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PubMed1992

Longitudinal prediction of adult blood pressure from juvenile blood pressure levels.

The link between blood pressure measured at juvenile ages (3-18 years) and subsequent adult ages (30 and 50 years) was investigated in a community-based longitudinal study conducted in the San Francisco Bay Area from 1928 to the present. The original sample of 550 persons decreased 61 percent by age 50 years, leaving only 211 persons in the cohort. Blood pressure was measured annually up to age 18 years and each decade thereafter, providing a unique opportunity to link childhood and adult blood pressures over periods of up to 50 years. Juvenile blood pressure measured from age 6 years onward was a positive predictor of blood pressure at age 30 years. Blood pressure measured at age 50 years was predicted best by juvenile pressures measured at early school age and early puberty. The juvenile-adult blood pressure association was partly explained by controlling for smoking and parental history of cardiovascular disease, but was not explained by controlling for juvenile height or body mass. It was stronger in children from blue collar families. The reported correlations probably represent an underestimation of the true strength of the association because of a greater loss to follow-up among subjects with higher blood pressure and the effects of antihypertensive medication in adulthood.

Adolescent↗

PubMed1994

Urinary electrolyte excretion in 24 hours and blood pressure in the INTERSALT Study. II. Estimates of electrolyte-blood pressure associations corrected for regression dilution bias. The INTERSALT Cooperative Research Group.

This is the second of two reports dealing with the reliability of measurements of 24-hour urinary electrolyte excretion and blood pressure and estimates of electrolyte-blood pressure associations in INTERSALT, an international study of the relations of electrolyte excretion and other factors to blood pressure, involving more than 10,000 persons from 52 centers in 32 countries. The first report (Am J Epidemiol 1994; 139:927-39) described methods of estimating reliability, taking into account age and sex, and provided estimates for several urinary variables, blood pressure, and pulse rate. This second report uses these estimates of reliability and multivariate procedures to correct associations with blood pressure for "regression dilution bias." In these analyses, the estimated mean change in systolic blood pressure associated with a 100-mmol decrease in sodium intake was -3.1 mmHg with adjustment for age, sex, body mass index, and alcohol intake. For potassium, the estimated mean change in systolic pressure associated with a 15-mmol increase in potassium intake was -1.0 mmHg. These estimates are 44%-50% larger than those previously reported in INTERSALT, based on simple corrections for reliability. Furthermore, compared with previously reported INTERSALT values, the estimated mean change in systolic pressure per unit of change in body mass index decreased by about 5% and that for consumption of > or = 300 ml of absolute alcohol per week increased by about 6%. These results further clarify the observed INTERSALT associations of systolic blood pressure with 24-hour urinary sodium and potassium excretion, body mass index, and alcohol intake.

Adult↗

PubMed2001

Effects of inverse ratio ventilation versus positive end-expiratory pressure on gas exchange and gastric intramucosal PCO(2) and pH under constant mean airway pressure in acute respiratory distress syndrome.

BACKGROUND: In patients with acute respiratory distress syndrome, whether inverse ratio ventilation differs from high positive end-expiratory pressure (PEEP) for gas exchange under a similar mean airway pressure has not been adequately examined. The authors used arterial oxygenation, gastric intramucosal partial pressure of carbon dioxide (PiCO(2)), and pH (pHi) to assess whether pressure-controlled inverse ratio ventilation (PC-IRV) offers more benefits than pressure-controlled ventilation (PCV) with PEEP. METHODS: Seventeen acute respiratory distress syndrome patients were enrolled and underwent mechanical ventilation with a PCV inspiratory-to-expiratory ratio of 1:2, followed by PC-IRV 1:1 initially. Then, they were randomly assigned to receive PC-IRV 2:1, then 4:1 or 4:1, and then 2:1, alternately. The baseline setting of PCV 1:2 was repeated between the settings of PC-IRV 2:1 and 4:1. Mean airway pressure and tidal volume were kept constant by adjusting the levels of peak inspiratory pressure and applied PEEP. In each ventilatory mode, hemodynamics, pulmonary mechanics, arterial and mixed venous blood gas analysis, PiCO(2), and pHi were measured after a 1-h period of stabilization. RESULTS: With a constant mean airway pressure, PC-IRV 2:1 and 4:1 decreased arterial and mixed venous oxygenation as compared with baseline PCV 1:2. Neither the global oxygenation indices with oxygen delivery and uptake nor PiCO(2) and pHi were improved by PC-IRV. During PC-IRV, applied PEEP was lower, and auto-PEEP was higher. CONCLUSION: When substituting inverse ratio ventilation for applied PEEP to keep mean airway pressure constant, PC-IRV does not contribute more to better gas exchange and gastric intramucosal PiCO(2) and pHi than does PCV 1:2 for acute respiratory distress syndrome patients, regardless of the inspiratory-to-expiratory ratios.

APACHE↗

PubMed1988

Change in blood pressure in offspring of parents with high or low blood pressure: the Dutch Hypertension and Offspring Study.

A family history of hypertension is an important predictor of high blood pressure. We investigated the question of whether this predisposition affects the level and change of blood pressure early in life, and in particular, at what age the familial aggregation of blood pressure occurs. Blood pressure and related characteristics were studied in children whose parents both had relatively high blood pressure ('high') and the results were compared with those from children whose parents both had a relatively low blood pressure ('low') and with children with one parent high and the other parent low ('mixed'). At the age of 8 years there were no clear differences in pressure but at the age of 20 years there was a difference of 7 mmHg for both systolic and diastolic pressure between the high- and low-risk offspring. These findings suggest that the magnitude of familial aggregation of blood pressure increases during childhood and adolescence.

Blood Pressure↗

PubMed1998

The determinants of long-term blood pressure stability: control of trough blood pressure during sleep.

Long-term blood pressure stability in humans is not affected by prolonged hypotensive drug therapy. After withdrawal of long-term hypotensive therapy from essential hypertensives, their blood pressures soon return to pre-treatment levels. Since the well-studied stabilizing systems all adapt to prevailing blood pressure levels, they cannot account for long-term stability of blood pressure. There is a parallel between trough blood pressure and the lower limit of cerebral autoregulation. Blood pressure goes down to a trough level once sleep has been established. This level is maintained for 3-4 h, with minor perturbations. For normal and hypertensive humans and rats, the level is almost the same as the lower limit of cerebral autoregulation. In essential hypertension the nocturnal fall of blood pressure and the lower limit for cerebral autoregulation could be set by atheromatous narrowing or occlusion of large cerebral arteries, especially those supplying the brain stem, from which the Cushing response is initiated. Constriction and maldevelopment of smaller cerebral arteries are probably the main causes of increased cerebrovascular resistance in spontaneously hypertensive rats (SHR). The structural difference between the two situations might explain the failure of prolonged hypotensive therapy to reduce the lower limit of cerebral autoregulation in humans, which it is able to achieve in young SHR. If trough blood pressure stability were the anchor which prevents casual blood pressures from drifting, a primary increase of cerebrovascular resistance would be a plausible explanation for essential hypertension. It could also make a major causal neurogenic contribution to hypertension in rat models, especially SHR and stroke-prone SHR.

Animals↗

PubMed2000

Excess mortality associated with increased pulse pressure among middle-aged men and women is explained by high systolic blood pressure.

OBJECTIVE: To assess the risk of death from coronary heart disease, stroke, all cardiovascular diseases and all-cause mortality associated with pulse pressure among the middle-aged population. METHODS AND DESIGN: A prospective 15-year follow-up cohort study was conducted of two independent cross-sectional random samples of the population who participated in baseline surveys in 1972 or 1977. Each survey included a self-administered questionnaire with questions on smoking and antihypertensive drug treatment, measurements of height, weight and blood pressure and the determination of the serum cholesterol concentration. Multivariate analyses were performed by using Cox proportional hazard models. SETTING: The provinces of North Karelia and Kuopio in eastern Finland PARTICIPANTS: Men and women aged 45-64 years with no history of myocardial infarction or stroke at the time of the baseline survey were selected. In total 4333 men and 5270 women took part in this follow-up study. RESULTS: The relative risk of coronary heart disease, stroke, cardiovascular disease and all-cause mortality increased with the increasing pulse pressure in individuals aged 45-64 years independent of the diastolic blood pressure level. Only in women with diastolic blood pressure > or = 95 mmHg was the relative risk of fatal stroke not statistically significant. After adjustment for systolic blood pressure, the positive association between mortality and increasing pulse pressure disappeared. CONCLUSION: Increasing pulse pressure is a predictor of death from coronary heart disease, stroke, cardiovascular disease and all causes in men and women aged 45-64 years, but the increase in risk is entirely associated with the increase in systolic blood pressure.

Blood Pressure↗

PubMedDate not supplied

Pressure ulcer prevention in homecare: do Dutch homecare agencies have an evidence-based pressure ulcer protocol?

OBJECTIVE: The purpose of this study was to gain insight into the availability and quality of protocols for pressure ulcer prevention in homecare agencies in the Netherlands. DESIGN: A descriptive study was completed. SETTING AND SUBJECTS: Forty-one homecare agencies in the Netherlands that provide nursing care were queried. INSTRUMENTS: Three instruments were used to collect data: (1) a structured questionnaire containing 46 closed and open-ended questions, (2) a checklist used by experts to analyze the protocols for conformity to guidelines, and (3) a tool used to generate a numerical score for each protocol based on the experts' reviews. METHODS: A questionnaire was mailed to all homecare agencies in the Netherlands that provided nursing care. The quality of each protocol was judged and scored by 3 pressure ulcer prevention experts. The scores were analyzed using descriptive statistics. RESULTS: A pressure ulcer protocol was available in 78% of the agencies. Seventy-five percent had at least 1 wound care nurse who spent an average of 10 hours per week on pressure ulcer prevention. In 20% of the agencies, no introduction or instruction was given to the nurses when the protocol was implemented. In 25% of the agencies, nurses did not participate in the revision of the protocol. At the end of 2003, only 13% of the agencies had executed 1 or more revisions of their protocol since 2002, when the last Dutch pressure ulcer guideline was introduced. The 26 pressure ulcer prevention protocols had a mean score of 47 points out of a maximum of 100 points (range 9 to 82; SD, 18). CONCLUSIONS: Although the use of protocols is considered an important adjunct in the prevention of pressure ulcers, 22% of the participating agencies did not have a pressure ulcer prevention protocol and 25% did not have wound care nurses, indicating a need for further promotion of standardized pressure ulcer prevention strategies. In addition, the available protocols were frequently of low quality or outdated, reflecting a need for increased attention to current and accurate tools to guide nursing practice.

Causality↗

PubMed2005

Benefits from angiotensin-converting enzyme inhibitor 'beyond blood pressure lowering': beyond blood pressure or beyond the brachial artery?

OBJECTIVE: The substantial benefits of ramipril over conventional therapy in high-risk patients are not always associated with clinically significant differences in brachial arterial pressure, and largely remain unexplained. We undertook this acute study to establish the magnitude of and reason for different acute effects of ramipril and atenolol on arterial pressure. METHODS: We enrolled 30 patients, who took 10 mg ramipril, 100 mg atenolol, and placebo at intervals of > or = 7 days, in a randomized, double-blind, placebo-controlled trial. After baseline, measurements were taken at 30-60 min intervals for 5 h, and comprised cuff brachial pressure, radial artery tonometry with generation of central aortic pressure, and pulse wave velocity for aorta, upper limb and lower limb arteries. RESULTS: Both ramipril and atenolol reduced arterial pressure, and the diastolic pressure fall was similar in the aorta and brachial artery, but the systolic pressure fall for ramipril was greater than for atenolol (by 5.2 mmHg, P < 0.0001) in the aorta compared with the brachial artery. The aortic systolic pressure difference with ramipril in comparison with atenolol was accompanied by an absolute difference of 10.7% (P < 0.0001) in the augmentation index, denoting a reduction in peripheral wave reflection by ramipril. The aortic pulse wave velocity fell to a similar degree with ramipril in comparison with atenolol, but fell to a greater degree (1.35 and 0.44 m/s, respectively, P < 0.0001 for both) in muscular arteries of the lower and upper limbs. CONCLUSION: A greater (average, 5.2 mmHg) decrease in aortic systolic pressure caused by ramipril may explain the greater benefit of ramipril over atenolol. The difference is attributable to decreased stiffness of peripheral arteries and a reduction in wave reflection.

Aged↗

PubMed1996

Low pressure leakage in anaesthetic machines. Evaluation by positive and negative pressure tests.

Positive and negative pressure tests for checking the low pressure section of 36 anaesthetic machines in order to detect gas leaks were prospectively compared. The low pressure section was checked by the soap bubble test as a 'gold standard'. The leakage rate was 86.1%. The sensitivity and specificity of the positive pressure tests were 92% and 100% respectively, whilst the sensitivity and specificity of the negative pressure test were both 100%. However, seven machines revealed a leak which was only detected by the positive pressure test: this problem arose through defects in the emergency oxygen flush devices which allowed oxygen to leak around the valve even though it was in the 'off' position. This might reduce the specificity of the negative pressure test to 41.7%. For security, both tests should be carried out in series; the positive pressure test followed by the negative pressure test. The possibility of gaseous leakage around the oxygen flush device is not generally recognised. This study emphasises the need for skilled servicing of anaesthetic machines on a regular basis.

Anesthesiology↗

PubMed1992

The accuracy of catheter-tip pressure transducers for the measurement of intrauterine pressure in labour.

OBJECTIVE: To assess the reliability of intrauterine pressure measurements in labour with transducer tipped catheters. DESIGN: Prospective clinical study. SETTING: Delivery ward, National University Hospital, Singapore. SUBJECTS: 20 women admitted in early labour were randomly allocated to two groups. INTERVENTIONS: Women in the first group had two catheters that had been tied together introduced transcervically into the same amniotic fluid pocket. The second group had two catheters introduced in different directions so that each catheter tip was in a different pocket of amniotic fluid. MAIN OUTCOME MEASURE: The contraction to contraction pressure difference recorded by the two catheters in the same uterus. In addition, the cumulative uterine active pressure generated by one catheter was compared with that of the other. RESULTS: There were differences in peak pressure of up to 4-5.3 kPa (30-40 mmHg) during some contractions. The difference in pressure recordings between the two catheters could not be explained by effects of loculation of amniotic fluid. However, the pressures recorded were not systematically higher in one catheter than in the other. Cumulative uterine activity was very similar when assessed by each catheter in the same uterus. CONCLUSION: Intrauterine pressure measurements using transducer tipped catheters provide reliable information on the cumulative pressure wherever the catheter tip was sited in the uterus, but there are variations in pressures recorded during individual contractions.

Catheterization↗

PubMed1970

Inotropic changes in the left ventricle: the effect of changes in heart rate, aortic pressure and end-diastolic pressure.

1. Under conditions where heart rate, mean aortic pressure and enddiastolic pressure in the left ventricle are held constant, the intravenous infusion of isoprenaline is accompanied by large changes in dP/dt max in the left ventricle.2. Under similar conditions, during stepwise increments in the rate of infusion of isoprenaline the changes in dP/dt max (measured at a constant paced heart rate) were proportional to changes in the free (intrinsic) heart rate. It is concluded that dP/dt max is a quantitative index of inotropic changes in the left ventricle.3. In comparison to dP/dt max, three other variables which have been used to indicate inotropic changes in the heart (peak pressure in the left ventricle, duration of systole and stroke work at constant end-diastolic pressure), were shown to be unreliable indices of inotropic changes.4. Using dP/dt max to indicate inotropic changes, alteration in the heart rate while mean aortic pressure and end-diastolic pressure in the left ventricle were held constant, and in mean aortic pressure while heart rate ane end-diastolic pressure in the left ventricle were held constant, were each shown to be accompanied by small inotropic changes in the heart.5. Under similar conditions, changes in end-diastolic pressure in the left ventricle alone were not accompanied by inotropic changes as indicated by dP/dt max.

Animals↗

PubMed1988

Characterisation of the normal right ventricular pressure-volume relation by biplane angiography and simultaneous micromanometer pressure measurements.

The normal right ventricular pressure-volume relation was studied by recording biplane right ventriculograms with simultaneous high fidelity pressure recordings in 10 adults found to have normal coronary arteries and haemodynamic function at diagnostic cardiac catheterisation. Right ventricular volume was measured frame by frame from digitised ventriculograms by a modification of Simpson's rule. The accuracy of this method was tested in a study of 22 human and animal right ventricular casts. There was excellent agreement between calculated volumes and those measured by fluid displacement. The derived regression equations were used to correct right ventricular volumes calculated from in vivo studies. The mean (SD) end diastolic volume index for the group was 62 (13) ml/m2, the stroke volume index was 43 (8) ml/m2, and the ejection fraction was 62 (6)%. Right ventricular pressure-volume loops were generated by combining simultaneous volume and pressure curves. The normal right ventricular pressure-volume loop was triangular, departing significantly from the square or rectangle of the normal left ventricular pressure-volume loop. Ejection from the right ventricle began early during the pressure rise and continued as right ventricular pressure fell. As a result phases of isovolumic contraction and relaxation were difficult to define. These observations show that normal right ventricular pressure-volume relations differ considerably from those of the normal left ventricle, presumably reflecting the different loading conditions of the two ventricles.

Adult↗

PubMed1977

Interaction of aortic pressure and left ventricular end-diastolic pressure in the dog.

Fiber length (preload) is an important determinant of left ventricular performance. Mean aortic blood pressure also influences ventricular performance. The present study was undertaken to examine the influence of mean aortic pressure on the fiber length-ventricular performance relationship. Fifteen anesthetized, adrenergically blocked dogs were studied on right-heart bypass at constant heart rate and coronary blood flow. An increase in mean aortic pressure permitted a greater improvement in performance as evaluated by stroke work for a given increase in left ventricular end-diastolic pressure. A given increase in mean aortic pressure at a constant stroke volume produced a greater rise in stroke work over intermediate ranges of left ventricular end-diastolic pressure than occurred with higher or lower left ventricular end-diastolic pressure. Thus, the degree of afterload-induced performance improvement depended on the magnitude of the preload. External circumference-left ventricular end-diastolic pressure data suggested a possible relationship between isovolumic systolic circumferential expansion and the improvement of ventricular performance at higher mean aortic pressures.

Animals↗

PubMed1989

Effect of renal perfusion pressure on renal interstitial hydrostatic pressure in rats.

The purpose of this study was to investigate the hypothesis that changes in renal perfusion pressure may be transmitted to the renal interstitium and cause alterations in renal interstitial hydrostatic pressure and sodium excretion. A method that utilizes a chronically implanted polyethylene matrix that allows for direct continuous measurement of renal interstitial hydrostatic pressure, and agrees well with subcapsular measurement in rats, was developed. Renal interstitial hydrostatic pressure, fractional excretion of sodium, and urine flow rate were 3.0 +/- 0.3 mmHg, 0.35 +/- 0.13%, and 19.44 +/- 3.00 microliter/min, respectively, when renal perfusion pressure was 101 +/- 0.8 mmHg. When renal perfusion pressure was increased to 123 +/- 0.9 mmHg renal interstitial hydrostatic pressure, fractional excretion of sodium, and urine flow rate increased significantly to 5.8 +/- 0.6 mmHg, 1.29 +/- 0.29%, and 50.76 +/- 8.83 microliter/min, respectively, in anesthetized male Sprague-Dawley rats. These changes occur despite a well-autoregulated glomerular filtration rate and renal blood flow. In conclusion, increasing renal perfusion pressure caused a significant increase in renal interstitial hydrostatic pressure as measured directly by the implanted polyethylene matrix method and was associated with a significant increase in sodium excretion.

Animals↗

PubMed1975

Effect of intrathoracic pressure on pressure-volume characteristics of the lung in man.

Quasi-static pressure-volume (P-V) curves in normal seated human subjects were determined with pressure at the airway opening (Pa0) set below (negative pressure), above (positive pressure), or equal to ambient pressure. Dynamic compliance (Cdyn) during controlled continuous negative pressure breathing (CNPB) was also studied. Quasi-static P-V curves at negative pressure were decreased in slope, reflected a decrease in total lung capacity, and intersected the P-V curve obtained at ambient Pa0. At positive pressure the P-V curves showed an increase in slope and an increase in total lung capacity. During CNPB a fall in Cdyn was found. The fall in Cdyn was rapid and persisted for the duration of CNPB. Cdyn promptly returned to control levels when Pa0 was adjusted to ambient pressure.

Adult↗

PubMed1975

Positive airway pressure and vertical transpulmonary pressure gradient in man.

Static transpulmonary pressure (Pao-Pes) and the vertical gradient of transpulmonary pressure were determined in five sitting conscious normal subjects at mean airway pressures of 0 (ambient), 11, and 21 cmH2O. All subjects exhibited a nonuniform transpulmonary pressure gradient down the esophagus. The vertical pressure gradient was consistently larger in the lower (8-20cm below esophageal artifact) than in the middle region (0-8cm) of the esophagus. The gradient was not significantly altered by continuous positive airway pressure (11 and 21 cmH2O) or by changes in lung volume (60, 70, and 80% of total lung capacity (TLC)). Continuous positive airway pressure also did not result in a consistent change of the overall static pressure-volume curve of the lung. There was a small but statistically significant increase in TLC with each increase in airway pressure.

Biomechanical Phenomena↗

PubMed1989

Pressure-flow behavior of a bronchopleural fistula during mechanical ventilation with positive pressure.

We examined the mechanical behavior of a bronchopleural fistula created by sectioning a small subpleural bronchus in seven anesthetized lambs. The pressure across the fistula was measured as the difference between the pressure recorded by a retrograde bronchial catheter inserted in the vicinity of the fistula and the outflow pressure at the fistula exit. The effective resistance of the fistula (Rf) was computed by dividing this pressure difference by the gas flow through the fistula measured at the outlet of an intrapleural tube adjacent to the fistula. Rf increased by 114 +/- 25% (SE) when we inflated the lungs in a stepwise manner from a tracheal pressure of 2-20 cmH2O. Rf also increased when inflation pressure varied continuously; this increase, however, was less evident when we decreased the inflation time from 1.0 to 0.2 s. The relationship between Rf and lung volume was similar during the stepwise inflations and deflations but showed marked hysteresis during the continuous inflation-deflation maneuvers, when Rf was greater during deflation than inflation. Our results suggest that the fistula behaves as a compliant pathway whose relevant transmural pressure is the transmural pressure at or near the fistula's exit. We attribute the increase in Rf during inflation to decreases in transmural pressure caused by convective and dissipative losses inside the fistula and by the stress applied by the chest wall on the outer surface of the fistula.

Animals↗

PubMed1992

Myocardial tissue pressure and blood flow during coronary sinus pressure modulation in anesthetized dogs.

To determine whether coronary sinus outflow pressure (Pcs) or intramyocardial tissue pressure (IMP) is the effective back pressure in the different layers of the left ventricular (LV) myocardium, we increased Pcs in 14 open-chest dogs under maximal coronary artery vasodilation. Circumflex arterial (flowmeter), LV total, and subendocardial and subepicardial (15-microns radioactive spheres) pressure-flow relationships (PFR) and IMP (needle-tip pressure transducers) were recorded during graded constriction of the artery at two diastolic Pcs levels (7 +/- 3 vs. 23 +/- 4 mmHg). At high Pcs, LV, aortic and diastolic circumflex arterial pressure, heart rate, myocardial oxygen consumption, and lactate extraction were unchanged; IMP in the subendocardium did not change (130/19 mmHg), whereas IMP in the subepicardium increased by 17 mmHg during systole and 10 mmHg during diastole (P < or = 0.001), independently of circumflex arterial pressure. Increasing Pcs did not change the slope of the PFR; however, coronary pressure at zero flow increased in the subepicardium (P < or = 0.008), whereas in the subendocardium it remained unchanged at 24 +/- 3 mmHg. Thus Pcs can regulate IMP independently of circumflex arterial pressure and consequently influence myocardial perfusion, especially in the subepicardial tissue layer of the LV.

Anesthesia↗