Effect of Continuous BFR Exercise on Tissues Oxygenation Characteristics in Incomplete Spinal Cord Injured Patients

Please download pdf version here

Associations Between Visceral Adipose Tissue Estimates Produced By Near-Infrared Spectroscopy, Mobile Anthropometrics, and Traditional Body Composition Assessments and Estimates Derived From Dual-Energy X-Ray Absorptiometry

Assessments of visceral adipose tissue (VAT) are critical in preventing metabolic disorders; however, there are limited measurement methods that are accurate and accessible for VAT. The purpose of this cross-sectional study was to evaluate the association between VAT estimates from consumer-grade devices and traditional anthropometrics and VAT and subcutaneous adipose tissue (SAT) from dual-energy X-ray absorptiometry (DXA). Data were collected from 182 participants (female = 114; White = 127; Black/African-American (BAA) = 48) which included anthropometrics and indices of VAT produced by near-infrared reactance spectroscopy (NIRS), visual body composition (VBC) and multifrequency BIA (MFBIA). VAT and SAT were collected using DXA. Bivariate and partial correlations were calculated between DXAVAT and DXASAT and other VAT estimates. All VAT indices had positive moderate–strong correlations with VAT (all P \u3c 0·001) and SAT (all P \u3c 0·001). Only waist:hip (r = 0·69), VATVBC (r = 0·84), and VATMFBIA (r = 0·86) had stronger associations with VAT than SAT (P \u3c 0·001). Partial associations between VATVBC and VATMFBIA were only stronger for VAT than SAT in White participants (r = 0·67, P \u3c 0·001) but not female, male, or BAA participants individually. Partial correlations for waist:hip were stronger for VAT than SAT, but only for male (r = 0·40, P \u3c 0·010) or White participants (r = 0·48, P \u3c 0·001). NIRS was amongst the weakest predictors of VAT which was highest in male participants (r = 0·39, P \u3c 0·010) but non-existent in BAA participants (r = –0·02, P \u3e 0·050) after adjusting for SAT. Both anthropometric and consumer-grade VAT indices are consistently better predictors of SAT than VAT. These data highlight the need for a standardised, but convenient, VAT estimation protocol that can account for the relationship between SAT and VAT that differs by sex/race

Increased hip flexion gait as an exercise modality for individuals with obesity

Purpose Exercise is a critical element for the management of body weight and improvement of quality of life of individuals with obesity. Due to its convenience and accessibility, running is a commonly used exercise modality to meet exercise guidelines. However, the weight-bearing component during high impacts of this exercise modality might limit the participation in exercise and reduce the effectiveness of running-based exercise interventions in individuals with obesity. The hip flexion feedback system (HFFS) assists participants in meeting specific exercise intensities by giving the participant specific increased hip flexion targets while walking on a treadmill. The resulting activity involves walking with increased hip flexion which removes the high impacts of running. The purpose of this study was to compare physiological and biomechanical parameters during an HFFS session and an independent treadmill walking/running session (IND). Methods Heart rate, oxygen consumption (VO2), heart rate error, and tibia peak positive accelerations (PPA) were investigated for each condition at 40% and 60% of heart rate reserve exercise intensities. Results VO2 was higher for IND despite no differences in heart rate. Tibia PPAs were reduced during the HFFS session. Heart rate error was reduced for HFFS during non-steady state exercise. Conclusion While demanding lower energy consumption compared to running, HFFS exercise results in lower tibia PPAs and more accurate monitoring of exercise intensity. HFFS might be a valid exercise alternative for individuals with obesity or individuals that require low-impact forces at the lower limbs

Fat-free mass is associated with exercise pressor responses, but not cold pressor responses, in humans: influence of maximal voluntary contraction

ObjectiveThis study examined the contributions of fat mass (FM) and fat-free mass (FFM) to the magnitude of exercise pressor responses in humans.MethodsThe cumulative blood pressure responses (blood pressure index; BPI) to handgrip exercise (BPIhg), post-exercise-circulatory-occlusion (BPIpeco), and cold-pressor activation (BPIcpt) were collected from 67 individuals grouped by BMI (27.8 ± 7.3 kg/m2), FFM index (FFMi, 29.1 ± 3.8 kg/m2), and FM index (FMi 12.5 ± 4.8 kg/m2) quartiles. BPI responses to HG were also normalized to the time-tension index of HG, providing a relative index of exercise pressor response magnitude (BPInorm).ResultsBPIhg and BPIpeco were significantly elevated in the third FFMi quartile (p ≤ 0.034), while BPInorm significantly decreased in the second and fourth quartiles (p ≤ 0.029). In contrast, no differences in BPIcpt were observed across any FFMi, BMI, or FMi quartiles (p ≥ 0.268). FFM was independently associated with BPIhg, BPI­peco, and BPInorm (all p ≤ 0.049), however, FFM was eliminated as an independent predictor when maximal voluntary contraction (MVC) was included in these regression models (all p ≥ 0.495). Neither FFM nor MVC was associated with BPIcpt (p ≥ 0.229).ConclusionsThese findings indicate that exercise pressor responses, but not cold-pressor responses, are significantly associated with FFM in humans, and that this association is driven by FFM related differences in MVC

INFLUENCE OF BODY POSITION ON VALSALVA RESPONSES IN YOUNG BLACK AND AFRICAN AMERICAN ADULTS

Ryan Aultman, Marshall Dearmon, Kenneth R. Ladner, Barry Faulkner, Ta\u27quoris Newsome, Jon Stavres. The University of Southern Mississippi, Hattiesburg, MS. BACKGROUND: Evidence suggests that Black and African American (BAA) individuals are more susceptible to autonomic dysfunction compared to White individuals. However, it remains unclear if these findings extend to the autonomic responses to the Valsalva (VL) maneuver. Accordingly, this study compared blood pressure and heart rate responses to the VL maneuver between BAA and White individuals. METHODS: Twenty individuals (10 BAA, 10 White) completed two VLs, each separated by 45 seconds, in both the seated and supine positions (4 VLs in total). VLs were maintained at 45 mmHg, and the order of conditions was counterbalanced between participants. Cardiac rhythm and beat-by-beat blood pressure were continuously recorded throughout each VL, and the relative changes in mean arterial pressure (ΔMAP), systolic blood pressure (ΔSBP), diastolic blood pressure (ΔDBP), pulse pressure (ΔPP), and heart rate (ΔHR) were recorded for phases I (initial hypertensive response), IIa (early phase II depressor response), IIb (late phase II blood pressure recovery), III (rebound hypotensive response after exhalation), and IV (45 second period following exhalation) of each VL. Responses were averaged across both VLs performed within each condition (seated vs. supine), and compared across conditions and between races using repeated measures analyses of variance. RESULTS: At baseline, the BAA group demonstrated a significantly lower mean PP compared to White individuals (-18 ± 8 mmHg, P=0.01), and tended to demonstrate an elevated mean DBP (+10 ± 4 mmHg, P=0.05). When VL responses were compared between groups and across conditions, a significant race by condition interaction was observed for the ΔMAP response during phase IIa (F1,18=6.80, P=0.01). This was explained by a significant exaggeration of the phase IIa ΔMAP response in White individuals during the seated condition (-9 ± 2 ΔmmHg, P\u3c0.01), which was not observed in the BAA group (-1 ± 2 ΔmmHg, P=0.64). Significant main effects of race were also observed for the absolute DBP responses, such that DBP was higher in the BAA group compared to White individuals during all phases (all P\u3c0.04), with the exception of phase IIb (P=0.34). CONCLUSIONS: These findings suggest that phase IIa VL responses are altered in BAA individuals compared to White individuals. This may have important implications for better understanding autonomic dysfunction in this population

INFLUENCE OF ISOMETRIC HANDGRIP AND BODY POSITION ON BAROREFLEX SENSITIVITY IN BLACK AND WHITE ADULTS

Ta\u27Quoris Newsome, Marshall Dearmon, Kenneth R. Ladner, Barry Faulkner, Hunter Haynes, Ryan Aultman, Jon Stavres. University of Southern Mississippi, Hattiesburg, MS. BACKGROUND: Resting sympathetic tone has been shown to be elevated in Black and African American (BAA) individuals compared to White individuals, but differences in Baroreflex Sensitivity (BRS) are less clear. Considering that exercise and orthostasis are both known to elicit acute changes in sympathetic tone, evaluating changes in BRS during handgrip exercise or during an orthostatic challenge may unmask any potential differences in BRS between BAA and White individuals. As such, the purpose of this study was to examine the relative influences of isometric handgrip exercise and body position on BRS in a sample of BAA and White participants. METHODS: Cardiac rhythm (via electrocardiography) and beat-by-beat blood pressure (via finger photoplethysmography) were continuously recorded in twenty participants (10 BAA, 10 White) during 3 minutes of rest and 3 minutes of isometric handgrip exercise (35% maximal voluntary isometric contraction) in the supine and seated positions. After manual exclusion of cardiac arrhythmias, BRS was evaluated for each 3-minute period using the sequence method (seq. length \u3e 3, r \u3e 0.8, delay = 0 beats). BRS was quantified as the total baroreflex gain of up-ramping sequences (BRSup), the gain of down-ramping sequences (BRSdown), and total gain (BRStotal). Each value was compared across conditions (supine rest vs. supine handgrip exercise vs. seated rest) and between races using analyses of variance with repeated measures. RESULTS: At baseline, no significant differences were observed for BRSup (-0.12 ± 10.97 ms/mmHg, P=0.99), BRSdown(-2.06 ± 8.24 ms/mmHg, P=0.80), or BRStotal (-3.14 ± 9.35 ms/mmHg, P=0.74) between BAA or White participants. When the influence of handgrip and body position were examined, no significant race by condition interactions were observed for any value (all P\u3e0.31). Instead, significant main effects of condition were observed for the entire sample (F1,32=9.75, P\u3c0.01), which was explained by significant decreases in BRSup (-21.82 ± 5.14 ms/mmHg, P\u3c0.01) and BRStotal (-13.41 ± 4.54 ms/mmHg, P=0.02) during handgrip compared to supine rest. BRSup was also significantly lower during handgrip exercise compared to seated rest (-10.43 ± 3.85 ms/mmHg, P=0.04). CONCLUSIONS: These results suggest that handgrip exercise decreases BRS similarly between BAA and White individuals, supporting the notion that BRS may not be significantly altered in healthy BAA adults

COMBINED INFLUENCE OF POSTURE AND ISOMETRIC HANDGRIP ON PHASE IIA RESPONSES TO THE VALSALVA MANEUVER

Barry Faulkner, Marshall Dearmon, Kenneth R. Ladner, Ta’Quoris Newsome, Ryan Aultman, Jon Stavres. University of Southern Mississippi, Hattiesburg, MS. BACKGROUND: The Valsalva maneuver (VL) is a well-documented assessment of autonomic function, and is characterized by 5 distinct blood pressure phases (Phases I, IIa, IIb, III, and IV). While body position is known to influence the early phase II (a.k.a. “phase IIa”) blood pressure responses, the influence of sympathoexcitation is less clear. The aim of this study was to examine the independent and combined effects of sympathoexcitation (via isometric handgrip) and body position on the phase IIa blood pressure responses to VLs in young healthy adults. METHODS: Seventeen subjects (9 male) participated in 4 separate experimental trials (T1-T4) repeated across 2 different conditions (supine and seated). Trials were conducted in sequential order, and included VLs performed without handgrip (Trials 1 [T1] and 4 [T4]), five minutes of isometric handgrip (HG; 35% MVC; Trial 2 [T2]), and VLs performed with superimposed HG (Trial 3 [T3]). Cardiac rhythm (electrocardiography) and beat-by-beat blood pressure data were collected continuously during each trial, and the relative changes in heart rate (ΔHR), mean arterial pressure (ΔMAP), systolic blood pressure (ΔSBP), and diastolic blood pressure (ΔDBP) were compared between conditions and across trials using analyses of variance with repeated measures. RESULTS: Phase IIa ΔSBP responses were significantly blunted during T3 compared to T1 in the supine condition (+6 ± 3 ΔmmHg, P=0.03), and ΔMAP, ΔSBP, and ΔDBP responses were significantly augmented during T1 in the seated condition compared to T1 in the supine condition (-9 ± 2 ΔmmHg, -15 ± 4 ΔmmHg, -8 ± 2 ΔmmHg, respectively, all P\u3c0.01). However, no significant differences were observed for ΔMAP, ΔSBP, or ΔDBP between T3 in the seated condition compared to T1 in the supine condition (-6 ± 3 ΔmmHg, -8 ± 4 ΔmmHg, and -3 ± 2 ΔmmHg, respectively, all P\u3e0.10), suggesting that handgrip mitigated the influence of orthostasis. No significant differences were observed for ΔHR responses during phase IIa for any comparison (all P\u3e0.40). CONCLUSIONS: Handgrip blunts the phase IIa blood pressure responses to VLs performed in the supine condition, and also appears to mitigate the exaggerated phase IIa responses observed during orthostasis. This information has important implications for understanding the physiological factors contributing to abnormal VL responses in young healthy adults

Limb blood flow and tissue perfusion during exercise with blood flow restriction.

INTRODUCTION: Exercise with blood flow restriction (BFR) is emerging as an effective modality for improving muscular function in clinical and athletic populations. Selection of cuff pressure is critical because it should maximize metabolic stress without completely occluding blood flow or compromising user safety. It is unknown how cuff pressures determined at rest influence blood flow hemodynamics during exercise. PURPOSE: We evaluated changes in blood flow and tissue perfusion before, during, and after exercise with BFR. METHODS: Ten males performed rhythmic handgrip exercise (30 contractions, 30% MVC) at 0%, 60%, 80%, 100%, and 120% of limb occlusion pressure (LOP). Brachial artery blood flow and tissue saturation were assessed using Doppler ultrasound and near-infrared spectroscopy, respectively. RESULTS: At rest blood flow generally decreased with increased pressure (0% \u3e 60% ≈ 80% \u3e 100% ≈ 120% LOP). During 60% and 80% LOP conditions, blood flow increased during exercise from rest and decreased after exercise (all P \u3c 0.05). Compared to 0% LOP, relative blood flow at 60% and 80% LOP decreased by 22-47% at rest, 22-48% during exercise, and 52-71% after exercise (all P \u3c 0.05). Increased LOP decreased tissue saturation during exercise with BFR (P \u3c 0.05). Heart rate, mean arterial pressure, and cardiac output did not differ across LOP. CONCLUSION: At pressures below LOP the cardiovascular system overcame the external pressure and increased blood flow to exercising muscles. Relative reductions in blood flow at rest were similar to those during exercise. Thus, the relative occlusion measured at rest approximated the degree of occlusion during exercise. Moderate cuff pressures increased metabolic stress without completely occluding blood flow

HEMODYNAMIC RESPONSES TO THE COLD PRESSOR TEST IN INDIVIDUALS WITH METABOLIC SYNDROME

BACKGROUND: The cold pressor test (CPT) is widely used sympathoexcitatory stimulus, and CPT responses are known to be exaggerated in individuals with hypertension and diabetes. Surprisingly, however, the hemodynamic responses to the CPT have not been explicitly characterized in individuals with metabolic syndrome (MetS). Hence, the purpose of this study was to characterize the hemodynamic responses to cold pressor activation in individuals meeting the criteria for MetS. METHODS: 75 individuals were initially screened for MetS based on the National Cholesterol Education Program Adult Treatment Panel III criteria, with the addition of HbA1C \u3e5.7% as a secondary marker of impaired glucose regulation. Of these 75 participants, 20 met the criteria for MetS, 17 completed all experiments and could be matched to control participants by age, biological sex, race, and ethnicity. Upon final analysis, one participant was excluded as an outlier (mean pressor response \u3e3.5 standard deviations above the inclusive group mean), resulting in a final matched comparison of 16 individuals with MetS and 16 control participants. Each CPT consisted of a 2-minute baseline period, followed by a 2-minute period of ice-water hand immersion, during which heart rate and beat-by-beat blood pressure were continuously recorded via a one-lead electrocardiogram and finger-photoplethysmography, respectively. CPT responses were quantified as the peak blood pressure and heart rate responses recorded during cold-water immersion, as well as the area-under-the-curve for mean arterial pressure (MAP) during cold-water immersion (BPI; mmHg*sec). RESULTS: As expected, individuals with MetS had a significantly higher BMI (p=0.001), waist circumference (p\u3c0.001), fasting blood glucose (p\u3c0.001), resting systolic blood pressure (p=0.01), resting diastolic blood pressure (p=0.008), and lower HDL cholesterol (p=0.006) compared to control participants. However, the only significant difference observed during the CPT was an exaggerated peak diastolic blood pressure response in the MetS group (p=0.045). In contrast, no significant differences were observed for the peak MAP (p=0.104), delta MAP (p=0.859), or BPI responses (p=0.114). CONCLUSIONS: Based on these findings, only diastolic blood pressure responses are exaggerated during cold pressure activation in individuals with MetS, whereas systolic, MAP, and HR response are similar between groups