CARDIAC OUTPUT IN MAN BY A DIRECT FICK METHOD: Effects of Posture, Venous Pressure Change, Atropine, And Adrenaline

STUDIES ON STARLING'S LAW OF THE HEART. IX. THE EFFECTS OF IMPEDING VENOUS RETURN ON PERFORMANCE OF THE NORMAL AND FAILING HUMAN LEFT VENTRICLE

The acute circulatory responses to impeding venous return to the heart by the inflation of a balloon in the inferior vena cava were determined in 14 patients undergoing left heart catheterization. In the five patients without clinical or hemodynamic evidence of impaired left ventricular function, left ventricular end-diastolic pressure fell, and the decrease was accompanied by reductions in the cardiac index, left ventricular stroke volume, and left ventricular stroke work. In nine patients with impaired left ventricular function, directionally similar responses were noted, although the left ventricular function curves relating left ventricular end-diastolic pressure to left ventricular stroke work were generally flatter and lower than those in the patients without left ventricular disease. In none of the patients did a significant increase in cardiac index, stroke volume, or left ventricular stroke work occur during inflation of the balloon. It is concluded that the Starling relationship appears to operate in a directionally similar manner both in the normal and the depressed human left ventricle, and that the left ventricles of patients with impaired function are not on a descending limb of the curve. However, a descending limb of the left ventricular Starling curve may become apparent when an additional work load is imposed on the diseased ventricle.

A new system for ambulatory pulmonary artery pressure recording

OBJECTIVE

To develop a complete system for the measurement, recording, and analysis of ambulatory pulmonary artery pressure.

DESIGN

The new system consists of a pulmonary artery catheter, an ambulatory recorder, and a desktop computer. Pulmonary artery pressure is measured by a micromanometer tipped catheter with an in vivo calibration system to allow correction for zero drift. This catheter is plugged into a small battery powered recorder. The recorder has two input channels, one for pressure and one for an event marker. The pressure wave is sampled 32 times/s, processed by an in built computer, compressed, and stored in semi-conductor memory. On completion of a recording, data is transferred from the ambulatory recorder through a serial data link to an Acorn Archimedes desktop computer on which further data processing, statistical analysis, graphics, and printouts can be obtained.

RESULTS

The system has been used in 18 patients, with technically successful recording in 14, less than 15 minutes of data loss in three, and 12 hours of data loss in one.

CONCLUSIONS

A new system for ambulatory pulmonary artery monitoring has been developed and used clinically with success. It may provide new perspectives on the pathophysiology of disease as it applies to everyday life.

Should a VVIR Pacemaker Increase the Heart Rate with Standing?

To assess the usefulness of incorporating a posture sensor into a ventricular inhibited rate modulated pacemaker, the hemodynamic effects of increasing the ventricular pacing rate with standing were studied in 15 pacemaker dependent patients aged 55 +/- 3.5 years. In a randomized cross-over design, the pacing rate remained at 70 or was increased to 100 beats/min immediately prior to standing. Blood pressure was monitored continuously and forearm blood flow was measured by venous occlusion plethysmography. There was no difference in supine blood pressure (117 +/- 4/63 +/- 3 compared to 118 +/- 5/64 +/- 4 mmHg) or forearm blood flow (2.88 +/- 0.36 vs 2.94 +/- 0.32 mL/100 mL/min) before the 70 or 100 pacing rate intervention. With standing, blood pressure fell to an equivalent degree at the two pacing rates (fall in mean blood pressure at 70 beats/min 6 +/- 4 and at 100 beats/min 8 +/- 2 mmHg, P = 0.7). After 1 minute of standing differences in blood pressure were similar, but after 2.5 minutes of standing the increase in mean blood pressure was less at 70 than at 100 beats/min (increase from control 28 +/- 2 compared to 36 +/- 3 mmHg, P = 0.002). Forearm blood flow decreased after standing for 1 and 2.5 minutes but there was no difference between the 70 and 100 pacing rates (fall in forearm blood flow at 2.5 minutes 0.50 +/- 0.24 and 0.59 +/- 0.25 mL/100 mL/cm2).(ABSTRACT TRUNCATED AT 250 WORDS)

Syncope associated with supraventricular tachycardia. An expression of tachycardia rate or vasomotor response?

BACKGROUND

Syncope in patients with supraventricular tachycardia has been suggested to be an ominous finding, predictive of rapid rates during tachycardia.

METHODS AND RESULTS

To explore the mechanism of syncope during supraventricular tachycardia, tachycardia was induced in the supine position and after passive head-up tilting to 60 degrees in 13 patients with atrioventricular (AV) node reentry, eight patients with AV reentry, and one patient with atrial tachycardia. Tilt testing was also performed in sinus rhythm for 30 minutes (the last 15 minutes with isoproterenol infusion). Mean +/- SEM age was 38 +/- 3 years, and 11 patients had a history of syncope (median number of syncopal episodes, three; range, one to 30). The cycle length of tachycardia when upright was shorter than when supine (297 +/- 9 compared with 357 +/- 10 msec, p less than 0.001), and mean blood pressure fell to a greater extent after the onset of tachycardia (fall in mean blood pressure, 53 +/- 6 compared with 24 +/- 3 mm Hg, p less than 0.001). Mean blood pressure correlated significantly with tachycardia cycle length when supine (r = 0.58, p = 0.005) but not when tilted upright (r = 0.18, p = 0.45). Syncope occurred in seven patients during upright tachycardia. These seven patients had a greater fall in mean blood pressure with upright tachycardia than the 15 patients without syncope (fall in mean blood pressure, 70 +/- 4 compared with 45 +/- 5 mm Hg, p = 0.01), but there was no difference in the tachycardia cycle length (311 +/- 10 compared with 290 +/- 11 msec, p = 0.29). Six of the seven patients with tachycardia-induced syncope also had syncope with tilt testing in sinus rhythm compared with four of the 15 patients without tachycardia-induced syncope (p = 0.02).

CONCLUSIONS

These data support the view that syncope during supraventricular tachycardia is related to vasomotor factors and does not predict a more rapid tachycardia rate.

Methodology of head-up tilt testing in patients with unexplained syncope

Prolonged 60 degree head-up tilt has been shown to be valuable in the investigation of unexplained syncope, diagnosing neurally mediated bradycardia/hypotension or malignant vasovagal syndrome. To evaluate the methodology of tilt testing, the following were examined: reproducibility of results, tilt duration, angle of tilt, method of tilt support and effect of age in patients and control subjects. Seventy-one patients with recurrent unexplained syncope underwent 60 min of 60 degree tilt; 53 (75%) had an abnormal test with vasovagal syncope at 24 +/- 10 min (mean +/- SD). Tilting to 60 degrees resulted in an abnormal test in only 2 (7%) of 27 control subjects without cardiovascular symptoms (p less than 0.001); and 5 (15%) of 34 patients with syncope and documented conduction tissue disease (p less than 0.001). Of 15 youthful fainters, 3 (20%) had vasovagal reactions as did 1 (8%) of 12 asymptomatic youthful control subjects. These 12 control subjects also underwent tilting with a saddle support and 7 (67%) had vasovagal reactions. It is concluded that the duration of tilting at 60 degrees should be 45 min (mean time to syncope +2 x SD in the 53 patients with abnormal results). Twenty percent of patients with an abnormal tilt test may not demonstrate syncope with repeat tilting. Saddle tilt testing in unexplained syncope may result in a loss of specificity. Tilting at less than 60 degrees results in a loss of sensitivity. Head-up tilt may be less useful in youthful subjects with vasovagal syncope than in other subjects.

Dual chamber pacing aborts vasovagal syncope induced by head-up 60 degrees tilt

To determine if pacing might prevent syncope in cardioinhibitory 'Malignant Vasovagal Syndrome' (also known as 'Neurally-Mediated Bradycardia/Hypotension'), a study of dual chamber pacing during head-up 60 degrees tilt was undertaken. Paired invasive tilts were performed in 10 patients who had a history of recurrent syncope, normal routine investigations including electrophysiological study and prior tilt-induced vasovagal syncope. Vasovagal reactions of identical severity were produced by prolonged 60 degrees head-up tilt on consecutive days in seven out of 10 patients. On day 2, without pacing, seven patients had tilt-induced vasovagal reactions and six became syncopal during the reaction. On day 3, with temporary DVI pacing with rate hysteresis, seven patients had tilt-induced vasovagal reactions and 1 patient was syncopal. Syncope was aborted in the other five patients. DVI pacing significantly improved cardiac index (CI) (one +/- 0.2 to 1.6 +/- 0.3 L/min/m2, P less than 0.01) and mean arterial blood pressure (MABP) (30 +/- 11 to 48 +/- 12 mmHg, P less than 0.01) during vasovagal reactions on day 3 compared with day 2. The mean period of time that patients could tolerate in the tilted position after the onset of the tilt-induced vasovagal reaction was significantly prolonged by pacing from 0.9 +/- 1.2 to 3.2 +/- 1.6 min (P less than 0.01). Dual chamber pacing may abort syncope in 85% of patients with cardioinhibitory malignant vasovagal syndrome. Pacing may prolong consciousness sufficiently during a vasovagal reaction to allow injury to be avoided.

Head-up tilt: a useful test for investigating unexplained syncope

Head-up tilt, a recognised stimulus to vasovagal syncope, was used to investigate syncope that remained unexplained despite full clinical and electrophysiological assessment in fifteen patients, mean age 65 +/- 10 years, who had had 15 +/- 19 episodes of unexplained syncope over periods of a week to 26 years. After overnight fast systolic blood pressure and heart rate were continuously monitored during 40 degrees head-up tilt for 60 min. Ten control subjects with no history of syncope were studied similarly. In ten patients (67%) and one control vasovagal syncope developed after 29 +/- 19 min (p less than 0.001). In symptomatic patients systolic blood pressure fell from 150 +/- 32 to 56 +/- 9 mm Hg (p less than 0.001) and heart rate from 62 +/- 9 to 38 +/- 12 beats per min (p less than 0.01). In each case symptoms during the test reproduced those previously experienced. No clinical findings predicted development of syncope during tilt. Baseline systolic blood pressure and heart rate did not differ significantly between patients and controls. Pacemakers were implanted in seven patients who have remained symptom-free since implant (follow-up 10 +/- 3 mo).

Effect of acute standing and prolonged upright activity on left ventricular hemodynamics, systolic and diastolic intervals, and QT-QS2 relationship

It is generally accepted that upright posture decreases preload and afterload, which could alter left ventricular (LV) performance. It is not known if changes occurring with acute standing persist after prolonged ambulatory activity (amb-act). In seven normal subjects echocardiographic end-diastolic and end-systolic diameters, percent shortening of the internal diameter (% delta D) and end-systolic wall stress (ES-WS), radionuclide diastolic volume and ejection fraction, preejection period over left ventricular ejection time (PEP/LVET), and diastolic time and QT-QS2 were measured supine, within 1 to 2 minutes after standing and after prolonged (60 minutes) amb-act. In addition, serial measurements were performed in PEP/LVET for 105 minutes at 15-minute intervals. With acute standing, end-diastolic diameter, diastolic volume, and ES-WS decreased (p less than 0.01); heart rate and PEP/LVET increased (p less than 0.01); while % delta D and ejection fraction remained unchanged. There was an inverse correlation between change in PEP/LVET and diastolic diameter (r = -0.59), but no correlation between PEP/LVET and ES-WS. The diastolic time per beat and per minute decreased (375 +/- 115 msec from 519 +/- 176 msec [p less than 0.01] and 31.3 +/- 4.2 sec/min from 33.7 +/- 4.5 sec/min [p less than 0.01]). The QT-QS2 increased when compared to supine (-7 +/- 7.6 msec from -22 +/- 7.7 msec [p less than 0.005]), but the QT-QS2 relationship remained normal (QT less than or equal to QS2). All the dynamic changes that occurred with acute standing tended to persist during prolonged amb-act.

Plasma vasopressin and blood pressure. Studies in normal subjects and in benign essential hypertension at rest and after postural challenge

Plasma vasopressin levels were compared in three groups comprising normotensive, mildly hypertensive, and more severely hypertensive patients, both under basal conditions and following an 85 degrees head-up tilt, a stimulus known to provoke vasopressin release in man. Vasopressin levels increased two- to fivefold in all subjects after tilt; however, neither the basal levels nor the maximal levels attained at 45 to 60 minutes after tilt differed in the three groups. These data do not support the postulated role for vasopressin in the causation or perpetuation of non-accelerated essential hypertension in man.

Hemodynamic measurements in clinical practice: a decade in review

Hemodynamic measurement is now an important and feasible adjunct to clinical practice. Its successful application to alleviate illness in human beings is evident in its contribution to an understanding of the pathophysiology of disease and the efficacy of various interventions to alter the course of a variety of diseases. Its application is widespread in the high risk patient undergoing surgery and the critically ill medically treated patient. Hemodynamic measurement permits accurate determination of the state and, if necessary, of the continuously changing function of the heart as related to disease process and guides treatment and interventions on a rational physiologic basis.

Left ventricular diastolic capacity in man

Plasma volume expansion with 500 ml of low-molecular-weight dextran was used in 27 patients (nine normal subjects, 13 patients with ischemic heart disease, four with aortic stenosis and one with cardiomyopathy) to increase left ventricular end-diastolic pressure (LVEDP) from a control value of 12.4 +/- 7.0 mm Hg (mean +/- SD) to 23.3 +/- 7.0 mm Hg and end-diastolic volume (EDV) from 84.0 +/- 23.8 ml/m2 to 97.6 +/- 22.9 ml/m2. EDV-LVEDP curves constructed for 12 patients from multiple angiograms at progressively increasing LVEDPs during plasma volume expansion showed an initial part where EDV increased in parallel with LVEDP and a final steep or perpendicular part where EDV increased minimally or not at all as LVEDP exceeded 20 mm Hg. Exponential equations were used to fit diastolic volume-pressure data obtained with catheter-tip manometers in seven patients: the exponential constant, k, was 0.012-0.044 ml-1 and was inversely related to EDV (Spearman's rank correlation coefficient = -1). For comparable EDV, there were no differences in k values between normal subjects and patients with a variety of heart diseases.

[Pathogenesis of renal hypertension (author's transl)]

99 patients with a chronic renal disease (glomerulonephritis, pyelonephritis, polycystic kidneys) with a GFR reduced to 2/3 normal and without anaemia were subjected to detailed haemodynamic investigation. The earliest haemodynamic abnormality was found even before the blood pressure became elevated. This consisted in a rise of the cardiac output. Ist most likely cause was an increase in the circulating blood volume. As the arteriolar and capacitance vessels adjusted to it, the blood pressure remained unchanged and the central venous pressure slightly decreased. Blood pressure rises, when this vascular adjustment subsides. At this moment the raised blood volume will drop to normal. These changes do not correlate with the minor fluctuations of the PRA which obviously are not responsible for the subsidance of the vascular adjustment and for the rise of blood pressure.

Orthostatic hypertension

A 40 year old man was found to have marked hypertension when he was in the upright position with normal pressures when he was supine. Investigations disclosed normal catecholamine and renin levels. The baroreceptor reflex was somewhat depressed. The mechanism of this orthostatic hypertension is not known. The condition has not been reported previously.

Evaluation of the CO2 rebreathing cardiac output method in seriously ill patients

The CO2 rebreathing cardiac output method is a totally noninvasive Fick procedure needing validation in various disease states to become clinically applicable. Simultaneous measurements of cardiac output by CO2 rebreathing and dye-dilution or direct Fick techniques were performed in 53 patients. In nine patients with pulmonary disease rebreathing cardiac output averaged 4.85 L/min compared to 5.18 L/min by dye-dilution or Fick (r = 0.16). In 14 instances of acute myocardial infarction cardiac output was 5.53 L/min by rebreathing and 5.87 L/min by dye-dilution (r = 0.95), while in nine shock cases it averaged 3.98 L/min by dye-dilution or Fick and 3.75 L/min by CO2 rebreathing (r = 0.94). In five heart failure cases with mitral insufficiency, which may distort dye durves, correlation between standard and rebreathing methods was r = 0.09, but in 16 cases without mitral regurgitation, r = 0.89. Acute interventions in ten patients increased dye-dilution cardiac output by 0.92 L/min and rebreathing outputs by 0.60 L/min (r = 0.87). The data suggest that the CO2 rebreathing cardiac output method may be useful in the CCU-MICU setting.

Is the adrenergic control of renin release dominant in man?

Two beta-blocking agents with different properties were used to define the adrenergic component of the renin release which follows orthostasis. Five normal young subjects were tilted to 85 degrees for 30 min on four separate occasions. In two control studies the release of renin, as indicated by changes in plasma-renin activity, was highly reproducible. The effects of intravenous oxprenolol and intravenous propranolol, were then compared under the same experimental conditions. Oxprenolol attenuated the renin response in all subjects without completely abolishing it. Propranolol completely abolished the renin response. The difference in the ability of these agents to suppress renin release may be related to the presence (oxprenolol) or absence (propranolol) of intrinsic sympathomimetic activity. The increased rate of renin release in orthostasis seems to be mediated entirely by the adrenergic nervous system.

The effect of upright tilt on the volume of the failing human left ventricle

The effect of a passive change from supine to 25-degree head-up tilted position on left ventricular volume was studied by echocardiography and other noninvasive techniques in 18 normal subjects, 6 patients with compensated LV volume overloading, and 12 patients with LV failure. In normal subjects and patients with compensated LV volume overloading, 10 minutes of head-up tilt resulted in a significant decrease in the echocardiographic LV internal dimension equivalent to a decrease in the calculated LV end-diastolic volume of 27 and 16 per cent, respectively. In contrast, no change in LV end-diastolic dimension and volume was noted during tilt in the patients with LV failure. The response of heart rate, blood pressure, and LV ejection fraction to this intervention was insignificant in all groups. These data indicate that volume preload is unresponsive to postural changes in patients with LV failure but not in normal subjects or in those with compensated LV volume overloading. It is suggested that the effect of posture on LV volume and output is primarily determined by the absence or presence of LV failure and the consequences of it on the peripheral circulation.

Diastolic closure rate of normal mitral valve

Images

Effects of blood volume expansion on left ventricular hemodynamics in man

The hemodynamic effects of acute blood volume expansion with low molecular-weight dextran were studied in 11 normal patients and 18 patients with coronary artery disease free of angina at the time of study and without evidence of heart failure. In the coronary artery disease group 350 ml (range 130-540 ml) was infused at the rate of 26.7 ml/min (range 19-36 ml/min). There was an increase in left ventricular end-diastolic pressure (LVEDP) from 10.3 to 18.7 mm Hg, brachial artery mean pressure (BAm) from 102 to 105 mm Hg, pulse pressure (PP) from 56.7 to 63.2 mm Hg, cardiac index (CI) from 3.1 to 3.8 liters/min/m 2 , stroke index (SI) from 37 to 44 ml/m 2 , and left ventricular stroke-work index (LVSWI) from 46 to 53 g-m/m 2 . There was no change in heart rate. In normal subjects, 387 ml (range 200-480 ml) was infused at the rate of 26.4 ml/min (range. 15-37 ml/min). There was an increase in LVEDP from 8.0 to 18.4 mm Hg, PP from 55.5 to 66.8 mm Hg, CI from 3.2 to 4.0 liters/min/m 2 , SI from 38 to 46 ml/m 2 , and LVSWI from 46 to 54 g-m/m 2 . Heart rate and BAm were unchanged. LVEDP increased to abnormal levels in every subject and was associated with small increases in SI and LVSWI. In the absence of myocardial ischemia the challenge of an acute volume did not differentiate left ventricular performance of patients with coronary artery disease from normal subjects.

Left ventricular systolic time intervals as indices of postural circulatory stress in man

The effects of graded increments of passive head-up tilt on the duration of the systolic time intervals corrected for heart rate were investigated in 15 normal subjects. Head-up tilt caused a prolongation of the pre-ejection period and a shortening of the left ventricular ejection time, while total electromechanical systole diminished minimally. The lengthening of the pre-ejection period and abbreviation of the left ventricular ejection time increased progressively with stepwise increments of head-up tilt. The application of venous occlusive tourniquets produced changes in the systolic intervals directionally similar to those observed with head-up tilt. In contrast to the normal subjects, three patients with congestive heart failure demonstrated no change in the systolic time intervals during head-up tilt. After diuresis in two of the patients with heart failure, the responses of their systolic time intervals to head-up tilt returned toward normal.

Effect of posture on cardiac output after myocardial infarction

Images

Hemodynamic effects of diuresis at rest and during intense upright exercise in patients with impaired cardiac function

Although diuretic therapy appears to improve the exercise capacity of patients with moderately impaired cardiac function, the hemodynamic basis for this improvement is not clear. It is also unknown to what extent the moderate diuresis that often occurs during the first few days of hospitalization contributes to the normal or nearly normal hemodynamic measurements obtained in certain patients with cardiac impairment who are thought clinically to have signs and symptoms of pulmonary congestion. Accordingly, the circulatory response to moderate diuresis resulting in a loss of weight averaging 3.4 kg was investigated in 15 patients with heart disease. At rest in the supine position mean pulmonary arterial wedge pressure fell after diuresis from an average of 24 to 13 mm Hg. Reductions also occurred in mean pulmonary arterial pressure (42 to 26 mm Hg), mean right atrial pressure (9 to 4 mm Hg), and right ventricular end-diastolic pressure (11 to 6 mm Hg). Cardiac output decreased by an average of 20%, mean systemic arterial pressure by 12%, right ventricular stroke work by 44%, and left ventricular stroke work by 25%. Diuresis also caused similar reductions in these values in the sitting position at rest and during mild and intense levels of treadmill exercise. Despite the reductions in cardiac output, all but one of the patients studied achieved substantial clinical improvement from the diuresis. Such improvement probably resulted from the fact that the beneficial effects of lower pulmonary vascular pressures outweighed the deleterious effect of a reduction in cardiac output. Thus, moderate changes in body weight brought about by either fluid retention or fluid loss may result in substantial alterations in circulatory dynamics. These changes, if unrecognized, can lead to considerable confusion when attempts are made to correlate the hemodynamic findings with the degree of cardiac decompensation as judged clinically.