A Comparison of Hemodynamic Changes during the Transition from Mechanical Ventilation to T-Piece, Pressure Support, and Continuous Positive Airway Pressure in Canines
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The immediate transition from positive pressure mechanical ventilation to spontaneous ventilation may generate significant cardiopulmonary hemodynamic alterations based on the mode of weaning selected, particularly in individuals with preexisting cardiac dysfunction. The purpose of this study was to compare hemodynamic responses associated with the initial transition to 3 modes of ventilator weaning (spontaneous ventilation/T-piece, pressure support [PS], and continuous positive airway pressure [CPAP]). Right ventricular hemodynamic responses were evaluated with a thermodilution pulmonary artery catheter; while left ventricular hemodynamic responses were measured by a transducer-tipped Millar catheter and conductance catheter. Two groups of canines were studied. Group 1: normal biventricular function (n = 10) and group 2: propranolol-induced biventricular failure (n = 10). Dependent variables were measured at baseline on controlled mechanical ventilation (MV) and following the initial transition to each of 3 randomized spontaneous ventilatory conditions: T-piece, PS 5 cmH2O, and CPAP 5 cmH2O. Both groups significantly increased cardiac output in response to T-piece. Right ventricular stroke work was also significantly increased with T-piece and CPAP in both groups of subjects. Left ventricular response depended on baseline ventricular function. Baseline ventricular function influenced hemodynamic response to the immediate transition from mechanical to spontaneous ventilation. There were also differential hemodynamic responses based on the ventilatory mode. Consideration of baseline cardiac function may be an important factor in the selection of an appropriate mode of spontaneous ventilation following controlled MV.Cardiac function was studied with Scintiview in 107 cases, 24 normal and 83 affected cases, and the following results were obtained. 1. Better data were obtained with converging collimeter than with parallel collimeter in cardiac study. (2) Red blood cells were sufficiently labeled with 99mTc using stannous chloride as reductant, and it was proven to be applicable to measurement of circulation blood volume. (3) Pulmonary circulation time and the systemic circulation time calculated from time activity curve, greater than 9.0 seconds and greater than 25 seconds, respectively, were considered abnormal prolongation. (4) Cardiac output index (cardiac output/circulation blood volume), less than 1.10 was considered decreased cardiac output. (5) Stroke volume index ((stroke volume/circulation blood volume)x 100, less than 1.70 was considered decreased stroke volume. (6) Ejection fraction, less than 60% was considered decreased left ventricular wall motion. (7) Cardiac function index (cardiac output index X ejection fraction), less than 80 was considered decreased cardiac performance.
Cardiac index
Circulation (fluid dynamics)
Blood circulation
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The adjustments of the cardiovascular system to muscular exercise were studied in dogs running on a treadmill at different speeds and at the incline of +10%. The cardiac output, measured by the thermodilution method, increased with increasing O 2 consumption, reaching 520 ml/kg min at an O 2 consumption of 70 ml/kg min. At still higher metabolic levels the cardiac output remained constant and the O 2 consumption increased by an increase of the arteriovenous O 2 difference only, which was calculated to attain 17 vol % at the highest O 2 consumption value reached in this study, 90 ml/kg min. The increase of the cardiac output was mainly due to increase of the heart rate, whereas the average maximum increment of the stroke volume was about 30% only. The mean arterial and the central venous blood pressures increased with exercise. The time course of the adjustment of the cardiac output was measured after the exercise of varied intensity had been abruptly begun or stopped. Both for start and recovery the “half reaction time” was about 20 sec; after 1 min no further measurable change of the cardiac output was detectable. cardiac output and O 2 consumption at increasing metabolic levels; heart rate and stroke volume in running dogs recovery following exercise Submitted on July 15, 1963
Treadmill
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Impedance cardiography
Cardiac index
End-systolic volume
Stroke
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Stroke
End-systolic volume
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"Classic" cardiovascular drift is characterized by findings of decreasing stroke volume and mean arterial pressure, rising heart rate, and stable cardiac output during sustained constant-load exercise. Recent studies in adults indicate that when dehydration is prevented by fluid intake, this pattern is altered, with no change in stroke volume and progressive rise in cardiac output. This study was designed to examine this influence of hydration in prepubertal subjects and assess the relationship between cardiovascular drift and aerobic drift (changes in VO2). Eight boys (Tanner stage 1, mean age 11.7 +/- 0.4 y) cycled at an average of 62.9% +/- 3.9% VO2 peak to exhaustion (41.38 +/- 6.30 min) in a thermoneutral environment. Rectal temperature rose from 37.6 +/- 0.1 degrees C at rest to 38.1 +/- 0.2 degrees C at end exercise. Between 5 min and end exercise, average heart rate rose by 13.2% and cardiac output rose by 14.9%, systemic vascular resistance fell by 10.5%, and stroke volume remained stable. Increases in cardiac output paralleled those of VO2, with no change in arterial venous oxygen difference. These findings are consistent with the conclusion that cardiovascular drift is a reflection of aerobic drift, a relationship obscured by the superimposed physiological effects of dehydration during sustained constant load. This study also suggests that such patterns are no different in prepubertal boys and young adult men.
Venous return curve
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The physiologic variables defining the circulatory and respiratory state in normal man have been measured in recumbency, standing at rest and during progressively severe grades of exercise approaching near-maximal levels. Indicator-dilution technique was used for determination of cardiac output with simultaneous radio-electrocardiographic recordings of heart rate. Direct intra-arterial pressure measurements were utilized for calculation of peripheral vascular resistance. Minute volume of ventilation, oxygen utilization, and carbon dioxide elimination were obtained from analysis of expired air collected at the time of each cardiac output determination. A peak mean workload of 1,501 kg-m/min was realized during the treadmill exercise. Increases in cardiac output over the range of exercise employed correlated well with indices of workload such as heart rate, oxygen utilization, and minute volume of ventilation. There was no correlation of stroke volume with these indices. It is concluded from examination of individual stroke-volume responses that a progressive increase in stroke volume is not a necessary or constant phenomenon in adapting to increasing workload. cardiac output in treadmill exercise; dye-dilution cardiac output determinations; arterial pressure during upright exercise; stroke-volume response to graded treadmill exercise; exercise response of cardiac output and stroke volume; peripheral vascular resistance response to position and exercise; treadmill exercise—effects on cardiac output, stroke volume, and oxygen uptake; minute ventilation, cardiac output, and stroke volume during exercise; carbon dioxide elimination during treadmill exercise; heart rate and cardiac output during treadmill exercise; exercise; physiology Submitted on July 12, 1963
Respiratory minute volume
Treadmill
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Abstract : If cardiac output could not be measured directly, it might be inferred from vital signs readily obtained clinically. The present study is an attempt to see whether such an estimation is possible. The Cardiac output per minute (C. O(m)) is obtained by Stroke volume (ml) X Heart rate (per minute). The heart rate could be obtained readily. Thus if the variation of Stroke volume (s.v.) could be estimated, then the variation of cardiac output per minute (C. O(m)) will be estimated. While exact statements cannot be made on the changes in stroke volume unless one knows the extensibility and calibre of the blood vessel, one can obtain the expected change of stroke volume from the age-specific degree of vascular extensibility derived statistically.
Pulse pressure
Extensibility
Stroke
Pulse rate
Degree (music)
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In the present study oxygen uptake, cardiac output, stroke volume (dye-dilution technique) and oxygen content of arterial blood were determined in 11 women and 12 men, 20–31 years of age, at rest, and when performing submaximal and maximal work. At rest plasma volume (T-1824) and heart volume were determined. Sitting on the bicycle ergometer the stroke volume was 40–90% (mean 63%) of the maximum attained during exercise. Maximal stroke volume was essentially reached at a workload with an oxygen uptake of about 40% of the maximum and a heart rate about 110. No tendency to a decrease in stroke volume was noticed when maximal work was performed. The variation in stroke volume was ±4% during exercise in the range from 40 to 100% of the individual's aerobic work capacity. The maximal cardiac output was 18.5 liters/min for women and 24.1 liters for men. The correlation between heart volume on one side and maximal stroke volume and cardiac output on the other side was high and the expected one from the dimension of the individual. On submaximal as well as maximal exercise the women had a higher cardiac output per liter oxygen uptake than the men, and this can be explained by the lower concentration of hemoglobin in the women's blood. cardiac function during exercise; cardiac output stroke volume; cardiac output and arterial O2 content Submitted on October 3, 1963
Stroke
End-systolic volume
Sitting
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The evolution of different hemodynamic parameters with ponderal growth has been studied in conscious Wistar rats. The thermodilution method has been used to determine cardiac output and related variables. The results suggest that, between animal weight and the different hemodynamic parameters, there is a direct proportional relationship to blood volume, mean arterial pressure, cardiac output, stroke volume and total peripheral resistance, and an indirect proportional relationship to heart rate, cardiac index and stroke volume index. Body weight, therefore, plays a major role in hemodynamic determination, this having to be kept in mind when designing the experiment.
Peripheral resistance
Cardiac index
Mean arterial pressure
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The authors used the pulse and continuous-wave Doppler technique to perform 51 measurements of stroke volume and cardiac output in 37 persons. Results were compared with those obtained using Fick's principle of thermodilution (immediately subsequent or simultaneous). Regression analysis showed a close correlation between Doppler and haemodynamic values - r = 0.86 for stroke volume and 0.94 for cardiac output (p less than 0.001). Using the paired t-test, the methods did not differ significantly. Standard deviation of Doppler stroke volume values from reference haemodynamic values was 10%, and only two measurements differed by more than 25%. Doppler determination of cardiac output can be therefore recommended as an alternative method in patients with high-quality echo Doppler recordings.
Stroke
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