Commissioning and quality assurance protocol for dual energy X-ray absorptiometry (DEXA) systems.

This study reports on the development and evaluation of a protocol for testing DEXA systems, which can be incorporated into a routine medical physics/engineering service. Methodologies are reported for (1) scatter measurement, (2) estimation of reference dose and (3) enquiry into potential sources of overexposure. Results show that fan-beam and cone-beam systems require shielding if the walls or operator are within 1 m of the table. Patient reference dose was estimated using the dose-area product (DAP). This varied over an order of magnitude from 2 to 36 mGy cm2 in the range of systems studied. The inquiry into potential sources of overexposure revealed some weaknesses in current practise including a design which prevents the inclusion of DAP metres; beam non-uniformity; incorrect specification of patient dose and the risk of overexposure when tube operates during patient positioning.

Effect of age on ocular microtremor activity.

BACKGROUND: Ocular microtremor (OMT) is a high-frequency tremor of the eyes. It is present in all individuals and is related to brainstem activity. The OMT signal appears as an irregular oscillatory movement with intermittent burst-like components. The clinical interest in OMT has centered on its use in the assessment of the comatose patient, with broad agreement among authors of its prognostic value. The purpose of this study was to examine the changes in OMT activity related to aging. METHODS: OMT was recorded from 72 normal healthy subjects using the piezoelectric strain gauge technique. The subjects ranged in age from 21 to 88 years (54.22 +/- 20.43 years, mean +/- SD). RESULTS: Our results show that the overall frequency and frequency content of the bursts falls with age (p < .002 and p < .001, respectively). There is a highly significant drop in all three frequency parameters of OMT (p < .0001) in subjects older than 60 years of age. CONCLUSIONS: These results suggest that different values of normality should operate for subjects over 60 years of age when considering the clinical application of OMT.

The application of d.c. electrical stimulation in evoking and recording gustatory brain potentials.

Evidence exists which supports the hypothesis that electrical stimulation of appropriate parameters can fulfil the fundamental requirements for an effective evoked potential taste stimulus. Nevertheless, it had previously been considered that electrical taste stimulation is inadequate for evoking gustatory brain potentials. Consequently, the majority of the earlier attempts to record gustatory evoked potentials (GEPs) reported in the literature have employed chemical stimulus techniques. The design of an electrical taste stimulator and its interface to an evoked potential recording unit is described. The first human brain potentials recorded with this system are presented, among which are those attributable to taste pathway activation. Following future work to unequivocally confirm that taste evoked brain potentials are achievable with this system, it has potential to become a clinically valuable tool.

Dominant frequency content of ocular microtremor from normal subjects.

Ocular microtremor (OMT) is a high frequency tremor of the eyes present during fixation and probably related to brainstem activity (Coakley, D. (1983). Minute eye movement and brain stem function. CRC Press, FL.). Published observations on the frequency of OMT have varied widely. Ocular microtremor was recorded in 105 normal healthy subjects using the Piezoelectric strain gauge technique. The dominant frequency content of a signal was determined using the peak counting method. Values recorded ranged from 70 to 103 Hz, the mean frequency being 83.68 Hz (S.D. +/- 5.78 Hz).

Ocular microtremor in patients with idiopathic Parkinson's disease.

Abnormalities in the oculomotor control mechanism of patients with idiopathic Parkinson's disease are well recognised. In this study the effect of Parkinson's disease on tonic output from oculomotor nuclei was studied by using oculomicrotremor as an index of such output. Oculomicrotremor readings were taken from 22 parkinsonian patients and 22 normal healthy volunteers using the piezoelectric strain gauge technique. There was a slower overall tremor frequency, baseline, and burst frequency in the parkinsonian group. There was also a significant increase in the duration of baseline, with a decrease in the number of bursts a second and a decrease in average duration of bursts in the patient group compared with the normal group. One patient, whose medication was withdrawn, showed a marked decrease in mean frequency and baseline frequency with a decrease in number of bursts and increase in baseline duration compared with readings taken when treatment recommenced. These results suggest that variables measured in oculomicrotremor are altered compared with normal subjects, reflecting altered tonic output from oculomotor nuclei in patients with idiopathic Parkinson's disease.

Ocular microtremor in oculomotor palsy.

OBJECTIVES: Ocular microtremor (OMT) is a high frequency tremor of the eyes present in all individuals. Recent reports suggest that OMT may be a useful indicator of brainstem function. However, the actual origin of ocular microtremor remains controversial. This study aims to provide evidence that OMT has a neurogenic origin. MATERIALS AND METHODS: The OMT activity of five subjects with unilateral oculomotor nerve palsy and one subject with complete unilateral internal and external ophthalmoplegia were recorded from both eyes of each subject using the piezoelectric strain gauge technique, with the normal eye acting as a control. Five parameters of OMT activity were studied in each subject: the peak count, the power of the high frequency peak, the percentage power between 60 and 100 Hz, the percentage power between 70 and 80 Hz, and the 10 dB cut-off point. RESULTS: In the five subjects with oculomotor nerve palsy, the mean peak count in the normal eye was 88.4 Hz (SD+/-16.9) and in the affected eye was 59 Hz (SD+/-8.6), P < 0.0096. There was also a fall in the peak power, the power between 60 and 100 Hz, and the power between 70 and 80 Hz. In subject six, who had complete opthalmoplegia, there was no evidence of OMT activity in the denervated eye. CONCLUSIONS: These results suggest that innervation of the extraocular muscles is necessary for normal OMT activity, and OMT therefore has a neurogenic origin.

Arterial closing pressure correlates with diastolic pseudohypertension in the elderly.

BACKGROUND: Pseudohypertension has frequently been reported in the elderly population, with the diastolic measurement being the most frequent source of error. There is no satisfactory noninvasive method of calculating the error in the blood pressure reading. We investigated the role of arterial closing pressure in the diagnosis of diastolic pseudohypertension. METHODS: Indirect and direct blood pressure were measured in 24 elderly patients. Brachial artery closure was visualized by ultrasound in all subjects. Arterial closing pressure (ACP) was recorded as zero if the vessel was seen to close spontaneously when it was isolated from central arterial pressure. If the vessel did not close spontaneously, a water cuff was applied externally over the artery and the additional pressure required to close it was recorded. RESULTS: Diastolic pseudohypertension was noted in 8 subjects. Spontaneous closure of the brachial artery occurred in the 16 without pseudohypertension; i.e., ACP = 0. Additional pressure of the water cuff (range: 30-158 mm Hg) was required to collapse the artery (ACP) in those with diastolic pseudohypertension. ACP correlated with the extent of diastolic pseudohypertension (range: 5-17 mm Hg); r = .85, p < .001). CONCLUSION: We propose that ACP may be used to diagnose the presence and extent of pseudohypertension.

Sources of variance in ocular microtremor.

This study presents a preliminary investigation of the sources of variance in the measurement of ocular microtremor frequency in a normal population. When the results from both experienced and relatively inexperienced operators are pooled, factors that contribute significantly to the total variance include the measurement procedure (p < 0.001), day-to-day variations within subjects (p < 0.001), and inter-subject differences (p < 0.01). Operator experience plays a role in determining the measurement precision: the intra-subject coefficient of variation is about 5% for a very experienced operator, and about 14% for a relatively inexperienced operator.

Ocular microtremor measurement system: design and performance.

The frequency of ocular microtremor (OMT) is related to the functional status of the brain stem, and thus OMT may be useful in the diagnosis and management of brain stem disorders. The paper discusses the design of an OMT measurement system and reports quantitative specifications for three portable systems. All systems use a piezo-electric element as the transducer, which measures the displacement of the sclera during eye rotations. The systems differ in the manner in which the signal is recorded. All systems can detect eye movements corresponding to displacements of the sclera ranging from 12 to over 3000 nm. The frequency responses of all systems are flat (< 2 dB deviation from peak response) between 20 and 150 Hz. The phase response shows deviations (< pi) at the extremes of this range, but qualitative comparison of input and measured signals demonstrates that phase distortion is not excessive. Thus all systems are acceptable for clinical studies involving OMT.

Measurement of arterial closing pressure.

It has been suggested that certain artifacts in blood pressure measurement by auscultation stem from stiffness of the tissues underneath the pressure cuff, resulting in a component of cuff pressure being required to overcome resistance to brachial artery collapse. This paper describes a technique for measuring the pressure required to collapse a segment of the brachial artery which has been isolated from central arterial pressure. This measurement is termed the arterial closing pressure. In a study of eleven elderly subjects, the artery collapsed spontaneously (zero closing pressure) after being isolated from central pressure in seven subjects. The remaining four required external pressures ranging from 4.6 to 10.7 kPa (35 to 81 mmHg) in order to collapse the artery. Thus arterial closing pressure may frequently be a significant fraction of arterial blood pressure in the elderly population, and may contribute to error in the measurement of blood pressure by auscultation. Arterial closing pressure may be a useful tool for investigating the origin of differences between indirect and direct blood pressure measurements, and also in the investigation of spontaneous arterial closure.

Observing the brachial artery through a pressure cuff.

A technique is described which enables ultrasonic imaging of the brachial artery whilst pressure is applied via a pressure cuff. This involves a new instrument--a sphygmomanometer, which uses water as opposed to air as the pressure medium, in order to permit ultrasonic imaging through the cuff. The technique was found to be acceptable in the clinical setting, and gave a measurement of the systolic blood pressure which correlated with the conventional cuff measurement in eleven elderly subjects (r = 0.89, p < 0.001). The technique should have an important role to play in studying the origin of differences which occur between direct and indirect blood pressure measurements.

The fast flush test: evaluation in radial artery catheter-manometer systems.

The 'fast flush test' is commonly used to determine the dynamic response of catheter-manometer systems in vivo. We compared the fast flush test with an established bench top test in vitro. The results of the two tests were compared in fifteen underdamped radical artery catheter-manometer systems. There were significant differences between the results, (P less than 0.001 for both resonant frequency and damping factor), and the variance of estimates within measurement systems was significantly greater in the case of the fast flush test (P less than 0.05 and P less than 0.005 for resonant frequency and damping factor respectively). Nevertheless, the differences between the tests were small by comparison with the errors associated with either test; in addition there was a significant linear correlation between the results of the two tests (r = 0.91, P less than 0.001 and r = 0.85, P less than 0.001 for resonant frequency and damping factor respectively). In the in vitro situation, therefore, the fast flush test provides a crude estimate of the dynamic parameters of underdamped catheter-manometer systems.

Tracheobronchial mucociliary clearance in asthma: impairment during remission.

Tracheobronchial mucociliary clearance was measured in eight non-smoking patients with asthma in complete remission. The patients were symptom free and required no medication whatsoever for one to six months before assessment. Mucociliary clearance was measured with an objective, radioaerosol technique. For comparison, mucociliary clearance of eight non-smoking, healthy subjects with physical characteristics and pulmonary function similar to those of the asthmatics was also measured on two occasions. In their first assessment the healthy subjects inhaled the tracer radioaerosol under experimental conditions similar to those used for the asthmatics; in the second assessment they inhaled the radioaerosol rapidly to simulate the asthmatic pattern of deposition. Under similar experimental conditions the radioaerosol was deposited more proximally in the asthmatic subjects than in the normal subjects and the difference was statistically significant (p less than 0.01). When, however, the depth of radioaerosol lung penetration was similar in the two groups, there was evidence of a significantly (p less than 0.01) poorer mucociliary clearance six hours after radioaerosol inhalation in the asthmatic than in the healthy group. These findings raise the question whether asthma ever remits completely.

Impaired tracheobronchial clearance in patients with mild stable asthma.

Tracheobronchial mucociliary clearance was measured with the radioaerosol technique in 25 patients with stable, mild asthma, none of whom was taking systemic corticosteroids. The results were compared with those obtained from a control group of 25 healthy subjects matched for age and sex. All patients and healthy subjects were non-smokers. Ventilatory function was significantly impaired in the asthmatic group, which resulted in a more central initial tracheobronchial deposition of inhaled radioaerosol than in the control group. Despite the shorter transit path along the ciliated airways for the tracer radioaerosol in the asthmatic group, mucociliary clearance was found to be significantly poorer than in the healthy control group. This may be important with respect to bronchial mucus plugging.

Effects of terbutaline sulphate aerosol on bronchodilator response and lung mucociliary clearance in patients with mild stable asthma.

Ventilatory function and whole lung mucociliary clearance have been assessed in 10 patients with mild stable asthma following inhalation of 1 mg of the beta-adrenergic receptor agonist terbutaline sulphate (Bricanyl, Astra Pharmaceuticals) from a metered dose inhaler (MDI). Compared to placebo inhalation, terbutaline produced marked bronchodilatation (mean percentage increase in FEV1 14%, P less than 0.01). Mucociliary clearance (measured by the in vivo radioaerosol technique) was assessed on three occasions--control, followed by placebo or terbutaline studies in a double-blind, cross-over manner. Particles were removed from the lung at a similar rate in all three studies. The mean (+/- s.e. mean) percentage of aerosol retained in the lungs after 6 h was 58 +/- 5%, 57% +/- 5% and 57 +/- 4% for control, placebo and drug studies respectively. It is concluded that terbutaline sulphate, given as a 1 mg acute dose, does not enhance mucociliary clearance in mild stable asthmatics, although it produces marked bronchodilatation.

Effect of oral corticosteroids on mucus clearance by cough and mucociliary transport in stable asthma.

Inhaled radioaerosol particles have been used to assess mucus clearance in 12 patients with stable asthma. Patients who coughed frequently showed faster clearance than those who coughed infrequently. Treatment with medium and high dose oral corticosteroids reduced coughing and thereby reliance on mucus transport by cough. Despite this, and despite increased penetration of the particles into the bronchial tree, mean particle clearance was slightly faster after four week treatment (two weeks on 15 mg prednisolone orally each day, plus two weeks on 30 mg). Mean clearance remained, however, markedly slower than in normal subjects. Five patients who were initially sputum producers (mean 1.4 g . h-1) ceased to produce sputum after four week treatment.

Lung mucociliary clearance in rheumatoid disease.

Lung mucociliary clearance rates were measured in 11 patients with rheumatoid disease and found to be unaltered when compared with those of a group of matched control subjects. The results are discussed in relation to the increased incidence of respiratory infection in patients with rheumatoid disease and also to the recently reported finding of increased airways obstruction in these patients.

Lung mucociliary clearance in patients wit Young's syndrome.

Lung mucociliary clearance was measured in 14 patients with primary obstructive azoospermia and chest involvement (Young's syndrome) using the objective, in vivo radioaerosol technique. Lung mucociliary transport was significantly reduced in patients with Young's syndrome compared to 14 control subjects matched for physical characteristics, tobacco consumption and initial topographic distribution of tracer particles within the lungs. This finding indirectly supports the hypothesis that congenital abnormality in the propulsion of sperm in the ciliated epididymis results in the absence of sperm in the ejaculate.

Is cough as effective as chest physiotherapy in the removal of excessive tracheobronchial secretions?

The relative value of chest physiotherapy (including cough) and cough alone for the removal of excessive tracheobronchial secretions has been assessed in six patients with stable chronic obstructive lung disease. After labelling with inhaled radioactive tracer particles, clearance of secretions from selected central and peripheral lung regions was followed with a gamma camera linked to a computer. Cough alone and chest physiotherapy (including cough) were equally effective in the enhancement of central lung clearance. Physiotherapy but not cough along accelerated peripheral lung clearance (p less than 0.05). Sputum yield was greater during physiotherapy than during cough (p less than 0.05). These findings confirm the value of chest physiotherapy and high-light the limitation of cough in patients with excessive tracheobronchial secretion and impaired mucociliary clearance.

Objective in vivo analysis of anti-smoking cigarette filters.

Cigarette filters have been introduced to reduce inhaled smoke and also as a means of breaking the smoking habit. Twelve volunteers smoked cigarettes through four ventilated anti-smoking filters (MD-4, Miles Laboratories) and one reference cigarette without an anti-smoking filter in a single-blind, crossover manner. The amount of smoke inhaled was monitored by a radiotracer technique using the isotope 81mkrypton. Compared to the reference cigarette the amount of isotope reaching the lung was reduced to 76%, 63%, 43%, and 37% for filters 1 to 4, respectively, which was less than the reduction to 70%, 40%, 30%, and 20% predicted by the manufacturers. In the case of filters 2, 3, and 4, the observed reductions in isotope inhalation were significant (p less than or equal to 0.01) but were also significantly less (p less than or equal to 0.01) than the manufacturers' predictions.