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At least 775 records · Page 43Linked to original sources

PubMed2005

Impact of sitting time on seat-interface pressure and on pressure mapping with multiple sclerosis patients.

OBJECTIVE: To examine changes in seat-interface pressure with multiple sclerosis (MS) patients. DESIGN: Case series. SETTING: Multiple Sclerosis Society's Resource Centre and community. PARTICIPANTS: Convenience sample of 15 MS wheelchair users and 12 MS non-wheelchair users. INTERVENTION: Interface pressure was measured for 8 minutes using the Force Sensing Array pressure mapping system. MAIN OUTCOME MEASURES: Number of activated sensors, standard deviation, average and maximum pressures. RESULTS: With the wheelchair users, significant decreases were found in the standard deviation and average and maximum pressures during 0 to 2 minutes of sitting ( P <.01). Average pressure was the only parameter to show a significant decrease in the non-wheelchair users ( P <.01) during 0 to 2 minutes. Significant increases were found in all output parameters during 2 to 4 minutes with both groups ( P <.05). Non-wheelchair users showed no significant changes in the output parameters after 4 minutes, but wheelchair users showed significant continued increases in the output parameters from 4 to 8 minutes ( P <.05). CONCLUSIONS: Because no significant changes in interface pressure occurred after 4 minutes of sitting with the non-wheelchair users, 4 minutes may be a reasonable sitting time before interface pressure is recorded with this group. Significant changes in interface pressure continued up to 8 minutes with the wheelchair users, therefore 8 minutes or beyond may be a reasonable sitting time before recording with this group.

Adult↗

PubMed1997

The effects of left ventricular stretch versus cavity pressure on intramyocardial pressure.

OBJECTIVE: Since muscles, vessels and interstitial spaces are in close physical proximity in the heart wall, interstitial (i.e., intramyocardial) pressure (IMP) should be affected by the stresses of the vessels and/or the muscular tissue surrounding the interstitial spaces. Thus, we tested the hypothesis that increasing the stresses (or stiffness) of the surrounding tissues by muscle contraction or stretching--produced externally by stretching the LV cavity or internally by increasing coronary perfusion pressure--has a greater effect than LV cavity pressure per se on IMP. METHODS: In isolated rabbit hearts we measured IMP with small (< 10 microns diam) glass micropipettes while stretching the vessels (by changing coronary perfusion pressure) and the wall (by inflating a balloon in the left ventricle) during the passive state as well as during barium contracture. RESULTS: With LV cavity pressure equal to 0 (balloon open to air) or equal to 30 mmHg, a 20 mmHg increase in perfusion pressure increased IMP by 3.6 and 5 mmHg, respectively, in the passive state and by 7.6 and 7.9 mmHg, respectively, in the contracted state. This 30 mmHg increase in LV pressure produced a significant but small (3-5 mmHg) increase in IMP in the passive state but no effect in the contracture state. CONCLUSIONS: These results can be explained by a unifying concept in which stretching of the tissues surrounding the intestinal spaces--produced externally by increasing ventricular cavity size or internally by pressurizing vessels--but not LV cavity pressure per se is the major determinant of IMP.

Animals↗

PubMed1995

The effect of arterial pressure on the ocular pressure-volume relationship in the rabbit.

The purpose of this study was to quantify the effect of mean arterial pressure (MAP) on the ocular pressure-volume relationship. The experiments were performed in pentobarbital anesthetized rabbits instrumented with occluders on the thoracic aorta and inferior vena cava to control MAP which was measured via a cannula in the central ear artery. To vary the ocular volume and measure the intraocular pressure (IOP), two 23 gauge needles were inserted through the pars plana into the vitreous: one needle was connected to a saline-filled syringe and the other needle was connected to a pressure transducer. In one group of animals (n = 5), pressure-volume curves were determined at MAPs of 100, 80, 60, 40 and 20 mmHg and post mortem by cumulative saline injections (2 microliters) every 1-1.5 sec. In a second group (n = 7), pressure-volume curves were obtained at MAPs of 80, 60 and 40 mmHg and post mortem by saline infusion at 0.5 microliter sec-1 until the IOP reached 100 mmHg. The infusion protocol was repeated in a third group (n = 11) where the choroidal flux and the concentration of moving blood cells (CMBC) were measured by a laser Doppler flowmeter as indices of choroidal blood flow and the blood volume, respectively. MAP had three primary effects on the ocular pressure-volume relationship: (1) the baseline IOP varied exponentially with MAP, (2) the steepness of the initial portion of the pressure-volume curves was MAP-dependent and (3) the curves exhibited a 'plateau' as the IOP approached the prevailing MAP at MAPs > or = 40 mmHg. All of the curves in the living eye intersected and became indistinguishable from the post mortem curve when the IOP exceeded the prevailing MAP. The flux and CMBC measurements indicated that the MAP-dependence of the initial portion of the curves was due to failure of choroidal autoregulation and diminished increases in choroidal blood volume at the lower MAPs, and that the plateau portion of the curves was due to expulsion of blood from the eye. It is concluded that MAP has a significant effect on the ocular pressure-volume relationship.

Animals↗

PubMed1995

Primary open-angle glaucoma, intraocular pressure, and systemic blood pressure in the general elderly population. The Rotterdam Study.

PURPOSE: The purpose of this study is to investigate the association of primary open-angle glaucoma (POAG), intraocular pressure (IOP), and systemic blood pressure. METHODS: Subjects participating in the Rotterdam Study (n = 4187, 55 years of age and older) were examined according to standard protocols, including a medical history interview, IOP measurement, perimetry, funduscopy, and blood pressure measurement. Primary open-angle glaucoma was defined by the presence of a glaucomatous visual field defect. Additionally, the distinction was made between high-tension glaucoma, defined as POAG with an IOP of more than 21 mmHg, and normal-tension glaucoma, defined as POAG with an IOP of 21 mmHg or less. The relation between blood pressure and hypertension with IOP, POAG, high-tension glaucoma, and normal-tension glaucoma was studied by means of regression analysis. RESULTS: A systolic blood pressure or diastolic blood pressure that was 10 mmHg higher was associated with an IOP that was, on average, 0.23 mmHg (95% confidence interval [CI], 0.19-0.27) or 0.24 mmHg (95% CI, 0.16-0.32) higher, respectively. The presence of hypertension was associated with a higher mean IOP of 0.66 mmHg (95% CI, 0.39-0.93). A higher systolic blood pressure of 10 mmHg was associated with an odds ratio of 1.22 (95% CI, 1.03-1.46) for high-tension glaucoma and 0.90 (95% CI, 0.72-1.12) for normal-tension glaucoma. Hypertension was associated with an odds ratio of 2.33 (95% CI, 0.99-5.47) for high-tension glaucoma and 0.77 (95% CI, 0.22-2.72) for normal-tension glaucoma. CONCLUSION: Systemic blood pressure and hypertension are associated with IOP and high-tension glaucoma. No association was found between blood pressure or hypertension and normal-tension glaucoma.

Aged↗

PubMed1997

A comparison of 24-h average blood pressures and blood pressure load following exercise.

Although the use of 24-h ambulatory blood pressure monitoring has been recommended in the study of blood pressure and exercise, consistent results have not been found for average 24-h systolic or diastolic blood pressures. Systolic load and diastolic load (the percentage of pressures >140/90 mm Hg during daytime hours and >120/80 mm Hg during sleep) have recently been identified as an important variable, but has had limited use with exercise. The purpose of this study was to compare the average systolic and diastolic pressures to systolic and diastolic loads from 24-h data recorded after a 50-min treadmill walk at 50% VO2max to data from a nonexercise control day. Subjects were 36 normotensive (116.9 +/- 10.7/77.0 +/- 8.9 mm Hg) and 25 hypertensive (141.0 +/- 13.7/96.6 +/- 9.0 mm Hg) adults. No significant differences were found for systolic and diastolic pressures or loads between the control and exercise days for normotensives. Even though no significant changes were found for any of the average systolic and diastolic pressures between the control and exercise days for the hypertensives, significant reductions were found in systolic load for 24-h (-25.7%), day (6 AM to 10 PM, -23.1%), work (6 AM to 5 PM, -22.9%), and leisure (5 PM to 10 PM, -26.7%) periods; and in diastolic load for the work (-22.5%) period. Thus, the measurement of systolic and diastolic load may be more sensitive than average systolic and diastolic blood pressures for the detection of 24-h ambulatory blood pressure changes with exercise in borderline hypertension.

Adult↗

PubMed2002

[Variability of the treatment pressure under continuous positive airway pressure treatment in obstructive sleep apnea syndrome].

BACKGROUND: Selfadjusting CPAP therapy is mostly employed if constant CPAP does not sufficiently suppress respiratory disturbances or is not accepted by the patient. The number of respiratory disturbances and thus the pressure need varies with sleep stages and body position during sleep. However, the analysis of the pressure profile during automatic CPAP therapy indicates a relevant variability of treatment pressure which is independent of the above mentioned criteria. Therefore, we aimed to quantify the pressure variability and its significance in patients with obstructive sleep apnea syndrome (OSAS). METHODS: We analysed the pressure profile during a six-week treatment period with selfadjusting CPAP therapy based on the measurement of the impedance (APAP FOT ). The variability index (VI) was calculated from the deviations of the treatment pressure from the mean pressure. The variability was considered to be low and clinically irrelevant if the VI did not exceed 0.75 as a mean value and in more than 10 % of the nights. PATIENTS: 20 patients (male 19, age 55.5 +/- 10.9 years, BMI 36.6 +/- 26.5 kg/m (2), AHI 36.9 +/- 21.3/h) who were treated with APAP FOT because of intolerance or inefficiency of constant CPAP. RESULTS: The VI was 0.9 +/- 0.7 (range 0.27 +/- 0.05 to 1.95 +/- 0.83). The number of nights with a figure >/= 0.75 reached 17.6 +/- 13.8 (range 0 - 40). In 50 % of the patients the mean VI was lower than 0.75. However, in 7 of these 10 patients the VI exceeded 0.75 in more than 10 % of the nights (4 - 15). Only 3 of 20 patients fulfilled both criteria of pressure stability. The VI showed a significant correlation with P mean (r: 0.66, p < 0.001). CONCLUSIONS: In most patients with difficult-to-treat OSAS a variability of the treatment pressure can be found.

Automation↗

PubMed1988

A method to define reference profiles for ambulatory blood pressure, with application to blood pressure profiles in 158 young subjects.

Ambulatory blood pressures (systolic, SBP, diastolic, DBP) and heart rate were determined over 24 h every 15 min in the day and every 15 min in the night in 72 normal subjects aged 21 +/- 1 SEM with normal casual office pressures (WHO's criteria: office DBP less than or equal to 90 mmHg, office SBP less than or equal to 140 mmHg) and in 86 essential hypertensive subjects aged 21 +/- 1, with borderline office pressure (WHO's criteria: office DBP less than or equal to 95 mmHg, office SBP less than or equal to 160 mmHg). Complete 24-hour profiles (mean +/- SD) were reported. In the average, mean ambulatory DBP in the normal group was about 72.5 mmHg in "day time" (9 a.m.-9 p.m.) and 63.5 mmHg in "night time" (midnight-7 a.m.). Ambulatory SBP in the normal group were about 126 mmHg and 110 mmHg for the same time periods. In the borderline hypertensive group, the figures were 74 mmHg (day-time) and 67 mmHg (night time) for diastolic pressure and 140 mmHg (day time) and 118 mmHg (night time) for systolic pressure. However, when the normal and borderline groups were defined as above on the basis of office pressure, ambulatory blood pressure profiles in the two groups showed a large overlap. A method was proposed to reduce this overlap by partially reallocating the subjects on the basis of ambulatory blood pressure. First, a typical profile was defined for each group and a distance was defined between two arbitrary profiles. Then a subject in the normal (resp. hypertensive) group was reallocated to the hypertensive (normal) group if his profile was closer to the typical profile of the hypertensive (normal) group than the typical profile of his own group. Applied to ambulatory DBP profiles, this method reallocated 49 subjects (over the total of 158), significantly reduced the initial overlap of BP profiles between the two groups, and defined reference profiles for "normal" and "borderline" ambulatory blood pressures.

Adult↗

PubMed1989

Blood pressure, catecholamines, and pancreatic polypeptide in obstructive sleep apnea with and without nasal Continuous Positive Airway Pressure (nCPAP) treatment.

In order to study blood pressure, adrenergic, and cholinergic activity in severe obstructive sleep apnea (OSA), 14 patients with apnea index (AI) greater than 30 apneas/h, mean apnea time index greater than 20 sec were studied before and with nasal Continuous Positive Airway Pressure (nCPAP). Sleep, respiration, arterial blood pressure, arterial plasma catecholamines [norepinephrine (NE) and epinephrine (E)], and plasma pancreatic polypeptide (PP) were measured without and after seven days treatment with nCPAP. Initially in the apnea, arterial blood pressure decreases, and thereafter steadily increases and shows a maximum during the first breath terminating the apnea. With nCPAP the arterial pressure variations disappeared. Awake morning systolic (SBP) and diastolic (DBP) blood pressure decreased the nCPAP treatment. A significant relation between the reduction in AI and the reduction in morning awake SBP and DBP with nCPAP treatment was observed. No significant changes in NE were observed with nCPAP treatment. Epinephrine decreased and PP increased significantly with nasal nCPAP treatment. The systolic and diastolic blood pressure reduction was significantly related to the decrease in E and the increase in PP. No association between sleep stages and plasma NE, E, and plasma-PP was found before treatment. With nCPAP treatment plasma-PP was higher during non-rapid eye movement (NREM) stage 2 to 4 sleep than during rapid eye movement (REM) sleep. Thus, morning awake arterial blood pressure and nocturnal arterial blood pressure decrease with nCPAP treatment in sleep apnea patients. These hemodynamic changes are related to the decrease in AI and sympathetic activity and the increase in parasympathetic activity.

Adult↗

PubMed1991

A study of the effects of delapril, a new angiotensin converting enzyme inhibitor, on the diurnal variation of arterial pressure in patients with essential hypertension using indirect and direct arterial pressure monitoring methods.

In order to investigate the effect of delapril, a new angiotensin converting enzyme inhibitor, on the diurnal variation of arterial pressure in patients with essential hypertension, this study examined 24 h arterial pressure using an indirect or a direct monitoring system. When the effect of twice-a-day administration of delapril at daily doses of 30 to 90 mg was examined using the indirect monitoring system in 12 outpatients, delapril decreased systolic and diastolic arterial pressures significantly only at limited points during the day. However, each of the averaged 24 h daytime and nighttime arterial pressures showed significant reductions. The 24 h intraarterial pressure monitoring demonstrated that delapril decreased systolic and diastolic arterial pressure at most of the measurement points. The arterial pressure reductions during daytime and nighttime were not significantly different, that is, there was no excessive reduction in nighttime arterial pressure. Heart rate and its variability were virtually unaffected by the delapril treatment in either monitoring study. No adverse reactions were observed in the indirect or direct monitoring studies. Thus, it is concluded that twice-a-day administration of delapril at daily doses of 30 to 90 mg brings about a safe and stable antihypertensive effect, without affecting the diurnal variation of arterial pressure.

Administration, Oral↗

PubMed1991

Continuous noninvasive finger blood pressure during controlled hypotension. A comparison with intraarterial pressure.

The Finapres is a noninvasive monitor that continuously displays the arterial waveform, pulse rate, and systolic, mean, and diastolic blood pressure. We determined its bias (mean prediction error) and precision (mean absolute error), relative to directly measured radial arterial blood pressure, in 16 otherwise healthy patients undergoing spinal fusion surgery under hypotensive anesthetic techniques. Data were recorded during three contiguous epochs: 20 min of normotension; 30 min following the initiation of hypotension; 20 min of hypotension. The Finapres demonstrated a systolic, mean, and diastolic bias (+/- standard deviation) of 3.6 +/- 12.3, 5.2 +/- 10.8, and 8.3 +/- 9.4 mmHg, respectively. There were no significant differences in systolic bias among the epochs, whereas mean and diastolic bias were both greater during the hypotensive epoch, compared to the normotensive epoch. In 2 of the 16 patients, systolic and mean arterial pressure bias exceeded 20 mmHg. Finapres precisions of systolic, mean, and diastolic blood pressures were 9.8 +/- 9.0, 8.7 +/- 7.6, and 10.4 +/- 8.2 mmHg, respectively. Precisions among the epochs were not significantly different. When Finapres pressures were "corrected" by subtracting the baseline difference between Finapres and oscillometrically determined mean pressure, bias decreased significantly. The correction process did not improve precision. The Finapres closely tracked changes in blood pressure, even in the presence of a large bias. In most patients, the Finapres is a useful continuous noninvasive blood pressure monitor. Periodic calibration of the Finapres by the difference between Finapres and oscillometrically determined mean arterial pressure is recommended.

Adolescent↗

PubMed2002

Clinical evaluation of a self blood pressure monitor according to the First International Consensus Conference on Self Blood Pressure Measurement.

BACKGROUND: The Calor TensioSense Bras automatic blood pressure monitor has obtained European Union certification, but the clinical validity of this new oscillometric device when handled by lay subjects has yet to be evaluated. DESIGN: The design employed prospective and blinded blood pressure measurements and a validation procedure according to the criteria set out by the First International Consensus Conference on Self Blood Pressure Measurement (1999). METHODS: Thirty-three subjects were recruited, 11 in each of three strata of systolic blood pressure (<130, 130-160 and >160 mmHg). Blood pressure was measured sequentially seven times, alternating observer and lay measurements. Two certified observers used two mercury columns and a double stethoscope; the subjects used the automatic device. All blood pressure readings and recordings were blinded. Adequate cuff sizes were used, and the subjects' position was standardized. Discrepancy analysis between manual and automatic measurements was carried out using VAPA software. RESULTS: Dispersion of the discrepancies between manual and automatic measurements showed no specific trend. Out of the 99 systolic blood pressure measurements, 53, 76 and 89 discrepancies were less than 5, 10 and 15 mmHg, respectively. Of the 99 diastolic blood pressure measurements, 62, 86 and 97 discrepancies were less than 5, 10 and 15 mmHg, respectively. The mean inter-observer discrepancy was 1 mmHg for both systolic and diastolic blood pressure comparisons. CONCLUSION: This evaluation showed that this device complies with the international validation protocol requirements. Thus, the device can, providing adequate instruction is given in the clinic, be recommended for self-measurement by patients at home, as well as for clinical or epidemiological research.

Blood Pressure Determination↗

PubMed2005

Is the area under blood pressure curve the best parameter to evaluate 24-h ambulatory blood pressure monitoring data?

BACKGROUND: Ambulatory blood pressure monitoring (ABPM) provides relevant data about blood pressure over a 24-h period. The analysis of parameters to determine the blood pressure profile from these data is of great importance. OBJECTIVES: To calculate areas under systolic and diastolic blood pressure curves (SBP-AUC/DBP-AUC) and compare with systolic and diastolic blood pressure load (SBPL/DBPL) and 24-h systolic and diastolic blood pressure (24-h SBP/24-h DBP) in order to determine which provides the best correlation with left ventricular mass index (LVMI). METHODS: ABPM measurements (1143 individuals) were analyzed to obtain 24-h SBP/24-h DBP, SBPL/DBPL, and SBP-AUC/ DBP-AUC, using Spacelabs (90207) and CardioSistemas devices. Left ventricular mass was determined using an echocardiograph HP Sonos 5500 and LVMI was calculated. RESULTS: The correlations between all possible pairs within the group 24-h SBP/SBPL/SBP-AUC and 24-h DBP/DBPL/DBP-AUC were high and statistically significant. The correlations between 24-h SBP/24-h DBP and SBP-AUC/DBP-AUC with SBPL/DBPL close to 100%, were lower than those mentioned above. The correlations of the parameters obtained by ABPM with LVMI were also high and statistically significant, except for blood pressure load between 90 and 100%, and for 24-h SBP of 135 mmHg or less and SBPL higher than 50%. CONCLUSIONS: SBPL/DBPL and SBP-AUC/DBP-AUC can be used for the evaluation of ABPM data owing to the strong correlation with 24-h SBP/24-h DBP and with LVMI, except when SBPL is close to 100% or 24-h SBP is below 135 mmHg but SBPL is above 50%. SBP-AUC/DBP-AUC, however, are a better alternative because they do not have the limitations of blood pressure load or even of 24-h blood pressure present.

Adult↗

PubMed1989

The influence of left ventricular pressure on the vascular responses to changes in carotid sinus pressure in anaesthetized dogs.

The aim of this study was to determine whether the degree of stimulation of left ventricular receptors influenced the sensitivity of the carotid sinus baroreceptor reflex. In anaesthetized dogs, the stimulus to left ventricular receptors was changed by changing aortic root and hence ventricular systolic pressure, using a preparation in which the applied pressure did not distend the aortic arch and in which left atrial pressure was controlled. A large step increase in either carotid or left ventricular pressure resulted in vasodilatation both in a perfused hindlimb and in the remainder of the systemic circulation and resulted in a reduction in the response to a change in pressure in the other area. The stimulus-response curves, relating limb and systemic perfusion pressures to small step changes in carotid sinus pressure, were displaced downwards at high left ventricular pressures. However, the curves remained parallel indicating the absence of an interactive effect. These results indicate that the vascular responses to changes in carotid and ventricular pressures show simple additive summation.

Animals↗

PubMed2002

Comparison of agreement between different measures of blood pressure in primary care and daytime ambulatory blood pressure.

OBJECTIVE: To assess alternatives to measuring ambulatory pressure, which best predicts response to treatment and adverse outcome. SETTING: Three general practices in England. DESIGN: Validation study. PARTICIPANTS: Patients with newly diagnosed high or borderline high blood pressure; patients receiving treatment for hypertension but with poor control. MAIN OUTCOME MEASURES: Overall agreement with ambulatory pressure; prediction of high ambulatory pressure (>135/85 mm Hg) and treatment thresholds. RESULTS: Readings made by doctors were much higher than ambulatory systolic pressure (difference 18.9 mm Hg, 95% confidence interval 16.1 to 21.7), as were recent readings made in the clinic outside research settings (19.9 mm Hg,17.6 to 22.1). This applied equally to treated patients with poor control (doctor v ambulatory 21.4 mm Hg, 17.3 to 25.4). Doctors' and recent clinic readings ranked systolic pressure poorly compared with ambulatory pressure and other measurements (doctor r=0.46; clinic 0.47; repeated readings by nurse 0.60; repeated self measurement 0.73; home readings 0.75) and were not specific at predicting high blood pressure (doctor 26%; recent clinic 15%; nurse 72%; patient in surgery 81%; home 60%), with poor likelihood ratios for a positive test (doctor 1.2; clinic 1.1; nurse 2.1, patient in surgery 4.7; home 2.2). Nor were doctor or recent clinic measures specific in predicting treatment thresholds. CONCLUSION: The "white coat" effect is important in diagnosing and assessing control of hypertension in primary care and is not a research artefact. If ambulatory or home measurements are not available, repeated measurements by the nurse or patient should result in considerably less unnecessary monitoring, initiation, or changing of treatment. It is time to stop using high blood pressure readings documented by general practitioners to make treatment decisions.

Blood Pressure Determination↗

PubMed1973

Effect of cerebrospinal fluid shunts on intracranial pressure and on cerebrospinal fluid dynamics. 2. A new technique of pressure measurements: results and concepts. 3. A concept of hydrocephalus.

Part 2 describes measurements of intracranial cerebrospinal fluid (CSF) pressure in 18 adult patients with CSF shunts, all pressure measurements being referred to a horizontal plane close to the foramina of Monro. All 18 patients had normal CSF pressure by lumbar puncture; however, in one patient an intracranial pressure of +280 mm was subsequently measured after pneumoencephalography. Twelve patients had pre-shunt CSF pressures measured intracranially: 11 ranged from +20 to +180 mm H(2)O and one was +280 mm H(2)O in the supine position. In the upright posture nine patients had values of -10 to -140 mm H(2)O, while three others were +60, +70, and +280 mm H(2)O. After CSF shunting in these 18 patients the pressures were -30 to +30 mm H(2)O in the supine position and -210 to -370 mm in the upright position. The effect of posture on the siphoning action of these longer shunts in the erect, adult patient is a major uncontrollable variable in maintenance of intracranial pressure after shunting. Other significant variables are reviewed. In Part 3 a concept of the hydrocephalus phenomenon is described. Emphasis is placed on the pressure differential (P(d)) and force differential (F(d)) causing pre-shunt ventricular enlargement and post-shunt ventricular size reduction. The site of P(d), which must be very small and not to be confused with measured ventricular pressure, P, must be at the ventricular wall.

Adult↗

PubMed1975

Raised intracranial pressure and cerebral blood flow. 5. Effects of episodic intracranial pressure waves in primates.

The effects of episodic waves of intracranial pressure on cerebral blood flow were studied in primates. Six pressure waves each of 20 minutes' duration and ranging from 50 to 100 mmHg in magnitude were induced in baboons, at intervals of 30 minutes, in an attempt to simulate clinical plateau waves. With pressure waves up to 75 mmHg, cerebral blood flow remained at control levels despite falling cerebral perfusion pressures. Between the initial pressure waves a marked hyperaemia developed, with cerebral blood flow increasing by as much as 100%, and this appeared to be a means whereby adequate flow was maintained during pressure waves. Later pressure waves, up to 100 mmHg, eventually reduced blood flow below control levels, although moderately high flows were maintained during periods of very low perfusion pressure. Brain metabolism was affected by eht episodic pressure waves, although no consistent change was seen.

Acetoacetates↗

PubMed1993

Simultaneous recording of cerebrospinal fluid pressure and middle cerebral artery blood flow velocity in patients with suspected symptomatic normal pressure hydrocephalus.

CSF pressure (intracranial pressure, in one patient lumbar pressure) was monitored continuously for one night in 23 patients with suspected symptomatic normal pressure hydrocephalus (NPH) to identify patients who might benefit from subsequent shunt surgery. In 20 patients middle cerebral artery (MCA) blood flow velocity by means of transcranial Doppler sonography (TCD) and CSF pressure were recorded simultaneously. In three patients transcranial Doppler signals were insufficient. Spontaneous changes in CSF pressure always paralleled changes in the TCD signal. Equivalents of B-waves as well as intermediate waves (in between B- and A-waves), and C-waves could be identified easily and always appeared in phase. The Doppler signal, however, could not be used to evaluate the absolute changes in CSF pressure. Fast Fourier Transform of the Doppler signal was a useful tool to indicate the relative frequency of B-wave equivalents. In five patients the injection of 10ml saline into the ventricle raised intracranial pressure considerably, but hardly affected the MCA blood flow velocity. Continuous TCD monitoring might be useful as a noninvasive screening procedure in patients with suspected symptomatic NPH before continuous invasive CSF pressure measurements are performed.

Aged↗

PubMed1976

Neuromuscular function at hyperbaric pressures: pressure-anesthetic interactions.

Hydrostatic pressure and anesthetic agents exert mutually antagonistic effects, including pressure reversal of anesthesia and anesthetic amelioration of the high-pressure nervous syndrome. To clarify the cellular basis for these phenomena, twitch tension and electromyogram (EMG) were monitored in the indirectly stimulated isolated rat diaphragm. Compression to 137 atm increased twitch tension without changing EMG amplitude. Partial phrenic nerve block accompanied EMG depression induced by methoxyflurane and chloroform; pressure antagonized these effects. To examine subthreshold pressure effects, calcium concentration was decreased from 2.5 to 0.5 mM. Compression to 137 atm then reversibly decreased EMG amplitude, while enhancing twitch tension. In 0.5 mM calcium, methoxyflurane and chloroform depressed EMG amplitude before blocking phrenic nerve conduction; pressure to 137 atm produced additional depression. These results suggest that pressure enhances twitch tension by acting on excitation-contraction coupling or on the contractile mechanism. They also indicate that pressure may inhibit transmission at the neuromuscular junction, and they do not support synaptic transmission as a site of pressure-anesthetic antagonism.

Action Potentials↗