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Biomedical subjects

S Purves

Publications and source records attributed to S Purves.

5 recordsLinked to original sources
PubMed1993

Dual task performance by patients with left or right speech dominance as determined by carotid amytal tests.

Patients who had their speech dominance determined by carotid Amytal testing were evaluated with a dual task procedure consisting of reading and finger tapping. As expected, the asymmetry of interference between tasks varied with speech dominance. Patients with left hemisphere speech tended to show greater interference in the right hand whereas patients with right hemisphere speech showed greater interference in the left hand. Since the right hemisphere dominant patients were also right-handed, the results suggest that interference effects are more closely linked to speech than to motor dominance.

Adolescent↗
PubMed1989

Improving the validity of clinical exercise testing: the relationship between practice and performance.

Many studies involving exercise testing fail to address the issue of practice. Those that do vary considerably with respect to the parameters of practice used. We evaluated the effect of two standardized practices on a horizontal submaximal exercise test performed on a treadmill. Healthy men (n = 20) with no previous treadmill exposure were alternately assigned to the experimental (practice) or control (no practice) group. Heart rate (HR), systolic blood pressure (SBP), rate pressure product (RPP), step cadence (CAD) and perceived exertion (PE) were recorded at the end of each work load of the practices and/or tests. We observed no significant differences in these variables over the common work loads for the first practice session in the experimental group and the exercise test in the control group (p greater than 0.05). The two groups were homogeneous with respect to fitness and magnitude of arousal on initial exposure to the treadmill. During the submaximal test, HR, SBP, RPP, CAD, and PE were systematically lower for the experimental group than for the control group. The SBP and RPP were significantly lower in the experimental group (p less than 0.01). The CAD tended toward statistical significance (p less than 0.07), whereas HR and PE were not significantly different for the two groups (p greater than 0.05). When the four common work loads were compared over the two practices and the exercise test for the experimental group, SBP and CAD were significantly higher for practice 1 than for practice 2 and the test (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1982

Central nervous system amplification: its potential in the diagnosis of early multiple sclerosis.

Ability to record a sizable somatosensory evoked potential (SEP) in the absence of a recordable sensory nerve action potential (SNAP) suggests a normally occurring central nervous system amplifying process. Increments in SEP and SNAP amplitude with increasing stimulus strength between threshold and 2.5 times threshold (maximum) were compared. A threshold (40% of maximum stimulus) and 50% maximum stimulus, amplification measured 2.3 +/- 0.7 and 2.0 +/- 0.6, respectively. In 21 MS patients, the SEP at threshold stimulation was absent in 15, but normal in 5 of these at maximum stimulation. It is postulated that normal central amplification is markedly attenuated in MS, and this may be a sensitive indicator of early disease.

Adult↗
PubMed1981

Occult fifth nerve dysfunction in multiple sclerosis.

Somatosensory evoked potentials (SEPs) were recorded following trigeminal nerve stimulation in 25 normal subjects. Mucosal stimulation of the lip resulted in a reduced stimulus artefact. The three initial peaks, N13, P19, and N30, measured respectively 12.8 +/- 0.9 S-3, 19.3 +/- 1.4 S-3, and 28.6 +/- 1.7 S-3. Blink reflex studies were also performed in most of these subjects. In 41.4% of 29 patients with established or suspected multiple sclerosis, the trigeminal SEP was abnormal. Additional use of the blink reflex raised the overall incidence of trigeminal nerve dysfunction to 51.7%. None of the patients had clinical evidence of fifth nerve involvement either historically or on examination. Four of seven patients with progressive spinal MS and two patients whose only deficit was that of optic neuritis, had abnormal trigeminal SEPs. It is concluded that occult involvement of the pontine fifth nerve structures occurs frequently in MS despite the rarity of corresponding clinical findings. The trigeminal SEP is a useful additional neurophysiological method.

Adult↗