Hemodynamic and Cerebrovascular Responses to an Acute Bout of Blood Flow Restriction Resistance Exercise

Blood flow restriction (BFR) training is a novel exercise modality characterized by restricting blood flow to active muscles by the use of an occlusive device. A hallmark of this training is the use of lighter resistance loads, making it a potentially valuable tool for the elderly as well as patients exercising in a rehabilitative setting. Despite the growing interest in this novel mode of exercise, no investigation has comprehensively assessed the combined arterial pressure and cerebrovascular responses (flow and oxygenation) to BFR training, factors which may limit its application for cardiac and stroke rehabilitation. One concern about these applications is the potential for an amplification of the exercise pressor reflex, which could cause an unsafe rise in arterial blood pressure. The aim of this investigation was to compare the hemodynamic and cerebrovascular responses between BFR resistance exercise and traditional resistance exercise (TE). We hypothesized that the exercise-induced elevation in arterial pressure and cerebral blood flow would be attenuated with BFR, due to the use of lower workloads. Five healthy human volunteers (3 males, 2 females; age, 25.4±1.1 years) performed 3 sets of 10 repetitions of bilateral leg press with (BFR) or without (TE) bilateral blood flow restriction (220 mmHg cuff pressure), separated by 1-min rest periods (randomized, cross-over design). BFR was performed at 20% of 1 repetition maximum (1RM) while TE was performed at 65% of 1RM. Heart rate (HR) and arterial pressures were collected via ECG and finger photoplethysmography. Middle cerebral artery blood velocity (MCAv) was measured via transcranial Doppler ultrasound, and oxygen saturation of the frontal cortex (ScO2) was measured via near-infrared spectroscopy. Rate pressure product (RPP) was calculated as systolic arterial pressure multiplied by HR, and used as an index of myocardial oxygen demand. Mean arterial pressure (MAP) and RPP were both higher during TE compared with BFR during sets 2 and 3 (MAP: TE, 116±10 mmHg vs. BFR, 104±6 mmHg for BFR, P=0.05 (Set 3); RPP: TE, 16229±2387 mmHg*bpm vs. BFR, 11889±978 mmHg*bpm, P≤0.02 (Set 3)). While MCAv and ScO2 increased with exercise (

Siluro-Devonian graptolite stratigraphy of the Catalonian Coastal Ranges

Two facies characterize the Silurian and lower Devonian of the Catalonian Coastal Ranges, namely euxinic and pelagic carbonate facies. The first, is represented by black shales in which the atavus, acinaces, cyphus, triangulatus, convolutus, ?sedgwickii, ellesae and tumescens zones have been recognized. The graptolite succesion is far from complete on present evidence, but this is probably due to unfavorable environmental (taphonomic) conditions. This facies is similar to that prevailing throughout the Iberian massif and most of western Europe. The pelagic carbonate facies is peculiar to the Pridoli and lower Devonian and corresponds to the facies type prevailing in the Western Mediterranean Area. It is characterized by the nodular texture of limestones and marls, with all gradations between nodular limestones, marls and slates. Massive nodular limestone, occur in the lower partof the sequence (La Creu Formation) while the alternation of limestones, marls and slates charaterizes the upper part (Olorda Formation). Orthoconic cephalopds, crinoids, conodonts and tentaculites are the most common fossils present; graptolites occur in some shale horizons in the lower part of the Olorda Formation. These graptolites give strong indications of the uniformis and hercynicus zones (Lochkovian). The uppermost part of the sequence has not provided any graptolite fauna, but according their dacrioconarid fauna it corresponds probably to the Pragian

Siluro-Devonian graptolite stratigraphy of the Catalonian Coastal Ranges

Two facies characterize the Silurian and lower Devonian of the Catalonian Coastal Ranges, namely euxinic and pelagic carbonate facies. The first, is represented by black shales in which the atavus, acinaces, cyphus, triangulatus, convolutus, ?sedgwickii, ellesae and tumescens zones have been recognized. The graptolite succesion is far from complete on present evidence, but this is probably due to unfavorable environmental (taphonomic) conditions. This facies is similar to that prevailing throughout the Iberian massif and most of western Europe. The pelagic carbonate facies is peculiar to the Pridoli and lower Devonian and corresponds to the facies type prevailing in the Western Mediterranean Area. It is characterized by the nodular texture of limestones and marls, with all gradations between nodular limestones, marls and slates. Massive nodular limestone, occur in the lower partof the sequence (La Creu Formation) while the alternation of limestones, marls and slates charaterizes the upper part (Olorda Formation). Orthoconic cephalopds, crinoids, conodonts and tentaculites are the most common fossils present; graptolites occur in some shale horizons in the lower part of the Olorda Formation. These graptolites give strong indications of the uniformis and hercynicus zones (Lochkovian). The uppermost part of the sequence has not provided any graptolite fauna, but according their dacrioconarid fauna it corresponds probably to the Pragian

Resting sympathetic baroreflex sensitivity in subjects with low and high tolerance to central hypovolemia induced by lower body negative pressure

Central hypovolemia elicited by orthostasis or hemorrhage triggers sympathetically-mediated baroreflex responses to maintain organ perfusion; these reflexes are less sensitive in patients with orthostatic intolerance, and during conditions of severe blood loss, may result in cardiovascular collapse (decompensatory or circulatory shock). The ability to tolerate central hypovolemia is variable and physiological factors contributing to tolerance are emerging. We tested the hypothesis that resting muscle sympathetic nerve activity (MSNA) and sympathetic baroreflex sensitivity (BRS) are attenuated in male and female subjects who have low tolerance (LT) to central hypovolemia induced by lower body negative pressure (LBNP). MSNA and diastolic arterial pressure (DAP) were recorded in 47 human subjects who subsequently underwent LBNP to tolerance (onset of presyncopal symptoms). LT subjects experienced presyncopal symptoms prior to completing LBNP of -60 mm Hg, and subjects with high tolerance (HT) experienced presyncopal symptoms after completing LBNP after -60 mmHg. Contrary to our hypothesis, resting MSNA burst incidence was not different between LT and HT subjects, and was not related to time to presyncope. BRS was assessed as the slope of the relationship between spontaneous fluctuations in DAP and MSNA during 5 min of supine rest. MSNA burst incidence/DAP correlations were greater than or equal to 0.5 in 37 subjects (LT: n= 9; HT: n=28), and BRS was not different between LT and HT (-1.8 ± 0.3 vs. -2.2 ± 0.2 bursts•(100 beats)-1•mmHg-1, p=0.29). We conclude that tolerance to central hypovolemia is not related to either resting MSNA or sympathetic BRS

Influence of Controlled Breathing on Cerebrovascular Control During Upright Tilt

Arterial pressures oscillate with the frequency of respiration, and these oscillations are translated directly to the cerebrovasculature. For this reason, intrinsic cerebrovascular control is assessed at the low frequency (LF; .07-.2 Hz). When humans breathe spontaneously, it is possible that breathing frequency encroaches on these non-respiratory rhythms, thereby confounding the interpretation of intrinsic cerebrovascular control. PURPOSE: To test the hypothesis that controlled breathing (CB) decreases, and spontaneous breathing (SB) increases the reliance of cerebral blood velocity on arterial pressure within the LF range in both the supine and upright postures. METHODS: We recorded ECG, finger arterial pressure (Finometer), transcranial Doppler ultrasound of the middle cerebral artery, and end-tidal CO₂ in 20 healthy male volunteers (24±2 yrs). Ten subjects breathed in time to a metronome set at a pace of 15 breaths/min (CB), and ten subjects breathed spontaneously (SB). Both groups were studied in the supine and head-up tilt (HUT) positions for 5-min. Reliance of mean cerebral blood velocity (CBVmean) on mean arterial pressure (MAP) was assessed over the LF with cross-spectral coherence analysis (COH). RESULTS: Respiratory rates were not different between CB and SB during supine (p=.86), but were lower for SB compared with CB during HUT (11.7±.7 vs. 14.8±.1; p\u3c.001). End-tidal CO₂ was decreased by CB during both supine and HUT (p\u3c.05). CBVmean was decreased with CB during supine (p=.04), but was similar between CB and SB during HUT (p=.14). Neither LFMAP nor LFCBVmean oscillations were different in the supine position (p\u3e.6), but were increased (with a trend for LFMAP) with SB during HUT (p=.003 for LF CBVmean and p=.09 for LFMAP). COH was not different in the supine position between CB and SB (.42±.05 for CB and .61±.06 SB; p=.13), but was lower for CB in the HUT position (.55±.05 for CB and .78±.08 for SB; p=.02). CONCLUSION: Reliance of CBVmean on MAP is increased in the LF range when subjects breathe spontaneously during HUT. We attribute changes in COH during HUT to entrainment of respiratory-mediated arterial pressure fluctuations on the cerebrovasculature. However, the potential confounding influence of hypocapnia warrants further investigation

Heart Rate Variability during Simulated Hemorrhage with Lower Body Negative Pressure in High and Low Tolerant Subjects

Heart rate variability (HRV) decreases during hemorrhage, and has been proposed as a new vital sign to assess cardiovascular stability in trauma patients. The purpose of this study was to determine if any of the HRV metrics could accurately distinguish between individuals with different tolerance to simulated hemorrhage. Specifically, we hypothesized that (1) HRV would be similar in low tolerant (LT) and high tolerant (HT) subjects at presyncope when both groups are on the verge of hemodynamic collapse; and (2) HRV could distinguish LT subjects at presyncope from hemodynamically stable HT subjects (i.e., at a submaximal level of hypovolemia). Lower body negative pressure (LBNP) was used as a model of hemorrhage in healthy human subjects, eliciting central hypovolemia to the point of presyncopal symptoms (onset of hemodynamic collapse). Subjects were classified as LT if presyncopal symptoms occurred during the −15 to −60 mmHg levels of LBNP, and HT if symptoms occurred after LBNP of −60 mmHg. A total of 20 HRV metrics were derived from R–R interval measurements at the time of presyncope, and at one level prior to presyncope (submax) in LT and HT groups. Only four HRV metrics (Long-range Detrended Fluctuation Analysis, Forbidden Words, Poincaré Plot Descriptor Ratio, and Fractal Dimensions by Curve Length) supported both hypotheses. These four HRV metrics were evaluated further for their ability to identify individual LT subjects at presyncope when compared to HT subjects at submax. Variability in individual LT and HT responses was so high that LT responses overlapped with HT responses by 85–97%. The sensitivity of these HRV metrics to distinguish between individual LT from HT subjects was 6–33%, and positive predictive values were 40–73%. These results indicate that while a small number of HRV metrics can accurately distinguish between LT and HT subjects using group mean data, individual HRV values are poor indicators of tolerance to hypovolemia

Cerebrovascular Hemodynamics during Concentric and Eccentric Phases of Heavy Resistance Exercise

Rapid and drastic fluctuations in arterial blood pressures, such as those occurring during heavy resistance exercise pose a unique challenge to the maintenance of cerebral perfusion. During high-intensity leg cycling, regulation of cerebral perfusion is reduced by rapid decreases in beat-to-beat fluctuations in blood pressure (diastolic phase) rather than rapid increases (systolic phase). The purpose of this study was to test the hypothesis that rhythmic heavy resistance exercise will similarly impair the regulation of cerebral blood flow during the diastolic phase of beat-to-beat fluctuations in pressure. We studied seven healthy male subjects. Beat-to-beat finger arterial pressures, and middle cerebral artery blood velocity (MCAv) were measured during 10 repetitions (REP) of rhythmic high intensity leg press exercise. Velocities and arterial pressures were evaluated during both the isotonic concentric and eccentric phases of each REP. The Gosling pulsatility index (PI) of MCAv of each REP was calculated as MCAv systolic-MCAv diastolic/MCAv mean. During the concentric phase, systolic arterial pressures progressively increased from REP 1 through REP 10 (P \u3c 0.001), while systolic MCAv was not different across all REPs (P \u3e0.2). Diastolic arterial pressures during the eccentric phase also increased from REP 1 through REP 10 (P = 0.03) however diastolic MCAv decreased during REPs 7-10 compared with REP 2 (P ≤ 0.02). MCAv PI also increased during REP 7-10 compared to REP 2 (P ≤ 0.02). Similar to high-intensity leg cycling, our data suggest that during rhythmic high-intensity leg press exercise, cerebral perfusion is well controlled during periods of rapid increases in blood pressure, but regulation of cerebral perfusion is impaired during the diastolic phase of beat-to-beat fluctuations in pressure

The position of graptolites within Lower Palaeozoic planktic ecosystems.

An integrated approach has been used to assess the palaeoecology of graptolites both as a discrete group and also as a part of the biota present within Ordovician and Silurian planktic realms. Study of the functional morphology of graptolites and comparisons with recent ecological analogues demonstrates that graptolites most probably filled a variety of niches as primary consumers, with modes of life related to the colony morphotype. Graptolite coloniality was extremely ordered, lacking any close morphological analogues in Recent faunas. To obtain maximum functional efficiency, graptolites would have needed varying degrees of coordinated automobility. A change in lifestyle related to ontogenetic changes was prevalent within many graptolite groups. Differing lifestyle was reflected by differing reproductive strategies, with synrhabdosomes most likely being a method for rapid asexual reproduction. Direct evidence in the form of graptolithophage 'coprolitic' bodies, as well as indirect evidence in the form of probable defensive adaptations, indicate that graptolites comprised a food item for a variety of predators. Graptolites were also hosts to a variety of parasitic organisms and provided an important nutrient source for scavenging organisms

How does diet influence our lives? Evaluating the relationship between isotopic signatures and mortality patterns in italian roman imperial and medieval periods

The present research investigates the relationship between dietary habits and mortality patterns in the Roman Imperial and Medieval periods. The reconstructions of population dynamics and subsistence strategies provide a fascinating source of information for understanding our history. This is particularly true given that the changes in social, economic, political, and religious aspects related to the transition from the Roman period to the Middle Ages have been widely discussed. We analyzed the isotopic and mortality patterns of 616 individuals from 18 archeological sites (the Medieval Latium sites of Colonna, Santa Severa, Allumiere, Cencelle, and 14 Medieval and Imperial funerary contexts from Rome) to compile a survivorship analysis. A semi-parametric approach was applied, suggesting variations in mortality patterns between sexes in the Roman period. Nitrogen isotopic signatures influenced mortality in both periods, showing a quadratic and a linear effect for Roman Imperial and Medieval populations, respectively. No influence of carbon isotopic signatures has been detected for Roman Imperial populations. Conversely, increased mortality risk for rising carbon isotopic values was observed in Medieval samples