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PubMed1982

Sensitivity of end-systolic pressure-dimension and pressure-volume relations to the inotropic state in humans.

The value for the slope of the left ventricular (LV) end-systolic pressure-dimension and pressure-volume relations has been proposed as a quantitative measure of the LV inotropic state. This measure of LV inotropic state is attractive because it is independent of preload and incorporates afterload. To investigate the sensitivity of the slope of these relations to alterations in contractile state, 10 normal subjects were studied using M-mode echocardiographic, phonocardiographic and indirect carotid pulse recordings during infusion of methoxamine to alter end-systolic pressure and during infusion of dobutamine (5 micrograms/kg/min) to increase LV inotropic state. Heart rate was maintained within a narrow range for each subject. End-systolic volume was calculated from end-systolic echocardiographic dimension by standard methods. End-systolic pressure was estimated from the dicrotic notch pressure determined from a calibrated carotid pulse recording; peak systolic pressure was also measured. Regardless of the method of approximating end-systolic pressure, the positive inotropic intervention caused a leftward shift in the end-systolic pressure-dimension and pressure-volume lines. With the dobutamine infusion, the value for the slope of the end-systolic pressure-dimension relation increased by 25% (range 16-46%, p less than 0.001), while the slope of the end-systolic pressure-volume relation increased by 55% (range 37-85%, p less than 0.001). In all cases, the curves were linear and became steeper with the positive inotropic intervention. In contrast, the value of the slope of the peak systolic pressure-end-systolic dimension relation showed a variable response to the dobutamine infusion (mean change 13%, range -77% to 73%; NS). Although the position of the peak systolic pressure-end-systolic dimension curve is consistently shifted with an alteration in inotropic state, the values of the slope of these curves are not reliable indicators of change in LV contractility. The values for the slope of the line relating end-systolic pressure (estimated by dicrotic notch pressure) to end-systolic dimension or volume, however, are highly sensitive to a change in inotropic state in human subjects.

Adult↗
PubMed1996

Stress-induced laboratory blood pressure in relation to ambulatory blood pressure and left ventricular mass among borderline hypertensive and normotensive individuals.

Our primary aim in the present study was to investigate the association between blood pressure measured in the laboratory and in the ambulatory state in a group of middle-aged borderline hypertensive men and age-matched normotensive control subjects. In addition, we examined the relation between stress-induced blood pressure measurements and left ventricular mass. Blood pressure and heart rate were measured noninvasively during a standardized laboratory stress protocol and four times per hour throughout 24 hours. Borderline hypertensive subjects had significantly higher systolic and diastolic pressures than normotensive subjects during both the daytime (systolic pressure, 141.1 +/- 9.7 versus 130.9 +/- 8.6 mm Hg; diastolic pressure, 88.8 +/- 7.0 versus 79.4 +/- 6.2 mm Hg, P < .001) and nighttime (systolic pressure, 114.0 +/- 9.9 versus 107.1 +/- 8.3 mm Hg; diastolic pressure, 71.5 +/- 7.5 versus 64.6 +/- 7.2 mm Hg, P < .001). The borderline hypertensive group also displayed increased systolic pressure reactivity in the laboratory compared with the normotensive group. The groups did not differ significantly in left ventricular mass (index). In both borderline hypertensive and normotensive individuals, blood pressure levels during stress testing were closely related to ambulatory blood pressure levels (r = .51 to .82). Furthermore, stress-induced blood pressure levels were significantly correlated to left ventricular mass in borderline hypertensive (r = .33 to .40) but not normotensive subjects. Since stress-induced blood pressure levels were significantly associated with both ambulatory blood pressure levels and left ventricular mass in borderline hypertensive subjects, the addition of standardized stress testing to casual blood pressure measurements may improve risk estimation.

Adult↗
PubMedDate not supplied

Blood pressure changes during adolescence and subsequent adult blood pressure level.

Serial data were analyzed for blood pressure recorded between the ages of 9 to 18 years for 278 children and for a subset of this group whose blood pressure was measured at the age of 30 +/- 5.0 years (n = 93). Blood pressures were measured by auscultation over the antecubital fossa with the participant seated. Systolic blood pressure was recorded when the first sound was heard, and diastolic blood pressure was recorded when all sounds disappeared (fifth phase). A linear regression model was fitted to the data for each individual, and adjustments were made for regression toward the mean using maximum likelihood procedures. There were no significant correlations between the estimated initial values of blood pressure and the rate of change from 9 to 18 years of age. The associations between the levels of blood pressure at 9 years of age and at 30 years of age were significant for systolic blood pressure only in male subjects and were not significant for diastolic blood pressure in either sex. The correlations between the rate of blood pressure change from 9 to 18 years of age and blood pressure levels at 30 years of age were nonsignificant. When the initial values and the rate of change in blood pressure from 9 to 18 years of age were taken into account simultaneously, they accounted for approximately 20% of the variation in systolic blood pressure levels at 30 years of age. This finding indicates that children with higher blood pressure levels at about 9 years of age and with rapid increases in blood pressure during pubescence may have an increased risk of becoming hypertensive.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1987

Characterization of capacitance-free pressure-flow relations during single diastoles in dogs using an RC model with pressure-dependent parameters.

Although previous studies have proposed a variety of models to characterize diastolic pressure-flow relations, the models' ability to predict capacitance-free pressure-flow relations from dynamic information in individual studies has not been determined. This study tested the ability of a lumped RC model with pressure-dependent parameters to predict diastolic capacitance-free flow during maximum vasodilation in anesthetized dogs. Model parameters were characterized by perturbing the circumflex coronary artery with a ramp pressure waveform that caused coronary artery pressure to decline at rates varying from 30-150 mm Hg/sec. Capacitance-free relations constructed from declining and rising ramp pressure-flow data corresponded with capacitance-free pressure-flow points constructed during constant-pressure coronary artery perfusion (which are model-independent). The model parameters derived from analysis of the ramp data indicate that conductance of the coronary bed varies directly with coronary pressure and is independent of the rate of coronary pressure decay. Values of coronary capacitance vary inversely with coronary artery pressure and with the magnitude of dPLC/dt. Thus, a simple, lumped diastolic model with pressure-dependent parameters can predict capacitance-free pressure-flow behavior from dynamic pressure-flow data and characterize model parameters over a wide range of coronary pressure.

Adenosine↗
PubMed2006

Measuring sub-bandage pressure: comparing the use of pressure monitors and pulse oximeters.

OBJECTIVE: To test the use of low-cost sub-bandage pressure monitors and pulse oximeters as part of a quality-control measure for graduated compression bandaging in leg ulcer clinics. METHOD: Twenty-five healthy volunteers (mean age 40 years) providing 50 limbs were bandaged with a four-layer compression bandaging system. The ankle systolic pressure (ASP) was measured using a pulse oximeter (Nellcor NBP-40) before applying the graduated compression bandages. Interface pressure was measured by placing pressure sensors on the skin at three points (2cm above the medial malleolus; the widest part of the calf; and a point midway between them) in the supine and standing positions. The ASP was measured again with the pulse oximeter after the bandage had been applied, and the effect of the bandage on the ASP was recorded. The actual pressure created by the bandage was compared with the required pressure profile. RESULTS: Interface pressures varied with change of position and movement. With the operator blinded to the pressure monitors while applying the bandages, the target pressure of 35-40mmHg at the ankle was achieved in only 36% of limbs ([mean +/- 95% confidence interval]; 32.3 +/- 1.6mmHg [supine]; 38.4 +/- 2.4mmHg [standing position]). With the help of the pressure monitors, the target pressure was achieved in 78% of the limbs. There was no correlation between the pressure monitors and pulse oximeter pressures, demonstrating that the pulse oximeter is not a useful tool for measuring sub-bandage pressures. CONCLUSION: The results suggest a tool (interface pressure monitors) that is easy to operate should be available as part of quality assurance for treatment, training of care providers and education.

Adult↗
PubMed2006

Aneurysm sac pressure monitoring: effect of pulsatile motion of the pressure sensor on the interpretation of measurements.

PURPOSE: To determine the effect of pulsatile motion of graft-attached pressure sensors on the accuracy of aneurysm sac pressure measurement. METHODS: Pressure inside a pressure box was measured with a sensor attached to a stent-graft (Sensorgraft) facing a sensor in fixed position (Sensorbox). Maximum inter-sensor variation of Sensorgraft and Sensorbox was determined in static experiments. Experiments with pulsatile circulation were performed with a compliant and a noncompliant stent-graft at 120/80 mmHg and 160/95 mmHg. Pressure measurements in the box were repeated after the box pressure was increased from 0 to 120 mmHg. Sensorgraft motion was measured by ultrasound. Measurements with Sensorgraft were compared to those with Sensorbox using Pearson correlation coefficients to determine the concordance between the sensors. RESULTS: The maximum inter-sensor variation was 4 mmHg. Increased box pressure induced progressive pulsatile graft and sensor motion during all experiments. During the experiments with the compliant graft at systemic pressures of 120/80 and 160/95 mmHg, the maximum inter-sensor variation was exceeded at box pressures of 65 and 75 mmHg, respectively. The sensor motion at these box pressures was 214+/-2.70 microm and 210+/-0.93 microm, respectively. Measurements of Sensorgraft were higher than Sensorbox, up to 13 mmHg at a box pressure of 120 mmHg. The Pearson correlation coefficients during these experiments were 0.99 and 1.00 (p < 0.001), respectively. In the experiments with the noncompliant graft, the maximum inter-sensor variation was not exceeded, and sensor motion was only 7 +/- 0.46 microm and 26 +/- 1.48 microm, respectively. The Pearson correlation coefficient during these experiments was 1.00 (p < 0.001). CONCLUSION: Pulsatile sensor motion can influence the accuracy of pressure measurement. More compliant grafts are more susceptible to this phenomenon. Despite false high pressure measurements, stent-graft-attached pressure sensors seem appropriate to follow pressure trends in the aneurysm sac.

Analysis of Variance↗
PubMed2001

Dynamics of inner ear pressure change caused by intracranial pressure manipulation in the guinea pig.

Previous studies have shown that pressure changes in the cerebrospinal fluid compartment are transmitted to the inner ear. The main route for pressure transfer is the cochlear aqueduct. about which little is known with regard to its dynamic properties. In the present study, sudden intracranial pressure changes (square waves and short pulses) were created in guinea pigs by means of an electronically controlled infusion system. Simultaneously with pressure manipulation, hydrostatic pressure was monitored in both the peridural space and the perilymphatic compartment of the inner ear. The onset of an inner ear pressure change following manipulation of intracranial pressure was immediate. Inner ear pressure increased or decreased without a measurable time lag, and equalized within a few seconds. During square wave intracranial pressure manipulation, inner ear pressure equalized somewhat more slowly after pressure increase than after pressure decrease. To a first approximation, the pressure equalization curves for the inner ear could be fitted with a single exponential function, rising or falling with a time constant in the range 1-3 s, and the system can be described as a low-pass filter composed of a constant compliance and a constant flow resistance. Detailed analysis, however, showed small deviations from a purely exponential recovery process. With a more complicated (non-linear) model, almost perfect fits to the inner ear pressure equalization curves could be obtained. This non-linearity may be a consequence of the dependence of the compliance and, or flow resistance on pressure.

Animals↗
PubMed1985

Cardiovascular alterations in severe pregnancy-induced hypertension: relationship of central venous pressure to pulmonary capillary wedge pressure.

The relationship between central venous pressure and pulmonary capillary wedge pressure was studied in 18 patients with severe pregnancy-induced hypertension. Although statistically a linear relationship for the group as a whole could be identified, analysis on a case-by-case basis revealed different results. In 10 patients, a linear correlation between central venous pressure and pulmonary capillary wedge pressure was observed. However, accurate prediction of pulmonary capillary wedge pressure from central venous pressure was not possible even in this group because of large interindividual variations. In seven patients no correlation between central venous pressure and pulmonary capillary wedge pressure could be identified. In the last patient a curvilinear relationship existed between central venous pressure and pulmonary capillary wedge pressure. Additionally, in five cases of pulmonary edema, a negative gradient of colloid osmotic pressure to pulmonary capillary wedge pressure gradient was observed. Our data suggest that central venous pressure is not a clinically reliable predictor of pulmonary capillary wedge pressure.

Central Venous Pressure↗
PubMed1993

Intraocular pressure during mechanical ventilation with different levels of positive end-expiratory pressure.

OBJECTIVE: To determine the effect of positive end-expiratory pressure (PEEP) on intraocular pressure. DESIGN: Prospective, controlled, longitudinal, dual center study. In one group, patients served as their own control. In the second group, isolated determinations of intraocular pressure were made in mechanically ventilated patients receiving PEEP. SETTING: Adult intensive care units of two university hospitals. PATIENTS: Intraocular pressures were measured serially in eight patients during the recovery phase of different clinical conditions and in 22 patients receiving mechanical ventilation with PEEP > or = 10 cm H2O for > 24 hrs. INTERVENTIONS: Group A) In eight patients, a PEEP dose-response curve was established (PEEP 0, 5, 10, 15, and 0 cm H2O every 15 mins). Intraocular pressures were measured at the end of each period. Group B) In 22 patients, measurement of intraocular pressures were done while the patients received mechanical ventilation with PEEP > or = 10 cm H2O for at least > 24 hrs. MEASUREMENTS AND MAIN RESULTS: In both groups, there was a positive correlation between the PEEP level and the central venous pressure (p < .05 in group A, and p < .03 in group B). No relationships between intraocular pressure and PEEP or central venous pressure were observed. However, there was a correlation between intraocular pressure and length of PEEP therapy (p < .03). We found ocular hypertension in only one patient (right eye intraocular pressure = 26 mm Hg; left eye intraocular pressure = 24 mm Hg). CONCLUSIONS: Short-term therapy with PEEP of < or = 15 cm H2O does not present a clinically important significant risk for intraocular pressure increase in a population with normal basal ocular tonometry. During prolonged mechanical ventilation with PEEP, increments in intraocular pressure may occur, but these increments appear to not be of a clinically relevant magnitude.

Adult↗
PubMed2006

Intrathoracic pressure regulation for intracranial pressure management in normovolemic and hypovolemic pigs.

OBJECTIVE: To evaluate the potential to use subatmospheric intrathoracic pressure to regulate intracranial pressure (ICP) in normovolemic and hypovolemic animals, we tested the hypothesis that mechanical devices designed to reduce intrathoracic pressure will decrease ICP in a dose-related manner. An inspiratory impedance threshold device was used in spontaneously breathing animals and an intrathoracic pressure regulator was attached to a positive pressure ventilator and used in apneic animals: both devices lower intrathoracic pressure. DESIGN: Prospective, randomized animal study. SETTING: Animal laboratory facilities. SUBJECTS: A total of 36 female farm pigs in four different protocols (n = 12, 6, 12, and 6, respectively). INTERVENTIONS, MEASUREMENTS, AND MAIN RESULTS: In all protocols, endotracheal, right atrial, central aortic, and ICP were measured continuously. In protocol 1, spontaneously breathing animals were randomized to breath for 15 mins through an impedance threshold device with a cracking pressure of -10 or -15 mm Hg. In protocol 2, after untreated ventricular fibrillation for 4 mins and successful defibrillation to a normal rhythm, spontaneously breathing pigs were used to evaluate the effect of two different impedance threshold device cracking pressures (-10 and -15 mm Hg) on increased ICP. In protocol 3, the acute effects of an intrathoracic pressure regulator on ICP were evaluated in combination with a positive pressure mechanical ventilator in apneic hypovolemic hypotensive pigs after 35% or 50% blood loss. In protocol 4, after 40% blood loss, an intrathoracic pressure regulator was applied for 120 mins and ICP was recorded to determine whether the intrathoracic pressure regulator effects were sustained over time. Inspiratory impedance successfully decreased ICP in spontaneously breathing pigs in a dose-dependent manner and decreased elevated ICP immediately after cardiac arrest and successful resuscitation. The same effect was seen in apneic animals with the use of the intrathoracic pressure regulator. The effect was more pronounced in hypovolemia, and it was sustained for >/=2 hrs. CONCLUSIONS: Reduction of intrathoracic pressure to subatmospheric levels resulted in an instantaneous and sustained reduction in ICP in spontaneously breathing and apneic animals. The effect was most pronounced in the hypovolemic animals.

Animals↗
PubMed1994

Estimation of pulmonary artery pressure from pulmonary vein wedge pressure.

Correlations between pulmonary artery and pulmonary vein wedge pressures were investigated in 13 patients with atrial septal defect and 1 patient with Tetralogy of Fallot. Pulmonary vein wedge pressure wave form resembled that of pulmonary artery pressure, and the former lagged behind the latter by 70 to 110 msec (mean 88 +/- 14) as observed by the fluid-filled catheter system. Diastolic pulmonary artery and diastolic pulmonary vein wedge pressures were nearly identical. Although systolic and mean pulmonary artery pressures correlated well with respective pulmonary vein wedge pressures, there were discrepancies when systolic and mean pulmonary artery pressure exceeded 35 and 20 mm Hg, respectively. However, systolic and mean pulmonary artery pressures could be estimated by adding the difference between the diastolic pulmonary vein wedge pressure and the mean left atrial pressure to corresponding systolic or mean pulmonary artery pressure. In conclusion, pulmonary artery pressures can be estimated by measuring pulmonary vein wedge pressures and the mean left atrial pressure.

Adult↗
PubMed1988

Accuracy of left atrial and pulmonary artery wedge pressure in pure mitral regurgitation in predicting left ventricular end-diastolic pressure.

In most clinical conditions pulmonary artery (PA) wedge pressure accurately reflects left ventricular (LV) end-diastolic pressure. In the presence of mitral regurgitation (MR), large V waves can distort PA wedge pressure and result in incorrect estimation of LV end-diastolic pressure. In 52 patients with MR simultaneous measurement of PA wedge pressure or left atrial pressure and LV end-diastolic pressure was recorded. Twenty-one (40%) patients had large V waves (V wave greater than A wave by greater than 10 mm Hg, group 1), and 31 (60%) patients had small V waves (group 2). Group 1 had significantly higher V waves than group 2 (46 +/- 3 vs 21 +/- 2 mm Hg, p less than 0.001). The LV end-diastolic pressure was similar in both groups (21 +/- 2 vs 19 +/- 2 mm Hg, difference not significant). The mean PA wedge or left atrial pressure in group 1 (26 +/- 2 mm Hg) overestimated LV end-diastolic pressure (21 +/- 2 mm Hg) by 30% (p less than 0.01), but the trough of the X descent (20 +/- 2 mm Hg) was similar to the LV end-diastolic pressure. In group 2 patients with small V waves the mean PA wedge pressure was not significantly different from the LV end-diastolic pressure (16 +/- 2 vs 19 +/- 2 mm Hg, p = 0.06), but the trough of the X descent (13 +/- 2 mm Hg) underestimated LV end-diastolic pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Use of pulmonary capillary wedge pressure to assess severity of mitral stenosis: is true left atrial pressure needed in this condition?

There is disagreement concerning the use of the pulmonary capillary wedge pressure (in place of left atrial pressure) in assessing the presence and severity of mitral valve disease. This study was done to assess the accuracy and reliability of an oximetrically confirmed pulmonary capillary wedge pressure in measuring the transvalvular pressure gradient and valve area in patients with mitral stenosis. In 10 patients with mitral stenosis (1 man and 9 women; mean age +/- SD 47 +/- 7 years), pulmonary capillary wedge pressure was measured through an 8F Goodale-Lubin catheter with its wedge position confirmed by oximetry (oxygen saturation greater than or equal to 95%). In addition, a transseptal left atrial pressure was measured through a Brockenbrough catheter and left ventricular pressure was measured through a pigtail catheter. The mean and phasic left atrial and pulmonary capillary wedge pressures were similar (mean left atrial pressure 18 +/- 6 mm Hg; mean pulmonary capillary wedge pressure 18 +/- 8 mm Hg; p = NS). When the pulmonary capillary wedge pressure was used without adjustment for time delay, the transvalvular pressure gradient (9.8 +/- 3.3 mm Hg) and valve area (1.5 +/- 0.5 cm2) were significantly different (p less than 0.05) from the values obtained with use of left atrial pressure (7.2 +/- 2.9 mm Hg and 1.7 +/- 0.6 cm2, respectively). In contrast, when the pulmonary capillary wedge pressure was adjusted for the time delay through the pulmonary vasculature, the difference in gradients averaged only 1.7 mm Hg and the mitral valve areas were similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial Function↗
PubMed2002

Bacterial inactivation by high-pressure homogenisation and high hydrostatic pressure.

The resistance of five gram-positive bacteria, Enterococcus faecalis, Staphylococcus aureus, Lactobacillus plantarum, Listeria innocua and Leuconostoc dextranicum, and six gram-negative bacteria, Salmonella enterica serovar typhimurium, Shigella flexneri, Yersinia enterocolitica, Pseudomonas fluorescens and two strains of Escherichia coli, to high-pressure homogenisation (100-300 MPa) and to high hydrostatic pressure (200-400 MPa) was compared in this study. Within the group of gram-positive bacteria and within the group of gram-negative bacteria, large differences were observed in resistance to high hydrostatic pressure, but not to high-pressure homogenisation. All gram-positive bacteria were more resistant than any of the gram-negative bacteria to high-pressure homogenisation, while in relative to high hydrostatic pressure resistance both groups overlapped. Within the group of gram-negative bacteria, there also existed another order in resistance to high-pressure homogenisation than to high hydrostatic pressure. Further it appears that the mutant E. coli LMM1010, which is resistant to high hydrostatic pressure is not more resistant to high-pressure homogenisation than its parental strain MG1655. The preceding observations indicate a different response of the test bacteria to high-pressure homogenisation compared to high hydrostatic pressure treatment, which suggests that the underlying inactivation mechanisms for both techniques are different. Further, no sublethal injury could be observed upon high-pressure homogenisation of Y. enterocolitica and S. aureus cell population by using low pH (5.5 7), NaCl (0 6%) or SDS (0-100 mg/l) as selective components in the plating medium. Finally, it was observed that successive rounds of high-pressure homogenisation have an additive effect on viability reduction of Y. enterocolitica and S. aureus.

Colony Count, Microbial↗
PubMed2001

The relationship between pressure ulcer incidence and buttock-seat cushion interface pressure in at-risk elderly wheelchair users.

OBJECTIVE: To investigate the relation between pressure ulcer incidence and buttock-wheelchair seat cushion interface pressure measurements. DESIGN: Secondary analysis of data from a randomized clinical trial. SETTING: Skilled nursing facility. PATIENTS: Thirty-two elderly patients (age, > or = 65 yr), with Braden score < or = 18 and Braden mobility and activity subscale score < or = 5, who used wheelchairs > or = 6 hr/d, were free of existing sitting-induced pressure ulcers, and weighed < or = 250 lb. INTERVENTIONS: Generic foam seat cushion or pressure-reducing seat cushion. MAIN OUTCOME MEASURES: The incidence of sitting-induced pressure ulcers over a 1- to 12-month period was compared with pressure measured between patients' buttocks and wheelchair seat cushions. A flexible pad with a 15 x 15 pressure sensor array was used to measure interface pressure. RESULTS: Interface pressure measured on wheelchair seat cushions was higher (p < or = .01 for both peak pressure and average of highest 4 pressures) for patients who developed sitting-acquired pressure ulcers compared with those patients who did not. CONCLUSIONS: Results indicated that higher interface pressure measurements are associated with a higher incidence of sitting-acquired pressure ulcers for high-risk elderly people who use wheelchairs.

Aged↗
PubMed2002

Dynamic cerebral autoregulatory response to blood pressure rise measured by near-infrared spectroscopy and intracranial pressure.

OBJECTIVES: Noninvasive near-infrared spectroscopy (NIRS) continuously monitors changes in cerebral hemoglobin saturation (Hb(Diff) ) and content (Hb(Total)). It may allow visualization of the dynamic cerebral autoregulatory response to rapid blood pressure increases without relevant contamination of the NIRS signal from extracerebral hemoglobin. DESIGN: Prospective cohort study. SETTINGS: Multidisciplinary pediatric intensive care unit. PATIENTS: Six consecutive children in coma due to severe encephalopathy (head trauma, five patients; mumps encephalitis, one patient) requiring artificial ventilation, invasive arterial blood, and intracranial pressure monitoring. INTERVENTIONS: Frontotemporal recording of Hb(Diff) and Hb(Total) while rapidly elevating blood pressure by bolus injection of phenylephrine. MEASUREMENTS AND RESULTS: During an increase of blood pressure of 13 +/- 1 mm Hg with a "rise time" of 16 +/- 1 secs (mean of a total of 31 injections +/- sem), a significant linear correlation was found between Hb(Diff) and intracranial pressure signals (mean coefficient, 0.46 +/- 0.04) but not between Hb(Total) and intracranial pressure. Three response patterns were observed. First, Hb(Diff) and intracranial pressure reduction, corresponding with vasoconstriction and normal dynamic autoregulation (n = 3); second, Hb(Diff) and intracranial pressure increase, corresponding with persistent vasodilation and abolished autoregulation (n = 11); and third, transient Hb(Diff) and intracranial pressure increase followed by a decrease at peak blood pressure elevation, called impaired autoregulation (n = 15). In one patient with fatal brain swelling, phenylephrine testing showed no effect on NIRS signals (n = 2). Furthermore, there were significant correlations between 31 pooled interindividual pairs of Hb(Diff) changes with intracranial pressure changes (values at baseline averaged over 60 secs subtracted from values at peak blood pressure elevation averaged over 5 secs), with a correlation coefficient of .82 (p <.001). CONCLUSIONS: NIRS represents a new and promising technique for bedside determination of dynamic cerebral autoregulation during acutely induced blood pressure rise. The significant correlations found between NIRS signals and intracranial pressure excluded relevant extracerebral contamination of the NIRS signals. In our patients with severe encephalopathy, dynamic autoregulation was in most instances not fully preserved.

Adolescent↗
PubMed2000

Is nurse-measured blood pressure a valid substitute for ambulatory blood pressure monitoring?

BACKGROUND: Because ambulatory blood pressure monitoring (ABPM) is not available everywhere, the objective of the study was to determine whether nurse-measured blood pressure could be an acceptable substitute to ABPM. METHODS: We analyzed the data of 2385 consecutive patients referred to our hypertension clinic for the performance of ABPM. Before ambulatory monitoring was performed, a nurse-measured BP was obtained three times using a Y-tube connecting the sphygmomanometer and the recorder. We compared the mean value of the three nurse-measured blood pressures with that of the 12h daytime ambulatory monitoring, considered as the reference. RESULTS: The difference between the nurse-measured and the ambulatory blood pressure was small but statistically significant, indicating that nurse-measured blood pressure tends to overestimate both diastolic and systolic blood pressure. The difference between the nurse blood pressure and ABPM was greater among treated hypertensive patients than untreated patients. To diagnose hypertension, defined as a blood pressure of over 140/90mmHg by ABPM, the positive predictive value of the nurse blood pressure was 0.81 and the negative predictive value 0.63. However, these predictive values could be improved with less stringent cut-off values of blood pressure. Thus, for a diastolic blood pressure above 100mmHg, the positive predictive value of nurse blood pressure was 0.55 and the negative predictive value 0.91. These figures were relatively similar for previously treated and untreated patients. CONCLUSION: Nurse blood pressure is less accurate than ABPM in diagnosing hypertension, defined as a blood pressure of over 140/90mmHg. It could, however, be an acceptable substitute, especially to exclude people who do not need to be treated, in situations where lower resources require a less rigorous definition of hypertension.

Adult↗
PubMedDate not supplied

Determination of ambulatory blood pressure control in treated patients with controlled office blood pressures.

Office blood pressure measurement is the standard for assessing blood pressure control. Many patients, however, take their antihypertensive medication in the morning, so they are likely to have their office blood pressure measured during the maximal antihypertensive effect. It is therefore unknown whether patients deemed by office blood pressure to be controlled do in fact have 24h blood pressure control. The objectives of this study were to determine blood pressure control, including blood pressure control while the patients were awake and during the first 6 hours after awakening, by ambulatory blood pressure monitoring (ABPM) in treated hypertensive patients deemed by office blood pressure measurements to be controlled. A total of 103 patients on a stable antihypertensive regimen and deemed to be controlled in terms of office blood pressure values (mean office blood pressure <140/90mmHg) were enrolled. Patients were stratified by cardiovascular risk status and the number of antihypertensive medications that they were taking. Seventy-eight out of 103 participants successfully completed ABPM. The mean ambulatory blood pressure was greater than 135/85mmHg and 140/90mmHg while awake for 37% (95% confidence interval [CI] 26-48%) and 23% (95% CI 14-32%) of all patients respectively. Forty-eight per cent (95% CI 33-63%) of patients taking monotherapy versus 25% (95% CI 11-39%) of patients on multiple antihypertensive medications were uncontrolled (P=0.039) using 135/85mmHg as the reference value. Thirty-one per cent (95% CI, 17-44%) of patients on monotherapy versus 14% (95% CI 3-25%) of patients on multiple antihypertensive medication were uncontrolled (P=0.064) using 140/90mmHg instead. These results demonstrate that a high number of patients deemed by office blood pressure to be under control do not have adequate blood pressure control based on ABPM.

Adult↗