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At least 721 records · Page 40Linked to original sources

PubMed2000

Mechanical ventilation with high positive end-expiratory pressure and small driving pressure amplitude is as effective as high-frequency oscillatory ventilation to preserve the function of exogenous surfactant in lung-lavaged rats.

OBJECTIVE: To demonstrate that under well-defined conditions, pressure-controlled ventilators (PCV) allow settings that are as good as high-frequency oscillatory ventilators (HFOV) at preserving the function of exogenous surfactant in lung-lavaged rats. DESIGN: Experimental, comparative study. SETTING: Research laboratory of a large university. SUBJECTS: Sixteen adult male Sprague-Dawley rats (280-310 g). INTERVENTIONS: Lung injury was induced by repeated lavage. After last lavage, all animals received exogenous surfactant and were then randomly assigned to two groups (n = 8 per group). The first group received PCV with small pressure amplitudes and high positive end-expiratory pressure. The second group received HFOV. In both groups, an opening maneuver was performed by increasing airway pressure to improve PaO2/F(IO2) to > or =500 torr. MEASUREMENTS AND MAIN RESULTS: Blood gases were measured every 30 mins for 3 hrs. Airway pressures were measured with a tip catheter pressure transducer. At the end of the study period, a pressure-volume curve was recorded and a broncho-alveolar lavage was performed to determine protein content and surfactant composition. The results showed that arterial oxygenation in both groups could be kept >500 torr during the 3-hr study period by using a mean airway pressure of 13+/-3 cm H2O in PCV and 13+/-2 cm H2O in HFOV. Further, there were no differences in the Gruenwald index, protein influx, or ratio of small to large aggregates between the study groups. CONCLUSION: PCV with sufficient level of positive end-expiratory pressure and small driving pressure amplitudes is as effective as HFOV to maintain optimal gas exchange, to improve lung mechanics, and to prevent protein influx and conversion of large into small aggregates after exogenous surfactant therapy in lung-lavaged rats.

Animals↗

PubMed2001

Estimation of intra-abdominal pressure by bladder pressure measurement: validity and methodology.

BACKGROUND: Increased intra-abdominal pressure (IAP) is an adverse complication seen in critically ill, injured, and postoperative patients. IAP is estimated via the measurement of bladder pressure. Few studies have been performed to establish the actual relationship between IAP and bladder pressure. The purpose of this study was to confirm the association between intravesicular pressure and IAP and to determine the bladder volume that best approximates IAP. METHODS: Thirty-seven patients undergoing laparoscopy had intravesicular pressures measured with bladder volumes of 0, 50, 100, 150, and 200 mL at directly measured intra-abdominal pressures of 0, 5, 10, 15, 20, and 25 mm Hg. Correlation coefficients and differences were then determined. RESULTS: Across the IAP range of 0 to 25 mm Hg using all of the tested bladder volumes, the difference between IAP and intravesicular pressures (bias) was -3.8 +/- 0.29 mm Hg (95% confidence interval) and measurements were well correlated (R2 = 0.68). Assessing all IAPs tested, a bladder volume of 0 mL demonstrated the lowest bias (-0.79 +/- 0.73 mm Hg). When considering only elevated IAPs (25 mm Hg), a bladder volume of 50 mL revealed the lowest bias (-1.5 +/- 1.36 mm Hg). A bladder volume of 50 mL in patients with elevated IAP resulted in an intravesicular pressure 1 to 3 mm Hg higher than IAP (95% confidence interval). CONCLUSION: Intravesicular pressure closely approximates IAP. Instillation of 50 mL of liquid into the bladder improves the accuracy of the intravesicular pressure in measuring elevated IAPs.

Abdomen↗

PubMed1982

Behavioral treatment of high blood pressure II. Acute and sustained effects of relaxation and systolic blood pressure biofeedback.

The effects on blood pressure of regular patient and professional monitoring of blood pressure, extensive patient-involved assessment of results, relaxation, and systolic blood pressure biofeedback are analyzed by comparisons of data from two 3-month treatment periods with results from a 1-month baseline period and by comparisons among control and treatment groups. Ninety borderline hypertensive patients completed the treatments. Major findings are: A Acute effects; 1) Both relaxation and systolic blood pressure biofeedback lowered blood pressure acutely. 2) Improvement in performance of relaxation and biofeedback with practice showed that they are learned skills. 3) Acutely, relaxation and biofeedback were equally effective for lowering systolic blood pressure, but relaxation lowered diastolic blood pressure more. B. Long-term effects; 1) Blood pressure declined for at least 6 months with regular monitoring and patient-involved assessment. 2) The greatest lowering of blood pressure by behavioral intervention occurred during periods when pressures tended to be highest. 3) A combination of relaxation and biofeedback, with biofeedback preceding relaxation, was better than either used alone and slightly, but not significantly, better than relaxation preceding biofeedback. 4) The long-term effects of biofeedback were slightly greater than those of relaxation. A staged, incremental behavioral treatment of borderline hypertension is proposed.

Behavior Therapy↗

PubMed2003

Application of continuous positive airway pressure to trace static pressure-volume curves of the respiratory system.

OBJECTIVE: To evaluate a new technique for pressure-volume curve tracing. DESIGN: Prospective experimental study. SETTING: Animal research laboratory. SUBJECTS: Six anesthetized rats. INTERVENTIONS: Two pressure-volume curves were obtained by means of the super-syringe method (gold standard) and the continuous positive airway pressure (CPAP) method. For the CPAP method, the ventilator was switched to CPAP and the pressure level was raised from 0 to 50 cm H2O in 5 cm H2O steps and then decreased, while we measured lung volume using respiratory inductive plethysmography. Thereafter, lung injury was induced using very high-volume ventilation. Following injury, two further pressure-volume curves were traced. Pressure-volume pairs were fitted to a mathematical model. MEASUREMENTS AND MAIN RESULTS: Pressure-volume curves were equivalent for each method, with intraclass correlation coefficients being higher than.75 for each pressure level measured. Bias and precision for volume values were 0.46 +/- 0.875 mL in basal measurements and 0.31 +/- 0.67 mL in postinjury conditions. Lower and upper inflection points on the inspiratory limb and maximum curvature point on the deflation limb obtained using both methods and measured by regression analysis also were correlated, with intraclass correlation coefficients (95% confidence interval) being.97 (.58,.99),.85 (.55,.95), and.94 (.81,.98) (p <.001 for each one). When inflection points were estimated by observers, the correlation coefficient between methods was.90 (.67,.98) for lower inflection points (p <.001). However, estimations for upper inflection points and maximum curvature point were significantly different. CONCLUSIONS: The CPAP method for tracing pressure-volume curves is equivalent to the super-syringe method. It is easily applicable at the bedside, avoids disconnection from the ventilator, and can be used to obtain both the inspiratory and the deflation limbs of the pressure-volume curve. Use of regression techniques improves determination of inflection points.

Animals↗

PubMed2005

Prevalence of self-reported high blood pressure awareness, advice received from health professionals, and actions taken to reduce high blood pressure among US adults--Healthstyles 2002.

High blood pressure awareness, advice received from health care providers, and adoption of heart-healthy behaviors were assessed using the Healthstyles 2002 survey. About 20% of respondents reported that they had high blood pressure, and 53% of these were currently taking medications to lower blood pressure. Black men had the highest adjusted prevalence of high blood pressure (32%). Medication use among persons with high blood pressure was lower among Hispanics (45%) than among blacks (54%) and whites (54%). Persons reporting having high blood pressure were five times more likely to report having received advice from a health care professional to go on a diet or change eating habits (p<0.05) and reduce salt or sodium in their diet (p<0.05), but five times less likely to have received advice to exercise (p<0.05) than those reporting not having high blood pressure, after adjustment for differences in sex, race/ethnicity, and age. Persons with self-reported high blood pressure were also more likely to be making these modifications (p<0.05). Among people with high blood pressure, current medication use was associated with both receiving and following advice for diet change and salt reduction (p<0.05). Future initiatives are needed to improve the proportion of Hispanics and blacks taking prescribed medications to improve high blood pressure control and reduce risk for serious sequelae such as heart disease and stroke.

Adolescent↗

PubMed2004

Activation of p38 MAPKalpha by extracellular pressure mediates the stimulation of macrophage phagocytosis by pressure.

We have previously demonstrated that constant 20 mmHg extracellular pressure increases serum-opsonized latex bead phagocytosis by phorbol 12-myristate 13-acetate (PMA)- differentiated THP-1 macrophages in part by inhibiting focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK). Because p38 MAPK is activated by physical forces in other cells, we hypothesized that modulation of p38 MAPK might also contribute to the stimulation of macrophage phagocytosis by pressure. We studied phagocytosis in PMA-differentiated THP-1 macrophages, primary human monocytes, and human monocyte-derived macrophages (MDM). p38 MAPK activation was inhibited using SB-203580 or by p38 MAPKalpha small interfering RNA (siRNA). Pressure increased phagocytosis in primary monocytes and MDM as in THP-1 cells. Increased extracellular pressure for 30 min increased phosphorylated p38 MAPK by 46.4 +/- 20.5% in DMSO-treated THP-1 macrophages and by 20.9 +/- 9% in primary monocytes (P < 0.05 each). SB-203580 (20 microM) reduced basal p38 MAPK phosphorylation by 34.7 +/- 2.1% in THP-1 macrophages and prevented pressure activation of p38. p38 MAPKalpha siRNA reduced total p38 MAPK protein by 50-60%. Neither SB-203580 in THP-1 cells and peripheral monocytes nor p38 MAPK siRNA in THP-1 cells affected basal phagocytosis, but each abolished pressure-stimulated phagocytosis. SB-203580 did not affect basal or pressure-reduced FAK activation in THP-1 macrophages, but significantly attenuated the reduction in ERK phosphorylation associated with pressure. p38 MAPKalpha siRNA reduced total FAK protein by 40-50%, and total ERK by 10-15%, but increased phosphorylated ERK 1.4 +/- 0.1-fold. p38 MAPKalpha siRNA transfection did not affect the inhibition of FAK-Y397 phosphorylation by pressure but prevented inhibition of ERK phosphorylation. Changes in extracellular pressure during infection or inflammation regulate macrophage phagocytosis by a FAK-dependent inverse effect on p38 MAPKalpha that might subsequently downregulate ERK.

Dimethyl Sulfoxide↗

PubMed2004

Remodeling of resistance arteries in organoid culture is modulated by pressure and pressure pulsation and depends on vasomotion.

The hypothesis was tested that pressure and pressure pulsation modulate vascular remodeling. Arterioles ( approximately 200 microm lumen diameter) were dissected from rat cremaster muscle and studied in organoid culture. In the first series, arterioles were kept at a stable pressure level of either 50 or 100 mmHg for 3 days. Both groups showed a progressive increase in myogenic tone during the experiment. Arterioles kept at 50 mmHg showed larger endothelium-dependent dilation, compared with vessels kept at 100 mmHg on day 3. Remodeling, as indicated by the reduction in maximally dilated diameter at 100 mmHg, was larger in arterioles kept at 50 mmHg compared with 100 mmHg: 34 +/- 4.5 versus 10 +/- 4.8 microm (P < 0.05). In the second series, arterioles were subjected to a stable pressure of 60 mmHg or oscillating pressure of 60 +/- 10 mmHg (1.5 Hz) for 4 days. Pressure pulsation induced partial dilation and was associated with less remodeling: 34 +/- 4.0 versus 19 +/- 4.5 microm (P < 0.01) for stable pressure versus oscillating pressure. Vasomotion was frequently observed in all groups, and inward remodeling was larger in vessels with vasomotion: 30 +/- 2.5 microm compared with vessels that did not exhibit vasomotion: 8.0 +/- 5.0 microm (P < 0.01). In conclusion, these results indicate that remodeling is not enhanced by high pressure. Pressure pulsation causes partial dilation and reduces inward remodeling. The appearance of vasomotion is associated with enhanced inward remodeling.

Animals↗

PubMed1977

Mucopolysaccharide osmotic pressure in the measurement of interstitial pressure.

Subatmospheric pressures were recorded from cotton wicks inserted into Wharton's jelly of human umbilical cords (mean=-7.6+/-5.0 (SD) cmH2O; n=10). Hyaluronate concentrations (mean=0.69+/-0.30 g/100 g) and wick pressures correlated negatively (r=-0.825; P less than 0.01) but calculated hyaluronate osmotic pressures (mean=4.0+/-2.7 cmH2O) were insufficient to explain the full wick pressure. In model systems composed of asbestos fibers (mean radius=0.5 micron) and 0.9% saline, subatmospheric pressures were recorded which varied with the volume of saline added. When hyaluronate (1 g/100 g) was substituted for saline, lower wick pressures were recorded at each volume. The pressure lowering effect of hyaluronate was not seen in a matrix of glass fibers (mean radius=1.0 micron). It is suggested that the effect of hyaluronate in asbestos fibers is due to its immobilization by the matrix and the consequent development of osmotic pressure recorded via the wick. In the coarser glass-fiber matrix, hyaluronate was not immobilized and therefore had no osmotic effect. These experiments support the hypothesis that subatmospheric interstitial pressures result from osmotic pressure of immobilized mucopolysaccharide macromolecules.

Asbestos↗

PubMed1989

Interaction between loop of Henle flow and arterial pressure as determinants of glomerular pressure.

Experiments were performed in anesthetized rats to study the relationship between loop of Henle perfusion rate, arterial pressure, and stop-flow pressure (SFP) as an index of glomerular capillary pressure. In one set of experiments we measured the SFP feedback response to changes in loop perfusion at three levels of arterial pressure. The maximum SFP response fell significantly from 13.1 +/- 1.44 to 8.14 +/- 1.72 and 3.13 +/- 0.76 mmHg when arterial pressure was reduced from 118.1 +/- 1.27 to 98.8 +/- 0.51 and 78.8 +/- 1.72 mmHg. In other experiments arterial pressure was altered while loop perfusion rate was fixed at one of three levels. Without loop perfusion SFP changed with a slope of 0.27 +/- 0.04 mmHg/mmHg in the arterial pressure range between 80 and 130 mmHg. During perfusion at the flow rate at which response is half maximum, the slope was significantly reduced to 0.12 +/- 0.04. During perfusion at 45 nl/min, it was 0.03 +/- 0.05, a value not significantly different from zero. During dopamine administration (70 micrograms/kg min) SFP was pressure-dependent even during loop perfusion at 45 nl/min. These results show that arterial pressure determines TGF responsiveness and that the TGF signal determines the range of a regulatory input that is directly dependent on arterial pressure.

Animals↗

PubMed1996

Microvascular pressures in isolated perfused immature lamb lungs: effects of flow rate, left atrial pressure and surfactant therapy.

To determine the effect of some physical factors on microvascular pressures in immature lungs, we studied the lungs of 125-day gestation immature lambs (term 150 days). Lambs were delivered and ventilated for 30 min prior to isolation of the lungs. Nine had surfactant (Survanta, 100 mg/kg) instilled into the lungs prior to delivery, and 7 did not (control group). Lungs were kept distended with airway pressure at 20 cm H2O and perfused with autologous blood, using a steady flow pump. Papaverine was added to the blood to eliminate vasomotion. We measured pulmonary artery and arterial, double and venous occlusion pressures, with flow at 100, 200 and 260 ml.kg-1.min-1 and left atrial pressure (Pla) at 0, 10 and 15 mm Hg. We found that the vascular pressure profile was similar in control and surfactant-treated lungs under similar conditions of flow and Pla. Our data show that elevation of Pla results in significant increases in capillary (double occlusion) pressure; however, the preterm lung accommodates increases in flow with little change in capillary pressure. An increase in flow rate in the presence of elevated Pla had the greatest effect on capillary pressure. All lungs became hemorrhagic when capillary pressure exceeded 30 mm Hg. We speculate that in preterm infants, stress failure of pulmonary capillaries and hemorrhage will occur when there is marked elevation of capillary pressures resulting from increased blood flow in the presence of pulmonary venous construction or left ventricular dysfunction.

Animals↗

PubMed1984

Low zero-flow pressure and minimal capacitance effect on diastolic coronary arterial pressure-flow relationships during maximum vasodilation in swine.

During maximum dilation with adenosine in dogs, the diastolic coronary pressure at which flow ceases (Pzf) has been observed to be up to 27 mm Hg above coronary sinus and right atrial pressures. We studied swine to measure the Pzf and to determine the effects of interventions that change collateral flow and coronary capacitance. In 44 swine, the left anterior descending coronary artery (LAD) was instrumented with two catheters, a hydraulic occluder, and a flowmeter. Late diastolic and mean pressure-flow relationships were constructed at a series of pressures produced by partial LAD occlusions during maximum vasodilation. The late diastolic Pzf was 7.0 +/- 2.2 mm Hg (mean +/- SD), less than 4 mm Hg above right atrial pressure; the mean Pzf was 12.1 +/- 3.1 mm Hg, less than 9 mm Hg above right atrial pressure. The Pzf in the LAD did not change significantly (1) during transient simultaneous occlusion of the right coronary artery (RCA) in seven swine (late diastolic Pzf with the RCA open was 6.6 +/- 1.5 mm Hg and with the RCA closed it was 6.0 +/- 1.5 mm Hg), (2) during increased left ventricular systolic pressure (LVSP) in seven swine (late diastolic Pzf with LVSP of 123 mm Hg was 5.5 +/- 2.2 mm Hg and with LVSP of 184 mm Hg it was 7.3 +/- 2.8 mm Hg), or (3) during increased heart rate in eight swine (late diastolic Pzf at heart rate of 107 per minute was 10.8 +/- 2.9 mm Hg and at 180 per minute it was 12.7 +/- 2.1 mm Hg). Similar results were obtained from analysis of the mean pressure and flow data. The Pzf in the LAD of swine is very close to right atrial pressure, and it did not change significantly during interventions that would modify collateral flow (reduced by RCA occlusion and enhanced by increased LVSP) and coronary capacitance (increased LVSP and increased heart rate). This low Pzf is beneficial in maintaining flow at lower coronary arterial perfusion pressures.

Adenosine↗

PubMed2004

Blood pressure differences between northern and southern Chinese: role of dietary factors: the International Study on Macronutrients and Blood Pressure.

Blood pressure and prevalence of high blood pressure are greater for northern than southern Chinese. Reasons for these differences are unclear. Relationships of north-south blood pressure differences with multiple dietary factors were investigated in 839 Chinese participants, International Study on Macronutrients and Blood Pressure (INTERMAP), 561 northern, 278 southern, aged 40 to 59 years. Daily nutrient intakes were determined from four 24-hour dietary recalls and 2 timed 24-hour urine collections. Average systolic/diastolic pressure levels were 7.4/6.9 mm Hg higher for northern than southern participants. Southern participants had lower body mass index, sodium intake, sodium/potassium ratio, and higher intake of calcium, magnesium, phosphorus, and vitamins A and C. Considered singly, with control for age and gender, several dietary variables (eg, body mass index, urinary sodium/potassium ratio, urinary sodium, dietary phosphorus, and magnesium) reduced north-south blood pressure differences by > or =10%. Controlled for age and gender, nondietary variables had little effect on north-south blood pressure differences. With inclusion in regression models of multiple dietary variables (sodium, potassium, magnesium or phosphorus, body mass index), north-south blood pressure differences became much smaller (systolic -1.1, diastolic 1.6 mm Hg) and statistically nonsignificant. In conclusion, multiple dietary factors accounted importantly for north-south blood pressure differences. Efforts are needed to improve nutrition in China, especially in the north, as well as in other populations including those in the United States, for prevention and control of adverse blood pressure levels and major adult cardiovascular disease.

Adult↗

PubMed2006

Role of renal medullary heme oxygenase in the regulation of pressure natriuresis and arterial blood pressure.

Recent studies have demonstrated that inhibition of renal medullary heme oxygenase (HO) activity and carbon monoxide (CO) significantly decreases renal medullary blood flow and sodium excretion. Given the crucial role of renal medullary blood flow in the control of pressure natriuresis, the present study was designed to determine whether renal medullary HO activity and resulting CO production participate in the regulation of pressure natriuresis and thereby the long-term control of arterial blood pressure. In anesthetized Sprague-Dawley rats, increases in renal perfusion pressure induced significant elevations of CO concentrations in the renal medulla. Renal medullary infusion of chromium mesoporphyrin (CrMP), an inhibitor of HO activity, remarkably inhibited HO activity and the renal perfusion pressure-dependent increases in CO levels in the renal medulla and significantly blunted pressure natriuresis. In conscious Sprague-Dawley rats, continuous infusion of CrMP into the renal medulla significantly increased mean arterial pressure (129+/-2.5 mm Hg in CrMP group versus 118+/-1.6 mm Hg in vehicle group) when animals were fed a normal salt diet (1% NaCl). After rats were switched to a high-salt diet (8% NaCl) for 10 days, CrMP-treated animals exhibited further increases in mean arterial pressure compared with CrMP-treated animals that were kept on normal salt diet (152+/-4.1 versus 130+/-4.2 mm Hg). These results suggest that renal medullary HO activity plays a crucial role in the control of pressure natriuresis and arterial blood pressure and that impairment of this HO/CO-mediated antihypertensive mechanism in the renal medulla may result in the development of hypertension.

Animals↗

PubMed1996

Pressure and angiotensin II synergistically induce aortic fibronectin expression in organ culture model of rabbit aorta. Evidence for a pressure-induced tissue renin-angiotensin system.

Aortic fibronectin (FN) expression is augmented in hypertension. Increasing evidence suggests that both angiotensin II (Ang II) and mechanical factors may induce vascular remodeling in response to hypertension. We have previously shown that, in vitro, increased transmural pressure enhances FN expression in rabbit aortic media. To investigate the existence of a link between the effects of pressure and Ang II and to explore the mechanisms underlying such a relationship, we quantified the effect of Ang II and Ang II inhibitors on the pressure-dependent FN expression in a 3-day organ culture model of rabbit aorta using immunolabeling analysis and detected FN mRNAs by in situ hybridization. A dose-dependent effect of Ang II on FN expression was observed at both 80 and 150 mm Hg but not at 0 mm Hg (relaxed vessels). One mumol/L Ang II increased the media cross-sectional surface, showing FN expression from 7.9 +/- 0.7% (n = 9) to 18.9 +/- 1.1% (n = 4) at 80 mm Hg (P < .01) and from 17.4 +/- 1.8% (n = 9) to 56.6% +/- 3.6 (n = 4) at 150 mm Hg (P < .001). In situ hybridization revealed that Ang II and pressure upregulated FN mRNA expression. Losartan, an AT1 antagonist, not only blocked the Ang II effect but also inhibited the transmural pressure effect. Angiotensin-converting enzyme inhibition abolished the pressure-dependent FN expression and significantly diminished the effect of pressure in the presence of Ang II. The effect of renin-angiotensin system inhibitors was specific for FN, since neither bFGF nor laminin expression was affected by these agents. Taken together, the results demonstrate that (1) the effect of transmural pressure is mediated by the stimulation of a local renin-angiotensin system, resulting in a net Ang II production in the culture medium, (2) transmural pressure and Ang II act synergistically to enhance vascular FN expression, (3) AT1 receptors mediate both the effects of pressure and of exogenous Ang II, and (4) the effect of Ang II on FN expression is regulated at a pretranslational level.

Angiotensin II↗

PubMed2000

Role of kinins in the control of renal papillary blood flow, pressure natriuresis, and arterial pressure.

The present study evaluated the effects of blocking kinins with the bradykinin B(2) receptor antagonist Hoe140 on the relationship between renal perfusion pressure, papillary blood flow (PBF), and sodium excretion. To determine the relevance of renal kinins in the long-term control of arterial pressure, the effect of a chronic intrarenal infusion of Hoe140 on arterial pressure and sodium balance was also studied. PBF was not autoregulated in volume-expanded rats, and the administration of Hoe140 reduced PBF (-30%) and improved PBF autoregulation. The kinin antagonist also decreased sodium excretion (-35%) and blunted pressure natriuresis with no whole-kidney renal hemodynamic changes. These effects may be mediated through nitric oxide (NO), because in rats pretreated with N(G)-nitro-L-arginine methyl ester, Hoe140 had no additional effects on PBF or pressure natriuresis. A role for NO in mediating the renal response to Hoe140 is also supported by the finding that Hoe140 reduced basal urinary NO(3)(-)/NO(2)(-) excretion (-33%), and it blunted the arterial pressure-induced increase in NO(3)(-)/NO(2)(-) excretion, which is compatible with the idea that the pressure-natriuresis response may be mediated through kinins and NO. The importance of kinins in long-term regulation of arterial pressure is demonstrated by the severe arterial hypertension (172+/-6 mm Hg) induced during the chronic intrarenal infusion of Hoe140 associated with sodium and volume retention. These data suggest that renal kinins and NO may be a part of the renal mechanism coupling changes in arterial pressure with modifications in PBF and sodium excretion, therefore contributing to the long-term control of arterial pressure.

Adrenergic beta-Antagonists↗

PubMed2006

Differential impact of blood pressure-lowering drugs on central aortic pressure and clinical outcomes: principal results of the Conduit Artery Function Evaluation (CAFE) study.

BACKGROUND: Different blood pressure (BP)-lowering drugs could have different effects on central aortic pressures and thus cardiovascular outcome despite similar effects on brachial BP. The Conduit Artery Function Evaluation (CAFE) study, a substudy of the Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT), examined the impact of 2 different BP lowering-regimens (atenolol+/-thiazide-based versus amlodipine+/-perindopril-based therapy) on derived central aortic pressures and hemodynamics. METHODS AND RESULTS: The CAFE study recruited 2199 patients in 5 ASCOT centers. Radial artery applanation tonometry and pulse wave analysis were used to derive central aortic pressures and hemodynamic indexes on repeated visits for up to 4 years. Most patients received combination therapy throughout the study. Despite similar brachial systolic BPs between treatment groups (Delta0.7 mm Hg; 95% CI, -0.4 to 1.7; P=0.2), there were substantial reductions in central aortic pressures with the amlodipine regimen (central aortic systolic BP, Delta4.3 mm Hg; 95% CI, 3.3 to 5.4; P<0.0001; central aortic pulse pressure, Delta3.0 mm Hg; 95% CI, 2.1 to 3.9; P<0.0001). Cox proportional-hazards modeling showed that central pulse pressure was significantly associated with a post hoc-defined composite outcome of total cardiovascular events/procedures and development of renal impairment in the CAFE cohort (unadjusted, P<0.0001; adjusted for baseline variables, P<0.05). CONCLUSIONS: BP-lowering drugs can have substantially different effects on central aortic pressures and hemodynamics despite a similar impact on brachial BP. Moreover, central aortic pulse pressure may be a determinant of clinical outcomes, and differences in central aortic pressures may be a potential mechanism to explain the different clinical outcomes between the 2 BP treatment arms in ASCOT.

Age Distribution↗

PubMed2003

Transdiaphragmatic pressure control of airway pressure support in healthy subjects.

We designed a new servoventilator that proportionally adjusts airway pressure to transdiaphragmatic pressure (Pdi) generated by the subject during inspiration. Each cycle is triggered by either a preset Pdi increase or a preset inspiratory flow value (whichever is reached first), whereas cycling-off is flow-dependent. We evaluated the servoventilator in seven healthy subjects at normocapnia and three levels of hypercapnia (normocapnia + 3, + 6, and + 9 mm Hg) comparatively with spontaneous breathing. Triggering was by Pdi in six subjects and flow in one. At all end-tidal carbon dioxide pressure levels, time from onset of diaphragm electromyographic activity to inspiratory flow was similar with and without the servoventilator. Airway pressure increased proportionally to Pdi variation during servoventilator breathing. Flow, tidal volume, respiratory rate, intrinsic positive end-expiratory pressure, and esophageal and transdiaphragmatic pressure-time products increased significantly with hypercapnia with and without the servoventilator. Breathing pattern parameters were similar in the two breathing modes, and no differences were found for intrinsic positive end-expiratory pressure or gastric pressure variation during exhalation. Esophageal and transdiaphragmatic pressure-time products were lower with than without the servoventilator. The Pdi-driven servoventilator was well synchronized to the subjects effort, delivering a pressure proportional to Pdi and reducing respiratory effort at normocapnia and hypercapnia.

Adult↗

PubMed1981

Zero-flow pressures and pressure-flow relationships during single long diastoles in the canine coronary bed before and during maximum vasodilation. Limited influence of capacitive effects.

The proposal that diastolic coronary flow is regulated by an intramyocardial "back-pressure" that substantially exceeds coronary venous and ventricular diastolic pressures has been examined in an open-chest canine preparation in which instantaneous left circumflex pressure and flow could be followed to cessation of inflow during prolonged diastoles. Despite correlation coefficients consistently >0.90, pressure-flow data during individual diastoles were concave to the flow axis before and during pharmacologically induced maximum coronary vasodilation. Data were better fitted (P < 0.01) by second-order equations than by linear equations in >90% of cases. Second-order pressure-axis intercepts (P(f=0))(1) averaged 29+/-7 (SD) mm Hg before vasodilation and 15+/-2 mm Hg during vasodilation; left and right atrial pressures were always substantially lower (8+/-3 and 5+/-2 mm Hg before vasodilation and 8+/-2 and 4+/-1 mm Hg during dilation). Values of P(f=0) before vasodilation varied directly with levels of coronary inflow pressure. A modification of the experimental preparation in which diastolic circumflex pressure could be kept constant was used to evaluate the suggestion that P(f=0) measured during long diastoles are misleadingly high because of capacitive effects within the coronary circulation as inflow pressure decreases. Decreases in P(f=0) attributable to capacitive effects averaged only 5.9+/-3.0 mm Hg before vasodilation and were smaller during dilation. We conclude that P(f=0) is a quantitatively important determinant of coronary driving pressure and flow, resulting from both factors related to, and independent of, vasomotor tone. Adjustments of flow during changing physiological situations may involve significant changes in P(f=0) as well as in coronary resistance.

Animals↗