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PubMed1994

Blood pressure and heart rate response of panic disorder patients receiving imipramine in a dose-response treatment paradigm.

This article reports the effects of imipramine on heart rate and blood pressure in panic disorder patients who participated in an 8-week double-blind dosage response treatment protocol. At the end of a placebo baseline, patients were randomly assigned to placebo or one of three weight-adjusted imipramine dosages: low (0.5 mg/kg per day), medium (1.5 mg/kg per day), or high (3.0 mg/kg per day). It was demonstrated that imipramine had no significant effect on sitting or standing diastolic or systolic blood pressure. Although there was a trend toward a systolic blood pressure drop with positional change, it did not reach statistical significance. There were no significant changes in diastolic blood pressure with postural change. Imipramine did increase sitting and standing heart rate without revealing a clear dosage correlation. In contrast to the pretreated state, the reflex heart rate response to postural change was significantly increased in the posttreatment state, also in a dosage-independent manner. Within the high-dose imipramine group, the baseline sitting to standing heart rate increase was significantly higher in those who dropped out because of drug side effects compared with those who remained. Evidence from this study suggests that imipramine has a dosage-independent effect on resting and reflex heart rate. Future studies should consider postural heart rate reactivity as a potential measure of intolerance to the side effects of high doses of imipramine.

Adult↗
PubMed1977

Influence of voluntary movement and posture on recurrent inhibition in human subjects.

Recurrent inhibition elicited by a conditioning H reflex is measured in normal man by the amount of inhibition of a test H reflex produced by motoneurones that have already given rise to the conditioning reflex. The recurrent inhibition of soleus motoneurones is lowered during a voluntary contraction of this muscle while it is enhanced during a voluntary contraction of its antagonist, the tibialis anterior, and not modified during a contraction of the quadriceps. This recurrent inhibition is also enhanced when the subject is standing without support. These changes in recurrent inhibition are thought to imply supraspinal mechanisms acting on Renshaw cells. The functional significance of these changes is discussed in relation to the recent finding in animals of recurrent depression of the transmission in the Ia inhibitory pathway.

Adult↗
PubMed1990

Lower-body suction and cardiovascular reflexes: physiological and applied considerations.

Lower body subatmospheric pressure (LBSP) can be applied in a graded manner to a supine subject enclosed in a box upto the level of the iliac crest in order to elicit cardiovascular reflexes without a change of posture, and without a gravity induced shift of the central blood volume into the periphery. The procedure effectively produces a controlled, non-haemorrhagic hypovolaemia. The method may be used to differentiate the reflex cardiovascular effects induced by the deactivation of the low-pressure cardiovascular receptors (LBSP less than 30mmHg), and those produced by the deactivation of the arterial baroreceptors (LBSP greater than 30 mmHg). The former results in an increase in the limb vascular resistance without a change in heart rate and blood pressure, while the latter produces a tachycardia, an increase in the diastolic BP with a fall in the sytolic BP. The CVP and the cardiac output reduce with increasing suction. Cardiovascular reflex effects of -40 mmHg are similar to those produced by a change of posture from supine to standing. Vaso-vagal syncope appears with increasing frequency when LBSP exceeds -60 mmHg even in the normal subjects. The test is useful in the aeromedical assessment of apparently normal individuals with low orthostatic tolerance, in the evaluation of the effects of physiological and pharmacological interventions on cardiovascular reflexes, and in the evaluation of patients of autonomic neuropathies. LBSP is also a means of inducing safe, well controlled syncope in order to study the genesis of this phenonmenon.

Animals↗
PubMed1992

The ontogenesis of sensorimotor reflexes in the Mongolian gerbil Meriones unguiculatus.

The ontogeny of a number of sensorimotor reflexes has been studied in the Mongolian gerbil. In contrast to a number of other mammals, the gerbil has relatively long and strong hindlimbs but small forelimbs, indicating their different importance for a number of locomotor acts, and during the developmental period studied, the hindlimbs grow at a much faster rate than the forelimbs. The following sequence of appearance and maturation of the reflexes was observed: rooting, forelimb hopping, surface body righting, forelimb grasp, hindlimb hopping, chin tactile placing, visual placing, air body righting and, at the same time, forelimb and hindlimb tactile placing. This sequence concords with the general gradient of development and maturation of the spinal and brain centers subserving these reflexes, as evaluated from Nissl preparations. The results indicate that there is no clearcut rostro-caudal gradient of postnatal maturation of the spinal cord and the spinally mediated reflexes, but that there is a general caudo-rostral gradient of brain maturation and of the brain-mediated reflexes. Comparisons with other mammals are made.

Aging↗
PubMed1999

Treatment based on H-reflexes testing improves disability status in patients with cervical radiculopathy.

BACKGROUND: Postural modification in patients with lumbosacral radiculopathy either causes further H-reflex suppression, indicating increased root compression, or it effects recovery, indicating decompression of the spinal root. The posture that effects maximum recovery of the H-reflex amplitude is called optimum spinal posture (OSP) and is suggested as a therapeutic exercise to decompress the compromised nerve root. The focus of this study was to identify the OSP that effects the maximum recovery of the flexor carpi radialis (FCR) H-reflex and to study its effect on the disability status in patients with cervical radiculopathy. SUBJECTS AND METHODS: Fourteen patients (46 +/- 12 y) with confirmed symptoms of C7 radiculopathy for the previous 6 months volunteered for the study. The FCR H-reflex was elicited by electrical stimulation of the median nerve at the cubital fossa (0.5 ms, 0.2 pps at H-max). Signals from the FCR muscle were recorded using a Cadwell 5200A EMG unit. The FCR H-reflex was recorded in natural sitting position with the head in natural position and in the OSP. Four traces of the H-reflex were recorded and averaged. The disability status was evaluated, using the Neck Disability Index (NDI), before exercising in the OSP and after 2 days of exercise in the OSP. DATA ANALYSIS: Paired t-test and Spearman's correlation coefficients were used. RESULTS: The H-reflex amplitude and latency were significantly different in the OSP and with the head in a natural position (P < 0.004; P < 0.011). Larger reflex amplitude and shorter latency were recorded in the OSP. The NDI scores were considerably improved after exercising in the OSP (P < 0.001). Spearman's correlation coefficient showed negative association between the H-reflex amplitude and the NDI scores (r = -0.64 to -0.54; P < 0.05). CONCLUSION: Exercising in the OSP increased the H-reflex amplitude and decreased latency of the compromised cervical root. It resulted in decreasing the disability status in this group of patients.

Activities of Daily Living↗
PubMed1977

Reversal of sign of long spinal reflexes dependent on the phase of the step cycle in the high decerebrate cat.

Reversal of the sign of long ascending and descending spinal reflexes dependent on the phase of the step cycle has been shown in the high decerebrate cat. Electrical stimuli were applied to the skin over the dorsum of the metacarpals and metatarsals and the effects were recorded in the corresponding hindlimb or forelimb of the same side. Stimulation generally evoked an increase in activity of flexor or extensor muscles shortly before, and during, activity of the muscle. Inhibition of a muscle occurred when its activity overlapped with the activity of an antagonist muscle. From the latencies it was concluded that at least the early components of the long reflex responses are due to spinal mechanisms. In the stimulated limb the activity of flexor and extensor muscles was also modulated in a phase dependent manner. No consistent long spinal responses to skin stimulation were obtained in high spinal cats during stepping. Electrical stimulation of cutaneous nerve trunks in decerebrate preparations during stepping gave variable though phase dependent long spinal reflex effects.

Animals↗
PubMed1991

Changes in alpha motoneuron excitability of the soleus muscle in relation to vestibular stimulation assessed by angular acceleration in man.

Variations in spinal motoneuron excitability, tested by the monosynaptic H reflex of the soleus muscle, were studied in man in relation to angular acceleration of the body in a damped rotating chair. Clockwise and anticlockwise rotation produced similar changes on the same spinal motoneurons, consisting of a first clear-cut facilitatory phase starting at 0.4 degrees of rotation (corresponding to 156 ms) with a peak between 10 and 30 degrees, followed by a second excitatory phase between 50 and 100 degrees; then, the amplitude of the H reflex progressively recovered to its control value. Both facilitatory phases showed a significant decrease by reducing the angular velocity and acceleration. Control experiments ruled out that both the startle reaction of the subject and variations in the somatosensory input during rotation could be responsible for generating the facilitatory effects on the H reflex. The mean value of the voluntary reaction to turning sensation was 1.1 degrees, corresponding to about 335 ms. It is concluded that the changes described in motoneuron excitability could represent a vestibulospinal reflex response originating from the horizontal semicircular canals.

Acceleration↗
PubMed2001

Stance control is not affected by paresis and reflex hyperexcitability: the case of spastic patients.

OBJECTIVES: Spastic patients were studied to understand whether stance unsteadiness is associated with changes in the control of voluntary force, muscle tone, or reflex excitability, rather than to abnormal posture connected to the motor deficit itself. METHODS: Twenty four normal subjects, 12 patients affected by amyotrophic lateral sclerosis (ALS), seven by spastic paraparesis, and 14 by hemiparesis were studied. All patients featured various degrees of spasticity and paresis but were free from clinically evident sensory deficits. Body sway during quiet upright stance was assessed through a stabilometric platform under both eyes open (EO) and eyes closed (EC) conditions. The sudden rotation of a supporting platform, in a toe up and toe down direction respectively, evoked short (SLR) and medium latency (MLR) reflex responses to stretch of the soleus or the tibialis anterior (TA) muscle. RESULTS: No relation was found between clinical findings (tone, muscle strength, tendon reflexes, plantar response, and duration of disease) and body sway. On average, all patient groups exhibited a forward shift of the centre of foot pressure (CFP) with respect to normal subjects; in addition, paraparetic and to a much larger extent hemiparetic patients showed a lateral shift of CFP. Body sway area was significantly increased only in the hemiparetic patients. No relation was found between position of the CFP and sway within any patient group. Soleus SLR was increased in all patients with respect to normal subjects. TA SLR was often seen in both patients with ALS and paraparetic patients, but only rarely in normal subjects and hemiparetic patients. However, no relation was found between amplitude of soleus or TA SLRs and stabilometric variables. The frequency and size of soleus MLR and TA MLR were decreased in all patients. These responses were decreased in size and not modulated by background EMG in the affected leg of hemiparetic patients, suggesting a disturbed control of spinal reflexes fed by spindle group II afferent fibres. CONCLUSIONS: It is proposed that body posture, paresis, or monosynaptic reflex hyperexcitability do not affect the control of equilibrium during quiet upright stance. In hemiparetic patients, the decreased amplitude of MLRs might be the main cause of the large postural instability. The results are congruent with the hypothesis of a role for group II afferent input in the reflex control of equilibrium.

Adult↗
PubMed1979

Facilitation of female reproductive behavior from mesensephalic central gray in the rat.

Electrical stimulation in the mesencephalic central gray (CG) and adjacent subtectum through chronically implanted electrodes in free-moving estrogen-primed ovariectomized female rats elicited a rapid and large facilitation of the lordosis reflex in response to either male mounts or manula cutaneous stimuli. Unilateral stimulation was sufficient for this effect. The facilitation increased in a graded manner to increased stimulus intensity, and was optimally evoked by stimuli delivered at 50--150 Hz. Facilitation disappeared rapidly following the end ot electrical stimulation, and within 15 min, reflex performance returned to the prestimulation level. Lordosis facilitation appeared when no aversive responses occurred; stimulation with comparable parameters at the lateral edge of CG or in the mesencephalic reticular formation often resulted in postural changes or aversive responses but was not able to facilitate lordosis. Lordosis refelx facilitation was probably mediated by projections descending from neurons in and around the CG, and represents stimulation of a functional link between ascending somatosensory and descending motor systems for the control of lordosis behavior.

Animals↗
PubMed1991

Contribution of the maculo-ocular reflex to gaze stability in the rabbit.

The contribution of the maculo-ocular reflex to gaze stability was studied in 10 pigmented rabbits by rolling the animals at various angles of sagittal inclination of the rotation and/or longitudinal animal axes. At low frequencies (0.005-0.01 Hz) of sinusoidal stimulation the vestibulo-ocular reflex (VOR) was due to macular activation, while at intermediate and high frequencies it was mainly due to ampullar activation. The following results were obtained: 1) maculo-ocular reflex gain decreased as a function of the cosine of the angle between the rotation axis and the earth's horizontal plane. No change in gain was observed when longitudinal animal axis alone was inclined. 2) At 0 degrees of rotation axis and with the animal's longitudinal axis inclination also set at 0 degrees, the maculo-ocular reflex was oriented about 20 degrees forward and upward with respect to the earth's vertical axis. This orientation remained constant with sagittal inclinations of the rotation and/or longitudinal animal axes ranging from approximately 5 degrees upward to 30 degrees downward. When the longitudinal animal axis was inclined beyond these limits, the eye trajectory tended to follow the axis inclination. In the upside down position, the maculo-ocular reflex was anticompensatory, oblique and fixed with respect to orbital coordinates. 3) Ampullo-ocular reflex gain did not change with inclinations of the rotation and/or longitudinal animal axes. The ocular responses were consistently oriented to the stimulus plane. At intermediate frequencies the eye movement trajectory was elliptic because of directional differences between the ampullo- and maculo-ocular reflexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

Contribution of local blood flow regulation mechanisms during head-up tilt in human subcutaneous tissue.

Local and remote regulation of subcutaneous blood flow in the forearm and leg was studied during head-up tilt (30 degrees, 45 degrees and 70 degrees) in 7 young healthy subjects. Relative blood flow was estimated by the local 133Xe washout technique. Incremental levels of head-up tilt elicited increasing vascular resistance on arm and leg, respectively. Positive pressure similar to a blood column of the same height was able to prevent a significant part of the vasoconstrictor response on the leg to head-up tilt. Thus if venous distension is prevented the local veno-arteriolar reflex is abolished, whereas arteriolar constriction due to centrally elicited reflexes remains unaffected. Subcutaneous blood flow in the extremities are regulated by remote (baroreceptor) as well as local sympathetic reflex mechanisms (veno-arteriolar reflex); but the relative influence of the local veno-arteriolar reflex on the increase in total peripheral resistance seems to decrease with increasing tilt angles.

Adult↗