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At least 919 records · Page 51Linked to original sources
PubMed1986

Mechanism of anesthesia: the potency of four derivatives of octane corresponds to their hydrogen bonding capacity.

The anesthetic potency of four derivatives of n-octane was measured by tadpole righting reflex and expressed as effective millimolar concentration of drug in membrane, EDM50. Potency diminished (ED50 increased) in this order: 1-octanol, EDM50 = 5.5; 1-(2-methoxyethoxy)octane, EDM50 = 28; 1-methoxyoctane, EDM50 = 61; and 1-chlorooctane, EDM50 greater than 100. Since the aliphatic chain length was kept constant it is concluded that the differences in anesthetic potency are a consequence of the differences in head group structure. This result is predicted by a theory (Lipids 17, 1001-1003 [1982]) which holds that anesthesia is the result of a drug-induced restructuring of the hydrogen belts, those strata of the membrane that contain the hydrogen bond receiving and donating CO and OH groups of the membrane lipids and the adjoining proteins. The Meyer-Overton rule for anesthetics should be modified: chemicals induce anesthesia at equimolar in-membrane concentration provided their hydrogen-bonding parts are identical.

Anesthesia↗
PubMed2001

Sympathetic autoregulation in peripheral vascular disease.

BACKGROUND: Lower limb venous pressure increases on dependency, stimulating a local sympathetic axon reflex which triggers precapillary and arteriolar vasoconstriction. The resulting decrease in arterial calf inflow, known as the venoarteriolar response (VAR), is impaired in critical leg ischaemia. The aim of the study was to evaluate the VAR in symptomatic non-critical leg ischaemia and after restoration of leg perfusion following successful revascularization. METHODS: The study included 30 normal subjects, 30 patients with stable intermittent claudication and 30 patients with severe ischaemia who had undergone successful infrainguinal revascularization. In all patients the foot skin blood flow (flux) in the horizontal (HBF) and sitting (SBF) positions was measured using laser Doppler fluxmetry. The VAR was calculated as (HBF - SBF)/HBF x 100 per cent. The pressure that elicited the reflex (pVAR) was evaluated in the horizontal position. RESULTS: The median VAR was significantly lower in patients with stable claudication than in normal subjects or patients following successful revascularization (29.1 versus 59.5 and 63.9 per cent respectively; P < 0.0001). Similar results were obtained for the pVAR (22 versus 45 and 40 mmHg respectively; P < 0.001). There was no difference, however, in either the VAR or pVAR between normal individuals and patients following a successful bypass. CONCLUSION: Patients with claudication had a significant impairment of orthostatic sympathetic autoregulation. After successful revascularization, and in spite of the extensive disease in the receiving circulation, this autoregulation returned to normal. Presented previously to the Vascular Surgical Society in London, November 1997 and published in abstract form as Br J Surg 1998; 85: 557

Aged↗
PubMed1980

Laryngeal reflex inhibition of breathing in piglets: influences of anemia and catecholamine depletion.

Laryngeal reflex inhibition of breathing was studied in 31 piglets of both sexes varying in age from 34 to 93 days. Continuing supramaximal electrical stimulation of one superior laryngeal nerve (SLN) was associated with spontaneous resumption of breathing within 1 min in animals more than 1 mo of age. Respiratory rate and depth were reduced, however. In contrast with normal piglets, electrical stimulation of the SLN in those with severe anemia (Hct = 8.0 +/- 0.5%) caused extended apnea. An intermediate effect was observed in animals with normal hematocrits but given reserpine (2 mg/kg) 2 days prior to study. The apnea response was potentiated in these animals by reduction of the hematocrit from 22.8 +/- 3.4% to 8.4 +/- 1.1% by hemodilution. In normal piglets similar degrees of hemodilution had no discernible effects; An interrelationship between oxygen availability, adrenergic activity, and SLN-induced respiratory depression in young piglets is suggested by these findings.

Aging↗
PubMed1992

The high-frequency oscillopsia test.

There is a need to develop bedside tests of the vestibulo-ocular reflex (VOR) that could be used in the clinical situation to screen patients who may be candidates for further evaluation. In 1984 Barber described the oscillopsia test, which compared visual acuity with and without head movement. Barber indicated that head movement should occur at greater than 1 Hz. This study was performed to evaluate the oscillopsia test at higher frequencies (2 to 7 Hertz) in the hope of improving its performance. The sensitivity and specificity of this test were evaluated using three examiners (the authors) and were referenced to clinical electronystagmographic results in 115 patients and 17 control subjects. The oscillopsia test evaluated in this study was highly specific, but not highly sensitive. It did not detect vestibular loss or subjective dizziness in more than 50% of cases. The high frequency oscillopsia test does not appear to be an effective screening test for VOR abnormalities or vestibular loss.

Electronystagmography↗
PubMed1995

Otolith function tests in patients with unilateral vestibular lesions.

This study was designed to assess the utility of otolith-ocular reflex testing in patients with complete unilateral peripheral vestibular deficits. Ten subjects were given a clinical vestibular test battery (ENG & vertical rotation) and research oriented tests of otolith function including dynamic posturography with head tilt and earth-horizontal axis rotation with otolith-visual interactions. Clinical tests confirmed the presence of a vestibular deficit and the side of the lesion. The results suggested the following: posturography during head tilt is not a reliable means of detecting unilateral peripheral vestibular dysfunction, while earth-horizontal axis rotation is a reliable means of assessing asymmetric otolith function. The Bias response during earth-horizontal axis rotation was significantly less during rotation ipsilateral to the lesioned ear compared to contralateral rotation while the Mod response was normal. The optokinetic test results in these subjects were normal while otolith-visual interactions were symmetrically reduced in these patients.

Adult↗
PubMed1985

Early development in mice: II. Sensory motor behavior and genetic analysis.

The genetic and environmental bases for differences in rate of development were investigated in 2 inbred strains of mice: C57BL/6By (B) and BALB/cBy (C). Twelve motor responses, aside from individual weight, were used to measure these differences. The Recombinant Inbred Strains method was chosen to perform the genetic analysis. Overdominance is shown to be present in 2 variables alone (eye opening, weight at 10 and 20 days). In most cases, each of the response reflexes was found to be associated with several genes (locomotion, hind limb, crossed extensor, righting, vibrissae placing, bar holding). Differences across strains are associated with one segregating unit for rate of disappearance of the rooting response. This unit is mapped on the part of the 4th chromosome including the loci b and H-21. The strain distribution pattern differs for each sensory motor response, consequently no one general genetic factor of development can be advanced. Maternal effects were found for 4 variables (grasping, fore limb placing, eye opening and weight). For two responses, the F1 pups developing the fastest were reared by mothers from the slowest developing parental strain. As regards this latter finding, the authors hypothesize that mothers differ as to the quality of the environment they furnish to their young and pups differ in their ability to benefit from these environments.

Animals↗
PubMed1984

Continuous ambulatory monitoring of blood pressure and assessment of cardiovascular reflexes in the elderly hypertensive.

Thirteen elderly hypertensives underwent continuous ambulatory blood pressure (BP) monitoring and measurement of cardiovascular reflexes. The results were compared with elderly normotensives and young hypertensives studied using the same protocol. There was a greater disparity between casual systolic BP (SBP) and ambulatory awake SBP in the elderly hypertensives than either the elderly normotensives or young hypertensives. Variability of SBP was greater in the elderly than the young, whilst baroreflex activity was reduced in the elderly, and more markedly so in the elderly hypertensives. Response to tilt and pressor tests was similar for the elderly. The elderly hypertensives showed a greater fall of SBP in response to tilt and a greater rise of SBP during dynamic exercise than the young hypertensives. Stimulation of plasma renin activity (PRA) in response to upright tilt was less in the elderly hypertensives than the young hypertensives. Resting plasma noradrenaline (PNA) increased with age.

Adolescent↗
PubMed1993

Influence of gravity on the eye movement response elicited by periodic lateral linear acceleration.

Periodic linear acceleration elicits eye movements in human beings. This is generally considered to be the result of the otolithic-ocular reflex (OOR). However, otolith organs respond not only to the resultant inertial force caused by head motion, but also to the gravitational force. We investigated the influence of the resultant gravito-inertial vector on the OOR using a linear acceleration sled. Subjects were 10 healthy volunteers. The sled moving back and forth parallel to the lateral head axis stimulated the subjects. We tested each subject in 7 different positions in the pitch plane. Horizontal eye movements with nystagmic patterns were elicited by these stimuli. The results indicate that the responses were larger in the forward tilted positions than in the backward tilted positions. It can be concluded that the horizontal OOR is influenced by the gravity vector. The cause of this phenomenon is still unclear. However, it could be closely related to the nystagmus observed during off vertical axis rotation.

Acceleration↗
PubMed1997

Bedside autonomic function testing in patients with vasovagal syncope.

The factors that determine the individual susceptibility to vasovagal syncope (VVS) are largely unknown, including the role of the autonomic nervous system. We therefore studied common vagal and sympathetic reflexes in 12 patients with VVS (mean age 37 (18-75) years, 6 men). The Valsalva maneuver and deep breathing were performed to assess vagal responsiveness and mental arithmetic stress; the cold-pressor test and isometric handgrip were performed to assess sympathetic responsiveness. Standing up was performed to assess the combined responsiveness. With the exception of a subnormal response to deep breathing in one patient, all vagal tests were normal. In contrast, the response to mental stress, the cold-pressor test, and isometric handgrip was subnormal in 4 patients, 6 patients, and 4 patients, respectively. The response to standing up was normal in all patients. It is concluded that many patients with VVS are characterized by normal vagal responsiveness, but sympathetic hyporesponsiveness. Sympathetic hyporesponsiveness might explain the inadequate vasoconstruction, which plays an important, early role in VVS.

Adolescent↗
PubMedDate not supplied

Comparison of different exercise programs in the rehabilitation of patients with chronic peripheral vestibular dysfunction.

The purpose of this study was to evaluate the effects of two exercise programs on balance performance in patients with chronic peripheral vestibular dysfunction and to assess whether these exercise programs induce adaptive modifications of the vestibulo-ocular reflex (VOR). Patients were randomly assigned to one of two groups. (1) Those in the Rehab (Reh) group (n = 11) received a comprehensive exercise program that consisted of balance retraining and goal-directed eye-head exercises under combinations of varied visual and somatosensory sensory conditions. Patients received 45-minute training sessions, three times per week for 12 weeks, and were instructed on a custom home exercise program. (2) Those in the Home group (n = 12) were instructed to perform the Cooksey-Cawthorne eye-head exercises at home, on a daily basis, for 12 weeks. In addition, after completion of the exercise program and a follow-up period, 7 of the participants in the Home group (here defined as the A group) chose to enter the Reh program (here defined as the B group). Balance performance was assessed by measuring the peak-to-peak magnitude and total amount of anterior-posterior body sway, and of horizontal (shear) ground reaction force during six test conditions, in which visual and somatosensory orientation cues were reduced or altered by rotation of the visual surround or support surface in proportion to the subject's sway, and in which vision was eliminated (eyes closed). The VOR response to step chair rotations of 60 degrees/s and 120 degrees/s, and the optokinetic reflex (OKN) response to 60 degrees/s constant velocity optokinetic stimuli were recorded. Left-right difference in VOR gain, VOR time constant, and OKN gain were determined. These tests were performed 1 day prior to start of treatment (TD 1), 6 weeks after start of treatment (TD 2), at the end of the 12-week treatment period (TD 3), and 5 months after end of treatment (TD 4). The findings revealed a significant improvement in standing balance performance under dynamic conditions for patients in the Reh program (Reh and B groups) but not for patients performing the eye-head exercise (Home or A groups). Thus, even in patients with chronic vestibular dysfunction, compensation for the loss or disruption of peripheral vestibular inputs can be effectively induced by exercises that provide sensory feedback appropriate for behavioral changes involving sensory substitution or sensory-motor reorganization.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1996

Horizontal angular VOR changes in orbital and parabolic flight: human neurovestibular studies on SLS-2.

Further evidence was found for adaptive changes in the vestibular "velocity storage" (VS) component of the vestibuloocular reflex in four shuttle astronauts tested in parabolic flight and before, during, and after a 14-day mission. Nystagmus was recorded during and after 1 min of 120 degrees/s rotation. Gains and time constants were determined by computer analysis. Responses correlated with experience. Two subjects were making their first spaceflight. In parabolic flight, their time constants shortened to an average of 60% of 1 G values, presumably because unfamiliar otolith cues reduced VS. However, after 4-10 days in orbit, their time constants were similar or greater than those preflight, indicating VS recovery. The other two subjects had previously flown in space. Their time constants shortened in orbit to an average of 69% of 1 G values, indicating a persisting reduction of VS. This correlation with spaceflight experience has been seen in 9 of 11 subjects on 3 missions. Head pitch did not significantly "dump" nystagmus as it does on Earth.

Adult↗
PubMedDate not supplied

Cervico-ocular reflex in the normal adult.

(1) The cervico-ocular reflex (COR) in humans was measured while the subjects (n = 10) stood on a rotatable platform in a dark room with the head fixed by a stationary biteplate. Eye movements were measured in response to active and passive rotations about a vertical axis. (2) The COR gain (i.e., horizontal eye movement/amplitude of body rotation) was as great as 22% at low frequency of body rotation (0.025 Hz). With increasing frequency (e.g., at 0.4 Hz) the gain decreased to about 2%. (3) The phase angle of the eye movement ranged generally between -80 and -240 degrees with an average response around -180 degrees. (4) During active rotation, the COR response was similar to the responses measured during passive body rotation. (5) The principal conclusion drawn is that in normal adult humans the COR does not aid in stabilization of the image on the retina during passive or active body rotations. A theoretical function for the COR is presented and discussed.

Adult↗
PubMed1984

Patterns of QT/QS2 ratio in vasomotorically labile young men.

The QT/QS2 ratio in seven 21-year-old men with a history of vasomotor lability was measured when they were resting supine and during orthostatic, Valsalva and diving reflex tests. The vasolability was characterized by an abnormal sympathicotonic heart rate (HR) response to the orthostatic test and vacillating inferoapical T waves in the ECG. The results of the vasolabile subjects were compared to those of seven fit control subjects of the same age. In spite of equal HR's in both groups the vasolabile subjects' QT/Q2 ratio constantly exceeded 1.00 during the whole test protocol and it was higher than of the controls (P = 0.04). The reversed QT/QS2 relationship in the test subjects seemed to be due both to a prolongation of the QT time and a shortening of the QS2 time. This difference prevailed throughout although the reaction pattern to autonomic stimulations was equal in both groups. We considered an inadequate neural control of the heart, possibly with metabolic and haemodynamic interactions, responsible for the prolongation of the electrical systole in relation to the electromechanical systole in the heart of the vasomotorically labile subjects.

Adult↗
PubMed1991

Autonomic nervous system function in patients with primary obstructive sleep apnoea syndrome.

Ten patients with obstructive sleep apnoea syndrome cured by uvulopalatopharyngoplasty were compared to nine patients considered as surgical failures, using cardiovascular reflex tests--Valsalva manoeuvre, respiratory sinus arrhythmia, isometric handgrip and head-up tilt. Two patients had signs of moderate vagal dysfunction, but no case of definite autonomic nervous dysfunction was diagnosed. The overall results indicated sympathetic overreactivity, positively correlated to oxygen desaturation indices and remaining after successful treatment. Four patients did not exhibit bradycardia during sleep apnoea. Two of them had decreased respiratory sinus arrhythmia when awake, but two had normal values. This implies a difference in vagal responsiveness between the awake and sleeping states, or that other factors besides vagus function influence the bradycardia response to apnoea. The group mean values were all within normal limits. There was no significant difference between the two groups in any test. Autonomic nervous dysfunction therefore does not seem to contribute to surgical failure, nor to occur with increased incidence among patients with primary obstructive sleep apnoea syndrome.

Adult↗
PubMed1994

Reflex sympathetic dystrophy: result of autonomic denervation?

1. To investigate the nature of sympathetic dysfunction in the pathogenesis of reflex sympathetic dystrophy, the microcirculatory vasoconstrictive responses to dependency were investigated in the skin of the hand of 76 reflex sympathetic dystrophy patients with unilateral disease by means of laser Doppler flowmetry (in perfusion units) and capillary microscopy. The patients were divided into three stages according to their perception of skin temperature (stage I in the case of a stationary warmth sensation, stage II in the case of an intermittent warmth and cold sensation, and stage III in the case of a stationary cold sensation). The vasoconstrictive responses were induced by lowering of the affected hand. 2. As compared to controls, the mainly sympathetically mediated vasoconstrictive response at thermoregulatory level of the skin microcirculation, as measured by laser Doppler flowmetry, was attenuated at stage I (1.82 versus 1.41, P < 0.05), stage II (1.82 versus 1.09, P < 0.0001) and stage III (1.82 versus 1.14, P < 0.01), suggesting the involvement of sympathetic denervation at all stages of the reflex sympathetic dystrophy syndrome. This sympathetic denervation may also account for the observed increase in thermoregulatory skin blood flow at stage I as compared to controls (152 versus 81, P < 0.01). 3. Since sympathetic denervation has been reported to cause increased sensitivity of vascular structures to catecholamines, the decrease in thermoregulatory skin blood flow at stages II (54 versus 81, P < 0.05) and III (31 versus 81, P < 0.05), both as compared to controls, may result from hypersensitivity to catecholamines of skin microvessels. 4. The sympathetically independent vasoconstrictive response at the nutritive level of skin microcirculation, as measured by capillary microscopy, was impaired only at stage III as compared to controls (1.04 versus 2.06, P < 0.05). This divergence in microvascular reactivity upon dependency of the nutritive and thermoregulatory subsystems also supports the hypothesis of sympathetic dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1985

Plasticity in the vestibulo-ocular and optokinetic reflexes following modification of canal input.

The vestibulo-ocular reflex (VOR), the optokinetic reflex (OKR), and their interactions were studied before and after unilateral horizontal canal (HC) plug. Two independent changes occur in the VOR following HC plug: (a) a drop in VOR gain which recovers rapidly, provided that monkeys are permitted normal visual-vestibular interaction (VVI); and (b) a deterioration in response characteristics at low frequencies, consistent with a decrease in effective VOR time constant. The latter occurs regardless of VVI and VOR gain recovery and progresses over several days. The time constant may recover, but only after several months. OKR responses are in keeping with the notion that they represent a combination of fast and slow processes. Results after HC plug suggest that the gain of the slow OKR process rises along with that of the VOR. Response characteristics of synergistic and antagonistic VVI behave as linear combinations of VOR and OKR response characteristics both before and after HC plug. Changes in VVI arising after HC plug simply reflect modifications in VOR and OKR response characteristics.

Adaptation, Ocular↗
PubMed2004

Torsional vestibulo-ocular reflex during whole-body oscillation in the upright and the supine position: II. Responses in patients after vestibular neuritis.

In a recent study we demonstrated that otolith input modifies the torsional angular vestibulo-ocular reflex (torVOR) of healthy human subjects: Compared to turntable oscillations in supine position, oscillations in upright position increased the gain of torVOR by 0.1 and cancelled the phase lead originating from low-frequency semicircular canal signals. We asked whether these otolith-related changes of torVOR are still present in patients after vestibular neuritis (VN). Eight patients were sinusoidally oscillated about their naso-occipital axis in supine (canal-only stimulation) and upright (canal-and-otolith stimulation) position. Three-dimensional eye movements were recorded with dual search coils. The patients showed similar otolith-related gain and phase changes of the torVOR as healthy subjects: the gain increased by about 0.1 (p < 0.05) and the low-frequency phase lead from semicircular canal signals was abolished. These results indicate that otolith function after VN is still sufficient to interact with semicircular canal signals to optimize torsional gaze stabilization when the head is upright.

Adult↗
PubMed1993

Adaptation of the vestibulo-ocular reflex with the head in different orientations and positions relative to the axis of body rotation.

We investigated the influence of static head orientation and position, relative to the axis of body rotation, upon vestibular adaptation. With the head centered, displaced anterior to the axis of body rotation, or tilted 40 degrees to 45 degrees in roll or pitch, the gain of the vestibulo-ocular reflex (VOR) was trained (to go either up or down) for one hour using artificial manipulation of the visual surround to produce a visual-vestibular mismatch. Before and after each training session, the VOR was measured in darkness with the head in the training as well as in several non-training positions. We found that transfer of VOR adaptation to non-training positions was almost complete when comparing head eccentric versus head-centered rotations. For tilts, however, transfer of VOR learning was far less complete suggesting that static otolith signals provide a strong contextual cue that gates the expression of an adaptive VOR response. Finally, following training to increase the VOR, gain was greater for centripetally than centrifugally directed slow phases. Centripetally directed postsaccadic drift also developed. These findings imply that the gain increase paradigm also leads to abnormal function of the velocity-to-position neural integrator, which holds eccentric positions of gaze.

Adaptation, Physiological↗