scholarly journals Cardiovascular responses to antigravity muscle loading during head-down tilt at rest and after dynamic exercises

2018 ◽  
Author(s):  
Cristiano Alessandro ◽  
Amirehsan Sarabadani Tafreshi ◽  
Robert Riener
Keyword(s):  
Muscle Activity ◽  
Human Subjects ◽  
Cardiovascular Responses ◽  
Bed Rest ◽  
Cardiovascular Regulation ◽  
Upright Position ◽  
The Body ◽  
Healthy Human ◽  
Arterial Blood ◽  
Muscle Loading

AbstractThe physiological processes underlying hemodynamic homeostasis can be modulated by muscle activity and gravitational loading. The effects of antigravity muscle activity on cardiovascular regulation has been observed during orthostatic stress. Here, we evaluated such effects during head-down tilt (HDT). In this posture, the gravitational gradient along the body is different than in upright position, leading to increased central blood volume and reduced venous pooling. We compared the cardiovascular signals obtained with and without antigravity muscle loading during HDT in healthy human subjects, both at rest and during recovery from leg-press exercises. Further, we compared such cardiovascular responses to those obtained during upright position. We found that loading the antigravity muscles during HDT at rest led to significantly higher values of arterial blood pressure than without muscle loading, and restored systolic values to those observed during upright posture. Maintaining muscle loading post-exercise altered the short-term cardiovascular responses, but not the values of the signals five minutes after the exercise. These results demonstrate that antigravity muscle activity modulates cardiovascular regulation during HDT. This modulation should therefore be considered when interpreting cardiovascular responses to conditions that affect both gravity loading and muscle activity, for example bed rest or microgravity.

Respiratory measurements of cardiac output: from elegant idea to useful test

2004 ◽  
Vol 96 (2) ◽  
pp. 428-437 ◽  
Author(s):  
Gabriel Laszlo
Keyword(s):  
Cardiac Output ◽  
Human Subjects ◽  
Venous Blood ◽  
The Body ◽  
Mixed Venous Blood ◽  
Indirect Determination ◽  
Arterial Blood ◽  
Pulmonary Capillary ◽  
Pulmonary Arterial ◽  
Mixed Venous

The measurement of cardiac output was first proposed by Fick, who published his equation in 1870. Fick's calculation called for the measurement of the contents of oxygen or CO2 in pulmonary arterial and systemic arterial blood. These values could not be determined directly in human subjects until the acceptance of cardiac catheterization as a clinical procedure in 1940. In the meanwhile, several attempts were made to perfect respiratory methods for the indirect determination of blood-gas contents by respiratory techniques that yielded estimates of the mixed venous and pulmonary capillary gas pressures. The immediate uptake of nonresident gases can be used in a similar way to calculate cardiac output, with the added advantage that they are absent from the mixed venous blood. The fact that these procedures are safe and relatively nonintrusive makes them attractive to physiologists, pharmacologists, and sports scientists as well as to clinicians concerned with the physiopathology of the heart and lung. This paper outlines the development of these techniques, with a discussion of some of the ways in which they stimulated research into the transport of gases in the body through the alveolar membrane.

Heart rate control and mechanical cardiopulmonary coupling to assess central volume: a systems analysis

2002 ◽  
Vol 283 (5) ◽  
pp. R1210-R1220 ◽  
Author(s):  
Riccardo Barbieri ◽  
John K. Triedman ◽  
J. Philip Saul
Keyword(s):  
Human Subjects ◽  
Venous Pressure ◽  
Multivariate Techniques ◽  
Healthy Human ◽  
Sinus Arrhythmia ◽  
Arterial Blood ◽  
Reflex Tachycardia ◽  
Central Volume ◽  
Central Hypervolemia

Small negative changes of central volume reduce cardiac output without significant alterations of arterial blood pressure (ABP), suggesting an adequate regulatory response. Furthermore, evidence has arisen supporting a Bainbridge reflex (tachycardia with hypervolemia) in humans. To investigate these phenomena, multivariate autoregressive techniques were used to evaluate the beat-to-beat interactions between respiration, R-R interval, and ABP at six levels of decreased and increased central volume. With reductions of central volume below control, baroreflex and respiratory sinus arrhythmia gains were reduced, while with increases of volume above control, gains increased for the first two levels but decreased again at the highest volume level, suggesting the presence of a Bainbridge reflex in healthy human subjects. The mechanical influence of respiration on central venous pressure (CVP) had an unexpected shift in phase at the point of mild central hypervolemia, with the expected negative relation at lower volumes (inspiration lowers CVP) but a positive relation at higher volumes (inspiration raises CVP). We conclude that multivariate techniques can quantify the relations between a variety of respiratory and hemodynamic parameters, allowing for the in vivo assessment of complex cardiorespiratory interactions during manipulations of central volume. The results identify the presence of a Bainbridge reflex in humans and suggest that short-term cardiovascular control is optimized at mild hypervolemia.

scholarly journals Fractionation of muscle activity in rapid responses to startling cues

2017 ◽  
Vol 117 (4) ◽  
pp. 1713-1719 ◽  
Author(s):  
Lauren R. Dean ◽  
Stuart N. Baker
Keyword(s):  
Muscle Activity ◽  
Human Subjects ◽  
Activity Patterns ◽  
Reaction Times ◽  
Principal Component ◽  
Similar Proportion ◽  
Descending Pathways ◽  
Healthy Human ◽  
Wide Range ◽  
The Right

Movements in response to acoustically startling cues have shorter reaction times than those following less intense sounds; this is known as the StartReact effect. The neural underpinnings for StartReact are unclear. One possibility is that startling cues preferentially invoke the reticulospinal tract to convey motor commands to spinal motoneurons. Reticulospinal outputs are highly divergent, controlling large groups of muscles in synergistic patterns. By contrast the dominant pathway in primate voluntary movement is the corticospinal tract, which can access small groups of muscles selectively. We therefore hypothesized that StartReact responses would be less fractionated than standard voluntary reactions. Electromyogram recordings were made from 15 muscles in 10 healthy human subjects as they carried out 32 varied movements with the right forelimb in response to startling and nonstartling auditory cues. Movements were chosen to elicit a wide range of muscle activations. Multidimensional muscle activity patterns were calculated at delays from 0 to 100 ms after the onset of muscle activity and subjected to principal component analysis to assess fractionation. In all cases, a similar proportion of the total variance could be explained by a reduced number of principal components for the startling and the nonstartling cue. Muscle activity patterns for a given task were very similar in response to startling and nonstartling cues. This suggests that movements produced in the StartReact paradigm rely on similar contributions from different descending pathways as those following voluntary responses to nonstartling cues. NEW & NOTEWORTHY We demonstrate that the ability to activate muscles selectively is preserved during the very rapid reactions produced following a startling cue. This suggests that the contributions from different descending pathways are comparable between these rapid reactions and more typical voluntary movements.

scholarly journals Cardiovascular responses to the ingestion of sugary drinks using a randomised cross-over study design: does glucose attenuate the blood pressure-elevating effect of fructose?

2014 ◽  
Vol 112 (2) ◽  
pp. 183-192 ◽  
Author(s):  
Erik K. Grasser ◽  
Abdul Dulloo ◽  
Jean-Pierre Montani
Keyword(s):  
Blood Pressure ◽  
Endothelial Function ◽  
Study Design ◽  
Human Subjects ◽  
Cardiovascular Responses ◽  
Healthy Human ◽  
Sugary Drinks ◽  
Healthy Human Subjects ◽  
Microvascular Endothelial ◽  
Microvascular Endothelial Function

Overconsumption of sugar-sweetened beverages has been implicated in the pathogenesis of CVD. The objective of the present study was to elucidate acute haemodynamic and microcirculatory responses to the ingestion of sugary drinks made from sucrose, glucose or fructose at concentrations similar to those often found in commercial soft drinks. In a randomised cross-over study design, twelve young healthy human subjects (seven men) ingested 500 ml tap water in which was dissolved 60 g of either sucrose, glucose or fructose, or an amount of fructose equivalent to that present in sucrose (i.e. 30 g fructose). Continuous cardiovascular monitoring was performed for 30 min before and at 60 min after ingestion of sugary drinks, and measurements included beat-to-beat blood pressure (BP) and impedance cardiography. Additionally, microvascular endothelial function testing was performed after iontophoresis of acetylcholine and sodium nitroprusside using laser Doppler flowmetry. Ingestion of fructose (60 or 30 g) increased diastolic and mean BP to a greater extent than the ingestion of 60 g of either glucose or sucrose (P< 0·05). Ingestion of sucrose and glucose increased cardiac output (CO; P< 0·05), index of contractility (P< 0·05) and stroke volume (P< 0·05), but reduced total peripheral resistance (TPR; P< 0·05), which contrasts with the tendency of fructose (60 and 30 g) to increase resistance. Microvascular endothelial function did not differ in response to the ingestion of various sugary drinks. In conclusion, ingestion of fructose, but not sucrose, increases BP in healthy human subjects. Although sucrose comprises glucose and fructose, its changes in TPR and CO are more related to glucose than to fructose.

scholarly journals Changes in Cerebral Blood Flow during Steady-State Cycling Exercise: A Study Using Oxygen-15-Labeled Water with PET

2013 ◽  
Vol 34 (3) ◽  
pp. 389-396 ◽  
Author(s):  
Mikio Hiura ◽  
Tadashi Nariai ◽  
Kenji Ishii ◽  
Muneyuki Sakata ◽  
Keiichi Oda ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Steady State ◽  
Human Subjects ◽  
Insular Cortex ◽  
Cardiovascular Responses ◽  
Healthy Human ◽  
Cycling Exercise ◽  
Positron Emission ◽  
Steady State Cycling

Cerebral blood flow (CBF) during dynamic exercise has never been examined quantitatively using positron emission tomography (PET). This study investigated changes in CBF that occur over the course of a moderate, steady-state cycling exercise. Global and regional CBF (gCBF and rCBF, respectively) were measured using oxygen-15-labeled water (H215O) and PET in 10 healthy human subjects at rest (Rest), at the onset of exercise (Ex1) and at a later phase in the exercise (Ex2). At Ex1, gCBF was significantly ( P<0.01) higher (27.9%) than at Rest, and rCBF was significantly higher than at Rest in the sensorimotor cortex for the bilateral legs (M1Leg and S1Leg), supplementary motor area (SMA), cerebellar vermis, cerebellar hemispheres, and left insular cortex, with relative increases ranging from 37.6% to 70.5%. At Ex2, gCBF did not differ from Rest, and rCBF was significantly higher (25.9% to 39.7%) than at Rest in only the M1Leg, S1Leg, and vermis. The areas showing increased rCBF at Ex1 were consistent with the central command network and the anatomic pathway for interoceptive stimuli. Our results suggest that CBF increases at Ex1 in parallel with cardiovascular responses then recovers to the resting level as the steady-state exercise continues.

Spinai cord serotonin receptors in cardiovascular regulation and potentiation of the pressor response to intrathecal substance P after serotonin depletion

1993 ◽  
Vol 71 (7) ◽  
pp. 453-464 ◽  
Author(s):  
Haroutioun Hasséssian ◽  
Philippe Poulat ◽  
Edith Hamel ◽  
Tomás A. Reader ◽  
Réjean Couture
Keyword(s):  
Spinal Cord ◽  
Substance P ◽  
Pressor Response ◽  
Cardiovascular Effects ◽  
Cardiovascular Responses ◽  
Cardiovascular Regulation ◽  
Cardiac Effect ◽  
Receptor Subtypes ◽  
Dependent Manner ◽  
Arterial Blood

The aim of this study was to characterize, in conscious rats, the spinal cord 5-hydroxytryptamine (5-HT) receptors involved in mean arterial pressure (MAP) and heart rate (HR) regulation as well as to examine the influence of bulbospinal 5-HT fibers on cardiovascular responses to intrathecal (i.t.) substance P (SP). The i.t. injection of 5-HT or 5-carboxamidotryptamine (5-CT) (5-HT1A, 1B, 1D agonist) reduced MAP and increased HR in a dose-dependent manner. In contrast, the agonists 8-hydroxy-2-(di-n-propylamino)tetraiin (8-OH-DPAT, 5-HT1A agonist) and α-CH3-5-HT (5-HT1C and 5-HT2) only caused a decrease in HR, while the agonist 2-CH3-5-HT (5-HT3) was devoid of cardiovascular effects. The vasodepressor response to 5-CT was antagonized by methiothepin but not affected by mesulergine, ketanserin, propranolol, or yohimbine. However, all five antagonists reduced the HR increase to 5-CT. Ketanserin, propranolol, mesulergine, yohimbine, and methysergide were without effect on resting MAP, while methiothepin reduced MAP. Methiothepin, ketanserin, and methysergide increased resting HR, yet the other antagonists had no effect on this parameter. Rats treated with p-chlorophenylalanine or 5,7-dihydroxytryptamine, but not with 6-hydroxydopamine, exhibited higher resting HR than that of control rats. Although the resting MAP was unaffected, the pressor response to i.t. SP was significantly enhanced by either 5-HT toxin. The results suggest that the receptor mediating the depressor response to 5-HT and 5-CT conforms with the broad pharmacological profile of a 5-HT1-like receptor and is unlikely to be of the 5-HT2 or 5-HT3 subtype. Since the HR response evoked by 5-CT was blocked by antagonists that exhibit affinities for various 5-HT receptor subtypes, it is suggested that a nonspecific blockade or, alternatively, that more than one receptor contributes to this cardiac effect. In addition, the results raise the possibility that a spinal 5-HT input, likely mediated by 5-HT2 receptors, tonically inhibits HR. Hence, an antagonistic interaction between 5-HT and SP is proposed to play a role in the control of arterial blood pressure in the spinal cord.Key words: 5-hydroxytryptamine, 5-HT receptors, substance P, spinal cord, cardiovascular regulation.

Dissociated Hysteresis of Static Ocular Counterroll in Humans

2006 ◽  
Vol 95 (4) ◽  
pp. 2222-2232 ◽  
Author(s):  
A. Palla ◽  
C. J. Bockisch ◽  
O. Bergamin ◽  
D. Straumann
Keyword(s):  
Second Harmonic ◽  
Human Subjects ◽  
Body Position ◽  
Three Dimensional ◽  
Upright Position ◽  
Whole Body ◽  
Eye Position ◽  
Healthy Human ◽  
Ocular Counterroll ◽  
Head Roll

In stationary head roll positions, the eyes are cyclodivergent. We asked whether this phenomenon can be explained by a static hysteresis that differs between the eyes contra- (CE) and ipsilateral (IE) to head roll. Using a motorized turntable, healthy human subjects ( n = 8) were continuously rotated about the earth-horizontal naso-occipital axis. Starting from the upright position, a total of three full rotations at a constant velocity (2°/s) were completed (acceleration = 0.05°/s2, velocity plateau reached after 40 s). Subjects directed their gaze on a flashing laser dot straight ahead (switched on 20 ms every 2 s). Binocular three-dimensional eye movements were recorded with dual search coils that were modified (wires exiting inferiorly) to minimize torsional artifacts by the eyelids. A sinusoidal function with a first and second harmonic was fitted to torsional eye position as a function of torsional whole body position at constant turntable velocity. The amplitude and phase of the first harmonic differed significantly between the two eyes (paired t-test: P < 0.05): on average, counterroll amplitude of IE was larger [CE: 6.6 ± 1.6° (SD); IE: 8.1 ± 1.7°), whereas CE showed more position lag relative to the turntable (CE: 12.5 ± 10.7°; IE: 5.1 ± 8.7°). We conclude that cyclodivergence observed during static ocular counterroll is mainly a result of hysteresis that depends on whether eyes are contra- or ipsilateral to head roll. Static hysteresis also explains the phenomenon of residual torsion, i.e., an incomplete torsional return of the eyes when the first 360° whole body rotation was completed and subjects were back in upright position (extorsion of CE: 2.0 ± 0.10°; intorsion of IE: 1.4 ± 0.10°). A computer model that includes asymmetric backlash for each eye can explain dissociated torsional hysteresis during quasi-static binocular counterroll. We hypothesize that ocular torsional hysteresis is introduced at the level of the otolith pathways because the direction-dependent torsional position lag of the eyes is related to the head roll position and not the eye position.

Cardiovascular responses to upright tilting in healthy subjects

1988 ◽  
Vol 74 (1) ◽  
pp. 17-22 ◽  
Author(s):  
R. Hainsworth ◽  
Y. M. H. Al-Shamma
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Cardiac Output ◽  
Diastolic Pressure ◽  
Age Groups ◽  
Cardiovascular Responses ◽  
Healthy Population ◽  
Healthy Human ◽  
Arterial Blood ◽  
Postural Responses

1. The cardiovascular responses to passive upright tilting were determined in healthy human subjects of various ages using entirely ‘non-invasive’ techniques. Cardiac output was determined by a single breath method and arterial blood pressure by an automatic sphygmomanometer. 2. Steady-state responses were achieved within 4–6 min from the onset of the tilt and were maintained for at least 15 min. 3. The reproducibilities of the responses to tilting by 60°, expressed as two standard deviations of the differences between responses on two occasions (mean responses in parentheses), were: cardiac output ±0.70 (−1.41) litre/min, heart rate ±7.6 (+ 14.7) beats/min, systolic blood pressure ± 15.5 (+ 1.0), and diastolic blood pressure μ13.1 (+ 13.6)mmHg. 4. Tilting by 20° resulted in no significant responses but between 20° and 60° responses were linearly related to the angle of tilt. 5. Supine values and responses to tilting by 60° were compared in subjects in four age groups between 20 and 80 years. With increasing age, the supine values of cardiac output declined and those of arterial blood pressures increased. Responses of heart rate, cardiac output and diastolic pressure declined by increasing age. These results, obtained from a healthy population, provide reference values for comparison with individuals who may have deficient postural responses.

scholarly journals The effects of milk as a food matrix for polyphenols on the excretion profile of cocoa ( − )-epicatechin metabolites in healthy human subjects

2008 ◽  
Vol 100 (4) ◽  
pp. 846-851 ◽  
Author(s):  
Elena Roura ◽  
Cristina Andrés-Lacueva ◽  
Ramon Estruch ◽  
M. Lourdes Mata Bilbao ◽  
Maria Izquierdo-Pulido ◽  
...  
Keyword(s):  
Human Subjects ◽  
The Body ◽  
Food Matrix ◽  
Healthy Human ◽  
Cocoa Powder ◽  
Whole Milk ◽  
Metabolite Profiles ◽  
Healthy Human Subjects ◽  
The Matrix ◽  
Excretion Rates

The effect of different food matrices on the metabolism and excretion of polyphenols is uncertain. The objective of the study was to evaluate the possible effect of milk on the excretion of ( − )-epicatechin metabolites from cocoa powder after its ingestion with and without milk. Twenty-one volunteers received the following three test meals each in a randomised cross–over design with a 1-week interval between meals: (1) 250 ml whole milk as a control; (2) 40 g cocoa powder dissolved in 250 ml whole milk (CC–M); (3) 40 g cocoa powder dissolved in 250 ml water (CC–W). Urine was collected before consumption and during the 0–6, 6–12 and 12–24 h periods after consumption. ( − )-Epicatechin metabolite excretion was measured using liquid chromatography–MS. One ( − )-epicatechin glucuronide and three ( − )-epicatechin sulfates were detected in urine excreted after the intake of the two cocoa beverages (CC–M and CC–W). The results show that milk does not significantly affect the total amount of metabolites excreted in urine. However, differences in metabolite excretion profiles were observed; there were changes in the glucuronide and sulfate excretion rates, and the sulfation position between the period of excretion and the matrix. The matrix in which polyphenols are consumed can affect their metabolism and excretion, and this may affect their biological activity. Thus, more studies are needed to evaluate the effect of these different metabolite profiles on the body.

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