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PubMed1997

Hemodynamic monitoring: a comparison of research and practice.

BACKGROUND: Measurement of hemodynamic parameters is a common practice and is well researched, but little information is available on the translation of the research into actual practice. OBJECTIVES: To determine (1) the current practice of hemodynamic measurement in relation to positioning of patients and (2) the barriers to use of research related to hemodynamic monitoring. METHODS: A stratified, random, national sample of 1000 members of the American Association of Critical-Care Nurses was surveyed by mail about hemodynamic monitoring procedures related to the positioning of patients and beds, technique used to determine the position of the bed, number of measurements of cardiac output, use of iced versus room-temperature injectate, use of printed or digital information, nurses' input into written procedures, and barriers to research utilization. RESULTS: In actual practice, 24.1% of the respondents always keep the bed flat when measuring pulmonary artery pressures, 55.0% elevate the head of the bed 30 degrees or less, 80.7% always have patients supine for measurements, and 13.3% place patients in lateral or other positions. Unit policy dictated the flat position in 25.8% of the sample; nurse managers (41.4%), staff nurses (27.5%), and staff committees (31.2%) were involved in writing the procedure. Respondents viewed research related to hemodynamic monitoring procedures as relevant and valuable. The greatest barriers to utilization were lack of staff support for implementation, insufficient time to implement research findings, and feelings among nurses that they lacked authority to implement change. CONCLUSIONS: Research findings are generally being implemented at the bedside, although not completely or consistently. Minimizing the barriers to use of research is within the scope of nurses' practice.

Cardiac Output↗
PubMed1991

Nuclear hemodynamic vertebrobasilar insufficiency. A new approach with the xenon Xe 133 method.

Vertebrobasilar insufficiency is a well-known syndrome, but no corresponding hemodynamic deficit has yet been established. We propose to define nuclear hemodynamic vertebrobasilar insufficiency on the basis of an oligemia lower than 35 mL/100 g per minute in the brain stem-cerebellar region with use of the xenon Xe 133 inhalation method. Fifteen patients fulfilling this criterion underwent four-vessel angiography, computed tomography, and a standardized neurologic examination. An acetazolamide test showed poor reactivity in more than half of the patients, sometimes specifically in the vertebrobasilar area. With use of single-photon emission computed tomography and intravenous technetium Tc 99m-labeled hexamethylpropyleneamineoxime in two cases, the considerable decrease of regional cerebral blood flow in the brain stem-cerebellar region was confirmed. An excellent correlation was observed between the existence of nuclear hemodynamic vertebrobasilar insufficiency and angiographically proved arterial occlusions. The dominant nuclear oligemic zone was regularly on the side of the anatomic arterial chief lesion. Clinical manifestations included rare transient ischemic attacks (in one of 15 patients), intermittent basilar symptoms (in 15 of 15 patients), and a subacute vertebrobasilar "threatening" syndrome. Thus, imaging of a nuclear hemodynamic vertebrobasilar deficit provides an objective basis to the diagnosis of vertebrobasilar insufficiency and useful objective data for revascularization surgery.

Acetazolamide↗
PubMed2001

Hemodynamic effects of supervised calf muscle exercise in patients with venous leg ulceration: a prospective controlled study.

HYPOTHESIS: Because more than two thirds of patients with venous ulcer have an impaired calf muscle pump, enhancement of its ejecting ability with physical training may generate an improved hemodynamic milieu sufficient to promoting ulcer healing. This study evaluated the effects of short-term supervised calf exercise on calf muscle pump function and venous hemodynamics in limbs with venous ulceration. DESIGN: Prospective controlled study. SETTINGS: University-associated tertiary care hospital. PATIENTS: The study consisted of 2 groups. An exercise group comprised 10 patients (median age, 72 years) receiving supervised isotonic calf muscle exercise for 7 consecutive days. A control group comprised 11 patients matched with those in the exercise group for age, sex, ulcer size, and ulcer duration (all, P>.09). Patients in both groups had perimalleolar venous leg ulcers, impaired calf muscle function (ejection fraction, <60%), and full ankle joint movement. INTERVENTIONS: After providing a complete clinical history, both groups underwent a physical examination, venous duplex scanning, and air plethysmography. The venous filling index, venous volume, residual venous volume, and residual volume fraction of the calf on standing were measured plethysmographically at baseline and on day 8, in addition to calf muscle endurance as determined by the maximal number of plantar flexions performed against a fixed 4-kg resistance during 6 minutes (1 flexion/s). Operators were blinded to the subject's group. Exercise in the first group entailed consecutive active plantar flexions using a standardized 4-kg resistance pedal ergometer. Subjects daily completed 3 sets of flexions of 6 minutes each. All patients had short-stretched compression bandaging. MAIN OUTCOME MEASURES: The ejected venous volume and ejection fraction were evaluated in both groups at baseline and on day 8. RESULTS: Both groups had a similar hemodynamic performance at baseline for all the variables evaluated (P>.10). After 7 days of exercise, patients in the exercise group improved their ejected venous volume by 67.5%, ejection fraction by 62.5%, residual venous volume by 25% (all 3, P =.006), and their residual volume fraction by 28.6% (P =.008). Changes in the control group within the same period were small (all, P>.10). By day 8, the exercise group had a significantly better ejected venous volume (P<.001) and ejection fraction (P<.001) than the control group. The venous filling index and the venous volume did not change (P>.50) in either study group. Calf muscular endurance in the exercise group increased 135%, from a median 153 plantar flexions at baseline to 360 on day 7 (P<.001). CONCLUSIONS: By increasing the muscular endurance, efficacy, and power of the calf muscle, isotonic exercise improves its ejecting ability and the global hemodynamic status in limbs with venous ulceration. Prospective evaluations of the clinical effects of calf muscle pump strengthening for the treatment of venous leg ulceration are indicated by the results of this study.

Aged↗
PubMed2002

Clinical and hemodynamic significance of the greater saphenous vein diameter in chronic venous insufficiency.

HYPOTHESIS: As the compliant greater saphenous vein (GSV) adjusts its luminal size to the level of transmural pressure, measurement of its diameter, reflecting the severity of hemodynamic compromise in limbs with GSV reflux, may simplify the hemodynamic criteria of patient selection for saphenectomy. OBJECTIVE: To evaluate the clinical significance of GSV diameter determined in the thigh and calf as a marker of global hemodynamic impairment and clinical severity in a model comprising patients with saphenofemoral junction and truncal GSV incompetence. DESIGN: A cohort study. SETTING: University-associated tertiary care hospitals in Brazil and England. PATIENTS: Eighty-five consecutive patients, aged 28 to 82 (mean, 46.2) years; 112 lower limbs with saphenofemoral junction and truncal GSV incompetence were investigated. INTERVENTIONS: Clinical examination was followed by clinical, etiological, anatomical, and pathophysiological classification (CEAP), vein duplex, and air plethysmography. The GSV diameter was measured on standing at the knee, and at 10, 20, and 30 cm above and below the knee, and in the thigh and calf, respectively, using B-mode imaging. The venous filling index (VFI), venous volume (VV), and residual volume fraction (RVF) were measured by air plethysmography. MAIN OUTCOME MEASURES: The GSV diameter was correlated with the VFI, VV, RVF, and CEAP. The value of the GSV diameter for predicting the presence of critical reflux (VFI >7 mL/s) or the absence of abnormal reflux (VFI <2 mL/s) was determined with receiver-operator curves. RESULTS: The GSV diameter increased significantly overall with CEAP (P<.001) and also increased progressively with proximity to the saphenofemoral junction. The VFI, VV, and RVF increased significantly from CEAP(0) through CEAP(4-6); the VFI correlated well with VV, RVF, and CEAP (P<.001 for all). The GSV diameter at all 7 limb levels studied correlated well with VV (except at the distal calf), VFI, RVF, and CEAP (P< or =.009 for all). A GSV diameter of 5.5 mm or less predicted the absence of abnormal reflux, with a sensitivity of 78%, a specificity of 87%, positive and negative predictive values of 78%, and an accuracy of 82%. A GSV diameter of 7.3 mm or greater predicted critical reflux (VFI >7 mL/s), with an 80% sensitivity, an 85% specificity, and an 84% accuracy. CONCLUSION: The GSV diameter proved to be a relatively accurate measure of hemodynamic impairment and clinical severity in a model of saphenofemoral junction and GSV incompetence, predicting not only the absence of abnormal reflux, but also the presence of critical venous incompetence, assisting in clinical decision making before considering greater saphenectomy.

Adult↗
PubMed2002

Defining the role of computed tomography in blunt abdominal trauma: use in the hemodynamically stable patient with a depressed level of consciousness.

HYPOTHESIS: Controversy exists regarding the use of diagnostic peritoneal lavage (DPL) vs computed tomography (CT) in the evaluation of blunt abdominal trauma. It has been suggested that one role for DPL is to diagnose bowel injuries in hemodynamically stable patients with an unreliable abdominal examination result. Our hypothesis is that CT is specific and sensitive for diagnosing hollow viscus injuries and is therefore an appropriate diagnostic modality in the hemodynamically stable blunt trauma patient with an unreliable abdominal examination result due to a depressed level of consciousness. DESIGN: Retrospective consecutive case review. SETTING: An urban level II trauma center. PATIENTS: The medical records of 1388 consecutive patients admitted between January 1, 1991, and December 31, 2000, were reviewed. Inclusion criteria included blunt trauma patients who were hemodynamically stable (defined as a systolic blood pressure >90 mm Hg) with unreliable abdominal examination results secondary to a depressed level of consciousness (Glasgow Coma Scale score <11). MAIN OUTCOME MEASURES: Hollow viscus injury diagnosed by CT and missed diagnosis of hollow viscus injury by CT. RESULTS: Of 1388 patients who met entry criteria, 87 had hollow viscus injuries; CT identified 85 of these injuries. Computed tomography diagnosed intestinal injury with a sensitivity of 97.7%, specificity of 98.5%, and an overall accuracy of 99.4%. CONCLUSION: At our institution, CT is a reliable and accurate diagnostic modality when used to evaluate hollow viscus injuries in the hemodynamically stable blunt trauma patient with an unreliable abdominal examination result due to a depressed level of consciousness.

Abdominal Injuries↗
PubMed1979

Periorbital ultrasound findings. Hemodynamics in patients with cerebral vascular disease.

The direction of supraorbital and frontal artery flow and its response to compression of the superficial temporal, facial, and angular arteries were measured in 250 carotid arteries in 114 patients. All patients had arch and/or selective carotid arteriography. The carotid arteries were placed into the following three groups: hemodynamically normal, greater than 60% occlusion of the internal carotid artery, and total occlusion of the internal carotid artery. The test's accuracy was 94.5% in the hemodynamically normal group, 68.8% in the totally occluded group, and only 51.4% in the group with hemodynamically significant stenosis. Although the carotid Doppler examination is not reliable in detecting hemodynamically significant lesions of the internal carotid artery, it is valuable in assessing the adequacy of collateral cerebral circulation.

Carotid Artery Diseases↗
PubMed1980

Role of the systemic vasculature in the hemodynamic response to changes in plasma ionized calcium.

Hemodynamic consequences of sustained (one hour) hypocalcemia and hypercalcemia (plasma ionized calcium concentration [Ca++] maintained approximately 60% below or above normal, encompassing the clinical range) were studied and the influence of beta blockade on these hemodynamic alterations examined in 16 anesthetized, closed-chest dogs. Alterations in [Ca++] were associated with directionally similar changes in mean arterial pressure, whereas on the average cardiac output remained unchanged. Thus, the peripheral vasculature played an important role in the hemodynamic response to alterations in [Ca++]. The state of beta adrenergic activity was an important determinant of the hemodynamic response to hypocalcemia. Prior to beta blockade, hypocalcemia was associated with decreased systemic vascular resistance, whereas after beta blockade with propranolol hydrochloride, systemic vascular resistance was not different from control except at the five-minute observation period, and cardiac output and stroke volume fell.

Adrenergic beta-Antagonists↗
PubMed1984

Abdominal aortic cross-clamping. Metabolic and hemodynamic consequences.

We address the question of whether an oxygen debt develops during a period of abdominal aortic cross-clamping that may explain observed hemodynamic changes. Group 1 received morphine sulfate (1 mg/kg) during induction of anesthesia. Group 2 received same dose of morphine sulfate. Group 3 received 4 mg/kg of morphine sulfate. We measured the oxygen consumption (VO2) and the carbon dioxide production levels (VCO2), as well as hemodynamic and biochemical parameters. In groups 1 and 3, VO2 and VCO2 decreased 10% to 13% following abdominal aortic cross-clamping compared with values measured before cross-clamping. In group 2, VO2 and VCO2 decreased 3% and 7%, respectively. On unclamping, the greatest increase in VO2 was observed in group 3 (26%), while in groups 1 and 2, VO2 rose 18% and 5%, respectively. In all three groups, metabolic changes were not paralleled by hemodynamic or temperature changes. Results indicate that oxygen debt developed during abdominal aortic cross-clamping, but this has no effect on hemodynamic changes seen after unclamping. Higher dosage of narcotic administered during anesthetic induction did not temper increase in metabolic rate observed after unclamping.

Aged↗
PubMed1988

Systemic complement activation produces hemodynamic changes characteristic of sepsis.

Zymosan was administered intravenously in graded doses to Sprague-Dawley rats to investigate the hemodynamic effects of systemic complement activation. At two hours, thermodilution cardiac output, mean arterial pressure, heart rate, systemic vascular resistance, hematocrit, effective hepatic and renal blood flows, and percent change in total hemolytic complement activity were measured on all animals. Progressively increasing doses of zymosan produced characteristic hemodynamic changes of progressively deteriorating stages of hyperdynamic sepsis. In addition, complement activation resulted in a redistribution of systemic blood flow with hepatic hypoperfusion similar to that seen in sepsis. Renal blood flow was unaffected early after complement activation. Additional rats were studied from the control and a representative zymosan-treated group at 24 and 48 hours to determine if the hemodynamic changes observed at two hours persisted or resolved. All systemic hemodynamic measures returned to normal at both 24 and 48 hours. Liver blood flow, however, remained depressed and actually deteriorated over time. Renal perfusion, which was stable at both two and 24 hours, fell below control values in the zymosan-treated group at 48 hours. We conclude that complement may be a mediator of both systemic and visceral flow abnormalities that precede, and perhaps precipitate, organ failure in trauma and sepsis.

Animals↗
PubMed1997

Effects of pneumoperitoneum with carbon dioxide, argon, or helium on hemodynamic and respiratory function.

OBJECTIVE: To evaluate the effects of pneumoperitoneum with carbon dioxide, argon, and helium; different abdominal pressures (ie, 8, 12, and 16 mm Hg); and different positions (ie, head up, head down, supine) on hemodynamic and respiratory function in a porcine model. DESIGN: Prospective randomized trial. SETTING: Animal research laboratory. ANIMALS: Eighteen pigs weighing 25.5 +/- 6.9 kg (mean +/- SD). INTERVENTIONS: General anesthesia with endotracheal intubation. Implantation of pulmonal artery catheter and central venous line in jugular vein and catheters in femoral artery and vein. Carbon dioxide, argon, or helium was insufflated through a cannula in the left upper quadrant. The type of gas was randomly assigned to each animal. After recording baseline values at the beginning and at the end without pneumoperitoneum, each animal was placed in 1 of the 3 positions and under 1 of the 3 pressures kept by the insufflator. After 15 minutes of adaptation to the new circumstances, all factors were recorded. This procedure was repeated until all 9 combinations of pressures and positions were evaluated. MAIN OUTCOME MEASURES: Cardiac output; heart rate; stroke volume; right ventricular stroke work; pressures in the pulmonal artery, vena cava, and femoral artery and vein; systemic vascular resistance; respiratory pressure; tidal volume; pH; base excess; oxygen partial pressure; and carbon dioxide partial pressure. RESULTS: The type of gas did not affect cardiac output. Only carbon dioxide demonstrated negative effects on respiratory function. Argon markedly increased afterload. Carbon dioxide increased central venous and mean arterial pressure, which was only moderate using helium. A head-up position decreased cardiac output and central venous pressure and increased mean arterial and peripheral venous pressures, which were partly compensated in a head-down position. An intraperitoneal pressure of 16 mm Hg increased peripheral and central venous pressures, heart rate, and respiratory pressure, and decreased cardiac output, tidal volume, and pH. CONCLUSIONS: Helium may be an alternative gas to establish pneumoperitoneum because it does not have any effect on respiratory function and has only a moderate effect on hemodynamic function. Argon insufflation has some hemodynamic disadvantages. An intraperitoneal pressure greater than 12 mm Hg and a head-up position should be avoided because both have a markedly negative effect on respiratory and hemodynamic factors.

Animals↗
PubMedDate not supplied

Hemodynamic monitoring and pacing with one catheter: a pilot study.

Attempts to incorporate the monitoring of central pressures and pacing into one catheter have heretofore been unsuccessful. Recently, a new catheter for monitoring central hemodynamic pressures, which has a right ventricular port (Chandler pacing port), has been devised, which has been reported to allow for simultaneous acquisition of hemodynamic data and reliable pacemaker function as well. To assess the reliability of this catheter, we studied ten consecutive Swan-Ganz catheterizations utilizing this new catheter system. In all instances, hemodynamic monitoring was established without difficulty. In three instances, because of right heart enlargement, fluoroscopy was necessary to position the pacing probe at the right ventricular apex. In all ten instances, a threshold of less than 2.5 mV was obtained. Isolated PVCs and nonsustained ventricular tachycardia were common during insertion. After initial placement, the threshold for sensing and pacing was assessed every 6 hr. Malfunction occurred in three patients. In all, repositioning was accomplished without marked difficulty; in one it required fluoroscopy. In three instances, the Swan-Ganz pacing catheter system malfunctioned. These data are similar to data utilizing other modalities of temporary pacing and suggest that this catheter may be capable of providing hemodynamic monitoring and pacing from a single percutaneous procedure.

Adult↗
PubMed2005

Renal fractional flow reserve: a hemodynamic evaluation of moderate renal artery stenoses.

The objective of this study was to perform a hemodynamic evaluation of moderate (50-90%) renal artery stenosis (RAS) under conditions of rest and maximum hyperemia. Identifying patients with RAS who have hemodynamically significant stenoses and are most likely to benefit from revascularization is clinically important. Current methods used to evaluate RAS, including angiography, have limitations. Physiologic evaluation of RAS may have a role in identifying patients with hemodynamically significant stenosis. Patients with suspected renovascular hypertension due to aorto-ostial RAS were included in the study. Hyperemia was induced by administration of intrarenal papavarine. Translesional pressure gradients were measured and renal fractional flow reserve (FFR) was calculated using a 0.014'' pressure guidewire. Thirteen patients and 14 arteries with moderately severe (50-90%) RAS were studied. The mean translesional pressure gradient rose from a baseline of 6.3 +/- 3.9 to 17.5 +/- 10.8 mm Hg with maximal hyperemia. The renal FFR ranged from 0.58 to 0.95. There was a poor correlation between angiographic stenosis measurement and the renal FFR (r = -0.18; P = 0.54) and the hyperemic translesional mean pressure gradient (r = 0.22; P = 0.44). There was an excellent correlation between renal FFR and the resting mean translesional pressure gradient (r = -0.76; P = 0.0016) and the hyperemic mean translesional pressure gradient (r = -0.94; P < 0.0001). Selective renal arterial papavarine administration induces maximum hyperemia, permitting the calculation of renal FFR in renal arteries with aorto-ostial stenoses. The renal FFR correlates well with other hemodynamic parameters of lesion severity, but poorly with angiographic measures of lesion severity.

Aged↗
PubMed2000

Rest and exercise hemodynamics before and after valve replacement--a combined Doppler/catheter study.

BACKGROUND: Hemodynamic improvement is a common finding following valve replacement. However, despite a normally functioning prosthesis and normal left ventricular ejection fraction, some patients may show an abnormal hemodynamic response to exercise. METHODS: In a combined catheter/Doppler study, rest and exercise hemodynamics were evaluated in 23 patients following aortic (n = 12) (Group 1) or mitral valve (n = 11) (Group 2) replacement and compared with preoperative findings. Patient selection was based on absence of coronary artery disease and left ventricular failure as shown by preoperative angiography. Cardiac output, pulmonary artery pressure, pulmonary capillary pressure, and pulmonary resistance were measured by right heart catheterization, whereas the gradient across the valve prosthesis was determined by Doppler echocardiography. Postoperative evaluation was done at rest and during exercise. The mean follow-up was 8.2 +/- 2.2 years in Group 1 and 4.2 +/- 1 years in Group 2. RESULTS: With exercise, there was a significant rise in cardiac output in both groups. In Group 1, mean pulmonary pressure/capillary pressure decreased from 24 +/- 9/18 +/- 9 mmHg preoperatively to 18 +/- 2/12 +/- 4 mmHg postoperatively (p < 0.05), and increased to 43 +/- 12/30 +/- 8 mmHg with exercise (p < 0.05). The corresponding values for Group 2 were 36 +/- 12/24 +/- 6 mmHg preoperatively, 24 +/- 7/17 +/- 6 mmHg postoperatively (p < 0.05), and 51 +/- 2/38 +/- 4 mmHg with exercise (p < 0.05). Pulmonary vascular resistance was 109 +/- 56 dyne.s.cm-5 preoperatively, 70 +/- 39 dyne.s.cm-5 postoperatively (p < 0.05), and 70 +/- 36 dyne.s.cm-5 with exercise in Group 1. The corresponding values for Group 2 were 241 +/- 155 dyne.s.cm-5, 116 +/- 39 dyne.s.cm-5 (p < 0.05), and 104 +/- 47 dyne.s.cm-5. There was a significant increase in the gradients across the valve prosthesis in both groups, showing a significant correlation between the gradient at rest and exercise. No correlation was found between valve prosthesis gradient and pulmonary pressures. CONCLUSION: Exercise-induced pulmonary hypertension and abnormal left ventricular filling pressures seem to be a frequent finding following aortic or mitral valve replacement. Both hemodynamic abnormalities seem not to be determined by obstruction to flow across the valve prosthesis and may be concealed, showing nearly normal values at rest but a pathologic response to physical stress.

Adult↗
PubMed1988

Pathogenesis of diabetic glomerulopathy: hemodynamic considerations.

Early stages of diabetes mellitus are characterized by glomerular hyperfiltration in humans and experimental animals. In diabetic rats, single nephron hyperfiltration results from elevations in the glomerular capillary plasma flow rate and hydraulic pressure, which are in turn associated with progressive albuminuria and morphologic injury. Interventions that ameliorate these hemodynamic adaptations afford protection against structural injury. Dietary protein restriction, which lowers glomerular filtration, perfusion, and hydraulic pressure, retards glomerular injury and limits capillary basement membrane thickening in both the glomerular and retinal circulatory beds. Alternatively, selective control of glomerular capillary hypertension using angiotensin I converting enzyme inhibitor therapy limits glomerular injury in this model as well. Each of these interventions is effective even in the absence of improved metabolic control, implying that hemodynamic factors per se are important in this pathogenic process. The pathophysiologic mechanisms of diabetic hyperfiltration remain incompletely elucidated. Recent studies invoke a potential role for atrial natriuretic peptide (ANP). Strict metabolic control abolishes the elevations of glomerular filtration rate and of plasma ANP levels in moderately hyperglycemic diabetic rats. Moreover, infusion of a specific ANP antibody reverses hyperfiltration in diabetic rats. Thus, hyperglycemia-induced chronic volume expansion may trigger ANP release, which in turn contributes to diabetic hyperfiltration. Hemodynamic factors may play an important role in the pathogenesis of extrarenal microangiopathy as well. Elevated peripheral capillary blood flows and/or hydraulic pressure may be found in many peripheral capillaries, in association with thickening of the capillary basement membrane. Dietary protein restriction, which lowers blood flow to many organs, limits retinal as well as glomerular basement membrane thickening in diabetic rats, suggesting that hemodynamically mediated structural injury is a diffuse phenomenon in the diabetic state.

Animals↗
PubMed1996

Vasoactive intestinal peptide in cirrhotic rats: hemodynamic effects and mesenteric arterial receptor characteristics.

Vasoactive intestinal peptide (VIP) blood levels in cirrhosis are elevated, but its hemodynamic and receptor characteristics remain unclarified. We aimed to quantify VIP receptor characteristics in mesenteric arteries, plasma VIP concentration by radioimmunoassay (RIA), and the hemodynamic effects of VIP infusion in bile duct-ligated (BDL) cirrhotic and sham-operated control rats. Mesenteric arterial membranes were prepared by ultracentrifugation, and receptor characteristics were studied using 125I-labeled VIP as a radioligand. For the hemodynamic study, there were four groups: cirrhotic and sham-operated rats were infused with either VIP (50 ng/kg/min for 15 minutes) or equivolumic isotonic saline. Regional blood flows were measured in conscious rats with radioactive microspheres. Receptor studies showed high- and low-affinity binding sites for VIP, which had similar equilibrium dissociation constants (binding affinities) and receptor densities for both the cirrhotic and control rats. Plasma VIP concentrations were significantly elevated in the cirrhotic rats. In both cirrhotic and sham-operated rats, VIP infusion produced plasma levels approximately twofold to threefold increased over the basal levels observed in cirrhotic rats. In cirrhotic rats, VIP infusion did not affect any hemodynamic parameter, whereas in the sham-operated rats VIP infusion significantly increased the mesenteric visceral blood flow. These results show that the hyporesponsiveness to VIP in cirrhotic rats is not attributable to receptor downregulation, implying postreceptor alterations. This suggests that VIP may not play a major role in the maintenance of splanchnic hyperemia in cirrhosis.

Analysis of Variance↗
PubMed1987

Characterization of the dose-concentration-dependent hemodynamic effects of nifedipine in heart failure.

The hemodynamic effects of increasing oral doses of nifedipine (10 to 30 mg) were studied in 12 patients who had low output heart failure. With each set of hemodynamics, serum concentrations of nifedipine were measured to determine the concentration/response relationships. Eleven of twelve patients responded acutely to nifedipine, defined as a reduction in systemic vascular resistance (SVR), and an augmentation in cardiac index (CI) and stroke volume index (SVI). The differential dose effects (X +/- SD) for SVR and SVI for baseline (N = 11), 10 mg (N = 10), 20 mg (N = 3) and 30 mg (N = 4) were: 1913 +/- 486, 1102 +/- 221, 1128 +/- 166, 803 +/- 176 and 17.9 +/- 4.8, 23.8 +/- 4.5, 31 +/- 0.42, 33 +/- 3.5, respectively. All nifedipine doses reduced SVR and increased CI and SVI compared with baseline (P less than .001). The increase in CI and SVI was significantly correlated to the mg/kg dose of nifedipine (r = 0.79; P less than .001). Nifedipine administration resulted in no significant change in central venous pressure, pulmonary capillary wedge pressure, or pulmonary vascular resistance. No relationship could be demonstrated between serum concentrations of nifedipine and any hemodynamic effect. Conclusions drawn were: (1) the afterload reduction effects of nifedipine are acutely efficacious in a large portion of patients with heart failure and this activity supercedes the negative inotropic effects of the drug at doses between 10 and 30 mg; (2) the magnitude of the hemodynamic effects are dose dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Dose-Response Relationship, Drug↗
PubMed1994

Hemodynamic response to the upright posture.

The authors' objective was to review previous studies of immediate (first 30 seconds) and stabilized (30 seconds to 20 minutes) hemodynamic responses of healthy adults to the head-up posture, with particular reference to alteration of such responses in the elderly and the usefulness of such data in the diagnosis of orthostatic hypotension. The immediate response in healthy young adults is characterized by a prompt rise in heart rate, which peaks at about 8 to 15 seconds and then tapers; the arterial pressure and total vascular resistance decrease sharply at 5 to 10 seconds, followed by a rapid rebound and overshoot. Over the first 30 seconds there is a steady parallel decline of thoracic blood volume and stroke volume; there is also an initial surge of cardiac output followed by a steady decrease. During the stabilized response (30 seconds to 20 minutes), the hemodynamic variables are relatively steady, showing average increases in heart rate of about 15 to 30%, in diastolic pressure of 10 to 15%, and in total vascular resistance of 30 to 40%; during the 5th to 20th minutes there are also decreases in thoracic blood volume averaging about 25 to 30%, in cardiac output 15 to 30%, and in pulse pressure about 5 to 10%. It is evident that in normal human subjects, assumption of the upright posture results in profound hemodynamic changes, most of them occurring during the first 30 seconds. In elderly subjects (aged 60-69 years), there are, in the upright posture, lesser increments of heart rate and diastolic pressure, but no significant differences from younger age groups in the response of thoracic blood volume, cardiac output or total vascular resistance. However, beginning at about age 75, there is an increasing incidence of orthostatic hypotension, which averages about 14 to 20% at age 75 and older. The tendency toward orthostatic hypotension in the elderly is due (1) to the structural and functional changes in the circulation itself, (2) to a decline in autonomic function, and (3) to a probable functional deficiency of the skeletal muscle pump. The authors believe that closer hemodynamic monitoring of orthostatic hypotension patients would considerably increase our understanding and aid in the diagnosis of this condition.

Adult↗
PubMed2002

Reconstruction of carotid bifurcation hemodynamics and wall thickness using computational fluid dynamics and MRI.

A thorough understanding of the relationship between local hemodynamics and plaque progression has been hindered by an inability to prospectively monitor these factors in vivo in humans. In this study a novel approach for noninvasively reconstructing artery wall thickness and local hemodynamics at the human carotid bifurcation is presented. Three-dimensional (3D) models of the lumen and wall boundaries, from which wall thickness can be measured, were reconstructed from black-blood magnetic resonance imaging (MRI). Along with time-varying inlet/outlet flow rates measured via phase contrast (PC) MRI, the lumen boundary was used as input for computational fluid dynamic (CFD) simulation of the subject-specific flow patterns and wall shear stresses (WSSs). Results from a 59-year-old subject with early, asymptomatic carotid artery disease show good agreement between simulated and measured velocities, and demonstrate a correspondence between wall thickening and low and oscillating shear at the carotid bulb. High shear at the distal internal carotid artery (ICA) was also colocalized with higher WSS; however, a quantitative general relationship between WSS and wall thickness was not found. Similar results were obtained from a 23-year-old normal subject. These findings represent the first direct comparison of hemodynamic variables and wall thickness at the carotid bifurcation of human subjects. The noninvasive nature of this image-based modeling approach makes it ideal for carrying out future prospective studies of hemodynamics and plaque development or progression in otherwise healthy subjects.

Adult↗