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Abstract
Introduction Very little is known about daily life dynamics and mutual influences that tie together well-being and psychobiological stress responses in persons with spinal cord injury (SCI) and their romantic partners in particular. The role of social support and physical activity in the associations between emotional well-being and stress has not been investigated in the context of SCI yet and studies applying a dyadic approach, exploring the role of a romantic partner, are currently unavailable. The overall objective is thus to better understand the interplay between emotional well-being and the psychobiological stress marker cortisol, and to investigate the potentially moderating role of social support and physical activity in the well-being–stress association among persons with SCI and their romantic partners using a dyadic perspective.
Methods and analysis The stRess and Health Among romantic couPles with Spinal cOrD injurY study, funded by the Swiss National Science Foundation (10001C_204739), aims to recruit N=150 community-dwelling persons with SCI and their romantic partners including three phases of data collection. The first phase includes a baseline questionnaire. The second phase, the time sampling phase, comprises an ecological momentary assessment design in the everyday life of couples where both partners provide concurrent salivary cortisol samples five times a day and complete assessments four times a day over seven consecutive days. Wrist-worn accelerometers record physical activity during this period. The third phase is an observational study in the laboratory, where a couples’ discussion on the SCI management in their everyday life is recorded and coded to identify a couple-specific coping with SCI to enrich data. The dyadic data will be analysed using multilevel modelling, based on the actor−partner interdependence model framework.
Ethics and dissemination The study was approved by the ethics committee of Northwest and Central Switzerland (2022–01072) and findings will be disseminated through peer-reviewed publications and conference presentations.
- mental health
- social interaction
- social support
- stress, psychological
- stress, physiological
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Strengths and limitations of this study
The greatest strength of this study lies in its ecological momentary assessment design, allowing to follow romantic couples living with spinal cord injury in their everyday life in the context of spinal cord injury.
The assessments in everyday life will be complemented with observational data in the laboratory.
Although a limitation of this study might be the fact that self-report or self-selection bias can occur, and no causal effects can be interpreted.
Introduction
The burden of limitations in human functioning (ie, biological health, lived health)1 in ageing populations provides a major challenge to health and social policies,2 and the realisation of the Sustainable Development Goals 2030 is particularly challenging in persons living with an impairment.3
The prevalence of living with a disability is increasing as people live longer and are more likely to experience limitations in functioning with increasing age.2 Although prevalence is highest in older age groups, limitations in functioning also occur at earlier stages of the lifespan. An early onset of a disability has not only severe consequences on the engagement in productive activities, such as paid work or family responsibilities, social participation and economic self-sufficiency, but also puts affected persons at risk for reduced emotional well-being and the development of comorbidities.2 3 Spinal cord injury (SCI) is one extreme example that often results from an injury in early or middle adulthood.4 Data from the population-based community survey of the Swiss Spinal Cord Injury Cohort Study (SwiSCI5) shows the onset of SCI with a mean age of 35 years.6 Every year, approximately 250 000−500 000 people around the world incur an SCI,7 and the incidence in Switzerland is estimated at about 200 traumatic cases per year,8 with an unknown number of non-traumatic cases. An SCI is caused by traumatic or non-traumatic damage to the spinal cord, soft tissue made up of nerve tracts and constitutes the extended portion of the central nervous system linking the brain and muscles of the body and most sensory nerves to the brain.4 Depending on the level and completeness of the damage, SCI is classified into tetraplegia (upper spine section) or paraplegia (lower spine section), complete (total loss sensation and movement loss) or incomplete injury (partial loss sensation or movement loss).4 7 Therefore, SCI mostly leads to severe consequences for physical health and emotional well-being.4 7 As around 60% of persons with SCI depend on assistance from informal caregivers, the diagnosis of an SCI not only affects the person concerned, but usually also has consequences for their partners and families.9 The serious consequences of SCI on everyday life and social interactions may put persons living with SCI and their family members at increased risk for psychobiological stress.
Psychobiological stress, well-being and health
Stress is a significant health problem of the 21st century.10–13 The most popular definition of stress is the transactional definition conceptualising stress as a particular relationship between the person and the environment appraised by the individual as exceeding their resources.14 In essence, stress is experienced whenever an individual perceives their current situation as threatening and as exceeding their resources for coping with the threat.15 According to this definition, stress in a given situation is understood as the result of cognitive appraisal processes resulting in an emotional, behavioural and physiological stress response.14 The physiological stress response involves various bodily systems, including the hypothalamus-pituitary-adrenal (HPA) axis and is dependent on the cognitive appraisal processes involved in subjective experiences of stress.16 The most important marker for measuring HPA axis activity is the biomarker cortisol, which shows a distinct diurnal rhythm.17 An acute cortisol response is adaptive if it helps an individual to manage challenges.18 However, chronically elevated cortisol levels can have adverse effects on health and emotional well-being.19 20 The detrimental impact on health resulting from chronically heightened cortisol levels has been described as allostatic load. Allostatic load represents the physiological consequence of chronic exposure to heightened cortisol response due to recurrent stress, which the body system can no longer regulate through allostasis.21
The most commonly used tissue to measure cortisol is saliva, because collection can be performed in field studies as it is simple, painless, non-invasive and more feasible compared with methods such as blood draws.17 22 23 Diurnal cortisol sampling is a popular biomarker suitable to address time-varying situational characteristics that elicit stress responses as individuals navigate their everyday lives.17 23 Since everyday salivary cortisol involves the collection of data in the target person’s natural environment, ecological validity is enhanced compared with laboratory studies.24 Moreover, saliva is a body fluid that most people can easily collect themselves at home, making it suitable for repeated daily life assessments capturing within-person fluctuations in HPA axis activity.11 17
According to the transactional model of stress, the individual’s appraisal shapes the stress reaction and not the objective nature of the encounter per se.14 Measures of emotional well-being are adequate to assess an individual’s appraisal from a cognitive and an emotional component, including a global cognitive judgement of satisfaction with one’s life and the assessment of experiences of positive and negative emotions.25 26 In this study, we focus on emotional aspects of well-being and operationalise emotional well-being as the two distinct dimensions of positive and negative affect.27 An impressive body of research has been conducted on the topic of well-being in persons with SCI, and it has been described that well-being is generally lower in persons with SCI as compared with the general population.28–30
Despite the importance to link emotional well-being, health and stress in populations that are particularly vulnerable to enhanced stress levels, the investigation of HPA axis reactivity and stress in persons with various limitations in functioning is very limited.24 Studies of cortisol secretion in response to stress have mostly been conducted in laboratory settings. For example, a study assessing cortisol levels in the inpatient setting of initial rehabilitation detected that people with SCI showed higher cortisol levels compared with healthy controls.31 However, these results are hardly transferable to the everyday life of persons with SCI as these measures were performed shortly after the occurrence of the injury during the acute phase of initial rehabilitation. This situation represents an extreme scenario in which psychological distress is certainly enhanced. Studies on subjective stress measuring stress with the Perceived Stress Scale (PSS32), suggested that persons with SCI experienced higher levels of stress related to the consequences and demands of their injury. Furthermore, in a study on global stress perceptions, men with SCI reported higher subjective stress than men from the general population.33
Because research on HPA axis regulation under controlled laboratory conditions or in clinical settings lack ecological validity, ecological momentary assessment studies are needed to complement current evidence in research on persons living with SCI. One exception is an ecological momentary assessment study investigating the effects of daily stressors on salivary cortisol and mood ratings in 25 people living with SCI and 26 healthy controls for two consecutive days.24 No differences were found between the experience of daily stressors in persons with SCI and controls and additionally, overall concentration and diurnal variation of salivary cortisol in participants with SCI were similar to those without SCI.24 Although study results might have certain restrictions due to low sample size, they demonstrate the feasibility of using ecological momentary assessment to collect biological and behavioural data from participants with SCI.
Moving beyond the individual perspective on stress: the dyadic systemic-transactional stress model
Everyday life is shaped by interactions with others34 35 and the nature and quality of those interactions is closely linked to emotional well-being and health.36 37 The romantic partner relationship is particularly relevant for emotional well-being and health and can have an important protective function.38–40 As emotional well-being and health are closely linked between the two members of a couple,41 studying emotional well-being and health in a dyadic setting is crucial.
A dyadic context is also fundamentally important for stress responses.42 For several decades, stress processes were examined from models focusing on the individual.36 The previously perceived notion of stress as an individual experience can, however, be redefined as a dyadic construct that impacts both individuals within an interdependent dyad.43 Therefore, the systemic-transactional stress model (STM44) in close relationships moves beyond an individually oriented focus and understands stress and coping in couples as a result of a reciprocal and dynamic interplay between both partners behaviours and stress responses.44 Overall, the STM assumptions have received support not only from cross-sectional studies, but also from daily diary studies in the dyadic research literature.36 45 46 The finding that cortisol levels are systematically linked among close others47 48 supports the assumptions that moving beyond an individual perspective on stress is necessary. Moreover, another aspect is modelling co-regulation or synchrony of physiological processes between dyads as dynamic systems. Therefore, the biomarker cortisol can be modelled simultaneously with measurements from both partners of a dyad to illustrate how the biomarker of one person in the dyad affects that of the other person.23 For example, a study examining dyadic synchrony in cortisol secretion showed that favourable cortisol diurnal profiles occurred in couples reporting high marital satisfaction and intimacy.49 Another study showed that on days when one partner experienced a slower or faster cortisol decline, the spouse also exhibited similar cortisol regulation.23 However, to the best of our knowledge, no study has yet investigated time-varying couple synchrony and concordance in emotional well-being and salivary cortisol in persons with SCI and their romantic partners.
Moderators between emotional well-being and psychobiological stress
To date, person-level characteristics have been demonstrated to be associated with the relationship between situational characteristics and cortisol indices.17 However, moderators of the association between emotional well-being and salivary cortisol in couples’ everyday life remain poorly understood and have not been addressed in the context of SCI. Investigating such potential moderators in couples’ everyday life can be important for the development of future dyadic stress interventions.
Social support
Social support is one form of social exchange with a romantic partner and is defined as an act of offering resources intended to assist the receiver’s ability to cope in times of need.50 Social support can be divided into different types, functions and perspectives. Regarding different types of social support, it can be differentiated between perceived available support and actual received support, the former being anticipatory and the latter being retrospectively collected.51 Regarding functions of social support, it can be distinguished between emotional, instrumental and informational support, whereas instrumental and informational can be merged into practical support.52 53 Emotional support covers aspects such as encouraging and comforting, whereas practical support refers to practical help or assistance.52 53 Moreover, it can be distinguished between received and provided social support for partners of romantic couples. Received support is defined as a resource provided by a significant other, encompassing retrospective reports of actual support transactions between two partners, exhibit only small to moderate correlations with reports of support given from a provider referring to provided support.52 53
The buffering hypothesis54 assumes that social support can attenuate or buffer stress and strain. It is hypothesised that the buffering effect can be explained by a favourable assessment of coping options in the face of stressful events, changed assessment of the stressors themselves, coping and favourable physiological and behavioural responses to stress.50 Besides, scientific studies identified that social support buffered stress from adversity and thus having an indirect effect on health.55 56 Literature linking social contextual factors with salivary cortisol in everyday life demonstrated that social stressors such as loneliness or time spent alone were constantly associated with increased cortisol levels.57 58 A study in older couples showed that higher overall solitude was associated with negative affective and biological correlates, indicating that spending a lot of time alone in old age has negative ramifications for well-being and health.57 For example, loneliness moderated within-person cortisol associations in such a way that individuals with high loneliness showed higher cortisol levels on weekends compared with work days.59 In another study, high social support was associated with elevated cortisol levels on leisure but not on work days.60 Further evidence shows that social support moderates the association between affective states and cortisol indices: In a study examining social support from friends among adolescents, it was found that social support moderated the association between within-person increases in momentary negative affect and increases in cortisol secretion, indicating that adolescents who reported high levels of social support from friends experienced attenuated cortisol responses to negative affect compared with adolescents’ who reported average or low levels of social support from friends.61 However, to the best of our knowledge, social support as a social exchange process between partners has not yet been investigated as a moderator in the association between affective states and psychobiological stress using a dyadic approach. The moderating role of social support might be particularly important, as people with SCI more often reported feeling lonely than their able-bodied partners.62
Physical activity
Physical activity has well-established benefits for well-being and health and helps to prevent or delay the onset of chronic disease and disability in older adults.63 It is also of high relevance for health maintenance in persons with SCI.64 65 Some of the health benefits of physical activity are hypothesised to occur through the effects on the neuroendocrine system.66 Studies supporting this assumption observed, for example, that young adults who engaged in exercise showed lower subsequent cortisol response to laboratory stressors.67 68 In a recent study with older adults with a focus on the moderating role of device-based measured physical activity levels in HPA axis activity, results showed that everyday physical activity moderated the negative affect-cortisol associations, indicating that individual differences in older adults’ physical activity may buffer cortisol secretion in moments of heightened negative affect.18 There is one study investigating the effects of exercise on well-being and stress in a randomised controlled trial, providing support for the role of exercise in buffering the effects of emotional well-being on stress and highlighting the importance of exercise for people with SCI.69 This moderating role of physical activity has not been investigated in the everyday life of persons with SCI neither with device-based sensor systems nor in a dyadic context. The dyadic design of this study allows to assess the physical activity of both, the persons with SCI and their able-bodied partners.
Open questions
Evidence on daily life dynamics and mutual influences that tie together emotional well-being, health and stress in persons living with a disability and their romantic partners is very scarce. Everyday associations between emotional well-being and cortisol responses correlates of psychobiological stress have not been investigated in this context. Furthermore, studies applying a dyadic approach to explore the role of a romantic partner within these associations are currently unavailable. The present study uses persons with SCI and their romantic partners as a case in point to generate evidence that is potentially transferrable to other couples in which one partner experiences limitations in functioning. Additionally, the present study extends current research by investigating whether social support and daily physical activity moderate associations between momentary emotional well-being and concurrent salivary cortisol. The study fosters to understand if social support and physical activity may mitigate negative health ramifications associated with cortisol dysregulation in everyday life of people with SCI and their romantic partners. Identifying moderators in the well-being-stress-association is highly important for the development of evidence-based interventions aiming at reducing psychobiological stress in couple’s daily life.
In order to gauge the immediate impact of couples’ SCI-related conversation from everyday life, an observational study in the laboratory complements time sampling data. This additional data collection allows a more accurate description of how emotional well-being and stress unfold in a couple’s discussion.70 71 Furthermore, it serves as a crucial supplement to the time sampling phase, particularly considering that the former phase involves an ecological momentary assessment of naturalistic behaviour in couples’ everyday lives. The time sampling phase may not fully capture a comprehensive discussion about behavioural and emotional aspects of SCI-related concerns that are relevant to the couple’s coping with SCI. Overall, the present study extends available evidence and closes current research gaps by applying an innovative design, that is, a dyadic ecological momentary assessment design.
Aims and research questions
The overall objective of this study is to better understand dyadic associations between emotional well-being and psychobiological stress in the everyday life of persons living with SCI and their romantic partners in the dyadic framework of the actor–partner interdependence model (APIM72). These associations will be investigated in two different settings, namely in everyday life as well as in an observational setting in the laboratory. Moreover, the potential moderating role of social support and physical activity within these dyadic associations will be addressed.
The specific aims of the study are (see also figure 1):
To examine moment-by-moment covariations between partners in emotional well-being and psychobiological stress (ie, synchrony, concordance),
To investigate time-varying associations of emotional well-being and psychobiological stress (ie, salivary cortisol levels) applying a dyadic approach, exploring not only the effect of one’s own emotional well-being on psychobiological stress (actor effect), but also the effect of the partner’s emotional well-being on own psychobiological stress (partner effect) within the framework of the APIM,72
To examine the potential moderating role of momentary social support and daily physical activity within the association between emotional well-being and psychobiological stress in persons with SCI and their romantic partners applying moderation testing within the framework of the APIM,73 and
To gain an in-depth understanding of couples’ coping with SCI, that is, how emotional well-being and stress unfold in a couples’ discussion.
Analytical framework of the study and specific study aims. SCI, spinal cord injury.
Methods and analysis
Study design
The stRess and Health Among romantic couPles with Spinal cOrD injurY study is funded by the Swiss National Science Foundation grant number (10001C_204739), and comprises three phases of data collection. After the introductory baseline assessment including comprehensive instructions and the assessment of the basic characteristics of study participants, the study follows an ecological momentary assessment design with a time sampling phase and an observational phase examining persons with SCI and their romantic partners in their everyday life. In the time sampling phase, both partners will answer short surveys on their mobile phone four times a day over 7 days. Moreover, both partners will provide corresponding saliva samples for cortisol estimation five times a day and will wear an accelerometer for the device-based assessment of physical activity over the same 7-day period. In the observational study phase in the laboratory, a 10 min videotaped discussion between partners about SCI-related everyday-life concerns will be examined (please see figure 2 for an overview of the study design). Data collection will take around 1.5 years, as not all eligible individuals will be contacted at the same time. The planned start date for the study is February 2024 and the planned end date is September 2025.
Study design including baseline assessment, time sampling phase and observational phase.
Baseline assessment
Eligible couples are invited to the SwiSCI study centre at Swiss Paraplegic Research, Nottwil, Switzerland for a baseline assessment. These assessments are planned to be performed in the study centre, however, to optimise study participation, the baseline assessment may also take place at the couple’s home if it is more convenient for participants. During the baseline assessment, couples receive comprehensive information about the study, are given a brief overview of the study goals and sign the informed consent form. Afterwards, the blood pressure of the target persons is measured as a crude index of autonomic completeness of SCI, serving later as a covariate for the affectedness of the HPA axis response for analysis with the biomarker cortisol. Moreover, participants independently complete a self-report questionnaire (blinded to the partners’ responses) assessing demographic variables and potentially relevant constructs at baseline that are not assessed on a daily basis, but will later serve as covariates.
After completing the questionnaire, the assessments in the time sampling phase are explained in detail to the study participants. Face-to-face instructions on the daily questionnaires, the salicaps and the accelerometers are important in order to maximise data quality. Instructions include an explanation of how to complete the daily self-report questionnaires on study participants own smartphones, how to take saliva samples using salicaps and how to wear the accelerometers. In addition to the oral instructions, both members of a couple receive a written manual on the handling of salicaps and accelerometers. All participants complete a test run for using the salicaps in front of the research assistant to ensure that they understood the procedure. The baseline assessment also provides the opportunity to ask any remaining questions and to schedule the observational phase in the laboratory of the SwiSCI study centre.
Time sampling phase
The time sampling phase starts for all couples on the Monday following the baseline assessment and ends the following Sunday night in order to have the same sequence of days for all participants. In order to depict the everyday life of the couples adequately, the start of the time sampling phase is planned in a way that the week reflects a ‘normal’ week in the participants’ life, for example, not a holiday week. The measurement over 7 days is considered important, as both weekdays and weekends are included since studies found differences in cortisol profiles according to days within a week.59 60 Both partners receive an automatically generated text message to their personal smartphone on Sunday evening reminding them that the study starts the following day. During the 7-day period, both partners complete four self-report questionnaires each day at the following points in time: 30 min after waking up, 11:00, 14:00 and 18:00. The first questionnaire 30 min after waking up, is self-initiated and depends on the waking up time as well as morning routine procedures of the target persons with SCI, making it individually variable. In addition, participants receive a text message on their smartphone to signal that it is time to complete the day questionnaire at 11:00, 14:00 and 18:00. Participating couples are instructed to complete each day questionnaire when they receive the text message, but are allowed to complete the questionnaire for up to 2 hours. Participants do not have the option to change these pre-set times. Based on experiences from other daily dairy studies with couples in different contexts, the estimated burden for participants is approximately 10 min per self-report questionnaire during the time sampling phase.74–76 At each point in time (with an additional one directly after waking up), both partners also provide a saliva sample. Given that cortisol exhibits a robust diurnal pattern,22 the exact timing of the first saliva sample can be individual, based on the waking up time. Additionally, each participant wears an accelerometer on their non-dominant wrist for the whole 7-day period.
Observational phase: couple discussion and exit questionnaire
The observational study takes place once the couple has finished the 7-day time sampling phase, and is usually conducted in-laboratory (SwiSCI study centre), but occasionally can take place at the couple’s home if this makes participation easier and more appealing for them. At the beginning of this phase the salicaps and accelerometers are returned.
The observational study examines emotional well-being and stress by analysing a couple’s videotaped 10 min discussion about SCI-related concerns to provide insights into a couple’s coping with living with SCI in everyday life. Previous literature describes that this additional data collection method allows a more accurate description of how emotional well-being and stress unfold in a couple’s discussion.70 71 This is an important completion to the time sampling phase, especially because the former phase is an ecological momentary assessment of naturalistic behaviour in couples’ everyday lives and may not capture a full discussion about behavioural and emotional aspects of SCI-related concerns. Following the procedure used by Badr et al 70 and Lüscher et al,75 persons with SCI and their partners are asked to list their SCI-related concerns in their everyday life and to select one that causes them considerable distress. Next, they are invited to discuss the issue together for about 10 min in a videotaped session. The task is introduced by a psychologist who leaves the room during the discussion. Following the discussion, both partners report their perception of the discussion and independently rate the discussion in terms of the degree to which it has been typical of their discussions at home, how helpful it was and how it made them feel. Trained observers will subsequently code the videotaped discussions according to a specifically developed codebook based on previously published work70 71 for well-being and stress. Two trained blinded coders, showing high inter-rater-reliability (kappa) after training, will review the videotaped discussions.
Finally, couples individually complete a self-report exit questionnaire, without consulting each other, assessing, for example, potential improvements for future studies. All the couples receive a compensation of Swiss Francs (CHF) 200 for their time and travel expenses.
Study population and recruitment strategy
The present study plans to include German-speaking community-dwelling persons with SCI and their romantic partners. The SwiSCI community survey database5 serves as the basis for the recruitment of persons with SCI. German-speaking individuals who indicate being in a romantic relationship with a partner for at least 1 year and living in a common household for at least 6 months are eligible for our study. Couples in which both partners have an SCI are excluded as the dyadic analysis framework requires a clear definition of the role within a couple, that is, whether someone is the person with SCI or the romantic partner of the person with SCI. All German-speaking persons with SCI from the SwiSCI community survey database will thus be contacted for eligibility screening with the support of the SwiSCI study centre. Initially, all persons will receive an invitation letter explaining the study in detail. Based on experiences from the SwiSCI community survey6 and the pro-WELL study,77 personal contact by telephone has proved to be highly effective to enhance study participation. Therefore, a research assistant will contact persons in case of no reaction 4 weeks after the invitational letter was sent.
Patient and public involvement
The present study has been discussed and designed with persons living with SCI and experts from the field whereas there was widespread enthusiasm for the study and agreement that the research set out in this protocol is needed, acceptable to the participants and feasible to perform. Moreover, it was approved by all members of the Steering Committee of the SwiSCI study (approval date: 20 March 2020/project number: SwiSCI 2020-N-001).
Measures
Device-based and self-report data will be assessed from both partners throughout the study in order to allow dyadic analysis.
Baseline assessment
Basic demographic characteristics of the person with SCI are not assessed again as information will be retrieved from the SwiSCI community survey database (ie, age, gender, time since injury, lesion level, aetiology of SCI). The selection of potentially relevant covariates is based on directed acyclic graphs derived from the literature.8 Financial strain, life events during the past 6 months, general mental health (Mental Health Index, 36-Item Short Form Health Survey; SF-3679) pain (Brief Pain Inventory80), duration of the relationship, duration of cohabiting, relationship quality (Dyadic Adjustment Scale81), closeness, life satisfaction (Satisfaction With Life Scale82) and time spent together were identified as potential confounders and are therefore assessed in the baseline assessment. General satisfaction with sexuality is included with the item ‘How satisfied are you with your sex life?’ (World Health Organization Quality of Life; WHOQOL-Bref83). Moreover, the baseline assessment questionnaire includes the Perceived Stress Scale; PSS-10.32 The PSS-10 is used to assess which situations in an individual’s life are appraised as stressful comprising 10 items with the following topics: upset, control of important things, nervousness, handling personal problems, feeling and coping with things, control irritations, being on top of things, anger about uncontrollable things and dealing with difficulties.
Besides, the blood pressure of target persons measured at baseline assessments will serve as a covariate for the affectedness of the HPA axis response as a crude index of autonomic completeness of SCI.
Time sampling phase
All items on emotional well-being and social exchange processes in the daily questionnaires are presented on participating couples own smartphones. For study target persons with complete tetraplegia with limited or no independent hand function, a research assistant will call them four times daily for the short questionnaire as almost all of those persons dispose of a cell phone with voice recognition that can be operated without hand use to get independent and unbiased answers from their romantic partners. This procedure has already been applied in the pro-Well study.77
Emotional well-being is operationalised as positive and negative affect and is measured with the short form of the positive and negative affect schedule including five items each for positive and negative affect.84
Social support is assessed with items already used in daily diary studies adapted for the context of SCI (c.f., 74–76). An item example for received and provided social support is asking persons with SCI ‘Since the last questionnaire, I received emotional/instrumental support from my partner’. And asking partners ‘Since the last questionnaire, I provided emotional/instrumental support to my partner’. Emotional and instrumental support will be briefly defined for participants.
Psychobiological stress: For the 7-day period, each partner provides five saliva samples each day (on waking up, 30 min later, 11:00, 14:00, 18:00) using salicaps to capture cortisol’s diurnal rhythm.85 For target persons with limited or no hand function, the saliva samples can be collected and stored by the romantic partners as they have to take them for themselves at the same time prompts five times daily. If this procedure during the day is not feasible, another caretaker can alternatively collect the saliva samples.
Couples are instructed to fill their saliva samples into the salicaps using a tube before filling out the questionnaires. Completed saliva samples are stored in a personal freezer (or fridge if a freezer is not available) until they return to the laboratory. All saliva samples are stored in a freezer at Swiss Paraplegic Research until the end of the study. Afterwards, all saliva samples are couriered to the Biochemical Laboratory of the Department of Psychology at the University of Zurich for analysis. For controlling diurnal cortisol changes, participants are asked if their sleep was restful, whether they smoked, consumed caffeine, alcohol or food, engaged in physical activity, or took medication in the hour prior to the saliva collection.
Additionally, momentary stress is assessed from each partner four times a day with the item ‘At the moment, I feel stressed’. Moreover, momentary stressors are measured with the question whether certain stressors had occurred since the last questionnaire (1=yes, 0=no) including having an argument with someone, almost having an argument but avoiding it, a stressful event at work or school, a stressful event at home, experiencing discrimination, having something bad happen to a close friend or relative and having had anything else bad or stressful happen since the last questionnaire.86 87
Physical activity is assessed with a body-worn sensor to accurately measure daily physical activity (moderate-to-vigorous physical activity) in the free-living environment for the SCI population who use wheelchairs and a corresponding body-worn sensor for the partners. All participants wear an accelerometer on their non-dominant wrist for the 7-day period.65 Recently, several reviews have been published on the validation of everyday life physical activity monitoring devices for wheelchair users.65 88–90 The available devices assess physical activity in terms of energy expenditure or type and intensity of activities but not all examined devices appeared to be suitable for the monitoring of physical activity in wheelchair users. Besides that, the estimation of energy expenditure could benefit from multisensor systems, custom algorithms and individual calibration. However, the ActiGraph GT3X+showed to be a valid type of accelerometer for monitoring physical activities and intensities in manual wheelchair users, when wearing the device on the arm or wrist and will thus be used in this study.65 91 92 This device has also been used and validated for monitoring physical activity in able-bodied persons in numerous studies.93 94 Participants are instructed to wear the accelerometer for 24 hours in the time sampling phase (continuously from Monday to Sunday).
Data analysis
On completion of data collection, data will be cleaned and prepared for data analysis. Outcome variables will be checked for normal distribution, outliers and missing patterns.95 All analyses will follow intention-to-treat principles by taking into account all available data points. Intermittent missing data will be handled by maximum likelihood estimation. As the present study will use dyadic ecological momentary assessment data for the main data analysis, multilevel modelling will be employed to account for the interdependence among couple members’ momentary observations, using a two-level statistical model for distinguishable dyads as indicated for patient−partner dyads.72 96 To examine the first specific research aim on time-varying associations between emotional well-being and psychobiological stress using the ecological momentary assessment data and cortisol data from both partners, a set of general linear mixed models will be performed in SPSS and R following the procedure for the widely used APIM.97 Therefore, psychobiological stress will be modelled as a function of time across all points in time and times of day as well as between-person and within-person actor and partner effects of emotional well-being by centring the variables accordingly.96 To address the second specific research aim, we will calculate intraclass correlations between partners as well as coordinated multilevel models to analyse co-variation between partners (c.f.,98). To test the third specific research aim on the moderating role of physical activity and social support, we will use a multilevel approach for moderation analysis by including interaction terms between the predictor variables and the moderator variables of persons with SCI and their partners.73 To test the fourth specific research aim, data from the observational study will be transcribed and a coding manual will be developed for couple’s coping style. How emotional well-being and stress unfold in a couple’s discussions is then analysed again with multilevel modelling.
To secure adequate statistical power to adequately address the research questions of the present study, an a priori sample size calculation based on Cohen99 was performed using the G*Power program.100 Based on a power of 0.90 and a two-tailed type 1 error probability of 0.05, a minimum sample of N=65 persons with SCI and their partners was determined to be appropriate for detecting a small effect of emotional well-being on stress, drawing on comparable ecological momentary assessment studies with unstandardised effects on the association between everyday emotional well-being and salivary cortisol in older persons (r=0.02–0.2718 101), given the absence of available meta-analyses. To assure adequate power for the moderation analysis and making a prediction under high (sample mean +1 SD) versus low conditions (sample mean −1 SD) of the moderating variables, a sample size of N=130 persons with SCI and their partners is necessary. Monte Carlo simulation, the recommended method to estimate the sample size for analyses of intraindividual, time-varying associations during the time sampling phase102 could not be conducted due to the fact that detailed information on parameters from previous studies are required and are not available as this study is the first of its kind. However, the calculated sample size fits the requirement of Kenny et al 72 allowing to test for non-independence of the dyadic data. Furthermore, drop-outs have to be taken into account. Previous ecological momentary assessment studies from various contexts resulted in very low dropout rates (ie, ≤10%73 103 104). This can be explained with a high commitment in couples participating in these kinds of studies. Given the additional observational phase, we added 15% to the calculated sample size accounting for potential dropout resulting in a total required sample size of N=150 couples.
Strengths and limitations
For further research and practice it is crucial to investigate everyday life interactions of emotional well-being and psychosocial stress in romantic couples coping with limitations in functioning in the context of SCI. The current study has a number of strengths. The greatest strength of this study is its ecological momentary assessment design allowing to follow romantic couples coping with SCI in their everyday life. This study will contribute to gain an in-depth knowledge on everyday life processes that shape dyadic associations between emotional well-being and psychobiological stress in the context of SCI. Another strength is the supplementation of everyday life assessments with observational data collected in the laboratory.
As this study investigates tangible and thus modifiable factors, such as social support and physical activity, the ultimate goal of this innovative study is to deliver empirical evidence to guide practical measures (ie, dyadic stress interventions) targeting couples coping with SCI in their everyday life.
Besides, the present study has several limitations. Regarding participation, self-selection bias can occur. People who are generally in good health are often more willing to participate in a study.105 However, the baseline questionnaire includes an item on the general health status which could serve as covariate.
Certain scales are conducted via self-report data (eg, emotional well-being, social support). Therefore, self-report biases like response tendencies or social desirability can occur. Regarding social desirability, items that could serve as covariates are included in the exit questionnaire.
Since this is an observational study, no causal effects can be interpreted. Moreover, missings and reactivity must be considered in ecological momentary assessment (EMA) studies. Study participation may act as an intervention and consequently influence the behaviour and experience of the participating couples.96 Furthermore, EMA studies can lead to participants overburden. High rates of refusal or attrition rates can be the result. However, there are similar studies among couples demonstrating the feasibility of this methodology.72
Participant and public involvement
The present study has been discussed and formulated with persons living with SCI and experts from the field whereas there was widespread enthusiasm for the study and agreement that the research set out in this protocol is needed, acceptable to the participants and feasible to perform. Moreover, it was approved by all members of the steering committee of the SwiSCI study (approval date: 20 March 2020/project number: SwiSCI 2020-N-001).
Ethics and dissemination
The study was approved by the ethics committee of Northwest and Central Switzerland (EKNZ) (2022–01072). All participants will attend voluntarily, sign an informed consent and will be treated in accordance to the standards of the Declaration of Helsinki (World Medical Organisation, 1996).
The research results will be made public in scientific peer-reviewed research journals with high impact factors. Moreover, findings will be disseminated through scientific communities at national and international conferences Additionally, it is intended to present findings also to an audience of practitioners in the field of rehabilitation medicine and rehabilitation psychology. Besides, results will also be disseminated to participating couples.
Ethics statements
Patient consent for publication
References
Footnotes
Contributors JL is the principal investigator of the study. JL and SL were involved in the design and conception of the study. JL and SL drafted the manuscript. Both authors reviewed and approved the final version of the manuscript. JL is the guarantor of this study.
Funding This study and the second author are supported by the Swiss National Science Foundation (SNSF) grant number (10001C_204739).
Competing interests None declared.
Patient and public involvement Patients and/or the public were involved in the design, or conduct, or reporting, or dissemination plans of this research. Refer to the Methods section for further details.
Provenance and peer review Not commissioned; peer reviewed for ethical and funding approval prior to submission.