Does a magnetic blanket induce changes in muscular blood flow, skin temperature and muscular tension in horses?

REASONS FOR PERFORMING STUDY: Static magnetic blankets are often claimed to induce increases in blood flow, reduce muscle tension and tenderness, and be beneficial in both prevention and treatment of musculoskeletal injuries in horses. However, there are no studies that confirm alleged beneficial effects of magnets on muscles of the back in healthy horses. OBJECTIVES: To investigate whether static magnets sewn into a blanket affect back muscle blood flow, skin temperature, mechanical nociceptive threshold (MNT) and behaviour in healthy horses. STUDY DESIGN: Prospective, randomised, blinded, placebo-controlled crossover study. METHODS: The following outcome measurements of the back of 10 healthy horses were performed; blood flow by photoplethysmography, skin temperature by use of thermistors in conjunction with digital infrared thermography, and MNTs by algometry. The horses' behaviour was filmed during the procedure and scored on an ethogram. Measurements were performed repeatedly for a 30 min baseline period. Thereafter a blanket with active, static magnets (900 gauss) or placebo magnets was placed on the horse and measurements were performed for a 60 min treatment period and a 30 min post treatment period. The study procedure was repeated on the consecutive day, when the horse received the alternative treatment. RESULTS: Blood flow in muscle, skin temperatures, MNTs and behavioural traits did not differ between active and placebo magnetic blankets. Skin temperature increased similarly during both active and placebo blanket treatment. CONCLUSIONS: In healthy horses, magnetic blankets did not induce additional significant effects on muscle blood flow, skin temperature, MNTs and behaviour when compared with nonmagnetic blankets.

A technique based on laser Doppler flowmetry and photoplethysmography for simultaneously monitoring blood flow at different tissue depths.

The aim of this study was to validate a non-invasive optical probe for simultaneous blood flow measurement at different vascular depths combining three photoplethysmography (PPG) channels and laser Doppler flowmeter (LDF). Wavelengths of the PPG were near-infrared 810 nm with source-to-detector separation of 10 and 25 mm, and green 560 nm with source-to-detector separation of 4 mm. The probe is intended for clinical studies of pressure ulcer aetiology. The probe was placed over the trapezius muscle, and depths from the skin to the trapezius muscle were measured using ultrasound and varied between 3.8 and 23 mm in the 11 subjects included. A provocation procedure inducing a local enhancement of blood flow in the trapezius muscle was used. Blood flows at rest and post-exercise were compared. It can be concluded that this probe is useful as a tool for discriminating between blood flows at different vascular tissue depths. The vascular depths reached for the different channels in this study were at least 23 mm for the near-infrared PPG channel (source-to-detector separation 25 mm), 10-15 mm for the near-infrared PPG channel (separation 10 mm), and shallower than 4 mm for both the green PPG channel (separation 4 mm) and LDF.

Combined photoplethysmographic monitoring of respiration rate and pulse: a comparison between different measurement sites in spontaneously breathing subjects.

BACKGROUND: The non-invasive photoplethysmographic (PPG) signal reflects blood flow and volume in a tissue. The PPG signal shows variation synchronous with heartbeat (PPGc), as used in pulse oximetry, and variations synchronous with breathing (PPGr). PPGr has been used for non-invasive monitoring of respiration with promising results. Our aim was to investigate PPG signals recorded from different skin sites in order to find suitable locations for parallel monitoring of variations synchronous with heartbeat and breathing. METHODS: PPG sensors were applied to the forearm, finger, forehead, wrist and shoulder on 48 awake healthy volunteers. From these sites, seven PPG signals were simultaneously recorded during normal spontaneous breathing over 10 min. Capnometry served as respiration and electrocardiogram (ECG) as pulse reference signals. PPG signals were compared with respect to power spectral content and squared coherence. RESULTS: Forearm PPG measurement showed significantly higher power within the respiratory region of the power spectrum [median (quartile range) 42 (26)%], but significantly lower power within the cardiac region [9 (10)%] compared with the other skin sites. PPG finger measurement showed the opposite; in transmission mode, the power within the respiratory region was significantly lower [4 (10)%] and within the cardiac region significantly higher [45 (25)%] than the other sites. PPGc coherence values were generally high [>0.96 (0.08)], and PPGr coherence values lower [0.83 (0.35)-0.94 (0.17)]. CONCLUSION: Combined PPG respiration and pulse monitoring is possible, but there are significant differences between the respiratory and cardiac components of the PPG signal at different sites.

[On line monitoring using ultraviolet absorption for surveillance of clinical events during hemodialysis]. / Die Online Messung mit Ultraviolett-Absorption zur Uberwachung klinischer Ereignisse während der Hämodialyse.

BACKGROUND: On-line monitoring systems of spent dialysate, used to estimate dialysis dose, have been developed with different instrumentation during the last two decades. The routine use of an on-line monitoring system has been suggested to provide an adequate dialysis dose to the haemodialysis (HD) patient. The aim of this study was to show that monitoring the spent dialysate using UV-absorbance might bring new information about the clearance process. METHODS: 108 HD treatments distributed among 16 clinical stable patients were monitored on-line using ultra violet (UV) absorbance. For the measurement of UV-absorbance a spectrophotometer was connected to the fluid outlet of the dialysis machine with all spent dialysate passing through a flow cuvette. The UV-absorbance curves were examined in combination with the recorded observations of events that occurred during the studied treatments. RESULTS: The study demonstrates that UV-absorbance visualizes different kinds of events such as hypotension, conductivity alarms and restricted flow in artery needle blood pump stops that often occur during dialysis treatment. CONCLUSION: An on-line UV-monitoring system with a high sampling rate makes it possible to identify variations in dialysis clearance of different origin and gives feedback after performing interventions during a dialysis session.

Automatic ankle pressure measurements using PPG in ankle-brachial pressure index determination.

OBJECTIVE: To evaluate a new technique using a photoplethysmographic (PPG) probe for automatic ankle pressure measurements. DESIGN: Comparative study on two techniques for ankle pressure measurement. SETTING: University hospital. MATERIAL: Thirty-five patients with leg arterial disease and eight healthy volunteers. Ankle-brachial indices (ABPI) were measured using conventional CW Doppler technique and PPG-based prototype equipment for the ankle pressure recordings. CHIEF OUTCOME MEASURES: ABPIs calculated from CW Doppler and PPG ankle pressure measurements. The PPG signals were analysed both by visual judgement and by a software based, automatic algorithm. MAIN RESULTS: The mean difference between ABPIs calculated from CW Doppler recordings and PPG (visual analysis) was -0.01 (limits of agreement (+/-two standard deviations) +0.16 to -0.19). The correlation coefficient was 0.93. When the algorithm was used, the mean difference (CW Doppler-PPG) was 0.05 (limits of agreement 0.28 to -0.18, r=0.89). CONCLUSIONS: The PPG method is a promising technique with an inherent potential for automatisation of the ankle pressure measurements, thereby reducing the observer-dependency in ABPI recordings.

Non-invasive monitoring of muscle blood perfusion by photoplethysmography: evaluation of a new application.

AIM: To evaluate a specially developed photoplethysmographic (PPG) technique, using green and near-infrared light sources, for simultaneous non-invasive monitoring of skin and muscle perfusion. METHODS: Evaluation was based on assessments of changes in blood perfusion to various provocations, such as post-exercise hyperaemia and hyperaemia following the application of liniment. The deep penetrating feature of PPG was investigated by measurement of optical radiation inside the muscle. Simultaneous measurements using ultrasound Doppler and the new PPG application were performed to elucidate differences between the two methods. Specific problems related to the influence of skin temperature on blood flow were highlightened, as well. RESULTS: Following static and dynamic contractions an immediate increase in muscle perfusion was shown, without increase in skin perfusion. Liniment application to the skin induced a rapid increase in skin perfusion, but not in muscle. Both similarities and differences in blood flow measured by Ultrasound Doppler and PPG were demonstrated. The radiant power measured inside the muscle, by use of an optical fibre, showed that the near-infrared light penetrates down to the vascular depth inside the muscle. CONCLUSIONS: The results of this study indicate the potentiality of the method for non-invasive measurement of local muscle perfusion, although some considerations still have to be accounted for, such as influence of temperature on blood perfusion.

Non-invasive measurement of systolic blood pressure on the arm utilising photoplethysmography: development of the methodology.

Photoplethysmography (PPG) can be used to measure systolic blood pressure at the brachial artery. With a specially designed probe, positioned in the most distal position beneath a pressure cuff on the upper arm, this is possible. The distance between the light source (880 nm) and the photodetector was 20 mm. A test was performed on neuro-intensive care patients by determining blood pressure from the PPG curves, and, when it was compared with systolic blood pressure obtained from inserted indwelling arterial catheters, a correlation factor of r = 0.95 was achieved. The difference between blood pressure obtained using PPG and invasive blood pressure measurement was 3.9 +/- 9.1 mmHg (mean +/- SD), n = 19. The depth to the brachial artery was 13.9 +/- 4.1 mm (mean +/- SD), n = 18. A digital PPG system utilising pulsating light was also developed.

A new probe for ankle systolic pressure measurement using photoplethysmography (PPG).

An automated method for ankle systolic pressure measurement, less operator dependent than the standard continuous wave (CW) Doppler technique, would imply an advantage both in patient measurements and in epidemiological studies. We present a new photoplethysmographic (PPG) probe that uses near-infrared light (880 nm) to detect pulsatory blood flow underneath the distal end of a standard pneumatic cuff. The probe is adapted to the anatomical conditions at the ankle, permitting recording of pressures in both ankle arteries separately. The validity of the equipment was tested with CW Doppler-derived systolic pressures and invasive blood pressure measurements for reference. In 20 healthy subjects, visual analysis of the PPG curves revealed a mean difference between CW Doppler and PPG measurements of -0.5 mmHg (SD 6.9). Corresponding results for the anterior and posterior tibial arteries separately were -1.8 mmHg (SD 6.2) and 0.9 mmHg (SD 7.3), respectively. A correct probe position was essential for the results. In direct recordings from the dorsalis pedis artery in 10 intensive care patients, PPG underestimated systolic pressure in the anterior tibial artery by 4.5 mmHg (SD 12.1). With further development, the PPG probe, integrated in the pneumatic cuff, may simplify measurements of ankle systolic pressures.

Muscle blood flow in response to concentric muscular activity vs passive venous compression.

AIM: To measure muscle blood flow (MBF) using photoplethysmography (PPG) following concentric muscular activity of the leg (active treatment) or passive venous compression (passive treatment) with or without venous obstruction. METHODS: In study A, blood flow in the anterior tibial muscle was measured in 15 healthy subjects with a mean age of 30 years. In study B, blood flow in the gastrocnemius muscle was measured in nine healthy subjects with a mean age of 34 years. Subjects performed concentric muscular activity in one leg. Passive venous compression by a venous foot pump was applied in the contralateral leg. RESULTS: MBF increased significantly following concentric muscular activity, but not following passive venous compression. MBF decreased in both legs when venous obstruction, induced by a thigh tourniquet, was applied. However, MBF was significantly higher following concentric muscular activity than passive venous compression. CONCLUSION: We conclude that concentric muscular activity produces higher MBF values than passive venous compression.

On-line monitoring of solutes in dialysate using wavelength-dependent absorption of ultraviolet radiation.

The aim of the study was to assess the wavelength dependence of the UV absorbance during monitoring of different compounds in the dialysate. UV absorbance was determined by using a double-beam spectrophotometer on dialysate samples taken at pre-determined times during dialysis, over a wavelength range of 180-380 nm. Concentrations of several removed substances, such as urea, creatinine, uric acid, phosphate and beta2-microglobulin, were determined in the blood and in the spent dialysate samples using standard laboratory techniques. Millimolar extinction coefficients, for urea, creatinine, monosodium phosphate and uric acid were determined during laboratory bench experiments. The correlation between UV absorbance and substances both in the dialysate and in the blood was calculated at all wavelengths. A time-dependent UV absorbance was determined on the collected dialysate samples from a single dialysis session over a wavelength range of 200-330 nm. The highest contribution from observed compounds relative to the mean value of the absorbance was found around 300 nm and was approximately 70%. The main contribution to the total absorbance from uric acid was confirmed at this wavelength. The highest correlation for uric acid, creatinine and urea was obtained at wavelengths from 280 nm to 320 nm, both in the spent dialysate and in the blood. The wavelength region with the highest correlation for phosphate and beta2-microglobulin, with a suitable UV-absorbance dynamic range, was from 300 to 330 nm. In the wavelength range of 220-270 nm the highest absorbance sensitivity for the observed substances was obtained. A suitable wavelength range for instrumental design seems to be around 290-330 nm. The relatively high correlation between UV absorbance and the substances in the spent dialysate and in the blood indicates that the UV-absorbance technique can estimate the removal of several retained solutes known to accumulate in dialysis patients.

On-line monitoring of solutes in dialysate using absorption of ultraviolet radiation: technique description.

PURPOSE: The aim of this work was to describe a new optical method for monitoring solutes in a spent dialysate using absorption of UV radiation. METHOD: The method utilises UV-absorbance determined in the spent dialysate using a spectrophotometrical set-up. Measurements were performed both on collected dialysate samples and on-line. During on-line monitoring, a spectrophotometer was connected to the fluid outlet of the dialysis machine, with all spent dialysate passing through a specially-designed cuvette for optical single-wavelength measurements. The concentrations of several substances of various molecular sizes, electrical charge, transport mechanism, etc. were determined in the dialysate and in the blood using standard laboratory techniques. The correlation coefficient between UV-absorbance of the spent dialysate and concentration of the substances in the spent dialysate and in the blood was calculated from data based on the collected samples. RESULTS: The obtained on-line UV-absorbance curve demonstrates the possibility to follow a single hemodialysis session continuously and to monitor deviations in the dialysator performance using UV-absorbance. The experimental results indicate a very good correlation between UV-absorbance and several small waste solutes removed such as urea, creatinine and uric acid in the spent dialysate and in the blood for every individual treatment at a fixed wavelength of 285 nm. Moreover, a good correlation between the UV-absorbance and substances like potassium, phosphate and beta2-microglobulin was obtained. The lowest correlation was achieved for sodium, calcium, glucose, vitamin B12 and albumin. CONCLUSIONS: A technique for on-line monitoring of solutes in the spent dialysate utilising the UV-absorbance was developed. On-line monitoring during a single hemodialysis session exploiting UV-absorbance represents a possibility to follow a single hemodialysis session continuously and monitor deviations in dialysis efficiency (e.g. changes in blood flow and clearance). The UV-absorbance correlates well to the concentration of several solutes known to accumulate in dialysis patients indicating that the technique can be used to estimate the removal of retained substances.

Effects of limb elevation and increased intramuscular pressure on human tibialis anterior muscle blood flow.

The effects of limb elevation and increased intramuscular pressure (IMP) on blood flow in the tibialis anterior muscle and leg neuromuscular function were studied in eight healthy subjects. Muscle blood flow (MBF) was measured by photoplethysmography using a custom-designed probe. IMP was elevated bilaterally by vein obstruction (60-65 mmHg) lasting 30 min induced by a thigh tourniquet of casted legs. Skin sensibility of the feet and the amplitude and area of the compound muscle action potentials from the extensor digitorum brevis muscle were evaluated. The subject kept one leg elevated 32 cm above heart level and the contralateral leg at heart level. All recordings were made before, during and after vein obstruction. IMP increased to 40 mmHg in the vein-obstructed casted legs. Perfusion pressure decreased from [mean (SD)] 42 (5.8) mmHg to 17 (6.4) mmHg in the elevated leg and from 65 (9.9) mmHg to 43 (8.4) mmHg in the non-elevated leg. MBF decreased by 50% in the elevated leg and by 42% in the non-elevated leg. Subjects experienced sensory dysfunction and muscular weakness in the elevated leg. In conclusion, increased IMP, induced by venous obstruction of a casted leg, reduced perfusion pressure and MBF, and resulted in a diminished amplitude and area of the compound muscle action potentials. Limb elevation above heart level combined with venous stasis of a casted leg further reduced perfusion pressure and MBF, and induced sensory dysfunction and muscular weakness.

A non-invasive measure of changes in blood flow in the human anterior tibial muscle.

We used photoplethysmography (PPG) to monitor blood flow changes in the human anterior tibial muscle during arterial occlusion and during isometric and concentric contractions. Single-fibre laser-Doppler flowmetry (LDF) was used as a reference in 12 healthy subjects (5 men, 7 women; mean age 24 years). Post-exercise hyperaemic muscle blood flow (MBF) was measured immediately after isometric dorsiflexion of the ankle joint at maximal contraction for 1 min and full range-of-motion dorsiflexion and plantar flexion of the ankle joint for 1 min. A thigh tourniquet was applied for the evaluation of post-occlusive reactive hyperaemia. The MBF (baseline = 100%) was [mean (SD)] 150 (31)% (P = 0.003) by PPG (880 nm) and 182 (66)% (P = 0.012) by LDF. After 1 min of maximal isometric contraction, MBF increased to 150 (51)% (P = 0.003) by PPG (880 nm) and to 169 (43)% (P = 0.005) by LDF. After 1 min of maximal concentric contractions, MBF increased to 158 (59)% (P = 0.003) by PPG (880 nm) and to 170 (99)% (P = 0.008) by LDF. Skin blood flow, PPG (560 nm), did not change significantly after isometric or concentric contractions. The results indicate that reactive hyperaemia after exercise and arterial occlusion can be assessed in the human anterior tibial muscle using PPG.

Is oscillometric ankle pressure reliable in leg vascular disease?

The objective of the study was to evaluate the validity of oscillometric systolic ankle pressure in symptomatic leg arterial occlusive disease. Ankle pressure measurements using oscillometric curves obtained using a standard 12-cm cuff with a specially designed device for signal processing were validated against the continuous wave (CW) Doppler technique. Thirty-four subjects without signs or symptoms of peripheral vascular disease (68 legs) and 47 patients with leg ischaemia (85 legs) varying from moderate claudication to critical ischaemia were examined. The oscillometric curves were analysed using several algorithms reported in the literature, based on the assumption that maximum oscillations are recorded near mean arterial pressure. In normals, reasonable agreement between CW Doppler and oscillometric methods was seen. When an algorithm that determined the lowest cuff pressure at which maximum oscillations occurred, and a characteristic ratio for systolic pressure of 0.52 was used, the mean difference between CW Doppler and oscillometry was 1.7 mmHg [range -19 to +27, limits of agreement (2 SD) 21.1 mmHg]. In ischaemic legs, oscillometry overestimated systolic ankle pressure by a mean of 28.8 mmHg [range -126 to +65, limits of agreement 82.8 mmHg]. The difference was more pronounced among patients with critical ischaemia compared with claudicants, and also more evident among diabetics. The error of oscillometric pressure determination in subjects with leg arterial disease inversely increased with CW Doppler ankle pressure. In 39% of the recordings in legs with a CW Doppler systolic pressure below 100 mmHg, the oscillometric mean arterial pressure was higher than the recorded CW Doppler systolic pressure. In conclusion, the oscillometric method to determine systolic ankle pressure, based on the concept of maximum cuff oscillations occurring near mean arterial pressure, is not reliable in leg arterial disease, usually overestimating ankle pressure.

Optical non-invasive technique for vessel imaging: I. Experimental results.

This paper investigates some prerequisites for vessel imaging based on diffuse reflectance measurements in order to develop an optical non-invasive method for the imaging and monitoring of vessels. The method utilizes near-infrared (NIR) radiation (890 nm) from a light emitting diode. The light is guided into the tissue via an optical fibre (diameter 1.0 mm). The backscattered light is collected by an optical fibre of the same type and detected by an optical power meter. The fibres are moved over the skin in two directions with the aid of two motors operated by a microcomputer. Spatially resolved reflectance at the skin surface could be presented as a vessel-map in a colour-coded form on a computer screen. Experimental results indicate that the vessel imaging facility depends upon source-detector separation, relative position and vessel depth, and does not depend essentially on the radiant power from the light source. It is shown that, by a proper choice of probe parameters, one can improve the vessel identification ability. After vessel imaging the technique can potentially be used to monitor several physiological parameters on a selected vascular bed or to distinguish between injured and healthy tissue by monitoring local blood flow, oxygen saturation and the recirculation, pre- and post-operatively.

Optical non-invasive technique for vessel imaging: II. A simplified photon diffusion analysis.

The purpose of this paper is to explain theoretically the origin of previously presented experimental results by an optical non-invasive method using NIR for imaging blood vessels based on a specific combination of several physical parameters. The theoretical model is based on the diffusion approximation derived from the transport theory deep in a bulk tissue. An analytical solution was obtained describing photon behaviour under certain conditions during vessel identification. The modelled results indicate that the vessel identification facility depends upon source-detector separation and vessel depth, and does not depend essentially on the radiant power from the light source. The solution offers a relatively simple theoretical explanation of the experimental results and can be applied to several other clinical applications using similar technical solutions.

Pulse oximetry--clinical implications and recent technical developments.

The pulse oximeter has been shown to be a reliable monitor of arterial oxygen saturation and has therefore been recommended as mandatory monitoring for patients during anaesthesia and intensive care. In 1989 two review articles on pulse oximetry were published (1, 2) and two years ago Severinghaus and Kelleher summarized the literature between 1989 and October 1991 (3). Our aim is to focus the discussion on technical aspects and applications of pulse oximetry with special attention centered on recent developments. This review is consequently an update on pulse oximetry since the end of 1991, and the first on technically-based publications in the two last decades.

Presentation and evaluation of a new optical sensor for respiratory rate monitoring.

A new optical sensor for respiratory rate monitoring was simultaneously compared with an acoustic sensor and a transthoracic impedance plethysmograph during normoventilation in the respiratory rate range of 9-17 breaths per minute. The response characteristics of the optical sensor were then measured during simulation of central apnoea and tachypnoea. Visual observation was chosen as the reference method for monitoring the respiratory rate. The measurements were performed in ten healthy volunteers and the respiratory signals recorded on an analogue tape and strip-chart recorder and analysed off-line. The response characteristics of the fibre optic sensor corresponded well with those of the acoustic sensor and impedance plethysmograph. All three methods responded rapidly to an apnoeic event.

Accuracy of pulse oximetry at various haematocrits and during haemolysis in an in vitro model.

In situations in which it may be impossible and/or unethical to evaluate pulse oximetry in humans, an in vitro model with circulating blood may be a necessity. The main objective was to develop such an in vitro model and, in this model, validate the pulse oximetry technique at various haematocrit levels. The pulsating character of arterial blood flow in a tubing system was simulated by using a specially constructed pressure-regulated roller pump. The tubing system was designed to minimise damage to red blood cells. The pulse oximeter readings (SpO2) were compared with oxygen saturation analyses by a haemoximeter (SaO2). The pulse oximetry readings were recorded at various haematocrit levels and during haemolysis in the SaO2 range 60-100 per cent. At a haematocrit level of 41-44 per cent, there was no correlation between SaO2 and SpO2 readings. After diluting the blood with normal saline to a haematocrit of 10-11 per cent, a good correlation between SaO2 and SpO2 was found. Following haemolysis, the agreement between SaO2 and SpO2 was further improved. Using the developed in vitro model, the results indicate that the accuracy of a pulse oximeter may be dependent on the haematocrit level.