Impairment of carotid-cardiac vagal baroreflex in wheelchair-dependent quadriplegics

1991 ◽  
Vol 260 (3) ◽  
pp. R576-R580 ◽  
Author(s):  
V. A. Convertino ◽  
W. C. Adams ◽  
J. D. Shea ◽  
C. A. Thompson ◽  
G. W. Hoffler
Keyword(s):  
Buffer Capacity ◽  
Prolonged Exposure ◽  
Bed Rest ◽  
Maximum Slope ◽  
Stimulus Response ◽  
Carotid Baroreceptors ◽  
Blood Pressures ◽  
Pressure Changes ◽  
Neck Chamber ◽  
Interval Response

The incidence of orthostatic hypotension can increase after prolonged exposure to chair rest and bedrest and is associated with post-bed rest impairment of the carotid-cardiac baroreflex response. We therefore hypothesized that the hypotension observed in humans confined to wheelchairs may be manifested by a reduced baroreflex sensitivity. We compared baroreflex responses of 16 wheelchair-dependent (WCD) quadriplegics with those of 15 able-bodied subjects (ABS) matched for age, height, and weight. Beat-to-beat R-R intervals were measured during application of graded pressures from 40 to -65 mmHg using a neck chamber for noninvasive stimulation of the carotid baroreceptors. Changes of R-R intervals were plotted against carotid distending pressures. The maximum slope of the stimulus-response relationship was greater (P less than 0.0001) in ABS (6.1 +/- 0.6 ms/mmHg) than in WCD (2.6 +/- 0.4 ms/mmHg). The range of the R-R interval response, i.e., the capacity to buffer blood pressure changes, was only 138 +/- 19 ms in WCD compared with 253 +/- 19 ms in ABS (P less than 0.001). Mean sitting systolic-to-diastolic blood pressures in WCD (92/60 mmHg) were less (P less than 0.0001) than in ABS (120/77 mmHg), although there were no significant differences between groups in supine resting blood pressures. Chronic loss of stimulation to carotid baroreceptors by routine standing posture is associated with attenuated sensitivity and reduced buffer capacity of the arterial baroreflex and hypotension during sitting in WCD patients.

Reproducibility of human vagal carotid baroreceptor-cardiac reflex responses

1992 ◽  
Vol 263 (1) ◽  
pp. R215-R220 ◽  
Author(s):  
D. L. Eckberg ◽  
V. A. Convertino ◽  
J. M. Fritsch ◽  
D. F. Doerr
Keyword(s):  
Correlation Coefficients ◽  
Experimental Session ◽  
Experimental Conditions ◽  
Reduced Pressure ◽  
Maximum Slope ◽  
Reflex Responses ◽  
Stimulus Response ◽  
Carotid Baroreceptor ◽  
Neck Pressure ◽  
Pressure Changes

Published information on the reproducibility of human baroreflex responses in the absence of interventions is limited. Therefore, we analyzed retrospectively vagally mediated carotid baroreceptor-cardiac reflex responses of 34 healthy young adult volunteers whom we studied twice, 7-10 days apart (all 34 subjects) or 10 wk apart (8 subjects). We delivered a sequence of neck pressure changes during held expiration: A computer-driven bellows initially raised pressure to approximately 40 mmHg for five heart beats, and then reduced pressure in a stepwise series of R-wave-triggered 15-mmHg decrements to about -65 mmHg. R-R interval changes were plotted as functions of the carotid distending (systolic less neck) pressure occurring within each interval. Each experimental session yielded one stimulus-response relation, which comprised the average of seven separate trials. Six measures were derived from these relations: minimum, maximum, and range of R-R intervals; maximum slope; and operational point [(R-R interval shortening/R-R interval range) x 100%]. Linear regression correlation coefficients for measurements made on two occasions were all highly significant (range: 0.64-0.99). Our results indicate that human vagally mediated carotid baroreceptor-cardiac reflex responses, studied serially under exacting experimental conditions, are highly reproducible.

Changes in Blood Pressure, Heart Rate and Breathing Rate During Moderate Swimming Activity in Rainbow Trout

1967 ◽  
Vol 46 (2) ◽  
pp. 307-315 ◽  
Author(s):  
E. DON STEVENS ◽  
D. J. RANDALL
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Rainbow Trout ◽  
Venous Blood ◽  
The Body ◽  
Swimming Activity ◽  
Breathing Rate ◽  
Blood Pressures ◽  
Ventral Aorta ◽  
Pressure Changes

1. Changes in blood pressure in the dorsal aorta, ventral aorta and subintestinal vein, as well as changes in heart rate and breathing rate during moderate swimming activity in the rainbow trout are reported. 2. Blood pressures both afferent and efferent to the gills increased during swimming and then returned to normal levels within 30 min. after exercise. 3. Venous blood pressure was characterized by periodic increases during swimming. The pressure changes were not in phase with the body movements. 4. Although total venous return to the heart increased during swimming, a decreased blood flow was recorded in the subintestinal vein. 5. Heart rate and breathing rate increased during swimming and then decreased when swimming ceased. 6. Some possible mechanisms regulating heart and breathing rates are discussed.

Baroreflex responses to acute changes in blood volume in humans

1990 ◽  
Vol 259 (4) ◽  
pp. R792-R798 ◽  
Author(s):  
C. A. Thompson ◽  
D. L. Tatro ◽  
D. A. Ludwig ◽  
V. A. Convertino
Keyword(s):  
Lower Body Negative Pressure ◽  
Venous Pressure ◽  
Peripheral Resistance ◽  
Cardiac Response ◽  
Stimulus Response ◽  
Cardiopulmonary Baroreflex ◽  
Low Levels ◽  
Acute Changes ◽  
Pressure Changes ◽  
Forearm Vascular Resistance

To test the hypothesis that acute changes in plasma volume affect the stimulus-response relations of high- and low-pressure baroreflexes, eight men (27-44 yr old) underwent measurements for carotid-cardiac and cardiopulmonary baroreflex responses under the following three volemic conditions: hypovolemic, normovolemic, and hypervolemic. The stimulus-response relation of the carotid-cardiac response curve was generated using a neck cuff device, which delivered pressure changes between +40 and -65 mmHg in continuous steps of 15 mmHg. The stimulus-response relationships of the cardiopulmonary baroreflex were studied by measurements of forearm vascular resistance (FVR) and peripheral venous pressure (PVP) during low levels of lower body negative pressure (0 to -20 mmHg). Altered vascular volume had no effect on response relations of the carotid-cardiac baroreflex but did alter the gain of the cardiopulmonary baroreflex (-7.93 +/- 1.73, -4.36 +/- 1.38, and -2.56 +/- 1.59 peripheral resistance units/mmHg for hypovolemic, normovolemic, and hypervolemic, respectively) independent of shifts in baseline FVR and PVP. These results indicate greater demand for vasoconstriction for equal reductions in venous pressure during progressive hypovolemia; this condition may compromise the capacity to provide adequate peripheral resistance during severe orthostatic stress. Fluid loading before reentry after spaceflight may act to restore vasoconstrictive capacity of the cardiopulmonary baroreflex but may not be an effective countermeasure against potential post-flight impairment of the carotid-cardiac baroreflex.

Sympathetic transients caused by abrupt alterations of carotid baroreceptor activity in humans

1982 ◽  
Vol 242 (2) ◽  
pp. H185-H190 ◽  
Author(s):  
B. G. Wallin ◽  
D. L. Eckberg
Keyword(s):  
Sympathetic Activity ◽  
Chamber Pressure ◽  
Reduced Pressure ◽  
Cardiac Responses ◽  
Carotid Baroreceptor ◽  
Sympathetic Responses ◽  
Nerve Muscle ◽  
Neck Pressure ◽  
Pressure Changes ◽  
Neck Chamber

We examined the role of carotid baroreceptors in the short-term modulation of sympathetic outflow to the muscle vascular bed and parasympathetic outflow to the heart in 10 healthy adults. Afferent carotid baroreceptor activity was modified with 30-mmHg neck suction or pressure applied during held expiration, and efferent sympathetic activity was measured with microelectrodes inserted percutaneously into peroneal nerve muscle fascicles. Sympathetic responses were conditioned importantly by directional changes of carotid transmural pressure: increased pressure (onset of neck suction or offset of neck pressure) inhibited (totally) sympathetic activity, and reduced pressure (offset of neck suction or onset of neck pressure) augmented sympathetic activity. Responses occurred after a latency of about 2 s and did not persist as long as changes of neck-chamber pressure. Cardiac intervals were prolonged by increased carotid transmural pressures and shortened by decreased carotid transmural pressures, but, in contrast to sympathetic responses, cardiac responses adapted only slightly during neck-chamber pressure changes. Our results suggest that in the human a common baroreceptor input is processed differently in central vagal and sympathetic networks. Muscle sympathetic responses to changing levels of afferent baroreceptor traffic are profound but transitory. They appear to be conditioned more by changes of arterial pressure than by its absolute levels.

Enhanced vagal baroreflex response during 24 h after acute exercise

1991 ◽  
Vol 260 (3) ◽  
pp. R570-R575 ◽  
Author(s):  
V. A. Convertino ◽  
W. C. Adams
Keyword(s):  
Acute Exercise ◽  
Systolic Pressure ◽  
Underlying Mechanism ◽  
Chamber Pressure ◽  
External Application ◽  
Maximum Slope ◽  
Acute Bout ◽  
Graded Exercise ◽  
Pressure Stability ◽  
Neck Chamber

We evaluated carotid-cardiac baroreflex responses in eight normotensive men (25-41 yr) on two different test days, each separated by at least 1 wk. On one day, baroreflex response was tested before and at 3, 6, 12, 18, and 24 h after graded supine cycle exercise to volitional exhaustion. On another day, this 24-h protocol was repeated with no exercise (control). Beat-to-beat R-R intervals were measured during external application of graded pressures to the carotid sinuses from 40 to -65 mmHg; changes of R-R intervals were plotted against carotid pressure (systolic pressure minus neck chamber pressure). The maximum slope of the response relationship increased (P less than 0.05) from preexercise to 12 h (3.7 +/- 0.4 to 7.1 +/- 0.7 ms/mmHg) and remained significantly elevated through 24 h. The range of the R-R response was also increased from 217 +/- 24 to 274 +/- 32 ms (P less than 0.05). No significant differences were observed during the control 24-h period. An acute bout of graded exercise designed to elicit exhaustion increases the sensitivity and range of the carotid-cardiac baroreflex response for 24 h and enhances its capacity to buffer against hypotension by increasing heart rate. These results may represent an underlying mechanism that contributes to blood pressure stability after intense exercise.

The Autonomic Nervous Tone Abnormalities in the Genesis of the Impaired Baroreflex Responsiveness in Borderline Hypertensive Subjects

1982 ◽  
Vol 62 (6) ◽  
pp. 581-588 ◽  
Author(s):  
Massimo Volpe ◽  
Bruno Trimarcoy ◽  
Bruno Ricciardelli ◽  
Carlo Vigorito ◽  
Nicola De Luca ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Arterial Pressure ◽  
Normal Subjects ◽  
Tissue Pressure ◽  
Combined Administration ◽  
Propranolol Treatment ◽  
The Mean ◽  
Pressure Changes ◽  
Neck Chamber

1. The effects of intravenous administration of neostigmine and propranolol, individually or in combination, on baroreflex responsiveness have been evaluated in 18 borderline hypertensive subjects and in 14 age-matched control subjects. 2. Baroreceptor sensitivity was tested by evaluating both heart rate response to phenylephrine-induced increase in arterial pressure, and heart rate and blood pressure changes induced by increasing neck-tissue pressure by means of a neck-chamber. 3. In borderline hypertensive subjects a reduced baroreflex responsiveness was demonstrated with both stimuli as compared with normal subjects. Neostigmine administration improved consistently both reflex responses. Similarly, after propranolol treatment, borderline hypertensive subjects showed a significant enhancement of the baroreflex sensitivity. Finally, the combined administration of neostigmine and propranolol restored the baroreflex responses. In fact, both the mean slopes of the regression lines between blood pressure and R-R interval after phenylephrine and the increase in mean arterial pressure and heart rate induced by the reduction in carotid transmural pressure in borderline hypertensive subjects were similar to those observed in normals. 4. These findings indicate that in borderline hypertensive subjects the impairment of baroreflex responsiveness is mainly due to abnormalities of autonomic regulation.

Cardiovascular responses to stimulation of carotid baroreceptors in healthy subjects

1988 ◽  
Vol 75 (2) ◽  
pp. 159-165 ◽  
Author(s):  
R. Hainsworth ◽  
Y. M. H. Al-Shamma
Keyword(s):  
Heart Rate ◽  
Cardiac Output ◽  
Cardiovascular Responses ◽  
Pulse Interval ◽  
Healthy Population ◽  
Control Value ◽  
Carotid Baroreceptors ◽  
Single Breath ◽  
Arterial Blood ◽  
Blood Pressures

1. Carotid baroreceptors were stimulated by application of a subatmospheric pressure to a chamber fitted round the anterior and lateral aspects of the subject's neck (neck suction). Pulse interval and heart rate were determined from an electrocardiogram, cardiac output by a single-breath method and arterial blood pressure by an automatic sphygmomanometer. 2. The maximal prolongation of the pulse interval, determined during held expiration, occurred within 2–3 s from the onset of the neck suction. All the measured variables were in steady states between 2 and 3 min from the start of neck suction. 3. Neck suction at − 10 mmHg resulted only in an immediate change in pulse interval. All variables changed approximately linearly with the magnitude of the neck suction between − 10 and − 40 mmHg. 4. The reproducibilities of the responses to neck suction at − 30 mmHg, expressed as two standard deviations of the differences between responses on two occasions, were (mean responses in parentheses): immediate pulse interval, ± 32 (+ 236) ms; steady-state heart rate, ± 2.5 (− 6.5) beats/min; cardiac output ± 0.14 (− 0.59) 1/min; systolic and diastolic blood pressures, ± 10.0 (− 16.9) and ± 5.4 (− 10.1) mmHg, respectively. 5. Control values and responses to neck suction at − 30 mmHg were compared in subjects grouped in four age bands between 19 and 80 years. With increasing age, the control value of cardiac index (cardiac output divided by calculated body surface area) decreased, systolic and diastolic pressures increased, and the responses of all the measured variables to neck suction decreased. These results, obtained from a healthy population, provide reference values for comparison with those of individuals who may have abnormal baroreceptor reflexes.

scholarly journals Skin surface cooling improves orthostatic tolerance following prolonged head-down bed rest

2011 ◽  
Vol 110 (6) ◽  
pp. 1592-1597 ◽  
Author(s):  
David M. Keller ◽  
David A. Low ◽  
Scott L. Davis ◽  
Jeff Hastings ◽  
Craig G. Crandall
Keyword(s):  
Negative Pressure ◽  
Prolonged Exposure ◽  
Lower Body Negative Pressure ◽  
Thermal Conditions ◽  
Bed Rest ◽  
Skin Surface ◽  
Stress Index ◽  
Orthostatic Tolerance ◽  
Thermal Stimulus ◽  
Surface Cooling

Prolonged exposure to microgravity, as well as its ground-based analog, head-down bed rest (HDBR), reduces orthostatic tolerance in humans. While skin surface cooling improves orthostatic tolerance, it remains unknown whether this could be an effective countermeasure to preserve orthostatic tolerance following HDBR. We therefore tested the hypothesis that skin surface cooling improves orthostatic tolerance after prolonged HDBR. Eight subjects (six men and two women) participated in the investigation. Orthostatic tolerance was determined using a progressive lower-body negative pressure (LBNP) tolerance test before HDBR during normothermic conditions and on day 16 or day 18 of 6° HDBR during normothermic and skin surface cooling conditions (randomized order post-HDBR). The thermal conditions were achieved by perfusing water (normothermia ∼34°C and skin surface cooling ∼12–15°C) through a tube-lined suit worn by each subject. Tolerance tests were performed after ∼30 min of the respective thermal stimulus. A cumulative stress index (CSI; mmHg LBNP·min) was determined for each LBNP protocol by summing the product of the applied negative pressure and the duration of LBNP at each stage. HDBR reduced normothermic orthostatic tolerance as indexed by a reduction in the CSI from 1,037 ± 96 mmHg·min to 574 ± 63 mmHg·min ( P < 0.05). After HDBR, skin surface cooling increased orthostatic tolerance (797 ± 77 mmHg·min) compared with normothermia ( P < 0.05). While the reduction in orthostatic tolerance following prolonged HDBR was not completely reversed by acute skin surface cooling, the identified improvements may serve as an important and effective countermeasure for individuals exposed to microgravity, as well as immobilized and bed-stricken individuals.

Indirect blood pressure determination by Doppler technique in renal hypertensive cats

1979 ◽  
Vol 237 (6) ◽  
pp. H720-H723 ◽  
Author(s):  
L. R. Klevans ◽  
G. Hirkaler ◽  
J. L. Kovacs
Keyword(s):  
Blood Pressure ◽  
Diastolic Pressure ◽  
Systolic Pressure ◽  
Pressure Measurements ◽  
Blood Pressure Determination ◽  
Monitoring Period ◽  
Direct Pressure ◽  
Blood Pressures ◽  
Pressure Changes ◽  
Indirect Blood Pressure

The Doppler ultrasonic recording technique was used to measure systolic and diastolic blood pressures indirectly in renal hypertensive cats. The accuracy of the method was evaluated by comparing indirect blood pressures from one leg of a cat with direct pressure measurements from the other leg. A linear relationship existed between indirect and direct systolic and diastolic pressures. The consistency of the method was assessed by measuring blood pressure during a 5-h monitoring period in normotensive and renal hypertensive cats. No significant variation occurred over this period. The sensitivity of the method to blood pressure changes was determined also. A significant reduction in systolic and diastolic pressure induced by hydralazine, 10 mg/kg po, was recorded during a 5-h monitoring period. The development of renovascular hypertension was followed for approximately 70 days. Systolic pressure rose in a logarithmic fashion from 160 to a maximum of 240 mmHg. It was concluded that the Doppler ultrasonic technique is a simple and reliable method for recording indirect blood pressure acutely and chronically in conscious unrestrained cats.

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