Role of leg vasculature in the cardiovascular response to arm work in wheelchair-dependent populations

To assess the effects of leg vasculature on cardiovascular dynamics during submaximal arm work, oxygen uptake (VO2), cardiac output (Q) and heart rate (HR) were measured during arm-crank ergometry (ACE) at 35 W (45% peak ACE VO2) in five able-bodied subjects, five wheelchair-dependent paraplegics, and five wheelchair-dependent bilateral amputees who represented the conditions of active, passive, and absence of leg musculature respectively. Arteriovenous oxygen difference (a-v O2) and stroke volume (SV) were calculated from VO2, Q and HR. An index of leg fluid accumulation and leg blood flow was measured in the paraplegics and able-bodied subjects during rest and ACE. VO2, Q, and a-v O2 during ACE were not statistically different among the three groups. However, paraplegics exhibited higher HR (P less than 0.05) and lower SV (P less than 0.06) during exercise compared to both amputees and able-bodied subjects. Greater (P less than 0.05) leg fluid accumulation was measured in paraplegics compared to able-bodied subjects, although no statistically significant differences in leg blood flow were observed. Although our results are limited to a small number of subjects, these data suggest that an active muscle pump contributes significantly to elevated venous return and stroke volume during ACE. The legs of the paraplegic appear to act as a reservoir for fluid accumulation which may limit cardiac filling, particularly during moderate arm work to support wheelchair function.     

Combined left and right ventricular volume determination by radionuclide angiocardiography using double bolus and equilibrium technique

Eighteen patients with ischaemic heart disease were studied. Left and right ventricular volumes including cardiac output (forward flow) were determined by radionuclide angiocardiography using a double bolus and equilibrium technique. As reference, cardiac output was simultaneously measured by indicator dilution. The radionuclide technique comprised four steps: (1) a first-pass study of right ventricle; (2) a bolus study of left ventricle; (3) an equilibrium study of left ventricle; (4) determination of the distribution volume of red blood cells. Absolute volumes of left ventricle were determined from steps 2 + 3 + 4. Absolute volumes of right ventricle were calculated from stroke volume and right ventricular ejection fraction (EF) which in turn was determined from step 1 by creating composite systolic and composite diastolic images. There was an acceptable agreement between stroke volume determinations by radionuclide angiocardiography and indicator dilution (r = 0.74; P less than 0.001). Stroke volume determination by radionuclide was 83 +/- 20 ml (mean +/- SD) and by indicator dilution 84 +/- 20 ml with a difference of -1 +/- 15 ml (NS). Cardiac output determination by radionuclide was 5.24 +/- 1.37 l min-1 and by indicator dilution 5.28 +/- 1.23 l min-1 with a difference of -0.04 +/- 0.95 l min-1 (NS). Left ventricular EF was 0.44 +/- 0.14 and right ventricular EF 0.57 +/- 0.10. The intra-observer coefficient of variation for duplicate calculations of the radionuclide determinations was 5.5% for stroke volume, 2.5% for left ventricular EF and 4.8% for right ventricular EF.     

Cardiac output determined by ultrasound-Doppler: clinical applications

A non-invasive method for cardiac output determination (COD) based on ultrasound-Doppler technique was evaluated in patients with cardiac disease at rest and during exercise, including patients with heart transplants. The aortic blood flow velocity was measured with pulsed Doppler technique from the jugulum, placing the sample volume just above the aortic valve, and the area from a parasternal 2-D echocardiographic measurement of the aortic annulus diameter assuming a circular area. Cardiac output was calculated as the product of the systolic velocity integral, the aortic annulus area and the heart rate. A high correlation was found between this method and a simultaneously performed invasive cardiac output (COF) and stroke volume (SVF) determination by the direct Fick method (COD = 0.3 + 0.9 x COF, r = 0.96, SDres = 0.5 l min-1 and SVD = 3.9 + 0.92 x SVF, r = 0.94, SDres = 6.9 ml). However, looking just at the systolic velocity integral compared to stroke index determined with the Fick method we found a low correlation, especially in patients with heart transplants. We conclude that cardiac output can reliably be measured non-invasively with this method--also in patients with heart transplants. The systolic velocity integral alone can be used for assessing changes in stroke volume but for absolute values of stroke volume and stroke index flow area should also be determined.     

Changes of cardiac output during treadmill exercise by impedance cardiography

Nine athletes and ten nonathletes were selected randomly to study the changes of cardiac function during exercise by impedance cardiography. The speed of the treadmill was maintained at 3.4 mph, and its grade was increased by 1% (Balke protocol). The exercise was continued until the target heart rate (THR), 85% of maximum oxygen uptake (VO2max). The measured parameters for pre- and post-exercise were stroke volume (SV), heart rate (HR), and cardiac output (CO). Average stroke volume of athletes at pre-exercise, 71.1 ml, was higher than that of nonathletes, 64.6 ml, and stroke volume of the former at post-exercise, 97.0 ml, was also higher than that of the latter, 85.2 ml. Therefore, despite the lower heart rate, cardiac outputs of athletes at pre- and post-exercise, 4.98 and 16.3 L/min, were higher than those of nonathletes, 4.87 and 14.2 L/min. For the second phase of the study, cardiac outputs of three subjects were measured during the continuous treadmill exercise with newly developed electrodes and shoes for minimizing motion artifact. Though there were several studies measuring cardiac output during continuous bicycle exercise, this is thought to be the first study in the world measuring cardiac output during continuous treadmill exercise without aid of ensemble averaging.     

Cardiac response to exercise in young,normal weight and overweight men and women

Overweight and obesity are associated with hemodynamic changes at rest. Whether these changes are mirrored during exercise is uncertain. We compared cardiac output (Q) and stroke volume (SV) in 12 overweight (OW) and 12 normal weight (NW) adults at rest and during exercise. Participants were assessed for body composition, peak oxygen consumption, and Q and SV at rest and during cycling exercise at 50, 75 and 100 W. Cardiac output was significantly higher at rest and during exercise in OW than NW when fat mass and ethnicity were used as covariates. When fat free mass was added as a covariate, Q was no longer different between groups. Stroke volume tended to be higher in OW than NW when fat mass and ethnicity were used as covariates (P = 0.055) with no differences in heart rate observed. Although the total change in Q and SV was similar between groups with each exercise intensity, overall Q was higher in the OW than NW participants. The higher Q is likely explained by a higher SV, secondary to a greater blood volume in the OW. The elevated hemodynamic response in OW may reflect the early cardiac adaptations of excess body mass. University of Texas Research Institute funded part of this study.     

Central and peripheral cardiovascular adaptations to exercise in endurance-trained children

Stroke volume (SV) response to exercise depends on changes in cardiac filling, intrinsic myocardial contractility and left ventricular afterload. The aim of the present study was to identify whether these variables are influenced by endurance training in pre-pubertal children during a maximal cycle test. SV, cardiac output (Doppler echocardiography), left ventricular dimensions (time-movement echocardiography) as well as arterial pressure and systemic vascular resistances were assessed in 10 child cyclists (VO2max: 58.5 +/- 4.4 mL min-1 kg-1) and 13 untrained children (UTC) (VO2max: 45.9 +/- 6.7 mL min-1 kg-1). All variables were measured at the end of the resting period, during the final minute of each workload and during the last minute of the progressive maximal aerobic test. At rest and during exercise, stroke index was significantly higher in the child cyclists than in UTC. However, the SV patterns were strictly similar for both groups. Moreover, the patterns of diastolic and systolic left ventricular dimensions, and the pattern of systemic vascular resistance of the child cyclists mimicked those of the UTC. SV patterns, as well as their underlying mechanisms, were not altered by endurance training in children. This result implied that the higher maximal SV obtained in child cyclists depended on factors influencing resting SV, such as cardiac hypertrophy, augmented myocardium relaxation properties or expanded blood volume.     

Maximum aerobic power and physical dimensions of children.

Age, height, mass, fat-free mass and vital capacity were used as predictors of maximum aerobic power (VO2 max). The variables were cast in linear form by logarithmic transfomation and submitted to multiple regression analysis. Results indicate VO2 max as a power function of age, height and mass in 50 untrained boys aged 7 to 13 years. In this group the relationship between VO2 max and body mass may be expressed by the equation Y=0.076X0.88 (r=0.92, P <0.01). Age, height and mass together accounted for 89 per cent of the variance in VO2 max (R=0.94, P <0.01). In 30 girl swimmers and in 14 young boys during 22 months of running training, VO2 max was proportional to body mass and indicated greater maximum aerobic power for their size and age. In normally growing children, VO2 max appears to increase more slowly than body mass. Children subjected to aerobic training evidently maintain VO2 max in proportion to their increasing mass throughout adolescence.     

Evaluation of a modified acetylene rebreathing method for the determination of cardiac output

In order to evaluate a computerized modified acetylene rebreathing method for the determination of cardiac output, 15 healthy subjects were studied at different levels of their maximal oxygen uptake (VO2max). Submaximal exercise was performed on a cycle ergometer and maximal exercise on a treadmill. Oxygen uptake, heart rate, and cardiac output (acetylene method) were determined in all test situations. In seven subjects simultaneous determinations of cardiac output were made by a modified acetylene rebreathing method (QA) and a dye dilution method (QD). Furthermore, a new resting rebreathing technique was used. The methodological error for QA (means of double samples) was 0.37 litre min-1 (2.8%) in the same individual at 150 W. The corresponding values between individuals were 0.71 (rest), 0.41 (50 W), 0.69 (150 W), and 0.40 litre min-1 (VO2max). Thus the methodological error of the modified acetylene method was very low. There was a significant difference (P less than 0.01), however, between the acetylene method and the dye dilution method, which showed a lower value for QA at all levels. This was probably due to the long response time of the mass spectrometer combined with anatomical and physiological arteriovenous shunt effects in the lungs during exercise. When these factors were considered the correcting formula was: QAc = QA + 0.005 X Q2A. There was no significant difference between the corrected cardiac output values (QAc), and the corresponding QD values. In conclusion, this modified acetylene rebreathing method is a very useful non-invasive method for measuring cardiac output at rest as well as during heavy exercise.     

Simultaneous measurement of cardiac output and pulmonary diffusing capacity for CO by a rebreathing method

A rebreathing method was developed to obtain the pulmonary diffusing capacity for CO, DL(CO) and the cardiac output, Q, simultaneously at rest and during exercise. From DL(CO) and Q, contact time of the red blood cell (RBC) through the lung capillary, tc, was estimated by referring to a reaction rate factor of CO with RBC, Fc(CO). The DL(CO) and Q were calculated from the changes in CO, O2, and CO2 concentrations in rebreathing air. The Fc(CO) was evaluated so as to attain a proportional relation between the DL(CO) and Fc(CO) by varying a transfer coefficient for CO across the RBC boundary including the capillary wall. The PO2 dependence of Q was also taken into account in the above analyses. The tc was determined by dividing the DL(CO) by Fc(CO), Q, and fractional hematocrit. The DL(CO) and Q measured in five normal subjects in a sitting position were 26.6 +/- 2.9 ml X min-1 X Torr-1 and 5.9 +/- 0.6 l X min-1 (mean +/- S.D.), respectively, which increased during moderate exercise up to 34.6 +/- 3.9 ml X min-1 X Torr-1 and 13.0 +/- 1.2 l X min-1. The tc was 0.70 +/- 0.06 s at rest and 0.40 +/- 0.05 s during exercise. The rebreathing method for measuring DL(CO) was more advantageous than the single breath method, because the tc could be obtained as well as the Q and the influence of the dead space and ventilation-perfusion uneveness on DL(CO) was reduced.     

Sham-feeding decreases cardiac output in normal subjects.

The cardiovascular effect of sham-feeding was measured in seven healthy non-obese human subjects by the Fick principle using the carbon dioxide rebreathing method. The subjects were resting in the sitting position and were exposed to the sight and smell but not the taste of a breakfast meal. Cardiac output decreased significantly from a mean value of 4.0 1 min-1 to 3.5 1 min-1 during sham-feeding (Friedman, P = 0.004). The cardiac output returned to basal values in all seven subjects when the sensory stimulus was removed. The decrease in cardiac output was due to a decreased stroke volume, whereas heart rate and blood pressure did not change. The mechanism of the decrease in cardiac output during sham-feeding remains to be established.     

Cardiac output decline in prolonged dynamic exercise is affected by the exercise mode

The aim of this study was to compare the cardiovascular responses to prolonged submaximal cycling and running. Eleven males [maximal oxygen uptake (VO(2max)): 3.58+/-0.15 l min(-1) for running and 3.84+/-0.16 l min(-1) for cycling; mean+/-SE] either cycled (C) or ran (R) for 90 min at 60% of mode-specific VO(2max), on two randomly assigned occasions. Cardiac output declined after 85 min of exercise in C (-1.9+/-0.5 l min(-1), P<0.01) but not in R, as a result of a more pronounced decrease in stroke volume in the former exercise mode (-22.7+/-3.8 ml beat(-1) vs -14.3+/-1.9 ml beat(-1), P<0.01) since heart rate did not differ between trials. Stroke volume responses were despite a higher level of dehydration (-3.3+/-0.2% in R vs -2.8+/-0.2% in C, P<0.05) and hyperthermia in R (39.6+/-0.1 vs 38.8+/-0.1 degrees C in C at 90 min, P<0.01). Finally, mean skin blood flow was lower in R than C (72+/-8 vs 89+/-10%; P<0.05). In conclusion, stroke volume and cardiac output decline was more pronounced in cycling than in running despite lower dehydration and rectal temperature in the former exercise mode.     

Reproducibility of cardioventilatory measurements using a respiratory mass spectrometer

The aim of this study was to assess the within subject reproducibility of cardioventilatory measurements and the maximum permitted 'normal' variability over time at rest and exercise using the respiratory mass spectrometer (RMS). Ten subjects underwent an incremental exercise test on three separate occasions utilising rebreathing (RB) and helium dilution mixed expired gas analysis (HME) functions of the RMS. Measurements included heart rate (HR), oxygen consumption (V(O2)), carbon dioxide excretion (V(VO2)), effective pulmonary blood flow (Q(eff)), stroke volume (SV), arteriovenous oxygen content difference (AVO), transfer factor (Dl(CO)), functional residual capacity (FRC), minute ventilation (VE), tidal volume (VT) and respiratory quotient (RQ). The coefficients of variation for each variable for the 10 subjects were calculated. At rest, the 90th centile variability for measured cardiopulmonary variables (RB only) was <35%. During exercise, the 90th centile for variability for measured cardiopulmonary variables for HME and RB were < or =20 and <40%, respectively. These measurements in healthy adults should inform sample size in research studies.     

Effect of Physical Training on Hemodynamic Response during Submaximal and Maximal Exercise in 11–13-Year Old Boys

Nine healthy boys, mean age 11.7 years (11.0–13.0), height 150.4 cm and weight 45.1 kg, were examined with determinations of maximal oxygen uptake (1.85 1×min^-1), heart volume (499 ml) and total hemoglobin (391 g). Cardiac output was determined at rest and during exercise, including maximal exercise, using the dye-dilution technique and i.a. pressures were recorded. Cardiac output was approximately 2 1×min^-1 lower and the systemic a-v oxygen difference (AVD) was correspondingly higher than for young adult men at the same sub-maximal oxygen uptake. At maximal exercise cardiac output was 12.5 1×min^-1, stroke volume 67 ml, AVD 14.2 ml × 100 ml^-1, systolic, diastolic and mean blood pressure 160, 71 and 105 mm Hg respectively and total peripheral resistance 8.6 mm Hg×1–¹×min. After a training period of 4 months a normal increase in height was found in all boys, but body weight was unchanged. Maximal oxygen uptake increased to 2.21 1×min^-1 (p < 0.01), almost entirely due to increased stroke volume (80 ml), resulting in a maximal cardiac output of 14.6 1×min^-1. No significant increase in AVD was found. Mean blood pressure at maximal exercise increased significantly, total peripheral resistance was unchanged. Both heart volume and total hemoglobin showed minor increases, but the changes found were not significantly larger than expected from body growth. The hemoglobin concentration was normal (13 g%) for the age and unaffected by training.     

Sex Differences in the Relation of Body Composition to Cardiovascular Parameters and Functions in Korean Adolescents: A School-Based Study

ObjectiveObesity in adolescence is associated with increased cardiovascular risk. The patterns of obesity and body composition differ between boys and girls. It is uncertain how body composition correlates with the cardiovascular system and whether such correlations differ by sex in adolescents.MethodsBody composition (fat-free mass (FFM), adipose mass, waist circumference (WC)) and cardiovascular parameters and functions were studied in 676 healthy Korean adolescents aged 12-16 years. Partial correlation and path analyses were done.ResultsWC correlated with stroke volume (SV) and cardiac output (CO), systolic blood pressure (SBP) and pulse pressure (PP), cardiac diastolic function (ratio of early to late filling velocity (E/A ratio)), and vascular function (pulse wave velocity (PWV)) in boys. Adipose mass was related to SV, CO, SBP, PP, left ventricular mass (LVM), and PWV in girls – and to E/A ratio in both sexes. FFM affected SV, CO, SBP, and PP in both sexes and LVM in boys. Cardiac systolic functions had no relation with any body composition variable in either sex.ConclusionIn adolescence, the interdependence of the cardiovascular system and the body composition differs between sexes. Understanding of those relations is required to control adolescent obesity and prevent adult cardiovascular disease.Key Words: Adolescent, Body composition, Cardiac output, Blood pressure, Pulse wave velocity     

Non-invasive assessment of cardiac output and stroke volume in patients during exercise

Summary A one-step CO₂ rebreathing method for the determination of cardiac output and stroke volume (SV) has been evaluated by comparison with the direct Fick technique during recumbent exercise (10–90 W) in 13 patients. In an initial analysis, the influence of different rebreathing times and of correction for haemoglobin concentration was studied. The best correlation with the direct Fick technique was obtained with the longest analysis time, i. e. 21 s, and correction for variations in haemoglobin concentration further improved the correlation. Consequently, an analysis time of 21 s and correction for haemoglobin have been used. At low cardiac outputs, the CO₂-rebreathing method overestimated the flow compared to the Fick technique. The correlation between the methods, however, was so good that a valid estimate of cardiac output could be obtained from the CO₂ rebreathing method with appropriate corrections (Cardiac output, CO₂ method=2.7+0.77. Cardiac output, Fick; r=0.91; Residual Standard deviation (SD res) =0.77 l · min⁻¹). Stroke volumes measured with the CO₂ rebreathing method did not differ significantly from those obtained with the direct Fick technique, although there was a tendency to overestimate stroke volume with the CO₂ rebreathing method (SV, CO₂ method=12+0.89 · SV, Fick; r=0.82; SD res=11 ml).     

Heart rate-independent energetics and systolic pressure-volume area in dog heart

Left ventricular (LV) systolic pressure-volume area (PVA), a new measure of total mechanical energy for the contraction, linearly correlates with its oxygen consumption per beat (VO2) regardless of contraction mode in a canine heart with stable chronotropism and inotropism. PVA is the area in the pressure-volume (PV) diagram circumscribed by the end-systolic and end-diastolic PV relation curves and the systolic segment of the PV loop and has dimensions of energy. We investigated whether primary changes in heart rate would affect the VO2-PVA relation. In the excised cross-circulated canine heart with left ventricular load controlled with a servo pump, we changed heart rate by pacing to compare the VO2-PVA relations at low [124 +/- 17 (SD) min-1] and high (193 +/- 23) heart rates. In 15 left ventricles, VO2 (ml O2 X beat-1 X 100 g LV-1) was (1.75 +/- 0.57) X 10(-5) PVA (mmHg X ml X beat-1 X 100 g LV-1) + 0.031 +/- 0.011 (ml O2 X beat-1 X 100 g LV-1). The VO2-PVA relation was virtually independent of heart rate in individual hearts. We conclude that the load-independent VO2-PVA relationship is not affected by chronotropism in a given canine left ventricle.     

Cardiorespiratory reactions to static, isometric exercise in man.

Cardiac output (Q), stroke volume (SV), heart rate (HR), and respiratory variables were measured in ten healthy men performing static, isometric muscular contraction (handgrip) during air breathing. We found an instantaneous rise in ventilation (VI) and in HR, accompanied by a minimal rise in cardiac output. The rise in VI was due to a rise in tidal volume (VT) and a reduction in expiratory duration (TE). These effects of isometric exercise are explainable as due to a muscle reflex instantly inhibiting the cardiac, vagal motoneurons and, at the same time, stimulating neurons in the respiratory area of the medulla. These medullary neurons seem capable of independent operation. The rise in mean arterial pressure (MAP) during isometric exercise is 27% just as the rise in total peripheral vascular resistance (TPVR). The MAP rise is too high to be caused by vascular occlusion due to the high tension of contracted muscles in only one upper extremity. Thus, redistribution of Q in the system of many parallel vascular resistances is a likely possibility--with possible cutaneous vasodilation and dominating vasoconstriction of other vascular regions.     

Non-invasive determination of effective stroke volume. Evaluation of a CO2-rebreathing method in normal subjects and patients

A CO2-rebreathing method for the determination of stroke volume (SV) was evaluated at rest by comparison with the direct Fick technique in 50 randomly selected patients with valvular heart disease. Patients with intracardiac shunts were excluded. Objective criteria for acceptance of a measurement were set to ensure reliable results. Forty-six of the 50 patients fulfilled these criteria. The rebreathing manoeuvre is, in itself, an effort for the patient, leading to a change in steady state which excludes simultaneous comparison with the direct Fick method. Day-to-day variation of the SV measured with the CO2-method was therefore assessed first, and found to be low. Because of this low day-to-day variation, a comparison of stroke volumes measured one day with the CO2-method and next day with the direct Fick technique was found to be acceptable. In the determination of SV in the supine position, there was no significant difference between the two methods (SVCO2 = 5.2 + 0.90 X SVFick, r = 0.90, SDres = 9.4 ml, n = 46), while cardiac output was significantly higher when measured with the CO2 technique than with the direct Fick method (22%, P less than 0.001). Ten of 12 patients with signs of obstructive lung disease managed to produce registrations which fulfilled the criteria of acceptance. The method is well suited for clinical use.     

Physical fitness in aging men

Of 56 middle-aged male joggers (mean age 43.3 yr), 38 were measured for maximal oxygen uptake (VO2max) and 18 for cardiac output at a heart rate of 170 bpm (Q170). Each Q170 was divided by subject body surface area to yield cardiac index (CI170). A treadmill protocol was used to elicit maximal exercise during measurement of VO2max. The bicycle ergometer was employed when measuring Q170. For maximal exercise, termination was upon subject-declared fatigue. In subjects measured for VO2max, heart rate at 3.5 miles/h and 5% treadmill grade (HRsubmax) as well as heart rate at maximal exercise (HRmax) were noted. Heart rates were monitored electrocardiographically. A modified Douglas bag technique was applied when sampling expired air for determination of VO2max. Carbon dioxide rebreathing was used to estimate Q170. Data were grouped according to age (43 yr and older; 42 yr and younger). There were significant (P less than 0.05) positive relationships between VO2max and HRmax and between HRsubmax and age. Significant negative relationships existed between HRmax and HRsubmax, and between CI170 and 10 km running time. There were no significant differences (P greater than 0.05) between means achieved by the age groups. The overall mean for VO2max was 43.36 ml/kg per min and for Q170 33.53 1/min. Findings suggest that men who remain physically active retain youthful characteristics of cardiorespiratory function.     

Prediction of maximal aerobic power from the 20-m multi-stage shuttle run test.

The purpose of this study was to test the accuracy of the 20-m multi-stage shuttle run (SR) test to predict VO2max in young adults. VO2max was measured during a graded treadmill test in 60 men and 62 women (mean age 25.3 and 25.1 years, respectively). Each subject was familiarized with the SR procedure and the completed the SR test to predict VO2max on a separate day. The mean terminal SR stage was 9.5 for men and 7.8 for women. The regression equations of Léger et al. (1988) and Léger and Gadoury (1989) systematically underpredicted VO2max for both males and females (p < 0.05). New regression equations were developed from present data to predict VO2max for males: Y = 2.75X + 28.8 (r2 = 0.77, SEE = 4.07 ml.kg-1.min-1); and for females: Y = 2.85X + 25.1 (r2 = 0.66, SEE = 3.64 ml.kg-1.min-1), where X equals the last half-stage of the SR completed. We suggest that these gender-distinct equations provide more accurate predictions of VO2max from the SR.