Influence of respiratory rate on the variability of blood volume pulse characteristics

Photoplethysmogram (PPG) measures have been proven useful for the quantification of sympathetic reactivity and continuous monitoring of vascular reactivity. This study was designed to delineate the influence of respiratory rate on the variability of various PPG characteristics in time and frequency domains. PPG, electrocardiogram (ECG) and respiration were simultaneously recorded for 2 min from eight healthy volunteers during paced respiration of 6, 12 and 18 cycles min^?1. The PPG characteristics such as peak-to-peak interval (PPI), systolic peak amplitude, slope, T_crest, T_decay and pulse transit time (PTT) were computed for every pulse. In time domain, the mean of amplitude, slope and T_crest were not significantly different amongst three different respiratory rates. However, the mean of T_decay, PPI and PTT were significantly increased (p < 0.05, p < 0.05 and p < 0.01, respectively) during respiration of 6 cycles min^?1 compared to 12 cycles min^?1. The maximal spectral powers of the variability of all PPG measures were centred on the respiratory frequency in frequency domain. In conclusion, the results that the amplitude and slope in time domain are not altered by the respiratory frequency suggest their application in faithful assessment of cardiovascular reactivity. As the variability of PPI, T_decay and PTT are altered by the slow respiration, the influence of respiration on these time derivatives should not be ignored during interpretation of vascular reactivity.     

Voluntary Control of Pulse Transmission Time to the Ear

Two experiments involving voluntary control of pulse transmission time (PTT) to the ear were performed. In Experiment I (within-subject, 3 sessions), 12 male subjects attempting to control PTT with feedback showed significant bidirectional PTT changes in the target directions accompanied by parallel changes in pre-ejection period (PEP). There was no evidence of concomitant changes in respiration rate or general somatic activity. PTT control deteriorated across sessions. In Experiment II (between-subjects, 3 sessions), 10 male subjects attempting to decrease PTT with feedback produced significant PTT decreases accompanied by PEP decreases. There was marginal evidence of increases in respiration rate but no changes in general somatic activity in this condition. Five subjects attempting to increase PTT with feedback and 5 subjects attempting bidirectional PTT control without feedback showed no significant changes in PTT or PEP. The results from these experiments indicate that subjects demonstrate a modest degree of control over PTT to the ear when provided with feedback. This control of PTT is accompanied by parallel changes in PEP but is relatively free of somatic and respiratory concomitance.     

The Cardiac and Vascular Components of Pulse Transmission Time: A Computer Analysis of Systolic Time Intervals

Systolic time interval methodology was used to explore the relative contributions of intracardiac and vascular delays to modifications in pulse transmission time elicited by a series of behavioural and physical challenges. The following variables were recorded on every cardiac cycle: interbeat interval (IBI), the interval between Q and R wave of the EKG, Q wave to pulse arrival (QPT) at the ear and wrist, left ventricular ejection time, and cardiac pre-ejection period (PEP). The true arterial pulse transit time (PTT), inversely related to pulse wave velocity, was calculated by subtracting PEP from QPT. Modifications of QPT were generally associated with PEP rather than PTT responses. But QPT to the ear and wrist were not equivalent; PEP showed closer correlations with QPT to the ear, while PTT was correlated more consistently with QPT to the wrist. Similar patterns were observed with monitoring from the Q and R waves of the EKG. Important differences also emerged between individuals in the degree to which QPT reactions were correlated with the cardiac or vascular components. A supplementary analysis of correlations between blood pressure and the components of QPT was carried out through hand-scoring of systolic time intervals. Both PEP and PTT contributed to the correlations of systolic pressure with QPT. The uses of pulse transmission times as indices of pulse wave velocity, or alternatively of PEP and ventricular contractility, are considered.     

New monitoring test for sleep apnea syndrome

We introduce change in pulse transit time (change in PTT: noninvasive intrathoracic pressure monitoring) as a new monitoring test of sleep apnea syndrome, which is being developed for clinical application. In addition, we report the kinetics of cardiogenic oscillation (CGO: noninvasive upper airway obstruction monitoring), which was published in this journal in 2003, and the response of the upper airway in clinical practice (under an endoscope). We also review diaphragmatic movement by abdominal echography (respiration generator monitoring).     

The Effects of Stress on Components of the Respiration Cycle

Some respiratory correlates of affect were examined by a computer partitioning of breath duration mid inspiration, expiration, and postexpiration pause components. Negative affects (primarily anxiety and hostility) were induced by showing stress films. The subjects' affects were assessed by a mood adjective checklist, and respiration by measures of thoracic and abdominal circumference during the viewing of stress and neutral films. No stress effect was observed on total breath time (respiration rate). However, expiration nines were longer and pause limes shorter during the stress than during the neutral 61ms. It is suggested that these changes may be due to increased tension in respiratory muscle groups. It was also found that breath times were longer during the first film viewed by the subjects than during then during subsequent films This pattern was observed when the subjects were cautiously attentive, and is attributed primarily to an increase in inspiration duration.     

Pre-ejection Period: Measuring Beta-adrenergic Influences Upon the Heart

Increasing interest among psychophysiologists in sympathetic (beta-adrenergic) influences upon the heart has created the need for noninvasive techniques for assessing these influences. The validity of pre-ejection period (PEP), a systolic time interval, as a measure of beta-adrenergic influences upon myocardial contractility is evaluated. Details of a procedure for determining PEP using a polygraph and digital computer are presented. This methodology is then applied to an experiment in which the intracardiac (PEP) and arterial subintervals of pulse transmission time (PTT) are measured during biofeedback-assisted control of PTT in order to evaluate the relative contribution of changes in PEP to PTT control.     

Task Difficulty, Heart Rate Reactivity, and Cardiovascular Responses to an Appetitive Reaction Time Task

Cardiovascular responses of 72 young men were assessed during an appetitive reaction time task where winning money incentives was either easy, difficult, or impossible. The impossible condition led to reduced responses (e.g., longer pre-ejection period (PEP) and pulse transit time (PTT) and greater falls in systolic and diastolic pressures) as well as reports of trying less hard than the easy or the difficult condition. Regardless of task difficulty, subjects showing greater heart rate (HR) increases at task onset maintained higher HR levels than low HR reactors throughout the task. Overall, these high HR reactors also showed higher SBP and shorter PEP, PTT and left ventricular ejection time than low HR reactors, although these differences were less pronounced by the end of the task. Based on their responses to various standardized inventories, high and low HR reactors did not differ in behavioral traits such as Type A, suppressed hostility, or active coping as the preferred coping style. However, a subsample of subjects with extreme scores indicating suppressed hostility (N = 12) did show elevated HR and systolic pressure during both relaxation and the appetitive task.     

Pulse Transit Time and Blood Pressure: An Intensive Analysis

Relationships between pulse transit time (PTT) and intra-arterial systolic (SBP), diastolic (DBP), and mean arterial blood pressure (MAP) were examined in 4 subjects under three conditions: rest, paced respiration, and mental arithmetic. PTT was measured from the EKG R-wave to two peripheral pulses (brachial and radial) and from one pulse to the other. Three points on each pulse wave were used (peak, foot, slope) in the measurements, yielding nine different measures of PTT. The nine PTT measures were not consistently intercorrelated. PTTs initiated by the R-wave were moderately correlated with SBP, but not with DBP or MAP. Brachial to radial PTTs were not correlated with any measures of BP. Relationships between PTT and BP also varied from subject to subject. The limited magnitude of the correlations and their inconsistency suggest caution in the simple substitution of PTT for beat-to-beat measures of BP.     

A novel method for extracting respiration rate and relative tidal volume from infrared thermography

In psychophysiological research, measurement of respiration has been dependent on transducers having direct contact with the participant. The current study provides empirical data demonstrating that a noncontact technology, infrared video thermography, can accurately estimate breathing rate and relative tidal volume across a range of breathing patterns. Video tracking algorithms were applied to frame-by-frame thermal images of the face to extract time series of nostril temperature and to generate breath-by-breath measures of respiration rate and relative tidal volume. The thermal indices of respiration were contrasted with criterion measures collected with inductance plethysmography. The strong correlations observed between the technologies demonstrate the potential use of facial video thermography as a noncontact technology to monitor respiration.     

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.     

A study on a non-contacting respiration signal monitoring system using Doppler ultrasound

We proposed non-contacting respiration signal monitoring system for sleep apnea syndrome. Experiments were conducted by emitting 40 kHz ultrasound beam, which is set tone burst mode by 1 ms period to a subject chest. Normal respiration condition and a simulated sleep apnea syndrome condition were measured while subjects were holding breath. To obtain the actual respiration signal from the raw signal, ultrasound attenuation characteristics were considered. The Doppler ultrasound signal was detectable once the received signal obtained by demodulation circuits passed through a low pass filter (LPF). The signal’s ripples were eliminated by moving average method and the signal’s peaks were detected by phase portrait reconstruction method to measure the respiration rate. This paper is the WC2006 special issue paper.     

Unconstrained and non-invasive measurement of heart-beat and respiration periods using a phonocardiographic sensor

Witthe rapid growth in the number of elderly people in the population, interest in health monitoring is increasing. Therefore the development of an unconstrained and non-invasive vital signs measurement system could be important for monitoring health status at home or in hospitals or nursing facilities. A simple system is proposed for measuring heart-beat and respiration periods for home healthcare. This was achieved with a phonocardiographic (PCG) sensor set on a water-mat or air-mat. The PCG sensor was an acceleration sensor that extracted the vibration of the mat caused by heart-beat and respiration. By calculating an autocorelation function of the fully rectifiedsensor output or by local pattern matching between the rectifiecbutput and a reference signal (pre-memorised for each subject), the system measured the average and instantaneous periods of both heart-beat and respiratin. Results showed that these periods were measured to a similar level of accuracy as for the electrocardiogram and thermistor respiration pickup. The comparative accuracies were within the following ranges: average heartbeat 0.19% to 0.67%, instantaneous heartbeat 0.53%to 1.15%, average respiration 0.51% to 2.17% and instantaneous respiration 2.51% to 5.20%.     

Behavioral Control Over Sleeping Respiration in Normals for Ten Consecutive Nights

Behavioral control over sleeping respiration in 5 healthy college students was tested over 10 consecutive nights and 1 additional night 1–2 weeks later. Participants were polygraphically recorded each night and the records scored using standardized criteria. They were informed while awake that tones (.5 s on/off, 4000 Hz) would be presented to them (variable interval schedule, X?=7.5 min) during nighttime sleep and that their task was to terminate them by taking a deep breath. Behavioral control over respiration was maintained over the 10 nights. Latency to respond gradually increased over the first 5 nights and then leveled out for the remaining 5 nights. On the test night, 1–2 weeks following Night 10, latency to respond was similar to Nights 1 and 2. Percentage of time spent in each sleep stage and the pattern of arousals to tones and responses were similar to earlier reports (more stage 1, less stage 3–4; frequent arousals). It was concluded that behavioral control over sleeping respiration can be obtained and maintained in normal college students over at least 10 nights but a limiting factor may be the increase in response latency.     

Vascular and metabolic reserve in Alzheimer's disease

Vascular and metabolic reserve were analyzed in probable Alzheimer's disease (AD) and vascular dementia (VaD). Cerebral blood flow (CBF), cerebral blood volume (CBV), cerebral metabolic rate of oxygen (CMRO(2)), and oxygen extraction fraction (OEF) were measured quantitatively with positron emission tomography (PET). Vascular reactivity (VR) was also calculated by comparing the CBF during 5% CO(2) inhalation with the CBF during normal breathing. Vascular transit time (VTT) that was calculated as a ratio of CBV/CBF and VR reflect vasodilating capacity of the small resistance vessels, whereas OEF designates metabolic (oxygen-extraction) reserve in threatening brain ischemia. Significant increase in OEF was seen in the parieto-temporal cortex and both VTT and VR were preserved in AD patients. By constrast, there was no significant increase in OEF whereas VTT was prolonged and VR was markedly depressed in VaD patients. The increase of OEF and preserved VTT and VR seen in AD patients indicate the possible participation of vascular factors in the pathogenesis of AD perhaps at the capillary level.     

The Covariation of Blood Pressure and Pulse Transit Time in Hypertensive Patients

To examine the relationship between blood pressure (BP) and pulse transit time (PTT) as measured by the time between the ECG R-wave and an associated peripheral pulse, BP was recorded via a radial artery catheter in 3 hvpertensive subjects who underwent a variety of conditions to alter BP. Overall. 70% of the data was usable. Absolute levels of systolic blood pressure (SBP) but not diastolic blood pressure (DBP) were found to correlate appreciably with PTT. There were significant associations between PTT and both SBP and mean BP but not DBP for direction of BP change. With large SBP changes (> 4 mmHg) an increase in the strength of association occurred in 14 of the 21 conditions across subjects. Overall, PTT did not accurately predict actual BP. PTT and SBP covaried more appreciably in these hypertensives than has been reported for normotensives.     

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.     

Detection of autonomic modulation in permanent atrial fibrillation

A new signal processing method for the detection of cyclic variations in atrial fibrillation frequency is presented. The objective was to investigate whether or not respiration, through the autonomic nervous system, modulates the fibrillation frequency in patients with permanent atrial fibrillation. A group of eight patients with permanent atrial fibrillation, atrioventricular block III and a permanent pacemaker were studied during rest, rhythm-controlled respiration, with each breath lasting for 8s (i.e. a breathing frequency of 0.125 Hz), and rhythm-controlled respiration after full vagal blockade by atropine. Using the new method, a spectral peak could be detected, in two of the patients, at the breathing frequency during rhythm-controlled respiration then disappeared after injection of atropine.     

Normalized peripheral transit time to monitor hypertensionin 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.     

呼吸、体温两生理参数检测电路的设计

介绍了一种由8Xc196单片机控制的用于检测人体呼吸节律、体温参数监护仪的设计。系统采用液晶显示器（LCD）作为显示屏,具有实时显示呼吸波及其频率、体温参数以及呼吸频率、体温24h趋势图和自动报警功能。并可通过RS232接口与PC机之间进行数据传输。     

Improved use of the [13C]octanoic acid breath test as intra-individual parameter to study the effect of a prokinetic drug on gastric emptying in preterm infants with oral feeding intolerance

The [13C]octanoic acid breath test was used for the measurement of differences in gastric emptying in preterm infants for the evaluation of pharmacological therapy. In order to perform a good intra-individual comparison of the gastric emptying in preterm infants under non-standardisable test conditions, we adjusted t1/2 for variations in non-recovered label (=label retention) and introduced an "effective half 13CO2 breath excretion time" t1/2eff = t1/2/m expressed as min per percentage of the cumulative dose recovered. In a pilot study, we investigated the action of the gastrointestinal prokinetic drug cisapride on gastric emptying in seven premature infants, of whom four suffered from gastric stasis and three had constipation. The postnatal age and weight at the start of treatment ranged from 15 to 64 days and from 815 to 1635 g, respectively. All infants received the standard formula for premature infants (Nenatal, Nutricia). Cisapride was administered orally 0.2 mg/kg, four times daily. The changes in gastrointestinal motility were studied using the total bowel transit time of carmine red. After 7 days of treatment in all children, the gastric emptying coefficient and the half 13CO2 breath excretion time adjusted for label retention were improved (n=7, the gastric emptying coefficient range before treatment was 1.69-3.34 (mean 2.59 +/- 0.80) and after treatment it was 2.79-3.76 (mean 3.28 +/- 0.30); the half 13CO2 breath excretion time adjusted for label retention range before treatment was 3.0-14.7 min/% dose (mean 7.0 +/- 5.0) and after treatment 2.6-4.0 min/% dose (mean 3.1 +/- 0.6). The total bowel transit time was only slightly improved in two patients (n=7, mean total bowel transit time before: 23.7 h compared to mean total bowel transit time after 7 days of treatment: 35.5 h). Side effects during cisapride treatment were not seen. We conclude that in premature infants cisapride is effective in shortening gastric emptying time and reducing gastric stasis; the therapeutic role in constipation has to be further investigated.