Physiological measurement
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Physiological measurement · Aug 2003
Comparative StudyDo the Finapres and Colin radial artery tonometer measure the same blood pressure changes following deflation of thigh cuffs?
The objective of this work was to determine if systematic differences exist between blood pressure time series measured by two non-invasive techniques. Cerebral blood flow autoregulation is often measured while a change in blood pressure is induced by deflation of thigh cuffs. To interpret the result a continuous measurement of arterial blood pressure is required. ⋯ Peripheral vasoaction may be distorting the measurement of blood pressure by the Finapres. This would account for the difference that exists between the techniques. Comparison with a direct arterial line would confirm which non-invasive measurement is more accurate.
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Physiological measurement · Aug 2003
Impact of bradycardia on cerebral oxygenation and cerebral blood volume during apnoea in preterm infants.
Apnoea in prematurity is a common problem in neonatology; and it is the impaired oxygen delivery during apnoea, which can harm the brain. The aim of this study was to evaluate the effect of bradycardia (below 80 beats min(-1)) on 'cerebral haemoglobin oxygenation index' (cHbD) and cerebral blood volume (CBV) during apnoea in stable preterm infants measured by means of near infrared spectroscopy. Twenty-six episodes of mixed and central apnoea with bradycardia (bradycardia group) in 20 preterm infants were compared to 26 episodes of mixed and central apnoea without bradycardia (non-bradycardia group) in 19 preterm infants. cHbD decreased significantly more in the bradycardia group (-11.33 micromol 1(-1) after 30 s) than in the non-bradycardia group (-6.36 micromol 1(-1) after 30 s) (p < 0.05). ⋯ Peripheral oxygen saturation (SaO2) decreased similarly in both groups. The aggravation of decrease of cHbD and the decrease of CBV during bradycardia in association with apnoea could be explained by decrease in cerebral blood flow, which caused decrease in cerebral oxygen delivery. This decrease of oxygen delivery during bradycardia might worsen long-term neurodevelopmental outcome in preterm infants with apnoea.
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Physiological measurement · May 2003
Age-related changes in the characteristics of the photoplethysmographic pulse shape at various body sites.
It is accepted that older subjects have increasing arterial stiffness resulting in changes in the propagation of the pulse to the periphery, and thereby influencing the peripheral pulse timing and shape characteristics. However, this age association with pulse shape is less clear in younger subjects and for different peripheral measurement sites. The aim of this study was to determine the association between age and changes in pulse shape characteristics at the ears, fingers and toes. ⋯ Subtle, gradual and significant changes in the pulse shape were found at all sites with overall elongation of the systolic rising edge (p < 0.05) and damping of the dicrotic notch (p < 0.05) with age. The overall age-related changes in multi-site PPG pulse shape characteristics at the ear, finger and toe sites have been demonstrated and quantified. Age-matched normal ranges must be considered when evaluating pulses from patients with possible vascular disease.
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Physiological measurement · Feb 2003
Transfer function analysis for clinical evaluation of dynamic cerebral autoregulation--a comparison between spontaneous and respiratory-induced oscillations.
Oscillations of arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV) can be used for non-invasive assessment of cerebral autoregulation using transfer function analysis. Either spontaneous oscillations (SPO) around 0.1 Hz or respiratory induced oscillations during deep breathing (DB) at a rate of 6/min have been used so far. We investigated 168 patients with severe carotid stenosis or occlusion to evaluate transfer function analysis and compare the SPO and DB approaches. ⋯ Analysing reproducibility in 16 patients, only for P(LF, HF) of DB was a highly significant correlation found (Spearman's r up to 0.78). For G(LF, HF) correlations were significant for both SPO and DB with slightly higher r coefficients for SPO. In conclusion, the present study showed that (1) transfer functions P and G represent different information for characterization of dynamic cerebral autoregulation in the frequency domain. (2) Inter-method agreement between DB and SPO is poor for P and moderate for G values. (3) P extracted from DB has a higher reproducibility. (4) The extraction of P and G from the SPO phase spectra is critical and future work on standardizing this process is needed. (5) At present, the DB protocol might be slightly advantageous as a routine diagnostic tool.
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Physiological measurement · Feb 2003
Graphical display of variability and inter-relationships of pressure signals in children with traumatic brain injury.
A prospective observational study was undertaken to examine time series ICU data of pressure variables (mean arterial pressure (MAP), intracranial pressure (ICP) and cerebral perfusion pressure (CPP)) and relate their variability (SD) to outcome, together with simple graphical displays which could be useful at the ICU bedspace. Forty-three children (aged < 1-15 years) were admitted to the intensive care unit for Regional Neurosurgical Service, Edinburgh, following traumatic brain injury (TBI). The standard deviations from 221,291 validated pressure data measurements (representing three variables) were calculated for the duration of ICP monitoring (and in 48 h epochs from the time of injury). ⋯ Only one patient with type I pattern died in this series. While variability of ICP during the first 48 h post-injury is predictive of the outcome, the pattern behaviour of three pressure signals gives useful outcome prediction information throughout monitoring. These displays may help interpret some of the plethora of data produced at the bedside.