Gordon R. Williams

Pulse transit time changes observed with different limb positions

Pulse transit time (PTT) is a non-invasive measure of arterial compliance. It can be used to assess instantaneous blood pressure (BP) changes in continual cardiovascular measurement such as during overnight respiratory sleep studies. In these studies, periodic changes in limb position can occur randomly. However, little is known about their possible effects on PTT monitored on the various limbs. The objective of this study was to evaluate PTT differences on all four limbs during two positional changes (lowering and raising of a limb). Ten healthy adults (seven male) with a mean age of 27.0 years were recruited in this study. The results showed that the limb that underwent a positional change had significant (p < 0.05) local PTT differences when compared to its nominal baseline value, whereas PTT changes in the other remaining limbs were insignificant (p > 0.05). The mean PTT value measured from a vertically-raised limb increased by 42.7 ms, while it decreased by 28.1 ms with a half-lowered limb. The PTT differences observed during positional change can be contributed to by the complex interactions between hydrostatic pressure changes, autonomic and local autoregulation experienced in these limbs. Hence the findings herein suggest that PTT is able to reflect local circulatory responses despite changes in the position of other limbs. This can be useful in prolonged clinical observations where limb movements are expected.

Screening of obstructive and central apnoea/hypopnoea in children using variability: a preliminary study.

AIM Polysomnography (PSG) is the current standard protocol for sleep disordered breathing (SDB) investigation in children. Presently, there are limited reliable screening tests for both central (CE) and obstructive (OE) respiratory events. This study compared three indices, derived from pulse oximetry and electrocardiogram (ECG), with the PSG gold standard. These indices were heart rate (HR) variability, arterial blood oxygen de-saturation (SaO2) and pulse transit time (PTT). METHODS 15 children (12 male) from routine PSG studies were recruited (aged 3-14 years). The characteristics of the three indices were based on known criteria for respiratory events (RPE). Their estimation singly and in combination was evaluated with simultaneous scored PSG recordings. RESULTS 215 RPE and 215 tidal breathing events were analysed. For OE, the obtained sensitivity was HR (0.703), SaO2 (0.047), PTT (0.750), considering all three indices (0) and either of the indices (0.828) while specificity was (0.891), (0.938), (0.922), (0.953) and (0.859) respectively. For CE, the sensitivity was HR (0.715), SaO2 (0.278), PTT (0.662), considering all indices (0.040) and either of the indices (0.868) while specificity was (0.815), (0.954), (0.901), (0.960) and (0.762) accordingly. CONCLUSIONS Preliminary findings herein suggest that the later combination of these non-invasive indices to be a promising screening method of SDB in children.

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.

Predictive regression equations and clinical uses of peripheral pulse timing characteristics in children

Studies have shown that increased arterial stiffening can be an indication of cardiovascular diseases like hypertension. In clinical practice, this can be detected by measuring the blood pressure (BP) using a sphygmomanometer but it cannot be used for prolonged monitoring. It has been established that pulse wave velocity (PWV) is a direct measure of arterial stiffening but its usefulness is hampered by the absence of non-invasive techniques to estimate it. Pulse transit time (PTT) is a simple and non-invasive method derived from PWV. However, limited knowledge of PTT in children is found in the present literature. The aims of this study are to identify independent variables that confound PTT measure and describe PTT regression equations for healthy children. Therefore, PTT reference values are formulated for future pathological studies. Fifty-five Caucasian children (39 male) aged 8.4 +/- 2.3 yr (range 5-12 yr) were recruited. Predictive equations for PTT were obtained by multiple regressions with age, vascular path length, BP indexes and heart rate. These derived equations were compared in their PWV equivalent against two previously reported equations and significant agreement was obtained (p < 0.05). Findings herein also suggested that PTT can be useful as a continuous surrogate BP monitor in children.

Pulse transit time ratio as a potential marker for paediatric crural and brachial blood pressure index.

Pulse transit time (PTT) has shown to be inversely correlated with blood pressure ( BP). 1 However, there is limited understanding in the current literature about the potential use of PTT-related measurement in assessing the ratio of the crural and brachial BP or the ankle brachial index (ABI).

Effects of poorly perfused peripheries on derived transit time parameters of the lower and upper limbs.

Abstract A simple and non-intrusive approach termed the pulse transit time ratio (PTTR) has recently been shown to be a potential surrogate of the ankle-brachial index (ABI). PTTR is based on the principle of PTT, which is known to be temperature-sensitive. In this study, 23 healthy adults with normally perfused peripheries and 10 with poorly perfused peripheries were recruited. No significant change in PTTR was observed between those with cold (1.287±0.043) and normal (1.290±0.027) peripheries (p>0.05). A cold periphery may cause pulse waveform changes and indirectly affect PTT owing to poor skin microcirculation, but may have a limited effect on PTTR, which is useful as an ABI alternative.

Effect of ethnicity and growth on ratio-based transit time surrogate ankle-brachial index marker from a Chinese children's perception

Objective — Since its introduction, ankle brachial index (ABI) measurements have been used in numerous clinical studies for its diagnostic and epidemiological values. However, conventional methods to acquire ABI are known to have limitations such as their suitability on uncooperative children when multiple prolonged monitoring is required. A simple and non-occluding technique termed pulse transit time ratio (PTTR) has been recently proposed to be a surrogate ABI marker. This methodological approach is based on the working principle of pulse transit time (PTT). It is known that age and ethnicity have confounding effects on the body proportion but little is known about their effect on the PTTR value. Methods and results — In this study, 128 healthy subjects (43 Chinese adults, 55 Caucasian and 30 Chinese children) were recruited to assess the effect of the two physiologic parameters. Statistical analyses reveal that age and ethnicity have diverse effects on the acquired transit time-related measurements. Particularly, both the PTT and PTTR parameters were influenced by age (P < 0.05) but not ethnicity (P > 0.05). However, age did not have any effect on either parameter for the adult group (P > 0.05). Conclusions — Similar to the ABI concept, the PTTR is the quotient of the transit time acquired from the lower limb and upper limb that indirectly reflects the stiffness of the respective arterial wall. Hence, the findings herein suggest that the PTTR approach shows promise to be a surrogate ABI marker.

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 (les12years) 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

Screening of obstructive and central apnoea/hypopnoea in children using variability: A preliminary study: Screening of sleep disordered breathing with three indices

Aim: Polysomnography (PSG) is the current standard protocol for sleep disordered breathing (SDB) investigation in children. Presently, there are limited reliable screening tests for both central (CE) and obstructive (OE) respiratory events. This study compared three indices, derived from pulse oximetry and electrocardiogram (ECG), with the PSG gold standard. These indices were heart rate (HR) variability, arterial blood oxygen de‐saturation (SaO2) and pulse transit time (PTT). Methods: 15 children (12 male) from routine PSG studies were recruited (aged 3–14 years). The characteristics of the three indices were based on known criteria for respiratory events (RPE). Their estimation singly and in combination was evaluated with simultaneous scored PSG recordings. Results: 215 RPE and 215 tidal breathing events were analysed. For OE, the obtained sensitivity was HR (0.703), SaO2 (0.047), PTT (0.750), considering all three indices (0) and either of the indices (0.828) while specificity was (0.891), (0.938), (0.922), (0.953) and (0.859) respectively. For CE, the sensitivity was HR (0.715), SaO2 (0.278), PTT (0.662), considering all indices (0.040) and either of the indices (0.868) while specificity was (0.815), (0.954), (0.901), (0.960) and (0.762) accordingly.

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