Noncontact measurements of avian embryo heart rate by means of the laser speckle: comparison with contact measurements

Non-Invasive PPG-Based System for Continuous Heart Rate Monitoring of Incubated Avian Embryo

The chicken embryo is a widely used experimental animal model in many studies, including in the field of developmental biology, of the physiological responses and adaptation to altered environments, and for cancer and neurobiology research. The embryonic heart rate is an important physiological variable used as an index reflecting the embryo's natural activity and is considered one of the most difficult parameters to measure. An acceptable measurement technique of embryonic heart rate should provide a reliable cardiac signal quality while maintaining adequate gas exchange through the eggshell during the incubation and embryonic developmental period. In this paper, we present a detailed design and methodology for a non-invasive photoplethysmography (PPG)-based prototype (Egg-PPG) for real-time and continuous monitoring of embryonic heart rate during incubation. An automatic embryonic cardiac wave detection algorithm, based on normalised spectral entropy, is described. The developed algorithm successfully estimated the embryonic heart rate with 98.7% accuracy. We believe that the system presented in this paper is a promising solution for non-invasive, real-time monitoring of the embryonic cardiac signal. The proposed system can be used in both experimental studies (e.g., developmental embryology and cardiovascular research) and in industrial incubation applications.

Avian embryo monitoring during incubation using multi-channel diffuse speckle contrast analysis

Determining the survival rate of avian embryos during incubation is essential for cost-saving in the poultry industry. A multi-channel diffuse speckle contrast analysis (DSCA) system, comprising four optical fiber channels, is proposed to achieve noninvasive in vivo measurements of deep tissue flow. The system was able to monitor chick embryo vital signs over the entire incubation period. Moreover, it proved useful in distinguishing between chick embryos in healthy and weakened conditions.

Measurement of vital sign in chick embryo using multi-channel diffuse speckle contrast analysis

In poultry industry which is avian breeding program, the determination whether chick embryos survive in the artificial incubation periods or not is essential to reduce the financial resources. We developed the multi-channel diffuse speckle contrast analysis (DSCA) system composed of four optical fiber detectors enabling to achieve in-vivo measurements of deep tissue flow noninvasively. The system could confirm vital sign of the chick embryo in early incubation stage. Moreover, it demonstrates the change of relative blood flow index and depth information with simplicity, low cost, and flexibility.

Noninvasive vasculature detection using laser speckle imaging in avian embryos through intact egg in early incubation stage

Monitoring the vital signs of a developing embryo is very useful in avian breeding programs, especially during early days of incubation, so that dead or unfertilized eggs can be timely removed from incubator and new eggs can be placed in. A noninvasive system for detecting the vital signs of avian embryo through intact egg in early stage of incubation has been developed using laser speckle imaging (LSI). The system was based on the measurement of intensity fluctuations of speckle caused by the embryo's blood flow in the intact egg under laser light illumination. This system was found to be feasible in imaging the vasculature in the egg as well as confirming its fertilization or survival from the second day to fifth day of incubation while other reported noninvasive methods cannot detect vital signs of the embryo until the sixth day of incubation.

Heart rate and heart rate variability in chicken embryos at the end of incubation

Our immediate goal was to study heart rate variability (HRV) in chicken embryos in the egg. Instantaneous heart rate data were needed for this purpose, and accordingly an ECG recording method in the egg was developed. The aim of this work was to test the hypothesis that autonomic nervous cardiac modulation, as shown from HRV parameters, is present at the end of development and that it reaches a constant value during the last days of incubation. Embryonic chicken heart rate was obtained at the final incubation period (days 19 and 20) from ECG recordings. Tachograms were computed and time- and frequency-domain indices of HRV were determined. No significant differences were found between HRV indices from day 19 and day 20. The power spectra extended in two frequency bands with centre frequency around 0.6-0.7 Hz (low frequency (LF) component), and another around 1.2-1.5 Hz (high frequency (HF) component); the latter was shown to reflect respiratory sinus arrhythmia. A relation between mean RR interval and some HRV parameters (rMSSD, pNN5 and HF power) was shown. HRV results obtained from embryonic chickens, showed the presence of modulation of cardiovascular function by the autonomic nervous system. The results suggested that sympathetic and parasympathetic activities have already reached a constant level at day 19 of incubation. High frequency oscillations (0.78-2.5 Hz) were detected and are considered to reflect respiratory sinus arrhythmia.

Cardiac rhythms in chick embryos during hatching

Avian embryos develop within a hard eggshell which permits the measurement of heart rate while maintaining an adequate gas exchange through the chorioallantoic membrane. Heart rate has been determined from cardiogenic signals detected either noninvasively, semi-invasively or invasively with various transducers. Firstly, we reviewed these previously-developed methods and experimental results on heart rate fluctuations in prenatal embryos. Secondly, we presented new findings on the development of heart rate fluctuations during the last stages of incubation, with emphasis on the perinatal period, which remained to be studied. Three patterns of acceleration of the instantaneous heart rate were unique to the external pipping period: irregular intermittent large accelerations, short-term repeated large accelerations and relatively long-lasting cyclic small accelerations. Besides these acceleration patterns, respiratory arrhythmia, which comprimised oscillating patterns with a period of 1-1.5 s, appeared during the external pipping period. Furthermore, additional oscillating patterns with a period of 10-15 min were found in some externally pipped embryos.

Dynamical systems analysis of arterial blood pressure signals in relation to heart rate fluctuations in chick embryos

We attempted a new approach based on a modern dynamical system theory to reconstruct the arterial blood pressure signals in relation to heart rate fluctuations of developing chick embryos. The dynamical systems approach in general is to model a phenomenon that is presented by a single time series record and approximate the dynamical property (e.g. heart rate fluctuations) of a system based only on information contained in a single-variable (arterial blood pressure) of the system. The time-series data of the arterial blood pressure was reconstructed in 3-dimensional space to draw characteristic orbits. Since the reconstructed orbits of the blood pressure should retain information contained in the pressure signals, we attempted to derive instantaneous heart rate (IHR) from the reconstructed orbits. The derived IHR presenting HR fluctuations coincided well with the IHR obtained conventionally from the peak-to-peak time intervals of the maximum blood pressure. Movements of the reconstructed orbits of the arterial blood pressure in 3-dimensional space reflected HR fluctuations (i.e. transient decelerations and accelerations).

Ballistocardiogram of avian eggs determined by an electromagnetic induction coil

As an avian embryo grows within an eggshell, the whole egg is moved by embryonic activity and also by the embryonic heartbeat. A technical interest in detecting minute biological movements has prompted the development of techniques and systems to measure the cardiogenic ballistic movement of the egg or ballistocardiogram (BCG). In this context, there is interest in using an electromagnetic induction coil (solenoid) as another simple sensor to measure the BCG and examining its possibility for BCG measurement. A small permanent magnet is attached tightly to the surface of an incubated egg, and then the egg with the magnet is placed in a solenoid. Preliminary model analysis is made to design a setup of the egg, magnet and solenoid coupling system. Then, simultaneous measurement with a laser displacement measuring system, developed previously, is made for chicken eggs, indicating that the solenoid detects the minute cardiogenic ballistic movements and that the BCG determined is a measure of the velocity of egg movements.

Comparisons between invasive and noninvasive determinations of embryonic heart rate in chickens

The embryonic heart rate (HR) of chicken eggs was determined by ballistocardiography, electrocardiography, impedance-cardiography and acoustocardiography. The effects of these different methods on the HR were examined for young (12-day-old) and late (16- and 18-day-old) embryos. Ballistocardiography is a non-invasive method. Nevertheless, the mean HRs determined using this method at 5-hr intervals were significantly different in many embryos. This difference was caused by the natural variability of embryonic HR. The statistical analyses indicated that any of these four methods did not influence the HR measurement and can be used as a simple means for determination of the embryonic HR.

Simple, noninvasive system for measuring the heart rate of avian embryos and hatchlings by means of a piezoelectric film

Using a flexible piezoelectric film, the authors developed a simple system to determine noninvasively the heart rate of chicken embryos and hatchlings. The film was piezoelectric polyvinylidene fluoride (PVDF), which is sensitive enough to detect cardiogenic ballistic movements of the egg (ballistocardiogram (BCG)) and precordial movements of the hatchling attributable to cardiac contractions (apexcardiogram (ACG)). The BCG could be detected, during the second half of incubation, by placing the egg on the PVDF film on a soft substrate. The detected signal was found to be a measure of movement velocity. The ACG could be measured when the hatchling's chest wall made contact with the PVDF film installed in a box in which the hatchling was confined. The heart rate was counted from the lag time of autocorrelation calculated for a certain time segment (e.g. 2 s) of the BCG and ACG recordings.

Non-invasive determination of heart rate in newly hatched chicks

1. Using a flexible piezoelectric probe, we detected non-invasively the cardiogenic precordial movements of domestic fowl chicks and measured heart rate (HR) daily over the first week after hatching (day 0) for comparison with previously measured embryonic HR. 2. HR of the hatchlings was much more variable than embryonic HR. The mean HR at a given age also varied among the 5 chicks measured. 3. The overall mean HR was 280 +/- 20 (SD, n = 5) bpm on day 0. This value was similar to the prepipping HR and lower than that of externally pipped embryos. It increased to 342 +/- 39 bpm 3 days later.

Embryonic heart rate of the domestic fowl (Gallus domesticus) in a quasiequilibrium state of altered ambient temperatures

1. The heart rates (fH) of 12-day-old embryos (young), 16- and 18-day-old embryos (late) and of 20-day-old embryos (externally pipped eggs, EP) were measured noninvasively at a temperature of 38 degrees C and after a 5 hr exposure to an ambient temperature (Ta) within the range 34-46 degrees C. 2. All embryos survived the 5 hr exposure to Ta of 42 degrees C. The lethal Ta ranged from 44 degrees C (EP eggs) to 46 degrees C (young embryos). 3. The temperature coefficient (Q10) of fH became smaller than 2 in EP eggs as Ta was decreased or increased from 38 degrees C, implying an incipient homeothermic response of fH.

Cardiogenic ballistograms of chicken eggs: comparison of measurements

In the incubated avian egg, minute movements occur that are synchronised with embryonic cardiac contractions. We previously developed two systems to noninvasively record this cardiogenic ballistic movement of the egg (referred to as the ballistocardiogram, BCG); one was based on applying an audiocartridge and the other a laser speckle phenomenon. A third system, which detects the ballistic movement as the measurement of displacement (referred to as displacement BCG), is applied in the present study, together with the previous two systems, to the ballistocardiography of the egg. The BCG is measured with three systems simultaneously for comparison. The differentiation of the displacement BCG produces a pattern identical to the BCG recorded by the cartridge method, and the integrated pattern of the latter BCG is identical to the displacement BCG. This indicates that the cartridge system detects the cardiogenic movement as the measure of velocity and it may be referred to as velocity BCG. The BCG by the laser speckle method is not related to that recorded by the other two systems, which may be referred to as movement BCG.