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. Author manuscript; available in PMC: 2024 May 6.
Published in final edited form as: Heart Lung. 2021 Feb 24;50(4):542–545. doi: 10.1016/j.hrtlng.2021.02.008

Daytime activity and sleep are associated with motor function in older intensive care unit survivors

Maya N Elías a,*, Cindy L Munro b, Zhan Liang c
PMCID: PMC11073789  NIHMSID: NIHMS1927188  PMID: 33637322

Abstract

Background:

Hospitalized older intensive care unit (ICU) survivors are often inactive and experience sleep disturbances.

Objective:

We explored associations between post-ICU activity, sleep/rest, and motor function among hospitalized older ICU survivors.

Methods:

We enrolled 30 older ICU survivors, ages 65 and older, within 24–48 h of ICU discharge. Actigraphy measured post-ICU activity and sleep/rest. Selected measures from the National Institutes of Health Toolbox Motor Battery assessed grip strength and dexterity. Multivariate regression examined associations between post-ICU activity, sleep/rest, and motor function, adjusting for covariates.

Results:

Lower daytime activity (β = 0.258, p = .035) and greater daytime sleep/rest (β = −0.295, p = .022) were associated with worse grip strength. Lower daytime activity (β = −0.376, p = .037) and greater daytime sleep/rest (β = 0.409, p = .026) were associated with worse dexterity.

Conclusion:

Post-ICU inactivity and prolonged rest periods are associated with worse motor function in hospitalized older ICU survivors.

Keywords: Older adults, Activity, Sleep, Motor function, Critical illness, Post-intensive care syndrome

Introduction

Impairments in motor function after hospitalization in the intensive care unit (ICU) are prevalent among older ICU survivors. Post-ICU motor impairment is commonly referred to as ICU-acquired weakness and is a component of post-intensive care syndrome.1,2 Hospitalized older patients are often inactive; in fact, inactivity among hospitalized older adults has been described as an epidemic. Inactivity is particularly worse among older ICU survivors and contributes to significant morbidity and impairments in activities of daily living.3,4 Moreover, hospitalized ICU survivors who were mechanically ventilated often experience significant nighttime sleep disturbances and fragmented sleep despite transfer out of ICU, and greater sleep duration as measured by actigraphy does not necessarily entail uninterrupted sleep.5 Poor activity and/or sleep could potentially exacerbate post-ICU motor impairment. Considering the relationships among sleep disturbances and protein synthesis/degradation via endocrinological pathways observed in experimental animal models,6 it is hypothesized that disturbances in the sleep/wake cycle could be linked to worse motor function in ICU patients.7 Currently there is little research examining associations between post-ICU activity, sleep/rest, and motor function in hospitalized older ICU survivors immediately following ICU discharge. Early identification of inactivity and prolonged sleep/rest periods among hospitalized older ICU survivors following ICU discharge could estimate risk for worse outcomes of motor function and post-intensive care syndrome. Thus, the aim of this study is to explore the relationships between early post-ICU activity, sleep/rest, and motor function among a cohort of hospitalized older ICU survivors.

Methods

Design and Sample

A cross-sectional design was used for analyses. We enrolled 30 hospitalized older adults, ages 65 and older, who were functionally independent prior to hospital admission, mechanically ventilated while in ICU, and within 24–48 h of ICU discharge at a Level 1 trauma hospital. All participants must have been community-dwelling older adults (i.e., admitted from home) who were functionally independent prior to hospital admission. Functional independence was determined by the Katz Index of Independence in Activities of Daily Living8; validity and reliability of the Katz Index has been established.9 Additional exclusion criteria included pre-existing diagnosis of dementia, active palliative care or hospice orders, and/or spinal cord injury. The university’s Institutional Review Board and affiliated Level 1 trauma hospital approved our protocol prior to study initiation, and all participants signed informed consent in English.

Measures

Sample characteristics

Demographic characteristics were collected from participants and electronic medical records. Selected clinical characteristics (e.g., medical history, admission diagnoses, ICU length of stay, length of mechanical ventilation, ICU severity of illness, and medication administration during the observation period, and discharge disposition) were obtained from the participants’ electronic medical records.

Post-iCU activity counts and sleep/rest time

Wrist actigraphy (Actiwatch Spectrum) objectively measured post-ICU activity and sleep/rest after ICU discharge. When compared to the gold standard of polysomnography, which is not feasible for data collection in the post-ICU environment, actigraphy has reasonable validity and reliablility in assessing sleep-wake patterns.10 Two systematic reviews have discussed the use of actigraphy to measure both activity and sleep/rest in ICU patients.11,12 In this study, actigraphy estimated post-ICU activity counts and total sleep/rest time based on software-based accelerometry algorithms. Actigraphs were placed on the dominant hand of each participant. An activity count was generated for each 15-s epoch; if the activity count fell below the preset threshold scored as “wake,” then the epoch was scored as sleep/rest. Missing and off-wrist data were excluded from the raw data by hand. Actigraphy observation began immediately following study enrollment, for two consecutive nighttime periods (22:00–05:59) and one daytime period (06:00–21:59). ‘Post-ICU daytime activity’ was defined as activity counts/minute throughout the daytime period, and ‘post-ICU daytime total sleep/rest time’ was defined as the total sleep/rest time in hours throughout the daytime period. ‘Post-ICU 24-hour activity’ was calculated as follows: [(mean activity counts/min over the two consecutive nighttime periods) + (mean activity counts/min during the daytime period)]. ‘Post-ICU 24-h total sleep/rest time’ was calculated as follows: [mean total sleep/rest time in hours over the two consecutive nighttime periods) + (mean total sleep/rest time in hours during the daytime period)]. Means for the nighttime periods and daytime period were calculated separately to describe differences in activity and sleep/rest between nighttime and daytime periods in older ICU survivors after ICU discharge, given that 50% of total sleep time in ICU patients occurs during the daytime.13 The hours chosen for daytime versus nighttime periods were based upon established hospital routines (e.g., vital signs, medication administration, scheduled mealtimes, nursing care, rehabilitation therapy).

Post-ICU motor function

Selected assessments from the NIH Toolbox Motor Battery objectively measured two domains of motor function at the time of enrollment: grip strength and dexterity. The Grip Strength Test assessed dominant hand grip strength in lbs using handgrip dynamometry, where higher grip strength in lbs indicates better performance.14 Normative reference scores for hand grip strength among community-dwelling older adults has been established in the literature.15 Grip strength is also a feasible measure of ICU-acquired weakness.16 The 9-Hole Pegboard Dexterity Test assessed dominant hand dexterity using a pegboard task; scores were calculated by time in seconds, where lower/faster time in seconds indicates better performance.17 Normative reference scores for dexterity among community-dwelling adults have also been established in the literature.18 Validity and reliability for both the Grip Strength Test and 9-Hole Pegboard Dexterity Test have been reported.14

Data analysis

Data were analyzed with IBM SPSS Statistics Version 26. Pearson correlation coefficients examined bivariate correlations; covariates with correlations less than 0.20 were considered for inclusion in the exploratory regression analyses. Multivariate regression models were conducted to explore the relationships between predictor variables (activity and sleep/rest) and outcome variables of motor function (grip strength and dexterity), adjusting for selected covariates (age, sex, history of obstructive sleep apnea, and length of mechanical ventilation).

Results

Sample characteristics

Our study cohort of older ICU survivors had a mean age of 71.4 ± 5.4 years, were mostly male (63.3%), and predominately identified as White and non-Hispanic/Latino (76.7%). The average ICU length of stay was almost 12 days, and the average length of mechanical ventilation was about 5 days. About 43.3% of study participants were discharged to either a skilled nursing facility or long-term acute care facility. One participant did not complete the full actigraphy observation period due to surgical ICU readmission, and three participants could not complete at least one of the motor function assessments. Other demographic and clinical characteristics of the sample are presented in our previous manuscript (blinded citation).

Descriptive analyses

The mean post-ICU 24-hour activity was 39.7 ± 27.2 counts/min. The mean 24-h total sleep/rest time was 12.6 ± 5.9 h: specifically, the mean daytime total sleep/rest time was 7.6 ± 4.3 h (out of 16 ‘daytime’ hours). The overall mean grip strength was 44.9 ± 23.6 lbs: the mean grip strength among males was about 54.2 ± 23.1 lbs, and the mean grip strength among females was about 28.8 ± 14.5 lbs. The mean dexterity score was 55.9 ± 36.9 s.

Activity, sleep/rest, and grip strength

The regression model exploring the relationship between post-ICU daytime activity and grip strength was significant (R2 = 0.689, p < .001): daytime activity counts positively correlated with grip strength (β = 0.258, p = .035), indicating that lower daytime activity was associated with worse performance on the Grip Strength Test. The regression model exploring the relationship between post-ICU daytime total sleep/rest time and grip strength was also significant (R2 = 0.69, p < .001): daytime total sleep/rest time was inversely related to grip strength (β = −0.295, p = .022), indicating that greater daytime total sleep/rest time was associated with worse performance on the Grip Strength Test.

Activity, sleep/rest, and dexterity

The regression model exploring the relationship between post-ICU daytime activity and dexterity was significant (R2 = 0.453, p < .019): lower daytime activity counts were associated with greater/longer time in seconds to complete the 9-Hole Pegboard Dexterity Test (β = −0.376, p = .037), indicating that lower daytime activity was associated with worse performance on dexterity. The regression model exploring the relationship between post-ICU daytime total sleep/rest time and dexterity was also significant (R2 = 0.478, p = .016): daytime sleep/rest time correlated with dexterity (β = 0.409, p = .026). Greater daytime sleep/rest time was associated with greater/longer time in seconds to complete the 9-Hole Pegboard Dexterity Test, indicating that greater daytime sleep/rest was associated with worse performance on dexterity. Table 1 summarizes the results of all exploratory regression analyses.

Table 1.

Associations between Post-ICU Activity, Sleep/Rest, and Motor Function.

Predictor variable Outcome variable Modelg
R 2 F P β(95% CI) p
Post-ICU daytime activitya Grip Strength Test, dominant hand, lbse 0.689
F(5, 24) = 10.649		 P < .001* 0.258
(.017, .415)		 p = .035*
Post-ICU 24-hour activityb Grip Strength Test, dominant hand, lbse 0.674
F(5, 23) = 9.527		 p < .001* 0.259
(.01, .439)		 p = .041*
Post-ICU daytime total sleep/rest timec Grip Strength Test, dominant hand, lbse 0.69
F(5, 23) = 10.24		 p < .001* −0.295
(−2.96, −.259)		 p = .022*
Post-ICU 24-hour total sleep/rest timed Grip Strength Test, dominant hand, lbse 0.699
F(5, 23) = 10.669		 p < .001* −0.312
(−2.187, −.261)		 p = .015*
Post-ICU daytime activitya 9-Hole Pegboard Dexterity Test, secondsf 0.453
F(5, 21) = 3.48		 p = .019* −0.376
(−.975, −.034)		 p = .037*
Post-ICU 24-hour activityb 9-Hole Pegboard Dexterity Test, secondsf 0.391
F(5, 20) = 2.571		 p = .059 −0.260
(−.912, .162)		 p = .161
Post-ICU daytime total sleep/rest timec 9-Hole Pegboard Dexterity Test, secondsf 0.478
F(5, 20) = 3.657		 p = .016* 0.409
(.495, 7.016)		 p = .026*
Post-ICU 24-hour total sleep/rest timed 9-Hole Pegboard Dexterity Test, secondsf 0.432
F(5, 20) = 3.045		 p = .033 0.344
(−.188, 4.749)		 p = .068
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R2: regression coefficient of determination; β: standardized coefficients; CI: confidence intervals.

a

Post-ICU daytime activity: mean activity counts/minute over one daytime period (06:00–21:59).

b

Post-ICU 24-hour activity: mean activity counts/minute averaged over two nighttime periods (22:00–05:59) and one daytime period (06:00–21:59).

c

Post-ICU daytime total sleep time: mean total sleep time in hours over one daytime period (06:00–21:59).

d

Post-ICU 24-hour total sleep time: mean total sleep time in hours averaged over two nighttime periods (22:00–05:59) and one daytime period (06:00–21:59).

e

Grip Strength Test: National Institutes of Health Grip Strength Test via handgrip dynamometry. Dominant hand grip strength in lbs: higher values indicate better performance.

f

9-Hole Pegboard Dexterity Test: National Institutes of Health 9-Hole Pegboard Dexterity Test. Best/fastest time in seconds: lower values indicate better performance.

g

Model: adjusted for age, sex, history of obstructive sleep apnea, and days on mechanical ventilation.

Discussion

Hospitalized older ICU survivors exhibit inactivity and likely spend a considerable proportion of time resting or sleeping, which may affect motor function. Importantly, we report that, throughout this immediate post-ICU transition period, older ICU survivors’ sleep/rest periods accounted for almost 50% of a 24-h period, including daytime hours. This is similar to the equal distribution of sleep/rest between daytime and nighttime hours observed in ICU patients,19 and may reflect that older ICU survivors are still recovering from poor sleep and prolonged rest periods after transfer out of ICU. Moreover, post-ICU activity was about 40 counts/min, which equates to activity levels that range between lying down while resting and sitting passively.20 This suggests that hospitalized older ICU survivors who were mechanically ventilated may continue to display sedentary behavior and profound inactivity beyond the ICU. Given that a study inclusion criterion was functional independence prior to hospital admission, our results are clinically significant for older ICU survivors.

Inactivity in this population may indicate prolonged states of rest or sleep. The average total sleep time among relatively healthy, community-dwelling 70-year-old adults is approximately 6 h21; to compare, the mean 24-h total sleep/rest time found in this sample of hospitalized older ICU survivors was double this amount, at 12.6 h. Yet, while the quantity of sleep appears more than adequate, quality of sleep is likely poor with high sleep fragmentation.5,22 A potential explanation of the inactivity and/or prolonged sleep/rest could be related to these older ICU survivors’ reasons for ICU admission: over half of the sample had been admitted to a surgical or trauma ICU and thus underwent surgical procedure(s) during hospitalization. Acute pain related to surgery also necessitated administrations of pain medications, which are commonly administered to ICU patients.23 During our actigraphy observation period, about one-fourth had received more than two doses of opioids and/or benzodiazepines, which may have affected activity levels and increased daytime sleepiness.

Results from our study support findings from other studies of older adults. The average grip strength for relatively healthy, community-dwelling 70-year-old males is about 86 lbs and the average grip strength for females is about 53 lbs.15 The average dexterity score for community-dwelling older males is about 23–25 s, and the average dexterity score for older females is about 20–23 s.18 In comparison, the mean dominant hand grip strength and dexterity score were much lower in our study sample, despite their independence in activities of daily living prior to hospital admission. Previous large cross-sectional studies of community-dwelling older adults have found significant associations between self-reported longer sleep duration and worse grip or muscle strength.24–26 Perhaps the relationship between sleep/rest and motor function is exacerbated by critical illness and mechanical ventilation: risk factors for ICU-acquired weakness include older age and longer length of mechanical ventilation.27,28 Post-ICU motor function is particularly relevant for older adults. For example, grip strength, identified as a simple test for ICU-acquired weakness, is associated with mortality.16 In addition, both grip strength and dexterity are associated with discharge to a care facility.29,30

The Clinical Practice Guidelines for the Prevention and Management of Pain, Agitation/Sedation, Delirium, Immobility, and Sleep Disruption in Adult Patients in the ICU31 discuss potential targets to inform the design of interventions to promote activity and sleep. Additionally, early mobilization and family engagement, as proposed by the ABCDEF bundle,32,33 could serve as a framework to focus on symptom management in activity and sleep promotion for older adults recovering from critical illness. Important directions for future research interventions to improve daytime activity and nighttime sleep include tailored approaches according to patient conditions and disease profiles.

Study limitations include the small sample size and short actigraphy observation period; these data were collected as an exploratory study of older ICU survivors and post-intensive care syndrome within the early transition period following ICU discharge. Further, the cross-sectional design of this study does not imply causality in the relationships between post-ICU activity, sleep/rest, and motor function. Delirium may also affect activity and sleep in older ICU survivors. Per our protocol, we reviewed provider documentation of ICU delirium via electronic medical records. However, clinical documentation of delirium in older ICU patients is unreliable34 for use in research studies; therefore, these data were not included as a covariate. While actigraphy tends to overestimate total sleep/rest time compared to polysomnography, the mean total sleep/rest time found among this sample was very high, and this may imply large proportions of daytime sleep/rest. Although there are risks of confounding with the use of actigraphy to measure sleep in ICU patients,35 the measurement of activity counts and total sleep/rest time during daytime hours may be a useful biomarker within the post-ICU transition period for early identification of poor motor function, a component of post-intensive care syndrome.

Conclusion

After transition of care out of ICU, older ICU survivors are inactive and likely spend a majority of a 24-hour cycle either resting or sleeping, especially during daytime hours. Post-ICU inactivity and prolonged sleep/rest are associated with poor motor function and, within the early transition period out of ICU, may identify older ICU survivors at risk for post-intensive care syndrome. Inactivity was associated with worse grip strength and dexterity, while greater total sleep time/rest periods was associated with worse grip strength and dexterity. Increasing daytime activity may prevent sedentary behavior and exacerbation of motor impairment and ICU-acquired weakness. Ultimately, our study findings may reflect that daytime activity could be a target for clinical research interventions to promote motor function in hospitalized older ICU survivors following ICU discharge.

Acknowledgments

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Declaration of Competing Interest

The authors (MNE, CLM, ZL) have no conflicts of interest to disclose. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. All authors have contributed substantially to the development of this manuscript, and all authors have read and approved the final submission. The study protocol was approved by the Institutional Review Boards of the university and affiliated medical center.

Footnotes

Ethical Conduct of Research

The study protocol was approved by the Institutional Review Boards of the university and affiliated medical center.

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