Ramírez-Marrero, Farah A.

Physical activity (PA) is inversely related with body fat, insulin resistance (IR), and leptin. However, these associations are not clear in patients after gastric bypass surgery (GBS). We hypothesized an inverse relation between PA, BMI, IR, and leptin; and a positive relation between leptin, BMI, and IR in a group of 9 patients after GBS, 8 obese (Ob), and 7 non‐obese (N‐Ob) controls (age=39.0±5.7, 27.7±6.9, 28.0±10.2 yr, respectively). Subjects wore an accelerometer from 6‐7 days, and underwent measurements of height, weight, DEXA, blood glucose, insulin and leptin. IR was estimated using HOMA. Between group differences in PA, BMI, IR, and leptin were determined with ANOVA; and the relation between these variables was determined with simple linear regressions. Between group differences were observed for BMI (Ob=38.7±1.6, GBS=30.4±1.5, N‐Ob=23.8±1.7 kg/m2), IR (Ob=3.0±0.5, GBS=1.1±0.5, N‐Ob=0.7±0.5), and leptin (Ob=55.9, GBS=28.7±4.5, N‐Ob=5.1±5.6 ng/ml). PA was not different between groups. Inverse associations were observed between PA and BMI (r= ‐ 0.55), and leptin (r= ‐ 0.56); and positive associations were observed between leptin and BMI (r= 0.92), and IR (r= 0.63). PA appears to be associated with the control of obesity and IR possibly via reductions in leptin, a mechanism that requires further study. Funded by NIH CTSA UL1‐RR24150, NIH CTSA KL2‐ RR024151

Orthostatic stress such as head‐up tilt (HUT) elicits a wide range of HR and BP responses among healthy individuals. In this study, we evaluated cardiovascular dynamics of subjects with different HR responses to HUT but without autonomic dysfunction. We measured BP (brachial artery) and HR (ECG) during 5 min of 60° HUT in 76 healthy young individuals, while norepinephrine (NE) was assayed during the final 30 s. We then chose 30 individuals based on the extremes of HR responses to HUT: 15 with the highest (ΔHR≥ 20 bpm) and 15 with the lowest response (ΔHR ≤10 bpm). Age and BMI were not different between groups; however, gender distribution was different (high: 5F, 10 M; low: 10F, 5M). Peak HR during HUT was 87.2±10.4 bpm in the high and 69.1±14.1 bpm in the low group (P< 0.05). Baseline HR was not different between groups. High HR responders had lower SBP at baseline (120.9±9.4 vs. 129.4±11.0 mmHg) and during HUT (119.9±9.7 vs. 131.4±13.1 mmHg). High HR responders also had higher plasma NE response to HUT (ΔNE: 156.9±82.1 vs. 89.0±48.0 pg/ml; P< 0.05). Higher HR with lower BP during HUT is consistent with normal baroreflex mechanisms of integration. Although inter‐individual variability appears to be a fundamental part of cardiovascular regulation, the mechanisms of these differences and the gender discrepancy requires further investigation. Supported by K23 RR17520, HL46493, NS32352, KL2 RR024151 ‐01.

The forearm blood flow response to mental stress (MS) is due to circulating epinephrine (Epi), release of nitric oxide, and forearm sympathetic withdrawal. We recently demonstrated that forearm venous Epi predicts the vascular conductance (FVC) and HR response to MS. In a large, ongoing phenotyping study of sympathoexcitation and adrenergic receptor gene variation, we hypothesized that arterial Epi would predict the forearm vasodilator response to MS, while norepinephrine (NE) would predict the pressor response. In 54 healthy, normotensive young adults, FVC (plethysmography), HR (ECG), and blood pressure (brachial artery) were measured in a recumbent chair at rest and during 3 min of a computerized Stroop colored‐word test. During the final 30 sec of stress, arterial Epi and NE were assayed (HPLC). MS increased HR, BP, FVC, Epi, and NE (p < 0.05 for all). Unexpectedly, during MS the arterial Epi levels did not correlate with HR or FVC. However, a robust correlation existed for HR and FVC (r = 0.73, p < 0.001). Further, systolic pressure correlated with FVC (r = 0.36, p < 0.01) and NE (r = 0.46, p < 0.001). We conclude that the HR response to MS is a major contributor to FVC, independent of arterial Epi, suggestive of mechanical effects and potentially flow‐mediated dilation. This also confirms previous work that catecholamine spillover assays are more indicative of sympathoadrenal activation and hemodynamic responses. Support: K23 RR17520, HL 46493.

Resting energy expenditure (REE) equations multiplied by a predetermined physical activity factor (PAF) are commonly used to determine energy requirements However, estimated vs. actual REE and PAF among post‐gastric‐bypass surgery (GBS), obese (Ob) and lean (L) adults have not been compared. We hypothesized that GBS, Ob and L adults will have: 1) actual REE lower than estimated and 2) actual PAF lower than estimated. A group of 13 GB, 15 Ob and 11 L adults completed REE measurements by indirect calorimetry following standard clinical procedures. The Harris‐Benedict equation (HB) and pre‐determined PAF were used to estimate energy requirements. Physical activity energy expenditure (PAEE) was determined with accelerometry and PAF with the equation: (Actual REE + accelerometry PAEE)/Actual REE. Two‐way ANOVAs were used to detect differences by group and method, and agreement between methods using Bland & Altman plots. Group differences in actual REE (1631±174, 1830±290, 1441±151 kcal/day, respectively; P<0.01) and HB REE (1600±131, 1970±274, 1542±225 kcal/day, respectively, P<0.01) were observed, with no differences by method. Actual PAEE (269±70, 365±98, 228±112 kcal/day, respectively, P=0.002) yielded PAF ranging from 1.1 to 1.3, while HB PAF ranged from 1.2 to 1.7; causing higher predicted vs. actual energy requirement in all groups. While HB REE appeared adequate, predetermined PAF are not recommended.

Head up tilt (HUT) is a meaningful diagnostic tool for baroreflex dysfunction or autonomic failure. We sought to determine if baroreflex sensitivity (BRS), the rise in plasma catecholamines, or 24‐hr ambulatory HR variability (HRV) would correlate with HR and BP during HUT. We performed 60° HUT for 5 min followed by 2 modified Oxford trials in 46 young healthy males and females. Blood pressure (brachial artery) and HR (ECG) were recorded, while arterial epinephrine (Epi) and norepinephrine (NE) were assayed during the final 30 s of HUT. HUT increased HR (mean ± SD: 63 ± 9 to 79 ± 12), MAP (89 ± 7 to 93 ± 8), Epi (28 ± 13 to 61 ± 45), and NE (111 ± 57 to 242 ± 85) (p< 0.05 for all). Individuals with a high 24‐hr HRV had a greater increase in HR during HUT (r= 0.41, P<0.05). Interestingly, a negative correlation was observed between BRS and the NE response to HUT (r= −0.36, p<0.05), such that individuals with low NE response to tilt also had a high BRS. The Epi response was not correlated with any of the measures. These findings suggest that subjects with high vagal activity (high BRS) require a lower sympathetic response (NE) to maintain BP during orthostatic stress. Supported by: K23 RR17520, HL 46493, K12 RR023263 ‐03