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Biomedical subjects

A Prochazka

Publications and source records attributed to A Prochazka.

At least 37 records · Page 2Linked to original sources
PubMed1999

Contact-evoked changes in EMG activity during human grasp.

Contact-evoked changes in EMG activity during human grasp. 2215 Cutaneous receptors in the digits discharge bursts of activity on contact with an object during human grasp. In this study, we investigated the contribution of this sensory activity to the responses of muscles involved in the task. Twelve subjects performed a standardized precision grasp task without the aid of vision. Electromyographic (EMG) responses in trials when the object was present were compared with those in which the object, and hence the associated afferent responses, were unexpectedly absent. Significant differences in EMG amplitude occurred in the interval 50-100 ms after contact in all subjects and in 33/46 of the muscles sampled. The differences emerged as early as 34 ms after contact and comprised as much as a fourfold change in EMG from 50 to 100 ms after contact with the object. Typically, EMG responses were larger when the object was present (OP), though there were cases, particularly in the thenar muscles, in which the responses increased when the object was absent (OA). Local anesthesia of the thumb and index finger attenuated contact-evoked EMG activity in at least one muscle in all four subjects tested. In one subject, contact-evoked responses were abolished completely during the anesthesia in all four muscles sampled. The results indicate that the sensory activity signaling contact plays a key role in regulating EMG activity during human grasp. Much of this feedback action is attributable to cutaneous receptors in the digits and probably involves both spinal and supraspinal pathways.

Adult↗
PubMed1998

Muscle history, fusimotor activity and the human stretch reflex.

1. The previous history of contraction and length changes of a muscle influences the size of the stretch reflex and H reflex. Here we ask, is this dependence due to changes in mechanical properties of extrafusal fibres, intrafusal fibres of spindles, or both? 2. The soleus muscle of human subjects was conditioned using either a voluntary contraction or a contraction evoked by low-strength electrical stimulation, in the range 0-25 % of maximum. Following conditioning, reflexes were increased by more than twofold above the no-contraction value by a voluntary contraction of 5 % of maximum, or more, but not by electrical stimulation which presumably did not contract the intrafusal fibres of spindles. 3. When the muscle was conditioned with a contraction at a length shorter than the test length, rather than at the test length, a depressing effect on reflexes was attributed to both the burst of impulses generated in spindles when the muscle was stretched back to the test length and to a reduced stretch sensitivity of muscle spindles. 4. The experiments demonstrate the importance of keeping the muscle and its spindles in a defined mechanical state when measuring reflexes. They also point to the powerful facilitating influences of conditioning muscle contractions provided they recruit the intrafusal fibres of spindles.

Adult↗
PubMed1998

Muscular sense is attenuated when humans move.

1. Muscle receptors play an important role in our conscious perception of movement, but there are no published accounts of our ability to detect their signals during different motor tasks. The present experiments introduce a method to test muscular sense when humans move. 2. Muscle receptors were excited by an electrically induced twitch of the right extensor carpi ulnaris muscle. The muscle was stimulated via percutaneously inserted intramuscular electrodes or using surface stimulation through anaesthetized skin. Muscular sense was represented by the ability to detect the twitch and was compared between various tasks and stationary control trials. 3. Three hertz voluntary wrist movements significantly attenuated muscular sense to 37 % of control. This velocity-dependent attenuation was present over a range of twitch amplitudes suggesting it does not simply reflect a masking of low intensity stimuli. Perceptual ratings of twitch amplitude during fast imposed passive movements were reduced by 40 %, though this did not quite reach statistical significance. However, perceptual ratings of twitches evoked up to 2 s after the termination of the passive movements were significantly different from control. 4. Reaching with the stimulated, but not the contralateral, arm also significantly reduced muscular sense (to 40 %). 5. Attenuation to 58 % of control during cyclic stretching of the skin on the dorsum of the hand showed that signals from peripheral receptors may play a role. Attenuation prior to a single wrist flexion movement indicated that central sources can also contribute. 6. The results are consistent with current findings of a general attenuation of sensory feedback during movement and raise questions regarding the role of muscular sense in movement control.

Adult↗
PubMed1998

Models of ensemble firing of muscle spindle afferents recorded during normal locomotion in cats.

1. The aim of this work was to compare the ability of several mathematical models to predict the firing characteristics of muscle spindle primary afferents recorded chronically during normal stepping in cats. 2. Ensemble firing profiles of nine hamstring spindle primary (presumed group Ia) afferents were compiled from stored data from 132 step cycles. Three sets of profiles corresponding to slow, medium and fast steps were generated by averaging groups of step cycles aligned to peak muscle length in each cycle. 3. Five models obtained from the literature were compared. Each of these models was used to predict the spindle firing profiles from the averaged muscle length signals. The models were also used in the reverse direction, namely to predict muscle length from the firing profiles. A sixth model incorporating some key aspects of the other models was also included in the comparisons. 4. Five of the models predicted spindle firing well, with root mean square (r.m.s.) errors lower than 14 % of the modulation depth of the target profiles. The key variable in achieving good predictions was muscle velocity, the best fits being obtained with power-law functions of velocity, with an exponent of 0.5 or 0.6 (i.e. spindle firing rate is approximately proportional to the square root of muscle velocity). The fits were slightly improved by adding small components of EMG signal to mimic fusimotor action linked to muscle activation. The modest relative size of EMG-linked fusimotor action may be related to the fact that hamstring muscles are not strongly recruited in stepping. 5. Length was predicted very accurately from firing profiles with the inverse of the above models, indicating that the nervous system could in principle process spindle firing in a relatively simple way to give accurate information on muscle length. 6. The responses of the models to standard ramp-and-hold displacements at 10 mm s-1 were also studied (i.e. velocities that were an order of magnitude lower than that during stepping). In these cases components of spindle primary response related to length as well as velocity were needed for good fits. Because these length-related components detracted from rather than improved predictions of the step cycle data, an attenuation of length dependence at high muscle velocities emerged as a possibility. 7. We conclude that in this study we have identified models and parameters that may be used to predict spindle afferent firing from the time course of muscle length in the cat step cycle.

Animals↗
PubMed1998

Ensemble firing of muscle afferents recorded during normal locomotion in cats.

1. The main purpose of this study was to collate population data on the firing characteristics of muscle afferents recorded chronically during normal stepping in cats. 2. Ensemble firing profiles of forty-seven muscle spindle and tendon organ afferents were compiled from stored data. The relationships between the firing profiles and the displacement and force signals were analysed with the help of mathematical models of the response characteristics of spindle primary and secondary afferents and tendon organs. 3. Whereas the firing of hamstring spindle afferents could be predicted with reasonable accuracy from the length and velocity signals alone, the firing profiles of triceps surae spindle afferents deviated from the predicted profiles, particularly during electromyogram (EMG) activity. This indicated that the components of fusimotor action linked to extrafusal muscle activity were significant in triceps surae, possibly because this muscle is more strongly recruited in the cat step cycle. 4. From the limited data available, it was not possible to identify the 'best' or most general mathematical function to predict spindle secondary firing. In the two triceps surae spindle secondary units studied, firing was well predicted by using the simplest possible model, rate proportional to displacement, whereas in the hamstring spindle secondary data, a more complex linear transfer function was needed. The results of modelling the spindle secondary data were consistent with a modest amount of phasic, static fusimotor action linked to EMG activity. 5. The averaged ensemble of tendon organ afferent activity from the triceps surae gave predictions of whole-muscle force that agreed well with separate triceps force measurements in normal cat locomotion. This supports the idea that ensembles of tendon organ afferents signal whole-muscle force. 6. Our overall conclusion is that to a first approximation, large muscle afferents in the cat hindlimb signal muscle velocity, muscle length and muscle force, at least in movements of the speed and amplitude seen in locomotion.

Animals↗
PubMed1997

Phasic activity in the human erector spinae during repetitive hand movements.

1. Phasic activity in the human back muscle erector spinae (ES) was studied during repetitive hand movements. The hand movements were elicited voluntarily by the subject or induced passively by the experimenter through a servomotor or through cyclical electrical stimulation of muscles acting about the wrist. The aim of the study was to determine whether the rhythmical activation of ES was of supraspinal, intersegmental or segmental origin. 2. When voluntary rhythmical hand movements were performed as fast as possible, cyclical ES EMG bursts occurred at the same frequency. This frequency was significantly higher than that reached when the task was to contract the back muscles as rapidly as possible. This suggests that the ES activity during the fast hand movements was not generated by direct commands descending to the ES muscles from the motor area of the cerebral cortex responsible for voluntary back muscle activation. 3. During imposed rhythmical hand movements, ES EMG bursts remained entrained to the hand movements, even when movement frequencies far exceeded those attainable voluntarily either for the hand or the back. This showed that ES EMG responses could be evoked by the hand movements even when these were not generated by descending neural commands. Two alternative mechanisms of ES activation were considered: (a) propriospinal transmission of afferent input entering the spinal cord from the upper extremity; (b) afferent input from ES and other trunk muscles, responding to local oscillations transmitted mechanically from the hand to the lower back. 4. Activation of ES via proprioceptive signals from the forearm was unlikely since (a) simultaneous electrical stimulation of wrist extensor and wrist flexor muscles did not result in repetitive ES EMG bursting; (b) cyclical vibration of the wrist extensors did not evoke ES EMG bursting; (c) when the forearm was constrained and the hand was moved passively, the lower trunk accelerations and cyclical ES EMG both occurred at a harmonic of the hand movement frequency. 5. We conclude that the repetitive ES EMG bursting during hand movements was probably due to a local segmental reflex rather than to descending commands. Remote mechanical oscillations of the trunk caused by hand movements evidently elicited proprioceptive reflexes in ES that presumably contributed to trunk stabilization.

Adult↗
PubMed1997

Measurement of rigidity in Parkinson's disease.

Clinical assessment of rigidity in parkinsonian patients is largely qualitative. The reliability and validity of the assessments are sometimes in doubt. Several "engineering" methods of quantifying rigidity have been described, but none has been adopted into general clinical practice. A possible reason is that these methods differ in crucial aspects from the clinical exam. We therefore tackled the problem by monitoring the clinical exam itself, using small sensors to measure the forces and displacements applied. Limb impedance (Z) was computed using parameter identification methods and compared to raters' verbalized ratings of rigidity based on a 5-point scale: the Unified Parkinson's Disease Rating System. The qualitative and quantitative estimates of impedance covaried over a fourfold range, depending on the forces imposed and the subject's motor set. Raters differed by up to 1 full point in their mean qualitative ratings and sometimes disagreed on whether levodopa reduced rigidity. This was not due to any significant differences in the overall range of rigidity they evoked, but rather to the way they scored this range [the ratio of mean rating to mean impedance (R/Z) varied between raters and subjects]. On the other hand, the R/Z ratio was reproducible over separate sets of ratings and may therefore serve to convert measured impedance into a standardized rating. Our results indicate that the current clinical exam may be too abbreviated to detect the sometimes quite small reductions in rigidity after levodopa. We conclude that a device that conveniently quantifies the clinical assessment of rigidity is now available and will lead to more standardized protocols for rating rigidity in the near future.

Antiparkinson Agents↗
PubMed1997

The bionic glove: an electrical stimulator garment that provides controlled grasp and hand opening in quadriplegia.

OBJECTIVE: This report describes the operation of the Bionic Glove, a new functional electrical stimulation (FES) device designed to improve the function of the paralyzed hand after spinal cord injury (SCI) or stroke. DESIGN: Signals from a sensor in the glove detecting voluntary wrist movement are used to control FES of muscles either to produce hand-grasp or to open the hand. When the glove is donned, conductive areas on its inside surface automatically make contact with self-adhesive electrodes on the skin. SETTING AND PATIENTS: This report concerns nine people with SCI who have used the device in their daily lives for up to a year or more. Measurements were made at clinics in Edmonton, Miami, and Chicago as part of a multicenter clinical trial. OUTCOME MEASURES AND RESULTS: The mean peak force of tenodesis grasp in the nine subjects increased from 2.6N (passive) to 11.3N (glove active). Active force was significantly greater than passive grasp force even when muscles were fatigued after repetitive grasp-release cycles. Most manual tasks improved significantly with the use of the glove, as judged by the number of tasks completed in a minute or the subjects' qualitative ratings of task difficulty. CONCLUSION: The Bionic Glove can provide significant improvement of hand function in people with C6-C7 SCI.

Adult↗
PubMed1997

Positive force feedback control of muscles.

This study was prompted by recent evidence for the existence of positive force feedback in feline locomotor control. Our aim was to establish some basic properties of positive force feedback in relation to load compensation, stability, intrinsic muscle properties, and interaction with displacement feedback. In human subjects, muscles acting about the wrist and ankle were activated by feedback-controlled electrical stimulation. The feedback signals were obtained from sensors monitoring force and displacement. The signals were filtered to mimic transduction by mammalian tendon organ and muscle spindle receptors. We found that when muscles under positive force feedback were loaded inertially, they responded in a stable manner with increased active force. The activation attenuated the muscle stretch (yield) that would otherwise occur in the absence of feedback. With enough positive force feedback gain, yield could actually reverse. This behavior, which we termed the affirming reaction, was reminiscent of the mammalian positive supporting reaction, a postural response elicited by contact of the foot with the ground. Muscles under positive force feedback remained stable, even when the loop gain (Gf) was set at levels of 2 or 3. In a linear system, if Gf > 1, instability occurs when the loop is closed. On further investigation, we found that Gf changed with joint angle: it declined as the load-bearing muscle actively shortened. We inferred that in closed-loop operation, the active muscles always shortened until Gf approached unity. In other words, the length-tension curve of active muscle ensures stability even when force-related excitation of motoneurons is very large. Concomitant negative displacement feedback reinforced and stabilized load compensation up to a certain gain, beyond which instability occurred. In further trials we included delays of up to 40 ms in the positive force feedback pathway, to model the delays recently described for tendon organ reflexes in cat locomotion. Contrary to expectations, this did not destabilize the loop. Indeed, when instability was deliberately evoked by setting displacement feedback gain high, delays in the positive force feedback pathway actually stabilized control. The stabilization of positive force feedback by inherent properties of the neuromuscular system increases the functional scope to be expected of feedback from force receptors in biological motor control. Our results provide a rationale for the delayed excitatory action of Ib heteronymous input on extensor motoneurons in cat locomotion.

Adult↗
PubMed1997

Implications of positive feedback in the control of movement.

In this paper we review some theoretical aspects of positive feedback in the control of movement. The focus is mainly on new theories regarding the reflexive role of sensory signals from mammalian tendon organ afferents. In static postures these afferents generally mediate negative force feedback. But in locomotion there is evidence of a switch to positive force feedback action. Positive feedback is often associated with instability and oscillation, neither of which occur in normal locomotion. We address this paradox with the use of analytic models of the neuromuscular control system. It is shown that positive force feedback contributes to load compensation and is surprisingly stable because the length-tension properties of mammalian muscle provide automatic gain control. This mechanism can stabilize control even when positive feedback is very strong. The models also show how positive force feedback is stabilized by concomitant negative displacement feedback and, unexpectedly, by delays in the positive feedback pathway. Other examples of positive feedback in animal motor control systems are discussed, including the beta-fusimotor system, which mediates positive feedback of displacement. In general it is seen that positive feedback reduces the sensitivity of the controlled extremities to perturbations of posture and load. We conclude that positive force feedback can provide stable and effective load compensation that complements the action of negative displacement and velocity feedback.

Afferent Pathways↗
PubMed1996

Movement illusions evoked by ensemble cutaneous input from the dorsum of the human hand.

1. In this study we tested the hypothesis that ensemble activity in human cutaneous sensory afferents evoked by the stretching of skin over and around the finger joints contributes to the conscious perception of movement of the fingers. 2. In nineteen normal adults, ensembles of cutaneous afferents were activated either by electrical stimulation, delivered through an array of electrodes on the dorsum of the hand and fingers, or by mechanical stretching of the skin over and around the joints. The stretching was applied through an array of threads stuck to the skin, in such a way as to avoid or minimize moving the underlying joints and to avoid applying pressure to underlying tendons and ligaments. Perceived movements were mimicked by voluntary movements of the fingers of the contralateral hand. 3. By way of comparison, kinaesthetic illusions were also evoked by activation of muscle receptors by vibration. 4. Illusions of movement were elicited with each type of stimulus. Electrical stimulation of skin afferents caused clear illusory movements in six out of seventeen subjects (35%), and borderline movement illusions in three out of the same seventeen subjects (total 9/17, 53%). Various other localized skin sensations were also reported. Skin stretch evoked movement illusions in eleven out of nineteen of subjects (58%). In all subjects who received both cutaneous stimuli, twelve out of seventeen (71%) reported some movement sensations with one or other of the stimulation techniques. Vibration tended to be the most reliable stimulus modality, eliciting illusory movements in fourteen out of sixteen subjects (88%). 5. Although the skin stretching technique did cause minute movements of nearby joints in several cases, these were monitored and shown in separate control experiments to be below perceptual threshold, and so the movement illusions could be safely attributed to the cutaneous afferent input evoked by skin stretch. 6. The results support the hypothesis that input from skin stretched during finger movement contributes to the conscious perception of the movement. Vibration-evoked muscle afferent input tended to be more reliable than the skin input in producing kinaesthetic illusions, though comparisons of the relative efficacy of the three techniques must be made with caution.

Adolescent↗
PubMed1996

Cytopathological analysis of sputum in patients with airflow obstruction and significant smoking histories.

Advances in the understanding of lung cancer biology have led to observations that specific genetic changes occur in premalignant dysplasia. These observations have occurred predominantly in molecular studies of resected lung tumors and consequently, they may not be fully representative of those biological abnormalities characterizing premalignant lesions in individuals without overt lung cancer. Studies of premalignant epithelial cell biology and chemoprevention are needed in this patient subgroup. Such an initiative is now underway through the lung cancer Specialized Program of Research Excellence (SPORE) grant awarded to the University of Colorado Cancer Center (and affiliated institutions) by the National Cancer Institute. To identify participants for the early detection and chemoprevention trials of the Colorado SPORE, we initiated a sputum cytology screening program targeting persons with chronic obstructive pulmonary disease and smoking histories of 40 or more pack-years. During the first 26 months after activation of the screening program, sputum samples from 632 participants were evaluated. Of these, 533 (84%) of the subjects submitted specimens deemed adequate for cytopathological interpretation; 99 (16%) provided sputum samples unsuitable for cytodiagnosis. Of those participants who submitted adequate samples, 48% had cytodiagnoses of mild dysplasia, 26 % had moderate to severe dysplasia, and 2% presented with carcinoma in situ or invasive carcinoma. Logistic regression modeling was pursued to determine whether selected demographic and/or clinical status variables could be identified as statistically significant predictors of the specific cytological outcome to be expected (mild dysplasia, moderate dysplasia, and so forth). The only apparent associations found from both univariate and multivariate analyses were that the total number of pack-years of smoking history decreased with severity of cytodiagnosis and that those individuals with mild or moderate dysplasia were more likely to be ex-smokers than those with grades of regular metaplasia or lower. Based on the initial results of the Colorado SPORE sputum cytology screening program, we conclude that persons with chronic obstructive pulmonary disease and 40 or more pack-years of smoking history have a high prevalence of premalignant dysplasia detectable through sputum cytology and should be targeted for research programs focusing on lung cancer prevention, early detection, and exploratory biomarker studies.

Adult↗
PubMed1996

A comparison of nicotine delivery systems in a multimodality smoking cessation program.

Cigarette smoking remains the single most preventable cause of death in the United States. Nurses can be instrumental in assisting patients in quitting. A prospective quasi-experimental design was employed to investigate the differences in quit rates, adverse drug reactions, time to relapse, and secondary factors that contribute to smoking cessation in two groups of patients who attended a group program and used either a nicotine patch or nicotine gum. Although there were no significant differences in quit rates at one year, the patch group showed a significant increase in short-term quit rates and a decrease in adverse reactions as well as a longer time to relapse. Older patients demonstrated a longer time to relapse while a high degree of nicotine dependency was correlated with a shorter time to relapse.

Administration, Cutaneous↗
PubMed1996

Contribution of hind limb flexor muscle afferents to the timing of phase transitions in the cat step cycle.

1. In this investigation, we tested the hypothesis that muscle spindle afferents signaling the length of hind-leg flexor muscles are involved in terminating extensor activity and initiating flexion during walking. The hip flexor muscle iliopsoas (IP) and the ankle flexors tibialis anterior (TA) and extensor digitorum longus (EDL) were stretched or vibrated at various phases of the step cycle in spontaneously walking decerebrate cats. Changes in electromyogram amplitude, duration, and timing were then examined. The effects of electrically stimulating group I and II afferents in the nerves to TA and EDL also were examined. 2. Stretch of the individual flexor muscles (IP, TA, or EDL) during the stance phase reduced the duration of extensor activity and promoted the onset of flexor burst activity. The contralateral step cycle also was affected by the stretch, the duration of flexor activity being shortened and extensor activity occurring earlier. Therefore, stretch of the flexor muscles during the stance phase reset the locomotor rhythm to flexion ipsilaterally and extension contralaterally. 3. Results of electrically stimulating the afferents from the TA and EDL muscles suggested that different groups of afferents were responsible for the resetting of the step cycle. Stimulation of the TA nerve reset the locomotor step cycle when the stimulus intensity was in the group II range (2-5 xT). By contrast, stimulation of the EDL nerve generated strong resetting of the step cycle in the range of 1.2-1.4 xT, where primarily the group Ia afferents from the muscle spindles would be activated. 4. Vibration of IP or EDL during stance reduced the duration of the extensor activity by similar amounts to that produced by muscle stretch or by electrical stimulation of EDL at group Ia strengths. This suggests that the group Ia afferents from IP and EDL are capable of resetting the locomotor pattern generator. Vibration of TA did not affect the locomotor rhythm. 5. Stretch of IP or electrical stimulation of TA afferents (5 xT) during the flexion phase did not change the duration of the flexor activity. Stimulation of the EDL nerve at 1.8-5 xT during flexion increased the duration of the flexor activity. In none of our preparations did we observe resetting to extension when the flexor afferents were activated during flexion. 6. We conclude that as the flexor muscles lengthen during the stance phase of gait, their spindle afferents (group Ia afferents for EDL and IP, group II afferents for TA) act to inhibit the spinal center generating extensor activity thus facilitating the initiation of swing.

Afferent Pathways↗
PubMed1996

The fuzzy logic of visuomotor control.

Biological sensorimotor control is characterized by the use of signals from large numbers of sensors, monitoring numerous variables. Among these are the exteroceptive signals from the eyes and ears. Many of the sensory signals are under efferent control, and the motor responses they evoke, whether at a simple reflex level or routed through the higher centres, appear to be task and context dependent. In technology the analysis and management of multiple-input, multiple-output systems clearly exceed the capabilities of classical servo control theory. In this commentary, new types of control system based on conditional logic are discussed in relation to the rules animals use to control movement. It is argued that the concepts of fuzzy logic control provide a useful and "biologically compatible" way of describing sensorimotor behaviour. An example is given of a robotic device under fuzzy control, in which behaviours are selected according to a visual assessment of motor task and context. Each behaviour is associated with a small subset of rules relating specific sensory variables to specific motor actions. The rule-based approach is also discussed in relation to neurophysiological theories regarding the interneuronal control of locomotion, including the recently adduced "parliamentary principle." The analysis and classification of behaviours and rules is seen as a useful preliminary to the future study of interneuronal systems.

Animals↗
PubMed1995

Failure of the community-based Vita-Stat automated blood pressure device to accurately measure blood pressure.

OBJECTIVE: To evaluate the Vita-Stat automated blood pressure computer (a patient-operated blood pressure measuring device available in the community) to determine its value as an instrument to monitor blood pressure in the ambulatory patient. DESIGN: Comparative study using the Vita-Stat vs a gold standard, the mercury sphygmomanometer. SETTING: Three local grocery stores. PARTICIPANTS: Sixty-three passersby who agreed to answer questions and to sit for several measurements of blood pressure. INTERVENTIONS: Simultaneous measurement of blood pressure with each subject wearing a Vita-Stat cuff on the left arm and a mercury sphygmomanometer cuff on the right arm. Two pressures were measured sequentially in the same manner. MAIN OUTCOME MEASURES: The reproducibility, accuracy, sensitivity, and specificity of the Vita-Stat computer compared with the gold standard. RESULTS: In sequential measurements, the Vita-Stat readings of both systolic and diastolic blood pressure correlated less well with each other than did the mercury readings (intramachine differences). The Vita-Stat readings also correlated poorly with the mercury readings of systolic and diastolic blood pressure (intermachine differences). The variability in readings recorded by the Vita-Stat were striking, with differences of up to 60 mm Hg from the mercury readings. More than half (63.2%) of the subjects had Vita-Stat readings that were more than 5 mm Hg different from the mercury readings. Vita-Stat systolic readings were usually lower than mercury readings and also varied by as much as 60 mm Hg below in one patient to 58 mm Hg above the mercury reading in another. The sensitivity of the Vita-Stat in correctly diagnosing hypertension was 0.26; the negative predictive value was 0.45. CONCLUSIONS: Our data suggest that the Vita-Stat is not only inconsistent but inaccurate in measuring blood pressure in the ambulatory patient and is, therefore, not appropriate to use as a monitoring device.

Blood Pressure Determination↗