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PubMed1981

The influence of hemoglobin concentration on exercise cardiac output.

Two experiments were performed to study the cardiac output (Q) vs. hemoglobin concentration (Hb) relationship during constant load submaximum eexercise. The first experiment examined the relationship between submaximum exercise Q and Hb in 28 females. A correlation of r = -0.83 (P less than 0.05) was observed between Q and Hb during xercise at 88 W (mean Q = 11.04 l . min-1) and 118 W (mean Q = 13.10 l . min-1) (mean steady rate VO2 = 1.40 l . min-1 and 1.79 l . min-1, respectively). By removing the influence of stroke volume (SV) from Q (part correlation analyses), the relationship between Q and Hb is compromised (r = -0.29, P greater than 0.05, 88 W and r = -0.33, P greater than 0.05, 118 W). The second experiment compared the VO2 max and submaximum exercise (118 W) Q responses in six males before and after blood donation. Experimentally reducing Hb 18.6% (P less than 0.05) caused a 6.2% decrease (P less than 0.05) in VO2 max. Additionally, submaximum exercise Q increased 12% (P less than 0.05) 6 days following hemodilution., The Q remained elevated 11 days (10% higher, P less than 0.05) and 16 days (9% higher, P less than 0.05) post-blood donation and progressively returned to pre-donation levels by 21 days post-withdrawal. The higher Q's during submaximum exercise were ascribed primarily to an 8% (P less than 0.05) higher SV in comparison to pre-donation levels. collectively, the data from the two experiments indicate that individual differences in submaximum exercise Q are due, in part, to individual differences in Hb concentration. Furthermore, it is suggested that the stimulus for the SV-induced Q vs. Hb association is related to maintaining maximal myocardial efficiency.

Adult↗
PubMed1993

Dependence of cardiac filling pressure on cardiac output during rest and dynamic exercise in dogs.

At rest, central venous pressure (CVP) falls when cardiac output (CO) rises. This can be attributed to flow-dependent redistribution of blood volume from central to peripheral blood vessels. In contrast, CVP rises during dynamic exercise despite a rise in CO. Therefore peripheral circulatory changes during exercise must counteract the factors that lower CVP when CO rises during rest. Our objectives were to determine the importance of blood flow, the muscle pump, and reflexes on changes in ventricular filling pressure during dynamic exercise. In seven dogs with a surgically produced atrioventricular (AV) block, normal relationships between CO and CVP were established by AV-linked pacing (normal heart rates) during rest and exercise. Cardiac output was altered during rest and treadmill exercise (4 miles/h at 0, 10, or 20% grade) by changing ventricular pacing rate to establish curves relating delta CVP to delta CO. These curves were displaced rightward (higher CO) and upward (higher CVP) by exercise because of the muscle pump. Changing CO by pacing during rest and exercise revealed a constant slope for delta CVP/delta CO of -2.7 mmHg.l-1.min-1. Blockade of reflex vasoconstriction and venoconstriction with hexamethonium at rest and during mild exercise (to isolate effects of the muscle pump) did not alter these slopes or the displacement of the curves by exercise, although CVP was 4.3 mmHg lower at a given CO after blockade.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1997

Measurement of cardiac output by transesophageal echocardiography in mechanically ventilated patients. Comparison with thermodilution.

OBJECTIVE: The determination of basal cardiac output (CO) and of its variations during different therapeutic interventions liable to increase or decrease it in mechanically ventilated patients using transesophageal echocardiography (TEE). DESIGN: To compare CO measurements simultaneously obtained by transmitral single-plane TEE and thermodilution. SETTING: Medical intensive care unit. PATIENTS: Twenty-two consecutive mechanically ventilated patients hospitalized for various medical conditions were included. INTERVENTIONS: The comparisons between transmitral single-plane TEE and thermodilution measurements were made at baseline and after different therapeutic interventions affecting CO (fluids or dobutamine infusion or positive end-expiratory pressure titration). MEASUREMENTS: Seventy-four measurements were obtained. Cardiac output using TEE was the product of the mitral valve area, the time-velocity integral of flow at the same site and the heart rate. RESULTS: A significant correlation was observed between thermodilution and TEE measurements of CO (n = 74, r = 0.78, p < 0.001) despite wide limits of agreement (mean +/- 2SD = -0.3 +/- 3.1 l/min). Thermodilution and TEE CO determinations both had significant inverse correlation with the arterial-venous oxygen content difference in ten consecutive patients (r = 0.77, p < 0.01 and r = 0.71, p < 0.01, respectively). The correlation between variations of CO greater than 20% obtained by thermodilution and TEE was significant (r = 0.89, p < 0.001). The operative characteristics implied the ability of TEE to predict significant variations of thermodilution CO (sensitivity 85% and negative predictive values 86%). Moreover, arterial-venous oxygen content difference changes of 5% or more were better detected using TEE than thermodilution. CONCLUSIONS: These results suggest that although transesophageal CO measurements cannot replace thermodilution ones, the determination of CO variations obtained using TEE may be useful in the management of critically ill mechanically ventilated patients. This technique may make it possible to monitor hemodynamics during initial therapeutic interventions in those patients in whom right heart catheterization cannot be performed immediately.

Adult↗
PubMed1995

[The effect of an intracardiac left-right shunt on thermodilution measurements of cardiac output. An extracorporeal circulation model].

Thermodilution measurements of cardiac output (CO) by means of Swan-Ganz catheters, in a strict sense, represent pulmonary arterial blood flow (PBF). In principle, this is also true in the presence of intracardiac left-to-right shunts due to atrial or ventricular septal defects. However, early recirculation of indicator may give rise to serious methodological problems in these cases. We sought to determine the influence of intracardiac left-to-right shunts on different devices for thermodilution measurements of CO using an extra-corporeal flow model. METHODS. Blood flow was regulated by means of a centrifugal pump that at the same time enabled complete mixing of the indicator after injection (Fig. 1). Pulmonary and systemic parts of the circulation were simulated using two membrane oxygenators and a systemic-venous reservoir to delay systemic recirculation of indicator. Control measurements of PBF (Qp) and systemic (Qs) blood flow were performed by calibrated electromagnetic flow-meters (EMF). Blood temperature was kept constant using a heat exchanger without altering the indicator mass balance in the pulmonary circulation. Left-to-right shunt was varied at different systemic flow levels applying a Qp:Qs ratio ranging from 1:1 to 2.5:1. Thermodilution measurements of PBF were performed using two different thermodilution catheters that were connected to commercially available CO computers. Additionally, thermodilution curves were recorded on a microcomputer and analysed with custom-made software that enabled iterative regression analyses of the initial decay to determine that part of the downslope that best fits a mono-exponentially declining function. Extrapolation of the thermodilution curve was then based on the respective curve segment in order to eliminate indicator recirculation due to shunt flow. RESULTS. At moderate left-to-right shunts (Qp:Qs < 2:1) all thermodilution measurements showed close agreement with control measurements. At higher shunt flows (Qp:Qs > or = 2:1), however, conventional extrapolation procedures of CO computers considerably underestimated PBF (Fig. 2). This was particularly true when a slow-response thermistor catheter was used (Fig. 3). The reason for this underestimation of Qp was an overestimation of the area under curve because of inadequate mathematical elimination of indicator recirculation by standard truncation methods (Fig. 4). However, curve-alert messages of the commercially implemented software did not occur. A high level of agreement could be consistently obtained using a fast-response thermistor together with individual definition of extrapolation limits according to logarithmic regression analyses. DISCUSSION AND CONCLUSION. Under varying levels of left-to-right shunt, both the response time of thermodilution catheters and the algorithms for calculation of flow considerably influenced the validity of thermodilution measurements of PBF in an extracorporeal flow model. The use of computer-based regression analyses to define the optimal segment for monoexponential extrapolation could effectively eliminate indicator recirculation from the initial portion of the declining thermodilution curve and showed the closest agreement with EMF measurements of Qp. The quality of thermodilution curves with respect to recirculation peaks in the flow model was slightly better than in clinical routine. Nevertheless, the clinical applicability of the modified extrapolation algorithm could be illustrated during pulmonary thermodilution measurements in an exemplary patient with a ventricular septal defect (Fig. 5). PBF at extremely high shunt ratios, however, cannot be assessed by monoexponential extrapolation in principle (Fig. 6). Insufficient elimination of indicator recirculation resulted in flow values that closely resembled systemic rather than PBF. This finding is in accordance with a mathematical analysis of the underlying Steward-Hamilton equation if an infinite number of recirculations would be

Cardiac Output↗
PubMed2003

Relationship between impaired chronotropic response, cardiac output during exercise, and exercise tolerance in patients with chronic heart failure.

The present study was undertaken to investigate the relationship between the extent of impaired chronotropic response and cardiac output during exercise, and exercise tolerance in patients with chronic heart failure. The subjects consisted of 24 patients (mean 60.1 +/- 14.0 years) who had mild chronotropic incompetence. Cardiopulmonary exercise testing was performed in all patients, and heart rate (HR), anaerobic threshold (AT), maximum oxygen uptake (peak VO2), slope of the regression line relating the ventilatory equivalent to carbon dioxide output (VE/VCO2 slope), and exercise time were measured. Cardiac output (CO) was measured by a thoracic bioimpedance method and cardiac index (CI) was calculated. Plasma norepinephrine (NE) was measured at rest and immediately after the exercise test. The changes in HR, NE, and CI from the resting state to immediately after exercise were calculated as deltaHR, deltaNE, and deltaCI, respectively. The deltaNE was converted to a logarithmic scale and deltaHR/log deltaNE was used as a parameter of HR response to sympathetic nerve stimulation. The results were as follows: HR and NE in the resting state had no correlation with AT and with peak VO2. DeltaHR/log deltaNE correlated positively with both AT and peak VO2, and negatively with the VE/CO2 slope. DeltaHR/log deltaNE correlated positively with peak CI, %deltaCI, and deltaCI/exercise time. The data suggest that one of the mechanisms of low exercise tolerance in chronic heart failure patients was due to an inadequate increase in CO response against exercise caused by an impaired HR response to increased NE.

Adult↗
PubMed1990

Alpha-adrenergic regulation of splanchnic volume and cardiac output in the dog.

The present study examined whether alpha-adrenergic stimulation causes a change in splanchnic intravascular volume in the anaesthetized animal with an intact circulation, which region(s) mediate the volume change, and whether the splanchnic volume change influences cardiac output. In order to ascertain that a radionuclide imaging technique could be used to assess total splanchnic volume changes, drugs known to increase or decrease splanchnic volume were infused on 21 occasions in eight dogs studied under conditions of selective perfusion and drainage of the splanchnic vasculature with erythrocytes labelled with 99Tcm and a gamma camera placed over the abdomen. For these 21 infusions, volume and radionuclide count changes were related: r greater than or equal to 0.90 (n = 20), r = 0.76 (n = 1). After ascertaining tissue attenuation and blood radioactivity in four of the animals, the standard error for a single estimate of the absolute volume change using the radionuclide technique was determined to be 75 ml. In six animals with intact circulations, phenylephrine (40-80 micrograms min-1) for 20 min was associated with an increase in cardiac output of 12 +/- 2% (P less than 0.001) and a decrease in total splanchnic volume estimated to be 431 +/- 95 ml (P less than 0.001). The splanchnic volume decrease was due entirely to decreases in splenic and intestinal volume. In eight eviscerated animals, cardiac output decreased by 30 +/- 2% (P less than 0.001) during phenylephrine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2003

Comparison between cardiac output measured by the pulmonary arterial thermodilution technique and that measured by the femoral arterial thermodilution technique in a pediatric animal model.

This study compares the correlation between two methods for the determination of cardiac output-the pulmonary arterial thermodilution technique using the Swan-Ganz catheter and the femoral arterial thermodilution technique using a pulse contour analysis computer (PiCCO) catheter. We performed a prospective animal study using 16 immature Maryland pigs weighing 9 to 16 kg. A 5.5- or 7.5-Fr Swan-Ganz catheter was introduced into the femoral or jugular vein, and a 4- or 5-Fr arterial PiCCO catheter was introduced into the femoral artery. In each animal, we made measurements of cardiac output at 30-minute intervals, simultaneously by pulmonary arterial thermodilution and femoral arterial thermodilution, before, during, and after hemodiafiltration carried out via different venous catheters, recording a total of 78 measurements. The mean Swan-Ganz cardiac output was 2.22 +/- 0.94 L/min, and mean PiCCO cardiac output was 1.94 +/- 0.80 L/min (no significant difference). The mean difference (bias) of differences (limits of agreement) was 0.2812. The differences between the methods increased with higher cardiac output, but the percentage differences in relation to cardiac output remained stable. Good correlation was found between the two methods: single-measure intraclass correlation was 0.8892 (95% confidence interval, 0.54-0.95). There were no differences between the 5.5- and 7.5-FR Swan-Ganz catheters or between the 4- and 5-Fr PiCCO catheters. Femoral arterial thermodilution cardiac output measurements correlated well with pulmonary arterial thermodilution cardiac output measurements in a pediatric animal model.

Animals↗
PubMed2004

Noninvasive evaluation of cardiac output during postural change and exercise in humans: comparison between the modelflow and pulse dye-densitometry.

To investigate whether the Model-flow method, by simulating the aortic input impedance model from a noninvasive monitoring of arterial blood pressure, reflected a reliable measure of cardiac output (CO) during postural change and whole-body exercise occurring in daily life, we compared the Modelflow-estimated CO with a simultaneous reference determined by the pulse dye-densitometry. Nine healthy volunteers performed postural change from supine to upright and dynamic stepping exercise. The Modelflow-estimated CO decreased to 4.8 +/- 0.5 l/min, from 5.8 +/- 0.6 l/min, during the postural change and increased to 12.8 +/- 1.3 l/min during a stepping exercise, returning to 5.1 +/- 0.4 l/min at 5 min after exercise. When comparing the pooled data of CO during resting and following exercise between the Modelflow and pulse dye-densitometry, we found that the average CO did not differ between the two estimates and that there was a significant correlation between them; the slope of the linear regression line corresponded to approximately 1.0. Although such linear relationship was also observed in an individual subject, the slope of the regression line varied from 0.737 to 1.588 among the subjects. The calibration of the Modelflow-estimated CO with the dye-densitometry value at supine or upright improved a correlation between the two estimates. Thus it is likely that the noninvasive Modelflow simulation from arterial blood pressure can provide a reliable estimation of group-average cardiac output during postural change and stepping exercise occurring in daily life. It will be recommended for a more accurate estimation of cardiac output in a given subject to calibrate the Modelflow data with an independent measure.

Adult↗
PubMed1988

In vivo analysis of partitioning of cardiac output between systemic and central venous sinus circuits in rainbow trout: a new approach using chronic cannulation of the branchial vein.

Freshwater-acclimated rainbow trout were chronically and non-occlusively cannulated in the dorsal aorta (DA), sinus venosus (SV) and branchial vein (BV), the latter returning the blood perfusing the central venous sinus (CVS) of the gill after being shunted away from the systemic circuit. After recovery, blood samples from these three sites were analysed for haematocrit (Hct) and [Hb]. Branchial venous blood was found to have considerably lower Hct and [Hb] (Hct = 3.5 +/- 3.1%; [Hb] = 1.04 +/- 0.75 g 100 ml-1) than systemic blood (DA: Hct = 24.3 +/- 8.9%, [Hb] = 6.54 +/- 2.90 g 100 ml-1; SV: Hct = 23.1 +/- 8.8%, [Hb] = 6.15 +/- 2.55 g 100 ml-1; means +/- S.D. N = 8), which strongly suggests that plasma skimming occurred at arteriovenous anastomoses and arterioles draining into the CVS. The partitioning of cardiac output, calculated on the basis of the [Hb] data, showed that the systemic flow accounted for 93 +/- 4.6% (N = 7) of the total cardiac output with only 7 +/- 4.7% of cardiac output being diverted into the CVS, thus bypassing the systemic vasculature. Previous results using in vitro experiments are compared with the present data in an evaluation of the usefulness of the isolated perfused gill and head preparations in the experimental analysis of circulatory physiology in fish gills.

Animals↗
PubMed1991

Cardiac output and oxygen delivery during exercise in sickle cell anemia.

Desaturation in patients with sickle cell anemia (SCA) can lead to intravascular sickling and vascular occlusion. The increased metabolic demands of exercise tend to increase oxygen extraction, giving rise to a fall in saturation in the capillary bed that may predispose to sickling. This could be minimized with an increase in cardiac output. The aims of this study were to assess the role of increased stroke volume (SV) in augmenting cardiac output (Q) and to estimate the role of enlarged arteriovenous O2 content difference in maintaining O2 transport in children with SCA. A group of 30 children with SCA (Hb 65 to 133 g/L) and 16 healthy controls of the same racial group and of similar height and weight performed incremental and steady-state exercise at 50% Wmax. Cardiac output (Q) was measured by the indirect (CO2) Fick method during steady state. The slope of delta HR/delta VO2 during incremental exercise was higher in SCA subjects compared with controls (4.01 +/- 1.73 versus 2.80 +/- 0.61 bpm per ml/min/kg VO2, p = 0.001). Q for VO2 was abnormally high in patients, particularly older ones with lower Hb levels. HR (% predicted) was higher in patients than in controls (106 +/- 11 versus 92 +/- 8% predicted, p less than 0.0001), as was SV (113 +/- 16 versus 98 +/- 14% predicted, p = 0.002). Multiple linear regression of Q % predicted and SV % predicted on Hb and age showed a positive correlation with age and a negative correlation with Hb (r = 0.84 for Q and r = 0.76 for SV).(ABSTRACT TRUNCATED AT 250 WORDS)

Anemia, Sickle Cell↗
PubMed1990

Effect of rate-adapting atrioventricular delay on stroke volume and cardiac output during atrial synchronous pacing.

The need to adjust atrioventricular delay relative to pacing rate in atrial synchronous pacemakers was assessed in eight subjects treated for complete heart block (mean age 61 +/- 3.4 years). First, an inverse relationship between heart rate and PR interval was confirmed in two groups of healthy subjects and one group of patients recovering from myocardial infarction. Due to the limitations of the available pacemakers this relationship could not be precisely reproduced. Subjects with pacemakers performed an initial exercise test on a bicycle ergometer to determine heart rate response; this information was used in part 2 to program atrioventricular delay relative to heart rate. During a second exercise test, a rate-adapting atrioventricular delay was compared to a constant atrioventricular delay of 200 ms at matched heart rates. Cardiac output was measured noninvasively by impedance cardiography. The results of part 1 showed an abnormal pattern in the response of stroke volume to exercise in seven subjects. Part 2 results demonstrated no significant difference (P greater than 0.05) between a rate-adapting atrioventricular delay and a constant delay of 200 ms for heart rate, stroke volume, cardiac output, blood pressure or Borg scale. A trend towards increased stroke volume with a rate-adapting atrioventricular delay was observed. Stroke volume was 13% larger with a rate-adapting atrioventricular delay of 125 ms at a heart rate of 125 beats/min. These results suggest that subjects with atrial synchronous pacemakers have a variable stroke volume response to exercise. It appears that in these subjects the ability to increase heart rate is the key factor for raising cardiac output during exercise.

Adult↗
PubMed1977

Effects of heart rate augmentation on left ventricular volumes and cardiac output of the transplanted human heart.

The response of the donor left ventricle to atrial pacing was measured in 11 patients 12 to 64 days after cardiac transplantation. At operation seven miniature tantalum coils were placed into the midwall of the donor left ventricle so as to outline the ventricle in a 30 degrees right anterior oblique projection. Computer aided fluoroscopic analysis of marker dynamics allowed calculation of end-diastolic and end-systolic volumes, stroke volume, cardiac output, and ventricular filling characteristics. Recipients were studied in a resting, unsedated state during a period of clinical stability that did not immediately follow or precede an episode of graft rejection. Augmentation of heart rate by an average of 40 beats per minute above sinus rate produced significant reductions in end-diastolic volume (-19%), end-systolic volume (-8%), stroke volume (-31%), and the duration of systole (-19%), and diastole (-40%). Cardiac output was invariant with rate. In all patients, end-diastolic volume reduction at augmented rates was brought about by abbreviated diastolic filling as initiation of contraction occurred at an earlier point on a common, incremental filling curve. Previous studies have shown that the normal inverse relationship between heart rate and stroke volume is not available to the transplanted heart in the immediate postoperative period. The present study shows that this intrinsic mechanism becomes available to the denervated heart in the subsequent recovery period after surgery.

Cardiac Output↗
PubMed1981

Cardiac output and venous return as interdependent and independent variables.

Under steady states the heart pumps whatever it receives and receives whatever it pumps. In other words, cardiac output (CO) and venous return (VR) are equal and the distinction between the two seems unnecessary. However, under nonsteady states the two are temporarily unequal and the distinction becomes significant. VR varies directly with the difference in pressure between the end of systemic capillaries and the right ventricle during filling and inversely with the total resistance of the venous system. Thus, the energy for VR is derived from CO. In some transient states VR becomes an independent variable and CO dependent until a new steady state is reached (e.g., exercise, hemorrhage, fevers, hyperthyroidism, severe anemia, etc.). In other conditions the opposite is true (e.g., myocardial infarction, altered ventricular contractility, etc.). Explanation of changes in cardiac output in various perturbations of circulation are based on the identification of the independent variable (VR or CO) in a given physiologic or pathologic condition during the period that a nonsteady state exists.

Animals↗
PubMed1984

Cardiac output determined by the CO2 rebreathing method with correlation of lung-bag volume shrinkage.

The purpose of this study was to elucidate the effect of lung-bag volume shrinkage on P'VCO2 estimated by the CO2 rebreathing method and to correct its effect in calculation of cardiac output. The P'VCO2 was extrapolated with the linear relationship between dPACO2/dt and PACO2 during rebreathing. The P'VCO2 was higher than real mixed PCO2 by 0.82 mmHg at rest, by 1.35 mmHg at 50W, 1.57 mmHg at 100W, and 3.06 mmHg at 150W considering the effect of lung-bag volume shrinkage detected by argon concentration. The cardiac output obtained by the CO2 rebreathing method with correction of above differences was in good agreement with that determined by the acetylene method (r = 0.930, p less than 0.001). When the cardiac output was plotted against O2 uptake, our results and the regression line were fairly close to the reported regression lines.

Carbon Dioxide↗
PubMed2002

Effect of endovascular cooling on myocardial temperature, infarct size, and cardiac output in human-sized pigs.

Mild hypothermia reduces myocardial infarct size in small animals; however, the extent of myocardial protection in large animals with greater thermal mass remains unknown. We evaluated the effects of mild endovascular cooling on myocardial temperature, infarct size, and cardiac output in 60- to 80-kg isoflurane-anesthetized pigs. We occluded the left anterior descending coronary artery for 60 min, followed by reperfusion for 3 h. An endovascular heat-exchange catheter was used to either lower core body temperature to 34 degrees C (n = 11) or maintain temperature at 38 degrees C (n = 11). Additional studies assessed myocardial viability and microvascular perfusion with (99m)Tc-sestamibi autoradiography. Endovascular cooling reduced infarct size compared with normothermia (9 +/- 6% vs. 45 +/- 8% of the area at risk; P < 0.001), whereas the area at risk was comparable (19 +/- 3% vs. 20 +/- 7%; P = 0.65). Salvaged myocardium showed normal sestamibi uptake, confirming intact microvascular flow and myocyte viability. Cardiac output was maintained in hypothermic hearts because of an increase in stroke volume, despite a decrease in heart rate. Mild endovascular cooling to 34 degrees C lowers myocardial temperature sufficiently in human-sized hearts to cause a substantial cardioprotective effect, preserve microvascular flow, and maintain cardiac output.

Animals↗
PubMed1977

[Determination of cardiac output by the method of tetrapolar chest rheography and evaluation of its metrological possibilities].

Tetrapolar chest rheography is an up-to-day, convenient and bloodless method of determining the cardiac stroke volume (CSV) and cardiac output (CO) in dynamic observations. The paper presents and analysis of the method and considers the possibilities and limits of its application in determining the stroke volume and cardiac output. Advantages of the Kubicek procedure as modified by the authors by comparison with other rheographic methods are shown, along with methodological procedures employed for dtermining the CSV and CO and a nomogram that significantly facilitates the calculation of the values under study is offered. Results of contrasting the cardiac ejection values in patients with congenital heart diseases and an increased pulmonary circulation as against those in patients with ischemic heart disease, obtained by means of tetrapolar chest rheography and direct Fick's method are cited. The possibility of applying tetrapolar chest rheography in assessing the effect operative treatment in patients with congenital cardiac defects and also when investigating compensatory reactions of the cardio-vascular system in patients with hypertensive disease in the course of the orthostatic and Valsalva tests is demonstrated.

Adult↗
PubMed1976

Cardiac output during physical exercises following real and simulated space flight.

During moderate physical work (after 5 min) the cardiac stroke volume in the cosmonauts who made 2--8-day flights in the Soyuz spacecraft was lower and the pulse rate was higher than the pre-flight level. By the end of the 49-day bed-rest experiment the stroke volume during physical exercises (after 5 min) was lower than at the 5th min of the pre-test period in both the supine and sitting positions. The cosmonauts performed physical exercises in the sitting position. Therefore, it can be assumed that the major factor changing cardiac output may be the effect of the earth's gravity against the background of decreased orthostatic tolerance. Results of simulated experiments give evidence that in both cases one of the major factors responsible for changes in the cardiac output was a decline in the contractile capacity of the myocardium.

Bed Rest↗