physical fatigue concerns physical feelings related to fatigue. Mental fatigue is linked to cognitive functioning, such as difficulty concentrating. The reduced activity subscale assesses the influence of psychological and physical factors on one's level of activity. The low motivation subscale reflects a lack of motivation to start an activity. The total score ranges from 4 to 20 on each subscale, and 20 to 100 for total fatigue score with higher score indicating higher fatigue levels. Cronbach‘s α coefficients of almost all MFI-20 subscales ranged from 0.63 to 0.93.
36-Item Short Form Medical Outcome Questionnaire. The 36-Item Short Form Medical Outcome Questionnaire (SF-36) evaluates eight major domains of HRQoL including physical function, role limitations due to physical problems, role limitations due to emotional problems, social functioning, mental health, vitality, pain, and general health perception. Each of the eight SF-36 subscales are scored on a scale from 0 to 100, with higher scores indicating better HRQoL58. In the current study, Cronbach‘s coefficients α of almost all SF-36 subscales ranged from 0.71 to 0.83, except for the social functioning subscale with Cronbach’s α = 0.45. Several authors suggest that such a coefficient might tentatively be accepted if the subscale is comprised of few items59, but that results relating to this subscale should be interpreted with caution. The SF-36 was validated in Lithuania60 and previous studies have reported similar internal consistency of Lithuanian translation of the SF-36 in individuals with CAD61,62.
Trier Social Stress Test. To evaluated cortisol response during acute psychosocial stress in laboratory settings, we used the TSST63, which is considered as a golden standard for evaluating the neurobiology of acute stress64. We followed the standard TSST protocol65–67, with the exception of an adjustment to the arithmetic task68. Instead of using serial subtraction, we employed the Paced Auditory Serial Addition Test (PASAT)69–71.
Experimental sessions of TSST were conducted between 2:30 and 3:30 PM and were comprised of several phases. In the beginning, participants were given time to rest (Baseline rest, 10 min.), after which they were exposed to initial anticipatory stress in the form of instructions for the first task (Task instructions, 5 min.). Participants then underwent Preparation time (5 min.), after which they had to present themselves at the simulated job interview (Public Speech, 5 min.) in front of a committee comprised of trained researchers. Then, participants underwent the Arithmetic task (8 min.) as a second stressor, after which they sat for a final Recovery period (15 min.).
Saliva samples were obtained after Baseline rest at time + 0 min. (T1), Preparation time at time + 10 min. (T2), Public speech at time + 15 min. (T3), Arithmetic task at time + 23 min. (T4) and Recovery period at time + 38 min. (T5) for subsequent analysis of cortisol concentration. Saliva samples were obtained using “Salivette” (Sarstedt, Inc.) swabs (which the participant chews for 30–90 seconds until filled with 0.5-1.0 mL of saliva. Samples were then stored at -70oC and cortisol levels were determined in a licensed laboratory using commercial enzyme kits. Test samples were taken by a registered nurse.
The value of cortisol response (Δnmol/l) was derived by subtracting the cortisol value sampled during Baseline rest from the cortisol value taken during the specific TSST phase.
Due to physical safety, the participants were monitored by the cardiologist during the study and the TSST was terminated for a participant earlier if he/she was at high risk of maladaptive exaggerated cardiovascular reactivity (i.e. a rise of blood pressure ≥ 210/115 mmHg)72.
Visual Analog Scales. After the TSST, study participants were debriefed about the purpose of the study and the subjective measured of perceived efforts and perceived difficulty of the tasks were collected by using Visual Analog Scales (VAS). The scales ranged from 0 (maximum difficulty/efforts) to 100 (minimum difficulty/efforts). VAS was chosen based in its applicability experimental clinical studies73 and common use in combination with TSST74.