Baroreflex control of the rat tail circulation in normothermia and hyperthermia

1989 ◽  
Vol 66 (3) ◽  
pp. 1234-1241 ◽  
Author(s):  
D. S. O'Leary ◽  
J. M. Johnson
Keyword(s):  
Venous Occlusion ◽  
Baroreflex Control ◽  
Thermal Status ◽  
In Series ◽  
Phenylephrine Infusion ◽  
Baroreceptor Reflex Control ◽  
Conscious Animals ◽  
Rat Tail ◽  
Tail Blood

The role of thermoregulatory background in the baroreceptor reflex control of the tail circulation was investigated 1) in anesthetized rats with a constant flow technique and 2) in conscious rats by measuring tail blood flow (venous occlusion plethysmography). In series I, during normothermia, systemic intravenous phenylephrine infusion increased mean arterial pressure (MAP) by 61.0 +/- 3.6 mmHg and induced a reflex decrease in tail perfusion pressure (TPP) from 105.0 +/- 6.3 to 84.2 +/- 4.4 mmHg (P less than 0.005). Hyperthermia decreased TPP to 66.5 +/- 5.1 mmHg (P less than 0.001) and abolished the TPP response to increased MAP (P greater than 0.05). Increases in MAP via systemic infusion of whole blood caused reductions in TPP during normothermia but failed to reduce TPP further during hyperthermia. Graded decreases in MAP during both normothermia and hyperthermia caused tail vasoconstriction. The increase in TPP was greater (P less than 0.025) during hyperthermia. In series II, conscious animals showed similar responses to hemorrhage. Graded decreases in MAP produced graded decreases in tail vascular conductance (TVC, ml.100 ml-1.min-1.100 mmHg-1). The slope of the TVC-MAP relationship averaged 0.011 +/- 0.003 TVC U/mmHg during normothermia and was markedly steeper (P less than 0.01) during hyperthermia (1.99 +/- 0.39 TVC U/mmHg). Thus the participation of the cutaneous vasculature of the rat in baroreceptor reflexes depends on thermal status, probably through the level of background sympathetic vasoconstrictor nerve activity.

Body temperature control of rat tail blood flow

1983 ◽  
Vol 245 (3) ◽  
pp. R426-R432 ◽  
Author(s):  
E. R. Raman ◽  
M. F. Roberts ◽  
V. J. Vanhuyse
Keyword(s):  
Blood Flow ◽  
Heat Exchange ◽  
Body Temperature ◽  
Heat Flow ◽  
Thermal Conductance ◽  
Venous Occlusion ◽  
Albino Rats ◽  
Blood Flows ◽  
Rat Tail ◽  
Tail Blood

Tail blood flow (BF) and heat flow (HF) were measured in five albino rats during transients in rectal temperature (Tre) caused by body heating at rest. During heating, tail temperature (Tt) was kept at 15, 20, 25, 30, 35, or 42 degrees C by enclosing the tail in a water-perfused tube. Thermal conductance (K) was computed as HF/(Tre-Tt). BF was measured by venous occlusion plethysmography. Heating caused a rise in Tre that was accompanied by proportional increases in both K and BF. The ratio R = K/BF represents conductance per unit BF and reflects the amount of heat exchange for a given BF. R can thus be used to estimate the distribution of BF within the tail. R was independent of Tre at all Tt, indicating that BF distribution is controlled by the tail. R was low at low Tt and rose at higher Tt. This suggests that at low Tt, blood flows primarily in central veins of the tail and at higher Tt blood flows in peripheral tail veins.

Role of Dissipation Characteristics in Predicting Flow from Dissimilar Centrifugal Pumps

1994 ◽  
Vol 208 (4) ◽  
pp. 285-294 ◽  
Author(s):  
E A Bunt ◽  
B Parsons ◽  
F Holtzhausen
Keyword(s):  
Flow Characteristics ◽  
Maximum Flow ◽  
Centrifugal Pumps ◽  
Graphical Solution ◽  
Dissipative Flow ◽  
In Series ◽  
Lower Maximum ◽  
Output Field ◽  
High Series

Examination of flows in a particular case of dissimilar pumps coupled in series or in parallel (without check valves) showed that the ‘classical’ graphical solution of combined characteristics in the [+H, +Q] quadrant did not accord with the output field in certain regions. To predict the full flow fields, it was necessary to take into account dissipative flow characteristics in two other quadrants: for low-output parallel flow (when there is still flow available from the pump of higher head when the ‘weaker’ pump's flow has been reduced to zero), that in the [+H, –Q] quadrant; and for high series flow (after the output head of the pump of lower maximum flow has been reduced to zero), that in the [–H, +Q] quadrant. This problem does not arise when the pumps have identical characteristics.

Induction of Vasoactive Substances Differs in LPS-Induced and TF-Induced DIC Models in Rats

2002 ◽  
Vol 88 (10) ◽  
pp. 663-667 ◽  
Author(s):  
Mariko Okudaira ◽  
Tomotaka Yoshida ◽  
Yasuo Ontachi ◽  
Masahide Yamazaki ◽  
Eriko Morishita ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Organ Dysfunction ◽  
Disseminated Intravascular Coagulation ◽  
Rat Model ◽  
Plasma Levels ◽  
Fibrinolytic Activity ◽  
Tail Vein ◽  
Vasoactive Substances ◽  
Rat Tail

SummaryWe have investigated the role of two vasoactive substances, nitric oxide (NO) and endothelin (ET), in the pathophysiology of disseminated intravascular coagulation (DIC), using two types of DIC models. Experimental DIC was induced by sustained infusion of 0.1, 1, 10, or 50 mg/kg lipopolysaccharide (LPS), or 3.75 U/kg thromboplastin (TF), for 4 h via the rat tail vein. Plasma levels of both NOX (metabolites of NO) and ET were significantly increased following infusion of 0.1 mg/kg or greater of LPS in the LPS-induced DIC rat model. In contrast, although a marked increase in the plasma levels of NOX was observed, only a slight increase in plasma ET levels was seen in the TF-induced DIC rat model. No significant differences in the plasma levels of platelets or thrombin-ATIII complex were observed among the TF-induced and LPS (50 mg/dl)-induced DIC models. However, plasma NOX levels rose significantly higher in the TF-induced model, relative to the LPS-induced model (p <0.01). Conversely, plasma ET levels were significantly greater after LPS-induction, compared to TF-induction, of DIC (p <0.01). Vasoconstriction, as well as depressed fibrinolytic activity, may be additional factors leading to severe organ dysfunction in the LPS-induced DIC rat model. Moreover, vasodilatation, as well as enhanced fibrinolytic activity, may help to prevent rats from severe organ dysfunction in the TF-induced DIC model. Our results suggest that modulator of vasoactive substances should be examined in the treatment of DIC.

scholarly journals Identifying the role of group III/IV muscle afferents in the carotid baroreflex control of mean arterial pressure and heart rate during exercise

2018 ◽  
Vol 596 (8) ◽  
pp. 1373-1384 ◽  
Author(s):  
Thomas J. Hureau ◽  
Joshua C. Weavil ◽  
Taylor S. Thurston ◽  
Ryan M. Broxterman ◽  
Ashley D. Nelson ◽  
...  
Keyword(s):  
Heart Rate ◽  
Mean Arterial Pressure ◽  
Arterial Pressure ◽  
Muscle Afferents ◽  
Baroreflex Control ◽  
Group Iii ◽  
Carotid Baroreflex

Abstract 15839: Effect of Serotonin Neuron Depletion on Arterial Blood Pressure Regulation in Young Rats

Circulation ◽  
2014 ◽  
Vol 130 (suppl_2) ◽  
Author(s):  
Jennifer Magnusson ◽  
Kevin Cummings
Keyword(s):  
Blood Pressure ◽  
Arterial Blood Pressure ◽  
Recovery Period ◽  
Sudden Infant Death ◽  
Sudden Infant ◽  
Sprague Dawley ◽  
Baroreflex Control ◽  
Hypoxic Conditions ◽  
Arterial Blood

Infants dying of Sudden Infant Death Syndrome (SIDS) have reduced brainstem serotonin (5-hydroxytryptamine, 5-HT) where some cases die following episodes of severe bradycardia and hypoxemia. The specific role of central 5-HT in resting arterial blood pressure (BP) and on baroreflex sensitivity during neonatal life has not been studied. In adult animals, systemic depletion of 5-HT increases BP with no effect on heart rate (HR) and reduces the sensitivity of the baroreflex. Other studies have also shown that a loss of central 5-HT beginning in embryogenesis reduces resting BP and HR in adulthood. Based on these reports, we hypothesized that loss of brainstem 5-HT neurons in the neonatal period would reduce baseline BP and HR as well as reduce baroreflex gain. To test this, we utilized 3-week old Sprague Dawley rats treated centrally with 5,7-dihydroxytryptamine (5,7-DHT, n=4; ~120 ug in saline, i.c.v.), a chemical that is toxic to serotonergic neurons. Littermate controls were injected with saline (CTRL, n=5, ~3ul, i.c.v.). We measured BP with a femoral artery catheter. HR was derived from BP. Following a recovery period, we measured resting variables for 15 minutes and then injected phenylephrine (PE; 3mg/kg s.c.) followed by sodium nitroprusside (SNP; 2.5mg/kg s.c.), separated by 15 minutes, to induce pressor or depressor responses, respectively. For both responses, baroreflex gain was calculated as the [[Unable to Display Character: &#8710;]]HR at the maximum [[Unable to Display Character: &#8710;]]BP following drug injection. We found that a loss of 5-HT neurons did not alter baseline BP (p>0.05) but did reduce baseline HR when compared to control littermates (p<0.02). 5-HT neuron deficiency tended to reduce baroreflex gain in response to PE (CTRL: -2.756 ± 0.483 beats/mmHg; 5,7-DHT: -1.499 ± 0.348 beats/mmHg; p=0.058), but not SNP (CTRL: -2.408 ± 0.351 beats/mmHg; 5,7-DHT: -3.316 ± 1.214 beats/mmHg; p>0.05). Our data indicate that brainstem 5-HT maintains resting HR, and is involved in baroreflex control of HR in response to hypertensive stimuli. Reduced brainstem 5-HT may predispose an infant to SIDS via altered autonomic control of BP and HR. The role of 5-HT in BP regulation during hypoxic conditions remains to be elucidated.

Endogenous ANG II supports lumbar sympathetic activity in conscious sodium-deprived rats: role of area postrema

1998 ◽  
Vol 275 (1) ◽  
pp. R46-R55 ◽  
Author(s):  
Ling Xu ◽  
John P. Collister ◽  
John W. Osborn ◽  
Virginia L. Brooks
Keyword(s):  
Sympathetic Activity ◽  
Food Restriction ◽  
Sympathetic Nerve Activity ◽  
Area Postrema ◽  
Ang Ii ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Maximal Gain

This study tests the hypothesis that the area postrema (AP) is necessary for endogenous ANG II to chronically maintain lumbar sympathetic nerve activity (LSNA) and heart rate (HR) in conscious sodium-deprived rats. The effect of the ANG II type 1-receptor antagonist, losartan, on LSNA and HR was determined in rats that were either AP lesioned (APX) or sham lesioned. The sham rats were divided into groups, with (SFR) or without (SAL) food restriction, to control for the decreased food intake of APX rats. Before losartan, basal mean arterial pressure (MAP), HR, and baroreflex control of LSNA and HR were similar between groups, with the exception of lower maximal reflex LSNA and higher maximal gain of the HR-MAP curve in APX rats. In all groups, losartan similarly shifted ( P < 0.01) the LSNA-MAP curve to the left without altering maximal gain. Losartan also decreased ( P < 0.05) minimal LSNA in all groups, and suppressed ( P < 0.01) maximal LSNA (% of control) in SFR (240 ± 13 to 205 ± 15) and SAL (231 ± 21 to 197 ± 26) but not APX (193 ± 10 to 185 ± 8) rats. In general, losartan similarly shifted the HR-MAP curve to a lower MAP in all groups. The results suggest that the AP is not necessary for endogenous ANG II to chronically support LSNA and HR at basal and elevated MAP levels in sodium-deprived rats. However, the AP is required for endogenous ANG II to increase maximal reflex LSNA at low MAP levels.

scholarly journals The Effect of the Pivot Stiffness on the Performances of Five-Pad Tilting Pad Bearings

Lubricants ◽  
2019 ◽  
Vol 7 (7) ◽  
pp. 61 ◽  
Author(s):  
Phuoc Vinh Dang ◽  
Steven Chatterton ◽  
Paolo Pennacchi
Keyword(s):  
Excitation Frequency ◽  
Experimental Results ◽  
Dynamic Force ◽  
Dynamic Coefficients ◽  
Pivot Bearing ◽  
Tilting Pad ◽  
In Series ◽  
Stiffness And Damping ◽  
Tilting Pad Journal Bearings

The role of the pivot flexibility in tilting-pad journal bearings (TPJBs) has become essential, particularly for bearings working at high applied load and relatively high rotor speeds. Predictions from a simple bearing model with rigid pivots show incorrect estimation of the dynamic coefficients in comparison with the experimental results. Normally, the more flexible the pad pivot, the lower the dynamic coefficients because the stiffness of the pivot takes in series with the stiffness and damping of the oil film. This paper investigates the influence of pivot stiffness on the dynamic force coefficients of two different five-pad TPJBs as a function of the applied static load and excitation frequency: rocker-backed pivot and spherical pivot bearings. In order to highlight the effect of the pivot stiffness in the spherical pivot bearing, displacement restriction components and elastic copper made shims have been used. Firstly, a thermo-elasto-hydrodynamic model for the static and dynamic characteristics of the two bearings is described. This model takes into account the flexibility of both pad and pivot. The pivot stiffnesses calculated by means of the Hertz theory and those obtained by experiments have been introduced and compared in the model. The clearance profiles of two tested bearing and the shaft center loci obtained by measurement and prediction are also shown. The dynamic coefficients of the two bearings obtained from the numerical simulation were compared with the experimental results. By the analysis it can be concluded that the effect of the pivot flexibility on the clearance profile, the shaft locus and on the dynamic coefficients is very significant. More important, it is important to estimate the pivot stiffness of each single pad using experimental measurements.

Role of the descending pressor pathway in the conscious and pentobarbital-anesthetized dog

1978 ◽  
Vol 234 (2) ◽  
pp. H152-H156
Author(s):  
G. S. Geis ◽  
G. Barratt ◽  
R. D. Wurster
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Cardiovascular Control ◽  
Conscious Dogs ◽  
Cardiovascular Parameters ◽  
Bilateral Carotid ◽  
Before And After ◽  
Anesthetized Dogs ◽  
Conscious Animals

Resting cardiovascular parameters and the responses to bilateral carotid occlusions (BCO) were monitored in pentobarbital-anesthetized and conscious dogs before and after placing lesions in the dorsolateral funiculi at C7-C8 and after spinal transections at C7. Pre- and postlesion blood pressure (BP) and heart rate (HR) responses to exercise were also monitored. The lesions significantly attenuated the responses to BCO and decreased resting BP in anesthetized dogs. Yet neither resting HR in anesthetized or conscious dogs nor the resting BP in conscious dogs was affected by the lesions. Subsequent spinal transections significantly decreased resting HR and BP and the responses to BCO but did not affect the BP response to BCO in anesthetized dogs as compared with corresponding postlesion parameters. BP responses to exercise were significantly attenuated by the lesions, but HR responses were not affected. Since stimulation and BP studies indicated that the descending pressor pathway had been ablated, the data suggest that the pathway mediates BP and HR responses to BCO in pentobarbital-anesthetized and conscious dogs. It does not maintain resting HR in anesthetized or conscious animals, and the resting BP in conscious dogs. This pathway is important for BP responses to exercise but is not necessary for HR responses. Finally, other spinal pathways are involved in cardiovascular control.

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