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Biomedical subjects

N E Almond

Publications and source records attributed to N E Almond.

11 recordsLinked to original sources
PubMed1992

Measurement of hepatic perfusion in rats by laser Doppler flowmetry.

Little is known about the performance of the laser Doppler flowmeter (LDF) with changes in flow characteristics in the hepatic microcirculation. Red blood cell (RBC) flux, as measured by LDF, is sensitive to alterations in RBC velocity and RBC concentration, and both parameters must be considered when evaluating the technique. In vitro, linearity of LDF signal with RBC velocity up to 4 mm/s (r greater than 0.99) and RBC volume fractions up to 1.5% were demonstrated (r greater than 0.98). At higher velocities and volume fractions, RBC flux was underestimated. In portally perfused rat liver, LDF output was linearly related to total liver blood flow (TLBF; r greater than 0.9) for perfusate hematocrits between 2.5 and 40%, although the slope varied between preparations. At constant TLBF (2 ml.min-1.g-1), the LDF output changed linearly with perfusate hematocrit up to 20% (r greater than 0.99) but underestimated the increase at 40%. These results suggest that the LDF responds linearly to velocity-mediated flow changes but that it may underestimate a change if mediated through alteration in tissue RBC concentration. With hepatic nerve stimulation, TLBF fell to 51 +/- 14% of prestimulation (P less than 0.001), whereas the LDF output and superficial flow measured by 85Kr clearance fell to 12 +/- 10 and 14 +/- 10% (both P less than 0.01 vs. TLBF), respectively, suggesting that the LDF may be used to follow rapid flow changes in the periphery of the liver.

Animals↗
PubMed1989

Comparison of intravenous infusions of iloprost and oral nifedipine in treatment of Raynaud's phenomenon in patients with systemic sclerosis: a double blind randomised study.

OBJECTIVE: To compare the long term effects of short term intravenous infusions of iloprost with those of oral nifedipine in patients with Raynaud's phenomenon associated with systemic sclerosis. DESIGN: Double blind, placebo controlled, randomised group comparison. SETTING: Dermatology outpatient clinic. PATIENTS: Twenty three patients with Raynaud's phenomenon associated with well documented systemic sclerosis (American Rheumatism Association criteria) and with typical abnormalities in fingernail folds on capillaroscopy. INTERVENTIONS: Twelve patients were randomised to receive intravenous infusions of iloprost starting at 0.5 ng/kg/min and increased by 0.5 ng/kg/min every 15 minutes to a maximum of 2.0 ng/kg/min for eight hours on three consecutive days with a further single infusion at week 8. Placebo capsules were given concurrently. Eleven patients were randomised to receive nifedipine, starting at 30 mg daily and increased to 60 mg daily after four weeks for another 12 weeks. Infusions of placebo were given in the same manner as the infusions of iloprost. One patient from each group withdrew because of social reasons and three patients receiving nifedipine withdrew because of side effects. END POINT: Reduction in number, duration, and severity of attacks of Raynaud's phenomenon, reduction in number of digital lesions, increase in digital blood flow. MEASUREMENTS AND MAIN RESULTS: Measurements were taken at 0, 4, 8, 12, and 16 weeks. Both regimens produced a reduction in the number, duration, and severity of attacks of Raynaud's phenomenon. The mean (SE) number of digital lesions was reduced with iloprost (from 3.5 (1.6) to 0.6 (0.3] and with nifedipine (from 4.3 (0.8) to 1.4 (0.5] after 16 weeks. Hand temperature and digital and microcirculatory blood flow were increased with iloprost but not with nifedipine. CONCLUSION: Both iloprost and nifedipine are beneficial in the treatment of Raynaud's phenomenon. With nifedipine, however, side effects are common. Short term infusions of iloprost provide longlasting relief of symptoms, and side effects occur only during the infusions and are dose dependent.

Administration, Oral↗
PubMed1989

Effect of captopril on skin blood flow following intradermal bradykinin measured by laser Doppler flowmetry.

The effect of captopril on skin response to intradermal injection of bradykinin was investigated by laser Doppler flowmetry (LDF) and weal and flare measurements in this randomised, double-blind, placebo-controlled, cross-over balanced study. Intradermal injections of 1 and 2.5 micrograms of bradykinin and normal saline were made into the forearm skin of six healthy volunteers between 1 and 2 h (t1) and between 3 and 4 h (t2) after either 25 mg captopril or placebo. Skin blood flow outside the induced weal was monitored continuously by LDF for 15 min and the mean LDF values over the last 15 s were used for analysis. Weal and flare sizes were measured at 15 min. On the placebo days, the mean LDF output, weal volume and flare area increased with incremental bradykinin dose. Pre-treatment with captopril significantly increased LDF output following intradermal bradykinin at t1 but not at t2. At both t1 and t2, captopril significantly increased weal volume. There was no significant difference between treatments in flare areas. Skin response following intradermal normal saline, measured by the above parameters, was not affected by captopril. This study showed that captopril potentiated the effects of intradermal bradykinin both with respect to blood flow changes and weal formation. The non-invasive technique of LDF can be used to detect the skin blood flow changes induced by intradermal bradykinin and the potentiation of this effect by captopril. It appears to be a useful and more objective method of quantifying local cutaneous blood flow changes than measurement of flare area.

Adult↗
PubMed1989

Observations on the photoplethysmograph pulse derived from a laser Doppler flowmeter.

A photoplethysmograph signal has been derived from a laser Doppler flowmeter which uses optical fibres separated by 1 mm. When compared with a conventional photoplethysmograph, the trace contains a higher proportion of random signal superimposed on the pulse. The bandlimited laser photoplethysmograph (0.5-16 Hz) was recorded from the finger in six subjects. At low blood flows or during arterial occlusion the random component was more evident, producing a significant signal power increase in the range 8-16 Hz. It is proposed that this noise associated with laser photoplethysmographs is partly intrinsic signal due to low frequency Doppler shifts, which predominate at low blood flows, or intensity fluctuations as slow moving blood cells traverse the laser speckle pattern. Increasing the fibre separation above 2-3 mm reduces the relative amplitude of the random component producing a much improved photoplethysmograph signal. Multiple scattering at this separation tends to reduce the proportion of low frequency Doppler shifts. Signal averaging may be used to smooth the photoplethysmograph from the 1 mm fibre separation to give a pulse essentially identical to the improved signal obtained at higher separations. Photoplethysmograph amplitude demonstrated a non-linear relationship with the laser Doppler value from the same site during finger re-warming following cold stress.

Arterial Occlusive Diseases↗
PubMed1989

Reflex sympathetic dystrophy (algoneurodystrophy): temperature studies in the upper limb.

The temperature response of the hands to mild cold stress (20 degrees C for one minute) has been measured in 20 normal subjects, 20 patients with reflex sympathetic dystrophy (RSD) and 10 patients with chronic upper limb pain (CULP) of uncertain origin. The results of RSD and CULP groups were significantly (p less than 0.05) different from normal but were indistinguishable. For each patient, 11 variables obtained from the thermal stress test were compared with the normal range. Ten of the RSD group and seven of the CULP group had four or more abnormal variables and were considered to have a thermoregulatory abnormality. The thermal stress test is useful in the objective assessment of RSD. It is non-invasive, patient acceptable and reproducible.

Adult↗
PubMed1988

High quality photoplethysmograph signals from a laser Doppler flowmeter: preliminary studies of two simultaneous outputs from the finger.

An improvement in the quality of a photoplethysmography signal derived from a laser Doppler flowmeter probe has been achieved by incorporating an auxiliary fibre in the probe head. This fibre is positioned at an optimum distance from the laser light transmitting fibre and overcomes the problem of high frequency signals which mask the detailed features of the photoplethysmograph pulse when a small fibre separation is used. These two signals may be recorded simultaneously from the same site and a correlation between the Doppler output and the photoplethysmograph amplitude has been demonstrated in the finger. The amplitude is shown to be affected by the relative position of the point of measurement with respect to the heart, a factor which does not appear to influence significantly the Doppler output.

Equipment Design↗
PubMed1988

Noninvasive measurement of the human peripheral circulation: relationship between laser Doppler flowmeter and photoplethysmograph signals from the finger.

Under certain conditions laser Doppler flowmeter (LDF) signals obtained from the finger pulp may appear very similar to those obtained by use of a direct current (dc) photoplethysmograph (PPG). A combined LDF/PPG system was used in conjunction with a circumference strain gauge as an index of volume change to identify the conditions in which the correlation between these signals was good. Simultaneous LDF and dc PPG measurements were made on 10 normal volunteers by using arterial occlusion and on 7 normal subjects by using the Valsalva maneuver at different elevations of the forearm and hand with respect to the midsternum. By altering the elevation of the upper limb the influence of venous filling on each of the signals during these maneuvers was observed. Since the dc PPG signal always appeared similar to the volume change indicated by the circumference strain gauge, it is concluded that the dc PPG signal is related to blood volume change if allowance is made for the effects of blood oxygenation. In circumstances of low venous filling, however, blood volume changes correlate well with blood flow changes, producing the correlation between the dc PPG and LDF traces. The dc PPG signal may be used as a means of monitoring changes in blood flow in the finger only when venous filling is low and the return remains unrestricted. Thus, in investigations using this method, the relative position of the limb with respect to the heart should always be indicated. The LDF method appears to be a reliable indicator of blood flow changes in the microcirculation irrespective of the degree of venous filling.

Adult↗
PubMedDate not supplied

Skin blood flow changes following intradermal bradykinin injections measured by laser Doppler flowmetry: comparison with weal and flare.

Intradermal injections of normal saline and different concentrations of bradykinin were made into the forearms of healthy volunteers. Cutaneous blood flow was recorded just outside and over the centre of the weals by laser Doppler flowmetry (LDF), and flare area and weal volume were measured. There were concentration-related changes in the mean LDF output adjacent to the weal, flare area and weal volume. LDF recordings performed over the centre of the weals, however, failed to show any dose-response relationship. When similar concentrations of bradykinin were injected intradermally and the skin response measured by the above parameters, there was less variation in the mean LDF output adjacent to the weal than flare or weal measurements. The non-invasive technique of LDF is a useful, objective and sensitive technique of quantifying the skin blood flow changes induced by intradermal bradykinin and provides an alternative method of quantifying skin response to intradermal bradykinin to measurement of flare or weal sizes.

Adult↗