Forehead monitoring of heart rate in neonatal intensive care.

Heart rate is an extremely important physiological parameter to measure in critically unwell infants, as it is the main physiological marker that changes in response to a change in infant condition. Heart rate is routinely measured peripherally on a limb with a pulse oximeter. However, when infants are critically unwell, the blood supply to these peripheries is reduced in preference for central perfusion of vital organs such as the brain and heart. Measurement of heart rate with a reflection mode photoplethysmogram (PPG) sensor on the forehead could help minimise this problem and make it easier for other important medical equipment, such as cannulas, to be placed on the limbs. This study compares heart rates measured with a forehead-based PPG sensor against a wrist-based PPG sensor in 19 critically unwell infants in neonatal intensive care collecting 198 h of data. The two heart rates were compared using positive percentage agreement, Spearman's correlation coefficient and Bland-Altman analysis. The forehead PPG sensor showed good agreement with the wrist-based PPG sensor with limits of agreement of 8.44 bpm, bias of -0.22 bpm; positive percentage agreement of 98.87%; and Spearman's correlation coefficient of 0.9816. The analysis demonstrates that the forehead is a reliable alternative location for measuring vital signs using the PPG.

Measurement of the cardiac time intervals of the fetal ECG utilising a computerised algorithm: A retrospective observational study.

Objective: Establish whether the reliable measurement of cardiac time intervals of the fetal ECG can be automated and to address whether this approach could be used to investigate large datasets. Design: Retrospective observational study. Setting: Teaching hospitals in London UK, Nottingham UK and New York USA. Participants: Singleton pregnancies with no known fetal abnormality. Methods: Archived fetal ECG's performed using the MonicaAN24 monitor. A single ECG (PQRST) complex was generated from 5000 signal-averaged beats and electrical cardiac time intervals measured in an automated way and manually. Main Outcome measure: Validation of a newly developed algorithm to measure the cardiac time intervals of the fetal ECG. Results: 188/236 (79.7%) subjects with fECGs of suitable signal:noise ratio were included for analysis comparing manual with automated measurement. PR interval was measured in 173/188 (92%), QRS complex in 170/188 (90%) and QT interval in 123/188 (65.4%). PR interval was 107.6 (12.07) ms [mean(SD)] manual vs 109.11 (14.7) ms algorithm. QRS duration was 54.72(6.35) ms manual vs 58.34(5.73) ms algorithm. QT-interval was 268.93 (21.59) ms manual vs 261.63 (36.16) ms algorithm. QTc was 407.5(32.71) ms manual vs 396.4 (54.78) ms algorithm. The QRS-duration increased with gestational age in both manual and algorithm measurements. Conclusion: Accurate measurement of fetal ECG cardiac time intervals can be automated with potential application to interpretation of larger datasets.

Optical fiber sensors for monitoring in critical care.

Monitoring of key physiological and pharmacological parameters is an important part of a closed loop control system in critical care. Optical fiber sensors provide a versatile platform technology that can be easily incorporated into existing in-dwelling catheters or face masks. With appropriate functional coatings they can be used to monitor a range of relevant parameters and two different examples are presented: (i) respiration monitoring; (ii) drug level monitoring. Respiration monitoring involves monitoring of temperature and humidity in inhaled and exhaled breath. The optical fiber sensor consists of a fiber Bragg grating to measure temperature and a tip coating whose refractive index changes with humidity. The sensor is demonstrated to be able to track breath to breath changes when incorporated into a mask. Drug level monitoring is demonstrated in vitro using a long period grating coated with molecularly imprinted polymer nanoparticles that are sensitive to fentanyl. The sensor has a limit of detection of 50ng/ml.

Motion limitations of non-contact photoplethysmography due to the optical and topological properties of skin.

Non-contact photoplethysmography (PPG) provides multiple benefits over in-contact methods, but is not as tolerant to motion due to the lack of mechanical coupling between the subject and sensor. One limitation of non-contact photoplethysmography is discussed here, specifically looking at the topology and optical variations of the skin and how this impacts upon the ability to extract a photoplethysmogram when a subject moves horizontally across the field of view of the detector (a panning motion). When this occurs it is shown that whilst the general relationships between the speed of traversal, detection area and resultant signal quality can be found, the quality of signal in each individual case is determined by the properties of the area of skin chosen.

An automated quasi-continuous capillary refill timing device.

Capillary refill time (CRT) is a simple means of cardiovascular assessment which is widely used in clinical care. Currently, CRT is measured through manual assessment of the time taken for skin tone to return to normal colour following blanching of the skin surface. There is evidence to suggest that manually assessed CRT is subject to bias from ambient light conditions, a lack of standardisation of both blanching time and manually applied pressure, subjectiveness of return to normal colour, and variability in the manual assessment of time. We present a novel automated system for CRT measurement, incorporating three components: a non-invasive adhesive sensor incorporating a pneumatic actuator, a diffuse multi-wavelength reflectance measurement device, and a temperature sensor; a battery operated datalogger unit containing a self contained pneumatic supply; and PC based data analysis software for the extraction of refill time, patient skin surface temperature, and sensor signal quality. Through standardisation of the test, it is hoped that some of the shortcomings of manual CRT can be overcome. In addition, an automated system will facilitate easier integration of CRT into electronic record keeping and clinical monitoring or scoring systems, as well as reducing demands on clinicians. Summary analysis of volunteer (n = 30) automated CRT datasets are presented, from 15 healthy adults and 15 healthy children (aged from 5 to 15 years), as their arms were cooled from ambient temperature to 5°C. A more detailed analysis of two typical datasets is also presented, demonstrating that the response of automated CRT to cooling matches that of previously published studies.

Forehead reflectance photoplethysmography to monitor heart rate: preliminary results from neonatal patients.

Around 5%-10% of newborn babies require some form of resuscitation at birth and heart rate (HR) is the best guide of efficacy. We report the development and first trial of a device that continuously monitors neonatal HR, with a view to deployment in the delivery room to guide newborn resuscitation. The device uses forehead reflectance photoplethysmography (PPG) with modulated light and lock-in detection. Forehead fixation has numerous advantages including ease of sensor placement, whilst perfusion at the forehead is better maintained in comparison to the extremities. Green light (525 nm) was used, in preference to the more usual red or infrared wavelengths, to optimize the amplitude of the pulsatile signal. Experimental results are presented showing simultaneous PPG and electrocardiogram (ECG) HRs from babies (n = 77), gestational age 26-42 weeks, on a neonatal intensive care unit. In babies ⩾32 weeks gestation, the median reliability was 97.7% at ±10 bpm and the limits of agreement (LOA) between PPG and ECG were +8.39 bpm and -8.39 bpm. In babies <32 weeks gestation, the median reliability was 94.8% at ±10 bpm and the LOA were +11.53 bpm and -12.01 bpm. Clinical evaluation during newborn deliveries is now underway.

64×64 pixel smart sensor array for laser Doppler blood flow imaging.

What is believed to be the first fully integrated two-dimensional complementary metal oxide semiconductor (CMOS) imaging array for laser Doppler blood flow imaging is demonstrated. The sensor has 64×64 pixels and includes both analog and digital on-chip processing electronics. This offers several potential advantages over commercial sensors as the processing is tailored to the signals of interest and the data bottleneck that exists between the sensor and processing electronics is overcome. To obtain a space efficient design over 64×64 pixels means that standard processing electronics used off-chip cannot be implemented. Images of both simulated blood flow responses and a blood flow occlusion test demonstrate the capability.

Prenatal Foetal Non-invasive ECG instead of Doppler CTG - A Better Alternative?

Introduction: This study aimed to evaluate foetal signal quality obtained using an antenatal foetal ECG system (Monica 24™) and compare it with Doppler ultrasound CTG monitoring (Corometrics® 250 series). Material and Methods: Seventy pregnant women (gestational age: between 20 + 0 weeks and 40 + 0 weeks) were examined using the Monica AN24™ system and also underwent Doppler CTG. The signal quality of both methods was compared and correlated with gestational age and pre-pregnancy body mass index (BMI). Results: Overall, ECG had a signal quality of 77.4 % and CTG had a signal quality of 73.1 % (p > 0.05). In gestational weeks (GW) 20-26, the signal quality of ECG was significantly better compared to that obtained with CTG (75.5 vs. 45.3 %; p = 0.003), while in GW 27-36, the signal quality was better with CTG (72.3 vs. 83.0 %, p = 0.001). No difference in signal quality was found between the two methods after the 37th GW (87.7 vs. 86.1 %; p > 0.05). CTG showed a statistically significant correlation with BMI (rho 0.25, p < 0.05) while ECG showed no such correlation. Conclusion: The use of non-invasive ECG is particularly indicated in the early weeks of pregnancy, while CTG offers superior results during the vernix period. There was no difference in signal quality after the vernix period. The signal quality with ECG was found to be independent of BMI, while the signal quality of CTG deteriorated with increasing BMI.

Change of Spectral Analysis of Fetal Heart Rate During Clinical Hypnosis: a Prospective Randomised Trial from the 20th Week of Gestation Till Term.

Objective: To investigate the functional adaptive process of the fetal autonomic nervous system during hypnosis from the 20th week of gestation till term. Are there changes in the power spectrum analysis of fetal heart rate when the mother is having a clinical hypnosis or control period? Study Design: Fourty-nine FHR recordings were analysed. Included recordings were from singletons and abdominal fetal ECG-monitored pregnancies. All women were randomised to receive clinical hypnosis followed by a period with no intervention or vice versa. Statistical analyses were performed with the Wilcoxon signed ranks and Spearman rho correlation tests. Results: There was a significant difference found between fetal heart rate at baseline (144.3 ± 6.0) and hypnosis (142.1 ± 6.4). A difference was also detected between the standard deviation of the heart rate between baseline (6.7 ± 1.9) and hypnosis (6.8 ± 3.5). LFnu was smaller during baseline (80.2 ± 5.3) than during hypnosis (82.1 ± 5.7), whereas HFnu was significantly larger (19.8 ± 5.3 vs. 17.9 ± 5.7). There was no correlation between the gestation age and the change in LFnu, HFnu or ratio LF/HF due to the hypnosis intervention. Conclusion: The functional adaptive process of the fetal autonomic system during hypnosis is reflected by a sympathovagal shift towards increased sympathetic modulation.

Uterine activity monitoring during labour--a multi-centre, blinded two-way trial of external tocodynamometry against electrohysterography.

PURPOSE: The aim of this study was to determine the quality of intrapartum uterine activity (UA) monitoring in daily practice during the first and second stages of labour. The total duration of inadequate UA monitoring is quantified in relation to the technique applied, namely, external tocodynamometry (TOCO) or electrohysterography (EHG). MATERIAL AND METHODS: 144 UA recordings, collected from 1st September 2008 until 15th October 2009 from deliveries at the Marien-Hospital Witten, Germany, were analysed by obstetricians based at different centres. The included recordings were from singleton and simultaneously with external TOCO and EHG monitored pregnancies. External TOCO and EHG UA recordings were blinded. RESULTS: The percentages of "adequate" UA recordings in the first and second stages of labour were much higher for the external EHG than the external TOCO mode (p<0.001). All doctors evaluated the UA assessment as "easier" (p <0.001) using the EHG compared with TOCO. CONCLUSION: Intrapartum UA monitoring in -daily practice via the EHG mode provides a more recognisable UA trace than the TOCO.

Towards a computational reconstruction of the electrodynamics of premature and full term human labour.

We apply virtual tissue engineering to the full term human uterus with a view to reconstruction of the spatiotemporal patterns of electrical activity of the myometrium that control mechanical activity via intracellular calcium. The three-dimensional geometry of the gravid uterus has been reconstructed from segmented in vivo magnetic resonance imaging as well as ex vivo diffusion tensor magnetic resonance imaging to resolve fine scale tissue architecture. A late-pregnancy uterine smooth muscle cell model is constructed and bursting analysed using continuation algorithms. These cell models are incorporated into partial differential equation models for tissue synchronisation and propagation. The ultimate objective is to develop a quantitative and predictive understanding of the mechanisms that initiate and regulate labour.

A field-programmable gate array based system for high frame rate laser Doppler blood flow imaging.

This paper presents a general embedded processing system implemented in a field-programmable gate array providing high frame rate and high accuracy for a laser Doppler blood flow imaging system. The proposed system can achieve a basic frame rate of flow images at 1 frame/second for 256 x 256 images with 1024 fast Fourier transform (FFT) points used in the processing algorithm. Mixed fixed-floating point calculations are utilized to achieve high accuracy but with a reasonable resource usage. The implementation has a root mean square deviation of the relative difference in flow values below 0.1% when compared with a double-precision floating point implementation. The system can contain from one or more processing units to obtain the required frame rate and accuracy. The performance of the system is significantly higher than other methods reported to date. Furthermore, a dedicated field-programmable gate array (FPGA) board has been designed to test the proposed processing system. The board is linked with a laser line scanning system, which uses a 64 x 1 photodetector array. Test results with various operating parameters show that the performance of the new system is better, in terms of noise and imaging speed, than has been previously achieved.

Detection of previously unrecognized daytime desaturation in children with chronic lung disease.

PRIMARY OBJECTIVE: The prime rationale of this research is to investigate the possible occurrence of previously unrecognized episodes of desaturation apparent in preterm infants with chronic lung disease as they freely move around a non-artificial environment. RESEARCH DESIGN: The study comprises 58 hours of telemetric recordings of SpO2, heart rate, body movement and temperature, along with full ECG and photoplethysmographic waveforms for eight preterm subjects in their home environment. MAIN OUTCOME/RESULTS: The data is analysed for remarkable events, more particularly periods of spontaneous desaturation. Statistical results for all case studies are collated into a table along with examples of graphical analysis. CONCLUSIONS: This study has shown that some patients are prone to episodes of hypoxemia during the course of normal daily activity or daytime sleep that would usually go unrecognized and that more effective management of supplemental oxygen treatment may be possible with continual unobtrusive monitoring.

Simulation of the generation and processing of Doppler ultrasound fetal heart signals to obtain directional motion information.

In fetal heart monitoring using Doppler ultrasound signals the cardiac information is commonly extracted from non-directional signals. As a consequence often some of the cardiac events cannot be observed clearly which may lead to the incorrect detection of the valve and wall motions. Here, directional signals were simulated to investigate their enhancement of cardiac events, and hence provide clearer information regarding the cardiac activities. First, fetal Doppler ultrasound signals were simulated with signals encoding forward and reverse motion then obtained using a pilot frequency. The simulation results demonstrate that the model has the ability to produce realistic Doppler ultrasound signals and a pilot frequency can be used in the mixing process to produce directional signals that allow the simulated cardiac events to be distinguished clearly and correctly.

Detrended fluctuation analysis: a suitable method for studying fetal heart rate variability?

We evaluate the suitability of an enhanced detrended fluctuation analysis for studying fetal heart rate series involving imperfect quality of information. Our results indicate that to explore persistent long-range correlations, or fractality, the collection requirements of the data can be relaxed by allowing the possibility of using averaged fetal heart rate series. In addition, it also appears feasible to employ, without producing major alterations in the long-range scaling behaviour, fragmented fetal heart rate series involving up to 50% of random missing values, or up to 50 min of consecutive missing samples in recordings of approximately equal to 8 h length. These are crucial advantages to overcome the often variable quality of fetal data. Consequently, these findings may open the possibility of obtaining information concerning the development of neural processes from fetal heart rate series, despite their non-stationary and fragmented nature.

Interpretation of heart rate variability via detrended fluctuation analysis and alphabeta filter.

Detrended fluctuation analysis (DFA), suitable for the analysis of nonstationary time series, has confirmed the existence of persistent long-range correlations in healthy heart rate variability data. In this paper, we present the incorporation of the alphabeta filter to DFA to determine patterns in the power-law behavior that can be found in these correlations. Well-known simulated scenarios and real data involving normal and pathological circumstances were used to evaluate this process. The results presented here suggest the existence of evolving patterns, not always following a uniform power-law behavior, that cannot be described by scaling exponents estimated using a linear procedure over two predefined ranges. Instead, the power law is observed to have a continuous variation with segment length. We also show that the study of these patterns, avoiding initial assumptions about the nature of the data, may confer advantages to DFA by revealing more clearly abnormal physiological conditions detected in congestive heart failure patients related to the existence of dominant characteristic scales.

Application of empirical mode decomposition to heart rate variability analysis.

The analysis of heart rate variability, involving changes in the autonomic modulation conditions, demands specific capabilities not provided by either parametric or non-parametric spectral estimation methods. Moreover, these methods produce time-averaged power estimates over the entire length of the record. Recently, empirical mode decomposition and the associated Hilbert spectra have been proposed for non-linear and non-stationary time series. The application of these techniques to real and simulated short-term heart rate variability data under stationary and non-stationary conditions is presented. The results demonstrate the ability of empirical mode decomposition to isolate the two main components of one chirp series and three signals simulated by the integral pulse frequency modulation model, and consistently to isolate at least four main components localised in the autonomic bands of 14 real signals under controlled breathing manoeuvres. In addition, within the short time-frequency range that is recognised for heart rate variability phenomena, the Hilbert amplitude component ratio and the instantaneous frequency representation are assessed for their suitability and accuracy in time-tracking changes in amplitude and frequency in the presence of non-stationary and non-linear conditions. The frequency tracking error is found to be less than 0.22% for two simulated signals and one chirp series.

Selection of pulse oximetry equipment for ambulatory monitoring.

PRIMARY OBJECTIVE: This communication describes the initial stage of a research project concerning the monitoring of SpO2 in infants prone to periods of spontaneous oxygen desaturation whilst freely moving around their home environment. The primary aim was to determine an appropriate probe type and site together with an assessment of the suitability of two commercially available oximeter units. RESEARCH DESIGN: The study comprised 19 comparative tests, totalling 162 hours of recordings at resolution one sample every four seconds. Comparisons are drawn between probes, probe sites and pulse oximeters. MAIN OUTCOMES/RESULTS: The bias and precision is presented with respect to the probe and measurement site. Also, correlation between the trial and reference recordings is considered. CONCLUSIONS: It is concluded that ambulatory recording of SpO2 in infants utilizing equipment suitable for home monitoring can produce diagnostic data equivalent to that of the Ohmeda 3700 biox, but that an indication of movement artefact may be required for confirmation of accuracy. It became apparent that 'wrap around' probes, used on the index finger or big toe are the most suitable.

Compact long-term recorder for the transabdominal foetal and maternal electrocardiogram.

Foetal heart rate (FHR) monitoring is a proven means of assessing foetal health during the antenatal period. Currently, the only widely available instrumentation for producing these data is based on Doppler ultrasound, a technology that is unsuitable for long-term use. For nearly a century, it has been known that the foetal electrocardiogram (FECG) can be detected using electrodes placed on the maternal abdomen. Although these signals suggest an alternative means of FHR derivation, their use has been limited owing to problems of poor signal-to-noise ratio. However, the eminent suitability of the transabdominal FECG for long-term FHR monitoring has suggested that perseverance with the technique would be worthwhile. The paper describes the design, construction and use of a compact, long-term recorder of three channels of 24 h antenatal transabdominal data. Preliminary use of the recorder in around 400 short recording sessions demonstrates that FHR records of equivalent quality to those from Doppler ultrasound-based instruments can be extracted from such data. The success of FHR derivation is, on average, around 65% of the recording period from around 20 weeks gestation (although this figure is reduced from around 28-32 weeks, and the success rates exhibit a wide range when individual subjects are considered). These results demonstrate that the technique offers, not only a means of acquiring long-term FHR data that are problematic to obtain by other means, but also a more patient-friendly alternative to the Doppler ultrasound technique.

The information content of Doppler ultrasound signals from the fetal heart.

Knowledge of the content of Doppler ultrasound signals from the fetal heart is essential if the performance of fetal heart rate (FHR) monitors based upon this technology is to be improved. For this reason instrumentation was constructed to enable the simultaneous collection of Doppler audio signals and the transabdominal fetal ECG (for signal registration), with a total of 22 recordings being made with an average length of around 20 minutes. These data demonstrate the transient nature of the Doppler audio data with wide variations in the signal content observable on a beat-to-beat basis. Short-time Fourier analysis enabled the content of the Doppler signals to be linked to six cardiac events, four valve and two wall motions, with higher frequency components being associated with the latter. This differing frequency content together with information regarding the direction of movement that can be discerned from Doppler signals provided a potential means of discriminating between these six events (which are unlikely to all contribute to the Doppler signal within the same cardiac cycle). Analysis of 100 records showed that wall contractions generate the most prominent signals, with atrial contraction recognisable in all records and ventricular wall contraction in 95% (although its amplitude is only around 30% of that of the atrial signal). Valve motion, with amplitudes between 15 and 25% that of the atrial wall signal, were visible in 75% of records. These results suggest means by which the six events that contribute to the Doppler signal may be distinguished, providing information that should enable an improvement in the current performance of Doppler ultrasound-based FHR monitors.