Thigh Cuff Research Articles

THE VALIDITY AND RELIABILITY OF THE HANDHELD OXIMETER TO DETERMINE LIMB OCCLUSION PRESSURE FOR BLOOD FLOW RESTRICTION EXERCISE IN THE LOWER EXTREMITY.

The limb occlusion pressure (LOP) is determined to calculate the relative LOP. The different levels of relative LOP (percentage of LOP) influence the treatment effect and perceived discomfort during low-load blood flow restriction (BFR) strength training. Thus, determining the LOP is of the utmost importance when using BFR in clinical practice. The objective of this study was to investigate the concurrent validity and intra-rater (test-retest), intra-day reliability of an inexpensive, portable, easy-to-use handheld (HH) oximeter compared to a high-resolution Doppler ultrasound scanner in detecting LOP in the lower extremity. Cross-sectional validity and reliability study. Two raters who were blinded from each other simultaneously assessed 50 healthy participants (mean age of 25.8 years). A 20 cm-wide thigh cuff with an attached sphygmomanometer was inflated until the raters independently registered the LOP with the HH oximeter and the Doppler ultrasound scanner. The test session was repeated once after a five-minute time interval. The HH oximeter recorded a non-significantly higher LOP than the Doppler ultrasound scanner, with a mean difference of 6.3 mmHg in the test session (95% limits of agreement (LoA): -16.2 to 28.8, p = 0.13) and 5.4 mmHg in the retest session (95% LoA: -13.3 to 24.0, p = 0.10). The intra-rater reliability for both devices was moderate (ICC = 0.72-0.79). The measured LOP was significantly lower (p < 0.005) in the retest session than in the test session for both the HH oximeter (mean difference: -5.7 mmHg) and the Doppler ultrasound scanner (mean difference: -4.8 mmHg). The HH oximeter is a valid and reliable measuring device for determining the LOP in the lower extremity in healthy adults. The authors recommend performing at least two LOP measurements with a one-minute rest interval. 2, Validity and reliability study.

Thigh Cuff Effects on Venous Flow Redistribution During 4 Days in Dry Immersion.

PURPOSE: The objective was to quantify the venous redistribution during a 4-d dry immersion (DI) and evaluate the effect of thigh cuffs.METHODS: The study included nine control (Co) and nine subjects wearing thigh cuffs during the daytime (CU). Ultrasound measures were performed Pre-DI, on day 4 AM (D4 AM) and D4 PM: left ventricle stroke volume and ejection fraction (SV, EF), jugular vein volume (JVvol), portal vein diameter (PV), and middle cerebral vein velocity (MCVv). An additional measure of JVvol was performed on Day 1 after 2 h in DI.RESULTS: After 2 h in DI, JVvol increased significantly from Pre in both groups, but increased more in the Co compared to the CU subjects (Co: 0.27 0.15 cm³ to 0.94 0.22 cm³; CU: 0.32 0.13 cm³ to 0.64 0.32 cm³). At D4 AM, SV and EF decreased from Pre (SV: 111 23 cm³ to 93 24 cm³; EF: 0.66 0.07 to 0.62 0.07). JVvol was slightly increased (Co: 0.47 0.22 cm³ CU: 0.35 014 cm³). MCVv and PV remained unchanged from Pre-DI. No difference was found between the two groups for any of the parameters measured. From D4 AM to PM, no significant change was observed for any parameter.CONCLUSION: The results confirm that DI induces, during the first 2-3 h, a significant cephalic fluid shift as observed in spaceflight. During this early phase, the thigh cuffs reduced the amplitude of the fluid shift toward the head, but after 4 d in DI there was only a slight memory (residual) effect of DI on the jugular volume and no residual effect of the thigh cuffs.Arbeille P, Greaves D, Guillon L, Besnard S. Thigh cuff effects on venous flow redistribution during 4 days in dry immersion. Aerosp Med Hum Perform. 2020; 91(9):697702.

The Short-Term Effects of Remote Ischaemic Conditioning on Cerebral Haemodynamics and Cerebral Autoregulation in Healthy Individuals

Remote Ischaemic conditioning (RIC), where brief cycles of ischaemia and reperfusion are applied to the limbs, may improve neurological outcome in acute stroke and reduce recurrent stroke. The short-term effect of RIC on the regulation of cerebral blood flow (CBF), one possible mechanism for these benefits, was investigated. Healthy participants underwent 5-minute recordings in beat-to-beat blood pressure (BP), electrocardiogram (heart rate, HR), end-tidal CO2 and cerebral blood flow velocity (CBFV) with transcranial Doppler insonation of the middle cerebral arteries, before and after four cycles of RIC using 5-min inflation of bilateral thigh cuffs followed by 5-min deflation. Mean values were calculated together with estimates for cerebrovascular resistance, transfer function analysis (TFA) and autoregulation index (ARI). Twenty-five individuals (10 male), aged 28 ± 11 years, had increases in mean and diastolic BP after RIC (113 ± 13 vs. 116 ± 13, p = 0.046; 74 ± 8 vs. 76 ± 9 mmHg, p = 0.03; respectively). Systolic and mean CBFV decreased after RIC (94.5 ± 17.7 vs. 90.0 ± 15.5, p = 0.001; 63.9 ± 11.1 vs. 62.2 ± 10.5 cm s–1, p = 0.02; respectively), as well as pulsatility index (0.77 ± 0.11 vs 0.73 ± 0.11, p = 0.001). No changes occurred in ARI. TFA showed changes in very low frequency range with significantly increased power oscillations (BP and CBFV) and reduction in phase shift (1.04 ± 0.35 vs. 0.76 ± 0.34 radians, p < 0.01). RIC using bilateral thigh cuffs achieved short-term changes to the cerebrovascular and cardiovascular systems. Further evidence is required to establish the effects in a stroke population.

Exercise With Blood Flow Restriction To Improve Muscular And Physical Function After Total Knee Arthroplasty

After a total knee arthroplasty (TKA), quadriceps strength and physical function can be impaired for several years. Blood flow restriction (BFR) exercise is an effective method to improve muscular and physical function in clinical populations with knee joint pathologies. To date, there are two case studies documenting application of BFR after TKA. A next step is to determine the feasibility of BFR in a larger TKA cohort. PURPOSE: To evaluate the effectiveness of a 10wk home-based BFR exercise program to improve muscular and physical function after TKA. METHODS: Six adults (age: 59±9yrs, BMI: 33±5) with a unilateral TKA (2.7±1.7yrs post-surgery) performed body weight half squats, isolated knee extension using a resistance band, and walking exercises with BFR 3x/wk for 10wk. During exercise, blood flow in the affected limb was restricted using a 15cm wide thigh cuff inflated to 50% of limb occlusion pressure which was identified using Doppler ultrasound. Outcome measures of vastus lateralis thickness, maximal knee extensor isometric torque, and physical function (repetitions performed during 30s chair stand test, distance covered during 6min walk test) were assessed at baseline and post-training. RESULTS: Participants completed 98% of the home-based BFR training sessions and tolerated the exercise program well as joint pain (0.6±0.1cm) and muscle soreness (0.5±0.1cm) were very low (0-10cm visual analogue scale). Vastus lateralis thickness and knee extensor strength in the affected leg increased by 18±11% and 17±13%, respectively (both P<0.05). After training, number of repetitions during the 30s chair stand test increased (11±2 vs. 18±4 repetitions, p<0.01) and this change (6 repetitions) exceeded the minimally important clinical difference. There was a significant increase in distance covered during the 6min walk test (511±28 vs. 556±36m, 9±7%, p=0.03) but this improvement (46m) did not exceed the clinical threshold. CONCLUSION: Results from this pilot study are promising and suggest that home-based BFR exercise can be feasible, safe, and effective for improving muscular and physical function after TKA. Further research is needed to confirm these initial findings in a larger randomized TKA control trial.

DI-5-Cuffs: Lumbar Intervertebral Disc Proteoglycan and Water Content Changes in Humans after Five Days of Dry Immersion to Simulate Microgravity.

Most astronauts experience back pain after spaceflight, primarily located in the lumbar region. Intervertebral disc herniations have been observed after real and simulated microgravity. Spinal deconditioning after exposure to microgravity has been described, but the underlying mechanisms are not well understood. The dry immersion (DI) model of microgravity was used with eighteen male volunteers. Half of the participants wore thigh cuffs as a potential countermeasure. The spinal changes and intervertebral disc (IVD) content changes were investigated using magnetic resonance imaging (MRI) analyses with T1-T2 mapping sequences. IVD water content was estimated by the apparent diffusion coefficient (ADC), with proteoglycan content measured using MRI T1-mapping sequences centered in the nucleus pulposus. The use of thigh cuffs had no effect on any of the spinal variables measured. There was significant spinal lengthening for all of the subjects. The ADC and IVD proteoglycan content both increased significantly with DI (7.34 ± 2.23% and 10.09 ± 1.39%, respectively; mean ± standard deviation), p < 0.05). The ADC changes suggest dynamic and rapid water diffusion inside IVDs, linked to gravitational unloading. Further investigation is needed to determine whether similar changes occur in the cervical IVDs. A better understanding of the mechanisms involved in spinal deconditioning with spaceflight would assist in the development of alternative countermeasures to prevent IVD herniation.

DI-5-CUFFS: Venoconstrictive Thigh Cuffs Limit Body Fluid Changes but Not Orthostatic Intolerance Induced by a 5-Day Dry Immersion.

Venoconstrictive thigh cuffs are used by cosmonauts to ameliorate symptoms associated with cephalad fluid shift. A ground simulation of microgravity, using the dry immersion (DI) model, was performed to assess the effects of thigh cuffs on body fluid changes and dynamics, as well as on cardiovascular deconditioning. Eighteen healthy men (25–43 years), randomly divided into two groups, (1) control group or (2) group with thigh cuffs worn 10 h/day, underwent 5-day DI. Cardiovascular responses to orthostatic challenge were evaluated using the lower body negative pressure (LBNP) test; body fluid changes were assessed by bio-impedance and hormonal assay; plasma volume evolution was estimated using hemoglobin-hematocrit; subjective tolerance was assessed by questionnaires. DI induced a decrease in plasma volume of 15–20%. Reduction in total body water of 3–6% stabilized toward the third day of DI. This reduction was derived mostly from the extracellular compartment. During the acute phase of DI, thigh cuffs limited the decrease in renin and the increase in N-terminal prohormone of brain natriuretic peptide (NT-proBNP), the loss in total body water, and tended to limit the loss in calf volume, extracellular volume and plasma volume. At the later stable phase of DI, a moderate protective effect of thigh cuffs remained evident on the body fluids. Orthostatic tolerance time dropped after DI without significant difference between groups. Thigh cuff countermeasure slowed down and limited the loss of body water and tended to limit plasma loss induced by DI. These observed physiological responses persisted during periods when thigh cuffs were removed. However, thigh cuffs did not counteract decreased tolerance to orthostatic challenge.

Aortic Vessel Wall Properties during 60 Days Strict Head down Tilt Bedrest

BackgroundChanges in large artery properties including increased arterial compliance and increased carotid artery stiffness have been described after space flight. Altered vascular structure, which heralds cardiovascular risk, and reversible changes in vascular function could contribute to the response. Compared with previous bedrest studies, which did not reproduce these findings, the artificial gravity bedrest study (AGBRESA) applied strict ‐6° head‐down tilt bedrest (HDT) for 60 days mimicking chronic cephalad fluid shifts in space. We assessed aortic vessel wall properties using state‐of‐the art imaging methods and pulse wave analysis and tested for possible protective effects of artificial gravity training.Material and MethodsThe AGBRESA Study is a joint project between NASA, ESA and DLR and is conducted in line with the declaration of Helsinki and the federal regulations of the U.S. Government. After the first of two AGBRESA campaigns, we present data from 12 healthy subjects (8 men, 4 women) obtained during baseline data collection 9–6 days before bedrest (BDC, supine position) and towards the end of two months head down tilt bedrest (MRI on day 56 and echocardiography on day 60 of HDT). Subjects were assigned to 30 minutes per day continuous short arm centrifugation (cAG), 6 times for 5 minutes interval short arm centrifugation, iAG), or a control group (ctr). We assessed aortic pulse wave velocity (PWV) using oscillometric upper arm and thigh cuffs (PWV‐2C, CardioCube, AIT, Vienna, Austria) and 4D‐flow cardiac velocity encoded phase contrast magnetic resonance imaging (PWV‐4D‐MRI). We also measured area, area changes, and distensibility (AoD) of the ascending aorta by 2D‐phase contrast cardiac MRI and arterial compliance (Ca) using transthoracic echocardiography.ResultsMean aortic area increased in all subjects after 60 days head down tilt bedrest (5.3±0.7 vs. 5.8±0.7 cm2, p&lt;0.05). Stroke volume decreased from 94±13 to 84±10 ml (p&lt;0.05) and pulse pressure from 56±11 to 46±9 mmHg (p&lt;0.05) in part through reductions in stroke volume. The figure illustrates individual data on aortic properties: Differences (end of HDT – BDC) in PWV measured with 2 cuffs (A) and with 4D‐Flow MRI (B), changes in AoD (C) and Ca (D) from BDC to the end of HDT (red diamonds = women). In contrast to the more consistent changes in aortic area, stroke volume, and pulse pressure, aortic distensibility, arterial compliance, and PWV responses show substantial inter‐individual variability.ConclusionThe important finding of our study is that 60 days strict head down bedrest elicit consistent changes in ascending aortic area, pulse pressure, and stroke volume. The resulting changes in vascular loading conditions likely confound vascular function measurements, both, in head down tilt bedrest studies and in space.Support or Funding InformationThe study was funded by the German Aerospace Center, the European Space Agency (contract number 4000113871/15/NL/PG) and the National Aeronautics and Space Administration (contract number 80JSC018P0078).Figure 1

INTEGRATED EFFECTS OF NORMOBARIC HYPOXIA AND METABOREFLEX ACTIVATION ON HEMODYNAMICS

IntroductionBoth metaboreflex activity and hypoxia affect hemodynamics. In particular, metaboreflex induces an augmentation in stroke volume (SV), systemic vascular resistance (SVR), and blood pressure (BP) by activating the sympathetic nervous system (SNS). In contrast, hypoxia produces a heart rate (HR)‐mediated increase in cardiac output (CO), while its effect on SVR is variable as it increases SNS activity but, at the same time, it triggers nitric oxide (NO) production in the endothelium, thus inducing venous and arteriolar dilation. Since studies on the possible interaction between metaboreflex and hypoxia are still lacking, our investigation aimed to study their combined effects on hemodynamics.Methods11 male subjects underwent a preliminary cardiopulmonary exercise test (CPET) on a cycle ergometer to assess their aerobic fitness. Then, a metaboreflex activation protocol in normoxia and normobaric hypoxia (fraction of inspired oxygen – FiO2 – of 13.5%) was conducted on separate days. Hypoxia was induced using a hypoxic gas generator (Everest Summit II Generator, Hypoxico, USA) connected to the subjects by a facemask. The metaboreflex activation protocol consisted of two randomly assigned sessions: one of post‐exercise muscle ischemia (PEMI) and one of control exercise recovery (CER). PEMI comprised a 3‐minute exercise bout pedaling at 30% of the maximum workload reached during the CPET followed by 3 minutes of vascular occlusion using an inflatable thigh cuff to stimulate the metaboreflex. CER was similar, but no occlusion was applied after the exercise session. SV, HR, CO, ventricular filling rate (VFR), and ventricular ejection rate (VER) were measured through impedance cardiography while mean blood pressure (MBP) was assessed using manual sphygmomanometer. SVR was calculated indirectly from CO and MBP according to Poiseuille’s law. Near‐infrared spectroscopy was employed to measure cerebral oxygenation (COX) and peripheral hemoglobin saturation (SPO2) to control the level of tissue hypoxia. Two‐way ANOVA and paired sample t‐test were utilized when appropriate.ResultsCO was increased during metaboreflex activation in normoxia (p= 0.013) but not in hypoxia. SV, CO, and VFR responses to metaboreflex (measured as the difference PEMI‐CER at the third minute after exercise) were reduced when the hypoxic stimulus was applied (p=0.02; p=0.02; p=0.003 respectively). Moreover, SVR response showed a nearly significant (p=0.07) increase in hypoxia, with MBP response being unchanged. COX and SPO2 confirmed that the hypoxic stimulus was effective.DiscussionResults demonstrated that hypoxia impaired the hemodynamic response to metaboreflex. Specifically, SV was reduced during metaboreflex in hypoxia because of a reduction in preload as a consequence of two mechanisms: 1) a reduction in venous return probably induced by NO‐mediated vasodilation of the venous bed; 2) an increase in right ventricle afterload likely produced by the pulmonary arterial system vasoconstriction. Of note, baroreflex successfully defended MBP response despite the reduced CO during hypoxia.

Dynamic cerebral autoregulation in anterior and posterior cerebral circulation during cold pressor test

We hypothesized that cerebral blood flow (CBF) regulation in the posterior circulation differs from that of the anterior circulation during a cold pressor test (CPT) and is accompanied by elevations in arterial blood pressure (ABP) and sympathetic nervous activity (SNA). To test this, dynamic cerebral autoregulation (dCA) in the middle and posterior cerebral arteries (MCA and PCA) were measured at three different conditions: control, early phase of the CPT, and the late phase of the CPT. The dCA was examined using a thigh cuff occlusion and release technique. The MCA and PCA blood velocities were unchanged at CPT compared with the control conditions despite an elevation in the ABP. The dCA in both the MCA and PCA remained unaltered at CPT. These findings suggest that CPT-induced elevations in the ABP and SNA did not cause changes in the CBF regulation in the posterior circulation compared with the anterior circulation.

Acute hypotension attenuates brachial flow-mediated dilation in young healthy men.

This study aimed to test our hypothesis that acute hypotension attenuates brachial flow-mediated dilation (FMD) as an index of endothelial function in healthy humans. Twelve healthy men (21.8 ± 1.6years, body mass index; 22.2 ± 1.6kg/m2) participated in this study. Brachial FMD was measured in three trials: standardized FMD protocol (control trial), abrupt decrease in blood pressure (BP) via thigh cuff inflation-deflation (hypotension trial) and decrease in shear rate (SR) via a shortened forearm occlusion time (SR reduction trial). Brachial diameter and blood velocity were measured using Duplex ultrasound. Mean arterial pressure during reactive hyperaemia showed a marked decrease in the hypotension trial (- 23.7 ± 6.0mmHg), but not in the control and SR reduction trials. SR area under the curve was attenuated in the SR reduction trial (P < 0.001), but not in the control and hypotension trials (P = 0.316). Consequently, FMD was attenuated in the hypotension and SR reduction trials compared with that in the control trial (P = 0.003 and P = 0.043, respectively), and was attenuated to a greater extent in the hypotension trial compared with the SR reduction trial (P = 0.006; control, 6.9 ± 3.5%; hypotension, 3.5 ± 1.7%; SR reduction, 5.0 ± 2.2%). After adjusting FMD using SR, FMD remained attenuated in the hypotension trial (P = 0.014), but not in the SR reduction trial. Our findings indicate that arterial pressure as well as sympathetic nervous system activation could be an important determinant of FMD. Blunted FMD of peripheral arteries may be a rational response to restore BP and/or prevent further reduction of BP following acute hypotension in healthy humans.

Acute reduction in cerebral blood velocity on supine-to-stand transition increases postural instability in young adults.

We tested the hypothesis that transient deficits in cerebral blood flow are associated with postural sway. In 19 young, healthy adults, we examined the association between the drop in cerebral blood flow during supine-to-stand transitions, indexed by transcranial Doppler ultrasound [middle cerebral artery blood velocity at diastole (MCAdv)] and near-infrared spectroscopy [tissue saturation index (TSI)] and the center of pressure displacement while standing. Participants performed transitions under three conditions aimed at progressively increasing the drop in MCAdv, in a randomized order: 1) a control transition (Con); 2) a transition that coincided with deflation of bilateral thigh cuffs; and 3) a transition that coincided with both thigh-cuff deflation and 90 s of prior hyperventilation (HTC). The deficit in diastolic blood velocity (MCAdv deficit) was quantified as the difference between MCAdv and its preceding baseline value, summed over 10 s, beginning at the MCAdv nadir. Compared with Con, HTC led to greater drops in MCAdv (P = 0.003) and TSI (P < 0.001) at nadir. The MCAdv deficit was positively associated with the center of pressure displacement vector-average using repeated-measures correlation (repeated-measures correlation coefficient = 0.56, P < 0.001). An a posteriori analysis identified a sub-group of participants that showed an exaggerated increase in MCAdv deficit and greater postural instability in both the anterior-posterior (P = 0.002) and medial-lateral (P = 0.021) directions in response to the interventions. These findings support the theory that individuals who experience greater initial cerebral hypoperfusion on standing may be at a greater risk for falls.NEW & NOTEWORTHY Dizziness and risk for falls after standing might link directly to reduced delivery of oxygen to the brain. By introducing challenges that increased the drop in brain blood flow in healthy young adults, we have shown for the first time a direct link to greater postural instability. These results point to a need to measure cerebral blood flow and/or oxygenation after postural transitions in populations, such as older adults, to assist in fall risk assessment.

Inflight leg cuff test does not identify the risk for orthostatic hypotension after long-duration spaceflight

Landing day symptoms from orthostatic hypotension after prolonged spaceflight can be debilitating, but severity of these symptoms can be unpredictable and highly individual. We tested the hypothesis that an impaired baroreflex response to an inflight leg cuff test could predict orthostatic intolerance on return to Earth. Eight male astronauts (44 ± 7 years of age (mean ± SD); mean mission length: 167 ± 12 days) participated in a standardized supine-to-sit-to-stand test (5 min–30s–3 min) pre- and postflight, and a 3 min thigh cuff occlusion test pre- and inflight with continuous monitoring of heart rate and arterial blood pressure. The arterial baroreflex was not changed inflight as shown by similar reductions in mean arterial pressure (MAP) response to leg cuff deflation (preflight −19 ± 2 mmHg vs. inflight −18 ± 5 mmHg). With the sit/stand test, the nadir of MAP was lower postflight (−17 ± 9 mmHg) than preflight (−11 ± 6 mmHg, p < 0.05). A greater increase in heart rate (25 ± 7; 16 ± 3 bpm) and decrease in stroke volume (−24 ± 11; −6 ± 4 mL) occurred with sit/stand postflight than leg cuffs inflight (p < 0.001). Inflight testing was influenced by elevated cardiac output resulting in a smaller drop in total peripheral resistance. Two of eight subjects exhibited orthostatic hypotension during the postflight stand test; their responses were not predicted by the inflight leg cuff deflation test. These results suggest that the baroreflex response examined by inflight leg cuff deflation was not a reliable indicator of postflight stand responses.

Exercise with Blood Flow Restriction to Improve Quadriceps Function Long After ACL Reconstruction.

Quadriceps atrophy and weakness can persist for years after anterior cruciate ligament reconstruction (ACLR). We evaluated the effectiveness of a home-based blood flow restriction (BFR) exercise program to increase quadriceps size and strength several years after ACLR. Nine adults with ACLR (5±2 yrs post-surgery, ≤90% symmetry in quadriceps size and strength) and nine uninjured controls volunteered. ACLR participants exercised at home for 25 min, 5×/wk for 4 wks (single-leg knee extension, bodyweight half-squats, walking). Blood flow in only the involved leg was restricted using a thigh cuff inflated to 50% of limb occlusion pressure. Rectus femoris and vastus lateralis thickness and knee extensor strength were measured before and after training. Baseline and post-training symmetry (involved leg/uninvolved leg) indices were compared to uninjured controls. Rectus femoris and vastus lateralis thickness and knee extensor strength in the involved leg increased by 11±5%, 10±6%, and 20±14%, respectively (all P<0.01). Compared to baseline, post-training knee extensor strength symmetry increased from 88±4 to 99±5% (P<0.01) and did not differ from uninjured controls (99±5%, P=0.95). Implementation of BFR exercise at home was feasible, safe and effective. Results extend upon early post-operative application of BFR exercise for ACLR recovery and demonstrate that BFR can improve quadriceps function long after ACLR.

Thigh Cuffs to Prevent the Deconditioning Induced by 5 Days of Dry Immersion

Thigh Cuffs to Prevent the Deconditioning Induced by 5 Days of Dry Immersion

The Impact of Caffeine on Dynamic Cerebral Autoregulation in Habitual Consumers

Caffeine is an adenosine receptor antagonist that is consumed daily by 90% of the United States population and can lead to adenosine receptor upregulation. In caffeine‐naïve individuals, drinking caffeine increases dynamic cerebral autoregulation as assessed by the rate of regulation (RoR) but the influence of caffeine in habitual users is unclear. We aimed to investigate whether dynamic cerebral autoregulation in middle and posterior cerebral arteries was altered by caffeine consumption in habituated consumers. Nine healthy subjects (age: 27 ± 6 yrs, Ht: 179 ± 14 cm, Wt: 76.1 ± 13.6 kg) completed three trials where they drank (6.25ml/kg body mass) either caffeinated coffee (CAF; 4mg caffeine/kg body mass), decaffeinated coffee (DECAF), or water (WATER). Before subjects drank anything (pre drink) we measured mean arterial pressure (MAP; mmHg), middle (MCAv; cm/s) and posterior (PCAv; cm/s) cerebral artery blood velocities at baseline and then during two successive thigh occlusion/release protocols to examine dynamic cerebral autoregulation (Rate of Regulation: RoR, 1/s). Subjects were then given one of the three drinks in a double‐blind, counterbalanced design. Thirty minutes later baseline measurements and the assessment of RoR were repeated (post drink). MAP decreased 14 ± 4 mmHg across all trials following thigh cuff deflation in the assessment of RoR pre drink. Pre drink RoR in the MCA was CAF: 0.19 ± 0.13, DECAF: 0.21 ± 0.14 and WATER: 0.21 ± 0.09 1/s. Pre drink RoR in the PCA was CAF: 0.24 ± 0.18, DECAF: 0.16 ± 0.15 and WATER: 0.23 ± 0.12 1/s. MAP increased from pre to post drink (CAF: 84 ± 7 to 98 ± 6 mmHg; DECAF: 88 ± 10 to 95 ± 6 mmHg and WATER: 89 ± 9 to 97 ± 5 mmHg; p = 0.002), but was not different between trials (p &gt; 0.05). MAP decreased 14 ± 3 mmHg across all trials following thigh cuff deflation in the assessment of RoR post drink. Post drink, MCA RoR demonstrated an interaction effect between trial and time (p = 0.047) and a main effect of time (p = 0.042). Post drink MCA RoR increased in the CAF trial relative to pre drink (0.40 ± 0.17 1/s; p = 0.008) but was unchanged in DECAF (0.23 ± 0.12 1/s) and WATER trials (0.23 ± 0.11 1/s) (both p &gt; 0.05 vs. pre drink). Post drink, PCA RoR was not different relative to pre drink (CAF: 0.35 ± 0.13, DECAF: 0.20 ± 0.11 and WATER: 0.21 ± 0.10 1/s) and did not demonstrate a main effect of time (p = 0.335), trial (p = 0.081) nor an interaction effect (p = 0.414). These findings suggest that caffeine consumption increases dynamic cerebral autoregulation in habituated consumers and supports the increased RoR found in the MCA following caffeine administration in caffeine naïve individuals.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The Effects of Remote Ischemic Preconditioning on Cognitive Function and Exercise Hyperemia in Isocapnic Hypoxia

Impairments in neurological and skeletal muscle function can occur in conditions of decreased oxygen delivery and vascular dysfunction can exacerbate any impairments. Remote ischemic preconditioning (RIPC) has been used to improve vascular functioning during exercise and cognitive tasks, but this intervention has yet to be tested in hypoxic conditions. Here, we test the hypothesis that RIPC can attenuate the hypoxia‐induced decline in cognitive function and also impact forearm blood flow during hypoxic exercise. Healthy, young men and women participated in two counterbalanced experimental sessions, consisting of two trials of rhythmic dynamic handgrip exercise (4 min, 10% maximal voluntary contraction) followed by computerized cognitive testing, once in normoxia (21% inspired O2), and once in isocapnic hypoxia (target O2 saturation ~85% via pulse oximetry). The cognitive tests (CNS Vital Signs) measured composite memory, verbal memory, visual memory, and processing speed. During rest and handgrip exercise, forearm blood flow (FBF) responses were determined via Doppler ultrasound and muscle oxygenation was assessed using near infrared spectroscopy (Moxy). Systemic hemodynamics [heart rate (ECG) and non‐invasive beat‐to‐beat blood pressure (Finometer)] were collected throughout. One experimental session consisted of RIPC (4 × 5 min thigh cuff inflation; 200 mmHg) between the normoxic and hypoxic trials whereas the other was a sham (~10 mmHg cuff pressure) intervention. Percent change (%Δ) from normoxia to hypoxia was determined for cognitive test scores. Preliminary results (n=6, mean±sem) demonstrate modest hypoxia‐induced declines in composite, verbal, and visual memory (−8.6±4.4%, −11.2±6.6%, −5.2±3.8%) but not processing speed in sham conditions. The RIPC intervention had no consistent impact on these hypoxia‐induced changes. Exercise hyperemia was increased in hypoxia vs normoxia (177±12 vs 163±6 ml/min in hypoxia vs normoxia, respectively) and RIPC modestly increased exercise hyperemia in hypoxia (191±10 ml/min) but had little effect during normoxia (167±12 ml/min). We conclude that RIPC has a minimal effect on the impact of hypoxia on cognitive function and can augment hypoxic exercise hyperemia in young, healthy humans.Support or Funding InformationUniversity of Dayton University Honors Program, Berry Summer Thesis Institute (JNS)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Cardiorespiratory and Cerebrovascular Responses to Leg Cycling Exercise during Muscle Metaboreflex Activation with Blood Flow Restriction in Moderate Normobaric Hypoxia

Skeletal muscle blood flow restriction and normobaric hypoxia are strategies adopted during exercise training because the associated reductions in local or systemic oxygenation may enhance athletic performance. Both manoeuvres evoke cardiorespiratory and cerebrovascular responses but have not been studied in combination. Blood flow restriction during exercise activates metabolically sensitive group III and IV skeletal muscle afferents (i.e., muscle metaboreflex activation), while systemic hypoxia activates the peripheral chemoreflex. We sought to determine whether the cardiorespiratory and cerebrovascular response to muscle metaboreflex activation with blood flow restriction during leg cycling exercise is augmented in moderate normobaric hypoxia.Nine healthy men (age 23±2 years; mean±SE) participated in two experimental trials performed under normoxic (fraction of inspired O2 [FiO2] = 21 %) and hypoxic (FiO2 = 13.5 %; equivalent of altitude of 3500 m) conditions whilst seated in a semi‐recumbent position in an environmental chamber. Trials consisted of a resting baseline period (3 min), followed by low intensity leg cycling exercise (64±7 Watts) under free‐flow conditions (~3½ min), and then bilateral thigh cuff inflation to 100 mmHg to induce blood flow restriction and muscle metaboreflex activation (~3 ½ min). Peripheral capillary oxygen saturation (SpO2; finger pulse oximetry), mean arterial pressure (MAP; Finometer and SunTech), heart rate (HR; electrocardiogram), the partial pressure of end‐tidal carbon dioxide (PETCO2; capnography), minute ventilation (VE; pneumotachometer) and middle cerebral artery mean blood flow velocity (MCAV; transcranial Doppler) were recorded.At baseline, SpO2 was lower during hypoxia (87±1 %) than normoxia (97±1 %; P&lt;0.05), but MAP, HR, PETCO2, VE and MCAv were not different between trials (P&gt;0.05). Leg cycling under free‐flow conditions significantly increased MAP, HR, PETCO2, VE and MCAv (P&lt;0.05 vs. baseline), with no differences observed between hypoxic and normoxic trials (P&gt;0.05). MAP (Δ14±2 vs. Δ16±2 mmHg; P=0.215), HR (Δ10±2 vs. Δ8±3 b·min−1; P=0.251), PETCO2 (Δ−1.1±0.3 vs. Δ−3.4±1.8 mmHg; P=0.596), VE (Δ4±1 vs. Δ4±1 L·min−1; P=0.446) and MCAv (Δ4±2 vs. Δ4±1 cm·s−1; P=0.408) responses to blood flow restriction during leg cycling (i.e., muscle metaboreflex activation) were not different in the hypoxic and normoxic trials.These preliminary findings suggest that moderate normobaric hypoxia (FiO2 = 13.5 %) does not augment the cardiorespiratory and cerebrovascular responses to muscle metaboreflex activation with blood flow restriction during low intensity leg cycling.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Quantitative measurements of cerebral blood flow with near-infrared spectroscopy.

We propose a new near-infrared spectroscopy (NIRS) method for quantitative measurements of cerebral blood flow (CBF). Because this method uses concepts of coherent hemodynamics spectroscopy (CHS), we identify this new method with the acronym NIRS-CHS. We tested this method on the prefrontal cortex of six healthy human subjects during mean arterial pressure (MAP) transients induced by the rapid deflation of pneumatic thigh cuffs. A comparison of CBF dynamics measured with NIRS-CHS and with diffuse correlation spectroscopy (DCS) showed a good agreement for characteristic times of the CBF transient. We also report absolute measurements of baseline CBF with NIRS-CHS (69 ± 6 ml/100g/min over the six subjects). NIRS-CHS can provide more accurate measurements of CBF with respect to previously reported NIRS surrogates of CBF.

Modeling of the hemodynamics in the feet of patients with peripheral artery disease.

To simulate the hemodynamic effects in the feet in response to a thigh cuff occlusion, we have developed a multi-compartmental model in which the circulatory system for the leg is represented by its electrical equivalents. Dynamic vascular optical tomographic imaging data previously obtained from 20 patients with peripheral artery disease (PAD) and 20 healthy subjects is used to test the model. Analyzing the clinical data with the support of the model yields diagnostic specificity and sensitivity in the 90-95% range, significantly higher than previously reported.

Multi-distance frequency-domain optical measurements of coherent cerebral hemodynamics.

We report non-invasive, bilateral optical measurements on the forehead of five healthy human subjects, of 0.1 Hz oscillatory hemodynamics elicited either by cyclic inflation of pneumatic thigh cuffs, or by paced breathing. Optical intensity and the phase of photon-density waves were collected with frequency-domain near-infrared spectroscopy at seven source-detector distances (11-40 mm). Coherent hemodynamic oscillations are represented by phasors of oxyhemoglobin (O) and deoxyhemoglobin (D) concentrations, and by the vector D/O that represents the amplitude ratio and phase difference of D and O. We found that, on average, the amplitude ratio (|D/O|) and the phase difference (∠(D/O)) obtained with single-distance intensity at 11-40 mm increase from 0.1 and −330°, to 0.2 and −200°, respectively. Single-distance phase and the intensity slope featured a weaker dependence on source-detector separation, and yielded |D/O| and ∠(D/O) values of about 0.5 and −200°, respectively, at distances greater than 20 mm. The key findings are: (1) single-distance phase and intensity slope are sensitive to deeper tissue compared to single-distance intensity; (2) deeper tissue hemodynamic oscillations, which more closely represent the brain, feature D and O phasors that are consistent with a greater relative flow-to-volume contributions in brain tissue compared to extracerebral, superficial tissue.