The negative appendicectomy rate at Charlotte Maxeke Johannesburg Academic Hospital - a 10-year review.

BACKGROUND: The negative appendicectomy rate (NAR) is defined as the proportion of surgically removed appendices that are pathologically normal. The acceptable NAR has been a debated issue. Previously, a higher rate was accepted, whilst newer thinking favours a lower rate. Diagnosing appendicitis is often a clinical challenge and may require crosssectional imaging to assist in the diagnosis. METHODS: A retrospective review was conducted at the Charlotte Maxeke Johannesburg Academic Hospital. Appendix histopathological reports were retrieved for patients older than 18 years over a 10-year period. Reports of ultrasound (US) and/or computed tomography (CT) scans were analysed in the last 18 months. RESULTS: One thousand two hundred and seventeen appendicectomy specimens were included. The overall NAR was 19%. This demonstrated a significant downward trend over the period (p < 0.003). Per gender, the female NAR showed a significant decline (p = 0.002) while the male decline was not significant (p = 0.517). Reproductive-age females were found to have significantly higher NAR as compared to other age groups. The overall perforation rate was 17% which demonstrated a significant increase over the study period (p = 0.012). In the last 18 months, 240 appendicectomies were performed. One hundred and eleven patients underwent imaging (46%), of which 78 underwent ultrasound (70%), 14 CT (13%) and 19 US and CT (17%). CONCLUSION: The overall NAR declined significantly over the period. Females under the age of 45 were found to have significantly higher NARs. Further prospective studies are needed to determine the benefit and feasibility of preoperative CT in resource-limited settings, particularly in reproductive-age females to reduce the NAR.

Fine motor control in rats is disrupted by delta-9-tetrahydrocannabinol.

Evidence has suggested that cannabinoids such as THC, the active ingredient in marijuana, cause deficits in motor control and the production of movement. However, the specific components of motor control that are affected by cannabinoids have yet to be identified. The present study used an operant beam-press paradigm with a force criterion to determine the effects of THC on different parts of the force-time trajectory. Seven rats were trained to press a beam with at least 50 g of force to receive a sugar solution. THC was injected, as was apomorphine (APO), a selective dopamine D(2)/D(1) receptor agonist that acts as an antagonist at low doses. Low doses of APO, which have been found to cause deficits in motor execution, were used as a control for the effects of THC. Average peak force of a given press, as well as rate of rise of force, were significantly lowered by THC, as well as by apomorphine. Past research suggests that deficits in the rate of rise of force that can be attributed to depletions of dopamine in the nigrostriatal pathway, as in the case of low doses of APO, reflect failures of motor unit recruitment rather than of motor memory. Similarities in the motor effects of THC and APO suggest that THC plays a role in recruitment and synchronization of motor neurons appropriate for a given task.

A comparison of the effects of amphetamine and low doses of apomorphine on operant force production, inter-response times and response duration in rat.

RATIONALE: Low doses of apomorphine (APO), a non-selective dopamine (DA) agonist, are thought to suppress motor activity via the preferential activation of DA autoreceptors, which effectively reduces DA tone. OBJECTIVES: The suppressant effects on operant responding of low doses of apomorphine were explored and compared with the effects of amphetamine (AMP), an indirect DA agonist. METHODS: In an operant task, rats were trained to press sequentially three separate beams under the following different behavioral requirements: low-force beam (1 g50 g), and a long-duration beam (response duration>2 s). Inter-response times and kinetic measures, such as peak force, the rate of rise of force and response duration, were recorded. Following training, performance was assessed after systemic injection of low doses of APO (0.01, 0.03 and 0.1 mg/kg, s.c.) and AMP (0.1, 0.3 and 1.0 mg/kg, i.p.). RESULTS: APO decreased peak force for the high-force and the long-duration beams by decreasing the rate of rise of force, but did not affect performance success on the low-force beam or response duration on the long-duration beam. This indicates that APO impaired the ability to generate high forces but did not interfere with the memory or execution of an overall motor plan. Low doses of APO also increased the times taken to switch from one response to the next and to visit the tray when food was present. In contrast, AMP at 1.0 mg/kg shortened both the time taken to switch between responses and the time spent visiting the food tray. CONCLUSIONS: Low doses of APO interfered with response initiation and execution, suggesting that dopamine acts as a "gating" system, enabling certain processes to be carried out in an efficient and automated manner.

Control of operant response force.

Differences in motor-control strategies (feedback or feedforward) engaged by rats to produce operant response force were investigated under 2 conditions of external feedback. In the immediate condition, liquid sucrose reinforcers were delivered as soon as each forelimb response met the force requirement, whereas under the terminal condition, reinforcers were delivered at response termination. When feedback control of response force was precluded by delivering reinforcers at response termination, force was adjusted by modulation of the rate of rise of force. However, under immediate reinforcer delivery, response force was controlled by adjustments of time to peak force. Such adjustments of response time to meet response requirements of increasing difficulty are consonant with expressions of the speed-accuracy tradeoff commonly observed in studies of human motor control.

Palpitations and cardiac awareness after heart transplantation.

OBJECTIVE: The aim of this study was to examine the awareness of resting heartbeat in heart transplantation recipients, compare it with that found in other medical populations, and determine whether clinical characteristics are associated with accurate heartbeat awareness. METHODS: Eligible patients underwent a research battery consisting of a heartbeat detection task and self-report questionnaires assessing cardiac symptoms, psychosocial variables, and cognitive function. The accurate awareness of resting heartbeat was determined by presenting the patients with auditory stimuli at each of six different delays following the R wave on the ECG. Patients then selected the tones that they thought coincided with the sensation they had of their heart beating. The patients' physicians rated their cardiac morbidity. The results were contrasted with comparable data obtained in previous work with other ambulatory medical populations. RESULTS: Forty-one consecutive heart transplantation recipients who survived for at least 3 months after surgery were eligible. Thirty-four (82.9%) of them were studied and complete data were obtained on 26 (63.4%). Nine patients (34.6%) were reliably able to detect their resting heartbeat. When compared with the 17 patients who were not accurately aware of their heartbeat, the two groups did not differ significantly in cardiac morbidity, cognitive brain dysfunction, generalized psychiatric distress, depression, somatization, or hypochondriacal attitudes. A significantly higher proportion of heart transplantation recipients were accurately aware of their heartbeat than was found in a sample of general medical outpatients and in asymptomatic, nonpatient volunteers. CONCLUSIONS: One-third of heart transplant recipients are accurately aware of resting heartbeat, despite the absence of cardiac innervation.

Dopamine depletion in nucleus accumbens influences locomotion but not force and timing of operant responding.

This experiment examined the role of dopamine (DA) in the nucleus accumbens in regulating beam pressing and locomotor responses. Six rats were rewarded with sucrose on a partial reinforcement schedule for pressing force-sensitive beams. Open-field locomotor activity, and the force and timing characteristics of operant motor responses were recorded. It is known that low doses of apomorphine decrease DA tone through activating DA autoreceptors, resulting in suppression of both operant responses and locomotion. Our results showed that DA depletion in the nucleus accumbens, induced by bilateral injection of 6-hydroxydopamine, did not affect the force and timing of operant responses: neither did it reverse the suppressive effects of low doses of apomorphine on the force and timing of operant responses. However, accumbens DA depletion did block the suppressive effect of apomorphine on open-field locomotion. These results were interpreted as support for the hypothesis that the suppressive effects of low doses of apomorphine on locomotion, but not on operant beam pressing, are mediated mainly by DA autoreceptors in the mesolimbic pathway.

Sensitivity to mechanical stimuli and the role of general sensory and perceptual processes in heartbeat detection.

Sensitivity to heartbeat sensations is commonly assessed using tasks that require individuals to judge the simultaneity of heartbeats and tones. In two experiments, we investigated the suitability of this paradigm for examining cardioception. In the first experiment, participants judged the simultaneity of near-threshold vibrations and suprathreshold tones. Precision in judging vibration-tone simultaneity was directly related to the detectability of the mechanical stimuli, thereby supporting use of the simultaneity paradigm to assess heartbeat detection. In the second experiment, we examined the influences of sensitivity to mechanical stimuli and the ability to make intermodality simultaneity judgments on the precision of heartbeat detection. We measured participants' vibrotactile thresholds, precision in judging light-tone simultaneity, and precision in judging heartbeat-tone simultaneity. The ability to judge the simultaneity of lights and tones accounted for 24.3% of the variance in precision of heartbeat detection, and mechanical sensitivity accounted for a further 8.5%.

The work costs of earning food as a determinant of patch leaving.

Foraging theorists have long emphasized the role of the energy (work) costs of food items on foraging behavior. However, few experiments have measured this variable or demonstrated that animals are indeed sensitive to work costs. Experiment 1 assessed whether rats (Long-Evans) can use the work costs of food to determine whether a food patch is exhausted. Rats performed a fixed amount of work for each food item (fixed-work [FW] schedule), but food was withheld unpredictably to simulate sudden patch depletion. It was found that rats left patches only when the work costs of unsuccessful searches (giving-up work) exceeded the prevailing work costs of food. The time and response costs of unsuccessful food searches (giving-up time and giving-up responses) were not predictive of patch leaving. Experiment 2 showed how rats regulated work in this paradigm by examining the role of exteroceptive stimuli connected with fulfilling the FW schedule.

The antidepressant fluvoxamine increases natural killer cell counts in cancer patients.

Knowing the negative effect of depression on lymphocyte number and activity in humans, we investigated the effect of antidepressant therapy on various lymphocyte subgroups. Cancer patients receiving treatment for at least 6 months were asked to take the antidepressant, fluvoxamine, for 28 days. Before and at the end of the study, physical and psychiatric examinations were performed, and the severity of depression was assessed by the Hamilton Scale for Depression (HAM-D). In addition, a sample of blood was withdrawn from the patients to quantify the following parameters: total leukocyte and lymphocyte counts, T4, T8, and Natural Killer (NK) cells, and lymphocyte response to the mitogens phytohemagglutinin (PHA) and pokeweed (PWM). Ten adult patients completed the study. Five of the 10 responded favorably to fluvoxamine treatment. Mean improvement was 50% from the score on day one. There was a significant correlation between the change in the HAM-D score of the "responders" and the change in NK cell counts (p = 0.02). The mean increment in NK cell number was 53%. In 4 of the 5 "non-responders", NK cell number dropped by 65% (mean). No correlation between the change in HAM-D score and any other immunological parameters was detected. Fluvoxamine increases NK cell counts in cancer patients, probably by its antidepressant effect.

Influence of beliefs about heart rate and actual heart rate on heartbeat counting.

The heartbeat counting task is used widely to assess the ability to perceive cardiac sensations. However, performance on this task may be determined by processes other than sensitivity to cardiac stimuli. Beliefs about the effects of postural and exercise challenges on heart rate were assessed by questionnaire prior to performing the heartbeat counting task, and then actual heart rate was manipulated during the counting task by changes in posture and exercise. On average, counted heart rates were closer to beliefs about heart rate than to actual heart rate. Hierarchical multiple regression analyses indicated that (a) believed heart rates predicted counted heart rates while controlling for actual heart rates and (b) actual heart rates also predicted counted heart rate while controlling for heart rate beliefs. These data suggest that the rate of heartbeat counting is influenced by beliefs about heart rate and by the processing of cardiac sensations.

Low doses of apomorphine suppress operant motor performance in rats.

The purpose of this study was to examine the effects of low doses of apomorphine on motor performance. Six rats were rewarded with sugar water on a partial reinforcement schedule for pressing force-sensitive beams with a minimum force of 1 g. The kinetics of individual responses and the temporal characteristics of response sequences were measured; open field locomotor activity was also measured in a separate apparatus. Apomorphine (APO), amphetamine (AMP), and haloperidol (HAL) were administered systemically. It was found that low doses of APO (0.03 and 0.1 mg/kg, SC) produced weaker and longer beam presses. These decreases in response peak force resulted from decreases in the rate of rise of force. APO also caused disproportionate lengthening of beam release time. In addition, the low doses of APO increased the time intervals between consecutive components of response sequences. These low doses of APO are known to decrease dopaminergic tone. Hence, the observed pattern of motor dysfunctions produced by APO is similar to the bradykinesia seen in human Parkinson's disease.

Variation of Isometric Response Force in the Rat.

Hungry, unrestrained rats (N = 7) were rewarded for pressing a response beam in excess of 11 different force requirements. Changes in peak force production as a function of peak force requirement were examined by analyses of the first four moments of distributions of peak response forces: constant error, the within-subject standard deviation, skewness, and kurtosis. Results were similar to those previously obtained with human subjects: Constant error was positive at low and negative at high force requirements, the within-subject standard deviation increased as a negatively accelerating function of force requirement, and skewness and kurtosis were positive at low force requirements and decreased to negative values at the highest increments. Additional analyses of response kinetics indicated that rats, like humans, meet increasing force requirements by altering the rate of rise of force. The performance similarities suggest that common processes are engaged by the human and rat motor control systems to solve the problem of generating forces that are appropriate to the prevailing environmental constraints.

Accurate awareness of heartbeat in hypochondriacal and non-hypochondriacal patients.

We measured the accurate awareness of resting heartbeat in a sample of medical out-patients meeting DSM-III-R criteria for hypochondriasis (n = 60), and in a comparison group of non-hypochondriacal patients (n = 60) from the same general medical clinic. Patients also completed subjective self-report ratings of their sensitivity to benign bodily sensation and of functional somatic symptoms. Hypochondriacal patients did not differ significantly from non-hypochondriacal patients in their accurate awareness of heartbeat. They did, however, consider themselves more sensitive to benign bodily sensation and report more functional somatic symptoms. Within each sample, the only statistically significant association found was a negative correlation (r = -0.32, p = 0.025) between heartbeat awareness and the severity of hypochondriacal symptoms among the hypochondriacal patients. These results suggest that hypochondriacs may not be more accurately aware of normal cardiac activity, and therefore that hypochondriacal somatic complaints may not result from an unusually fine discriminative ability to detect normal physiological sensations that non-hypochondriacal individuals do not perceive.

Cardiac stimulus intensity and heartbeat detection: effects of tilt-induced changes in stroke volume.

The effects of variations in stroke volume on the intensity of cardiac stimuli was examined in a series of three experiments that employed classical psychophysical methods to assess heartbeat detection. Stroke volume was manipulated by passive body tilt and recorded using impedance cardiography while subjects performed heartbeat detection tasks. The postural manipulation generated little or no change in contractility or momentum but did produce substantial changes in stroke volume. However, this potential source of variation in cardiac stimulus magnitude did not influence either the precision of heartbeat detection or the temporal location of heartbeat sensations. It is concluded that the intensity dimension of the heartbeat stimulus is not determined by stroke volume.

Effects of data limitations on heartbeat detection in the method of constant stimuli.

In the method of constant stimuli applied to measuring heartbeat detection, subjects judge the simultaneity of heartbeats and exteroceptive comparison stimuli presented at various intervals after the R-wave (0, 100, 200, 300, 400, and 500 ms). Using versions of this procedure, investigators have found that between 20% (Yates, Jones, Marie, & Hogben, 1985) and 54% (Brener, Liu, & Ring, 1993) of subjects can detect heartbeat sensations. Whereas Yates et al. used a single comparison stimulus on each trial and Brener et al. used 10, the present study examined whether this disparity in heartbeat detection performance could be attributed to the number of comparison stimuli presented on each trial. In each of 360 trials, 30 subjects judged the simultaneity of heartbeat sensations and tones following 1, 5, or 10 comparison stimulus presentations. Significantly fewer subjects met the criterion for heartbeat detection with 1 tone presentation (13%) than with either 5 (43%) or 10 (47%) tone presentations. It is concluded that a single stimulus presentation imposes data limitations that result in underestimation of the accuracy of heartbeat detection. The presentation of at least 5 stimuli in each trial alleviates this limitation.

A method of constant stimuli for examining heartbeat detection: comparison with the Brener-Kluvitse and Whitehead methods.

A method of constant stimuli (MCS) for measuring heartbeat detection was examined by comparing performance on this method with the Brener and Kluvitse (BK) method and a variant of the Whitehead (WH') method. All methods required subjects to judge the simultaneity of heartbeat sensations and tones, and each yielded measures of judgment precision and of the temporal location of heartbeat sensations relative to the electrocardiogram R-wave. Both measures were found to be significantly correlated across tasks. A greater proportion of subjects met criteria for classification as heartbeat detectors on the MCS (54%) and BK (50%) tasks than on the WH' task (33%). In the MCS and BK tasks, subjects judged tones presented 100-300 ms after the R-wave to be most simultaneous with heartbeat sensations. Intratask correlations showed that only the MCS procedure yielded stable measurements of both judgment precision and temporal location. The MCS procedure possesses commendable psychometric properties and provides a simpler means than the BK procedure of examining heartbeat detection.

The perception of cardiac activity in medical outpatients.

This study compared several measures of cardiac perception and related them to patient' spontaneous reports of palpitations. One hundred and forty-five ambulatory patients referred for Holter monitoring for the evaluation of palpitations were compared with 70 asymptomatic nonpatients. Reports of palpitations during monitoring were compared with the ECG to determine whether they coincided with an arrhythmia. Subjects also completed a heartbeat detection task to determine whether they were accurately aware of cardiac systole while at rest. 20.7% of palpitation patients and 4.7% of asymptomatic controls demonstrated an accurate awareness of resting heartbeat (p = 0.01). Performance was unrelated to bodily amplification, somatization, hypochondriacal symptoms, ECG findings, or psychiatric morbidity. 34.3% of palpitation patients reported symptoms that consistently coincided with arrhythmias on ECG. These accurate patients had significantly lower levels of amplification, somatization, hypochondriacal symptoms, and psychiatric morbidity. Accuracy of symptom reporting and accuracy of heartbeat awareness were not statistically associated.(ABSTRACT TRUNCATED AT 250 WORDS)

The temporal locations of heartbeat sensations.

This experiment examined individual differences in the temporal location of heartbeat sensations and the reliability of their detection. Following practice on a familiarization task in judging light-tone simultaneity, 50 subjects were studied for two sessions on a heartbeat detection task, which required judging the simultaneity of heartbeat sensations and tones presented at six intervals following the onset of ventricular contraction. Subjects inspected the heartbeat-tone intervals as frequently and for as long as desired before choosing the one in which heartbeat sensations and tones were most simultaneous. The temporal locations of heartbeat sensations in subjects classified as "good heartbeat perceivers" (n = 16) ranged from 131 and 363 ms following ventricular contraction (mean = 228 ms). Correlations between the familiarization and heartbeat detection tasks in the accuracy of simultaneity judgments and in the frequency and duration of interval inspections suggest that general perceptual abilities and strategies may underlie success in detecting heartbeat sensations.

Energetic and motor responses to increasing force requirements.

The effects of increasing work (force) requirements on energy expenditure and response topography were examined in 7 rats pressing a beam to earn food. For the 1st 16 days, the force requirement was 5.52 x 10(-2) N (5.625 g). This increased by 4.91 x 10(-2) N (5 g) every 7th session until Ss had experienced 10 upward shifts. Following the 54.57 x 10(-2) N (55.625 g) condition, the original criterion was reinstated. During the augmented phase. Ss maintained stable reinforcement rates across conditions by increasing the peak force of beam pressing. These higher forces, occurring within 20 reinforcements of changing the force criterion, were produced primarily by increases in the rate of change of force (delta F/delta T). Also, while the rate of work performed on the beam increased, the overall energy expenditure fell. In contrast to these rapid adjustments, reinstating the original 5.52 x 10(-2) N (5.625 g) criterion resulted in only gradual alterations in motor performance.