ABSTRACT
Cardiovascular deconditioning and altered baroreflexes predispose returning astronauts to Orthostatic Intolerance. We assessed 7 astronauts (1 female) before and following long-duration spaceflight (146 ± 43 days) with minimal upright posture prior to testing. We applied lower body negative pressure (LBNP) of up to - 30 mmHg to supine astronauts instrumented for continual synchronous measurements of cardiovascular variables, and intermittent imaging the Portal Vein (PV) and Inferior Vena Cava (IVC). During supine rest without LBNP, postflight elevations to total peripheral resistance (TPR; 15.8 ± 4.6 vs. 20.8 ± 7.1 mmHg min/l, p < 0.05) and reductions in stroke volume (SV; 104.4 ± 16.7 vs. 87.4 ± 11.5 ml, p < 0.05) were unaccompanied by changes to heart rate (HR) or estimated central venous pressure (CVP). Small increases to systolic blood pressure (SBP) and diastolic blood pressure (DBP) were not statistically significant. Autoregressive moving average modelling (ARMA) during LBNP did not identify differences to either arterial (DBP â TPR and SBP â HR) or cardiopulmonary (CVP â TPR) baroreflexes consistent with intact cardiovascular control. On the other hand, IVC and PV diameter-CVP relationships during LBNP revealed smaller diameter for a given CVP postflight consistent with altered postflight venous wall dynamics.
Subject(s)
Astronauts , Baroreflex , Humans , Female , Baroreflex/physiology , Lower Body Negative Pressure , Blood Pressure/physiology , Heart Rate/physiology , ArteriesABSTRACT
PURPOSE: Orthostatic hypotension, leading to cerebral hypoperfusion, can result in postural instability and falls in older adults. We determined the efficacy of a novel, intermittent pneumatic compression system, applying pressure around the lower legs, as a countermeasure against orthostatic stress in older adults. METHODS: Data were collected from 13 adults (4 male) over 65 years of age. Non-invasive ultrasound measured middle cerebral artery blood velocity (MCAv) and finger photoplethysmography measured mean arterial blood pressure (MAP). Intermittent lower leg compression was applied in a peristaltic manner in the local diastolic phase of each cardiac cycle to optimize venous return during 1-min of seated rest and during a sit-to-stand transition to 1-min of quiet standing with compression initiated 15 s before transition. RESULTS: During seated rest, compression resulted in a 4.5 ± 6.5 mmHg increase in MAP, and 2.3 ± 2.1 cm/s increase in MCAv (p < 0.05). MAP and MCAv increased during the 15 s of applied compression before the posture transition (2.3 ± 7.2 mmHg and 2.1 ± 4.0 cm/s, respectively, p < 0.05) with main effects for both variables confirming continued benefit during the transition and quiet stand periods. CONCLUSIONS: Application of carefully timed, intermittent compression to the lower legs of older adults increased MAP and MCAv during seated rest and maintained an elevated MAP and MCAv during a transition to standing posture. Future research could assess the benefits of this technology for persons at risk for orthostatic hypotension on standing and while walking in an effort to reduce injurious, unexplained falls in older adults.
Subject(s)
Cerebrovascular Circulation/physiology , Leg/blood supply , Muscle, Skeletal/blood supply , Posture/physiology , Aged , Aged, 80 and over , Blood Flow Velocity , Female , Humans , Male , Middle Cerebral Artery/physiology , Muscle, Skeletal/physiology , Photoplethysmography , Regional Blood Flow , Standing PositionABSTRACT
This study tested the hypothesis that intermittent compression of the lower limb would increase blood flow during exercise and postexercise recovery. Data were collected from 12 healthy individuals (8 men) who performed 3 min of standing plantar flexion exercise. The following three conditions were tested: no applied compression (NoComp), compression during the exercise period only (ExComp), and compression during 2 min of standing postexercise recovery. Doppler ultrasound was used to determine superficial femoral artery (SFA) blood flow responses. Mean arterial pressure (MAP) and cardiac stroke volume (SV) were assessed using finger photoplethysmography, with vascular conductance (VC) calculated as VC = SFA flow/MAP. Compared with the NoComp condition, compression resulted in increased MAP during exercise [+3.5 ± 4.1 mmHg (mean ± SD)] but not during postexercise recovery (+1.6 ± 5.9 mmHg). SV increased with compression during both exercise (+4.8 ± 5.1 ml) and recovery (+8.0 ± 6.6 ml) compared with NoComp. There was a greater increase in SFA flow with compression during exercise (+52.1 ± 57.2 ml/min) and during recovery (+58.6 ± 56.7 ml/min). VC immediately following exercise was also significantly greater in the ExComp condition compared with the NoComp condition (+0.57 ± 0.42 ml·min-1·mmHg-1), suggesting the observed increase in blood flow during exercise was in part because of changes in VC. Results from this study support the hypothesis that intermittent compression applied during exercise and recovery from exercise results in increased limb blood flow, potentially contributing to changes in exercise performance and recovery. NEW & NOTEWORTHY Blood flow to working skeletal muscle is achieved in part through the rhythmic actions of the skeletal muscle pump. This study demonstrated that the application of intermittent pneumatic compression during the diastolic phase of the cardiac cycle, to mimic the mechanical actions of the muscle pump, accentuates muscle blood flow during exercise and elevates blood flow during the postexercise recovery period. Intermittent compression during and after exercise might have implications for exercise performance and recovery.
Subject(s)
Exercise/physiology , Intermittent Pneumatic Compression Devices , Leg/blood supply , Adult , Diastole , Female , Healthy Volunteers , Humans , Male , Regional Blood Flow , Young AdultABSTRACT
Currently, oxygen uptake () is the most precise means of investigating aerobic fitness and level of physical activity; however, can only be directly measured in supervised conditions. With the advancement of new wearable sensor technologies and data processing approaches, it is possible to accurately infer work rate and predict during activities of daily living (ADL). The main objective of this study was to develop and verify the methods required to predict and investigate the dynamics during ADL. The variables derived from the wearable sensors were used to create a predictor based on a random forest method. The temporal dynamics were assessed by the mean normalized gain amplitude (MNG) obtained from frequency domain analysis. The MNG provides a means to assess aerobic fitness. The predicted during ADL was strongly correlated (r = 0.87, P < 0.001) with the measured and the prediction bias was 0.2 ml·min-1·kg-1. The MNG calculated based on predicted was strongly correlated (r = 0.71, P < 0.001) with MNG calculated based on measured data. This new technology provides an important advance in ambulatory and continuous assessment of aerobic fitness with potential for future applications such as the early detection of deterioration of physical health.
Subject(s)
Activities of Daily Living , Biosensing Techniques/instrumentation , Biosensing Techniques/methods , Oxygen/metabolism , Adult , Humans , Machine Learning , Male , Monitoring, Ambulatory/methods , Oxygen/analysis , Wearable Electronic DevicesABSTRACT
NEW FINDINGS: What is the central question of this study? The pulmonary oxygen uptake (pVÌO2) data used to study the muscle aerobic system dynamics during moderate-exercise transitions is classically described as a mono-exponential function controlled by a complex interaction of the oxygen delivery-utilization balance. This elevated complexity complicates the acquisition of relevant information regarding aerobic system dynamics based on pVÌO2 data during a varying exercise stimulus. What is the main finding and its importance? The elevated complexity of pVÌO2 dynamics is a consequence of a multiple-order interaction between muscle oxygen uptake and circulatory distortion. Our findings challenge the use of a first-order function to study the influences of the oxygen delivery-utilization balance over the pVÌO2 dynamics. The assumption of aerobic system linearity implies that the pulmonary oxygen uptake (pVÌO2) dynamics during exercise transitions present a first-order characteristic. The main objective of this study was to test the linearity of the oxygen delivery-utilization balance during random moderate exercise. The cardiac output (QÌ) and deoxygenated haemoglobin concentration ([HHb]) were measured to infer the central and local O2 availability, respectively. Thirteen healthy men performed two consecutive pseudorandom binary sequence cycling exercises followed by an incremental protocol. The system input and the outputs pVÌO2, [HHb] and QÌ were submitted to frequency-domain analysis. The linearity of the variables was tested by computing the ability of the response at a specific frequency to predict the response at another frequency. The predictability levels were assessed by the coefficient of determination. In a first-order system, a participant who presents faster dynamics at a specific frequency should also present faster dynamics at any other frequency. All experimentally obtained variables (pVÌO2, [HHb] and QÌ) presented a certainly degree of non-linearity. The local O2 availability, evaluated by the ratio pVÌO2/[HHb], presented the most irregular behaviour. The overall [HHb] kinetics were faster than pVÌO2 and QÌ kinetics. In conclusion, the oxygen delivery-utilization balance behaved as a non-linear phenomenon. Therefore, the elevated complexity of the pulmonary oxygen uptake dynamics is governed by a complex multiple-order interaction between the oxygen delivery and utilization systems.
Subject(s)
Exercise/physiology , Oxygen Consumption/physiology , Oxygen/metabolism , Pulmonary Gas Exchange/physiology , Adult , Cardiac Output/physiology , Exercise Test/methods , Hemoglobins/metabolism , Humans , Lung/metabolism , Lung/physiology , MaleABSTRACT
South Asians (SA) suffer from a higher burden of heart disease and stroke compared with White Caucasians (CA). We hypothesized that increased arterial stiffness in older adults of SA origin would be associated with greater cerebrovascular pulsatile pressure and flow characteristics compared with CA older adults. Forty-four SA and CA older adults, free of known cardiovascular and cerebrovascular diseases, were assessed. Vascular ageing was characterized by brachial-ankle pulse wave velocity, carotid pulse pressure, compliance coefficient (CC) and intima-media thickness (IMT). Duplex ultrasonography of the internal carotid arteries estimated anterior cerebral blood flow (aCBF) and cerebrovascular resistance (aCVR), and transcranial Doppler ultrasound quantified middle cerebral artery blood flow velocity, resistive index (RI) and pulsatility index (PI). Fasting blood samples were collected to assess glycaemic status, lipid profile and C-reactive protein. SA had higher carotid pulse pressure and lower CC indicating stiffer arteries compared with CA. Multiple regression analyses revealed that ethnic differences in arterial stiffness were associated with glycated haemoglobin level in SA. Among SA, an inverse association was observed between carotid CC and aCVR. In turn, aCVR was associated with a steeper reduction in aCBF in SA than in CA. IMT was strongly associated with greater PI and RI (r>0.81, P<0.001) in SA, whereas a weaker relationship for PI (r=0.46, P=0.03) and no significant relationship for RI were found in CA. The study found stronger associations between pulsatile cerebrovascular haemodynamics and structural and functional alterations in central arteries in SA that may underlie the elevated risk for cerebrovascular disease.
Subject(s)
Cerebrovascular Circulation , Pulsatile Flow , Vascular Stiffness , Aged , Aged, 80 and over , Asia, Western/ethnology , Asian People , Cross-Sectional Studies , Humans , Male , Middle Aged , White PeopleABSTRACT
CD200 is a transmembrane protein that belongs to the immunoglobulin family of proteins and is ubiquitously expressed on a variety of cell types. Upon interaction with its receptors (CD200Rs) expressed on myeloid-derived cells and T lymphocytes, an immunoregulatory signal is delivered to receptor-expressing cells. Previous studies have implicated a role for CD200:CD200R in the regulation of the expression of mRNA markers of osteoclastogenesis/osteoblastogenesis, following interaction of CD200 (on osteoblast precursors) with CD200R1 (on osteoclast precursors). Signaling of CD200R1 is hypothesized to attenuate osteoclastogenesis. We have investigated whether levels of soluble forms of CD200 and/or CD200R1 (sCD200, sCD200R1) are altered in volunteers undergoing 6° head down tilt bed rest to mimic conditions of microgravity known to be associated with preferential osteoclastogenesis and whether countermeasures, reported to be beneficial in attenuation of bone loss under microgravity conditions, would lead to altered sCD200 and sCD200R1 levels. Our data suggest that, as predicted, sCD200 levels fall under bed rest conditions while sCD200R1 levels rise. In subjects undergoing 30-minute per day continuous centrifugation protocols, as a countermeasure to attenuate changes which may lead to bone loss, these alterations in sCD200 and sCD200R1 levels seen under conditions of bed rest were abolished or attenuated. Our results suggest that measurement of sCD200 and/or sCD200R1 may prove a useful and rapid means of monitoring subjects at risk of bone loss and/or accessing the efficacy of treatment regimes designed to counter bone loss.
Subject(s)
Antigens, CD/blood , Antigens, Surface/blood , Bed Rest , Bone Resorption/blood , Receptors, Cell Surface/blood , Adult , Alkaline Phosphatase/blood , Amino Acids/blood , Amino Acids/urine , Biomarkers/blood , Bone Resorption/urine , Bone and Bones/metabolism , Bone and Bones/pathology , Calcium/blood , Collagen Type I/urine , Humans , Male , Orexin Receptors , Peptide Fragments/blood , Peptides/urine , Procollagen/blood , RANK Ligand/blood , Solubility , Tumor Necrosis Factor-alpha/bloodABSTRACT
Limited data are available to describe the regulation of heart rate (HR) during sleep in spaceflight. Sleep provides a stable supine baseline during preflight Earth recordings for comparison of heart rate variability (HRV) over a wide range of frequencies using both linear, complexity, and fractal indicators. The current study investigated the effect of long-duration spaceflight on HR and HRV during sleep in seven astronauts aboard the International Space Station up to 6 mo. Measurements included electrocardiographic waveforms from Holter monitors and simultaneous movement records from accelerometers before, during, and after the flights. HR was unchanged inflight and elevated postflight [59.6 ± 8.9 beats per minute (bpm) compared with preflight 53.3 ± 7.3 bpm; P < 0.01]. Compared with preflight data, HRV indicators from both time domain and power spectral analysis methods were diminished inflight from ultralow to high frequencies and partially recovered to preflight levels after landing. During inflight and at postflight, complexity and fractal properties of HR were not different from preflight properties. Slow fluctuations (<0.04 Hz) in HR presented moderate correlations with movements during sleep, partially accounting for the reduction in HRV. In summary, substantial reduction in HRV was observed with linear, but not with complexity and fractal, methods of analysis. These results suggest that periodic elements that influence regulation of HR through reflex mechanisms are altered during sleep in spaceflight but that underlying system complexity and fractal dynamics were not altered.
Subject(s)
Blood Pressure/physiology , Heart Rate/physiology , Sleep/physiology , Space Flight , Weightlessness , Adult , Astronauts , Electrocardiography , Female , Humans , Male , Middle AgedABSTRACT
We tested the data repeatability for popliteal blood flow velocity (PBV), popliteal arterial diameter (AD(pop)), popliteal blood flow (PBF) and lower limb vascular conductance (VC) at rest and exercise in three body positions, two work rates and two inspired oxygen fractions. Fifteen, eleven and ten healthy volunteers participated in the three phases of the studies. Resting protocols were performed in horizontal (HOR), 35° head-down tilt (HDT) and 45° head-up tilt (HUT) for 5 min in each body position. Participants also exercised at lower and higher power outputs (repeated plantar flexion contractions at 20% and 30% maximal voluntary contraction, respectively) in HOR, HDT and HUT and in normoxia (21%O2) and hypoxia (14%O2) with the same work rates and body positions. PBV and AD(pop) were measured by ultrasound to determine PBF, and VC was estimated by dividing PBF by muscle perfusion pressure (MPP). PBV, AD(pop), PBF and VC were not different, demonstrated good agreement and consistency between the two days of testing during both rest and exercise conditions regardless of body position. Therefore, these data support the utilization of Doppler and echo Doppler ultrasound as a reproducible method to measure PBV and AD(pop) and consequently estimate PBF and VC responses in such conditions.
Subject(s)
Exercise , Head-Down Tilt/physiology , Lower Extremity/blood supply , Popliteal Artery/diagnostic imaging , Regional Blood Flow/physiology , Rest/physiology , Ultrasonography, Doppler/methods , Adult , Blood Flow Velocity , Humans , Hypoxia/physiopathology , Inhalation , Lower Extremity/diagnostic imaging , Male , Oxygen/metabolism , Popliteal Artery/physiology , Reproducibility of ResultsABSTRACT
Syncope from sustained orthostasis results from cerebral hypoperfusion associated with reductions in arterial pressure at the level of the brain (BPMCA) and reductions in arterial CO2 as reflected by end-tidal values (PetCO2). It was hypothesized that reductions in PetCO2 increase cerebrovascular tone before a drop in BPMCA that ultimately leads to syncope. Twelve men (21-42 yr of age) completed an orthostatic tolerance test consisting of head-up tilt and progressive lower body negative pressure to presyncope, before and after completing 5 days of continuous head-down bed rest (HDBR). Cerebral blood velocity (CBFV), BPMCA, and PetCO2 were continuously recorded throughout the test. Cerebrovascular indicators, cerebrovascular resistance, critical closing pressure (CrCP), and resistance area product (RAP), were calculated. Comparing from supine baseline to 6-10 min after the start of tilt, there were reductions in CBFV, PetCO2, BPMCA, and CrCP, an increase in RAP, and no change in cerebrovascular resistance index. Over the final 15 min before syncope in the pre-HDBR tests, CBFV and CrCP were significantly related to changes in PetCO2 (r = 0.69 ± 0.17 and r = 0.63 ± 0.20, respectively), and BPMCA, which was not reduced until the last minute of the test, was correlated with a reduction in RAP (r = 0.91 ± 0.09). Post-HDBR, tilt tolerance was markedly reduced, and changes in CBFV were dominated by a greater reduction in BPMCA with no relationships to PetCO2. Therefore, pre-HDBR, changes in PetCO2 with orthostasis contributed to increases in cerebrovascular tone and reductions in CBFV during the progression toward syncope, whereas, after 5 days of HDBR, orthostatic responses were dominated by changes in BPMCA.
Subject(s)
Blood Pressure , Carbon Dioxide/blood , Cerebral Arteries/physiopathology , Cerebrovascular Circulation , Orthostatic Intolerance/etiology , Syncope/etiology , Vasoconstriction , Adult , Biomarkers/blood , Blood Flow Velocity , Cerebral Arteries/diagnostic imaging , Humans , Lower Body Negative Pressure , Male , Orthostatic Intolerance/blood , Orthostatic Intolerance/diagnosis , Orthostatic Intolerance/physiopathology , Supine Position , Syncope/blood , Syncope/diagnosis , Syncope/physiopathology , Tilt-Table Test , Time Factors , Ultrasonography, Doppler, Transcranial , Vascular Resistance , Young AdultABSTRACT
Cardiovascular deconditioning after a 4-h head-down bed rest (HDBR) might be a consequence of the time of day relative to pre-HDBR testing, or simply 4 h of confinement and inactivity rather than the posture change. Ten men and 11 women were studied during lower body negative pressure (LBNP) before and after 4-h HDBR and 4-h seated posture (SEAT) as a control for time of day and physical inactivity effects to test the hypotheses that cardiovascular deconditioning was a consequence of the HDBR posture, and that women would have a greater deconditioning response. Following HDBR, men and women had lower blood volume, higher heart rate with a greater increase during LBNP, a greater decrease of stroke volume during LBNP, lower central venous pressure, smaller inferior vena cava diameter, higher portal vein resistance index with a greater increase during LBNP, but lower forearm vascular resistance, lower norepinephrine, and lower renin. Women had lower vasopressin and men had higher vasopressin after HDBR, and women had lower pelvic impedance and men higher pelvic impedance. Following SEAT, brachial vascular resistance was reduced, thoracic impedance was elevated, the reduction of central venous pressure during LBNP was changed, women had higher angiotensin II whereas men had lower levels, and pelvic impedance increased in women and decreased in men. Cardiovascular deconditioning was greater after 4-h HDBR than after SEAT. Women and men had similar responses for most cardiovascular variables in the present study that tested the responses to LBNP after short-duration HDBR compared with a control condition.
Subject(s)
Bed Rest/adverse effects , Cardiovascular Deconditioning , Cardiovascular System/physiopathology , Forearm/blood supply , Head-Down Tilt/adverse effects , Hemodynamics , Lower Body Negative Pressure/adverse effects , Pelvis/blood supply , Adult , Analysis of Variance , Angiotensin II/blood , Blood Volume , Brachial Artery/physiopathology , Central Venous Pressure , Dizziness/physiopathology , Female , Heart Rate , Humans , Male , Norepinephrine/blood , Portal Vein/physiopathology , Regional Blood Flow , Renin/blood , Sex Factors , Stroke Volume , Time Factors , Vascular Resistance , Vasopressins/blood , Vena Cava, Inferior/physiopathologyABSTRACT
This study tested the hypothesis that cardiovascular effects of sublingual nitroglycerin (NG) would be exaggerated after 56 days of 6° head-down bed rest (HDBR) in women, and that an aerobic and resistive exercise countermeasure (EX, n = 8) would reduce the effect compared with HDBR without exercise (CON, n = 7). Middle cerebral artery maximal blood flow velocity (CBFV), cardiac stroke volume (SV), and superficial femoral artery blood flow (Doppler ultrasound) were recorded at baseline rest and for 5 min following 0.3 mg sublingual NG. Post-HDBR, NG caused greater increases in heart rate (HR) in CON compared with EX (+24.9 ± 7.7 and +18.8 ± 6.6 beats/min, respectively, P < 0.0001). The increase in HR combined with reductions in SV to maintain cardiac output. Systolic, mean, and pulse pressures were reduced 5-10 mmHg by NG, but total peripheral resistance was only slightly reduced at 3 min after NG. Reductions in CBFV of -12.5 ± 3.8 cm/s were seen after NG, but a reduction in the Doppler resistance index suggested dilation of the middle cerebral artery with no differences after HDBR. The femoral artery dilated with NG and blood flow was reduced â¼50% with the appearance of large negative waves suggesting a marked increase in downstream resistance, but there were no effects of HDBR. In general, responses of women to NG were not altered by HDBR; the greater increase in HR in CON but not EX was probably a consequence of cardiovascular deconditioning. These results contrast with the hypothesis and a previous investigation of men after HDBR by revealing no change in cardiovascular responses to exogenous nitric oxide.
Subject(s)
Bed Rest , Blood Flow Velocity/drug effects , Nitroglycerin/administration & dosage , Stroke Volume/drug effects , Vasodilator Agents/administration & dosage , Administration, Sublingual , Adult , Blood Pressure/drug effects , Cardiovascular Deconditioning/drug effects , Female , Femoral Artery/diagnostic imaging , Femoral Artery/drug effects , Head-Down Tilt/physiology , Heart Rate/drug effects , Humans , Middle Cerebral Artery/diagnostic imaging , Middle Cerebral Artery/drug effects , Oxygen Consumption/drug effects , Resistance Training , Ultrasonography, Doppler , Vascular Resistance/drug effects , Weightlessness CountermeasuresABSTRACT
Long duration habitation on the International Space Station (ISS) is associated with chronic elevations in arterial blood pressure in the brain compared with normal upright posture on Earth and elevated inspired CO(2). Although results from short-duration spaceflights suggested possibly improved cerebrovascular autoregulation, animal models provided evidence of structural and functional changes in cerebral vessels that might negatively impact autoregulation with longer periods in microgravity. Seven astronauts (1 woman) spent 147 ± 49 days on ISS. Preflight testing (30-60 days before launch) was compared with postflight testing on landing day (n = 4) or the morning 1 (n = 2) or 2 days (n = 1) after return to Earth. Arterial blood pressure at the level of the middle cerebral artery (BP(MCA)) and expired CO(2) were monitored along with transcranial Doppler ultrasound assessment of middle cerebral artery (MCA) blood flow velocity (CBFV). Cerebrovascular resistance index was calculated as (CVRi = BP(MCA)/CBFV). Cerebrovascular autoregulation and CO(2) reactivity were assessed in a supine position from an autoregressive moving average (ARMA) model of data obtained during a test where two breaths of 10% CO(2) were given four times during a 5-min period. CBFV and Doppler pulsatility index were reduced during -20 mmHg lower body negative pressure, with no differences pre- to postflight. The postflight indicator of dynamic autoregulation from the ARMA model revealed reduced gain for the CVRi response to BP(MCA) (P = 0.017). The postflight responses to CO(2) were reduced for CBFV (P = 0.056) and CVRi (P = 0.047). These results indicate that long duration missions on the ISS impaired dynamic cerebrovascular autoregulation and reduced cerebrovascular CO(2) reactivity.
Subject(s)
Astronauts , Blood Pressure/physiology , Carbon Dioxide/blood , Cerebrovascular Circulation/physiology , Homeostasis/physiology , Space Flight , Adult , Blood Flow Velocity/physiology , Female , Humans , Male , Middle Aged , Middle Cerebral Artery/diagnostic imaging , Middle Cerebral Artery/physiology , UltrasonographyABSTRACT
Increased incidence of orthostatic hypotension and presyncopal symptoms in young women could be related to hormonal factors that might be isolated by comparing cardiovascular and cerebrovascular responses to postural change in young and older men and women. Seven young women, 11 young men, 10 older women (>1 yr postmenopausal, no hormone therapy), and 9 older men participated in a supine-to-sit-to-stand test while measuring systemic hemodynamics, end-tidal Pco(2), and blood flow velocity of the middle cerebral artery (MCA). Women had a greater reduction in stroke volume index compared with age-matched men (change from supine to standing: young women: -22.9 ± 1.6 ml/m(2); young men: -14.4 ± 2.4 ml/m(2); older women: -17.4 ± 3.3 ml/m(2); older men: -13.8 ± 2.2 ml/m(2)). This was accompanied by offsetting changes in heart rate, particularly in young women, resulting in no age or sex differences in cardiac output index. Mean arterial pressure (MAP) was higher in older subjects and increased with movement to upright postures. Younger men and women had higher forearm vascular resistance that increased progressively in the upright posture compared with older men and women. There was no difference between sexes or ages in total peripheral resistance index. Women had higher MCA velocity, but both sexes had reduced MCA velocity while upright, which was a function of reduced blood pressure at the MCA and a significant reduction in end-tidal Pco(2). The reductions in stroke volume index suggested impaired venous return in women, but augmented responses of heart rate and forearm vascular resistance protected MAP in younger women. Overall, these results showed significant sex and age-related differences, but compensatory mechanisms preserved MAP and MCA velocity in young women.
Subject(s)
Aging , Cerebrovascular Circulation , Hemodynamics , Hypotension, Orthostatic/etiology , Middle Cerebral Artery/physiopathology , Postmenopause , Posture , Adult , Age Factors , Analysis of Variance , Blood Flow Velocity , Blood Pressure , Female , Heart Rate , Humans , Hypotension, Orthostatic/diagnostic imaging , Hypotension, Orthostatic/physiopathology , Male , Middle Aged , Middle Cerebral Artery/diagnostic imaging , Ontario , Plethysmography , Risk Assessment , Risk Factors , Sex Factors , Stroke Volume , Supine Position , Ultrasonography, Doppler, Transcranial , Vascular Resistance , Young AdultABSTRACT
The objective of this study is to assess by echography and Doppler the Cerebral (Vmca), Aortic (Vao) and Femoral (Vfem) arterial flow velocity and calf vein (Tibial, Gastrocnemius) section (Tib, Gast) during orthostatic intolerance (OI) test after a 60-day, head down tilt bed rest (HDBR). Twenty-four women (25-40 years) underwent a 60-day HDBR at -6°: eight as control (Con), eight with exercise against lower body negative pressure (Ex-Lb) and eight with nutrition supplement (Nut). Before and after (R0) HDBR, all subjects underwent a 10-min, 80° tilt followed by progressive LBNP until presyncope. After the post-HDBR Tilt + LBNP test, two groups were identified: finishers (F, n = 11) who completed the Tilt and non-finishers (NF, n = 13). A higher percentage decrease in Vao flow, higher percentage distension of Tib vein and a lack of increase in Vmca/Vfem ratio during the post-HDBR Tilt + LBNP compared to pre-HDBR were correlated to OI, but not all of these abnormal responses were present in each of the NF subjects. Abnormal responses were more frequent in Con and Nut than in Ex-Lb subjects. (1) HDBR did not affect the cardiac, arterial and venous responses to the orthostatic test to the same extent in each subject. (2) Exercise within LBNP partially preserved the cardiovascular response to Tilt, while Nutrition supplementation had no efficacy. (3) Cerebral/femoral flow ratio and aortic flow were the parameters most closely related to OI. (4) Reduction in aortic flow was not the major hemodynamic change preceding syncope.
Subject(s)
Aorta/physiology , Arteries/physiology , Bed Rest , Brain/physiology , Cerebrovascular Circulation/physiology , Postural Balance/physiology , Veins/physiology , Adult , Blood Flow Velocity/physiology , Brain/blood supply , Female , HumansABSTRACT
Early evidence from long-duration flights indicates general cardiovascular deconditioning, including reduced arterial baroreflex gain. The current study investigated the spontaneous baroreflex and markers of cardiovascular control in six male astronauts living for 2-6 mo on the International Space Station. Measurements were made from the finger arterial pressure waves during spontaneous breathing (SB) in the supine posture pre- and postflight and during SB and paced breathing (PB, 0.1 Hz) in a seated posture pre- and postflight, as well as early and late in the missions. There were no changes in preflight measurements of heart rate (HR), blood pressure (BP), or spontaneous baroreflex compared with in-flight measurements. There were, however, increases in the estimate of left ventricular ejection time index and a late in-flight increase in cardiac output (CO). The high-frequency component of RR interval spectral power, arterial pulse pressure, and stroke volume were reduced in-flight. Postflight there was a small increase compared with preflight in HR (60.0 ± 9.4 vs. 54.9 ± 9.6 beats/min in the seated posture, P < 0.05) and CO (5.6 ± 0.8 vs. 5.0 ± 1.0 l/min, P < 0.01). Arterial baroreflex response slope was not changed during spaceflight, while a 34% reduction from preflight in baroreflex slope during postflight PB was significant (7.1 ± 2.4 vs. 13.4 ± 6.8 ms/mmHg), but a smaller average reduction (25%) during SB (8.0 ± 2.1 vs. 13.6 ± 7.4 ms/mmHg) was not significant. Overall, these data show no change in markers of cardiovascular stability during long-duration spaceflight and only relatively small changes postflight at rest in the seated position. The current program routine of countermeasures on the International Space Station provided sufficient stimulus to maintain cardiovascular stability under resting conditions during long-duration spaceflight.
Subject(s)
Baroreflex/physiology , Cardiovascular Deconditioning/physiology , Cardiovascular Physiological Phenomena , Space Flight , Adult , Arteries/physiology , Arteries/physiopathology , Astronauts , Blood Pressure/physiology , Cardiac Output/physiology , Heart Rate/physiology , Heart Ventricles/physiopathology , Humans , Male , Middle Aged , Posture/physiology , Respiration , Stroke Volume/physiology , Time FactorsABSTRACT
Arterial stiffness is an established cardiovascular risk factor influencing haemodynamic properties in the microcirculation. We tested the hypothesis that increased arterial stiffness is associated with an increase in cerebrovascular resistance in the elderly. Brachial-ankle pulse wave velocity (baPWV), using arterial tonometry, and anterior cerebral blood flow (aCBF), using extracranial ultrasound, were measured in 26 participants (67-92 years). Non-parametric statistics examined relationships between age, blood pressure, baPWV, cerebrovascular resistance (CVRi) and aCBF. Bivariate analysis suggested that baPWV was the only vascular characteristic associated with CVRi (r(s)=0.59; P=0.002). CVRi was strongly correlated with aCBF (r(s)=-0.89; P<0.001). Furthermore, compared with participants in the lower three quartiles of baPWV (LO), those in the upper quartile (HI) had elevated CVRi (median (interquartile range); HI: 0.240 (0.143) mm Hg ml(-1) min(-1); LO: 0.197 (0.072) mm Hg ml(-1) min(-1); P=0.02), and tended to have lower aCBF (HI: 394 (155) ml min(-1); LO: 459 (154) ml min(-1); P=0.09). This study found a positive correlation between baPWV and CVRi in the elderly, suggesting that haemodynamic characteristics associated with arterial aging influence cerebral circulation.
Subject(s)
Aging/physiology , Cerebrovascular Disorders/epidemiology , Cerebrovascular Disorders/physiopathology , Hypertension/epidemiology , Hypertension/physiopathology , Vascular Resistance , Age Distribution , Aged , Aged, 80 and over , Ankle Brachial Index , Blood Flow Velocity , Cerebrovascular Circulation , Cerebrovascular Disorders/diagnostic imaging , Female , Humans , Hypertension/diagnostic imaging , Male , Middle Aged , Pulsatile Flow , Risk Factors , UltrasonographyABSTRACT
We quantified the impact of a 60-day head-down tilt bed rest (HDBR) with countermeasures on the arterial response to supine lower body negative pressure (LBNP). Twenty-four women [8 control (Con), 8 exercise + LBNP (Ex-LBNP), and 8 nutrition (Nut) subjects] were studied during LBNP (0 to -45 mmHg) before (pre) and on HDBR day 55 (HDBR-55). Left ventricle diastolic volume (LVDV) and mass, flow velocities in the middle cerebral artery (MCA flow) and femoral artery (femoral flow), portal vein cross-sectional area (portal flow), and lower limb resistance (femoral resistance index) were measured. Muscle sympathetic nerve activity (MSNA) was measured in the fibular nerve. Subjects were identified as finishers or nonfinishers of the 10-min post-HDBR tilt test. At HDBR-55, LVDV, mass, and portal flow were decreased from pre-HDBR (P < 0.05) in the Con and Nut groups only. During LBNP at HDBR-55, femoral and portal flow decreased less, whereas leg MSNA increased similarly, compared with pre-HDBR in the Con, Nut, and NF groups; 11 of 13 nonfinishers showed smaller LBNP-induced reductions in both femoral and portal flow (less vasoconstriction), whereas 10 of 11 finishers maintained vasoconstriction in either one or both regions. The relative distribution of blood flow in the cerebral versus portal and femoral beds during LBNP [MCA flow/(femoral + portal flow)] increased or reduced < 15% from pre-HDBR in 10 of 11 finishers but decreased > 15% from pre-HDBR in 11 of 13 nonfinishers. Abnormal vasoconstriction in both the portal and femoral vascular areas was associated with orthostatic intolerance. The vascular deconditioning was partially prevented by Ex-LBNP.
Subject(s)
Bed Rest/adverse effects , Cardiovascular Deconditioning , Dietary Proteins/administration & dosage , Exercise , Lower Body Negative Pressure , Lower Extremity/blood supply , Orthostatic Intolerance/prevention & control , Splanchnic Circulation , Weightlessness Countermeasures , Cardiac Output , Cerebrovascular Circulation , Female , Femoral Artery/physiopathology , Head-Down Tilt/adverse effects , Humans , Middle Cerebral Artery/physiopathology , Muscle, Skeletal/blood supply , Muscle, Skeletal/innervation , Orthostatic Intolerance/etiology , Orthostatic Intolerance/physiopathology , Portal Vein/physiopathology , Regional Blood Flow , Space Flight , Sympathetic Nervous System/physiopathology , Vascular Resistance , Vasoconstriction , Weightlessness Simulation/adverse effectsABSTRACT
We examined the oxygen uptake (VO2) and carbon dioxide output (VCO2) during completion of a circuit developed for testing fire fighters and related performance time to laboratory measures of fitness. Twenty-two healthy university students (ten women) were trained in the tasks then performed the circuit as quickly as possible. Breath-by-breath gas exchange and heart rate were continuously measured with a portable system. Median circuit time was 6:13 (min:s, 25-75% = 5:46-6:42) for men and 7:25 (25-75% = 6:49-10:21) for 8 women finishers (P = 0.023), and VO2 averaged 68 and 64% VO2max for the men and women during the circuit. Both men and women had high respiratory exchange ratios (>1.0) suggesting marked anaerobic energy contribution. Physiological variables associated with circuit time were assessed by backward stepwise regression yielding a significant model that included only peak work rate during arm cranking exercise as a function of circuit completion time across men and women combined (P < 0.001). For men, but especially for women, the time required for the simulated victim drag (68.2 kg mannequin) was positively correlated with total time to complete the other circuit elements (r = 0.51, r = 0.96 respectively). The simple correlation between circuit time and VO2max (mL/kg/min) revealed poor relationships for men (r = -0.37, P > 0.05) and women (r = 0.20, P > 0.05). These data demonstrated that upper body fitness as reflected by peak work rate during arm cranking correlated with total circuit time for the men and women in our population sample.
Subject(s)
Fires , Occupational Health , Oxygen Consumption/physiology , Physical Fitness/physiology , Pulmonary Gas Exchange/physiology , Adult , Energy Metabolism/physiology , Female , Heart Rate/physiology , Humans , Male , Models, Biological , Physical Endurance/physiology , Predictive Value of Tests , Regression AnalysisABSTRACT
The objective of this study was to quantify by echography the changes in the intramuscular [gastrocnemius (Gast)] and nonintramuscular [posterior tibial (Tib)] calf veins cross-sectional area (CSA) and the superficial tissue thickness (STth) in response to lower body negative pressure (LBNP) after 60-day head-down bed rest (HDBR). Twenty-four healthy women (25-40 yr) were divided into three groups: control (Con), treadmill-LBNP and flywheel (Ex-Lb), nutrition (Nut; protein supplement). All underwent a LBNP (0 and -45 mmHg) before and on day 55 of HDBR. Subjects were identified as finisher (F) or nonfinisher (NF) of a 10-min tilt test after 60 days of HDBR. There were no differences in resting CSA of the Tib and Gast veins on HDBR day 55 compared with pre-HDBR for the Ex-Lb, Con and Nut, or the F groups; however, for NF both the Tib and Gast vein CSA at rest were significantly smaller after HDBR. At -45 mmHg LBNP, Tib and Gast CSAs were not significantly different from before HDBR in all groups (Ex-Lb, Con, Nut, F, NF). However, percent change in CSA of both veins from rest to -45 mmHg LBNP was significantly greater in the Con and Nut groups compared with Ex-Lb, and also NF compared with F. Similarly, the percent increase in STth on going from rest to -45 mmHg was higher after HDBR in the Con and Nut groups compared with Ex-Lb, as well as NF compared with F. These results showed that the Ex-Lb countermeasure minimized the bed rest effect on leg vein capacitance (CSA percent change) and STth increase during LBNP, whereas Nut had no effect and that higher leg vein and superficial tissue capacitance were associated with reduced orthostatic tolerance.