Discrimination of the direction of motion on the human hand: a psychophysical study of stimulation parameters.

1. In these experiments we assess the relative importance of the spatial and temporal properties of a moving tactile stimulus in determining the ability of humans to discriminate its direction of motion. Movement along the finger was simulated by applying a series of pulses to adjacent locations on the skin using the tactile array of an OPTACON stimulator. Simulated motion permitted us to vary independently the overall distance moved as well as the spacing, timing, and number of sequential stimuli. Different combinations of spatiotemporal parameters allowed us to further examine the relationship of apparent velocity of motion and sweep duration to behavioral performance. Discrimination accuracy was measured using signal detection techniques to calculate the discrimination parameter d' and PCmax, a bias-free measure of the percent correct identification of the direction of motion. 2. In experiments where the path length was constant, discriminability of the direction of motion increased as the spacing between successive pulses narrowed. Similarly, for a given interpulse spacing, the accuracy of discrimination increased linearly with distance, saturating at perfect performance. These apparent spatial effects on performance actually reflect the total number of stimuli presented to the skin rather than their proximity. Sweeps containing the same number of pulses are equally discriminable regardless of either their spacing or the total distance crossed on the skin. d' values obtained at 1.2-, 2.4-, and 4.8-mm spacings appear indistinguishable when plotted as a function of the total number of pulses in a sweep. 3. Experiments in which both the distance moved and the spacing between pulses was varied randomly confirmed that discrimination accuracy depends on the total number of pulses in a sweep rather than the spatial dimensions of the path traversed. Stimulation of only two points that mark the start and stop locations on the skin appears insufficient to enable subjects to discriminate correctly the direction of motion. Two-point stimulation elicits random performance whether the points lie 1.2 or 4.8 mm apart. Discriminability rises linearly to near-perfect performance when eight or more pulses are delivered sequentially. Extrapolation of the d' and PCmax curves suggests a mean threshold of approximately three points for 75% correct discrimination of the direction of motion across the skin. 4. The relationship of stimulus spacing to discriminability over a fixed path suggests that direction discrimination does not simply involve computation of the location of the start and stop points on the skin or their spatial disparity.(ABSTRACT TRUNCATED AT 400 WORDS)

Lidocaine inhalation attenuates the circulatory response to laryngoscopy and endotracheal intubation.

STUDY OBJECTIVE: To evaluate the effect of lidocaine inhalation on the circulatory response to direct laryngoscopy and endotracheal intubation. DESIGN: Prospective, randomized study. SETTING: Operating theater at a public hospital. PATIENTS: Eighty patients (ASA physical status I and II ages 25 to 45 years) scheduled for major abdominal surgery. INTERVENTIONS: In the first stage, 40 patients were randomly assigned to receive inhalation of either lidocaine 40 mg or a 0.9% solution of sodium chloride (placebo). In the second stage, the next 20 consecutive patients received inhalation of lidocaine 120 mg, and another 20 consecutive patients received intravenous (IV) lidocaine 1 mg/kg. MEASUREMENTS AND MAIN RESULTS: Mean arterial pressure rose significantly in the i.v. lidocaine group (21.2 mmHg; p < 0.05), the saline inhalation group (29.2 mmHg; p < 0.05), and the lidocaine 40 mg inhalation group (22.9 mmHg; p < 0.05), but not in the lidocaine 120 mg inhalation group (10.1 mmHg). The heart rate (HR) response to intubation with lidocaine inhalation was dose dependent. In the saline inhalation group, HR increased by 15.6 beats per minute (bpm) (p < 0.05); in the lidocaine 40 mg inhalation group, HR increased by 9.1 bpm (p < 0.05); and in the lidocaine 120 mg inhalation group, HR increased by only 3.1 bpm. CONCLUSION: Inhalation of lidocaine 120 mg prior to induction of anesthesia is an effective, safe, and convenient method to attenuate the circulatory response to laryngoscopy and endotracheal intubation.

Arm exercise testing with myocardial scintigraphy in asymptomatic patients with peripheral vascular disease.

Arm exercise with myocardial scintigraphy and oxygen consumption determinations was performed by 33 men with peripheral vascular disease, 40 to 74 years of age (group 2). None had evidence of coronary disease. Nineteen age-matched male control subjects (group 1) were also tested to determine the normal endurance and oxygen consumption during arm exercise in their age group and to compare the results with those obtained during a standard treadmill performance. The maximal heart rate, systolic blood pressure, pressure rate product, and oxygen consumption were all significantly lower for arm than for leg exercise. However, there was good correlation between all these parameters for both types of exertion. The maximal heart rate, work load and oxygen consumption were greater for group 1 subjects than in patients with peripheral vascular disease despite similar activity status. None of the group 1 subjects had abnormal arm exercise ECGs, while six members of group 2 had ST segment changes. Thallium-201 scintigraphy performed in the latter group demonstrated perfusion defects in 25 patients. After nine to 29 months of follow-up, three patients who had abnormal tests developed angina and one of them required coronary bypass surgery. Arm exercise with myocardial scintigraphy may be an effective method of detecting occult ischemia in patients with peripheral vascular disease. Those with good exercise tolerance and no electrocardiographic changes or 201T1 defects are probably at lower risk for the development of cardiac complications, while those who develop abnormalities at low exercise levels may be candidates for invasive studies.

Vibrotactile forward masking: psychophysical evidence for a triplex theory of cutaneous mechanoreception.

Threshold shifts for the detection of vibrotactile test stimuli were determined as a function of the intensity of a masker. A 50-ms sinusoidal test stimulus was applied to the thenar eminence of the hand 25 ms after the termination of a 700-ms sinusoidal masker applied to the same site. The frequency of the test stimulus and the frequency of the masker were varied. To eliminate the influence of the Pacinian receptor system, stimuli were delivered through a 0.01-cm2 contactor. The results support the hypothesis that the detection of vibration delivered through a small contactor is determined by two separate populations of non-Pacinian receptors. The study constitutes a psychophysical demonstration of the existence of three receptor systems responsible for the detection of vibration.

An alternative health delivery system for the chronically ill elderly.

The present health care system is fragmented, uncoordinated, and too costly for the chronically ill, elderly patient. Project OPEN provides preventive health and social services in order to reduce costs and provide more effective care. This alternative delivery system is based on a consortium brokerage model which provides functional assessment, care plan development and service coordination. A randomized sample of 338 elderly individuals participated in a time series experiment. Client functional status, service utilization, and all health costs were collected for six months. The results indicated a maintenance in functioning levels, a decrease in acute hospitalizations, and a 20% reduction in health care costs for the demonstration participants as compared to the control group. Project OPEN provided more effective care while simultaneously reducing health expenditures to the chronically ill elderly.