suggests that this effect is not sex dependent and cannot be attributed to a simple return to natural balding. Our observation suggests a direct effect of minoxidil on the hair follicle, perhaps in some way sensitising it and making it dependent on the drug for future growth. B. J. KIDWAI North Devon District Hospital, M. GEORGE Barnstaple EX31 4JB, UK 1. Kosman ME. Evaluation of a
new antihypertensive agent, minoxidil. JAMA 1980; 244: 73-75. 2. Olsen EA, Weiner MS. Topical minoxodil in male pattern baldness: effects of discontinuation of treatment. Am Acad Dermatol 1987; 17: 97-101. J 3. Bamford JT. A falling out following minoxidil: telogen effluvium. J Am Acad Dermatol 1987; 16: 144-45.
Gresty suggest that the sharp low frequency peak
may result from an increase in the output of a mechanism that contributes to physiological tremor. In an analysis of the tremor of 127 healthy subjects the averaged spectrum resembled that of a resonant system with broad-band forcing.2 There was no evidence
of a specific input at a low frequency. However, as we noted in our report, a few apparently healthy subjects do have a substantial low-frequency peak in their tremor spectrum. We do not know whether this is a symptom of inchoate disease or a physiological (but in our experience rare) oscillation. Applied Physiology Research Unit, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
CD, Meadows JC, Lange GW, Watson RS. The relation between physiological tremor of the two hands in healthy people. Electroenceph Clin Neurophysiol 1969; 27: 179-85. 2. Arblaster LA, Lakie M, Walsh EG. Human physiological tremor: a bilateral study. J Physiol 1990; 429: 123P. 1. Marsden
Mechanisms for essential tremor SIR,-Dr Lakie and colleagues (July 25, p 206) report postural hand tremor before and after left-sided thalamotomy in a patient with bilateral essential tremor. Postoperatively the spectrum of tremor in the right hand had a broad range of frequencies (2-14 Hz) characteristic of physiological tremor, together with a distinctive peak at 5-7 Hz that they claim to be a residuum of the pathological tremor. However, the remaining symptomatic tremor of the left hand, recorded simultaneously, was also at 57 Hz, suggesting that the peak in the right hand spectrum was due to passive mechanical transmission of tremor from the left. This possibility could have been assessed statistically by calculating the coherence between the right and left hand spectra and tested by restraining the left arm
during recording. Lakie et al interpret the distinct peak amidst a broad spread of frequencies as evidence that essential and physiological tremor have separate mechanisms. In fact many mechanisms are known to contribute to physiological tremor, including mechanical properties of the limb, the ballistocardiogram, and spinal and supraspinal neuromuscular mechanisms.1 These mechanisms combine to give low and high frequency spectral components that vary in relative magnitudes according to circumstances, such as constitutional factors, anxiety, and drugs. Physiological tremor may well receive a contribution from a mechanism whose oscillations become magnified in patients with essential tremor. MRC Human Movement and Balance Unit, Section of Neuro-Otology, Institute of Neurology, National Hospital for Neurology and Neurosurgery, London WC1 N 3BG, UK
T. C. BRITTON M. A. GRESTY
1. Marsden CD.
Origins of normal and pathological tremor. In: Findley LJ, Capildeo R, eds. Movement disorders: tremor. New York. Oxford University Press, 1984.
**This letter has been shown -ED.L.
Lakie, whose reply follows.
SiR,—Dr Britton and Dr Gresty raise two interesting points. We considered the possibility that the persistent low frequency rhythmic peak in the tremor spectrum of the right hand could have been due to transmission of energy from the tremulous side. In a series of measurements, both before and after operation, the low frequency peak ranged from 5-1Hz to 6Hz. The peak frequency was similar on both sides, but was not in general identical, both before and after surgery-for example, on one occasion after surgery there was a difference of 0-5 Hz between left and right sides. It seems unlikely that the oscillations have a common source and are phasically related. Furthermore, low frequency tremor of the right hand persisted when the left hand was at rest. Marsden et aP have noted that the size and frequency of physiological tremor mostly correspond quite well in both hands, and these variables usually alter in the same way on both sides with repeated measurements, although the tremor does not have a common origin. The situation is probably the same in essential tremor; in this patient, and in others with essential tremor, we have seen similar bilateral covariation of these indices.
Intrapartum fetal monitoring SiR,—Dr Westgate and colleagues’ findings (July 25,
that fetal electrocardiographic waveform (FECG) monitoring reduces the proportion of deliveries for fetal distress. We are doing similar research but so far our results differ from those of Westgate et al: the number of fetal blood samples needed in labour was reduced ten-fold in our study if ST analysis was used to guide management. There was no reduction in the number of operative interventions for fetal distress, and there was an equal number of babies with metabolic acidosis at delivery in each group (pH < 7-2, base deficit> 10). There may be several reasons for this difference: firstly, although our management guidelines for labour in the trial are broadly similar to those of Westgate et al, monitoring in the FECG group is based wholly on the ST waveform. Conventional cardiotocography (CTG) is not included since it has not been shown to be useful in successive randomised trials1 and the search for other indices of fetal wellbeing should not be hampered by the use of the CTG. Second, the senior obstetrician in our study withdrew 8% of labours from the FECG group. Third, we found that interference with the ECG signal in the second stage of labour from maternal muscles during pushing led to variation in the signal; this reduced the reliability and interpretability of the ST analysis. On average, only 64% of the second-stage traces printed had ST analysis, and a smaller percentage of the second-stage trace was accompanied by a normal check ECG assuring an acceptable signal for analysis. Prospective assessment is vital in such clinical decisions. Lastly, technical difficulties with monitors or signals were dealt with by an expert, dedicated team from the labour ward and the medical physics department at Plymouth. Without this immediately available expertise, such difficulties could hamper the use of FECG monitoring by clinical obstetricians. We, too, look forward to improvements in on-line computer analysis techniques, and are continuing our study. suggest
Department of Obstetrics and Gynaecology, St George’s Hospital Medical School,
J. E. COCKBURN J. M. PEARCE
London SW17 ORE, UK
G. V. P. C. CHAMBERLAIN
M, Kierse JNC, Chalmers I. A guide to effective care childbirth. Oxford: Oxford University Press, 1989 192-93
Chemoresistance of Plasmodium falciparum in central Africa appearance of drug-resistant strains of Plasmodium subsaharan Africa has made malaria control more difficult. Our organisation (OCEAC), with the government health services of the six member states, maintains epidemiological surveillance of chemoresistance. In-vivo studies of autochtonous
SiR,—The falciparuna in