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Biomedical subjects

N D Harris

Publications and source records attributed to N D Harris.

At least 37 records · Page 2Linked to original sources
PubMed1999

Early identification of diabetic foot ulcers that may require intervention using the micro lightguide spectrophotometer.

OBJECTIVE: Adequate tissue oxygenation is known to be essential for the healing of diabetic foot ulcers, but hypoxia has also been shown to be a potent stimulus for growth. There are no studies looking specifically at ulcer oxygen levels during the healing process. We measured the serial microvascular oxygen saturation (SaO2) of the foot ulcer, the ulcer margin, and a control site using the Erlangen micro lightguide spectrophotometer (EMPHO II; Bodenseewerk Geratetechnik, Erlangen, Germany) to study serial changes during healing. RESEARCH AND DESIGN METHODS: Studied over 9 months were 14 patients with neuropathy with a total of 24 foot ulcer sites. Of these patients, four (seven ulcers) had significant ischemia as determined by the ankle-brachial pressure index (ABPI) and transcutaneous oxygen tension. RESULTS: Of 21 ulcer sites with serial measurements, only 13 ulcers healed. In those ulcers, a significant reduction (P<0.05) in SaO2 occurred with healing. SaO2 dropped from 58% at initial presentation (mean area 2.6 cm2) to 47% at midsize (mean area 1.2 cm2 at 5.2 weeks) and finally reduced to 45% just before it healed. Similar trends were also seen around the margin of the ulcers (initial 49%, midsize 45%, and final 41%; P = 0.1). However, there were no such changes on the control sites (43, 40, and 40%; P = 0.5) or within the eight ulcers that did not heal (46, 42, and 53%; P = 0.2). CONCLUSIONS: Serial microvascular oxygen measurements may be used to identify at an early stage those ulcers that are unlikely to heal and, therefore, need surgical intervention.

Aged↗
PubMed1998

Black Sea TeleDiab: diabetes computer system with communication technology for Black Sea region.

BlackSea TeleDiab (BSTD) is a multidisciplinary research project whose aim is to promote the exchange of healthcare information between clinicians and scientists in countries of the Black Sea area to provide a means by which the care of patients with diabetes may be enhanced. The project is built on an existing organizational framework provided by the WHO Diabcare Quality Network (Q-Net) and the Black Sea Diab Action Project. The aim is to develop a standardized software package (in the national languages of the CCE/NIS Black Sea partners) for the storage and transfer of medical information and healthcare data between participating institutions. It will utilize a standard format for medical records based on the Good European Health Record (GEHR), a project within the Advanced Informatics in Medicine (AIM) program, which aims to develop and propagate a common architecture for computerized health records across Europe that can be used across clinical domains, countries, and computer systems.

Computer Communication Networks↗
PubMed1997

Altered ventricular repolarization during hypoglycaemia in patients with diabetes.

There is circumstantial evidence implicating hypoglycaemia in the sudden overnight death of young patients with insulin-dependent (Type 1) diabetes mellitus (IDDM), the mechanism of which is unknown. We have investigated the effects of hypoglycaemia on the electrocardiogram in 15 patients with diabetes (8 with IDDM and 7 with NIDDM) using a high resolution computer-based system. Patients were randomized to either 2 h of euglycaemia or hypoglycaemia (at around 3 mmol l(-1)) during the afternoon, using hyperinsulinaemic glucose clamps, the two visits separated by a period of at least 4 weeks. Corrected QT interval (QTc), plasma potassium, and adrenaline were measured at baseline and at 0, 60, and 120 min. The degree of QTc lengthening (from baseline) during clamped hypoglycaemia was greater compared to the euglycaemic control period in patients with IDDM (median[range] at 60 min, 156[8 to 258] vs 6[-3 to 28] ms, p <0.02) and NIDDM (120 min, 128[16 to 166] vs 4[-3 to 169] ms, p <0.05). The fall in plasma potassium was greater during clamped hypoglycaemia compared to euglycaemia in those with NIDDM (p <0.03) but not in those with IDDM (p> 0.06). The rise in plasma adrenaline was greater during clamped hypoglycaemia in both groups (IDDM p <0.02, NIDDM p <0.02) and there was a strong relationship between the rise in adrenaline and increase in QTc (r = 0.73, p <0.0001). These data demonstrate alteration of ventricular repolarization with lengthening of the QT interval during hypoglycaemia and suggest a possible mechanism by which hypoglycaemia could cause ventricular arrhythmias.

Adult↗
PubMed1997

Model for the dielectric properties of human lung tissue against frequency and air content.

Electrical impedance tomographic spectroscopy measurements of the lungs are taken from nine normal subjects, in the frequency range 9.6 kHz-1.2 MHz. The results show that resistivity rho'FRC relative to functional residual capacity increases almost linearly with inspiration volume V, with the slope of the curve increasing with frequency f. Resistivity rho'9.6 kHz relative to 9.6 kHz decreases with f. rho'9.6 kHz increases with V, at any given frequency. Curves for rho'9.6 kHz show a roughly linear trend with log10(f). Based on a discussion of the measurement results, a mathematical lung tissue model is designed that involves extra-capillary blood vessels and alveoli, the walls of which consist of blood-filled capillaries, epithelial cells and intercellular liquid. Using this model, the increase in rho'FRC with V is explained by the thinning of alveolar walls with increasing air content. The almost linear shape of curves for rho'9.6 kHz is attributed to four partly overlapping main dispersions caused by extra-capillary blood vessels, epithelial cells, blood and the capillary network.

Adult↗
PubMed1997

Preservation of physiological responses to hypoglycemia 2 days after antecedent hypoglycemia in patients with IDDM.

OBJECTIVE: To assess the effects of short-term antecedent hypoglycemia on responses to further hypoglycemia 2 days later in patients with IDDM. RESEARCH DESIGN AND METHODS: We studied eight type I diabetic patients without hypoglycemia unawareness or autonomic neuropathy during two periods at least 4 weeks apart. On day 1, 2 h of either clamped hyperinsulinemic (60 mU.m-2.min-1) hypoglycemia at 2.8 mmol/l or euglycemia at 5.0 mmol/l were induced. Hyperinsulinemic hypoglycemia was induced 2 days later with 40 min glucose steps of 5.0, 4.0, 3.5, 3.0, and 2.5 mmol/l. Catecholamine levels and symptomatic and physiological responses were measured every 10-20 min. RESULTS: When compared with the responses measured following euglycemia, the responses of norepinephrine 2 days after hypoglycemia were reduced (peak, 1.4 +/- 0.4 [mean +/- SE] vs.1.0 +/- 0.3 nmol/l [P < 0.05]; threshold, 3.4 +/- 0.1 vs. 2.9 +/- 0.1 mmol/l glucose [P < 0.01]). The responses of epinephrine (peak, 4.0 +/- 1.4 vs. 3.5 +/- 0.8 nmol/l [P = 0.84]; threshold, 3.8 +/- 0.1 vs. 3.6 +/- 0.1 mmol/l glucose [P = 0.38]), water loss (peak, 194 +/- 34 vs. 179 +/- 47 g-1.m-2.h-1 [P = 0.73]; threshold, 2.9 +/- 0.2 vs. 2.9 +/- 0.2 mmol/l glucose [P = 0.90]), tremor (peak, 0.28 +/- 0.05 vs. 0.37 +/- 0.06 root mean square volts (RMS V) [P = 0.19]; threshold, 3.2 +/- 0.2 vs. 3.1 +/- 0.2 mmol/l glucose [P = 0.70]), total symptom scores (peak, 10.6 +/- 2.1 vs. 10.8 +/- 1.9 [P = 0.95]; threshold, 3.3 +/- 0.2 vs. 3.6 +/0 0.1 mmol/l glucose [P = 0.15]), and cognitive function (four-choice reaction time: threshold, 2.9 +/- 0.2 vs. 3.0 +/- 0.2 mmol/l glucose [P = 0.69]) were unaffected. CONCLUSIONS: The effect on hypoglycemic physiological responses of 2 h of experimental hypoglycemia lasts for 1-2 days in these patients with IDDM . The pathophysiological effect of antecedent hypoglycemia may be of shorter duration in IDDM patients, compared with nondiabetic subjects.

Adult↗
PubMed1996

EITS changes following oleic acid induced lung water.

We present the results of using electrical impedance tomographic spectroscopy (EITS) to follow the changes in lung water induced by oleic acid. Measurements were made on three goats before and after the injection of oleic acid. In addition to the EITs measurements, lung water was also measured using a double-indicator technique. Large falls in lung electrical impedance were seen as a result of the increase in lung water but the size of the fall was a function of the frequency at which the measurements were made. These changes have been modelled using the Cole equation. Four-electrode measurements were also made on two extracted porcine lungs and Cole equation modelling carried out following the introduction of saline into the lungs. Results were similar in the two sets of animal experiments.

Animals↗
PubMed1995

Is ACE inhibition with lisinopril helpful in diabetic neuropathy?

Thirteen diabetic patients with hypertension (mean diastolic blood pressure 96.2 +/- 1.1 mmHg) were included in a study to assess the effects of lisinopril (20 mg day-1) on measures of nerve function. Patients had nerve conduction velocity (NCV), temperature discrimination threshold (TDT), and vibration perception threshold (VPT) measurements. At the end of 12 weeks of treatment with lisinopril, there was a significant improvement in median motor NCV (mean change +/- SEM 2.7 +/- 0.6 m s-1, p < 0.0001), median sensory NCV (2.1 +/- 0.9 m s-1, p = 0.03), peroneal motor NCV (1.0 +/- 0.4 m s-1, p = 0.03), and sural sensory NCV (1.9 +/- 0.7 m s-1, p = 0.01) values. There were also significant improvements in warm TDT and VPT. Diastolic BP decreased significantly, but there was no significant change in HbA1. Double blind controlled studies are now needed to confirm the effect of lisinopril on measures of nerve function.

Adult↗
PubMed1994

Detection of changes in intrathoracic fluid in man using electrical impedance tomography.

1. The Sheffield electrical impedance tomography system produces information on changes in the distribution of resistivity within tissue. We report on the assessment of electrical impedance tomography in monitoring changes in lung resistivity during a fluid challenge in normal man. 2. Eight normal subjects were studied. Electrical impedance tomography recordings were made at three different lung volumes before, during and after the intravenous infusion of 1 litre of 0.9% NaCl (saline). 3. The mean fall in lung resistivity during the infusion was -22% at total lung capacity (range -10% to -28%), -24% at tidal breathing (-15% to -37%) and -11% at residual volume (-5% to -19%) (P < 0.05 mean pre-infusion resistivity compared with the nadir value after infusion, Wilcoxon). 4. These changes in lung resistivity were probably due to a combination of a fall in haematocrit and an expansion of pulmonary blood volume.

Adult↗
PubMed1994

Clinical applications of electrical impedance tomography in the monitoring of changes in intrathoracic fluid volumes.

We have previously shown that EIT can detect changes in intrathoracic fluid volumes in normal subjects undergoing a fluid challenge. We now report the preliminary results of two studies designed to investigate the ability of EIT to monitor changes in intrathoracic fluid in disease states. All recordings were made using the Sheffield Mark 1 system with the 16 electrode array placed around the lower thorax. Ten patients were studied during the sequential aspiration of unilateral pleural effusions. Following recording of a baseline dataset during tidal breathing (600 cycles) fluid was aspirated in 300 ml aliquots up to a maximum of 1000 ml, 600 cycles of data being collected after each aspiration. On the side of the effusion there was a progressive increase in intrathoracic resistivity in all patients as the fluid was aspirated. The mean increase in resistivity per 100 ml aspirated was 7%, range 3%-13%, p < 0.01 pre- versus post-aspiration resistivity. In the contralateral lung there was a smaller increase in all subjects (mean 1.8%, range 1%-3%) consistent with a reduction in mediastinal shift following aspiration. In these preliminary observations we have shown that EIT can be used in the clinical environment to detect small changes in intrathoracic fluid.

Adult↗
PubMed1993

The performance of two intensive care humidifiers at high gas flows.

High continuous flow breathing systems are now available to provide fresh gas flows well in excess of 100 l.min-1 in continuous positive airway pressure systems used for respiratory support. The performance of two commonly used intensive care humidifiers, the Kendal Conchatherm and the Fisher and Paykel FP310 have been assessed at flows of 50, 75, 100, 125 and 150 l.min-1. Their performance when using two humidifiers connected in parallel and in series was also studied. At a fresh gas flow of 100 l.min-1 the single Conchatherm gave an absolute water vapour concentration of 15.6 g.m-3 and the single FP310 11.9 g.m-3. At all flows the best results were achieved using two Conchaterm humidifiers in series. It is concluded that with high continuous flow breathing systems the humidification achieved with conventional humidifiers may be inadequate and it may be necessary to combine two humidifiers to obtain clinically useful humidification.

Critical Care↗
PubMed1992

Exercise-induced conduction velocity increment: a marker of impaired peripheral nerve blood flow in diabetic neuropathy.

Severe microvascular disease exists at the stage of clinical diabetic neuropathy. A non-invasive test that will identify those diabetic subjects who will eventually develop neuropathy is essential for early intervention. Sural sensory conduction velocity was recorded (x3) in 12 non-neuropathic diabetic subjects, 15 diabetic subjects with established neuropathy and 16 age-matched normal control subjects, before and after exercise to 80% age/sex predicted maximum heart rate. Fixed sural electrodes were used. Subcutaneous temperature was recorded by a needle thermocouple placed near the sural nerve. Sural sensory conduction velocity increased significantly after exercise in normal subjects (p less than 0.01, mean increase 5.07 m/s) and non-neuropathic diabetic subjects (p less than 0.02, mean increase 3.99 m/s) but not in neuropathic subjects (mean increase 0.99 m/s). Subcutaneous temperature rose significantly in normal subjects (p less than 0.01, mean increase 2.07 degrees C) and non-neuropathic diabetic subjects (p less than 0.001, mean increase 2.52 degrees C) but not in neuropathic subjects (mean increase 0.15 degree C). However, sural sensory conduction velocity increased by 1.2 m.s-1.degree C-1 following direct warming of the limb in six neuropathic subjects which was comparable to that of normal and non-neuropathic subjects (1.49 and 1.48 m.s-1. degree C-1). The impairment of exercise conduction increment in diabetic neuropathy suggests impaired nerve blood flow in diabetic neuropathy.

Adult↗
PubMed1991

Acute effects of external negative pressure ventilation in chronic obstructive pulmonary disease compared with normal subjects.

This study compares the acute physiological effects of external negative pressure ventilation (ENPV) in normal subjects and patients with chronic obstructive pulmonary disease (COPD). The equipment consisted of an airtight jacket (Pneumosuit) and vacuum pump. Minute ventilation (Ve) was recorded using a light-emitting turbine transducer. Oxygen uptake (VO2) and carbon dioxide output (VCO2) were calculated every 30 s. Measurements were made at rest and during ENPV with pressures of -20 cmH2O and -40 cmH2O. The ventilator rate was fixed at 16.min-1. In 10 normal subjects, Ve increased from 8.6 to 22.9 l.min-1 (p less than 0.01) accompanied by an increase in VCO2 from 0.25 to 0.39 l.min-1 (p less than 0.01). In 10 normocapnic COPD patients (arterial carbon dioxide tension (PaCO2) less than 6.0 kPa) Ve increased from 11.5 to 17.1 l.min-1 (p less than 0.01) whilst in 10 hypercapnic patients (PaCO2 greater than 6.0 kPa) Ve increased from 9.7 to 12.4 l.min-1 (p less than 0.01). A change in VCO2 was not detected in the COPD patients, and VO2 did not change in any group. Arterial blood samples were obtained in eight hypercapnic patients. Baseline mean physiological deadspace ventilation (VD) was calculated to be 4.9 l.min-1 (56% of Ve) whilst Ve was 8.8 l.min-1 in this subgroup. During ENPV, arterial oxygen tension (PaO2) increased from 6.8 to 8.2 kPa (p less than 0.01) whilst PaCO2 decreased from 6.8 to 5.8 kPa (p less than 0.01) suggesting that despite the large physiological deadspace, a significant increase in alveolar ventilation had occurred. In advanced COPD, thoracic compliance falls and limits the ventilatory response to ENPV.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Evaluation of a turbine flow meter (Ventilometer Mark 2) in the measurement of ventilation.

We have evaluated a turbine flow meter (Ventilometer Mark 2, PK Morgan, Kent, UK) at low flow rates and levels of ventilation which are likely to be encountered during exercise in patients with chronic respiratory disease. Pulsatile flows were generated from a volume-cycled mechanical ventilator, the flow wave-form was modified by damping to simulate a human breathing pattern. Comparative measurements of ventilation were made whilst varying tidal volume (VT) from 0.22 to 1.131 and respiratory rate (fR) from 10 to 35 min-1. At lower levels of ventilation the instrument tended to underread especially with increasing fR. The calibration factor must be adjusted to match the level of ventilation if the measurement errors are to be within 5%.

Calibration↗
PubMed1988

Applied potential tomography: a new technique for monitoring pulmonary function.

An electrical impedance tomographic imaging system has been developed which can monitor changes in the resistivity of the thorax at a rate of 5 frames per second. There is a high correlation (r greater than 0.95) between changes in resistivity of the lungs and the volume of air inspired. Calibration of the system allows continuous monitoring of the level of ventilation on exercise up to a minute volume of 45 l min-1. The volumetric accuracy of the system is generally within +/- 10% of spirometric measurements. Studies of the effect of changes in posture on the calibration of the system show changes of between +9.5% and -3.8% in normal male subjects. The performance of the system compares favourably with existing techniques for the noninvasive monitoring of ventilation.

Humans↗
PubMed1987

Applications of applied potential tomography (APT) in respiratory medicine.

Impedance pneumography, electrical impedance measurements of the lung, is a technique which has been widely used to monitor respiration non-invasively and more recently, the onset of pulmonary oedema. Attempts have been made to try to localise the changes in impedance using electrode arrays and electrode guarding. These techniques allow localisation to a particular hemithorax, but the resolution of the majority of the systems remains poor. To assess the performance and possible clinical applications of APT, measurements have been made following increases in lung volume and pulmonary blood volume. During inspiration an increase in both the area and the magnitude of the impedance changes over the area of the lungs was observed. Numerical analysis of the impedance changes in normal subjects reveals a consistently high correlation between the volume of air inspired and the magnitude of the impedance changes. The resolution of the system is sufficient to monitor differences in ventilation in the right and left lung and to measure variations in these levels with posture. Preliminary clinical work suggests that APT may be used to detect ventilatory defects in certain types of lung disease. APT measurements show a decrease in resistivity over the area of the lungs when the pulmonary blood volume is increased by the intravenous infusion of 1.5 litres of isotonic saline. Similar changes in the volume of fluid in the lungs are known to occur in pulmonary oedema. APT measurements of lung impedance may detect the onset of pulmonary oedema in high risk patients.

Adult↗
PubMed1975

Effect of electronic cooking on fatty acids in meats.

This study was conducted to investigate the effects of microwave energy and conventional heating on the fatty acid composition of meats and poultry. Data on weight loss and cooking time with both heat treatments are reported. Gas-liquid chromatographic data of the methyl esters of myristic, palmitic, stearic, oleic, linoleic, and linolenic acids revealed no significant difference between fatty acid composition as a result of heat treatment. Decreases in fatty acids appeared to be mainly due to a change in oleic acid. Poultry appeared to be the species most affected by heat treatment. Cooking times were much shorter for the electronic method and varied among species. No significant difference was found in weight loss as a result of treatment of beef or pork. Poultry weight losses were greater for the conventional method.

Animals↗