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PubMed1986

The effects of intravenous infusion of solutions with different colloid osmotic pressures on rat mesenteric lymph pressure.

The effects of intravenous infusion of solutions of varied colloid osmotic pressure on mesenteric lymph pressure were measured by a glass micropipette. The lymph pressure was 4.0 +/- 1.6 cm H2O between the second and third valve of rat mesenteric lymphatic vessels with diameter of 101 +/- 25 micron (mean +/- SD). Intravenous infusion of 1 ml/100g body weight (B.W.) of isotonic saline, 5% glucose solution, and 20% glucose solution increased the lymph pressure by 1.6 +/- 0.5 cm H2O, 1.5 +/- 0.3 cm H2O and 2.0 +/- 1.0 cm H2O, respectively. Infusion of 2 ml/100g B.W. of the same solutions increased the lymph pressure by 3.3 +/- 1.3 cm H2O, 3.3 +/- 1.6 cm H2O and 3.7 +/- 0.8 cm H2O, respectively. Infusion of hydroxyethyl starch solution, with colloid osmotic pressure of 25 mmHg, minimally altered the lymph pressure. One ml/100g B.W. infusion of low molecular weight dextran solution, with colloid osmotic pressure of 162 mmHg, decreased the lymph pressure by 1.3 +/- 0.9 cm H2O, and 2 ml/100g B.W. infusion of this solution decreased the lymph pressure by 2.0 +/- 1.0 cm H2O. The different effects on lymph pressure derive from the differences in colloid osmotic pressure of these solutions in conformity with the Starling hypothesis.

Animals↗

PubMed1980

[The effects of changes in mean aortic pressure on the reliability of cardiac output determination from the aortic pressure curve (author's transl)].

In seven postoperative patients the effects of changes in mean aortic pressure on the reliability of cardiac output determination from the aortic pressure curve by the method of Wesseling et al. [8] were tested. Reference cardiac output (CO) was measured by thermal dilution technique. The wave impedance Zo, needed for the "contour method" of Wesseling, was derived from the initial CO-determinations. Overall correlation of both methods was good with a correlation coefficient of 4 = 0.8740. The percentage error of the contour method was -4.59 +/- 25.01%. In 4 of 7 patients there was an individual differing effect of pressure changes on the impedance Zo and by this on the error of the method. 1/Zo was clearly correlated to mean aortic pressure (r = -0.4021 to r = -0.8381). To examine the reliability of contour method also in great variations of mean aortic pressure additionally 6 aortic vessels of dogs and 1 human aortic vessel were tested in a perfusion model. In all cases increase of blood pressure was followed by a systematic failure of the contour method between +77% and +1112%. Corresponding to the mean pressure the individual failure curves were of exponential character. 1/Zo and mean aortic pressure showed high negative correlation coefficients (r = -0.9056 to r = -0.9923). The pressure dependent changes of the impedance Zo were comparable to the corresponding changes of volume elasticity coefficients. Subsequently for every vessel and patient respectively an estimation function for pressure dependent impedance Zo was calculated by use of two CO-determinations at different pressure levels. The correction of Zo by these functions resulted in a considerable reduction of the pressure dependent failure.

Adult↗

PubMed1991

Ambulatory blood pressure monitoring: assessing the diurnal variation of blood pressure.

The purposes of this paper are to examine the effects of activity, situation of measurement, mood, and occupation on the daily variation of blood pressure and to discuss the potential utility of ambulatory blood pressure monitoring in physical anthropological studies. The subjects of the blood pressure variability study are 125 men who were referred to the Hypertension Center at New York Hospital--Cornell Medical Center for evaluation of hypertension. There were 1,386 blood pressure measurements from these subjects available for study, which were taken using noninvasive ambulatory blood pressure monitoring techniques. Pressures were transformed to z scores using the subject's daily mean pressure and standard deviation to assess the relative elevation during the experience of the various factors. The results show that activity and mood are the most significant sources of blood pressure variation (P less than .005) and are additive. Occupation, which may be an indicator of social class in this population, also modified the mood effects. Because ambulatory blood pressure monitors obtain many readings over a day under a variety of circumstances, their use can improve epidemiological and human biological studies of the inheritance and variability of blood pressure. Ambulatory blood pressure monitoring is an important new tool in the study of human biological variation.

Affect↗

PubMed1998

Measurement of intraocular pressure during laparoscopy and its relationship to central venous pressure.

UNLABELLED: STUDY OBJECTIVE. To determine the effect of different positional degrees on hemodynamics, especially central venous pressure and intraocular pressure, and a possible interrelationship, during laparoscopic surgery. SETTING. University teaching hospital (Canadian Task Force classification II-1). PATIENTS: Seven women undergoing elective gynecologic laparoscopy. INTERVENTIONS: The women were monitored for heart rate, partial pressure of oxygen, end-tidal carbon dioxide, arterial blood pressure, central venous pressure, end-tidal isoflurane concentration, and intraocular pressure in several body positions during general anesthesia. MEASUREMENTS AND MAIN RESULTS: Intraocular pressure depends on body position (r2 = 0.58) related to central venous pressure (r2 = 0.7). Heart rate and arterial blood pressure are also dependent on the body position, but to a lesser degree. CONCLUSION: Continuous monitoring of intraocular pressure may help detect alterations in central venous pressure during general anesthesia for laparoscopic surgery. Undesirable alterations caused by degree of Trendelenburg position may negatively affect patients with high cardiac or ophthalmic risk.

Adult↗

PubMed1999

Effects of pressure ramp slope values on the work of breathing during pressure support ventilation in restrictive patients.

OBJECTIVE: To investigate, in restrictive patients, the influence of pressure ramp slope values on the efficacy of pressure support ventilation. DESIGN: Prospective study. SETTING: A university hospital medical intensive care unit. PATIENTS: Twelve intubated restrictive patients. INTERVENTIONS: Patients were randomly assigned to four sequences in which the values of the slope of the pressure ramp increase were modulated so that the plateau pressure was reached within a predetermined time: 0.1, 0.50, 1, or 1.50 secs. The more rapidly the pressure plateau was achieved, the higher was the initial flow rate. For convenience, these four different ventilatory settings were termed T 0.1, T 0.5, T 1, and T 1.5. MEASUREMENTS AND MAIN RESULTS: We measured the following parameters 10 mins after application of each pressure ramp slope: inspiratory work of breathing, breathing pattern, and intrinsic PEEP (PEEPi). Work of breathing was evaluated using Campbell's diagram, and expressed as a percentage of the values observed under spontaneous ventilation. A marked interindividual variation of the values for work of breathing was observed under spontaneous ventilation; the mean value for work of breathing was 1.97 +/- 0.82 joule/L, with a range of 1.22 to 4.10 joule/L. Comparison between the means for each sequence and each variable measured was performed by two-way analysis of variance with internal comparisons between sequences by Duncan's test. Between the first (T 0.1) and the last (T 1.5) sequence, the reduction of values of the pressure ramp slope induced a progressive increase in the values for work of breathing, regardless of the mode of expression (in joule, joule/L, or joule/min). The values for work of breathing (joule/ L), expressed as a percentage of the values observed under spontaneous ventilation, increased from 44.2 +/- 14.4% to 78.3 +/- 17.8% (p < .001). In contrast, the reduction of the pressure ramp slope values and initial flow rate did not induce any significant change in tidal volume, respiratory frequency, and PEEPi. CONCLUSION: Among the four tested slope values, the steepest was that which induced the lowest possible work of breathing in restrictive patients ventilated by pressure support ventilation. In this type of patient, we therefore suggest that the programmed pressure value should be reached by using a steep pressure ramp slope.

Acute Disease↗

PubMed1974

Circulatory effects of deep inspirations, blocked expirations and positive pressure inflations at equal transpulmonary pressures in conscious dogs.

1. Circulatory effects of deep inspirations, blocked expirations and constant endotracheal positive pressure inflations were studied in six conscious dogs under comparable geometries of the pulmonary vascular bed, i.e. at equal transpulmonary pressures (around 10.2 cm H(2)O) and similar lung volumes.2. In order to characterize these effects, we measured beat-by-beat left and right ventricular ejections, pulmonary arterial, left atrial and aortic mean transmural pressures, and concomitant intrathoracic and tracheal pressures. Changes in pulmonary-left heart blood volume were also computed.3. During inspiration when intrathoracic pressure became more negative, there was a slight increase in right ventricular output (+15%; P < 0.1) and always a net decrease in left ventricular output (-25%; P < 0.01) despite a significant increase in mean transmural left atrial pressure (+3 cm H(2)O, i.e. +40%; P < 0.005). It is concluded that the more negative intrathoracic pressure increases the left ventricular outflow impedance and that an inspiratory increase in pulmonary vascular capacity cannot explain the observed reduction in left ventricular output since this reduction occurs together with an increase in left ventricular filling pressure.4. During blocked expiration when intrathoracic pressure was positive, decreases in right ventricular output (-17%; P < 0.05) and in pulmonary-left heart blood volume (-12 ml.; P < 0.05) were observed while right ventricular outflow impedance increased. After an initial augmentation in left ventricular output (despite a concomitant progressive decrease in mean transmural left atrial pressure), left ventricular output also decreased (-17%; P < 0.05). Such circulatory changes were similar but less marked than those observed under constant positive pressure inflations. These observations suggest that the decrease in venous return (and consequently in right ventricular output) following the increase in intrathoracic pressure is the leading factor which overshadows the augmentation in left ventricular output associated with the simultaneous decrease in left ventricular outflow impedance.5. Similar experiments performed on two additional dogs in acute conditions showed the same circulatory effects before and after pharmacological blockade. These observations therefore confirm that mechanical factors play a leading part during these respiratory manoeuvres.

Animals↗

PubMed1991

[The noninvasive estimation of right atrial pressure improves the Doppler evaluation of the pulmonary systolic pressure].

The right ventricular systolic pressure can be evaluated with the Doppler method through the right ventricular-atrial gradient (RV-RA gradient) and the right atrial pressure. The former is expressed by the transtricuspid velocity of flow, the latter is generally assumed. In 50 patients with elevated pulmonary pressure we tested whether ultrasounds may be utilized for the evaluation of the right atrial pressure, and whether the derived values contribute to improve the accuracy of the method. We estimated the right ventricular systolic pressure with method A: RV-RA gradient + 10; and method B: RV-RA gradient x 1.1 + 14, where 10 and 14 are the assumed right atrial pressure (mmHg). Through the collapsibility index of the inferior vena cava, taken as an ultrasound-derived index of right atrial pressure, we were able to identify 3 groups of patients with normal (Group 1, 14 cases), elevated (Group 2, 21 cases) and moderately elevated (Group 3, 15 cases) right atrial pressure, respectively. In them the right ventricular systolic pressures obtained with both method A and method B were compared to those derived with catheter. In Group 1 the non-invasive values were significantly closer to the invasive ones when calculated with method A; the same was true of method B in Group 2. In Group 3 the accuracy of the 2 methods was similar. We conclude that ultrasound assists in the non-invasive approximation of the right atrial pressure as well as in the choice of the appropriate formula, so that Doppler estimation of the right ventricular systolic pressure is improved.

Adult↗

PubMed1980

Influence of extravascular pressure on changes induced in vascular resistance in the small intestine by elevated venous pressure.

The influence of the extravascular pressure on the size of the increase in vascular resistance after elevation of venous outflow pressure (venous-vasomotor response) was studied in an intestinal segment, perfused at a constant rate, in anaesthetized dogs. If pressure in the lumen of the intestine was elevated (spontaneously, pharmacologically, mechanically) or pressure in the plethysmograph was raised, venous-vasomotor responses were either smaller or absent. When pressure in the intestinal lumen was raised, blood volume increments produced in the segment by elevated venous pressure were significantly smaller than those observed in the presence of resting pressure. The presence of a venous-vasomotor response was correlated to the quantitative relationship between the extravascular and the venous pressure. Its induction was dependent on whether the outflow venous pressure was higher than the pressure values in the intestinal lumen or the plethysmograph; in that case it developed to an extent corresponding to the increment in transmural vascular pressure.

Animals↗

PubMed1997

Diagnosing intrinsic sphincteric deficiency: comparing urethral closure pressure, urethral axis, and Valsalva leak point pressures.

OBJECTIVES: Our purpose was to compare three measures proposed to diagnose intrinsic sphincteric deficiency: maximum urethral closure pressure, Valsalva leak point pressure, and straining urethral axis. STUDY DESIGN: A total of 159 women with pure genuine stress incontinence had the three measures determined in a standardized fashion. Critical cutoff values for the Valsalva leak point pressure (52 cm) and urethral axis (22 degrees) were established by examining relative frequency distribution curves, using closure pressure of 20 as the arbitrary benchmark value for the prevalence of intrinsic sphincteric deficiency. The distribution of cutoff values is described and differences among the measures with respect to risk factors for intrinsic sphincteric deficiency and incontinence severity were determined. RESULTS: Half the subjects fell below at least one cutoff value, but only 10% fell below all three. Sixty-four percent of subjects with either low closure pressure or leak point pressure had low values for the other, whereas 21% had discordance between them. Only 53% of subjects with low closure pressure and 40% with low leak point pressure had an axis < or = 22 degrees. Conversely, a substantial portion (36%) of subjects with pure genuine stress incontinence without urethral hypermobility had neither low urethral or leak point pressures. All three cutoff-values were associated with risk factors for intrinsic sphincteric deficiency, but only low closure and leak point pressures had significant associations with the severity of incontinence. CONCLUSIONS: Intrinsic sphincteric deficiency should be diagnosed by a composite of historic, urodynamic, anatomic, and clinical severity criteria. We would include a maximum urethral closure pressure < or = 20, a Valsalva leak point pressure < or = 50, and a stress urethral axis < or = 20 in this composite.

Adolescent↗

PubMed1991

Variable non-linearity in end systolic pressure-volume relationships results from interaction between end diastolic and developed pressure-volume relations.

OBJECTIVE: The aim was to determine the contributions of diastolic pressure to the shape of the relationship of total systolic left ventricular pressure with volume (pressure-volume relationship). STUDY DESIGN: The pressure-volume relationship was approximated (by least squares fit) to a parabola P = aV2 + bV + C. Non-linearity was indicated by values "a" significantly different from zero. Negative values indicated concavity to the volume axis, positive values convexity to the volume axis. MATERIALS: Langendorff perfused rabbit hearts (n = 8) with intraventricular balloon were used. Balloon pressure was measured for varying balloon volumes. RESULTS: The total systolic pressure-volume relationship was concave towards the volume axis at 2.4 mM extracellular calcium ions concentrations ([Cae++]) a = -47.2 (SD 5.4), p less than 0.05. It was nearly linear at [Cae++] = 0.6 mM; a = -0.8(5.8), p greater than 0.05. It was convex at [Cae++] = 0.3 mM; a = 25.3(4.0), p less than 0.01. The diastolic pressure-volume relationship was always convex: a = 30.1(6.7), 33.5(7.6), 42.2(6.6) for [Cae++] = 2.4, 0.6, and 0.3 mM respectively. When these diastolic values were subtracted from the total pressures, pressure-volume curves for developed pressure were obtained which were always concave: a = -76.9(10.2), -33.5(3.7), -16.3(2.9) for [Cae++] = 2.4, 0.6, and 0.3 mM. CONCLUSIONS: The true systolic pressure-volume relationship of the left ventricle is not linear but concave to the volume axis. The slope is therefore variable and not an index of contractility. Apparently linearity or convexity is due to inappropriate addition of the diastolic pressure-volume properties.

Animals↗

PubMed1984

Day-Night Variations in Malate Concentration, Osmotic Pressure, and Hydrostatic Pressure in Cereus validus.

Malate concentration and stem osmotic pressure concomitantly increase during nighttime CO(2) fixation and then decrease during the daytime in the obligate Crassulacean acid metabolism (CAM) plant, Cereus validus (Cactaceae). Changes in malate osmotic pressure calculated using the Van't Hoff relation match the changes in stem osmotic pressure, indicating that changes in malate level affected the water relations of the succulent stems. In contrast to stem osmotic pressure, stem water potential showed little day-night changes, suggesting that changes in cellular hydrostatic pressure occurred. This was corroborated by direct measurements of hydrostatic pressure using the Jülich pressure probe where a small oil-filled micropipette is inserted directly into chlorenchyma cells, which indicated a 4-fold increase in hydrostatic pressure from dusk to dawn. A transient increase of hydrostatic pressure at the beginning of the dark period was correlated with a short period of stomatal closing between afternoon and nighttime CO(2) fixation, suggesting that the rather complex hydrostatic pressure patterns could be explained by an interplay between the effects of transpiration and malate levels. A second CAM plant, Agave deserti, showed similar day-night changes in hydrostatic pressure in its succulent leaves. It is concluded that, in addition to the inverted stomatal rhythm, the oscillations of malate markedly affect osmotic pressures and hence water relations of CAM plants.

Journal Article↗

PubMed2005

Pressure support ventilation versus continuous positive airway pressure ventilation with the ProSeal laryngeal mask airway: a randomized crossover study of anesthetized pediatric patients.

Continuous positive airway pressure (CPAP) and pressure support ventilation (PSV) improve gas exchange in adults, but there are little published data regarding children. We compared the efficacy of PSV with CPAP in anesthetized children managed with the ProSeal laryngeal mask airway. Patients were randomized into two equal-sized crossover groups and data were collected before surgery. In Group 1, patients underwent CPAP, PSV, and CPAP in sequence. In Group 2, patients underwent PSV, CPAP, and PSV in sequence. PSV comprised positive end-expiratory pressure set at 3 cm H(2)O and inspiratory pressure support set at 10 cm H(2)O above positive end-expiratory pressure. CPAP was set at 3 cm H(2)O. Each ventilatory mode was maintained for 5 min. The following data were recorded at each ventilatory mode: ETco(2), Spo(2), expired tidal volume, peak airway pressure, work of breathing patient (WOB), delta esophageal pressure, pressure time product, respiratory drive, inspiratory time fraction, respiratory rate, noninvasive mean arterial blood pressure, and heart rate. In Group 1, measurements for CPAP were similar before and after PSV. In Group 2, measurements for PSV were similar before and after CPAP. When compared with CPAP, PSV had lower ETco(2) (46 +/- 6 versus 52 +/- 7 mm Hg; P < 0.001), slower respiratory rate (24 +/- 6 versus 30 +/- 6 min(-1); P < 0.001), lower WOB (0.54 +/- 0.54 versus 0.95 +/- 0.72 JL(-1); P < 0.05), lower pressure time product (94 +/- 88 versus 150 +/- 90 cm H(2)O s(-1)min(-1); P < 0.001), lower delta esophageal pressure (10.6 +/- 7.4 versus 14.1 +/- 8.9 cm H(2)O; P < 0.05), lower inspiratory time fraction (29% +/- 3% versus 34% +/- 5%; P < 0.001), and higher expired tidal volume (179 +/- 50 versus 129 +/- 44 mL; P < 0.001). There were no differences in Spo(2), respiratory drive, mean arterial blood pressure, and heart rate. We conclude that PSV improves gas exchange and reduces WOB during ProSeal laryngeal mask airway anesthesia compared with CPAP in ASA physical status I children aged 1-7 yr.

Anesthesia, Inhalation↗

PubMed1996

Preliminary noninvasive back-pressure recordings of bladder pressure.

Obstructive voiding is best evaluated with urodynamics, including bladder pressure and urine flow rates. Until recently, the recording of bladder pressure required the use of a urethral catheter. In preliminary observations, a noninvasive back-pressure method using an external condom catheter has been introduced to determine bladder pressure. This device uses a side tube for pressure recording and an outlet tube that is clamped for short periods of time. We have investigated design criteria for back-pressure recording techniques. In the laboratory setting using a plastic model, we determined that a low compliance condom is needed. In addition, a back flow of fluid during the clamping procedure helps to obtain quick back pressures and facilitates evaluation of pressure when low flow rates are present. These modified condom devices were evaluated in four male subjects. Back pressures were not statistically different than bladder pressures recorded with a urethral catheter. The use of back pressures in the evaluation for obstructive uropathy can be enhanced by using a pressure and flow nomogram.

Humans↗

PubMed1999

Wedged hepatic venous pressure adequately reflects portal pressure in hepatitis C virus-related cirrhosis.

Wedged hepatic venous pressure (WHVP) is equivalent to portal venous pressure in patients with alcoholic liver diseases. However, it may underestimate portal pressure in nonalcoholics, which is important because hepatitis C virus (HCV) infection is a frequent cause of chronic liver disease. We investigated the agreement between directly measured portal pressure and WHVP in alcoholic and HCV-related liver diseases. Seventy-one patients with liver disease resulting from HCV infection (n = 32), alcohol (n = 25), or both (n = 14) underwent simultaneous measurements of WHVP (by hepatic vein catheterization) and portal pressure (by direct puncture). In 9 patients, measurements were repeated 20 minutes after acute iv propranolol administration. WHVP showed an excellent agreement with portal pressure in patients with cirrhosis resulting from either HCV, alcohol or both (intraclass correlation coefficient: 0.94, 0.93, and 0.97, respectively; P <.001). A discrepancy of >/=5 mm Hg was observed in 7 cases. WHVP underestimated portal pressure in only 1 case and exceeded portal pressure by >/=5 mm Hg in 6 patients. The WHVP response to propranolol closely and significantly correlated with changes in portal pressure (intraclass correlation coefficient: 0.87; P <.004). The simple and safe measurement of WHVP accurately reflects portal pressure in alcoholic and HCV-related liver disease. This technique also allows us to accurately assess the portal pressure response to propranolol in both alcoholic and HCV-related cirrhosis.

Adult↗

PubMed2002

Why valve opening pressure plays a relatively minor role in the postural ICP response to ventricular shunts in normal pressure hydrocephalus: modeling and implications.

OBJECTIVES: In normal pressure hydrocephalus, there is no clear evidence that the opening pressure of differential pressure valves influences outcome. In this study, the objective was to determine whether the relationship between valve opening pressure and post-operative postural ICP changes was predictable. METHODS: Eight adult-onset hydrocephalus patients were evaluated using an intraparenchymal ICP microsensor. Postural ICP measurements were obtained before and after placement of a ventricular shunt (VP or VA) with a Codman Hakim programmable valve. RESULTS: Valve opening pressure had a poor correlation with ICP at any head-of-bed elevation across subjects (best r = 0.25). The degree of negative ICP encountered for any given patient did not appear to be determined by the valve pressure, and varied significantly between patients at the same valve pressure. Each individual's ICP correlated well to opening pressure (r > 0.76), but the response is more sigmoidal than linear, and the opening pressure at which ICP changed most was markedly different between patients. CONCLUSIONS: The hydrodynamic pressures generated by shunts with different pressure valves are unpredictable. Our data supports the use of programmable valves in patients with adult onset hydrocephalus and suggests that ICP be measured post-operatively to achieve an optimal clinical outcome.

Cerebrospinal Fluid Shunts↗

PubMed1985

Mean systemic filling pressure as a characteristic pressure for venous return.

Guyton's theory on venous return, implying a linear relationship between blood flow and central venous pressure, was tested in an intact circulation after thoracotomy and airtight chest closure. In eleven Yorkshire pigs (approx. 10 kg) we measured flow in the pulmonary artery and aorta and pressure in the central veins and aorta during pentobarbital anesthesia and mechanical ventilation. To change central venous pressure different lung volumes were randomly applied at intervals of 5 min in a series of inspiratory hold procedures of 7.2 s. During these short periods hemodynamic steady state circumstances were met without involvement of cardiovascular control mechanisms. We confirmed the linear relationship between venous return and central venous pressure and derived mean systemic filling pressure from the regression equation. Mean systemic filling pressure was on average 10.5 +/- 2.3 (SD) mm Hg. The time dependent changes during the inspiratory hold procedure showed that the increase in central venous pressure was the primarily dependent variable, followed by a decrease in venous return and right ventricular output. After a delay of 2-4 heart beats also a decrease in left ventricular output and aortic pressure occurred. Subsequently, the lower venous return during inspiratory hold was mainly sustained by the lower aortic pressure, but nevertheless fulfilled the linear relationship mentioned above. For analysis of flow and pressure changes in the systemic circulation during changes of central venous pressure a tube of constant flow resistance was used as a conceptual mode.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Comparative accuracies of a finger blood pressure monitor and an oscillometric blood pressure monitor.

A noninvasive blood pressure monitor (Finapres) that uses the methodology of Penaz to continuously display the arterial waveform from the finger has been introduced recently. The Finapres monitor overestimated systolic pressure by 5.8 +/- 11.9 mm Hg, while the Dinamap monitor underestimated systolic pressure by -6.9 +/- 9.2 mm Hg (P = 0.003). Dinamap mean and diastolic pressure biases were less than 2 mm Hg, while the Finapres biases for these variables were significantly greater (7.7 +/- 10.0 and 8.2 +/- 9.8 mm Hg, respectively). There was no difference in systolic or mean pressure precision between the two devices (approximately 10 mm Hg), but the diastolic precision of the Dinamap unit was superior to that of the Finapres. While in most patients the Finapres monitor provided continuous blood pressure data equivalent to the data from the radial artery, marked bias (greater than 15 mm Hg) was exhibited in 2 patients for all three pressure variables. Despite this bias, blood pressure changes were tracked closely in these 2 patients. We conclude that, in its current form, the Finapres monitor cannot be relied upon independently to accurately measure blood pressure in patients undergoing general anesthesia. Since the Dinamap monitor measures mean pressure reliably and accurately, we suggest that mean blood pressure values between the Finapres and Dinamap monitors be compared to guide one in interpreting Finapres data.

Adolescent↗

PubMed1992

Hydrostatic pressure mimics gravitational pressure in characean cells.

Hydrostatic pressure applied to one end of a horizontal Chara cell induces a polarity of cytoplasmic streaming, thus mimicking the effect of gravity. A positive hydrostatic pressure induces a more rapid streaming away from the applied pressure and a slower streaming toward the applied pressure. In contrast, a negative pressure induces a more rapid streaming toward and a slower streaming away from the applied pressure. Both the hydrostatic pressure-induced and gravity-induced polarity of cytoplasmic streaming respond identically to cell ligation, UV microbeam irradiation, external Ca2+ concentrations, osmotic pressure, neutral red, TEA Cl-, and the Ca2+ channel blockers nifedipine and LaCl3. In addition, hydrostatic pressure applied to the bottom of a vertically-oriented cell can abolish and even reverse the gravity-induced polarity of cytoplasmic streaming. These data indicate that both gravity and hydrostatic pressure act at the same point of the signal transduction chain leading to the induction of a polarity of cytoplasmic streaming and support the hypothesis that characean cells respond to gravity by sensing a gravity-induced pressure differential between the cell ends.

Calcium↗