We examined the relationship between total peripheral resistance (TPR) and central artery pressure and indices of wave reflection in 16 subjects (10F/6M; 26 ± 1 yr). Non‐invasive aortic pressure waveforms were synthesized from high‐fidelity radial pressure waveforms obtained from applanation tonometry of the radial artery. Radial blood pressure (BP) was calibrated from brachial artery BP (catheter). Central artery pressures, aortic augmentation index (AI a ), roundtrip travel time of the reflected wave to and from the periphery (Δt p ; inverse of pulse wave velocity), and wasted left ventricular energy (E w ) were calculated from the generated aortic pressure waveform. Cardiac output (CO) was measured using an open‐circuit acetylene uptake technique and used to calculate total peripheral resistance (mean arterial pressure/CO). TPR was positively related to aortic pulse pressure (r = 0.49), augmented pressure of the central artery wave (r = 0.60), pulse pressure amplification (r =0.54), AI a (r = 0.53), and E w (r = 0.66), (P < 0.05 for all). Additionally, TPR was inversely related to Δt p (r = − 0.51, P < 0.05). Our data suggests that increased levels of TPR are related to measures of central artery pressure, wave reflection characteristics and indices of central artery stiffness. Supported by NIH K23 DK‐082424 (TBC), AHA 2170087(ECH) and CTSA RR‐024150
Obesity is associated with an increase in resting levels of muscle sympathetic neural activity (MSNA) and a decrease in reflex sympathetic neural and cardiovagal responsiveness. Exercise and diet induced weight loss reverse these changes, however the potential effects of bariatric surgery induced weight loss are unknown. PURPOSE: We hypothesize that bariatric surgery will decrease baseline levels of MSNA and increase baroreflex sensitivity. METHODS: We measured MSNA (peroneal microneurography), R-R interval (ECG) and arterial pressure (arterial catheter) in three groups of subjects: (1) subjects > 12 months post bariatric surgery (N = 2) (2) obese subjects BMI > 35 kg/m2 (N = 7) (3) lean control subjects BMI < 25 kg/m2 (N = 5). MSNA, ECG and arterial blood pressure were measured continuously during intravenous vasodilator (sodium nitroprusside) and pressor (phenylephrine) boluses. Baroreflex control of sympathetic outflow and of the heart were determined by the relationships of arterial pressure with MSNA and R-R interval, respectively, during blood pressure fluctuations (modified Oxford technique). RESULTS: Our preliminary results indicate that chronic resting levels of MSNA were lower in post bariatric subjects [19 +/- 4 (SE) bursts/min vs 28 +/- 4 bursts/min in obese subjects] with values no different from non-obese control individuals (21 +/- 3 bursts/min). Bariatric surgery also appeared to increase the responsiveness of baroreflex control of the heart [14.23 msec/mmHg (RRI) vs 8.50 msec/mmHg for obese subjects (p <0.004)]. CONCLUSION: Preliminary results indicate bariatric surgery may reverse both obesity associated increases in chronic resting levels of MSNA and improve sensitivity of the baroreflex. Supported by NIH UL1 RR024150 (to the Mayo Clinic).
Fluid intake during military training is prescribed based on the interactions among environmental conditions, uniform configurations and work rates. The efficacy of this guidance has not been empirically assessed for work bouts lasting >4 hours. PURPOSE: To determine the acceptability of the fluid intake guidance, sweat losses were measured in a variety of conditions and modern uniform/body armor configurations and were then compared to prescribed fluid intakes for each condition (clothing, environment, workload, duration). METHODS: Whole body sweat losses of 141 soldiers were measured over a variety of environmental conditions (White-Black flag), uniform configurations (including Battle Dress Uniform and body armor), exercise intensities (easy, moderate, heavy), and work durations (2,4, and 8 hr). Using the prescribed fluid intake guidance for each condition, the differences between the prescribed fluid intake and the total observed sweat loss were calculated. Differences were then expressed as a percent loss or gain of body weight using the following equation: [% body water flux= ((drinking volume- sweating volume)/body weight) x 100]. Values within a threshold of ±2% body water flux (BWF) were deemed acceptable. This threshold was considered the starting point for performance and health concerns. To simulate a worst-case scenario, it was assumed no urine was produced throughout testing. RESULTS: During short work durations (2 and 4hr), 0 of 75 Soldiers exceeded the +2% BWF. During longer work durations (8hr), 50 of 66 Soldiers exceeded the +2% BWF. In all conditions, 50 of 141 Soldiers (35%) exceeded the +2% BWF. In no condition did a Soldier exceed the -2% BWF. CONCLUSION: Current fluid intake guidance appears to be sufficient (no over- or under-drinking ±2% BWF) during work durations lasting ≤4 hours. However, for conditions beyond published guidance (>4hr), recommended drinking rates over-prescribe water needs in worst-case scenarios where no urine was produced. It is recommended that military fluid intake guidance be re-evaluated to include longer work durations of 8 hours. The views expressed in this abstract are those of the authors and do not reflect the official policy of the Department of Army, Department of Defense, or the U.S. Government.
Changes in body water elicit reflex adjustments at the kidney, thus maintaining fluid volume homeostasis. These renal adjustments change the concentration and color of urine, variables that can, in turn, be used as biomarkers of hydration status. It has been suggested that vitamin supplementation alters urine color; it is unclear whether any such alteration would confound hydration assessment via colorimetric evaluation. We tested the hypothesis that overnight vitamin B2 and/or B12 supplementation alters urine color as a marker of hydration status. Thirty healthy volunteers were monitored during a 3-day euhydrated baseline, confirmed via first morning nude body mass, urine specific gravity, and urine osmolality. Volunteers then randomly received B2 (n = 10), B12 (n = 10), or B2 + B12 (n = 10) at ∼200 × recommended dietary allowance. Euhydration was verified on trial days (two of the following: body mass ± 1.0% of the mean of visits 1-3, urine specific gravity < 1.02, urine osmolality < 700 mmol/kg). Vitamin purity and urinary B2 concentration ([B2]) and [B12] were quantified via ultraperformance liquid chromatography. Two independent observers assessed urine color using an eight-point standardized color chart. Following supplementation, urinary [B2] was elevated; however, urine color was not different between nonsupplemented and supplemented trials. For example, in the B2 trial, urinary [B2] increased from 8.6 × 10(4) ± 7.7 × 10(4) to 5.7 × 10(6) ± 5.3 × 10(6) nmol/l (P < 0.05), and urine color went from 4 ± 1 to 5 ± 1 (P > 0.05). Both conditions met the euhydrated color classification. We conclude that a large overnight dose of vitamins B2 and B12 does not confound assessment of euhydrated status via urine color.
We hypothesized that muscle sympathetic nerve activity (MSNA) during head-up tilt (HUT) would be augmented during exercise-induced (hyperosmotic) dehydration but not isoosmotic dehydration via an oral diuretic. We studied 26 young healthy subjects (7 female, 19 male) divided into three groups: euhydrated (EUH, n = 7), previously exercised in 40°C while maintaining hydration; dehydrated (DEH, n = 10), previously exercised in 40°C during which ~3% of body weight was lost via sweat loss; and diuretic (DIUR, n = 9), a group that did not exercise but lost ~3% of body weight via diuresis (furosemide, 80 mg by mouth). We measured MSNA, heart rate (HR), and blood pressure (BP) during supine rest and 30° and 45° HUT. Plasma volume (PV) decreased similarly in DEH (-8.5 ± 3.3%) and DIUR (-11.4 ± 5.7%) (P > 0.05). Plasma osmolality was similar between DIUR and EUH (288 ± 4 vs. 284 ± 5 mmol/kg, respectively) but was significantly higher in DEH (299 ± 5 mmol/kg) (P < 0.05). Mixed-model ANOVA was used with repeated measures on position (HUT) and between-group analysis on condition. HR and MSNA increased in all subjects during HUT (main effect of position; P < 0.05). There was also a significant main effect of group, such that MSNA and HR were higher in DEH compared with DIUR (P < 0.05). Changes in HR with HUT were larger in both hypovolemic groups compared with EUH (P < 0.05). The differential HUT response "strategies" in each group suggest a greater role for hypovolemia per se in controlling HR responses during dehydration, and a stronger role for osmolality in control of SNA.NEW & NOTEWORTHY Interactions of volume regulation with control of vascular sympathetic nerve activity (SNA) have important implications for blood pressure regulation. Here, we demonstrate that SNA and heart rate (HR) during hyperosmotic hypovolemia (exercise-induced) were augmented during supine and tilt compared with isoosmotic hypovolemia (diuretic), which primarily augmented the HR response. Our data suggest that hypovolemia per se had a larger role in controlling HR responses, whereas osmolality had a stronger role in control of SNA.
