Filling and arterial pressures as determinants of RV stroke volume in the sheep fetus

Right ventricular (RV) function was investigated in nine fetal lambs (125-130 days gestation) that were instrumented with pulmonary artery electromagnetic flow sensors and vascular catheters. Control arterial CO2 and O2 tension, pH, and hematocrit values were 46.1 +/- 1.6 (SD) Torr, 20.6 +/- 1.8 Torr, 7.39 +/- 0.02, and 31 +/- 5.3%, respectively. Control values for right ventricular output (247 +/- 75 ml X min-1 X kg-1), stroke volume (SV, 1.5 +/- 0.4 ml X kg-1), right atrial pressure (3.7 +/- 1.2 mmHg), heart rate (166 +/- 18 beats X min-1), and arterial pressure (AP, 43 +/- 4 mmHg) were unchanged by administration of atropine and propranolol. Withdrawal and infusion of fetal blood with or without concomitant infusion of nitroprusside or phenylephrine produced RV function curves at low, normal, and high arterial pressures. All function curves had a steep ascending limb and a plateau. The breakpoint joining the limbs of the control curve was right atrial pressure 3.4 +/- 1.2 mmHg and SV 1.5 +/- 0.4 ml X kg-1. Increased AP shifted the breakpoint downward. Linear regression of SV on AP from 15 to 95 mmHg at right atrial pressure greater than breakpoint was SV = -0.016 ml X kg-1 mmHg-1 X AP + 2.25 ml X kg-1.     

MR guidance of laser disc decompression: preliminary in vivo experience

BACKGROUND: The mechanism of atrial natriuretic peptide (ANP) release has been difficult to demonstrate in patient studies because of inaccuracies in measuring atrial volumes using conventional techniques. METHODS: Magnetic resonance imaging was performed in 28 clinically stable patients (New York Heart Association class 3) with chronic heart failure to determine right atrial (RA), left atrial (LA), and ventricular volumes. In addition, right heart catheterization was serially performed and plasma ANP levels (in picograms per milliliter) were drawn from the right atrium. RESULTS: Five patients had to be excluded from data analysis for technical reasons. The remaining 23 patients had the following hemodynamic measurements (mean +/- SD): RA mean pressure 7+/-5 mm Hg, pulmonary artery mean pressure 28+/-10, pulmonary capillary wedge pressure 21+/-8 mm Hg, and cardiac index 2.9+/-1.4 (L/min/m2), respectively. Plasma ANP levels were significantly elevated at 162+/-117 (normal range 20 to 65 pg/ml, p < 0.05), as were LA and RA volumes compared with healthy controls (RA volume 128+/-64 ml vs 82+/-25 ml, p < 0.05; LA volume 157+/-54 ml vs 71+/-24 ml, p < 0.01, respectively). ANP showed a stronger relation with atrial volumes (RA volume, r = 0.91, p = 0.0001; LA volume, r = 0.80, p = 0.001) than with atrial pressures (RA mean pressure, r = 0.45, p = 0.03; pulmonary capillary wedge pressure, r = 0.67, p = 0.001). A subgroup analysis of patients with increased RA or LA volumes (>1 SD of mean of controls) revealed a stronger relation between ANP and RA volumes than between ANP and LA volumes. CONCLUSIONS: These data suggest that increased right heart volume with subsequent increased atrial stretch is the major determinant for ANP release in patients with stable CHF.     

Cardiac afferents attenuate the muscle metaboreflex in the rat

The influence of cardiac afferents on the muscle metaboreflex was examined in 16 rats instrumented with a Silastic-tipped catheter in the pericardial space and right atrium, Doppler ultrasonic flow probe and a pneumatic vascular occluder around the terminal aorta, and a Teflon catheter in the thoracic aorta. In protocol I (cardiac efferent and afferent blockade), the muscle metaboreflex was examined under three experimental conditions: 1) control, 2) cardiac autonomic efferent blockade [intrapericardial methylscopolamine (10 micrograms/kg) and propranolol (50 micrograms/kg)], and 3) combined cardiac autonomic efferent and afferent blockade (intrapericardial procainamide, 2%). In protocol II (blood volume expansion), the muscle metaboreflex was examined before and after 15% blood volume expansion. Mild treadmill exercise (9 m/min, 10% grade) increased heart rate (71 +/- 9.4 beats/min), mean arterial pressure (12 +/- 2.0 mmHg), and terminal aortic blood flow velocity (6 +/- 1.0 kHz). During exercise, a reduction of terminal aortic blood flow velocity (10.5 +/- 1.1%) reduced mixed venous PO2 18 +/- 6%. The gain of the muscle metaboreflex in the control condition was 14.6 +/- 2.9 mmHg/kHz. Efferent blockade reduced the gain 51 +/- 7%. However, combined cardiac efferent and afferent blockade increased the gain 207 +/- 64% above the efferent blocked condition and restored the gain to levels above those obtained in the control condition (18.3 +/- 4.6 mmHg/kHz). In addition, 15% blood volume expansion reduced the gain of the muscle metaboreflex regulation of mean arterial pressure and heart rate (44 +/- 9.5% and 41 +/- 12.0%, respectively). Thus cardiac afferents tonically inhibit the pressor response to a reduction in terminal aortic blood flow velocity during exercise.     

Central venous pressure, pulmonary capillary wedge pressure and intrathoracic blood volumes as preload indicators in cardiac surgery patients

OBJECTIVE: Monitoring of cardiac preload is mainly performed by measurement of central venous and pulmonary capillary wedge pressure in combination with assessment of cardiac output, applying the pulmonary arterial thermal dilution technique. However, the filling pressures are negatively influenced by mechanical ventilation and the pulmonary artery catheter is criticized because of its inherent risks. Measurement of right atria, right ventricular, global end diastolic and intrathoracic blood volume index by arterial thermal dye dilution utilizing the COLD-system may represent an alternative. METHODS: In 30 CABG patients with an uncomplicated postoperative course the mentioned parameters were measured 1, 3, 6, 12 and 24 h postoperatively to prove their qualification as preload indicators: As patients received no inotropic support, changes of cardiac index and stroke volume index must correlate to changes of presumably preload indicating parameters. RESULTS: When arterial and pulmonary arterial thermal dilution were compared, no differences were found; the correlation coefficient being 0.96, the bias 0.16 l/min per m2 (2.4%) and coefficients of variation did not exceed 7%. Changes of central venous pressure, capillary wedge pressure, right atrial end diastolic volume index and right ventricular end diastolic volume index did not correlate at all to changes of cardiac and stroke volume index (coefficients ranged from -0.01 to 0.28). In contrast, intrathoracic and global end diastolic blood volume indices with coefficients from 0.76 to 0.87, did show a good correlation to cardiac and stroke volume index. CONCLUSION: Central venous pressure, capillary wedge pressure, right atrial and right ventricular end diastolic volumes are no suitable preload parameters in cardiac surgery intensive care, compared to intrathoracic and global end diastolic blood volumes. The latter show a higher clinical value and can be obtained by less invasive methods, as no pulmonary artery catheter is required.     

Influence of urapidil on cerebrospinal fluid pressure in humans with uncompromised intracranial compliance

OBJECTIVE: Determine the influence of urapidil on mean lumbar cerebrospinal fluid pressure (CSFP), mean arterial pressure (MAP), mean central venous pressure (CVP) and heart rate (HR) in awake humans without any evidence of cerebral or cardiovascular disease. DESIGN: Open, single-dose volunteer study. INTERVENTIONS: CSFP was measured via a spinal needle after i.v. injection of a single dose of 0.2 mg kg-1 urapidil in six volunteers (2 female, 4 male). MEASUREMENTS AND RESULTS: After administration of urapidil, CSFP increased from 7 +/- 1 mmHg to 10 +/- 1 mmHg (p < 0.05), MAP decreased from 88 +/- 7 mmHg to 74 +/- 5 mmHg (p < 0.05), CPP decreased from 81 +/- 7 mmHg to 64 +/- 5 mmHg (p < 0.05) and CVP decreased from 0 +/- 1 mmHg to -3 +/- 1 mmHg (p < 0.05). CONCLUSION: Our data suggest that in humans with presumed normal intracranial compliance the administration of urapidil causes a small but statistically significant increase in CSFP due to a parallel decrease in MAP.     

Comparison of estimates of right atrial pressure by physical examination and echocardiography in patients with congestive heart failure and reasons for discrepancies

Clinical estimates of right atrial pressure from the jugular venous pulse were accurate when right atrial pressure was normal, but systematically underestimated elevated right atrial pressures. Because the increased distance from the mid-right atrium to the sternal angle is not accounted for, apparently normal right atrial pressure estimates by this technique do not reliably exclude elevated right atrial pressure in patients with congestive heart failure.     

The influence of smoking and of oral and transdermal nicotine on blood pressure, and haematology and coagulation indices

Nicotine is helpful in stopping smoking but its influence on cardiovascular risk factors is incomplete. Our aim was to determine its effect on blood pressure, routine haematology indices, and coagulation indices relevant to thrombosis. Eighteen subjects were seen whilst smoking (cotinine levels 1119 +/- 414 ng/ml), again after stopping smoking but while using nicotine chewing gum and/or skin patches (392 +/- 198 ng/ml), and again when not using nicotine (cotinine undetectable). There were no significant changes in blood pressures, platelet count, mean platelet volume, viscosity or anti-thrombin III. However, white blood cell count (p = 0.003), lymphocyte count (p = 0.016), red blood cell count (p = 0.02), haemoglobin (p <0.001), fibrinogen (p <0.001) and von Willebrand factor (p = 0.001) all fell between the first and second samples (when still using nicotine) but not between the second and third samples (when off nicotine). Oral and/or transdermal nicotine does not influence blood pressure or the haematology and coagulation indices we have measured.     

Continuous non-invasive blood pressure monitoring by brachial artery displacement method in high-risk surgical patients

Continuous non-invasive blood pressure (CNBP) measurements were compared to invasive radial artery pressure recordings in 26 patients with cardiac, vascular and/or pulmonary disease. Patients were studied during general anaesthesia (n = 6), regional anaesthesia (n = 10), or combined technique (n = 10) for abdominal or transurethral surgery. CNBP was obtained from a cuff placed around the upper arm and simultaneously compared to invasive pressure from the ipsilateral radial artery. A CNBP device (7001 Cortronic) used intermittent oscillometric measurement for calibration. Through a cuff continuously inflated to a pressure of 20 mmHg, a microprocessor-controlled electro-pneumatic acquisition system sensed displacements of the brachial artery wall. Amplified, digitally converted, filtered and transformed data were displayed as a continuous pulse pressure waveform and digital pressure values on the screen. The CNBP method functioned without disturbances before surgery in all patients. Intra-operative use of electrocautery or a spontaneous occurrence of warning on the screen repeatedly triggered oscillometric recalibration, hence CNBP measurements were discontinued in nine patients. Coefficients of correlation (r) of all invasive and CNBP pairs (n = 1111) were 0.68, 0.58 and 0.70 for systolic, diastolic, and mean blood pressures, respectively. Prediction errors (bias, mean +/- SD) were -13.6 +/- 22.5 mmHg (on average CNBP < invasive pressure) for systolic, +13.0 +/- 12.4 mmHg (CNBP > invasive pressure) for diastolic and +5.0 +/- 13.9 mmHg (CNBP > invasive pressure) for mean CNBP, as compared to radial artery pressure values. Absolute errors (precision) were 25.3 +/- 9.4 mmHg for systolic, 17.4 +/- 4.5 mmHg for diastolic, and 13.9 +/- 4.6 mmHg for mean CNBP. During anaesthesia induction (n = 672) the difference between consecutive measurements (trend of pressure changes) with invasive and CNBP method exceeded 20 mmHg in 90 (13.3%) instances for systolic, in 33 (4.9%) instances for diastolic, and in 45 (6.6%) instances for mean blood pressure. In conclusion, the CNBP method by brachial artery wall displacement failed to measure the blood pressure reliably and to display the trend of pressure changes correctly during anaesthesia induction. In its present form this CNBP method should not replace invasive blood pressure monitoring in high-risk patients neither for anaesthesia induction nor during non-thoracic surgical procedures.     

Hepatic venous compliance and role of liver as a blood reservoir

Changes in hepatic blood volume in response to rapid elevations in hepatic venous pressure were examined in cats using hepatic plethysmography. The liver was intact and received blood from an intact portal vein and hepatic artery. The hepatic blood volume increased in response to elevated venous pressure. Compliance of the hepatic capacitance vessels became greater as the distending venous pressure was increased over the range of venous pressures studied (0-9.4 mmHg). When hepatic venous pressure was elevated to 9.4 MMHg, the hepatic blood volume more than doubled. The liver serves as an important buffer for rapid changes in blood volume, the importance increasing with greater infused volumes of fluid. While overall venous compliance decreased at distending pressures in excess of 5-6 mmHg, the compliance of the hepatic capacitance vessels shows marked increases at pressures above this level. Expansions of the blood volume results in elevations of central venous pressure. Within a few minutes the hepatic capacitance vessels sequester a significant proportion of the added volume. As long as central venous pressure is raised, the liver demonstrates a secondary fluid buffering role by filtering large volumes of fluid across the vascular bed into the peritoneum.     

Effect of isosorbide dinitrate on pulmonary venous compliance

Irreversible poor pulmonary venous compliance (PV comp) could worsened natural course of patients (pts) with high pulmonary capillary wedge pressure especially pts with mitral stenosis. Nitrates (isosorbide dinitrate-ISDN) possessing venous dilating action could increase PV comp in most of pts. The main aim of that study was to assess hemodynamic effects of ISDN, in pts with MS, with special emphasis on PV com changes. PV comp was estimated according to Hirakawa equation (dV/dp = 0.4*k2*SV/(v-d) in 35 pts with MS, during preoperative right heart catheterisation with VYGON 5155-180 thermodilution catheters during rest and effort in supine position (25W). The same protocol was performed after Iso-Mack sprawy 3.75 mg. According to the PV comp response to ISDN, pts were divided in two groups: good responders (I)-15% and higher increase in PV comp and poor responders (II). ISDN increased PV comp in the whole group according to the response to ISDN, there were significant differences in stroke volume index (SVI) and heart rate (HR). In the group of good responders mean right atrial pressure (RA), mean pulmonary artery pressure (PAP), mean pulmonary wedge pressure (PWP) decreased significantly with simultaneous slight not significant decrease in SVI and not significant increase of HR. In the group of poor responders SVI decreased significantly by about 20% with significant increase of HR. In conclusion significant decrease in pulmonary pressures (PAP, PWP) in pts with good response to ISDN are secondary to the increase of PV comp, while among poor responders the same effects are due to diminished flow secondary to the decrease of the systemic venous return.     

Two-dimensional echocardiographic assessment of right cardiac pressure overload in patients with chronic obstructive airway disease

Two-dimensional echocardiography was used to estimate right cardiac pressure overload in patients with chronic obstructive airway disease. Area measurements of the four heart chambers were carried out from the apical four-chamber view. Additionally, the respiratory behaviour of the inferior vena cava was examined from the subcostal view. A good apical imaging of the four-chamber view for area measurement was obtained in 44 out of 48 patients with chronic obstructive airway disease. The respiratory behaviour of the inferior vena cava was investigated from the subcostal view in 38 patients. Within 8 days after echocardiography, right cardiac catheterization was carried out in order to measure pulmonary artery and right atrial mean pressures and to determine pulmonary vascular resistance. A good correlation was found between pulmonary artery mean pressure and the following echocardiographic parameters: area index (area/body surface) of the two right heart cavities (r = 0.83), right-to-left ventricular area ratio (r = 0.82) and right-to-left cardiac area ratio (ratio between the added areas of both right heart cavities on the one side and the added areas of both left heart cavities on the other; r = 0.82). Correlation between these parameters and pulmonary vascular resistance (r = 0.71, 0.66 and 0.71, respectively) and between the right atrial mean pressure and the right atrial area index was less close (r = 0.64). On the other hand, the respiratory behaviour of the inferior vena cava proved to be highly specific but not very sensitive in predicting a pathological right atrial pressure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Treatment of subclinical fluid retention in patients with symptomatic heart failure: effect on exercise performance

BACKGROUND: Patients with heart failure frequently have elevated intracardiac diastolic pressures but no clinical evidence of excess fluid retention. We speculated that such pressure elevations may indicate subclinical fluid retention and that removal of this fluid could improve exercise intolerance. METHODS: To test this hypothesis, we studied 10 patients with right atrial pressure > or = 8 mm Hg but without rales, edema, or apparent jugular venous distension. Right-sided heart catheterization was performed, after which patients underwent maximal treadmill cardiopulmonary testing. Patients were then hospitalized and underwent maximal diuresis, after which exercise was repeated. RESULTS: Before diuresis, right atrial pressure averaged 16 +/- 5 mm Hg (+/-standard deviation), pulmonary capillary wedge pressure 30 +/- 6 mm Hg, and peak exercise Vo2 11.2 +/- 2.3 ml/min/ kg. Patients underwent diuresis of 4.5 +/- 2.2 kg over 4 +/- 2 days to a resting right atrial pressure of 6 +/- 4 and wedge pressure of 19 +/- 7 mm Hg. After diuresis, all patients reported overall symptomatic improvement. Maximal exercise duration increased significantly from 9.2 +/- 4.2 to 12.5 +/- 4.7 minutes. At matched peak workloads, significant improvements were also seen in minute ventilation (45 +/- 12 to 35 +/- 9 L/min), lactate levels (42 +/- 16 to 29 +/- 9 mg/dl), and Borg dyspnea scores (15 +/- 3 to 12 +/- 4) (all p < 0.05). CONCLUSIONS: Invasive hemodynamic monitoring allows the identification of excess fluid retention in patients with heart failure when there are no clinical signs of fluid overload. Removal of this subclinical excess fluid improves exercise performance and exertional dyspnea.     

Fusion variations of pancreatic ducts in patients with anomalous arrangement of pancreaticobiliary ductal system

Portal vein flow was recorded by color Doppler sonography in 31 patients with chronic heart failure and 18 control subjects. Compared with patients showing a forward flow (Group A), those with reversed portal vein flow (Group B) had higher prevalence of tricuspid regurgitation (75% vs. 43%), hepatic congestion (100% vs. 30%) and ascites (50% vs. 18%), and showed higher right atrial pressure (25.3 +/- 3.01 mmHg vs. 11.8 +/- 5.75 mmHg, p < 0.01). In controls, portal vein pulsatility ratio was 0.66 +/- 0.08, in Group A it was 0.46 +/- 0.28 (p < 0.01), in Group B -0.60 +/- 0.19 (p < 0.01). Portal vein pulsatility ratio negatively correlated with right atrial pressure (r = -0.87; p < 0.01). In Group A, hepatic congestion, ascites and tricuspid regurgitation were associated with a higher portal vein pulsatility. This study indicates that portal vein pulsatility ratio reflects the level of impairment of the right heart.     

Intraperitoneal pressure: ascitic fluid and splanchnic vascular pressures, and their role in prevention and formation of ascites

Seventeen patients with ascites due to cirrhosis underwent hepatic venous catheterization and pressure measurement in the ascitic fluid. Intraperitoneal fluid hydrostatic pressure (IFP) ranged 3.5-22, mean 11.2 mm Hg, and correlated closely to the pressure in the inferior vena cava (r = 0.97, P < 0.001), which was on average 1.8 mmHg above that of ascitic fluid (P < 0.005). Wedged hepatic venous pressure (WHVP) (range 19-43, mean 32 mmHg) correlated directly to IFP (0.89, P < 0.001) and was significantly higher than that of ten cirrhotic patients without ascites (range 12-27, mean 20 mmHg, P < 0.005). After diuretic therapy WHVP decreased to an average of 20 mmHg. Mean plasma colloid osmotic pressures were 20 mmHg (range 18-24 mmHg)( and 23 mmHg (range 19-29 mmHg) in patients with and without ascites, the values being significantly different (P < 0.05). Colloid osmotic pressure of ascitic fluid ranged 1-14, mean 4.9 mmHg. Mean ratio between albumin concentration in ascitic fluid and plasma was 0.31 (range 0.12-0.77). In five pigs portal venous pressure (PVP) increased during infusion of fluid into the peritoneal cavity. The increase in PVP was smaller than that of IFP (P < 0.02), indicating that ascitic fluid stems the pressures in the splanchnic venous vascular bed up to a higher level, but that the transmural hydrostatic pressure difference decreases simultaneously. The results are discussed in relation to the local 'oedema-preventing' mechanisms: (a) increased interstitial hydrostatic fluid pressure, (b) decreased interstitial fluid colloid osmotic pressure, (c) increased lymph flow, and it is concluded that the peritoneal space can be considered as a special part of the interstitium in which IFP is considered to play an important role in regulation of ascitic fluid.     

Pulse pressure response to the strain of the valsalva maneuver in humans with preserved systolic function

Arterial pulse pressure response during the strain phase of the Valsalva maneuver has been proposed as a clinical tool for the diagnosis of left heart failure, whereas responses of subjects with preserved systolic function have been poorly documented. We studied the relationship between the aortic pulse amplitude ratio (i.e., minimum/maximum pulse pressure) during the strain phase of the Valsalva maneuver and cardiac hemodynamics at baseline in 20 adults (42 +/- 14 yr) undergoing routine right and left heart catheterization. They were normal subjects (n = 5) and patients with various forms of cardiac diseases (n = 15), and all had a left ventricular ejection fraction >/=40%. High-fidelity pressures were recorded in the right atrium and the left ventricle at baseline and at the aortic root throughout the Valsalva maneuver. Aortic pulse amplitude ratio 1) did not correlate with baseline left ventricular end-diastolic pressure, cardiac index (thermodilution), or left ventricular ejection fraction (cineangiography) and 2) was positively related to total arterial compliance (area method) (r = 0.59) and to basal mean right atrial pressure (r = 0.57) (each P < 0.01). Aortic pulse pressure responses to the strain were not related to heart rate responses during the maneuver. In subjects with preserved systolic function, the aortic pulse amplitude ratio during the strain phase of the Valsalva maneuver relates to baseline total arterial compliance and right heart filling pressures but not to left ventricular function.     

Atrial distension in humans during microgravity induced by parabolic flights

The hypothesis was tested that human cardiac filling pressures increase and the left atrium is distended during 20-s periods of microgravity (microG) created by parabolic flights, compared with values of the 1-G supine position. Left atrial diameter (n = 8, echocardiography) increased significantly during microG from 26.8 +/- 1.2 to 30.4 +/- 0.7 mm (P < 0.05). Simultaneously, central venous pressure (CVP; n = 6, transducer-tipped catheter) decreased from 5.8 +/- 1.5 to 4.5 +/- 1.1 mmHg (P < 0.05), and esophageal pressure (EP; n = 6) decreased from 1.5 +/- 1.6 to -4.1 +/- 1.7 mmHg (P < 0.05). Thus transmural CVP (TCVP = CVP - EP; n = 4) increased during microG from 6.1 +/- 3. 2 to 10.4 +/- 2.7 mmHg (P < 0.05). It is concluded that short periods of microG during parabolic flights induce an increase in TCVP and left atrial diameter in humans, compared with the results obtained in the 1-G horizontal supine position, despite a decrease in CVP.     

Relationship between end-systolic aortic pressure and mean aortic pressure in adults

The mean blood pressure is an accurate estimate of the end-systolic aortic pressure in children. The aim of this study was: 1) to assess the relationship between the pressure at the incisura (PIAo) and the mean (MAoP) and pulse (PAoP) pressures of the supravalvular aorta in adults: and 2) to evaluate MAoP as an estimate of PIAo in adults. High fidelity pressure recordings were carried out in the supravalvular aorta in 17 men. The pressures were measured at rest in 10 consecutive beats and. In 6 subjects, during a Valsalva manoeuvre. At rest, PIAo was greater than the MAoP (109 +/- 17.9 versus 99.6 +/- 12.5 mmHg, p = 0.0001). There was a positive linear correlation between PIAo and MAoP (r = 0.93) and between PIAo and PAoP (r' = 0.77) whereas no correlation was observed between PIAo and heart rate, cardiac output or estimated total systemic arterial compliance. A beat-to-beat relationship was observed between PIAo and MAOP: 1) at rest in 16 of the 17 subjects and 2) in each subject who performed a Valsalva manoeuvre. Both at rest and during Valsalva, MAOP underestimated PIAo significantly, especially when PIAo was increased (p = 0.0001). The authors conclude that end-systolic supraaortic pressure is mainly related to the mean component of aortic pressure. MAOP slightly but constantly underestimated PIAo and this should lead to caution in assimilating MAOP to end-systolic aortic pressure in adults, especially in subjects with very high aortic pressures.     

Epidermal growth factor-induced activation and translocation of c-Src to the cytoskeleton depends on the actin binding domain of the EGF-receptor

The relationship between retinal arterial (Pra) and aortic (Pa) pressures is unknown, and the relationship between retinal vein (Prv) pressure and intraocular pressure (IOP) is not clear. Also unclear is the effect of cerebrospinal fluid pressure (CSFp) upon retinal venous pressure. We aimed to measure the relationships among Pra, Prv, Pa, IOP, and CSFp. Dogs were anesthetized while IOP, CSFp, and Pa were monitored. Pipettes with 2.5-micron diameter tips, connected to a servonulling pressure transducer, were used to record pressures from the retinal arteries and veins. Across a range of IOP (16-22 mmHg), CSFp (0-21 mmHg), and Pa (23-195 mmHg) the Pra = 0.72 Pa + 4.3 (r = 0.99, n = 61, P < 0.01), which suggests that the relationship between Pra and Pa is linear over a broad range of systemic blood pressures. The correlation coefficient between Prv and IOP was greater than 0.96 (P < 0.01) at all venous sites and whether IOP was greater than or less than CSFp. The transmural pressure varied along the retinal vein from 1.3 +/- 0.3 mmHg (+/-95% CI, n = 30) at 1 disk diameter from the optic disk rim to 0.3 +/- 0.2 mmHg (n = 66) at the optic disk, with a 0.9-mmHg/mm pressure gradient. These are the first measurements demonstrating a retinal vein transmural pressure close to zero.     

Evaluation of a pulsatile pediatric ventricular assist device in an acute right heart failure model

BACKGROUND: The development of pulsatile ventricular assist devices for children has been limited mainly by size constraints. The purpose of this study was to evaluate the MEDOS trileaflet-valved, pulsatile, pediatric right ventricular assist device (stroke volume = 9 mL) in a neonatal lamb model of acute right ventricular failure. METHODS: Right ventricular failure was induced in ten 3-week-old lambs (8.6 kg) by right ventriculotomy and disruption of the tricuspid valve. Control group 1 (n = 5) had no mechanical support whereas experimental group 2 (n = 5) had right ventricular assist device support for 6 hours. The following hemodynamic parameters were measured in all animals: heart rate and right atrial, pulmonary arterial, left atrial, and systemic arterial pressures. Cardiac output was measured by an electromagnetic flow probe placed on the pulmonary artery. RESULTS: All results are expressed as mean +/- standard deviation and analyzed by Student's t test. A p value less than 0.05 was considered statistically significant. Base-line measurements were not significantly different between groups and included systemic arterial pressure, 80.6 +/- 12.7 mm Hg; right atrial pressure, 4.6 +/- 1.6 mm Hg; mean pulmonary arterial pressure, 15.6 +/- 4.2 mm Hg; left atrial pressure, 4.8 +/- 0.8 mm Hg; and cardiac output, 1.4 +/- 0.2 L/min. Right ventricular injury produced hemodynamics compatible with right ventricular failure in both groups: mean systemic arterial pressure, 38.8 +/- 10.4 mm Hg; right atrial pressure, 16.8 +/- 2.3 mm Hg; left atrial pressure, 1.4 +/- 0.5 mm Hg; and cardiac output, 0.6 +/- 0.1 L/min. All group 1 animals died at a mean of 71.4 +/- 9.4 minutes after the operation. All group 2 animals survived the duration of study. Hemodynamic parameters were recorded at 2, 4, and 6 hours on and off pump, and were significantly improved at all time points: mean systemic arterial pressure, 68.0 +/- 13.0 mm Hg; right atrial pressure, 8.2 +/- 2.3 mm Hg; left atrial pressure, 6.4 +/- 2.1 mm Hg; and cardiac output, 1.0 +/- 0.2 L/min. CONCLUSIONS: The results demonstrate the successful creation of a right ventricular failure model and its salvage by a miniaturized, pulsatile right ventricular assist device. The small size of this device makes its use possible even in small neonates.     

Exercise and extracorporeal blood cooling during hemodialysis

Intradialytic exercise may improve hemodialysis efficiency. Because exercise interferes with thermal energy and fluid balance, relative blood volume changes (deltaBV%), arterial blood temperatures (T(art)), mean arterial blood pressures, and heart rates (HR) were measured using different dialysate temperatures (Tdia). Four stable patients (age, 49.9 +/- 7.7 years) were studied during 22 treatments that either maintained Tdia at 35.9 degrees C +/- 0.1 degrees C (standard) or provided maximum extracorporeal cooling (cool, Tdia = 34.8 degrees C +/- 0.8 degrees C) in attempts to maintain a constant T(art). Patients exercised for 1 hr at a resistance of 21 +/- 5 W on a stationary bicycle ergometer. Energy expenditure monitored by indirect calorimetry increased from 117 +/- 38 W (baseline) to 338 +/- 116 W (exercise). Mean arterial blood pressures increased by 7 +/- 7 mmHg with cool Tdia, but remained unchanged (-1 +/- 4 mmHg) with standard Tdia (p < 0.05). However, the increase in T(art) was smaller with cool (0.1 degrees C +/- 0.3 degrees C) than with standard (0.3 degrees C +/- 0.2 degrees C) Tdia (p < 0.05). The larger increase in O2 uptake per change in HR (68 +/- 56 vs 38 +/- 17 ml/beat) indicated an increase in stroke volume when cool dialysate was used (p = NS). Exercise produced a small (0.95% +/- 0.95%), but significant, decrease in deltaBV% that reversed at the end of exercise. Intradialytic exercise was well tolerated, especially when Tdia was lowered such that hemodynamic stress to dissipate excess heat through the cutaneous circulation was reduced and blood pressure stability was improved.