Characteristics of hypertensive disorders in twin versus singleton pregnancies.

OBJECTIVE: To determine the characteristics of hypertensive disorders of pregnancy in twin compared with singleton pregnancies. STUDY DESIGN: Analysis of a prospectively recorded database of 4976 hypertensive pregnancies. MAIN OUTCOME MEASURES: Comparison of progression to pre-eclampsia and maternal and neonatal outcomes. RESULTS: There were 3942 singleton and 214 twin pregnancies. De novo hypertension in twin pregnancy was diagnosed earlier (p<0.001). In singleton pregnancies with de novo hypertension (n=3161), 60% had an initial diagnosis of gestational hypertension (GH) and 40% had pre-eclampsia (PE). In twin pregnancies with de novo hypertension (n=199), 35% of women were initially diagnosed with GH and 65% with PE (p<0.001). At delivery, 46% of the singletons had GH and 54% had PE, compared with twin pregnancies where 23% had GH and 77 % had PE (p<0.001). The progression from GH to PE for twins was twice that of singleton pregnancies (p<0.001). There were 781 singleton and 15 twin pregnancies with chronic hypertension (CH). Twin pregnancies complicated by CH were more likely to progress to PE than singletons (p<0.01). The gestation at delivery was earlier for twin pregnancies (p<0.001) and there were more twins that were smaller for gestational age (p<0.001). There were no differences in maternal outcomes. CONCLUSION: Women carrying twins with de novo hypertension are more likely to present earlier, have initial PE and to subsequently progress from GH to PE. Neonatal outcomes are worse in such pregnancies.

OS096. Characteristics of hypertensive disorders in twin versus singleton pregnancies.

INTRODUCTION: Pre-eclampsia is well characterised in single pregnancies but less well in twin pregnancies, where the risks are higher. OBJECTIVES: The aim of this study, therefore, was to determine the characteristics of hypertensive disorders of pregnancy (HDP) in twin compared with singleton pregnancies. METHODS: We performed an analysis of 4976 prospectively recorded hypertensive pregnancies. These included pre-eclampsia (PE), gestational hypertension (GH) and chronic hypertension (CH). The rates and characteristics of these disorders were compared between singleton and twin pregnancies as was the progression of GH to PE for both groups. Maternal outcomes for severe hypertension (BP⩾170/⩾110mmHg), eclampsia, total antihypertensive medication requirements and maternal death were compared. Neonatal outcomes evaluated included birth weight, small for gestational age (SGA) and perinatal mortality. RESULTS: After exclusion of higher order pregnancies (triplets (n=2), a quadruplet pregnancy (n=1)), those with known secondary HT, white coat HT, or not fulfilling strict criteria for an accurate diagnosis (n=470) and those without an initial diagnosis recorded, there were 4156 women comprising 3942 singleton and 214 (5%) twin pregnancies.Hypertension (GH or PE) in twin pregnancy was diagnosed earlier than in singleton pregnancy (34±3 v 36±3 weeks, p<0.001). In the singleton pregnancies with de novo hypertension (n=3161), 60% had an initial diagnosis of GH and 40% had PE. In the twin pregnancies with de novo hypertension (n=199), 35% of women were initially diagnosed with GH and 65% with PE (p<0.001, single v twins). At delivery, 46% of the singletons had GH and 54% had PE, compared with twin pregnancies where 23% had GH and 77 % had PE (p<0.001). The progression from GH to PE for twins was greater than that for singleton pregnancies (34% v 15%, p<0.001). There were also781 singleton pregnancies and 15 twin pregnancies with CH. Twin pregnancies complicated by CH were more likely to progress to PE than singletons (54% v 18%, p<0.01). Women carrying twins were older (p<0.01) and they required less medication compared to those carrying singleton pregnancies(0.9±1.2 v 1.3±1.5 medication score, p<0.05). Other maternal outcomes did not differ between the two groups. For neonatal outcomes, the gestation at delivery was earlier for twin than singleton pregnancies (36±2 v38±2 weeks, p<0.001) and SGA (less than 10th percentile) for twins was higher than singleton pregnancies (22% v 12%, p<0.001).No difference in perinatal mortality was noted. CONCLUSION: Women carrying twins who develop hypertension during pregnancy are more likely to present earlier, have initial PE rather than GH and to subsequently progress from GH to PE than in singleton pregnancy. Neonatal outcomes are worse in such pregnancies. It is thus reasonable for pregnant women with twins who develop de novo hypertension to be considered very high risk and possibly be managed in hospital.

Microchip system for monitoring microbial physiological behaviour under drug influences.

Single-step real-time high-throughput monitoring of drug influences on bacterial cell behaviour has become important with growing interests in personalized therapy and medication. Conventional microchip assemblies to perform similar work do exist. However, most of these devices have complex set-ups incorporating micromixers, separators, pumps, or valves. These microcomponents can sometimes damage the entities being monitored because of the creation of unfavourable biological environments. This paper presents a microchip-based system that enables single-step mixing of two solutions in various ratios, without the need for additional microcomponents such as mixers and pumps, in order to screen effectively their combinatory effects on cell outcomes. In this work, in-vitro experiments were carried out using ampicillin at various concentrations to investigate their effects on Escherichia coli (E. coli). Results showed that the microchip provided effective screening, which yielded useful results such as effective dosages, ineffective dosages, and other possible outcomes; for instance, in this case, the occurrence of adaptive mutation of the bacteria at certain drug concentrations. Comparative microbiological laboratory tests were carried out as standard for confirmation of the results.

Clinical applications of pulse transit time in paediatric critical care.

A simple and non-invasive technique, termed pulse transit time (PTT), has shown its potential in long-term investigations such as respiratory sleep studies and cardiovascular studies. Based on these findings, the PTT technique shows relevance for continuous haemodynamic monitoring in critical care. The objective of this review is to understand the potential, applications and limitations of PTT in this clinical setting. Present non-invasive haemodynamic monitoring methods such as automated oscillometric blood pressure (BP) and auscultatory techniques have their known limitations. They tend to underestimate systolic BP while overestimating diastolic BP. Due to the periodic increase in cuff pressure cycles during data acquisition, these techniques may cause much discomfort in elderly geriatric patients, or lessen the cooperation of younger paediatric patients. Thus, there can be adverse effects on therapeutic decisions and possibly clinical outcomes. Documented evidences have indicated that changes observed in PTT are inversely correlated to the corresponding BP changes. In critical care, a simple and accommodating technique like PTT may be useful in providing better comfort for patients during extended monitoring. Being a semi-quantitative measure, blanket recommendations for its utility can then become possible. The basic instrumentations needed are often part of standard critical care monitoring system. Furthermore, PTT also has the potential to monitor the often tachypnoeic respiratory dependent BP changes seen in small infants during critical care.

Use of the pulse transit time trend to relate tidal breathing and central respiratory events.

Central sleep apnoea (CSA) is a respiratory event where cessation of breathing effort and airflow occurs. Numerous lumped models have related the physical phenomena in the arterial tree to properties of the arterial wall. However, a limited model is available that describes pulse transit time (PTT) oscillations during CSA and tidal breathing. Data from 28 children (22 males; aged 6.2 +/- 3.6 years) were obtained during overnight polysomnography. Using a lumped-element model, PTT fluctuations during both respiratory events were described and compared with actual experimental data. 222 valid CSA and 222 tidal breathing events were acquired and analysed. For the tidal breathing, undamped PTT oscillations of 3.89 s were predicted while actual data showed a mean value of 3.68 +/- 0.83 s. Conversely, a damped PTT trend was observed during CSA as predicted by the model. The results attained showed that clustered CSA occurrences led to an increase of 7.23 +/- 3.34 per cent in PTT baseline value while the model predicted 7.86 +/- 2.63 per cent. The marginal increase in PTT baseline was expected since the blood pressure and heart rate decreased during such occurrences. The findings herein suggest that the described model has the potential to describe respiratory event characteristics of a sleeping child.

Normalized peripheral transit time to monitor hypertension in children.

Studies have demonstrated that a notable increase in arterial stiffening can signify the presence of cardiovascular abnormalities, such as hypertension. Presently, the mercury sphygmomanometer continues to be the clinical gold standard to identify such abnormalities, but due to its measuring nature it cannot be used for continuous observation. Pulse transit time (PTT), which has an inverse relationship with blood pressure (BP), is proposed here as a simple and non-invasive technique to monitor hypertension in children. In order to minimize inter-subject PTT differences, all obtained PTT data were normalized to the study population. The results indicated that normalized mean PTT value is able to differentiate hypertensive from normal children in a significant (p < 0.01) manner in both upper and lower limbs. Preliminary findings herein suggest that PTT can be useful tool to monitor for hypertension in children especially during prolonged clinical observations.

An investigation on pulse transit time in respiratory sleep studies for infants.

The main objective of this study was to assess the capability of pulse transit time (PTT) to identify obstructive and/or central apnoeas from normal breathing patterns in sleeping infants. Clinical trials were conducted with PTT being monitored as an adjunct measure in routine overnight polysomnography (PSG) studies. Standard PSG scorings of events were performed by two blinded observers to evaluate PTT accuracy. Data from eight infants (six male; aged 8.5 +/- 2.1 months; apnoea-hypopnoea index of 12.1 +/- 8.4 events per hour) were collected. Obstructive events were not successfully identified by PTT due to their low occurrence. However, PTT scored positive and negative predictive values of 0.803 and 0.788 for central events, respectively. Preliminary findings suggest that PTT has the potential to differentiate normal breathing from central events only in sleeping infants.

Difference in pulse transit time between populations: a comparison between Caucasian and Chinese children in Australia.

Pulse wave velocity (PWV) has shown to be a clinically important physiologic measure in the assessment of increased arterial stiffness that is linked to systolic hypertension. Pulse transit time (PTT), which is based on the principle of PWV, has become popular in childhood cardiovascular studies. A previous study has indicated PWV obtained from a Chinese population tends to be higher than that from their Caucasian counterpart of similar age but of different localities. In this study, 67 healthy children (55 Caucasian and 12 Chinese) were recruited to investigate the possible PTT difference between these two ethnic groups in the same region. However, the hypothesized PWV difference (p < 0.05) between them is not observed here in the corresponding PTT measurements (time-related PWV equivalent). Hence, preliminary results suggest that locality or inclusion of pre-ejection period, which forms the major component of the PTT measurement, may contribute to this discrepancy.

Detection method to minimize variability in photoplethysmographic signals for timing-related measurement.

Photoplethysmography (PPG) is a common optical technique used to monitor peripheral pulsation. Studies have shown that minimal variability in phase characteristics is critical to attain accurate estimation of timing-related measurements, such as heart rate and pulse transit time. Observed abrupt changes from baseline of these measurements have shown to identify abnormalities in clinical studies. This study investigates nominal fluctuations when different detection settings were used on the PPG signals. The results indicate that there can be differences in variations observed, and an appropriate detection setting can minimize phase-induced errors in clinical interpretation of timing-related physiologic measurements.

Pulse transit time as a derived noninvasive mean to monitor arterial distensibility changes in children.

Changes in arterial distensibility have been widely used to identify the presence of cardiovascular abnormalities like hypertension. Pulse wave velocity (PWV) has shown to be related to arterial distensibility. However, the lack of suitable techniques to measure PWV nonintrusively has impeded its clinical usefulness. Pulse transit time (PTT) is a noninvasive technique derived from the principle of PWV. PTT has shown its capabilities in cardiovascular and cardiorespiratory studies in adults. However, no known study has been conducted to understand the suitability and utility of PTT to estimate PWV in children. Two computational methods to derive PWV from PTT values obtained from 23 normotensive Caucasian children (19 males, aged 5-12 years old) from their finger and toe were conducted. Furthermore, the effects of adopting different postures on the PWV derivations were investigated. Statistical analyses were performed in comparison with two previous PWV studies conducted on children. Results revealed that PWV derived from the upper limb correlated significantly (P<0.05) regardless of computing methods or postures adopted. The findings here suggest that PTT measurement can be used as a convenient and noninvasive surrogate measure of derived PWV in prolonged clinical studies, especially on younger or less cooperative children. Furthermore, the simple set-up and noninvasive nature of PTT can promote its usefulness in ambulatory monitoring.

Age-related factors that confound peripheral pulse timing characteristics in Caucasian children.

Characteristics obtained from peripheral pulses can be used to assess the status of cardiovascular system of subjects. However, nonintrusive techniques are preferred when prolonged monitoring is required for their comfort. Pulse transit time (PTT) measurement has showed its potentials to monitor timing changes in peripheral pulse in cardiovascular and respiratory studies. In children, the common peripheries used for these studies are fingers or toes. Presently, there is no known study conducted on children to investigate the possible physiologic parameters that can confound PTT measure at these sites. In this study, PTT values from both peripheral sites were recorded from 55 healthy Caucasian children (39 male) with mean age of 8.4+/-2.3 years (range 5-12 years). Peripheries' path length, heart rate, systolic blood pressure, diastolic blood pressure (DBP) and mean arterial pressure (MAP) were measured to investigate their contributions to PTT measurement. The results reveal that PTT is significantly related to all parameters (P<0.05), except for DBP and MAP. Age is observed to be the dominant factor that affects PTT at both peripheries in a child. Regression equations for PTT were derived for measuring from a finger and toe, (6.09 age+189.2) ms and (6.70 age+243.0) ms, respectively.

Use of regression equation of peripheral pulse timing characteristics to predict hypertension in children.

Studies have shown that an increase in arterial stiffening can indicate the presence of cardiovascular diseases like hypertension. Current gold standard in clinical practice is by measuring the blood pressure of patients using a mercury sphygmomanometer. However, the nature of this technique is not suitable for prolonged monitoring. It has been established that pulse wave velocity is a direct measure of arterial stiffening. However, its usefulness is hampered by the absence of techniques to estimate it non-invasively. Pulse transit time (PTT) is a simple and non-intrusive method derived from pulse wave velocity. It has shown its capability in childhood respiratory sleep studies. Recently, regression equations that can predict PTT values for healthy Caucasian children were formulated. However, its usefulness to identify hypertensive children based on mean PTT values has not been investigated. This was a continual study where 3 more Caucasian male children with known clinical hypertension were recruited. Results indicated that the PTT predictive equations are able to identify hypertensive children from their normal counterparts in a significant manner (p<0.05). Hence, PTT can be a useful diagnostic tool in identifying hypertension in children and shows potential to be a non-invasive continual monitor for arterial stiffening.

Development of a Non-intrusive System to Monitor Radial PulseWave Velocity.

Understanding arterial distensibility has shown to be important in the pathogenesis of cardiovascular abnormalities like hypertension. It is also known that arterial pulse wave velocity (PWV) is a measure of the elasticity or stiffness of peripheral arterial blood vessels. However, it generally requires complex instrumentations to have an accurate measurement and not suited for continual monitoring. In this paper, it describes a simple and non-intrusive method to detect the cardiovascular pulse from a human wrist above the radial artery and a fingertip. The main components of this proposed method are a piezoelectric transducer and a photoplethysmography circuitry. 5 healthy adults (4 male) with age ranging from 25 to 38 years were recruited. The timing consistency of the detected pulsations is first evaluated and compared to that obtained from a commercial electrocardiogram. Furthermore, the derived PWV is then assessed by the predicted values attained from regression equations of two previous similar studies. The results show good correlations (p<0.05) and similarities for the former and latter respectively. The simplicity and non-invasive nature of the proposed method can be attractive for even younger or badly disturbed patients. Moreover, it can be used for prolonged monitoring for the comfort of the patients.

Relations between Physiologic Parameters and Pulse Transit Time during Loaded Breathing.

Pulse transit time (PTT) is a non-invasive measure, defined as time taken for the pulse pressure waves to travel from the R-wave of electrocardiogram to a selected peripheral site. Baseline PTT value is known to be influenced by physiologic variables like heart rate (HR), blood pressure (BP) and arterial compliance (AC). However, few quantitative data are available describing the factors which can influence PTT measurements in a child during breathing. The aim of this study was to investigate the effects of changes in breathing efforts on PTT baseline and fluctuations. Two different inspiratory resistive loading (IRL) devices were used to simulate loaded breathing in order to induce these effects. It is known that HR can influence the normative PTT value however the effect of HR variability (HRV) is not well-studied. Two groups of 3 healthy children (≤12years) were recruited; one group with insignificant (p>0.05) HR changes during all test activities. Results showed that HRV is not the sole contributor to PTT variations and suggest that changes in other physiologic parameters are also equally important. Hence, monitoring PTT measurement can be indicative of these associated changes during tidal or increased breathing efforts in healthy children.

Detection of central respiratory events using pulse transit time in infants.

The prevalence of sudden infant death syndrome (SIDS) has been well studied and central sleep apnea is deemed as one of the possible causes. Current gold standard for its diagnosis is nocturnal polysomnography (PSG). However, this procedure is complex and generally needs to be performed in a sleep laboratory. Pulse transit time (PTT) shows its potential to indicate abrupt blood pressure (BP) changes during the occurrences of upper airway obstruction. The main objective of this study was to assess the capability of PTT to differentiate central respiratory events from tidal breathing in infants. This study involved 5 infants (4 male) with mean age of 7.8 months. 50 valid central respiratory events were randomly selected. These events were free from motion artifacts and pre-scored in the corresponding PSG studies by two blinded observers. PTT measurements from these events were then evaluated against the PSG scorings. Using a two-tailed F-test for variance, it was observed that central events differed from tidal breathing in a significant manner (p<0.05). Furthermore, PTT has showed its sensitivity to monitor marginal BP fluctuations during tidal breathing. Hence, the results herein suggest that PTT can be a valuable non-invasive technique to monitor central apneic events in sleeping infants.

Motion artefact reduction of the photoplethysmographic signal in pulse transit time measurement.

Motion artefact is a common occurrence that contaminates photoplethysmographic (PPG) measurements. To extract timing information from signals during artefact is challenging. PPG signal is very sensitive to artefacts and can be used in applications like, pulse transit time (PTT) as part of the polysomnographic studies. A correlation cancellation or signal processing approach is implemented with the adaptive cancelling filter concept and a triaxial accelerometry. PPG signals obtained from a Masimo (Reference) pulse oximeter is used as reference to compare with the reconstructed PPG signals. Different hands are used for each PPG source, one stationary while the other involves typical movements during sleep. A second Masimo pulse oximeter is used to register intensity of timing errors on commercial PPG signals. 108 PTT measurements are recorded in three different movements with PTT estimates from unprocessed PPG signals showing 35.51+/-27.42%, Masimo 50.02+/-29.40% and reconstructed 4.32+/-3.59% difference against those from the Reference PPG. The triaxial accelerometry can be used to detect the presence of artefact on PPG signals. This is useful in PTT measurements when signal contaminated with artefacts are required for further analysis, especially after and during arousals in sleep. The suggested filtering model can then reconstruct these corrupted PPG signals.