Identifying an Acceptable Number of Ambulatory Blood Pressure Measurements for Accuracy of Average Blood Pressure and Nocturnal Dipping Status.

OBJECTIVE: We aimed to identify the minimum number of ABP measures to accurately determine daytime and nighttime systolic BP averages and nocturnal dipping status (i.e., relative daytime:nighttime change). METHODS: Forty-three midlife participants wore an ABP monitor for 24 hours with measurements every 20/30 minutes during the daytime/nighttime, as identified by a sleep diary. We calculated daytime/nighttime systolic BP average and dipping status from all available measurements per participant (i.e., normative data). We then calculated daytime and nighttime BP per participant based on a random selection of 8-20 and 4-10 measurements and replicated random selections 1000 times. We calculated accuracy by checking the proportion from 1000 different randomly selected samples for a particular number of measurements that systolic BP was ±5 mmHg of normative data, and dipping status remained unchanged for each participant compared to the normative value. The best fit for the regression model estimated the minimal number of measurements for an accuracy of 95% in BP averages. RESULTS: For a 95% accuracy in estimating daytime and nighttime systolic BP, 11 daytime and 8 nighttime measurements were required. The highest accuracy for dipping status was 91.6±13.4% using 20 daytime and 10 nighttime measures, while the lowest was (83.4±15.1%) using 8 daytime and 4 nighttime measures. CONCLUSION: Eleven daytime and eight nighttime measurements are likely enough to calculate average systolic BPs accurately. However, no minimum number is suggested to accurately calculate dipping status.

The endogenous circadian system worsens asthma at night independent of sleep and other daily behavioral or environmental cycles.

Asthma often worsens at night. To determine if the endogenous circadian system contributes to the nocturnal worsening of asthma, independent of sleep and other behavioral and environmental day/night cycles, we studied patients with asthma (without steroid use) over 3 wk in an ambulatory setting (with combined circadian, environmental, and behavioral effects) and across the circadian cycle in two complementary laboratory protocols performed in dim light, which separated circadian from environmental and behavioral effects: 1) a 38-h "constant routine," with continuous wakefulness, constant posture, 2-hourly isocaloric snacks, and 2) a 196-h "forced desynchrony" incorporating seven identical recurring 28-h sleep/wake cycles with all behaviors evenly scheduled across the circadian cycle. Indices of pulmonary function varied across the day in the ambulatory setting, and both laboratory protocols revealed significant circadian rhythms, with lowest function during the biological night, around 4:00 AM, uncovering a nocturnal exacerbation of asthma usually unnoticed or hidden by the presence of sleep. We also discovered a circadian rhythm in symptom-based rescue bronchodilator use (ß2-adrenergic agonist inhaler) whereby inhaler use was four times more likely during the circadian night than day. There were additive influences on asthma from the circadian system plus sleep and other behavioral or environmental effects. Individuals with the lowest average pulmonary function tended to have the largest daily circadian variations and the largest behavioral cycle effects on asthma. When sleep was modeled to occur at night, the summed circadian, behavioral/environmental cycle effects almost perfectly matched the ambulatory data. Thus, the circadian system contributes to the common nocturnal worsening of asthma, implying that internal biological time should be considered for optimal therapy.

Chronological distribution of readings in ambulatory blood pressure monitoring exams affects the nighttime average and the magnitude of blood pressure dipping.

STUDY OBJECTIVES: Averaged nighttime blood pressure (BP) is superior to daytime BP for cardiovascular risk stratification, and the relative change between daytime/nighttime BP (dipping%) significantly predicts cardiovascular risk. Newer reports suggest that 4 measurements at night may be enough for cardiovascular risk stratification. Since BP oscillates across the night, the temporal distribution of measurements across the night may impact nighttime BP and dipping%. Therefore, we compared average nighttime BP and dipping% when using measurements in the first half (1st-half), second (2nd-half), and a combination of both (combined). METHODS: Forty-three (17 females and twenty-six males) midlife adults aged 50±10 years old wore an ambulatory BP monitor for 24 hours at home, programmed to measure BP every 20 minutes when scheduled for daytime and every 30 minutes during a self-selected 8-hour nighttime for time-in-bed. We compared the nighttime BP averages and dipping% when using either the first four measurements from the 1st-half or 2nd-half of the nighttime and combined. RESULTS: Nighttime Systolic BP was significantly different across 1st-half, 2nd-half, and combined (111±9 vs.107±11 vs. 109±9 mmHg, p<0.01), respectively, with significant pairwise differences across all categories (p<0.01 for each). Systolic BP dipping% was significantly different across 1st-half, 2nd-half, and combined (9.9±5.5 vs.13.5±6.4 vs. 11.7±5.0 %, p<0.01), respectively, with significant pairwise differences across all categories (p<0.01 for each. Diastolic BP and diastolic dipping% were similar across the three different bins. CONCLUSION: In midlife adults, systolic nighttime BP and dipping% may depend upon when BP measurements are taken during the night.

Night shift work is associated with an increased risk of asthma.

INTRODUCTION: Shift work causes misalignment between internal circadian time and the external light/dark cycle and is associated with metabolic disorders and cancer. Approximately 20% of the working population in industrialised countries work permanent or rotating night shifts, exposing this large population to the risk of circadian misalignment-driven disease. Analysis of the impact of shift work on chronic inflammatory diseases is lacking. We investigated the association between shift work and asthma. METHODS: We describe the cross-sectional relationship between shift work and prevalent asthma in >280000 UK Biobank participants, making adjustments for major confounding factors (smoking history, ethnicity, socioeconomic status, physical activity, body mass index). We also investigated chronotype. RESULTS: Compared with day workers, 'permanent' night shift workers had a higher likelihood of moderate-severe asthma (OR 1.36 (95% CI 1.03 to 1.8)) and all asthma (OR 1.23 (95% CI 1.03 to 1.46)). Individuals doing any type of shift work had higher adjusted odds of wheeze/whistling in the chest. Shift workers who never or rarely worked on nights and people working permanent nights had a higher adjusted likelihood of having reduced lung function (FEV1 <80% predicted). We found an increase in the risk of moderate-severe asthma in morning chronotypes working irregular shifts, including nights (OR 1.55 (95% CI 1.06 to 2.27)). CONCLUSIONS: The public health implications of these findings are far-reaching due to the high prevalence and co-occurrence of both asthma and shift work. Future longitudinal follow-up studies are needed to determine if modifying shift work schedules to take into account chronotype might present a public health measure to reduce the risk of developing inflammatory diseases such as asthma.

Cardiac autonomic control during non-REM and REM sleep stages in paediatric patients with Prader-Willi syndrome.

Cardiac death is the second most prevalent cause in Prader-Willi syndrome (PWS). Paediatric patients with PWS often present cardiac autonomic dysfunction during wakefulness, obesity and sleep-disordered breathing. However, the extent of cardiac autonomic modulation during sleep in PWS has not been documented. The objective of this study was to assess alterations in cardiac autonomic modulation of paediatric patients with PWS during different sleep stages. Thirty-nine participants in three groups: 14 PWS, 13 sex and age-matched lean controls (LG) and 12 obese-matched controls (OB). All participants underwent overnight polysomnography, including continuous electrocardiogram recordings. Heart rate variability (HRV) was analysed during representative periods of each sleep stage through time and frequency domains calculated across 5-min periods. Between-within ANOVAs were employed (p < .05). The results show that total HRV was lower in PWS than OB and LG during slow-wave sleep (SWS) (standard deviation of all NN intervals [SDNN] ms, p = .006). Parasympathetic modulation assessed by time-domain analysis was lower during SWS in PWS compared to both OB and LG (square root of the mean of the sum of the squares of differences between adjacent NN intervals [RMSSD] ms, p = .004; SDSD, standard deviation of differences between adjacent NN intervals [SDSD] ms, p = .02; number of adjacent NN intervals differing by >50 ms [NN50] ms, p = .03; proportion of adjacent NN intervals differing by >50 ms [pNN50] ms, p = .01). Sympathovagal balance assessed by frequency-domain analysis was lower during both N2 and SWS than during the rapid eye movement (REM) sleep stage, but not different among groups. In conclusion, this group of paediatric patients with PWS had impaired cardiac autonomic balance due to reduced parasympathetic modulation during SWS. This result could imply an underlying increased cardiovascular risk in PWS even during early age and independent of obesity.

Interactions between home, work, and sleep among firefighters.

BACKGROUND: Firefighters endure large occupational burdens and generally operate under conditions of chronic sleep deficiency and circadian disruption due to long shifts, plus interrupted sleep due to emergency calls during the night. A typical shift for firefighters is 24-h on/48-h off, and firefighters are expected to use time-off to recover from any sleep debt, while balancing social, family, and home responsibilities. This qualitative study sets out to assess family dynamics and how firefighters prioritize sleep and recovery at home based on relationship or family status, as well as a fire department's current shift schedule. METHODS: Focus groups were conducted via convenience sampling in Portland, OR, with full-time firefighters, battalion chiefs, and their spouses. Grounded theory, using NVivo 12 Plus, was used to code transcripts to reveal reoccurring concepts and themes. RESULTS: Major themes centered around the increase of nonemergent calls contributing to compassion fatigue. Spouses can help improve the sleep of firefighters by creating opportunities for recuperative sleep at home. However, spouses also conveyed underlying tones of "resentment" relating to their firefighter being unavailable for emotional and instrumental support. While married firefighters discussed choosing family and home obligations over reducing sleep debt to maintain relationships, single and divorced firefighters spoke of fewer conflicts impeding their ability to prioritize sleep at home. CONCLUSIONS: These results improve our understanding of how firefighters prioritize sleep at home based on family dynamics and can inform future decision-making for fire departments in addressing concerns related to work-family conflict, sleep loss, and compassion fatigue among their members.

Optimization of Primary Care Among Black Americans Using Patient Portals: Qualitative Study.

BACKGROUND: Reduced patient portal use has previously been reported among Black Americans when compared with that of the general population. This statistic is concerning because portals have been shown to improve the control of chronic conditions that are more prevalent and severe in Black Americans. At their very simplest, portals allow patients to access their electronic health records and often provide tools for patients to interact with their own health information, treatment team members, and insurance companies. However, research suggests that Black American patients have greater concerns over a lack of support, loss of privacy, and reduced personalization of care compared with other Americans, which results in a disparity of portal use. OBJECTIVE: This qualitative investigation of primary care experiences of Black Americans from across the United States who participated in remote focus groups in April and May 2020 aims to explore the use and perceived value of patient portals to better understand any barriers to optimized treatment in the primary care setting. METHODS: We performed an inductive thematic analysis of 8 remote focus group interviews with 29 Black American patients aged 30-60 years to qualitatively assess the experiences of Black American patients with regular access to portals. RESULTS: Thematic analysis uncovered the following interrelated themes regarding patient portals in primary care: the optimization of care, patient empowerment, patient-provider communication, and patient burden. CONCLUSIONS: In contrast to what has been described regarding the reluctance of Black Americans to engage with patient portals, our focus groups revealed the general acceptance of patient portals, which were described overwhelmingly as tools with the potential for providing exceptional, personalized care that may even work to mitigate the unfair burden of disease for Black Americans in primary care settings. Thus, opportunities for better health care will clearly arise with increased communication, experience, and adoption of remote health care practices among Black Americans.

Circadian Rhythm of Vascular Function in Midlife Adults.

Objective- Adverse cardiovascular events occur more frequently in the morning than at other times of the day. Vascular endothelial function (VEF)-a robust cardiovascular risk marker-is impaired during this morning period. We recently discovered that this morning impairment in VEF is not caused by either overnight sleep or the inactivity that accompanies sleep. We determined whether the endogenous circadian system is responsible for this morning impairment in VEF. We also assessed whether the circadian system affects mechanistic biomarkers, that is, oxidative stress (malondialdehyde adducts), endothelin-1, blood pressure, and heart rate. Approach and Results- Twenty-one (11 women) middle-aged healthy participants completed a 5-day laboratory protocol in dim light where all behaviors, including sleep and activity, and all physiological measurements were evenly distributed across the 24-hour period. After baseline testing, participants underwent 10 recurring 5-hour 20-minute behavioral cycles of 2-hour 40-minute sleep opportunities and 2 hours and 40 minutes of standardized waking episodes. VEF, blood pressure, and heart rate were measured, and venous blood was sampled immediately after awakening during each wake episode. Independent of behaviors, VEF was significantly attenuated during the subjective night and across the morning ( P=0.04). Malondialdehyde adducts and endothelin-1 exhibited circadian rhythms with increases across the morning vulnerable period and peaks around noon ( P≤0.01). Both systolic ( P=0.005) and diastolic blood pressure ( P=0.04) were rhythmic with peaks in the late afternoon. Conclusions- The endogenous circadian system impairs VEF and increases malondialdehyde adducts and endothelin-1 in the morning vulnerable hours and may increase the risk of morning adverse cardiovascular events in susceptible individuals. Clinical Trial Registration- URL: http://www.clinicaltrials.gov . Unique identifier: NCT02202811.

Apnea-Hypopnea Event Duration Predicts Mortality in Men and Women in the Sleep Heart Health Study.

RATIONALE: Obstructive sleep apnea is a risk factor for mortality, but its diagnostic metric-the apnea-hypopnea index-is a poor risk predictor. The apnea-hypopnea index does not capture the range of physiological variability within and between patients, such as degree of hypoxemia and sleep fragmentation, that reflect differences in pathophysiological contributions of airway collapsibility, chemoreceptive negative feedback loop gain, and arousal threshold. OBJECTIVES: To test whether respiratory event duration, a heritable sleep apnea trait reflective of arousal threshold, predicts all-cause mortality. METHODS: Mortality risk as a function of event duration was estimated by Cox proportional hazards in the Sleep Heart Health Study, a prospective community-based cohort. Gender-specific hazard ratios were also calculated. MEASUREMENTS AND MAIN RESULTS: Among 5,712 participants, 1,290 deaths occurred over 11 years of follow-up. After adjusting for demographic factors (mean age, 63 yr; 52% female), apnea-hypopnea index (mean, 13.8; SD, 15.0), smoking, and prevalent cardiometabolic disease, individuals with the shortest-duration events had a significant hazard ratio for all-cause mortality of 1.31 (95% confidence interval, 1.11-1.54). This relationship was observed in both men and women and was strongest in those with moderate sleep apnea (hazard ratio, 1.59; 95% confidence interval, 1.11-2.28). CONCLUSIONS: Short respiratory event duration, a marker for low arousal threshold, predicts mortality in men and women. Individuals with shorter respiratory events may be predisposed to increased ventilatory instability and/or have augmented autonomic nervous system responses that increase the likelihood of adverse health outcomes, underscoring the importance of assessing physiological variation in obstructive sleep apnea.

Separate and interacting effects of the endogenous circadian system and behaviors on plasma aldosterone in humans.

Measurements of aldosterone for diagnosis of primary aldosteronism are usually made from blood sampled in the morning when aldosterone typically peaks. We tested the relative contributions and interacting influences of the circadian system, ongoing behaviors, and prior sleep to this morning peak in aldosterone. To determine circadian rhythmicity and separate effects of behaviors on aldosterone, 16 healthy participants completed a 5-day protocol in dim light while all behaviors ranging from sleep to exercise were standardized and scheduled evenly across the 24-h circadian period. In another experiment, to test the separate effects of prior nocturnal sleep or the inactivity that accompanies sleep on aldosterone, 10 healthy participants were studied across 2 nights: 1 with sleep and 1 with maintained wakefulness (randomized order). Plasma aldosterone was measured repeatedly in each experiment. Aldosterone had a significant endogenous rhythm ( P < 0.001), rising across the circadian night and peaking in the morning (~8 AM). Activity, including exercise, increased aldosterone, and different behaviors modulated aldosterone differently across the circadian cycle (circadian phase × behavior interaction; P < 0.001). In the second experiment, prior nocturnal sleep and prior rested wakefulness both increased plasma aldosterone ( P < 0.001) in the morning, to the same extent as the change in circadian phases between evening and morning. The morning increase in aldosterone is due to effects of the circadian system plus increased morning activities and not prior sleep or the inactivity accompanying sleep. These findings have implications for the time of and behaviors preceding measurement of aldosterone, especially under conditions of shift work and jet lag.

Morning impairment in vascular function is unrelated to overnight sleep or the inactivity that accompanies sleep.

Adverse cardiovascular events, such as myocardial infarction and sudden cardiac death, occur more frequently in the morning. Prior studies have shown that vascular endothelial function (VEF), a marker of cardiovascular disease, is attenuated during physical inactivity and declines across the night. We sought to determine whether a morning attenuation in VEF is a result of prior sleep or the inactivity that inevitably accompanies sleep. After 1 wk of a rigorously controlled sleep-wake schedule and behaviors, 10 healthy participants completed a randomized crossover protocol in dim light and constant conditions, incorporating a night of 6 h of sleep opportunity and a night of immobility while they were supine and awake. VEF was measured in the dominant brachial artery as flow mediated dilation (FMD) before and after each 6-h trial. To avoid disturbing sleep and posture of the participants, blood was drawn using a 12-ft catheter from an adjoining laboratory room before, during, and after each 6-h trial, and plasma was analyzed for markers of oxidative stress [malondialdehyde adducts (MDA)], and endothelin-1. Contrary to expectation, both nocturnal sleep and nocturnal inactivity significantly increased FMD ( P < 0.05). There was no significant change in MDA or endothelin-1 within and between trials. Contrary to expectations based on prior studies, we found that overnight sleep or the inactivity that accompanies sleep did not result in attenuation in VEF in the morning hours in healthy people. Thus, it is plausible that the endogenous circadian system, a remaining factor not studied here, is responsible for the commonly observed decline in VEF across the night.

Circadian rhythms govern cardiac repolarization and arrhythmogenesis.

Sudden cardiac death exhibits diurnal variation in both acquired and hereditary forms of heart disease, but the molecular basis of this variation is unknown. A common mechanism that underlies susceptibility to ventricular arrhythmias is abnormalities in the duration (for example, short or long QT syndromes and heart failure) or pattern (for example, Brugada's syndrome) of myocardial repolarization. Here we provide molecular evidence that links circadian rhythms to vulnerability in ventricular arrhythmias in mice. Specifically, we show that cardiac ion-channel expression and QT-interval duration (an index of myocardial repolarization) exhibit endogenous circadian rhythmicity under the control of a clock-dependent oscillator, krüppel-like factor 15 (Klf15). Klf15 transcriptionally controls rhythmic expression of Kv channel-interacting protein 2 (KChIP2), a critical subunit required for generating the transient outward potassium current. Deficiency or excess of Klf15 causes loss of rhythmic QT variation, abnormal repolarization and enhanced susceptibility to ventricular arrhythmias. These findings identify circadian transcription of ion channels as a mechanism for cardiac arrhythmogenesis.

Endogenous circadian system and circadian misalignment impact glucose tolerance via separate mechanisms in humans.

Glucose tolerance is lower in the evening and at night than in the morning. However, the relative contribution of the circadian system vs. the behavioral cycle (including the sleep/wake and fasting/feeding cycles) is unclear. Furthermore, although shift work is a diabetes risk factor, the separate impact on glucose tolerance of the behavioral cycle, circadian phase, and circadian disruption (i.e., misalignment between the central circadian pacemaker and the behavioral cycle) has not been systematically studied. Here we show--by using two 8-d laboratory protocols--in healthy adults that the circadian system and circadian misalignment have distinct influences on glucose tolerance, both separate from the behavioral cycle. First, postprandial glucose was 17% higher (i.e., lower glucose tolerance) in the biological evening (8:00 PM) than morning (8:00 AM; i.e., a circadian phase effect), independent of the behavioral cycle effect. Second, circadian misalignment itself (12-h behavioral cycle inversion) increased postprandial glucose by 6%. Third, these variations in glucose tolerance appeared to be explained, at least in part, by different mechanisms: during the biological evening by decreased pancreatic ß-cell function (27% lower early-phase insulin) and during circadian misalignment presumably by decreased insulin sensitivity (elevated postprandial glucose despite 14% higher late-phase insulin) without change in early-phase insulin. We explored possible contributing factors, including changes in polysomnographic sleep and 24-h hormonal profiles. We demonstrate that the circadian system importantly contributes to the reduced glucose tolerance observed in the evening compared with the morning. Separately, circadian misalignment reduces glucose tolerance, providing a mechanism to help explain the increased diabetes risk in shift workers.

Fractal regulation and incident Alzheimer's disease in elderly individuals.

INTRODUCTION: Healthy physiological systems exhibit fractal regulation (FR), generating similar fluctuation patterns in physiological outputs across different time scales. FR in motor activity is degraded in dementia, and the degradation correlates to cognitive decline. We tested whether degraded FR predicts Alzheimer's dementia. METHODS: FR in motor activity was assessed in 1097 nondemented older adults at baseline. Cognition was assessed annually for up to 11 years. RESULTS: Participants with an FR metric at the 10th percentile in this cohort had a 1.8-fold Alzheimer's disease risk (equivalent to the effect of being ∼5.2 years older) and 1.3-fold risk for mild cognitive impairment (equivalent to the effect of being ∼3.0 years older) than those at the 90th percentile. Consistently, degraded FR predicted faster cognitive decline. These associations were independent of physical activity, sleep fragmentation, and stability of daily activity rhythms. DISCUSSION: FR may be a useful tool for predicting Alzheimer's dementia.

Human circadian system causes a morning peak in prothrombotic plasminogen activator inhibitor-1 (PAI-1) independent of the sleep/wake cycle.

Serious adverse cardiovascular events peak in the morning, possibly related to increased thrombosis in critical vessels. Plasminogen activator inhibitor-1 (PAI-1), which inhibits fibrinolysis, is a key circulating prothrombotic factor that rises in the morning in humans. We tested whether this morning peak in PAI-1 is caused by the internal circadian system or by behaviors that typically occur in the morning, such as altered posture and physical activity. Twelve healthy adults underwent a 2-week protocol that enabled the distinction of endogenous circadian effects from behavioral and environmental effects. The results demonstrated a robust circadian rhythm in circulating PAI-1 with a peak corresponding to ∼6:30 am. This rhythm in PAI-1 was 8-times larger than changes in PAI-1 induced by standardized behavioral stressors, including head-up tilt and 15-minute cycle exercise. If this large endogenous morning peak in PAI-1 persists in vulnerable individuals, it could help explain the morning peak in adverse cardiovascular events.

Endogenous circadian regulation of pro-inflammatory cytokines and chemokines in the presence of bacterial lipopolysaccharide in humans.

Various aspects of immune response exhibit 24-h variations suggesting that infection susceptibility and treatment efficacy may vary by time of day. Whether these 24-h variations are endogenous or evoked by changes in environmental or behavioral conditions is not known. We assessed the endogenous circadian control and environmental and behavioral influences on ex-vivo lipopolysaccharide stimulation of whole blood in thirteen healthy participants under 48h of baseline conditions with standard sleep-wake schedules and 40-50h of constant environmental and behavioral (constant routine; CR) conditions. Significant 24-h rhythms were observed under baseline conditions in Monocyte Chemotactic Protein, Granulocyte-Macrophage Colony-Stimulating Factor and Interleukin 8 but not Tumor Necrosis Factor alpha whereas significant 24-h rhythms were observed in all four immune factors under CR conditions. The rhythm amplitudes, expressed as a percentage of mean, were comparable between immune factors and across conditions. In contrast, the acrophase time (time of the fitted peak) was different between immune factors, and included daytime and nighttime peaks and changes across behavioral conditions. These results suggest that the endogenous circadian system underpins the temporal organization of immune responses in humans with additional effects of external environmental and behavioral cycles. These findings have implications for understanding the adverse effects of recurrent circadian disruption and sleep curtailment on immune function.

Brachial artery endothelial function is stable across the morning in young men.

BACKGROUND: The morning hours are associated with increased cardiovascular (CV) risk, and vascular endothelial function (VEF) is a strong predictor of CV disease. A diurnal rhythm in VEF has been established but the morning variation in VEF is not well-documented. Thus, we tested if VEF is impaired across the vulnerable morning period. METHODS: After overnight fasts, eight healthy men (age 26.3 ± 3 yr) underwent assessments of VEF under standardized testing conditions every 2 h from 0700 to 1300 h on two separate days. VEF was estimated following 5 min brachial artery occlusions by hyperemic flow-mediated dilation (FMD). RESULTS: There was no significant change in FMD or hyperemic shear stimulus across the 6 h vulnerable period on either day, despite changes in physical activity and meals across these periods. CONCLUSION: In this healthy group of young men, VEF is stable across the vulnerable morning period when typical behaviors occurred (breakfast and physical activity). Future research should focus on the roles of sleep, physical inactivity during sleep and endogenous circadian rhythm in VEF.

Later circadian timing and increased sleep timing variability are associated with attenuations in overnight blood pressure dipping among chronic nightshift workers.

OBJECTIVE: Determine relationships between overnight blood pressure, circadian phase, and sleep variability among dayshift and chronic nightshift nurses. METHODS: Twenty participants working dayshift (n = 10) or nightshift (n = 10) schedules participated in a 7-day cross-sectional study. Participants underwent an evening in-laboratory melatonin assessment and wore ambulatory blood pressure devices to assess 24-hour blood pressure patterns. Overnight blood pressure dipping was calculated from sleeping/waking systolic blood pressure ratio and salivary dim-light melatonin onset determined circadian phase. Sleep variability was assessed using the standard deviation of 7-day sleep onset. RESULTS: Nightshift workers had later circadian phase, greater sleep onset variability, and an attenuated overnight blood pressure dipping pattern. Later circadian phase was associated with attenuated dipping patterns and sleep onset variability was negatively correlated with blood pressure dipping magnitude in nightshift, but not dayshift workers. CONCLUSIONS: Chronic circadian disruption via higher sleep onset variability among nightshift workers may contribute to attenuated blood pressure dipping and cardiovascular risk in this population.