Phasic Behavior Research Articles

Thermodynamic assessment of allocation of energy and exergy of the nutrients for the life processes during pregnancy.

Thermodynamic analyses are performed to quantify allocation of the nutritional energy and exergy to most of the life processes by pregnant mice. In these analyses, 'internal work performance' is calculated for the first time in the literature for metabolism during pregnancy and found substantially higher than the 'external work performance'. Variation of the daily entropy generation rates and the daily internal work performance rates during the course of pregnancy showed a highly similar phasic behaviour. With the progression of the pregnancy, external work performance decreased and second law efficiency increased significantly. On the 13th day of pregnancy, net energy extracted from the food at the cellular energy metabolism subsystem was 15·0 kJ; approximately 3 kJ of it was employed for daily internal work performance, 0·8 kJ was allocated to daily external work performance and 0·8 kJ was stored in the adipose tissue without entering into the cellular energy metabolism subsystem. Heat generation in association with internal and external work performance was 9·1 and 2·2 kJ, respectively. Energy, pertinent to the first law, and exergy (useful energy), pertinent to the second law, balances are described graphically, and comparison of these plots showed that the total exergy of the nutrients allocated to internal and external work performance and heat generation is substantially smaller in magnitude when compared with those of energy balance.

Evaluation of lipid extraction from microalgae based on different phase regions of CO2-expanded ethanol

CO2-expanded ethanol (CXE) has been proposed as an ideal green medium for performing natural products extractions and chemical reactions. However, its systematic complexity concerning vapor-liquid equilibrium (VLE) in extractions is not favorable to the industrial application. In this study, the isothermal binary system was theoretically split into three phase regions in consideration of the state of CO2 as well as the phasic behaviors. In different phase regions, the lipid extractions from microalgae were investigated, showing that subcritical CO2-expanded ethanol in one phase region exhibited higher solubility of lipids, with the maximum recovery approaching 25.0%(w/w), basically equivalent to the complete extraction with organic solvent. Meanwhile, subcritical CXE extracted 15.6 mg of lipids per milliliter of ethanol, significantly higher than 3–6 mg lipids per milliliter of other organic solvent, suggesting more efficient process than other methods. Compared with the conventional products, CXE extracts presented the higher DHA content, 41.92%(w/w) as well as the larger antioxidant capacity (IC50 of 2.49 mg/mL). This study revealed the necessity of the consideration of key factors such as phase equilibrium during employing CXE for the extraction of oxidizable or thermolabile products.

Functional Result of Tendon Transfers and Releases for the Upper Extremity in Spastic Hemiplegic Cerebral Palsy

Purpose: To evaluate the functional and postural outcomes with Shriners Hospital for Children Upper Extremity Evaluation (SHUEE) Test, stereognosis of tendon transfers, and releases for the upper extremity, in adolescents with spastic hemiplegic cerebral palsy (CP). Material and Methods: Prospective study of 11 patients with spastic hemiplegic CP, 8 men, 4 female, between 10 and 16 years of age (mean, 13 years). Inclusion criteria were no fixed articular deformity and patients capable to follow instructions. Surgery consists in a one-time procedure of tendon transfers and releases according to SHUEE and clinical preoperative evaluation. Surgical procedures were done considering individual evaluations as follows: adductor pollicis (AP) release and extensor pollicis longus (EPL) rerouting, 11 patients; extensor carpi ulnaris (ECU) to extensor carpi radialis longus transfer (ECRL), 6 patients; flexor carpi ulnaris (FCU) to extensor carpi radialis brevis (ECRB) transfer, 3 patients; pronator teres (PT) rerouting, 4 patients; release of the FCU, 3 patients; release of the PT, 4 patients; superficial finger flexor tendons release, 3 patients; and swan deformity correction, 3 patients. Before tendon transfer, muscles were previously assed by dynamic electromyography to confirm phasic behavior. Postoperative protocol includes 1-month cast immobilization followed by 20 sessions of physical therapy, orthotic, and scar compression. Assessment with SHUEE, 12-element stereognosis test, and HOUSE classification (JH House) were done at preoperative, 6 and 12 months after surgery. Results: Friedman analysis of the 3 sections of the SHUEE was done. The spontaneous functional analysis of SHUEE (SFA) improves from 53% preoperative to 62% at 12 month of surgery, which was not significant ( P, .12). Dynamic positional analysis (DPA) improves significantly from 53% preoperative to 64% at 6 months and 76% at 12 months of surgery ( P, .004), the best result was in wrist and the worse was thumb. There were significant improvements of the grasp and release analysis (GRA) from 82% to 100% at 12 months ( P, .002). No significant changes in stereognosis were observed improving from 50% to 75% ( P, .05). Functional classification of HOUSE before surgery was 3 to 7. All patients improved their function in HOUSE scale 1 or 2 levels at 6 months and 1 to 3 levels at 12 month. Conclusions: Tendon transfers and releases for the upper extremity in spastic hemiplegic CP adolescents without fixed articular deformities improves dynamic position, grasp and release, and HOUSE level of function.

A hypothesis for temporal coding of young and mature granule cells

While it has been hypothesized that adult neurogenesis (NG) plays a role in the encoding of temporal information at long time-scales, the temporal relationship of immature cells to the highly rhythmic network activity of the hippocampus has been largely unexplored. Here, we present a theory for how the activity of immature adult-born granule cells relates to hippocampal oscillations. Our hypothesis is that theta rhythmic (5–10 Hz) excitatory and inhibitory inputs into the hippocampus could differentially affect young and mature granule cells due to differences in intrinsic physiology and synaptic inhibition between the two cell populations. Consequently, immature cell activity may occur at broader ranges of theta phase than the activity of their mature counterparts. We describe how this differential influence on young and mature granule cells could separate the activity of differently aged neurons in a temporal coding regime. Notably, this process could have considerable implications on how the downstream CA3 region interprets the information conveyed by young and mature granule cells. To begin to investigate the phasic behavior of granule cells, we analyzed in vivo recordings of the rat dentate gyrus (DG), observing that the temporal behavior of granule cells with respect to the theta rhythm is different between rats with normal and impaired levels of NG. Specifically, in control animals, granule cells exhibit both strong and weak coupling to the phase of the theta rhythm. In contrast, the distribution of phase relationships in NG-impaired rats is shifted such that they are significantly stronger. These preliminary data support our hypothesis that immature neurons could distinctly affect the temporal dynamics of hippocampal encoding.

Brain-derived neurotrophic factor increases the motility of a particular N-methyl-d-aspartate /GABA-responsive subset of neural progenitor cells

Neurotrophins like brain-derived neurotrophic factor (BDNF) promote the migration of subsets of neural progenitor cells. The mechanism by which motility is increased and the functional properties of BDNF-responsive cells are not very well known. We have used the neurosphere model, combining time-lapse microscopy, immunocytochemistry, and Ca2+ imaging, to study the effect of BDNF on parameters such as motility and neurotransmitter responsiveness of migrating neural progenitors. At the initiation of differentiation thick glial glutamate-aspartate transporter (GLAST)-positive radial processes emerged from the neurosphere, followed by the exit of neuron-like cells. The neuron-like cells moved outside the radial processes in a phasic manner with intermittent surges of motility and stationary periods. BDNF increased the number and promoted the progress of the neuron-like cells by prolonging surges and decreasing the length of stationary phases. The average rate of cellular movement during surges was unaffected by BDNF. BDNF also caused a several fold increase in positive staining for tropomyosin-related kinase B (TrkB) receptors and neuronal markers such as Calbindin, microtubule-associated protein-2 (MAP-2), and neuron-specific nuclear protein (NeuN) in cells outside the radial network. Calcium imaging allowed for further characterization of the BDNF-responsive cell population. Kainate-responsive cells, denoting the expression of AMPA/kainate receptors, dominated in the outer migration layers while cells responding to (S)-3,5-dihydroxyphenylglycine (DHPG) via metabotropic glutamate receptor 5 (mGluR5) dominated in the inner migration layers. BDNF did not appreciably affect the distribution of these cells but promoted the redistribution of a small subpopulation (about 20%) of N-methyl-d-aspartate (NMDA)- and GABA-responsive cells to the outermost layers of migration. The results demonstrate that BDNF does not affect cell motility per se but alters the phasic behavior of cell movement by promoting periods of high motility in a defined subpopulation of cells which give a robust Ca2+ response to NMDA and GABA.

Hierarchical Micro/Nanostructures of Natural Polymer for Release Process

AbstractIn this paper the modeling of drug release process from hierarchical dispersed systems such as nano and microparticles prepared by thermal cross‐linking of multiple emulsions is described. The presented model considers the diffusion of a drug through spherical eroding natural polymer matrix and diffusion‐convection of the drug in the surrounding medium. Simulated release profiles were compared with experimental data of the drug release from microspheres of various structures. The differences in microspheres structure resulted from changes in mixing intensity of the external surrounding. The simulations of release profiles confirmed the importance of the internal structure of microspheres as well as an intensity of external mixing in the modeling of the controlled release process. The presented model allowed the mass of drug released to be determined with satisfactory agreement with experimental data after optimization of parameters describing internal microspheres structure. The proposed model describing release process of a drug from microspheres can be applied for simulation of release profiles with phasic behavior (primary/lag and continuous release). The model simulations were extended to drug release from nanoparticles with satisfactory results.

Modelling the In vivo Spike Activity of Phasically‐Firing Vasopressin Cells

A minimalist model of magnocellular vasopressin neurones was developed to examine the hypothesis that their phasic behaviour is the product of intrinsic voltage- and activity-dependent intracellular mechanisms that create a bistable dynamical system. The model can closely match a range of phasic behaviours recorded in vasopressin cells in vivo, as well as reproduce the three archetypal behaviours of vasopressin cells (continuous firing, sparse sporadic firing and phasic firing) by varying one of the fourteen model parameters. In addition, the mean and standard deviation of burst and silence periods can be matched by varying a further two parameters. In the model, the long-term behaviour (phasic characteristics) of cells is largely independent of the short-term behaviour (interspike intervals).

A Mathematical Model for Predicting Release Rate from Multiple Emulsions and Micro/Nanospheres

AbstractThis paper presents mass transfer models of the release process from hierarchical dispersed systems such as multiple emulsions and micro/nanospheres. The models were validated by experimental data of an active component released from multiple emulsions and microspheres obtained via multiple emulsion thermal cross‐linking. The simulations of release profiles confirmed the importance of the internal structure of multiple emulsions/microspheres, as well as the intensity of external mixing in the modeling of the controlled release process. The models presented allowed the mass released to be determined within satisfactory agreement with experimental data after optimization of parameters that describe internal emulsion/microsphere structure. The model proposed for describing the release process from microspheres can simulate release profiles that exhibit phasic behavior (primary/lag and continuous release). The model simulations were extended to nanoscale particles with satisfactory results.

Respiratory‐related pacemaker neurons in isolated turtle brainstems in vitro

For adult vertebrates, it is not known whether respiratory‐related pacemaker neurons exist and play a critical role in rhythm generation. To address this question, brainstems from adult turtles were isolated in vitro and respiratory motor bursts were recorded on hypoglossal (XII) nerve roots. Extracellular recordings of respiratory‐related neurons were acquired using multichannel silicon electrodes. While bathed in artificial cerebrospinal fluid, neurons (n=87) exhibited phasic behavior in relation to the XII motor bursts. Synaptic transmission was blocked with antagonists for GABAA (bicuculline), glycine (strychnine), AMPA (CNQX), and NMDA (APV) receptors. During synaptic transmission blockade, 14/87 neurons continued to fire with rhythmic bursts of action potentials and were considered putative pacemaker neurons. When [K+] was increased to 6.0–9.0 mM during ongoing synaptic blockade, 9/10 pacemaker neurons increased burst frequency and action potential firing rates within the bursts. Application of a mu‐opioid agonist (DAMGO) decreased burst frequency in 3/4 pacemaker neurons. These results suggest that respiratory pacemaker neurons, which respond to increased [K+] and mu‐opioid receptor activation, exist in adult turtles. We hypothesize that these pacemaker neurons may be critical for rhythm generation.

Implications of ‘cyclical’ population dynamics for the conservation of Irish hares (Lepus timidus hibernicus)

AbstractThe Irish hare Lepus timidus hibernicus is of priority conservation concern in Northern Ireland, based on a perceived decline in abundance during the 20th century and on two surveys in 1994–1996 and 2002 that suggested low densities. We reanalysed a 10‐year time series [Northern Ireland Rabbit Survey (NIRS)] that has been key evidence of decline, to derive an annual index of abundance during 1986–1995. This showed a rise to a double peak followed by a trough. We compared these Northern Ireland data with two datasets for Lepus timidus scoticus. A 40‐year annual index derived from hare bags on Scottish shooting estates [National Game‐Bag Census (NGC)] showed strong fluctuations, each lasting several years. Autocorrelation analysis of the NGC data showed elements of cyclical behaviour, with distinct phases and a 16‐year period. A previously published 30‐year survey of introduced L. t. scoticus in northern England also showed large multi‐year fluctuations and phasic behaviour, albeit on a shorter time scale. The NIRS index was strongly correlated with NGC data for the same years, suggesting that it too reflected part of a natural population dynamic. The Species Action Plan for L. t. hibernicus in Northern Ireland includes the aims of maintaining the existing range and demonstrating increase by 2005, and of doubling the population by 2010. We suggest that these aims and the supporting monitoring strategy are inappropriate for a species that shows multi‐annual fluctuations in abundance throughout its geographical range. It is important to distinguish self‐correcting population processes from trends requiring remedial conservation action.

Oscillatory and Intrinsic Membrane Properties of Guinea Pig Nucleus Prepositus Hypoglossi Neurons In Vitro

Numerous models of the oculomotor neuronal integrator located in the prepositus hypoglossi nucleus (PHN) involve both highly tuned recurrent networks and intrinsic neuronal properties; however, there is little experimental evidence for the relative role of these two mechanisms. The experiments reported here show that all PHN neurons (PHNn) show marked phasic behavior, which is highly oscillatory in approximately 25% of the population. The behavior of this subset of PHNn, referred to as type D PHNn, is clearly different from that of the medial vestibular nucleus neurons, which transmit the bulk of head velocity-related sensory vestibular inputs without integrating them. We have investigated the firing and biophysical properties of PHNn and developed data-based realistic neuronal models to quantitatively illustrate that their active conductances can produce the oscillatory behavior. Although some individual type D PHNn are able to show some features of mathematical integration, the lack of robustness of this behavior strongly suggests that additional network interactions, likely involving all types of PHNn, are essential for the neuronal integrator. Furthermore, the relationship between the impulse activity and membrane potential of type D PHNn is highly nonlinear and frequency-dependent, even for relatively small-amplitude responses. These results suggest that some of the synaptic input to type D PHNn is likely to evoke oscillatory responses that will be nonlinearly amplified as the spike discharge rate increases. It would appear that the PHNn have specific intrinsic properties that, in conjunction with network interconnections, enhance the persistent neural activity needed for their function.

The time-delay graph and the delayogram - new visualizations for time delay

For about 60 years, the spectrogram has been an excellent visualization tool for observing the acoustic and prosodic features of a speech signal. However, a visual tool has been lacking for information that is typically represented by the speech signal's phase. When a talker is remote from one or more microphones, the times of arrival of the direct wave and those of reflections become important. In this letter, we introduce two visualizations that have proven to be quite useful for us in understanding phasic behaviors of microphone arrays. A time delay versus frequency plot for a window of time is called the time-delay graph, and an ensemble of projected time-delay graphs is called the delayogram. These visualizations are introduced, and simulated and real-speech data examples of both displays are presented. The time-delay graph is compared to the phase transform generalized cross-correlation (GCC-PHAT) for two real-data examples.

Virtual Slope Control of a Forward Dynamic Bipedal Walker

Active joint torques are the primary source of power and control in dynamic walking motion. However the amplitude, rate, timing and phasic behavior of the joint torques necessary to achieve a natural and stable performance are difficult to establish. The goal of this study was to demonstrate the feasibility and stable behavior of an actively controlled bipedal walking simulation wherein the natural system dynamics were preserved by an active, nonlinear, state-feedback controller patterned after passive downhill walking. A two degree-of-freedom, forward-dynamic simulation was implemented with active joint torques applied at the hip joints and stance leg ankle. Kinematic trajectories produced by the active walker were similar to passive dynamic walking with active joint torques influenced by prescribed walking velocity. The control resulted in stable steady-state gait patterns, i.e. eigenvalue magnitudes of the stride function were less than one. The controller coefficient analogous to the virtual slope was modified to successfully control average walking velocity. Furture developments are necessary to expand the range of walking velocities.

Nitrous oxide suppresses tonic and phasic nociceptive behaviors but not formalin-induced c-Fos expression in the rat spinal cord dorsal horn.

The aim of this study was to investigate the anesthetic and analgesic effects of subanesthetic concentration of nitrous oxide and to compare these effects with halothane and fentanyl. The antinociceptive effects were assessed in male Sprague-Dawley rats by behavioral responses to phasic and tonic nociceptive stimulations and biochemical index of pain, formalin-induced Fos-like immunoreactivity (Fos-LI), in spinal cord dorsal horn. Neurological functions (proprioception, mental status and motor function) were monitored to determine whether or not behavioral responses were impaired by anesthetic action of the treatment. Four groups of rats treated with: (1) saline, (2) 75% nitrous oxide (0.5 MAC), (3) 0.5% halothane (0.5 MAC) and (4) fentanyl 100 micrograms/kg were subject either to graded intensity of CO2 laser stimulation (phasic pain) or s.c. injection of 50 microliters 2.5% formalin (tonic pain) in two separate studies. All rats in the tonic pain study were killed for immunohistochemistry at 60 min after formalin injection. Maximal counts of Fos-LI labelled neurons in rat spinal cord dorsal horn were compared according to the laminar distribution. We found that all rats exhibited normal righting reflexes regardless of whatever treatment. Nitrous oxide and halothane greatly impaired mental status and motor function, indicating that both agents could induce a modest degree of sedation and paresis at subanesthetic concentrations. Fentanyl increased the threshold level to noxious thermal stimulation, and reduced the formalin-induced licking/biting behaviors and the number of Fos-LI labelled neurons which are predominantly found in the neck of the dorsal horn. Nitrous oxide and halothane increased the thermal nociceptive threshold, suppressed licking/biting behavior in both early and late phases of the formalin test. Unlike fentanyl, nitrous oxide and halothane failed to suppress c-fos expression. The extent and pattern of nitrous oxide-induced antinociception was identical to halothane, which is known to have little or no analgesic effect. The lack of attenuated biochemical response to tonic pain stimulation may suggest that nitrous oxide fails to suppress spinal sensitization despite its potent inhibition on behavioral hyperalgesia. These findings suggest that, at the spinal level, subanesthetic concentration of nitrous oxide greatly attenuates nociceptive behaviors mainly due to a non-selective suppression of behavioral responses that are commonly associated with inhalation anesthetic drugs.

Assessment of Muscle Fatigue during Load Carrying

This paper presents preliminary results of a study to assess localized muscle fatigue during load carrying. The assessment procedure is based on parameters of the surface electromyographic (EMG) signal that allow one to measure changes in the amplitude and frequency content of the EMG data. Subjects were instructed to walk on a treadmill at 1.3 mph for approximately 10 minutes, carrying a standard box containing a weight equal to 10% of the subject's body weight. Foot switches and a two-camera motion analysis system were used to record walking cadence and kinematics of the task. EMG data were recorded bilaterally from the multifidus muscle at L5, the latissimus dorsii muscle at T10, the upper trapezius muscle, and the biceps brachii muscle. Preliminary analysis of the mechanics of movement indicated that only minor changes took place during the task. These changes appear to be mainly related to the observed decrease in stride length. Analysis of the EMG data showed that a considerable load was applied to the multifidus and the latissimus dorsii muscle as indicated by the amplitude of the EMG data that reached about 20 % of the EMG amplitude recorded during a maximum voluntary extension of the torso. The time-course of the root mean square (RMS) value of the EMG signal demonstrated an increase in the activation of the upper trapezius muscle during the task, indicating either increased force production or compensation for localized fatigue. Alternate phases of increase and decrease of the instantaneous median frequency (IMDF) was observed. This phasic behavior may reflect a load-sharing mechanism among muscle groups to minimize fatigue that is characterized by alternate phases of fatigue and recovery.

DELINQUENT PHASES: The Case of Temporally Intensified Shoplifting Behaviour

This article examines the prevalence and correlates of shoplifting phases among Finnish adolescents. The data are based on the Finnish Self-Report Delinquency Study (FSRD-96) whose target population consisted of 9th grade (15-16-year-old) students. The identification of phases was based both on behavioural sequences and subjective interpretations. Consequently a shoplifting phase was defined in a relative fashion as a period during which the respondent shoplifted more often than usually. Of the respondents, 23 per cent had experienced at least one such period. The typical (modal) shoplzfting phase began at the age of 13 and ended at the age of 14. It lasted for 26 weeks and amounted to 15 thefts. Among the correlates of phasic shoplifting behaviour were participation in other offences and low level of parental control.

Examination of tonic nociceptive behavior using a method of substance P-receptor desensitization in the dorsal horn

Substance P (SP) has been suggested as a neuromediator of nociception in the dorsal horn. Following a single injection of SP onto the rat spinal cord, nociceptive reflexes are facilitated. Following successive administration of a high dose of SP, these responses are attenuated. We have administered multiple injections of SP onto the rat spinal cord in order to produce desensitization to the SP response. With this procedure, we have observed that phasic behaviors (short-term reflex) are attenuated for up to 150 min and are associated with a reduction in the number and affinity of SP-binding sites in the dorsal horn. This study was performed to examine the effect of SP-receptor desensitization in two well-established models of tonic (prolonged) nociception: the formalin test and the monosodium urate (MSU) test. Repeated intrathecal administration of SP (15 μg) reduced the first phase but did not alter the second phase of formalin-induced pain-related behavior. Similarly, repeated administration of SP did not alter MSU-induced pain-related behavior. In both tests, an analgesic dose of morphine administered in combination with SP did reduce the nociceptive behavior. These data show that alteration of SP-receptor activity in the dorsal horn does not alter responses to two longer acting agents considered to be nociceptive. These results suggest that SP in the dorsal horn does not directly mediate tonic nociception but rather may be involved in the expression of phasic pain-related behavior.

Phasic behavior of EMG signals during gait: Use of multivariate statistics

The present study represents an attempt to ascertain whether there are some underlying trends that, in some combination, can explain all the variations in the linear envelopes of 16 EMG signals of selected leg muscles. Two kinds of analyses were performed: (a) a factor analysis of EMG data corresponding to 16 muscles of the lower limb and (b) a “multi-dimensional scaling” (MDS) procedure. The latter technique involved mapping the Cartesian coordinates for 16 points subject to the constraint that the distance between any two points reflected the degree of coactivity for the corresponding muscles. The results of these analyses showed that four factors could account for 91.5% of the variance in the original data set. These factors could be clearly demarcated on the “muscle map,” tending to support the notion that there are motor “programs” for groups of muscles that have to perform a given function during locomotion. Further analysis of the loading matrix (i.e., correlations between each EMG vector and each of the four factors) showed groups of muscles that acted in a similar manner. The muscle groups could be divided into those that act at the times of (a) heelstrike, (b) single limb loading response, (c) propulsion phase, or else (d) acted in a biphasic manner.

Evidence of the co-activation of ?-motoneurones and static ?-motoneurones of the sartorius medialis muscle during locomotion in the thalamic cat

The activity in alpha and gamma efferent axon populations and in group I and group II afferent fibre populations innervating a flexor muscle, the sartorius medialis, was observed during spontaneous locomotor movements in the thalamic cat. Multi-unit discharges of each kind of fibre were obtained by electronic sorting of the action potentials from the overall activity of a thin, intact branch of the sartorius medialis nerve. The following results were obtained: (1) The gamma-motoneurones have a phasic behaviour characterized by a single discharge period during the hip flexion (swing phase of the step-cycle). (2) The gamma-motoneurones are co-activated with the homonymous alpha-motoneurones. (3) Between rhythmic alpha and gamma discharges, i.e. during the hip extension (stance phase of the step cycle), both alpha- and gamma-motoneurones were normally silent. However, in 5 out of 17 experiments, a few units of the gamma population fired at very low frequency. (4) Two observations indicate that the gamma-motoneurones that are co-activated with the alpha-motoneurones by central locomotor commands are predominantly of the static type. In actual locomotion, the rhythmic fusimotor discharges over-compensate the depressor effect on the firing rate of the group II afferents of the unloading of muscle spindles by the active shortening of the parent muscle. In fictive locomotion, when the transmission of the excitation is blocked by selective curarization in alpha skeleto-motor junctions alone, the rhythmic fusimotor discharges elicit in-phase modulations not only of the group I but also of the group II fibres.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal vasomotion in essential hypertension: influence of vasodilators.

To assess factors responsible for phasic behavior of renal blood flow in essential hypertension, we applied an analytic method based on the estimation of power spectral density to xenon transit through the kidney and examined the renal vasodilator response to a range of agents in 53 normal subjects and 53 patients with essential hypertension. The renal vasodilator response to the calcium channel blocking agent diltiazem, but not the response to alpha-adrenergic blockade (phentolamine) or angiotensin converting enzyme inhibition (teprotide or captopril), was associated with a significant reduction in the amplitude of renal vasomotion. Acetylcholine, a vasodilator that acts through the release of a vasorelaxant factor or factors from endothelium, induced an unanticipated increase in renal vasomotion. These observations further dissociate factors responsible for basal renal vascular tone and periodic changes in renal vascular tone and raise the possibility that abnormalities in the flux of calcium into renal arterioles contribute to increased renal vasomotion in essential hypertension.