Greenlund, Ian M.

Abstract Purpose: Cardiovascular health disparities are present in African Americans, but it remains unknown whether this phenomenon affect Somali Americans. Study of Somali Americans is warranted due to distinct genetic and cultural differences from African Americans of western African ancestry. Orthostatic hemodynamic responses have implications for cardiovascular risk, especially among African American females. We sought to examine race and sex differences in systolic (SAP) and diastolic (DAP) arterial pressure and heart rate (HR) responsiveness to standing. We hypothesized that SAP, DAP, and HR change from supine to standing position would be higher in Somali Americans. Methods: We studied blood pressure and HR responsiveness in 139 (70 Somali; age: 29±10 years, 69 White; age: 31±9 years) participants. Supine SAP, DAP, and HR were measured after at least five minutes of supine rest, and again after one minute of standing. SAP, DAP, and HR change was compared between groups. Results: ΔSAP and ΔDAP were similar between groups (race × sex: p>0.05). However, HR responsiveness to orthostasis varied between race and sex comparisons (race×sex: p=0.011). Somali females exhibited an augmented HR response to orthostasis compared to White females (Δ19±13 vs. 11±9 beats/min, p=0.005) and Somali males (Δ19±13 vs. 12±9 beats/min, p=0.020). Conclusion: ΔHR to standing is augmented in young female Somali Americans. These findings highlight an early potential impairment in hemodynamic regulation that may heighten future cardiovascular risk. Further work is warranted to identify the potential autonomic nervous system underpinnings that may contribute to potentiated orthostatic responses and cardiovascular risk in Somali American females. Clinical Trial Registration: www.clinicaltrials.gov; unique identifier, NCT04124848; NCT05411029; NCT03308578.

BACKGROUND: Alcohol consumption is associated with cardiovascular disease, and the sympathetic nervous system is a suspected mediator. The present study investigated sympathetic transduction of muscle sympathetic nerve activity to blood pressure at rest and in response to cold pressor test following evening binge alcohol or fluid control, with the hypothesis that sympathetic transduction would be elevated the morning after binge alcohol consumption. METHODS: Using a randomized, fluid-controlled (FC) crossover design, 26 healthy adults (12 male, 14 female, 25±6 years, 27±4 kg/m 2 ) received an evening binge alcohol dose and a FC. All participants underwent next-morning autonomic-cardiovascular testing consisting of muscle sympathetic nerve activity, beat-to-beat blood pressure, and heart rate during a 10-minute rest period and a 2-minute cold pressor test. Sympathetic transduction was assessed at rest and during the cold pressor test in both experimental conditions. RESULTS: Evening alcohol increased heart rate (FC: 60±9 versus alcohol: 64±9 bpm; P =0.010) but did not alter resting mean arterial pressure (FC: 80±6 versus alcohol: 80±7 mm Hg; P =0.857) or muscle sympathetic nerve activity (FC: 18±9 versus alcohol: 20±8 bursts/min; P =0.283). Sympathetic transduction to mean arterial pressure (time×condition; P =0.003), diastolic blood pressure (time×condition; P =0.010), and total vascular conductance (time×condition; P =0.004) was augmented after alcohol at rest. Sympathetic transduction during the cold pressor test was also elevated after evening binge alcohol consumption ( P =0.002). CONCLUSIONS: These findings suggest that evening binge alcohol consumption leads to augmented morning-after sympathetic transduction of muscle sympathetic nerve activity to blood pressure, highlighting a new mechanism whereby chronic or excessive alcohol consumption contributes to cardiovascular disease progression via altered end-organ responsiveness to sympathetic neural outflow. REGISTRATION: URL: https://clinicaltrials.gov/study/NCT03567434 ; Unique identifier: NCT03567434.

The present study investigated the independent association between actigraphy-based sleep duration, efficiency, and measures of blood pressure, heart rate, and muscle sympathetic nerve activity (MSNA) in adult males and females. Contrary to our hypothesis, the findings do not support an independent association between habitual sleep and cardiovascular or sympathetic neural activity. However, these findings do not preclude a potential association between these parameters in populations with sleep disorders and/or cardiovascular disease.

Short sleep duration is associated with future cardiovascular disease including hypertension, especially in females, but mechanistic evidence is largely lacking. Experimental sleep restriction has been shown to cause short sleep-mediated tachycardia and reduced heart rate variability, indicative of autonomic cardiac instability, in some but not all studies. Heart rate (HR) response to spontaneous cortical arousals can be regarded as an index of autonomic cardiac control given its characteristic temporal pattern. Whether the HR response to cortical arousals is altered during experimental sleep restriction remains unknown. We hypothesized that sleep restriction would result in augmented HR reactivity to spontaneous arousals, and that this response would be more marked in females. We studied 19 young, healthy subjects (eight females, age: 23.5 ± 5 years, body mass index [BMI]: 24.5 ± 3.6 kg/m2). In a randomized, crossover design, participants were tested during a normal sleep (NS, 9 hr sleep opportunity) or sleep restriction (SR, 4 hr sleep opportunity) study arm. Each 16-day study visit consisted of a 4-day study acclimation phase, 9-day experimental sleep perturbation segment, followed by a 3-day recovery period. An overnight polysomnography (PSG) study was conducted on study days 2, 5 and 11 (at baseline and after 1 and 7 days of restricted versus control sleep). A registered PSG technician provided sleep staging and spontaneous arousal scoring, which was confirmed by an investigator with sleep expertise (IMG). For each identified spontaneous arousal, the HR change was quantified for 30 cardiac cycles post-arousal onset and compared to a pre-arousal baseline (average HR 5 – 10 cardiac cycles prior to arousal). An arousal was considered valid for analysis if at least one minute of stage N2 or rapid eye movement (REM) sleep occurred following sleep stage transition and was at least 30 seconds apart from other sleep disturbance-related events (e.g., limb movement, apneic event, etc.). Given low prevalence of slow wave sleep (SWS) arousals, arousals occurring in that sleep stage were excluded from present analysis. Statistical analysis, including repeated measures ANOVA (RMANOVA, p < 0.05) with condition and time (cardiac cycles) as within-subjects factors and sex as the between-subjects factor, was conducted to compare the beat-to-beat HR response to arousal between study conditions. Additionally, average and peak HR responses to spontaneous arousals were compared via RMANOVA with condition and time (study days) as within-subjects and sex as between-subjects factors. HR response to spontaneous arousal in stage two and REM sleep was similar between NS and SR on study day 5 or day 11 (condition × time: p = 0.943, 0.865). Secondary analysis of average and peak HR responsiveness to spontaneous arousals in stage two and REM sleep between conditions and study days was also not statistically different (condition × time: p = 0.193, 0.185). Last, no significant sex differences were detected across comparisons (condition × time × sex: p > 0.05 for all). These findings suggest that a 9-day sleep restriction paradigm may not alter cardiac autonomic function in otherwise healthy adults. Future work is warranted to determine whether these results extend to individuals with established cardiovascular risk factors or cardiovascular disease. Support: NIH T32-DK007013, R01-114676, and CTSA grant UL1-TR002377. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Patients with obstructive sleep apnea (OSA) have a heightened risk of developing cardiovascular diseases, namely hypertension. While seminal evidence indicates a causal role for sympathetic nerve activity in the hypertensive phenotype commonly observed in patients with OSA, no studies have investigated potential sex differences in the sympathetic regulation of blood pressure in this population. Supporting this exploration are large-scale observational data, as well as controlled interventional studies in healthy adults, indicating that sleep disruption increases blood pressure to a greater extent in females relative to males. Furthermore, females with severe OSA demonstrate a more pronounced hypoxic burden (i.e., disease severity) during rapid eye movement sleep when sympathetic nerve activity is greatest. These findings would suggest that females are at greater risk for the hemodynamic consequences of OSA and related sleep disruption. Accordingly, the purpose of this review is three-fold: (1) to review the literature linking sympathetic nerve activity to hypertension in OSA, (2) to highlight recent experimental data supporting the hypothesis of sex differences in the regulation of sympathetic nerve activity in OSA, and (3) to discuss the potential sex differences in peripheral adrenergic signaling that may contribute to, or offset, cardiovascular risk in patients with OSA.

Cardiovascular health disparities are present in several minority racial and ethnic groups including African Americans, who exhibit an increased risk of hypertension compared to non-Hispanic Whites. Somali Americans, a subgroup of African Americans of East African origins, exhibit high rates of diabetes and obesity, conditions often comorbid with impaired blood pressure (BP) regulation. Importantly, it remains unknown whether the disparate cardiovascular risk profile, namely poor nocturnal BP regulation, manifested in African Americans can be applied to Somali Americans. We therefore examined 24-hour BP patterns in Somali Americans compared to White control participants. We hypothesized that Somali Americans would present with heightened nocturnal BP and heart rate (HR). We utilized ambulatory blood pressure monitoring (ABPM) to quantify 24-hour BP patterns in 25 Somali (10 female, 15 male; age: 34 ± 3 years; BMI: 27 ± 1 kg/m2) and 25 White (13 female, 12 male; age: 38 ± 3 years; BMI: 27 ± 1 kg/m2) individuals. Each ABPM recorded a BP reading every 20 minutes throughout the 24-hour period. Subjects were instructed to abstain from caffeine, alcohol, and vigorous exercise during the recording period. From the 24-hour recording, an ambulatory arterial stiffness index (AASI) was calculated as 1 minus the regression slope of systolic (SAP) and diastolic (DAP) arterial pressure. SAP, DAP, and HR obtained between 12:00am and 6:00am were averaged to compute nocturnal means. BP and HR dipping was determined as the percent change between daytime and nocturnal BP and HR. Statistical analysis included independent samples t-tests to determine differences in BP and HR between racial groups (i.e., Somali vs. White). Nocturnal SAP (105 ± 2 vs. 106 ± 3 mmHg, p = 0.364) and DAP (60 ± 1 vs. 58 ± 2 mmHg, p = 0.093) were not different between Somali and White participants. In contrast, nocturnal HR was significantly higher in Somalis compared to Whites (72 ± 2 vs. 64 ± 2 beats/minute, p = 0.009). Similarly, SAP (12 ± 2% vs. 12 ± 1%, p = 0.437) and DAP (18 ± 2% vs. 21 ± 2%, p = 0.127) dipping were comparable between groups, while Somali individuals exhibited blunted HR dipping (11 ± 2% vs. 19 ± 2%, p = 0.008) compared to Whites. AASI (0.32 ± 0.03 vs. 0.24 ± 0.03 a.u., p = 0.031) was higher in Somali compared to White individuals. These findings suggest Somali Americans present with impaired nocturnal cardiovascular regulation and increased arterial stiffness, which may place this racial minority at increased cardiovascular risk. Future work to investigate the mechanistic relationships of cardiovascular dysfunction in Somali Americans is warranted. Research grant from Sleep Number to Mayo Clinic for studies of sleep and cardiovascular risk in Somali Americans, and by NIH R01-HL160619, T32-DK007013, T32-HL007111, and T32-HL105355. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Increased cognitive hyperarousal is a proposed mechanism associated with clinical poor sleep including insomnia. An objective marker of nocturnal hyperarousal is high frequency electroencephalography during sleep, including increased beta frequency during stage two (N2) sleep. Acute and chronic poor sleep quality are associated with autonomic dysfunction, but little is known regarding the relationship between nocturnal beta frequency intrusion and nocturnal autonomic function. The purpose of this study was to explore the association between beta spectral power during stage two (N2) sleep and nocturnal heart rate variability (HRV) in healthy female and male adults. We hypothesized that heightened beta spectral power during N2 sleep would be associated with reduced nocturnal HRV. Twenty-four participants (12 males, 12 females; age, 25 ± 1 years; BMI 27 ± 1 kg/m2) underwent an 8-hour overnight sleep opportunity with continuous polysomnography and 5-lead electrocardiogram monitoring. Periods of 5 – 10 minutes of stable N2 sleep absent of cortical arousals, respiratory events, and limb movement-associated arousals were identified (one per cycle) for analysis. Periods from the first two cycles of N2 sleep from the full night were selected for analysis. Beta spectral power from the central and frontal regions and nocturnal HRV data were analyzed and averaged across each hemisphere. Time-domain HRV was quantified as the root mean squared of successive differences (RMSSD) and proportion of R-R intervals (RRI) varying by greater than 50 ms (pNN50). An inverse correlation was observed between central beta power and RRI (R= -0.473, p=0.019), pNN50 (R= -0.450, p=0.028), and RMSSD (R= -0.406, p=0.049). This was paralleled by a similar relationship between frontal beta and RRI (R= -0.487, p=0.016) and pNN50 (R= -0.423, p=0.039). Our results indicate a negative association between N2 beta power and nocturnal HRV measures. These findings suggest that nocturnal hyperarousal may be associated with poor cardiac autonomic function and has implications for individuals with insomnia in whom cognitive hyperarousal is frequently reported. Support is provided by the National Institutes of Health (AA-024892, U54GM115371; P20GM103474, 2TL1 TR002318). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Heightened anxiety is associated with an increased risk for cardiovascular diseases such as coronary heart disease and hypertension. While hyperactivity of the sympathetic nervous system has been suggested to mediate this relationship, direct measures of muscle sympathetic nerve activity (MSNA) in people with elevated anxiety have indicated little, if any, alterations in baseline sympathetic function. However, studies examining anxiety and MSNA have been limited by small sample sizes and lack of detail on anxiety severity, limiting the ability to investigate subtle interactions. The present study assessed associations between trait anxiety, mean arterial pressure (MAP), and MSNA using a large, representative sample of healthy young men and women, with an exploratory assessment of sex-specific interactions. We hypothesized that heightened trait anxiety would be associated with elevated resting MAP and MSNA. Trait anxiety was assessed using the Spielberger Trait Anxiety Inventory (STAI) in 97 healthy adults (52 male, 45 female; 25±1 years; 26±1 kg/m2). In each participant, the average of three seated brachial blood pressures was recorded and used in subsequent analysis. All participants underwent an autonomic function test that simultaneously assessed heart rate (HR), beat-to-beat blood pressure, MSNA burst frequency (BF) and incidence (BI) during 5-10 minutes of supine rest. MSNA recordings were captured in 91 participants. Multiple regression was used to test the relationship between STAI, MAP, MSNA, and HR while accounting for age and sex. Sex-specific interactions were explored with correlations controlling for age. The regression model significantly predicted MAP (R2=.196, P<0.001), BF (R2=.136, P=0.005), and BI (R2=.150, P=0.003), but not HR (R2=.055, P=0.155). STAI scores were independently associated with MAP (β=.207, P=0.029), BF (β=.245, P=0.016), and BI (β=.224, P=0.027). In males, STAI was correlated with MAP (R=.277, P=0.049), BF (R=.363, P=0.009), and BI (R=.346, P=0.013), but not HR (R=.140, P=0.326). In contrast, STAI was not associated with MAP (R=.174, P=0.260), BF (R=.094, P=0.574), BI (R=.069, P=0.681), or HR (R=.226, P=0.141) in females. In a large sample of healthy adults, our results highlight the relationship between the severity of trait anxiety, resting blood pressure, and sympathetic outflow, with a more pronounced relationship in males. Support: NIH (AA-024892, 1R15HL140596-01, AG064038-01A1, U54GM115371; P20GM103474, 2TL1 TR002318). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Anxiety is associated with development of cardiovascular disease. Although the sympathetic nervous system is a likely mediator of this relationship, populations with chronic anxiety have shown little, if any, alteration in resting levels of directly recorded muscle sympathetic nerve activity (MSNA). The present study is the first to reveal an independent relationship between trait anxiety, resting blood pressure, and MSNA in a large cohort of healthy males and females devoid of cardiometabolic comorbidities.