Effect of high hematocrit and high blood flow rates on transmembrane pressure and ultrafiltration rate in hemodialysis.

Removal of prescribed ultrafiltration volumes in hemodialysis requires knowledge of both the ultrafiltration coefficient of the dialyzer and the average transmembrane pressure (TMP) in the dialyzer. While it has been a fairly common practice to assume that the TMP is constant along the length of the dialyzer, it actually decreases linearly from a maximum value at the blood inlet to a minimum value at the blood outlet. In the past, ignoring the difference between arterial and venous TMPs when calculating the dialysate pressure setting did not result in significant errors in ultrafiltration volume. However, with the introduction of erythropoietin therapy and the trend toward high-efficiency dialysis, increases in hematocrit and blood flow rate have led to axial variations in TMP which, if ignored, can lead to inaccurate fluid removal. The goals of this paper are to provide an understanding of how high hematocrits and high blood flow rates affect TMP and ultrafiltration rate, and to provide simple guidelines for ensuring accurate fluid removal. Sample calculations are given on the last page for easy reference.     

Noninvasive laser-based blood pressure measurement in rabbits.

To obtain serial blood pressure measurements without trauma in rabbits, we developed a laser-based method which permits noninvasive determination of systolic and diastolic arterial blood pressure. The ease and accuracy of this method were evaluated over a range of blood pressures in five New Zealand White rabbits. Laser-based pressures from the central ear artery were compared with cannula-based pressures from the contralateral central ear artery. Pressures were measured before and during infusions of saline (control), nitroprusside, or epinephrine, and following induction of anesthesia. Noninvasive measurements correlated highly with direct measurements (systole: r = 0.89; diastole: r = 0.93). The difference between the non-invasive and direct pressure measurements during saline, nitroprusside, and epinephrine infusions, and following anesthesia, respectively, were (mean +/- SD, systole/diastole): 4.2 +/- 2.4 (P = NS)/9.3 +/- 1.4 (P less than .001), 4.1 +/- 1.6 (P less than .02)/3.2 +/- 1.1 (P less than .01), 0.6 +/- 2.4 (P = NS)/-3.0 +/- 2.7 (P = NS), and -5.1 +/- 2.9 (P = NS)/0.3 +/- 1.3 (P = NS). The noninvasive method did not result in observable agitation of the animals. To optimize results, visual inspection was required to assure that the instrument's diaphragm was not deformed or dried from previous use, and that the diaphragm was placed over the center of the arterial lumen. It was also necessary to dim room lights and to direct heating lights away from the ears to avoid degrading light signal quality. These results, albeit involving a small number of animals, indicate the potential utility of this method in the study of chronic pathophysiological processes requiring long-term repeated determination of systolic and diastolic blood pressure.     

Noninvasive measurement of femoral blood flow and portal pressure response to propranolol in patients with cirrhosis

This study investigated the correlation between changes in hepatic and systemic hemodynamics and femoral blood flow (FBF), measured by dual-beam pulsed wave Doppler, in 58 portal hypertensive patients receiving propranolol (0.15 mg/Kg intravenously; n = 44) or placebo (n = 14) under double-blind conditions. Placebo administration had no effects. Propranolol caused significant reductions (P < .0001) in hepatic venous pressure gradient (HVPG; from 19.1 ± 4.1 to 16.2 ± 4.2 mm Hg), azygos blood flow (from 563 ± 204 to 387 ± 176 mL/ min), cardiac index (CI; from 4.4 ± 1.0 to 3.3 ± 0.8 L/m²/min), and FBF (from 237 ± 79 to 176 ± 58 mL/m²/min). In 17 patients HVPG decreased below 12 mm Hg and/or more than 20% of the baseline value (good response; mean change, −26 ± 8%); in the remaining 27 patients (poor response) the mean change in HVPG was less: −9 ± 6%. Patients with a good response had bled less often from varices, had significantly higher FBF (272 ± 73 vs. 215 ± 76 mL/m²/min) and lower baseline HVPG (16.8 ± 3.9 vs. 20.6 ± 3.6 mm Hg) than those with poor response in HVPG. The good response was also associated with greater decreases in FBF (−33 ± 12 vs. −19 ± 13% in poor responders), CI (−30 ± 9 vs. −19 ± 12%), and heart rate (−19 ± 5 vs. −16 ± 6%). A decrease in FBF of >20% predicted a good response in 16 of 28 patients (positive predictive value, 57%). A negative test (decrease in femoral blood flow of <20%) predicted a lack of response in HVPG in 15 of 16 patients (negative predictive value, 94%). This study suggests that the noninvasive measurements of FBF allow the identification of patients with a poor response of HVPG to propranolol. However, measurements of HVPG would still be needed for patients whose FBF decreased >20%, half of whom have an insufficient decrease in HVPG.     

Dynamic pressure measurement for detection of blood access stenosis

A novel method for detection of access failure has been developed. It is based on the continuous evaluation of pre-pump arterial and venous pressure in the extracorporeal circuit. Knowing the flow resistance properties of the arterial and venous branches of the extracorporeal circuit from in-vitro measurements and the height differences, calculating the fistula pressure dynamically is possible. The fistula pressure allows identification of access failure as has been shown by other authors. The dynamic measurement however allows identification of bad needle placement. Dynamic measurement at different flow rates and comparison with static measurements allow for the identification of intra-access stenosis. The mathematical algorithm is described and pressure-flow curves for two sets of extracorporeal circuits are shown. In-vivo examples show a "normal" fistula and a fistula with intra-access stenosis.     

Increased hematocrit before blood pressure in men who develop hypertension over 20 years

We have previously demonstrated that neurohormonal activity can predict left ventricular (LV) mass in men who developed hypertension over 20 years. The aim of the study was to investigate early markers of cardiac and hemorheological changes at baseline in these men, i.e., before a rise in blood pressure. Fifty-six middle-aged men were followed for 20 years; 22 were sustained hypertensives, 17 developed hypertension, and 17 were sustained normotensives. They were compared at baseline (42 years) and follow-up (62 years). We investigated Cornell voltage product and Sokolow-Lyon voltage, hematocrit (Hct), and echocardiographic LV parameters. There was no sign of LV hypertrophy by electrocardiography (ECG) at baseline. Baseline Hct discriminated between the groups (P= .015) and correlated to diastolic blood pressure (DBP) at baseline (r = 0.37, P= .006) and follow-up (r = 0.31, P= .020). Regression analysis identified baseline Hct as an independent correlate of DBP in the cohort at baseline when they were untreated (β = .33, P= .013, R² = 0.25), and of borderline significance at follow-up (β = .26, P= .060, R² = 0.12) despite possible interference by antihypertensive drugs. Hct was elevated at baseline compatible with the hypothesis that pathogenic hemorheological processes could be activated at the outset and prior to cardiac changes in men who later develop hypertension.     

Noninvasive measurement of portal venous blood flow in patients with cirrhosis

The present study aims to evaluate the usefulness of combined pulse Doppler-real-time ultrasonography as a noninvasive method for the measurement of portal blood flow in man. This measurement technique was performed on 12 healthy subjects and 20 patients with portal hypertension. Ten patients (group 1) were evaluated prior to and after ingestion of a standard meal (Ensure Plus) or placebo. In the remaining 10 patients (group 2), the effects of isosorbide dinitrate (5 mg/SL) administration or placebo were studied. In group 1, food intake caused a significant increase of portal blood flow (from 1038±539 to 1572±759 ml/min,P<0.02); this effect was due to a significant rise in mean blood velocity (from 18.5±3.7 to 23.9±3.9 cm/sec,P<0.02). In group 2, isosorbide dinitrate significantly reduced portal blood flow (from 985±491 to 625±355 ml/min,P<0.05); a significant decline of mean blood velocity (from 18.8 ±4.5 to 14.5±2.5 cm/sec,P<0.02) was observed. Placebo administration had no significant hemodynamic effects in either group. Our results suggest that Doppler measurements gave accurate noninvasive estimations of portal blood flow and that this technique may be used to monitor physiological and pharmological stimuli in patients with portal hypertension.     

Dialysis unit blood pressure two hours after hemodialysis is useful for predicting home blood pressure and ambulatory blood pressure in maintenance hemodialysis patients

This study aimed to determine which BP measurement obtained in the HD unit correlated best with home BP and ambulatory BP monitoring (ABPM). We retrospectively analyzed data from 40 patients that received maintenance HD who had available home BP and ABPM data. Dialysis unit BPs were the averages of pre-, 2hr- (2 h after starting HD), and post-HD BP during a 9-month study. Home BP was defined as the average of morning and evening home BPs. Dialysis unit BP and home BP were compared over the 9-month study period. ABPM was performed once for 24 h in the absence of dialysis during the final 2 weeks of the study period and was compared to the 2-week dialysis unit BP and home BP. There was a significant difference between dialysis unit systolic blood pressure (SBP) and home SBP over the 9-month period. No significant difference was observed between the 2hr-HD SBP and home SBP. When analyzing 2 weeks of dialysis unit BP and home BP, including ABPM, SBPs were significantly different (dialysis unit BP > home BP > ABPM; P = 0.009). Consistent with the 9-month study period, no significant difference was observed between 2hr-HD SBP and home SBP (P = 0.809). The difference between 2hr-HD SBP and ambulatory SBP was not significant (P = 0.113). In conclusion, the 2hr-HD SBP might be useful for predicting home BP and ABPM in HD patients.     

Noninvasive measurement of coronary artery blood flow using combined two-dimensional and Doppler echocardiography

Noninvasive measurement of left anterior descending coronary artery flow was attempted in 20 normal subjects and 80 patients with cardiovascular disease (valvular heart disease in 34, ischemic heart disease in 26, cardiomyopathy in 15 and other diseases in 5) using combined two-dimensional and Doppler echocardiography. A tubular structure about 2 mm in diameter containing Doppler flow signals was identified in the anterior interventricular sulcus in 7 (35%) of the normal subjects and 40 (50%) of the patients with cardiovascular disease. The blood flow within the tubular structure exhibited a biphasic flow pattern, consisting of systolic and diastolic phases with higher velocity during diastole. The highest velocities were observed in early diastole and, in several cases, a small peak was detected during the atrial contraction phase. On the basis of its spatial orientation and characteristic flow pattern, the tubular structure was identified as the midportion of the left anterior descending coronary artery. In a number of cases it was difficult to detect the systolic blood flow. Although blood flow was normally directed from the cardiac base to the apex, it was reversed toward the base in the patients with a bypass graft to the left anterior descending coronary artery. In patients with severe aortic insufficiency, however, flow velocity was lower during diastole than during systole and the duration of diastolic flow was reduced, failing to continue to the end of diastole. Flow velocity was high in patients with a bypass graft to the left anterior descending coronary artery, aortic stenosis or hypertrophic cardiomyopathy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Detection of vascular access stenosis by measurement of access blood flow from ionic dialysance

BACKGROUND/AIM: The measurement of the vascular access blood flow rate (Q(a)) in chronic hemodialyzed patients was proposed to predict access thrombosis. We have recently presented a new method based on the measurements of ionic dialysance at normal and reversed positions of the blood lines. We evaluate the reliability of the measurement of Q(a) by this method in detecting significant access stenoses. METHODS: Twenty-five patients on chronic hemodialysis and having a vascular access cannulated with two needles were studied. The Q(a) was evaluated by the Diascan ionic dialysance (Q(a-id)) method and by the ultrasound dilution technique (Q(a-us); Transonic) during the same dialysis session. The measurements were available for 23 patients. In addition, the patients had ultrasonography of their fistula followed by angiography, if a stenosis was detected. RESULTS: Q(a-id) and Q(a-us) were not significantly different, showing a difference in Q(a) at 32 +/- 469 ml/min. Q(a-id) was significantly different between patients with or without stenosis (508 +/- 241 vs. 1,125 +/- 652 ml/min, p < 0.05). Among patients with a Q(a) <500 ml/min by Q(a-id), 5 had a stenosis detected by ultrasonography (sensitivity 83%), and 3 had no stenosis (false-positive rate 18%). Of these 3 patients, 2 had a thrombotic event at 1 and 3 months, suggesting that a more sensitive detection of stenosis for this range of Q(a) is needed and that a Q(a) <500 ml/min has a higher power to predict thromboses than a stenosis by ultrasonography. CONCLUSIONS: The measurement of the access flow rate by the Q(a-id) method has a clinical relevance to the detection of vascular access stenosis. An intervention program based on the Q(a-id) has to be evaluated.     

Quantitative evaluation of carotid blood flow before and after surgery

Blood flow in 49 patients suffering from stenosing lesions of the supraaortic trunks was measured using an ultrasonic volume flow metre (VFM) before and after operation. Results showed a statistically significant increase in the values of carotid flow, after operation. This non-invasive quantitative determination of blood flow provides the surgeon with often essential information for correct operation and subsequent follow-up.     

Transcutaneous Doppler method of measuring cardiac output—II: Noninvasive measurement by transcutaneous doppler aortic blood velocity integration and M mode echocardiography

In 15 patients with acute myocardial infarction (group I) and in 14 patients undergoing routine cardiac catheterization (group II) cardiac output values obtained by multiplying the 1 minute sum of the systolic integral of aortic blood flow velocity by the average systolic diameter of the aortic root were compared with values obtained with the thermodilution and Fick methods, respectively. Patients in group I were studied under various hemodynamic conditions, whereas those in group II were studied in the baseline state only. In group I, the correlation between the two methods was excellent (r values ranged from 0.96 to 0.99) except in one severely anemic patient whose Doppler signals were noisy, but at heart rates exceeding 150 beats/min it was not as good. In group II, the correlation between the two methods was r = 0.96 with a standard error of the estimate of 0.226 liter. The Doppler method is totally noninvasive and is useful for monitoring changes in cardiac output in patients with acute myocardial infarction.     

Noninvasive quantitative measurement of tissue blood flow in hepatocellular carcinoma using xenon-enhanced computed tomography

The aim of this study was to quantitatively measure tissue blood flow (TBF) in hepatocellular carcinoma (HCC) by a noninvasive method using xenon (Xe) inhalation/CT scans and to correlate the measured TBF with histological features. TBF was measured in HCC with xenon-enhanced CT (xenon/CT) in 20 patients. In 15 patients with HCC diagnosed as hypervascular tumors by conventional CT, TBF of the tumors was significantly higher than that of noncancerous liver tissue (151.1 ± 20 vs 42.6 ± 20 ml/min/100 g). Histologically, these tumors were diagnosed as moderately-to-poorly differentiated HCC. In contrast, in five patients with hypovascular HCC, TBF of HCC was almost comparable to that of the noncancerous regions (45.3 ± 6 vs 48.3 ± 6 ml/min/100 g). All these tumors were well-differentiated HCC. In conclusions, the measured values of TBF correlate with the clinicopathologic features of liver tumors and nontumorous liver tissue in patients with HCC.