Criteria for set point estimation in the volume clamp method of blood pressure measurement.

When blood pressure is measured in the finger using the volume clamp method the value at which the vascular volume is clamped is of crucial importance. Since the discovery of the method, several criteria of finding a correct set point have been elaborated: 1. The volume oscillations reach their maximum amplitude at cuff pressure equalling mean blood pressure. 2. The form of the diastolic portion of volume pulsations changes if the cuff pressure moves around the mean blood pressure. 3. The set point can be positioned at one third of the arterial volume. 4. The dynamic vascular compliance (DVC) may be continuously measured as the instantaneous amplitude of vascular volume oscillations is elicited by a relatively small and rapid vibration of the cuff pressure. The shape of the DVC pulse characteristically depends on the transmural pressure (TP): at negative TP (cuff pressure exceeding the blood pressure) it shows a distinct positive systolic peak, at positive TP the polarity of the DVC pulse is reversed. In contrast to the first three ways to find the set point, the last one may operate even in closed-loop performance, i.e. during the blood pressure measurement.     

Non-invasive blood pressure measurement in Yucatan miniature swine using tail cuff sphygmomanometry

A relatively new non-invasive method using a photo-electric flow sensor in non-heated animals, was evaluated for its accuracy in measuring systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP) in 40-90 Kg normotensive and hypertensive Yucatan miniature swine. Directly measured SBP, DBP and electronically averaged MAP were recorded from chronic arterial catheters simultaneously with indirect pressures, cuff pressure and tail blood flow under various conditions. In all of the tests tail cuff SBP estimation averaged within 5% of directly measured SBP. The correlation of the two methods was significant (r = .95, P less than 0.01). Over a 60 to 202 mmHg range of blood pressure induced pharmacologically or due to DOCA hypertension, the tail cuff SBP was within 4-10% of directly measured SBP. The tail cuff method was also used to determine DBP and MAP. DBP determined from the tail cuff record was found consistently to underestimate the direct measured DBP by approximately 17%. The two methods were correlated (r = .87 P less than 0.01). The measured tail cuff MAP generally underestimated the direct MAP by approximately 5%. The correlation of directly measured MAP and tail cuff methods was significant (r = .72, P less than 0.01). These results indicated that this system may be used to accurately assess blood pressure in miniature swine.     

Evaluation of a new tail-cuff method for blood pressure measurements in rats with special reference to the effects of ambient temperature

We evaluated a recently developed tail-cuff apparatus for the indirect blood pressure measurement in rats with special reference to the effects of ambient temperature. For this purpose, we designed two preparations 1) an intact preparation to determine the effect of ambient temperature on blood pressure measurements and 2) an anesthetized and catheterized preparation for comparison of the values of blood pressure obtained by the indirect and by the direct method. This apparatus also required enough pulse volume oscillations to measure the accurate value of blood pressure. Sufficient pulse volume oscillations were obtained within 20 min at 30 and 40 degrees C. At 40 degrees C, the values of blood pressure, pulse rate and rectal temperature were significantly higher than those at 30 degrees C. Correlation between blood pressure and rectal temperature was significant, and blood pressure increased with rectal temperature dependently. The values of the indirect measurement were close to the values measured directly, and these correlations were highly significant. Thus, we showed the effects of temperature for indirect blood pressure measurement. This tail-cuff apparatus could measure the accurate value of indirect blood pressure without thermal stress at 30 degrees C.     

Indirect systolic and mean blood pressure determination by a new tail cuff method in spontaneously hypertensive rats

A new tail cuff method for determining systolic and mean blood pressure in rats was developed based on photoelectric detection of tail arterial blood flow and pulsatile volume oscillation. Indirect systolic and mean blood pressure measured by this method correlated well with direct systolic and mean blood pressures recorded by a transducer and polygraph after carotid artery cannulation in stroke-resistant spontaneously hypertensive rats (SHR), stroke-prone SHR and normotensive Wistar Kyoto rats. Blood pressures were sharply, and transiently raised for about 1 min when rats were picked up by an investigator to be placed in a hot box or immobilized in a restrainer for measuring blood pressure. Therefore, blood pressures should be measured at least 1 min after the rats are put in a restrainer. This new tail cuff method for measuring blood pressure provides reliable mean blood pressure readings in conscious rats.     

The hypertriglyceridemic rat as a genetic model of hypertension and diabetes.

Hypertriglyceridemia was demonstrated in untreated hypertensive patients as well as in animals with genetic and experimental hypertension. The main purpose of the present study was to evaluate the possibility to use the hereditary hypertriglyceridemic (HTG) nonobese rats in hypertensive research. Direct measurement of blood pressure demonstrated significantly higher systolic, diastolic and mean arterial pressures in HTG rats in comparison with control Wistar rats. There was significant positive correlation between blood pressure and plasma triglyceride concentration (r = 0.585, n = 40, p less than 0.001). In addition, there were significantly increased plasma norepinephrine and epinephrine concentrations in HTG rats, suggesting that the stimulation of sympathetic nervous system could be one of the pathogenetic mechanisms involved in the increase of blood pressure of HTG rats.     

Measurement of total pulmonary arterial compliance using invasive pressure monitoring and MR flow quantification during MR-guided cardiac catheterization

Pulmonary hypertensive disease is assessed by quantification of pulmonary vascular resistance. Pulmonary total arterial compliance is also an indicator of pulmonary hypertensive disease. However, because of difficulties in measuring compliance, it is rarely used. We describe a method of measuring pulmonary arterial compliance utilizing magnetic resonance (MR) flow data and invasive pressure measurements. Seventeen patients with suspected pulmonary hypertension or congenital heart disease requiring preoperative assessment underwent MR-guided cardiac catheterization. Invasive manometry was used to measure pulmonary arterial pressure, and phase-contrast MR was used to measure flow at baseline and at 20 ppm nitric oxide (NO). Total arterial compliance was calculated using the pulse pressure method (parameter optimization of the 2-element windkessel model) and the ratio of stroke volume to pulse pressure. There was good agreement between the two estimates of compliance (r = 0.98, P < 0.001). However, there was a systematic bias between the ratio of stroke volume to pulse pressure and the pulse pressure method (bias = 61%, upper level of agreement = 84%, lower level of agreement = 38%). In response to 20 ppm NO, there was a statistically significant fall in resistance, systolic pressure, and pulse pressure. In seven patients, total arterial compliance increased >10% in response to 20 ppm NO. As a population, the increase did not reach statistical significance. There was an inverse relation between compliance and resistance (r = 0.89, P < 0.001) and between compliance and mean pulmonary arterial pressure (r = 0.72, P < 0.001). We have demonstrated the feasibility of quantifying total arterial compliance using an MR method.     

A modified technique for tail cuff pressure measurement in unrestrained conscious rats

In physiological experiments, it is essential to measure arterial pressure (AP) and heart rate (HR) in animals. Tail cuff pressure (TCP) measurement using photoelectric volume oscillometry has been commonly used. We designed a new technique for continuous measurement of AP and HR in conscious, unrestrained rats. This is based on the observation that fixation of the rat's tail with tape keeps the animal in position without struggling. The animal is free to move its body. To test the accuracy of this new technique, Sprague-Dawley rats underwent four AP and HR measurement techniques. These included a new unrestrained method (UR), which was compared to the following three methods: traditional restrained TCP method with restrainer, direct monitoring of AP and HR with femoral artery catheterization and a combination of photoelectric volume oscillometry (with body heating to 37 degrees C) and femoral arterial recording. The results show that the modified UR measurement provides accurate data on AP and HR. This method obtains a lower value of HR and similar mean AP when compared to direct monitoring from femoral arterial catheterization. Accordingly, the modified unrestrained TCP measurement can be used in conscious rats as a noninvasive method.     

Diastolic pressure determines autonomic responses to pressure perturbation in humans

Arterial baroreceptors reflexly regulate sympathetic and heart rate responses to alteration of blood pressure. The primary mechanical determinant of arterial baroreceptor activity in humans remains unclear. We examined the influence of systolic, diastolic, pulse, and mean arterial pressures on efferent muscle sympathetic nerve activity (MSNA, microneurography) and heart rate responses during perturbation of arterial pressure in 10 normal human subjects [age 25 +/- 2 (SE) yr]. We directly measured arterial pressure, heart rate, and MSNA during intravenous vasodilator infusion (nitroprusside, 6 +/- 1 micrograms.kg-1.min-1, n = 6; or hydralazine, 16 +/- 2 mg, n = 4) while central venous pressure was held constant by simultaneous volume expansion. Changes in arterial pressures were compared with changes in heart rate and MSNA over 3-min periods of vasodilator infusion during which we observed increases in systolic and pulse pressures with simultaneous decreases in mean and diastolic pressures. During vasodilator infusion, there were increases in systolic (124.2 +/- 2.1 to 131.7 +/- 2.9 Torr, P less than 0.001) and pulse pressures (57.0 +/- 2.2 to 72.7 +/- 2.7 Torr, P less than 0.001) although mean arterial pressure fell (88.0 +/- 2.6 to 80.4 +/- 2.7 Torr, P less than 0.001) because of decreases in diastolic pressure (67.2 +/- 3.0 to 59.0 +/- 2.7 Torr, P less than 0.001). The changes in arterial pressures were accompanied by simultaneous increases in heart rate (66.4 +/- 3.0 to 92.6 +/- 4.8 beats/min, P less than 0.001) and MSNA (327 +/- 59 to 936 +/- 171 U, P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of direct and indirect blood pressure measurement in anesthetized dogs.

This study was conducted to determine whether blood pressures and pulse rate could be determined accurately by indirect measurements from the front and hind legs of 15- to 40-kg dogs anesthetized with isoflurane. Indirect measurements from each animal were compared to direct measurements obtained from a catheter placed into the abdominal aorta via the femoral artery at four ranges of systolic pressure. When systolic pressure was above 80 mm Hg, indirect measurements were either the same as direct measurements or slightly lower. However, when systolic pressures were below 80 mm Hg, indirect systolic pressure measurements were 6 to 15% higher than direct measurements. Larger differences in diastolic pressures were found, which resulted in differences in mean pressure. The most accurate measurements were found when the cuff width-to-limb circumference ratio was between 0.4 and 0.6 and when systolic pressure was between 80 and 100 mm Hg.     

Oscillometric measurement of systolic and diastolic blood pressures validated in a physiologic mathematical model

ABSTRACT: BACKGROUND: The oscillometric method of measuring blood pressure with an automated cuff yields valid estimates of mean pressure but questionable estimates of systolic and diastolic pressures. Existing algorithms are sensitive to differences in pulse pressure and artery stiffness. Some are closely guarded trade secrets. Accurate extraction of systolic and diastolic pressures from the envelope of cuff pressure oscillations remains an open problem in biomedical engineering. METHODS: A new analysis of relevant anatomy, physiology and physics reveals the mechanisms underlying the production of cuff pressure oscillations as well as a way to extract systolic and diastolic pressures from the envelope of oscillations in any individual subject. Stiffness characteristics of the compressed artery segment can be extracted from the envelope shape to create an individualized mathematical model. The model is tested with a matrix of possible systolic and diastolic pressure values, and the minimum least squares difference between observed and predicted envelope functions indicates the best fit choices of systolic and diastolic pressure within the test matrix. RESULTS: The model reproduces realistic cuff pressure oscillations. The regression procedure extracts systolic and diastolic pressures accurately in the face of varying pulse pressure and arterial stiffness. The root mean squared error in extracted systolic and diastolic pressures over a range of challenging test scenarios is 0.3 mmHg. CONCLUSIONS: A new algorithm based on physics and physiology allows accurate extraction of systolic and diastolic pressures from cuff pressure oscillations in a way that can be validated, criticized, and updated in the public domain.     

Pulse Decomposition Analysis of the digital arterial pulse during hemorrhage simulation

Background

Markers of temporal changes in central blood volume are required to non-invasively detect hemorrhage and the onset of hemorrhagic shock. Recent work suggests that pulse pressure may be such a marker. A new approach to tracking blood pressure, and pulse pressure specifically is presented that is based on a new form of pulse pressure wave analysis called Pulse Decomposition Analysis (PDA). The premise of the PDA model is that the peripheral arterial pressure pulse is a superposition of five individual component pressure pulses, the first of which is due to the left ventricular ejection from the heart while the remaining component pressure pulses are reflections and re-reflections that originate from only two reflection sites within the central arteries. The hypothesis examined here is that the PDA parameter T13, the timing delay between the first and third component pulses, correlates with pulse pressure. T13 was monitored along with blood pressure, as determined by an automatic cuff and another continuous blood pressure monitor, during the course of lower body negative pressure (LBNP) sessions involving four stages, -15 mmHg, -30 mmHg, -45 mmHg, and -60 mmHg, in fifteen subjects (average age: 24.4 years, SD: 3.0 years; average height: 168.6 cm, SD: 8.0 cm; average weight: 64.0 kg, SD: 9.1 kg).

Results

Statistically significant correlations between T13 and pulse pressure as well as the ability of T13 to resolve the effects of different LBNP stages were established. Experimental T13 values were compared with predictions of the PDA model. These interventions resulted in pulse pressure changes of up to 7.8 mmHg (SE = 3.49 mmHg) as determined by the automatic cuff. Corresponding changes in T13 were a shortening by -72 milliseconds (SE = 4.17 milliseconds). In contrast to the other two methodologies, T13 was able to resolve the effects of the two least negative pressure stages with significance set at p < 0.01.

Conclusions

The agreement of observations and measurements provides a preliminary validation of the PDA model regarding the origin of the arterial pressure pulse reflections. The proposed physical picture of the PDA model is attractive because it identifies the contributions of distinct reflecting arterial tree components to the peripheral pressure pulse envelope. Since the importance of arterial pressure reflections to cardiovascular health is well known, the PDA pulse analysis could provide, beyond the tracking of blood pressure, an assessment tool of those reflections as well as the health of the sites that give rise to them.     

Exercise reduces arterial pressure augmentation through vasodilation of muscular arteries in humans

Exercise markedly influences pulse wave morphology, but the mechanism is unknown. We investigated whether effects of exercise on the arterial pulse result from alterations in stroke volume or pulse wave velocity (PWV)/large artery stiffness or reduction of pressure wave reflection. Healthy subjects (n = 25) performed bicycle ergometry. with workload increasing from 25 to 150 W for 12 min. Digital arterial pressure waveforms were recorded using a servo-controlled finger cuff. Radial arterial pressure waveforms and carotid-femoral PWV were determined by applanation tonometry. Stroke volume was measured by echocardiography, and brachial and femoral artery blood flows and diameters were measured by ultrasound. Digital waveforms were recorded continuously. Other measurements were made before and after exercise. Exercise markedly reduced late systolic and diastolic augmentation of the peripheral pressure pulse. At 15 min into recovery, stroke volume and PWV were similar to baseline values, but changes in pulse wave morphology persisted. Late systolic augmentation index (radial pulse) was reduced from 54 +/- 3.9% at baseline to 42 +/- 3.7% (P < 0.01), and diastolic augmentation index (radial pulse) was reduced from 37 +/- 1.8% to 25 +/- 2.9% (P < 0.001). These changes were accompanied by an increase in femoral blood flow (from 409 +/- 44 to 773 +/- 48 ml/min, P < 0.05) and an increase in femoral artery diameter (from 8.2 +/- 0.4 to 8.6 +/- 0.4 mm, P < 0.05). In conclusion, exercise dilates muscular arteries and reduces arterial pressure augmentation, an effect that will enhance ventricular-vascular coupling and reduce load on the left ventricle.     

Release of vasoactive intestinal peptide in the dumping syndrome.

To determine the effect of gastric surgery on the plasma vasoactive intestinal peptide (VIP) concentration, 13 patients with gastrectomy and seven controls were given an oral hypertonic load (200 ml 50% glucose solution). Blood was taken at intervals during the test for measurement of VIP and blood glucose concentrations and packed cell volume. At the same time observations were made on the occurrence of dumping symptoms and a record kept of the pulse rate. VIP values in the patients with gastrectomy were significantly increased by glucose ingestion, while these did not alter in controls (p less than 0.001). There was a highly significant correlation between the rate of rise in plasma VIP concentration and the rates of rise in packed cell volume (r = 0.85; p less than 0.001) and blood glucose concentration (r = 0.76; p less than 0.01) in patients with gastrectomy. Changes in packed cell volume and blood glucose values and the occurrence of dumping symptoms during the test were significantly different when postoperative patients were compared with controls (p less than 0.001, p less than 0.005, and p less than 0.001 respectively). Furthermore, when the patients with gastrectomy were divided into those without symptoms and those with dumping after meals the latter group showed a significantly greater rise of VIP (p less than 0.05). Despite the increased plasma VIP concentrations observed during dumping, VIP cannot be taken as the sole factor in the pathogenesis of the dumping syndrome.     

人上臂加压时的脉波分析

将与动脉脉波测定装置相连的袖带,缠绕于上臂,借助袖带充气给袖带部位的动脉加压。当袖带内压从收缩压水平缓缓下降时,可以记录到一系列逐渐变化着的动脉脉波,与以前在动物动脉外直接描记到的脉波群相似。用“脉波分析法”可以获得袖带部位的收缩压和舒张压值。与柯氏音法比较,在105次体力负荷前后的12名健康人测定中,收缩压与舒张压的相关系数分别为0.98和0.97。分析“0 波”,尚可获得容积变化的信息,并能测得同时发生的压力变化值。进而可将此两值代入动脉顺应指数(I_C)式。20名正常人87次测定的I_C值,远高于20名高血压患者 78次测定的结果(P<0.001)。I_C值的降低与眼底动脉硬化的程度有关。此方法具有简易、无创伤的优点。     

Chronic sodium cyanate treatment induces "hypoxia-like" effects in rats

Three weeks of sodium cyanate (NaCNO) intraperitoneal treatment in rats (n = 15) induced high hemoglobin O2 affinity, i.e., low PO2 at 50% hemoglobin saturation (P50), 20.5 +/- 1.4 Torr, in comparison with the mean control values, 34.5 +/- 1.6 Torr (n = 15). NaCNO rats showed a reduction in mean body weight, 376 +/- 27 g, in comparison with controls, 423 +/- 23 g (P less than 0.001). Despite arterial O2 partial pressure (PaO2) within normal limits NaCNO-treated rats had a higher systolic right ventricular pressure (SRVP), 33.7 +/- 3.1 Torr, in comparison with control value, 29.0 +/- 2.5 Torr (P less than 0.001). Right ventricle weights were significantly increased (P less than 0.001). After 60 min of an hypoxic challenge (fractional concentration of inspired O2 = 0.10) NaCNO-treated rats increased SRVP of only 7 +/- 4% compared with 46 +/- 9% in the control animals. Inducing high hemoglobin affinity in rats (n = 10; 6 wk NaCNO treatment) resulted in increases in hematocrit ratio and hemoglobin concentration (P less than 0.001). The characteristics of the red blood cell (RBC) itself changed; values of mean cell volume, mean cell hemoglobin, and mean cell hemoglobin concentration being significantly increased (P less than 0.001) when compared with mean control values. The count of nucleated RBC's appeared to be significantly higher from the 2nd wk of NaCNO treatment. Chronic NaCNO treatment was demonstrated to exert "hypoxia-like" effects since it induced prevention of normal growth, polycythemia, pulmonary hypertension, right ventricular hypertrophy, and blunted pulmonary pressor response to acute hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Venous occlusion plethysmography reduces arterial diameter and flow velocity

The measurement of peripheral blood flow by plethysmography assumes that the cuff pressure required for venous occlusion does not decrease arterial inflow. However, studies in five normal subjects suggested that calf blood flow measured with a plethysmograph was less than arterial inflow calculated from Doppler velocity measurements. We hypothesized that the pressure required for venous occlusion may have decreased arterial velocity. Further studies revealed that systolic diameter of the superficial femoral artery under a thigh cuff decreased from 7.7 +/- 0.4 to 5.6 +/- 0.7 mm (P less than 0.05) when the inflation pressure was increased from 0 to 40 mmHg. Cuff inflation to 40 mmHg also reduced mean velocity 38% in the common femoral artery and 47% in the popliteal artery. Inflation of a cuff on the arm reduced mean velocity in the radial artery 22% at 20 mmHg, 26% at 40 mmHg, and 33% at 60 mmHg. We conclude that inflation of a cuff on an extremity to low pressures for venous occlusion also caused a reduction in arterial diameter and flow velocity.     

Auscultatory indirect measurement of blood pressure in dogs

An indirect method of measuring blood pressure (cuff plus stethoscope) was evaluated in 70 dogs weighing 15 to 30 kg (17.5 +/- 8.8 kg; mean +/- standard deviation). A cuff 12 cm wide was used. The measurements were most audible with the cuff on the upper foreleg of the dog and with the stethoscope placed in the medial epicondylar region just distal to the cuff. The cuff was inflated to greater than systolic pressure and allowed to deflate slowly. In 70 lightly sedated dogs, systolic blood pressures averaged 145 +/- 25 mmHg (mean +/- standard deviation) and diastolic blood pressures averaged 84 +/- 14 mmHg. Indirect measurements were compared to direct measurements (femoral arterial catheter). Systolic pressures obtained by this direct method averaged 138 +/- 29 mmHg (mean +/- standard deviation) and diastolic pressures averaged 84 +/- 17 mmHg. The correlation coefficient for systolic pressure was 0.96 and for diastolic pressure 0.97.     

Estimation of blood pressure-related parameters by electrical impedance measurement.

In 13 healthy volunteers a computerized experimental set-up was used to measure the electrical impedance of the upper arm at changing cuff pressure, together with the finger arterial blood pressure in the contralateral arm. On the basis of a model for the admittance response, the arterial blood volume per centimeter length (1.4 +/- 0.3 ml/cm), the venous blood volume as a percentage of the total blood compartment (49.2 +/- 12.6%), and the total arterial compliance as a function of mean arterial transmural pressure were estimated. The effective physiological arterial compliance amounted to 2.0 +/- 1.3 microliters.mmHg-1.cm-1 and the maximum compliance to 33.4 +/- 12.0 microliters.mmHg-1.cm-1. Additionally, the extravascular fluid volume expelled by the occluding cuff (0.3 +/- 0.3 ml/cm) was estimated. These quantities are closely related to patient-dependent sources of an unreliable blood pressure measurement and vary with changes in cardiovascular function, such as those found in hypertension. Traditionally, a combination of several methods is needed to estimate them. Such methods, however, usually neglect the contribution of extravascular factors.     

肺动脉血流时间间期法评估肺动脉压

为评价肺动脉血流时间间期法评估肺动脉压的价值,本文观察了37例左向右分流先天性心脏病患者。在相同体位及取样容积位置下测量心室射血前期(PEP)、射血时间(ET)、加速时间(AT)、加速度(ACC)、F[F=PEP/(ATET)];计算肺动脉/主动脉血流时间间期比(FPA/FAO),并以各项比例系数与肱动脉压(BAP)的乘积作为肺动脉压的估测值。结果显示:肺动脉/主动脉血流时间间期比与右心导管估测的肺动脉收缩压(PASP)、平均压(PAMP)取得了较好的相关性(r分别为0.84、0.81);ACC次之(r分别为0.72、0.65);PEP/AT较差(r分别为0.53、0.50)。提示:肺动脉/主动脉血流时间间期比为无创定量评估肺动脉压的最佳方法。     

Plasmodium berghei: malaria infection causes increased cardiac output in rats, Rattus rattus

Thirty-two 4-week-old male Wistar rats were infected with Plasmodium berghei malaria. On Days 12 through 14, blood volume, arterial blood pressure, right ventricular pressure, heart rate, cardiac output, stroke volume, hematocrit, and vascular resistances were determined. All of the cardiovascular parameters measured, with the exception of calculated pulmonary vascular resistance, changed progressively as the peripheral blood parasitemia increased. With a rising parasitemia, cardiac output increased, despite a reduced heart rate. The highest parasitemia of 63% was accompanied by a doubling of the normal cardiac output. The relationship between parasitemia and cardiac output can be described by the equation, cardiac output = (6.14) x % parasitemia + 452 ml/min/kg. The mean arterial blood pressure was lower than controls when parasitemia exceeded 20%, whereas systolic right ventricular pressure was elevated only at the highest parasitemias. When noninfected control rats were compared with those animals having parasitemias greater than 40%, in the infected animals, mean arterial pressure was 28% lower (P less than 0.01) and systolic right ventricular pressure rose by 21% (P less than 0.02). A 50% decline was observed in the total peripheral vascular resistance (P less than 0.01), although the pulmonary resistance was apparently unchanged. With P. berghei infection, there is also a marked anemia, an increase in plasma volume, and a 16% increase in blood volume (% body weight). It is concluded from these results that although the hemodynamic changes previously reported in the literature indicate that infection with malaria may result in focal blockages in microvessels and poor tissue perfusion, the total systemic effect, in the rat, is an increase in cardiac output secondary to a reduced peripheral resistance.(ABSTRACT TRUNCATED AT 250 WORDS)