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Biomedical subjects

A J Mearns

Publications and source records attributed to A J Mearns.

At least 37 records · Page 2Linked to original sources
PubMed1993

Plasma concentrations of bupivacaine and its enantiomers during continuous extrapleural intercostal nerve block.

Plasma concentrations of bupivacaine have been measured in 12 patients given bupivacaine through a paravertebral catheter placed under direct vision at thoracotomy. After an initial bolus of 0.5% bupivacaine 20 ml, mean (SEM) Cpmax was 1.45 (0.32) micrograms ml-1 and median (range) tCpmax was 25 (10-60) min. A concentration of 4.43 micrograms ml-1 measured in one patient was not associated with toxic signs. During continuous infusion of bupivacaine for 120 h, Cpmax was 4.9 (0.7) micrograms ml-1 and tCpmax 48 (5-96) h. No symptoms or signs of toxicity occurred. Separate measurement of R- and S-bupivacaine concentrations demonstrated significantly different concentration-time profiles.

Adult↗
PubMed1992

Periodic posture stimulation of the baroreceptors and the local vasomotor reflexes.

In a supine subject, lowering of the foot from heart level to 50 cm below is known to stimulate the local reflex response and the baroreceptor outflow. We lowered and raised the leg of a supine subject periodically, with the leg stationary between movements (square wave). The Traube-Hering-Mayer wave (THM congruent to 0.1 Hz) was captured by or locked on to the leg movement over a certain frequency range, this is usually called the entrainment range. Square wave periodic leg movement in this manner on 10 male subjects, mean age 22 years, demonstrated that the THM frequency can be entrained. The lower limit of the entrainment bandwidth is 0.0841 (SD 0.0030) Hz and the upper limit is 0.1176 (SD 0.0013) Hz. Further examination showed that this phenomenon is independent of the breathing input. Comparison with the Traube-Hering-Mayer entrainment techniques of breathing and periodic neck suction using the Eckberg collar which stimulates the baroreceptors showed similar results. This work supports the hypothesis that the local reflex response and the baroreceptor outflow entrain the THM frequency.

Adult↗
PubMed1991

Reversed-phase and chiral high-performance liquid chromatographic assay of bupivacaine and its enantiomers in clinical samples after continuous extraplural infusion.

A previously unreported coupled achiral-chiral high-performance liquid chromatographic method has been developed to assay the levels of bupivacaine and its enantiomers in plasma samples, after the local anaesthetic had been given as a continuous extrapleural intercostal nerve block for 4 days, to relieve postoperative pain following thoracotomy. The method has been used to determine maximum, individual enantiomer and steady state levels in conjunction with an assessment of whether accumulation of bupivacaine occurs. An off-line extraction sample preparation is involved before determination of the "total" levels and final sample clean-up on a cyanopropyl silica column prior to "heart cutting" of the bupivacaine peak to a Chiral-AGP column for assay of the enantiomeric ratio. For an initial 5 patient number the mean maximum level was 5.43 micrograms/ml against a reported toxic level of around 5 micrograms/ml, which was reached in 72 h and the S-enantiomer gave slightly increased concentrations over the R-enantiomer for which there is some evidence of higher toxicity.

Adult↗
PubMed1991

Quantitative measurement of sympathetic neuropathy in patients with diabetes mellitus.

Vasoconstriction occurs in the skin capillary blood flow of the healthy subject when posture changes from supine to standing. Using frequency analysis of the optical photoplethysmograph signal, a statistically significant difference (P less than 0.01) may be demonstrated between supine and standing positions in the lower frequency band (0.01-0.5 Hz) in the foot of normal subjects. This allowed us to develop a simple index: sympathetic power band change (SPBC). Patients with diabetes mellitus often suffer from degeneration in the sympathetic nervous system. This impairs the normal vasoconstrictor response to standing. We have applied the SPBC 'blind' to a group of diabetic patients. Such patients may be divided into three groups according to their SPBC indices: normals with SPBC greater than 2.6 (group A), intermediates with 2.6 greater than or equal to SPBC greater than or equal to 0.26 (group B) and poor with SPBC less than 0.26 (group C). All patients with retinopathy were in group C and five out of the six patients with electrophysiologically confirmed peripheral neuropathy were in group C. Frequency analysis of the photoplethysmograph signal has produced an index of sympathetic tone change when subjects move from supine to standing position. The application of this index to patients with diabetes mellitus shows some patients to have sympathetic vascular tone failure.

Adult↗
PubMed1991

Continuous extrapleural intercostal nerve block after pleurectomy.

A randomised, double blind trial was carried out in 16 patients undergoing pleurectomy to assess the effect of continuous extrapleural intercostal block on postoperative pain and pulmonary function. Subjective pain relief was assessed on a linear visual analogue scale. Pulmonary function was measured on the day before operation and daily for five days after surgery. Eight patients received bupivacaine and eight placebo (saline). The mean pain scores at 4, 8, 16, and 24 hours were 13.3, 8.5, 6.1, and 10 mm respectively in the bupivacaine group compared with 56.3, 41, 46.7, and 35 in the control group; in addition, the bupivacaine group required less papaveretum. Twenty four hours after surgery mean values of peak expiratory flow, forced expiratory volume in one second, and forced vital capacity were reduced to 82%, 76%, and 76% of preoperative control values in the bupivacaine group, and to 39%, 32%, and 36% in the control group. The speed of recovery of pulmonary function was superior in the bupivacaine group. There were no complications related to the infusion. Continuous extrapleural intercostal nerve blockade with bupivacaine provides safe and effective postoperative analgesia and improves respiratory mechanics after pleurectomy.

Adolescent↗
PubMed1991

Fine needle aspiration biopsy of pulmonary lesions: a 2-year experience in a district general hospital with a literature review.

During the 2 years of 1987 and 1988, 74 patients with suspected malignant lung lesions underwent fine needle aspiration biopsy at the Bradford Royal Infirmary. Using a 20Fr needle, sufficient specimen (smear and clot) was obtained in 70 (95%) patients for histological examination. The indications for the procedure were: failure to make a diagnosis at bronchoscopy and bronchial lavage in 32 (43%) patients, peripherally located lesion in 28 (38%) patients, poor anaesthetic risk in 20 (27%) patients, negative bronchoscopy and mediastinostomy in five (7%) patients and three (4%) patients refused operative intervention. There were no deaths and complications were few. Seven patients developed pneumothorax, three of whom required intercostal drainage. Transient haemorrhage as shown by haemoptysis occurred in one patient and one patient complained of pleuritic chest pain. Of the 60 patients with malignant disease eventually proven, 50 were diagnosed correctly. The overall sensitivity and specificity of the test were 81 and 100% respectively based on histological and/or clinical outcome of the lung lesion. The test was cost-effective, diagnostic yield was high and complications were few. The use of fine needle aspiration biopsy as part of the management policy in peripheral lung lesions is realistic in a district general hospital.

Adult↗
PubMed1990

Efficacy of continuous extrapleural intercostal nerve block on post-thoracotomy pain and pulmonary mechanics.

To assess the efficacy of continuous extrapleural intercostal nerve block on postoperative pain and pulmonary function, a prospective, randomized, double-blind, placebo-controlled trial was conducted on 56 patients undergoing elective thoracotomy. Infusion was started before closing the chest and was continued for 5 days. Subjective pain relief was assessed on a linear visual analogue scale. Pulmonary function was measured on the day before operation and daily for 5 days. There were 29 patients in a group which received bupivacaine and 27 in a control group which received saline. The bupivacaine group had lower pain scores (P less than 0.01) and required less papaveretum (P less than 0.01) than the control group. Forced vital capacity, forced expiratory volume in 1 s and peak expiratory flow rate were maximally reduced at 24 h to median values of 56, 60 and 57 per cent, respectively, of preoperative control values in the bupivacaine group, and to 25, 30 and 32 per cent in the control group. These differences are highly significant (P less than 0.01). Restoration of pulmonary function was superior in the bupivacaine group (P less than 0.01). There were no infusion-related complications. After thoracotomy, continuous intercostal blockade with bupivacaine is a safe and effective method of pain relief which reduces the early loss of postoperative pulmonary function significantly and more rapidly restores respiratory mechanics.

Adult↗
PubMed1990

Pulmonary complications after lung resection: the effect of continuous extrapleural intercostal nerve block.

To assess the efficacy of continuous extrapleural intercostal nerve block (CEINB) with 0.5% bupivacaine on postoperative pain, pulmonary function and pulmonary complications, a prospective, randomised, double blind controlled trial was conducted on comparable patients undergoing lung resections; n = 21 (control), n = 25 (bupivacaine). The bupivacaine group required less papaveretum in the first 24 h (P less than 0.01) and had lower pain scores over 5 postoperative days (P less than 0.01). Pulmonary function recovered earlier in the bupivacaine group. Pulmonary complications occurred in 1 patient with normal lung function and 12 patients with obstructive airways disease (COAD): FEV1/FVC less than 70%. There were no infusion-related complications. CEINB has been shown to be safe and effective in reducing postoperative pain and pulmonary complications. CEINB minimises the loss of lung function after thoracotomy and restores impaired pulmonary mechanics more rapidly.

Bupivacaine↗
PubMed1990

Chest wall reconstruction after resection of primary malignant chest wall tumours.

In order to review the development of chest wall reconstruction, 37 cases of primary malignant skeletal chest wall tumours treated since 1958 were studied. These included chondrosarcomas (20), Ewing's tumours (7) and solitary plasmacytomas (10). Skeletal reconstruction was performed in 24 patients. Before 1972, Marlex mesh alone was used. Since then, a sandwich of two layers of Marlex mesh with a filler of methyl methacrylate was utilised successfully producing better functional and cosmetic results. Primary soft tissue closure was possible in all but 5 cases in whom latissimus dorsi myocutaneous flaps were used. All but one patient had an uneventful postoperative recovery with none requiring postoperative ventilatory support. The overall survival of 46% at 5 years and 27% at 10 years was encouraging. Familiarity with the techniques of chest wall reconstruction enables wide excision of primary chest wall tumours and the palliation and treatment of other malignant, infective and degenerative conditions since even large defects can be reconstructed with little functional disturbance.

Adolescent↗
PubMed1990

Alterations in respiratory mechanics following thoracotomy.

Major alteration in respiratory mechanics occur in all patients following anaesthesia and thoracotomy because of a decrease in the functional residual capacity with minimal change in the closing volume leading to airway closure during tidal breathing and atelectasis. Diminished pulmonary reserve, because of non-pulmonary and pulmonary risk factors before operation, and/or restrictive ventilation and abnormal pattern of breathing due to postoperative pain sustain and aggravate these changes. These can proceed to postoperative pulmonary complications in some normal, and in many high risk, patients. Detection and correction of pre-existing pulmonary disease, smoking, sepsis and obesity is essential to reduce postoperative morbidity and mortality. Effective postoperative regional analgesia minimizes impairment of pulmonary function, aids in its recovery, and prevents postoperative pulmonary complications. The adjuvant use of chest physiotherapy and incentive spirometry should also help in decreasing the adverse affects of anaesthesia and surgery on the chest and thereby reduce the frequency and severity of postoperative complications.

Anesthesia, General↗
PubMed1990

Primary bony chest wall tumours.

A retrospective review of 81 cases of primary chest wall tumours was carried out to analyse their clinical, radiological and surgical features. There were 37 malignant and 44 benign lesions; 72 were found in the ribs and nine in the sternum, of which five were malignant and four benign. Benign tumours of the ribs outnumbered malignant ones by a ratio of 5:4. The distinction between benign and malignant lesions is difficult clinically and radiologically unless cortical destruction and soft tissue swelling are present. The pathological differentiation is also not possible in all cases. All the patients with benign tumours were treated by excision with no recurrences or deaths. The overall 5-year survival for primary malignant chest wall tumours was 43% and 10-year survival was 27%. These were the results of radical en bloc excisions. Based on our experiences we believe that all tumours of the bony chest wall should be considered potentially malignant and wide excision should be performed, not only to provide adequate tissue for diagnosis but also to allow the best chance of cure in malignant lesions.

Adolescent↗
PubMed1989

Malignant melanoma metastatic to the esophagus.

A rare case of metastatic malignant melanoma of the esophagus 11 years after wide excision of a cutaneous malignant melanoma is presented and the relevant literature reviewed. Symptomatic esophageal metastasis is unusual in malignant melanoma. Although the eventual outlook is poor in such cases, worthwhile palliation can be achieved by prompt diagnosis and treatment.

Adult↗
PubMed1989

Skin photoplethysmography--a review.

The photoplethysmograph has been used for over 50 years but there are still misconceptions in how and what is the information obtained. A photoplethysmograph signal from any site on the skin can be separated into an oscillating (a.c.) and a steady-state (d.c.) component, their amplitudes dependent upon the structure and flow in the vascular bed. Many simple applications are available: pulse counters, using the a.c. component, skin colour and haemoglobin saturation meters, using the d.c. component. The d.c. component of the photoplethysmograph signal is a function of the blood flux beneath the device. A good emitter for use in a photoplethysmograph of skin blood flow is one in the frequency range 600-700 nm and the best signal for a.c. analysis is obtained from the finger pulp. The frequency range of the electronic circuitry should be from 0.01 to 15 Hz, then all the information in the signal can be extracted about the autonomic nervous system control of the cardiovascular system, particularly between 0.01 and 2 Hz. Comparative studies may be drawn between similar skin sites on a subject or between subjects if the afferent inputs to the brain stem are controlled or driven at a known frequency. These afferents, inputs, will modulate the efferents, outputs, which generate variations in the a.c. component of the detected photoplethysmograph signal.

Equipment Design↗
PubMed1989

Dynamic radionuclide imaging with 99mTc-sucralfate in the detection of oesophageal ulceration.

Standard oesophageal scintigraphic techniques using 99mTc-colloids rarely identify oesophageal mucosal damage. Sucralfate can be labelled with 99mTc for the detection of oesophageal mucosal ulceration. This method uses two separate supine swallows of 10 MBq 99mTc-colloid in 10 ml, followed by a single supine swallow of 30 MBq 99mTc-sucralfate. The data are processed to give time-activity curves, mean transit times and condensed dynamic images. When oesophageal ulceration is detected, the time-activity curves using sucralfate show residual activity in the oesophagus after the transit time indicated by the colloid swallow. The condensed dynamic image shows a persistence of activity at the level of the ulceration. Erect sucralfate images taken immediately after the dynamic sequence show no oesophageal localisation. The results from a study of 62 patients have shown excellent correlation between the dynamic 99mTc-sucralfate images and endoscopy findings. Sequential sucralfate studies for healing also correlate well. The use of labelled sucralfate to detect oesophageal ulceration could modify the indications for endoscopy in gastrooesophageal reflux disease.

Adolescent↗
PubMed1988

Continuous intercostal nerve block for pain relief after thoracotomy.

Others have demonstrated the effectiveness of intercostal analgesia with bupivacaine hydrochloride (Marcain Plain; Astra). We present a greatly simplified method of effecting this. Our method is dependent on an intact pleura. To date, we have utilized this technique in 81 patients. Seventy-five (92.6%) required no additional analgesic in the first 24 hours following operation and 66 (81.5%), in the subsequent four days. Only 2 patients had postoperative pulmonary complications. No complication related either to the procedure or to the infusion of bupivacaine occurred. The technique as described here is a safe and reliable method of providing analgesia without any side effects after thoracotomy.

Adult↗
PubMed1986

Modelling of the control of heart rate by breathing using a kernel method.

The process of the breathing (input) to the heart rate (output) of man is considered for system identification by the input-output relationship, using a mathematical model expressed as integral equations. The integral equation is considered and fixed so that the identification method reduces to the determination of the values within the integral, called kernels, resulting in an integral equation whose input-output behaviour is nearly identical to that of the system. This paper uses an algorithm of kernel identification of the Volterra series which greatly reduces the computational burden and eliminates the restriction of using white Gaussian input as a test signal. A second-order model is the most appropriate for a good estimate of the system dynamics. The model contains the linear part (first-order kernel) and quadratic part (second-order kernel) in parallel, and so allows for the possibility of separation between the linear and non-linear elements of the process. The response of the linear term exhibits the oscillatory input and underdamped nature of the system. The application of breathing as input to the system produces an oscillatory term which may be attributed to the nature of sinus node of the heart being sensitive to the modulating signal the breathing wave. The negative-on diagonal seems to cause the dynamic asymmetry of the total response of the system which opposes the oscillatory nature of the first kernel related to the restraining force present in the respiratory heart rate system. The presence of the positive-off diagonal of the second-order kernel of respiratory control of heart rate is an indication of an escape-like phenomenon in the system.

Heart Rate↗