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PubMed1982

Effect of tilting on blood pressure and interstitial fluid pressures of bluefish and smooth dogfish.

Tolerance of the circulatory system of fish for gravitational stress has not been measured previously. We examined this in bluefish (Pomatomus saltatrix) and smooth dogfish (Mustelus canis) by placing them horizontally on a V-board in air while their gills were perfused with aerated seawater, then tilting them head up for 0.5 h, and finally returning them to horizontal. Meanwhile, we recorded the blood pressure, pulse pressure, and heart rate in the ventral aorta, and interstitial fluid pressure in the head and tail. All four bluefish tolerated a 30 degrees tilt or even a 60 degrees tilt with little change in blood pressure or interstitial pressure in the anterior and posterior regions. All recovered afterward. However, in the seven dogfish examined, the posterior interstitial fluid pressure increased from 2.8 +/- 1.0 cmH2O before tilting to 11.8 +/- 3.3 cmH2O toward the end of a 30 degrees tilt lasting 30 min. The blood pressure decreased as the pulse pressure approached zero, showing that circulatory insufficiency had developed due to insufficient venous return to the heart. Most of the dogfish died within a few hours after the experiment. These findings are in keeping with the conclusion that the vasculature of bluefish has more rigidity, less permeability, and perhaps more compensatory tone than that of smooth dogfish. We speculate that bluefish may have evolved their circulatory tolerance for gravity as a cross-adaptation to the stresses imposed on the circulation by forward acceleration and by regional differences of transcutaneous pressure occurring during fast carangiform swimming.

Animals↗

PubMed1976

Increased intracranial pressure in so-called 'normal-pressure hydrocephalus'.

Five patients exhibited an apparently communicating hydrocephalus -- type of disorder, with ventricular reflux on the cisternograms, lack of air-encephalographic parasagittal air-filling and clearly enlarged temporal horns. The group seemed heterogeneous, with regard to age distribution; possible etiological factors and duration of the hydrocephalic process. In all 5 patients increased intracranial/intrathecal pressure was observed: in 2 patients, only with intrathecal measurement in the lumbar area, but in the remaining 3 patients with epidural/ventricular fluid pressure monitoring. Continuously increased pressure extending over 1 or more days was observed in these patients. This pressure increase may seem different from the episodic pressure increase previously reported in normal-pressure hydrocephalus. These patients seem to be cases of so-called normal-pressure hydrocephalus according to the commonly accepted criteria. It is therefore suggested that the term normal-pressure hydrocephalus should be abandoned, and replaced by, e.g., low-pressure hydrocephalus, malresorptive or malabsorptive hydrocephalus.

Adult↗

PubMed2004

Role of pressure in angiotensin II-induced renal injury: chronic servo-control of renal perfusion pressure in rats.

Renal perfusion pressure was servo-controlled chronically in rats to quantify the relative contribution of elevated arterial pressure versus angiotensin II (Ang II) on the induction of renal injury in Ang II-induced hypertension. Sprague-Dawley rats fed a 4% salt diet were administered Ang II for 14 days (25 ng/kg per minute IV; saline only for sham rats), and the renal perfusion pressure to the left kidney was continuously servo-controlled to maintain a normal pressure in that kidney throughout the period of hypertension. An aortic occluder was implanted around the aorta between the two renal arteries and carotid and femoral arterial pressure were measured continuously throughout the experiment to determine uncontrolled and controlled renal perfusion pressure, respectively. Renal perfusion pressure of uncontrolled, controlled, and sham kidneys over the period of Ang II or saline infusion averaged 152.6+/-7.0, 117.4+/-3.5, and 110.7+/-2.2 mm Hg, respectively. The high-pressure uncontrolled kidneys exhibited tubular necrosis and interstitial fibrosis, especially prominent in the outer medullary region. Regional glomerular sclerosis and interlobular artery injury were also pronounced. Controlled kidneys were significantly protected from interlobular artery injury, juxtamedullary glomeruli injury, tubular necrosis, and interstitial fibrosis as determined by comparing the level of injury. Glomerular injury was not prevented in the outer cortex. Transforming growth factor (TGF)-beta and active NF-kappaB proteins determined by immunohistochemistry were colocalized in the uncontrolled kidney in regions of interstitial fibrosis. We conclude that the preferential juxtamedullary injury found in Ang II hypertension is largely induced by pressure and is probably mediated through the TGF-beta and NF-kappaB pathway.

Angiotensin II↗

PubMed1976

Ventricular pressure-volume curve indices change with end-diastolic pressure.

Many indices have been proposed to describee the diastolic pressure-volume curve mathematically and permit quantification of the elastic properties of the myocardium itself in hopes that changes in the muscle caused by disease would b.e reflected in the diastolic pressure-volume curve. To date, none of the proposed indices has been shown convincingly to discriminate one group of patients from another. While this situation in part arises from the relatively large amount of noise introduced by the technical difficulties of measuring synchronous pressures and volumes during diastole in man, ther is a more fundamental difficulty. In practice, one can measure only a short segment of the entire pressure-volume curve, and the values of all diastolic pressure-volume curve parameters investigated change significantly when one uses different segments of the same pressure-volume curve to compute them. These results were derived from relatively noise-free pressure-volume curves obtained by filling nine excised dog left ventricles at a known rate and monitoring pressure-volume curve used to compute the parameter. Merely increasing measurement fidelity will not resolve this problem, because none of these parameters accurately characterizes the entire diastolic pressure-volume curbe from a segment like that which one can reasonably expect to obtain from humans.

Animals↗

PubMed1990

Starling resistor versus compliance. Which explains the zero-flow pressure of a dynamic arterial pressure-flow relation?

Arterial pressure at zero flow (Pz = 0) that is higher than venous pressure (Pv) in dynamic pressure-flow relations has been explained by the presence of an arteriolar Starling resistor (SR) mechanism (i.e., vascular waterfall) or the discharge of vascular capacitance. To determine which was predominant, I studied in vivo hind limbs of 18 anesthetized dogs in which femoral arteries were cannulated with in-line electromagnetic flow probes to measure inflow (Qin), Pv was controlled, and collateral flow was eliminated with a tourniquet. Pz = 0 was obtained by turning flow to zero. Three tests were applied: 1) Pv was raised in steps with either constant Qin or constant arterial pressure (Pa) to determine the pressure at which upstream vascular characteristics were affected by a change in Pv, 2) the time to reach Pz = 0 was varied to determine compliance effects, and 3) an equation was developed to determine if experimentally derived parameters could explain Pz = 0 without invoking an SR. With constant Qin and a Pz = 0 of 56.9 +/- 11.7 mm Hg (time to Pz = 0, 3 seconds), Pv could be raised by 9.6 +/- 6.2 to 16.3 +/- 6.0 mm Hg before Pa increased, and with constant Pa, Pv could be raised by 6.8 +/- 7.3 to 14.0 +/- 8.0 mm Hg before Qin decreased. With increasing times to reach Pz = 0, Pz = 0 initially dropped precipitously, but then decreased by only a small amount over the next 5-10 seconds even though arterial pressure was much above Pv. This could be explained by an SR mechanism with a critical pressure of 42.3 +/- 11.4 mm Hg and an arterial compliance of 0.0104 +/- 0.0023 ml.mm Hg-1 (n = 6). There was no value for the compliance that described the results when the arterial outflow pressure was Pv. Thus, this study supports the hypothesis that an SR mechanism is present in the vascular system. It is most likely precapillary, and in the resting limb, it has a value of 40-50 mm Hg. However, Pz = 0 in dynamic pressure-flow studies of less than 4 seconds is also greatly influenced by capacitance effects and the initial Pa.

Animals↗

PubMed2000

Nasal continuous positive airway pressure reduces sleep-induced blood pressure increments in preeclampsia.

Preeclampsia is the predominant cause of admissions to neonatal intensive care. The diurnal blood pressure pattern is flattened or reversed in preeclampsia. We hypothesized that snoring and partial upper airway obstruction contribute to nocturnal rises in blood pressure. We tested this hypothesis by controlling sleep- induced upper airway flow limitation and snoring with nasal positive pressure. Eleven women with preeclampsia underwent two consecutive polygraphic sleep studies with simultaneous beat-to-beat blood pressure monitoring. Average blood pressure for the night overall and in each sleep stage was calculated. Sleep architecture was similar on the two study nights. Sleep-induced partial upper airway flow limitation occurred in all patients in the initial study. Autosetting nasal continuous positive airway pressure (CPAP) applied at a mean maximal pressure of 6 +/- 1 cm H(2)O eliminated flow limitation throughout sleep on the treatment night. Blood pressure was markedly reduced on the treatment night [(128 +/- 3)/(73 +/- 3)] when compared with the initial nontreatment study night [(146 +/- 6)/(92 +/- 4)], p = (0.007)/(0.002). We conclude that partial upper airway obstruction during sleep in women with preeclampsia is associated with increments in blood pressure, which can be eliminated with the use of nasal CPAP.

Adult↗

PubMed2006

Effects of tamsulosin on resting urethral pressure and arterial blood pressure in anaesthetized female dogs.

The purposes of the present study were to investigate the effects of the alpha1-adrenoceptor antagonists tamsulosin, prazosin and urapidil on resting urethral pressure in anaesthetized female dogs, and to compare the results with their effects on arterial blood pressure. Tamsulosin decreased resting maximal urethral pressure in the urethral pressure profile in a dose-dependent fashion, whereas it had almost no effect on mean arterial blood pressure. Prazosin and urapidil also dose-dependently decreased resting maximal urethral pressure, but these effects were accompanied by decreases in mean arterial blood pressure. Thus, of these three compounds, tamsulosin dose-dependently decreased resting maximal urethral pressure with negligible effect on mean arterial blood pressure in female dogs. These results suggest that tamsulosin will be useful in the treatment of voiding dysfunction associated with bladder outlet obstruction in women, with little hypotensive effect.

Adrenergic alpha-Antagonists↗

PubMed2002

Influence of quality of sleep on the nocturnal decline in blood pressure during ambulatory blood pressure monitoring.

OBJECTIVE: To assess the influence of the quality of sleep on the nocturnal physiological drop in blood pressure during ambulatory blood pressure monitoring. METHODS: We consecutively assessed ambulatory blood pressure monitoring, the degree of tolerance for the examination, and the quality of sleep in 168 patients with hypertension or with the suspected "white-coat" effect. Blood pressure fall during sleep associated with a specific questionnaire and an analogical visual scale of tolerance for ambulatory blood pressure monitoring were used to assess usual sleep and sleep on the day of examination. Two specialists in sleep disturbances classified the patients into 2 groups: those with normal sleep and those with abnormal sleep. RESULTS: Fifty-nine (35 %) patients comprised the abnormal sleep group. Findings regarding the quality of sleep on the day of ambulatory blood pressure monitoring as compared with those regarding the quality of sleep on a usual day were different and were as follows, respectively: total duration of sleep (-12.4 +/- 4.7 versus -42.2 +/- 14.9 minutes, P=0.02), latency of sleep (0.4 +/- 2.7 versus 17 +/- 5.1 minutes, P<0.001), number of awakenings (0.1 +/- 0.1 versus 1.35 +/- 0.3 times, P<0.001), and tolerance for ambulatory blood pressure monitoring (8 +/- 0.2 versus 6.7 +/- 0.35, P=0.035). An abnormal drop in blood pressure during sleep occurred in 20 (18%) patients in the normal sleep group and in 14 (24%) patients in the abnormal sleep group, P=0.53. CONCLUSION: Ambulatory blood pressure monitoring causes sleep disturbances in some patients, and a positive association between quality of sleep and tolerance for the examination was observed.

Blood Pressure↗

PubMed1989

Effects of venous pressure elevation on myogenic vasoconstrictive responses to static and dynamic arterial pressures.

In order to establish the nature of the stretch-evoked dynamic properties of vascular smooth muscle in arterioles, we have examined the static and dynamic effects of both arterial pulse pressure and elevated venous pressure on the resistance vessels (arteries and arterioles) in an intestinal mesenteric preparation derived from dogs. The dynamic myogenic response to stretch stimuli was directly related to both the frequency of arterial pulse pressure (1-20 c/min) and the level of venous pressure (0-45 mmHg). Under elevated venous pressure (20 mmHg), the mean arterial flow decreased with an increase in the frequency of arterial pulse pressure. The arteriolar vascular tone (namely, vascular resistance) was seen to be enhanced. We found that elevated venous pressure promotes active constriction (9-53%) of arteriolar smooth muscle (myogenic mechanism). The elevation of venous pressure also caused a rhythmic constriction (vasomotion) in the site of both vein and artery, which was completely abolished by an alpha-blocker (phentolamine). The results suggest that during venous pressure elevation a very pronounced myogenic constriction in terminal arterioles is caused by either a local neural reflex or a propagated myogenic response in the arteriolar network.

Animals↗

PubMed1977

Skin perfusion pressure measured as the external pressure required to stop isotope washout. Methodological considerations and normal values on the legs.

The skin perfusion pressure was measured as the external pressure required to stop blood flow, as evidenced by cessation of the washout of an intracutaneous depot of [131I-]antipyrine mixed with histamine. The external pressure on the skin was measured by an 11 x 11 cm slack air-filled plastic cushion connected to a mercury manometer and interposed between the labelled area and a blood pressure cuff. The 'flow cessation external pressure' (FCEP) varied parallel to the intra-arterial femoral mean blood pressure, but was on the average 10.8 mmHg (SD 6.4) lower. FCEP was measured on twenty normal subjects at four different segments of the leg. The average differences between auscultatory brachial mean blood pressure and FCEP were: thigh 12.0 mmHg (SD 7.6); calf 10.4 mmHg (SD 7.4); ankle 12.9 mmHG (SD 10.1); foot 20.2 mmHg (SD 12.1). The SD of the difference between measurements on two different days, performed in forty-four patients with different degrees of occlusive arterial disease, varied between 5.6 and 8.3 mmHg at the different levels. The present data indicate that the skin perfusion pressure on the legs in normal subjects lies approximately 10 mmHg lower than the systemic mean arterial blood pressure.

Arterial Occlusive Diseases↗

PubMed1997

Pressure relief characteristics in alternating pressure air cushions.

In this study a computerised system was used which continuously measured air pressure, interface pressure and pressure-time cycle characteristics of an alternating pressure air cushion (APAC), and calculated the time the interface pressure remained below three chosen thresholds of 20, 40 and 60 mm Hg. Ten healthy volunteers were used to evaluate the pressure relieving characteristics of four APACs. Results indicated significant differences between products when the threshold periods were analysed, showing some devices were not capable of relieving interface pressures below 20 mm Hg. Though deflation pressure decreased to nearer zero, interface pressure did not follow suit.

Adult↗

PubMed1999

Pain in the arms induced by markedly increased intravascular pressure decreases after repeated exposures to moderately increased pressures.

It is well documented that exposure to high gravitational (G)-load in the head-to-foot direction may induce arm pain. Such G-induced arm pain is of vascular origin and caused by markedly increased pressure in the arm vessels. It has been hypothesized that the arm pain is due to pressure-induced overdistension of local blood vessels. Indeed, elevation of local intravascular pressure to levels that induce considerable arm pain results in distension of both veins and arteries. There appears to be a paucity of data regarding the effects of repeatedly increasing intravascular pressure in the arms. Accordingly, the purpose of the present study was to investigate the effect of iterative exposures to moderate pressure elevations in the arm vessels (here termed "pressure training") on the pressure distension relationships of the vessels and on pressure-induced arm pain. To experimentally induce increased transmural pressure over the vessel walls of the arms we used a modified version of a method described elsewhere; this method has also proven a useful tool for simulating G-induced arm pain.

Adaptation, Physiological↗

PubMed1992

A clinical comparison of two pressure-reducing surfaces in the management of pressure ulcers.

The purpose of this study was to compare the clinical outcomes of pressure ulcers treated on a low-air loss bed and a foam mattress with loose-fitting top cover. The two-group, non-randomized study design consisted of a convenience sample of 20 subjects: 10 subjects treated on the low-air loss bed and 10 subjects treated on the foam mattress with loose-fitting top cover. Subjects were selected from among patients located in the medical/surgical, critical care, and the skilled nursing units of a metropolitan public teaching hospital. Descriptive data, laboratory data, pressure ulcer transparency drawing, and pressure ulcer photographs were obtained on each subject every seven days from two to four weeks. A one-way analysis of variance indicated that there was no statistically significant difference in the pressure ulcer outcomes of subjects treated on the low-air loss bed (Mediscus) compared to the pressure ulcer outcomes of subjects treated on the foam mattress with loose-fitting top cover (Comfortex). Analysis of covariance further indicated no statistically significant difference in the pressure ulcer outcome of subjects treated on either pressure-relieving surface according to the subjects': a) age, percent ideal body weight, presence of pressure ulcer infection; b) leukocyte count, total lymphocyte count, and albumin level; and c) level of sensory perception, moisture, activity, mobility, nutrition, friction, and shear. Results from this study indicate that the low-air loss bed and foam mattress with loose-fitting top cover provide comparable pressure ulcer outcomes. Implications for nursing and recommendations for further study are included in the text.

Air↗

PubMed1991

Effects of mechanical and pharmacologic manipulations on portal pressure, central venous pressure, and heart rate in dogs.

Central venous pressure (CVP), portal pressure (PP), and heart rate (HR) were monitored in 6 female, sexually intact, middle-age Beagles during temporary portal vein obstruction, anesthetic recovery, abdominal bandaging, and propranolol administration. Intraoperative baseline PP was 7.3 mm of Hg (+/- 1.7 SD). Portal pressure was significantly increased throughout portal vein occlusion, but returned to baseline values 2 minutes after release of the ligature. Central venous pressure was significantly decreased throughout portal vein occlusion, but did not differ significantly from baseline values 3 minutes after release of the portal vein ligature. Portal pressure increased significantly (8 +/- 3.3 mm of Hg) over baseline values after application of an abdominal bandage; however, CVP did not change significantly. During postoperative monitoring, CVP and PP did not change significantly from respective 18-hour mean postoperative values in resting dogs. At 60 and 75 minutes after surgery, heart rate was significantly increased over the 18-hour mean. Portal pressure and CVP, respectively, were significantly increased over intraoperative baseline values in the first hour and the first 8 hours after surgery. Postoperative CVP and HR were significantly correlated. Individual measurements of PP in dogs that were abdominal pressing during barking or defecation were significantly increased (9 +/- 3 mm of Hg) above measurements taken after cessation of abdominal press. Portal pressure measurements in standing dogs decreased 7.5 +/- 2 mm of Hg, compared with measurements of the same dog in lateral recumbency. Central venous pressure was inaccurate in dogs performing abdominal press. Portal pressure did not decrease significantly from baseline after injection of propranolol (2 mg/kg, IV).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

[Changes in CSF pressure induced by acetazolamide administration test--as an indicator of shunt operation for so-called normal pressure hydrocephalus].

Lumber subarachnoid pressure was monitored via intrathecally introduced catheter in 9 patients, who showed ventricular dilatation on brain CT and were suspected of normal pressure hydrocephalus. During the pressure measurement, 500 mg of acetazolamide was rapidly injected intravenously and changes of CSF pressure were recorded. The results of the study were compared to clinical signs, brain CT findings and results of continuous pressure monitoring. The types of response of CSF pressure induced by acetazolamide administration were classified into 2 groups. In 5 cases (Group A), more than 50 percent increase of CSF pressure compared to the resting value was noted. On the contrary, in the remaining 4 cases (Group B), CSF pressure showed only slight increase (less than 25 percent or none). VP shunt was performed in 4 cases in Group A. Definite improvement of clinical symptoms was observed in all of these surgically treated cases. Correlation was found between the response to Acetazolamide administration and the appearance of B wave in the continuous spinal pressure monitoring. This study suggests that Acetazolamide test may be useful diagnostic test to select the patients for shunt operation.

Acetazolamide↗

PubMed1990

[Clinical significance of nocturnal blood pressure and blood pressure variability: analysis of 522 cases].

Purpose of the study was to investigate whether and to what extent blood pressure variability and average night-time blood pressure are related to cardiovascular complications in hypertension. To this aim 60 normotensive and 462 hypertensive subjects were studied by means of non-invasive 24 hour blood pressure monitoring, using either the Avionics, or the ICR Spacelabs, or the Takeda system. Each subject was attributed a target organ damage score on the basis of 12-lead electrocardiogram, chest X-ray and fundoscopy, starting from 0 (no damage) up to 5 (maximum degree of damage). The 522 subjects were subsequently subdivided into 5 classes of increasing average daytime diastolic blood pressure. In each class a higher degree of cardiovascular complications was present in the subjects with the higher blood pressure variability and the higher average night-time blood pressure. From these results it may be inferred that both blood pressure variability and night-time blood pressure are related to the degree of target organ damage in hypertension. This stresses the importance of recording blood pressure throughout the 24 hours.

Adult↗

PubMed1989

The effects of propofol on intracranial pressure and cerebral perfusion pressure in patients with brain tumors.

In 7 patients with a brain tumor and intracranial hypertension treated by ventriculosubcutaneous drainage, intracranial pressure and cerebral perfusion pressure were continuously monitored during induction of anesthesia with fentanyl 1.5 micrograms/kg, propofol 2.5 mg/kg and vecuronium 0.1 mg/kg. End-tidal pCO2 was kept constant by manual ventilation and arterial pCO2 was verified before induction and before and after intubation. Five minutes after induction the patients were intubated and measurements continued for five more minutes. Mean arterial pressure decreased from 102 (+/- 9.8) mmHg to 57 (+/- 11.6) mmHg (p less than 0.01). Intracranial pressure did not change significantly before intubation. However in two patients intracranial pressure increased before intubation due to a significant rise in arterial pCO2. In 4 of the 7 patients an important increase to 25 (+/- 4.6) mmHg in intracranial pressure was observed during intubation. Cerebral perfusion pressure decreased from 88 (+/- 4.6) to 45 (+/- 9.8) mmHg (p less than 0.01) before intubation, but did not differ from the baseline during and after intubation. It is concluded that propofol 2.5 mg/kg in a bolus injection does not increase ICP but can produce a significant decrease of the cerebral perfusion pressure due to a marked decrease in mean arterial pressure in patients with a brain tumor.

Adult↗

PubMed1985

The relationship between subcutaneous tissue pressures and intramuscular pressures in normal and edematous legs.

The interstitial hydrostatic pressure is affecting fluid movements at microvascular level. A disturbance in the Starling equilibrium results in edema formation. The effect of venous outflow and lymphatic obstructions in human, on the interstitial fluid pressures subcutaneously and intramuscularly and the possible interaction between veins and lymphatics was studied. Utilizing a slit-catheter technique, subcutaneous tissue and intramuscular pressures were measured bilaterally in 10 patients with venous outflow obstruction and in 10 patients with lymphatic obstruction. In lymphatic obstruction the subcutaneous tissue pressure was significantly elevated as well as the intramuscular pressure, while in venous obstruction the subcutaneous tissue pressure was normal. The intramuscular pressure was significantly elevated during exercise reaching 60 mm Hg or more, combined with severe pain. Pain did not occur in patients with lymphatic obstruction. This study suggests that in lymphatic obstruction there is also an involvement of either deep lymphatics, venous dysfunction or a combination of both. Intramuscular pressures do not reach the critical level for pain during exercise. In venous obstruction mainly the intramuscular compartment is involved and interstitial pressure reaches values well above 60 mm Hg during exercise, at which level pain occurs, possibly due to tension of painreceptors in the muscle fascias.

Adult↗