Cardiovascular morbidity and mortality rates are highest among Black Americans (BA), the mechanisms of which are complex and not completely understood. Altered autonomic reflexes or sympathetic transduction could contribute to elevations in baseline blood pressure or an exaggerated exercise pressor response, thereby increasing CVD risk; though no studies have explored whether mechanoreflex sensitivity, a component of the exercise pressor reflex, is altered in BA. PURPOSE: Using passive leg movement (PLM), as model of activating the mechanoreflex and an assessment of lower limb vascular function, the aim of this study was to compare the central and peripheral hemodynamic responses in young healthy Black (BA) and White American (WA) males. METHODS: Young (21±4 yr) healthy BA (n = 9) and WA (n = 10) males, matched for physical activity, were instrumented to continuously monitor central and peripheral hemodynamics using Finger Photoplethysmography (Finometer) and frequency domain multi‐distance near‐infrared spectroscopy (NIRS) of the vastus lateralis (Oxiplex TS), respectively. After 1 minute of baseline, subjects underwent continuous PLM at 1 hz for two minutes, while tissue oxygen saturation (StO2%), cardiac output (CO), heart rate (HR), stroke volume (SV), and mean arterial pressure (MAP) were continuously recorded. RESULTS: Resting HR (61±3 vs. 62±3 beats/min), SV (89±5 vs. 92±5 mL/beat), CO (5.4±0.4 vs. 4.4±0.5 L/min), and MAP (92±5 vs. 86±3 mmHg) were not different between BA and WA, respectively (all, p>0.05). The individual peak PLM‐induced changes in HR (6±2 vs. 11±3 Δbeats/min, p = 0.06), SV (7.3±1.6 vs. 11.4±1.9 ΔmL/beat, p = 0.04), and CO (0.7±0.2 vs. 1.0±0.2 ΔL/min, p = 0.09) were lower in BA, however the MAP response (5.3±1.4 vs. 6.0±0.8 ΔmmHg, p > 0.05) was not different. The peak PLM‐induced change in StO2 was significantly attenuated in BA (1.6±0.5 vs. 3.8±0.4 Δ%, p=0.01). As a surrogate of nitric oxide, urinary nitrate+nitrate were not different between groups (2.89±1.67 vs. 2.00±1.35 μM, p>0.05). CONCLUSION: A novel insight from the current study reveals that Black American men had an attenuated mechanoreflex response to PLM as compared to White American men. However, Black Americans had a lower peripheral hemodynamic response, perhaps the result of the altered mechanoreflex or suggestive of lower limb vascular dysfunction, which might explain a propensity towards elevated rates of peripheral vascular disease in Black Americans.
Heart rate variability (HRV) estimates autonomic nervous system (ANS) influence on the heart and is sex‐specific. Sensory afferents exhibit sex‐specificity; although, there is a paucity of data on the potential effects of Capsaicin, an agonist for transient receptor potential vanilloid channel‐1 (TRPV1), on cardiac ANS activity and if the effect is sex‐dependent. Given the predictive nature of HRV on risk of developing hypertension, understanding the sex differences in factors governing HRV is paramount. PURPOSE Therefore, this study sought to determine the sex‐specificity in the effect of capsaicin on cardiac autonomic function estimated through HRV. It was hypothesized that females would have lower HRV than the age‐matched males and that capsaicin could attenuate these sex differences. METHODS HRV was measured in 38 young males (M: n=25) and females (F: n=13), in a blinded crossover design, after acute ingestion of placebo or capsaicin capsules. Resting measurements of HR, RR interval, root mean square of successive differences (RMSSD), natural log‐transformed RMSSD (LnRMSSD), standard deviation of n‐n intervals (SDNN), number of pairs of successive n‐n intervals that differ by more than 50 msec (NN50), and percent NN50 to total n‐n intervals (PNN50) were obtained using standard techniques. RESULTS Under placebo, males had significantly lower minimum HR (M: 49±9.7 vs. F: 58±16 beats/min, p=0.038, d=‐0.738) and significantly higher NN50 (M: 141±118 vs. F: 33±23, p=0.003, d=‐0.129) than females. There was a main effect of sex on HR (M: 59±9.3 vs. F: 65±12 beats/min, p=0.036, η2=0.098), minimum HR (M: 47±8.3 vs. F: 56±12 beats/min, p=0.014, η2=0.124), and NN50 (M: 177±143 vs. F: 29±17, p<0.001, η2=0.249). There was a significant interaction of sex and treatment (p=0.02, η2=0.027) for RMSSD, where males increased (Placebo: 78±55 vs. Capsaicin: 91±64 ms), and females decreased (Placebo: 105±83 vs. Capsaicin 76±43 ms). CONCLUSION This study recapitulates previously documented sex differences in HR and HRV. Acute ingestion of capsaicin increased RMSSD in men, but decreased RMSSD in women, suggesting a sexual dimorphism in parasympathetic response, perhaps due to differences in TRPV1‐sensitive afferents or sensitivity. The physiological ramifications of these findings, specifically in the regulation of blood pressure and ultimately cardiovascular disease risk remain to be explored, especially in the transition to menopause in women.
Previous work in vitro suggests that capsaicin, the spicy ingredient in peppers, attenuates the vascular response to sympathetic activity (“sympatholysis”), likely mediated through vascular transient receptor potential vanilloid type 1 (TRPV1), and was associated with improved vascular function, though translational studies are needed. Further, given racial disparities in vascular function, and reported racial differences in sensory TRPV1 activity, exploring the potential TRPV1‐related mechanisms underpinning these vascular differences is warranted. Purpose To determine if racial differences existed in the central hemodynamic responses to sympathetic stimuli, via lower body negative pressure (LBNP) at rest and during exercise. Second, using an acute dose of oral capsaicin, we sought to determine the potential role of TRPV1 receptors in mediating any racial differences in sympatholysis or vascular function. Methods In a blinded placebo‐controlled crossover design, 23 young healthy black (BM, n=13, 23±5 yrs) and white males (WM, n=10, 19±1 yrs) were given capsules containing either placebo (800mg fiber) or capsaicin (780 mg Chile pepper extract, 2.4±0.04 mg capsaicin, 0.5±0.04 mg dihydrocapsaicin). To assess microvascular responses, frequency‐domain, multi‐distance, near infrared spectroscopy (NIRS) was placed over the muscular medial forearm (i.e. flexor digitorum profundus) providing measure of oxyhemoglobin (HbO, in μM). Central hemodynamics, namely stroke volume (SV), cardiac output (CO), mean arterial pressure (MAP), and heart rate (HR), were measured continuously using a Finometer. To assess hemodynamic responses and potential differences in sympatholysis, these measures performed at rest, during LBNP (‐20 mmHg), handgrip (HG) exercise (30% MVC), and HG+LBNP. Results Under placebo conditions, at rest HR, SV, CO, and MAP were not different between BM and WM (p>0.05), and groups were unaffected by capsaicin (p>0.05). The LBNP‐induced changes at rest appeared larger for black males (SV ‐18±4ml vs. ‐8±11ml and MAP 4.6±6 vs. 1.3± 5mmHg, BM vs. WM), which were seemingly reversed with acute capsaicin (SV ‐11±13 vs. ‐9±16ml and MAP ‐2±9 vs. 1.2± 8mmHg, BM vs. WM). At rest, with placebo, the LBNP‐induced ΔHbO, was similar between groups (‐2±6 vs. ‐2±2μM, BM vs WM), and relatively unaffected by capsaicin (‐3±6 vs. ‐1±2 μM, BM vs WM). During HG exercise, the LBNP‐induced ΔHbO was disparate between groups (‐5±7 vs. 1±3 μM, BM vs WM), and this difference was ablated by the capsaicin (1±6 vs. 2±2 μM, BM vs WM). Conclusion There were racial differences in the central and peripheral hemodynamic response to LBNP at rest and during exercise, suggesting impaired sympatholysis or altered autonomic regulation. Capsaicin, and assumed activation of TRPV1 receptors, seems to affect the hemodynamic response to LBNP, in a relatively race‐specific manner at rest and during exercise, potentially mitigating race‐related differences. Further work is needed to determine whether such differences may be due to altered TRPV1 expression betwee...
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