Patient experience of nasal obstruction and its clinical assessment.

BACKGROUND: The correlation between objective and subjective nasal obstruction is poor, and dissatisfaction rates after surgery for nasal obstruction are high. Accordingly, novel assessment techniques may be required. This survey aimed to determine patient experience and preferences for the measurement of nasal obstruction. METHOD: Prospective survey of rhinology patients. RESULTS: Of 72 questionnaires distributed, 60 were completed (response rate of 83 per cent). Obstruction duration (more than one year) (χ2 = 13.5, p = 0.00024), but not obstruction severity, affected willingness to spend more time being assessed. Questionnaires (48 per cent) and nasal inspiratory peak flow measurement (53 per cent) are the most commonly used assessment techniques. Forty-nine per cent of participants found their assessment unhelpful in understanding their obstruction. Eighty-two per cent agreed or strongly agreed that a visual and numerical aid would help them understand their blockage. CONCLUSION: Many patients are dissatisfied with current assessment techniques; a novel device with visual or numerical results may help. Obstruction duration determines willingness to undergo longer assessment.

Blood transfusion in preterm infants improves intestinal tissue oxygenation without alteration in blood flow.

BACKGROUND AND OBJECTIVE: The objective of the study was to investigate the splanchnic blood flow velocity and oximetry response to blood transfusion in preterm infants according to postnatal age. MATERIALS AND METHODS: Preterm infants receiving blood transfusion were recruited to three groups: 1-7 (group 1; n = 20), 8-28 (group 2; n = 21) and ≥29 days of life (group 3; n = 18). Superior mesenteric artery (SMA) peak systolic (PSV) and diastolic velocities were measured 30-60 min pre- and post-transfusion using Doppler ultrasound scan. Splanchnic tissue haemoglobin index (sTHI), tissue oxygenation index (sTOI) and fractional tissue oxygen extraction (sFTOE) were measured from 15-20 min before to post-transfusion using near-infrared spectroscopy. RESULTS: The mean pretransfusion Hb in group 1, 2 and 3 was 11, 10 and 9 g/dl, respectively. The mean (SD) pretransfusion SMA PSV in group 1, 2 and 3 was 0·63 (0·32), 0·81 (0·33) and 0·97 (0·40) m/s, respectively, and this did not change significantly following transfusion. The mean (SD) pretransfusion sTOI in group 1, 2 and 3 was 36·7 (19·3), 44·6 (10·4) and 41·3 (10·4)%, respectively. The sTHI and sTOI increased (P < 0·01), and sFTOE decreased (P < 0·01) following transfusion in all groups. On multivariate analysis, changes in SMA PSV and sTOI following blood transfusion were not associated with PDA, feeding, pretransfusion Hb and mean blood pressure. CONCLUSION: Pretransfusion baseline splanchnic tissue oximetry and blood flow velocity varied with postnatal age. Blood transfusion improved intestinal tissue oxygenation without altering mesenteric blood flow velocity irrespective of postnatal ages.

Smart biosensors for multiplexed and fully integrated point-of-care diagnostics.

Point-of-care diagnostics (PoC) and personalised medicine are highly valuable for the improvement of world health. Smartphone PoC platforms which precisely diagnose diseases and track their development through the detection of several bioanalytes represent one of the newest and most exciting advancements towards mass-screening applications. Here we focus on recent advances in both multiplexed and smartphone integrated PoC sensors.

Cerebral blood flow and oximetry response to blood transfusion in relation to chronological age in preterm infants.

OBJECTIVE: Preterm infants frequently receive blood transfusion (BT) and the aim of this study was to measure the effect of BT on cerebral blood flow and oxygenation in preterm infants in relation to chronological age. PATIENTS: Preterm infants undergoing intensive care recruited to three chronological age groups: 1 to 7 (Group 1; n=20), 8 to 28 (Group 2; n=21) & ≥29days of life (Group 3; n=18). METHODS: Pre and post-BT anterior cerebral artery (ACA) time averaged mean velocity (TAMV) and superior vena cava (SVC) flow were measured. Cerebral Tissue Haemoglobin Index (cTHI) and Oxygenation Index (cTOI) were measured from 15-20min before to 15-20min post-BT using NIRS. Vital parameters and blood pressure were measured continuously. RESULTS: Mean BP increased significantly, and there was no significant change in vital parameters following BT. Pre-BT ACA TAMV was higher in Group 2 and 3 compared to Group 1 (p<0.001). Pre-BT ACA TAMV decreased significantly (p≤0.04) in all 3 groups; pre-BT SVC flow decreased significantly in Group 1 (p=0.03) and Group 3 (p<0.001) following BT. Pre-BT cTOI was significantly lower in Group 3 compared to Group 1 (p=0.02). cTHI (p<0.001) and cTOI (p<0.05) increased significantly post-BT in all three groups. PDA had no effect on these measurements. CONCLUSION: Baseline cTOI decreases and ACA TAMV increases with increasing chronological age. Blood transfusion increased cTOI and cTHI and decreased ACA TAMV in all groups. PDA had no impact on the baseline cerebral oximetry and blood flow as well as changes following blood transfusion.

Effect of blood in the cerebrospinal fluid on the accuracy of cerebral oxygenation measured by near infrared spectroscopy.

Near infrared spectroscopy (NIRS) is an optical technique used to examine the oxygenation state of tissues such as the brain in patients, including those with brain injury. We have examined the effect of a cerebrospinal fluid (CSF) contaminant, specifically haemoglobin, on the sensitivity of cerebral NIRS signals through computer simulation. Previous models of light transport in the head have shown that the clear CSF layer has a profound effect on the sensitivity profile of the NIRS signal due to its low absorbing, low scattering qualities. In subarachnoid haemorrhage, which may accompany brain injury, the principal near infrared chromophore, haemoglobin, is released into the CSF. Sensitivity was measured through forward modeling and the presence of haemoglobin within the CSF was modeled by increasing the absorption coefficient of the layer, with sensitivity quantified in terms of the partial pathlength of light within the brain. The model demonstrated that increases in the CSF absorption led to a marked decrease in the sensitivity to changes in the brain layer. This suggests that blood or other contaminants in the CSF may have a significant effect on the utility of NIRS for measurement of cerebral oxygenation, and merits further investigation.

Development of a hybrid microwave-optical thermoregulation monitor for the muscle.

This paper presents the latest development of the hybrid microwave-optical thermoregulation monitor for the muscle. It is capable of warming the muscle and measuring the subsequent blood volume changes, using a novel microwave applicator with integrated optical probes. The challenge is to measure the thermoregulation response in deep tissue while minimizing any effect from the skin layer. We have introduced a skin cooling device, an additional integrated optical Laser Doppler flow monitoring probe and a temperature sensor to measure skin blood flow and temperature, respectively. The result shows that skin cooling is essential to minimize skin flow changes during microwave warming. The hybrid probe was placed on a human thigh to measure oxy/deoxy/total haemoglobin concentration changes (ΔHbO2/ΔHHb/ΔHbT), skin flux and temperature upon microwave warming. Without skin cooling, the skin temperature was elevated by 4 °C and both ΔHbO2/ΔHbT and skin flux increased, showing microwave warming occurring in both the skin and muscle. With skin cooling, the skin temperature was kept relatively constant. While ΔHbO2/ΔHbT increased, the skin flux was relatively stable, showing a preferential microwave warming in the muscle, rather than the skin.

Superficial heat reduction technique for a hybrid microwave-optical device.

Microwave applicator in the form of a circularly polarized microstrip patch antenna is proposed to provide localized deep heating in biological tissue, which causes blood vessels to dilate leading to changes in tissue oxygenation. These changes are monitored by an integrated optical system for studying thermoregulation in different parts of the human body. Using computer simulations, this paper compares circularly and linearly polarized antennas in terms of the efficiency of depositing electromagnetic (EM) energy and the heating patterns. The biological model composes of the skin, fat and muscle layers with appropriate dielectric and thermal properties. The results show that for the same specific absorption rate (SAR) in the muscle, the circularly polarized antenna results in a lower SAR in the skin-fat interface than the linearly polarized antenna. The thermal distribution is also presented based on the biological heat equation. The proposed circularly polarized antenna shows heat reduction in the superficial layers in comparison to the linearly polarized antenna.

Light transport in tissue by 3D Monte Carlo: influence of boundary voxelization.

Monte Carlo (MC) based simulations of photon transport in living tissues have become the "gold standard" technique in biomedical optics. Three-dimensional (3D) voxel-based images are the natural way to represent human (and animal) tissues. It is generally believed that the combination of 3D images and MC based algorithms allows one to produce the most realistic models of photon propagation. In the present work, it is shown that this approach may lead to large errors in the MC data due to the "roughness" of the geometrical boundaries generated by the presence of the voxels. In particular, the computed intensity of the light detected on the tissue surface of a simple cubic tissue phantom may display errors from -80% to 120%. It is also shown that these errors depend in a complex manner on optical and geometrical parameters such as the interoptode distance, scattering coefficient, refractive index, etc. and on the degree of voxelization ("roughness") of the boundaries. It is concluded that if one wants to perform reliable 3D Monte Carlo simulations on complex geometries, such as human brain, skin or trabecular bone, it is necessary to introduce boundary meshing techniques or other equivalent procedures in the MC code to eliminate the deleterious effect of voxelization.

Investigation of in vivo measurement of cerebral cytochrome-c-oxidase redox changes using near-infrared spectroscopy in patients with orthostatic hypotension.

We have previously used a continuous four-wavelength near-infrared spectrometer to measure changes in the cerebral concentrations of oxy-haemoglobin (Delta[HbO(2)] and deoxy-haemoglobin (Delta[HHb]) during head-up tilt in patients with primary autonomic failure. The measured changes in light attenuation also allow calculation of changes in the concentration of oxidized cytochrome-c-oxidase (Delta[(ox)CCO]), and this paper analyses the Delta[(ox)CCO] during the severe episodes of orthostatic hypotension produced by this experimental protocol. We studied 12 patients during a passive change in position from supine to a 60 degrees head-up tilt. The challenge caused a reduction in mean blood pressure of 59.93 (+/-26.12) mmHg (Mean (+/-SD), p < 0.0001), which was associated with a reduction in the total concentration of haemoglobin (Delta[HbT] = Delta[HbO(2)] + Delta[HHb]) of 5.02 (+/-3.81) microM (p < 0.0001) and a reduction in the haemoglobin difference concentration (Delta[Hb(diff)] = Delta[HbO(2)] - Delta[HHb]) of 14.4 (+/-6.73) microM (p < 0.0001). We observed a wide range of responses in Delta[(ox)CCO]. Six patients demonstrated a drop in Delta[(ox)CCO] (0.17 +/- 0.15 microM); four patients demonstrated no change (0.01 +/- 0.12 microM) and two patients showed an increase in Delta[(ox)CCO] (0.21 +/- 0.01 microM). Investigation of the association between the changes in concentrations of haemoglobin species and the Delta[(ox)CCO] for each patient show a range of relationships. This suggests that a simple mechanism for crosstalk, which might produce artefactual changes in [(ox)CCO], is not present between the haemoglobin and the (ox)CCO NIRS signals. Further investigation is required to determine the clinical significance of the changes in [(ox)CCO].

Comment on 'the use of the Henyey-Greenstein phase function in Monte Carlo simulations in biomedical optics'.

In this letter the authors highlight the presence of an error appearing in the discussion of the note 'The use of the Henyey-Greenstein phase function in Monte Carlo simulations in biomedical optics' previously published by them (Binzoni et al 2006 Phys. Med. Biol. 51 N313). In the light of this error, the discussion and conclusions in the original paper are revised in this letter and the role of the use of the phase functions in MC simulations, interpreted in probabilistic terms, is better clarified. The exact definition for the probability density function for the deflection angle, in the case of the Henyey-Greenstein model, is also given.

The use of the Henyey-Greenstein phase function in Monte Carlo simulations in biomedical optics.

Monte Carlo (MC) simulations are often at the heart of the testing procedure in biomedical optics. One of the critical points in MC simulations is to define the new photon direction after each scattering event. One of the most popular solutions is to use the Henyey-Greenstein phase function or some linear combinations of it. In this note, we demonstrate that randomly generating the angle defining the new direction of a photon after a collision, by means of the Henyey-Greenstein phase function, is not equivalent to generating the cosine of this angle, as is classically done. In practice, it is demonstrated that for a nearly isotropic medium (asymmetry parameter g approximately 0) this discrepancy is not large, however for an anisotropic medium as is typically found in vivo (e.g. g = 0.98) the two methods give completely different results.

Anisotropic photon migration in human skeletal muscle.

It is demonstrated in the short head of the human biceps brachii of 16 healthy subjects (12 males and 4 females) that near infrared photon migration is anisotropic. The probability for a photon to travel along the direction of the muscle fibres is higher (approximately 0.4) than that of travelling along a perpendicular axis (approximately 0.3) while in the adipose tissue the probability is the same (approximately 0.33) in all directions. Considering that the muscle fibre orientation is different depending on the type of muscle considered, and that inside a given skeletal muscle the orientation may change, the present findings in part might explain the intrasubject variability observed in the physiological parameters measured by near infrared spectroscopy techniques. In other words, the observed regional differences might not only be physiological differences but also optical artefacts.

Absorption and scattering coefficient dependence of laser-Doppler flowmetry models for large tissue volumes.

Based on quasi-elastic scattering theory (and random walk on a lattice approach), a model of laser-Doppler flowmetry (LDF) has been derived which can be applied to measurements in large tissue volumes (e.g. when the interoptode distance is >30 mm). The model holds for a semi-infinite medium and takes into account the transport-corrected scattering coefficient and the absorption coefficient of the tissue, and the scattering coefficient of the red blood cells. The model holds for anisotropic scattering and for multiple scattering of the photons by the moving scatterers of finite size. In particular, it has also been possible to take into account the simultaneous presence of both Brownian and pure translational movements. An analytical and simplified version of the model has also been derived and its validity investigated, for the case of measurements in human skeletal muscle tissue. It is shown that at large optode spacing it is possible to use the simplified model, taking into account only a 'mean' light pathlength, to predict the blood flow related parameters. It is also demonstrated that the 'classical' blood volume parameter, derived from LDF instruments, may not represent the actual blood volume variations when the investigated tissue volume is large. The simplified model does not need knowledge of the tissue optical parameters and thus should allow the development of very simple and cost-effective LDF hardware.

Translational and Brownian motion in laser-Doppler flowmetry of large tissue volumes.

This study reports the derivation of a precise mathematical relationship existing between the different p-moments of the power spectrum of the photoelectric current, obtained from a laser-Doppler flowmeter (LDF), and the red blood cell speed. The main purpose is that both the Brownian (defining the 'biological zero') and the translational movements are taken into account, clarifying in this way what the exact contribution of each parameter is to the LDF derived signals. The derivation of the equations is based on the quasi-elastic scattering theory and holds for multiple scattering (i.e. measurements in large tissue volumes and/or very high red blood cell concentration). The paper also discusses why experimentally there exists a range in which the relationship between the first moment of the power spectrum and the average red blood cells speed may be considered as 'linear' and what are the physiological determinants that can result in nonlinearity. A correct way to subtract the biological zero from the LDF data is also proposed. The findings should help in the design of improved LDF instruments and in the interpretation of experimental data.

Non-invasive laser Doppler perfusion measurements of large tissue volumes and human skeletal muscle blood RMS velocity.

This study proposes the implementation of an algorithm allowing one to derive absolute blood root-mean-square (RMS) velocity values from laser Doppler perfusion meter (LDP) data. The algorithm is based on the quasi-elastic light scattering theory and holds for multiple scattering. While standard LDP measurements are normally applicable to a small region of interest (approximately 1 mm2), the present method allows the analysis of both small and large tissue volumes with small and large interoptode spacings (e.g., 1.5 cm). The applicability and the limits of the method are demonstrated with measurements on human skeletal muscle using a custom-built near-infrared LDP meter. Human brachioradialis muscle RMS velocity values of 9.99 +/- 0.01 and 5.58 +/- 0.03 mm s(-10 at 1.5 cm and of 5.18 +/- 0.01 and 2.54 +/- 0.09 mm s(-1) at 2 cm were found when the arm was (a) at rest and (b) occluded, respectively. At very large optode spacings or very high moving particle densities, the theory developed here would need to be amended to take into account second-order effects.

Corneal perforation with extrusion of lens in a burn patient.

The incidence of ophthalmologic injuries has been reported to be between 20 and 25% in all the burn patients. As most of the eye injuries are associated with severe burns, attention is often directed towards the life-threatening events and eye injuries may be overlooked and undertreated. This case report presents a patient who had 40% flame burn and had recently been transferred from another hospital. He was examined by an ophthalmologist at the referring hospital and it was documented that both of his eyes were normal. He was transferred into the Burns Unit at the Prince of Wales Hospital 8 h later. Unfortunately, all the attention was directed to save his life and it was not until post-burn day 11 that he was found to have right corneal ulceration. Despite vigorous ophthalmologic treatment, the cornea perforated 2 days later with subsequent extrusion of the lens. In view of his grave prognosis with multi-organ failure, he was treated conservatively and he died the following day. It is mandatory to refer patients with facial burns to the ophthalmologist for ocular examination. We recommend that serial eye examinations should be carried out in burn patients who are unconscious or intubated for ventilatory support even if the initial ophthalmologic examinations are normal as the potential risk of serious ocular injuries are high in this particular group of patients.

Bacterial colonisation of the upper pouch in neonates with oesophageal atresia.

The bacterial flora in the upper oesophageal pouch of forty neonates with oesophageal atresia was studied at daily intervals preoperatively. Of the twenty-nine infants whose oesophagus was anastomosed within 24 hours of admission, no organisms were isolated in sixteen, despite the fact that only nine of these patients had antibiotics. The remaining thirteen grew oropharyngeal organisms. Of eleven infants having delayed anastomosis eight received antibiotics. All eleven grew organisms in the upper pouch. Pseudomonas and serratia grew only in those receiving antibiotics. These results suggest that prophylactic antibiotics are rarely indicated. Efficient continuous aspiration of the pouch is probably more important.

Faecal flora in neonates with oesophageal atresia.

The bacteriological findings of a study of intestinal colonisation in 24 neonates with oesophageal atresia are reported. Only five of the patients received antibiotics. When compared with published findings in healthy neonates, the rate of intestinal colonisation in our series was prolonged, with Staphylococcus albus predominating in the first week. Anaerobic colonisation was delayed and bacteroides spp were present in only five patients by the third week. Bifidobacteria were almost completely absent. The onset of intestinal colonisation seemed to be related temporally to enteral feeding. The use of antibiotics in five patients resulted in colonisation by candida in four and clinical thrush in three.

Bacteriological examination of removed cerebrospinal fluid shunts.

A conventional method of bacteriological examination of removed cerebrospinal fluid shunts was compared with another method which relies on microscopic and cultural examination of intraluminal fluid. Fifty-five shunts were tested. All eight cases of clinical shunt infection gave positive results with the latter method, whereas a further 23 shunts yielded positive cultures by the conventional method in the absence of clinical infection. The consequences of missed infections due to omission of microscopic examination and overdiagnosis using the conventional culture method are discussed.