Charles R. Jorgensen

The rate-pressure product as an index of myocardial oxygen consumption during exercise in patients with angina pectoris.

SUMMARYIn order to evaluate hemodynamic predictors of myocardial oxygen consumption (MVO,), 27 normotensive men with angina pectoris were studied at rest and during a steady state at symptom-tolerated maximal exercise (STME). Myocardial blood flow (MBF) was measured by the nitrous oxide method using gas chromatography. MBF increased by 71% from a resting value of 57.4 ± 10.2 to 98.3 ± 15.6 ml/100 g LV/min (P < 0.001) during STME while MVO, increased by 81% from a resting value of 6.7 ± 1.3 to 12.1 ± 2.8 ml O,/100 g LV/min (P < 0.001). MVO2 correlated well with heart rate (HR) (r = 0.79), with HR X blood pressure (BP) (r = 0.83), and, adding end-diastolic pressure and peak LV dp/dt as independent variables, slightly improved this correlation (r = 0.86). Including the ejection period (tension-time index) did not improve the correlation (r = 0.80). Thus, HR and HR X BP, both easily measured hemodynamic variables, are good predictors of MVO, during exercise in normotensive patients with ischemic heart disease. Including variables reflecting the contractile state of the heart and ventricular volume may further improve the predictability.

Hemodynamic Predictors of Myocardial Oxygen Consumption During Static and Dynamic Exercise

Hemodynamic predictors of myocardial oxygen consumption (MVO2) during static and dynamic exercise were examined in ten normal subjects. Studies were done under the following circumstances: 1) during upright bicycle exercise at an average heart rate of 147 beats/min, 2) during static exercise with an isometric load in the left hand equal to 17% of the maximal voluntary contraction (MVC), and 3) during combined dynamic exercise (average heart rate 147 beats/min) and static exercise using 17% MVC of the left hand. Mean myocardial blood flow (MBF) was 181 ml/100 gm LV/min during dynamic exercise, 98 ml/100 gm LV/min during static exercise, and 201 ml/100 gm LV/min during combined static and dynamic exercise. Addition of a static load to the dynamic load resulted in a higher blood pressure (average 12 mm Hg), MVO2 and MBF than during dynamic exercise alone. MVO2 correlated best with products of heart rate and blood pressure regardless of whether the blood pressure was obtained by a central aortic catheter (r = 0.88) or by a blood pressure cuff (r = 0.85).When the current data were combined with previous data, 82 determinations of MVO2 and MBF in 29 normal subjects during several levels of upright exercise were available for analysis. Forty-four determinations were done during dynamic upright exercise, 18 during exercise after propranolol, ten during combined static and dynamic work, and ten during static work alone. MVO2 correlated best with the product of heart rate and blood pressure (r = 0.86). Heart rate alone correlated better with MVO2 (r = 0.82) than did the tension time index (r = 0.65) or the product of systolic blood pressure, heart rate, and ejection time (r = 0.68). The readily measured variables of heart rate and of heart rate × blood pressure correlated well with MVO2 in normal young men during exercise under a wide variety of circumstances.

Effect of Propranolol on Myocardial Oxygen Consumption and Its Hemodynamic Correlates during Upright Exercise

Measurements were made of heart rate, aortic blood pressure, systolic ejection period/beat, myocardial blood flow, and myocardial oxygen consumption in nine normal young men during three bouts of upright bicycle exercise: 1) at the workload which produced a heart rate of 120 beats/minute, 2) at the higher workload necessary to produce a heart rate of 120 beats/minute after administration of intravenous propranolol 0.25 mg/kg, and 3) with infusion of propranolol, at the same workload as the first exercise bout. Comparing exercises 1 and 2, we found a much higher workload was required to produce the same heart rate after propranolol. The blood pressure, heart rate-blood pressure product, and myocardial oxygen consumption were the same despite the much greater level of exertion. Comparing exercises 1 and 3, the heart rate, blood pressure, heart rate-blood pressure product, and myocardial oxygen consumption were all significantly lower during exercise 3 after propranolol despite the fact that the same degree of exercise was being done. As in previous studies, the heart rate-blood pressure product was an excellent correlate of myocardial oxygen consumption despite the change in contractility induced by propranolol. The systolic ejection period was prolonged significantly altering the tension-time index (TTI), which became an inadequate index of myocardial oxygen consumption. It is concluded that the heart rate-blood pressure product is a good index of myocardial metabolic needs during exercise and the relationship is undistorted by marked changes in contractility, but the tension-time index is a poor correlate. This data emphasizes the fact that the relative metabolic loads for the whole body and for the heart are determined separately and may not change in parallel with a given intervention.

Hemodynamic Effects of Exercise in Isolated Valvular Aortic Stenosis

Hemodynamic data, including simultaneously measured left ventricular and aortic pressures, were obtained from 20 patients with isolated valvular aortic stenosis at rest and during supine leg exercise. Changes in left ventricular end-diastolic pressure during exercise were not significantly related to the severity of aortic stenosis but were correlated with age; patients with abnormal left ventricular end-diastolic pressures during exercise were significantly older than those in whom this variable remained normal. Exercise resulted in significant increases in both the mean rate of systolic aortic blood flow and the mean systolic pressure gradient across the aortic valve. Analysis of this pressure gradient demonstrated symmetrical shortening of the ejection time per beat with an increase of the maximal systolic pressure gradient during exercise. Although changes in mean systolic aortic pressure gradient and mean aortic flow were significantly positively correlated, the increases in mean systolic pressure gr...

Cor Triatriatum Review of the Surgical Aspects with a Follow-up Report on the First Patient Successfully Treated with Surgery

A follow-up report on the first patient with cor triatriatum to undergo successful surgical treatment is presented. A second procedure was necessary 9½ years later because of stenosis of the initial surgically created orifice in the anomalous diaphragm. A review and ananalysis have been made of 17 cases from the literature reporting successful operations for this lesion. Total excision of the accessory septum utilizing cardiopulmonary bypass is presently the appropriate surgical treatment of this entity. Preoperative and postoperative hemodynamic data are discussed. Recognition and correction of this defect are emphasized in order to avoid permanent pulmonary vascular changes attended by a relatively fixed cardiac output.

Myocardial blood flow and oxygen consumption during exercise.

Our concepts of what variables determine myocardial oxygen consumption (MV(,*) have evolved considerably over the last six to seven decades. Perhaps the earliest significant investigation of this problem was published in 1912 showing that oxygen use in an isovolumetrically contracting preparation was proportional to the product of pulse rate and left ventricular pulse pressure.’ For many years stroke work, the product of stroke volume and arterial pressure, was considered the primary factor, although it was recognized early that pressure work is more expensive than volume work and that pressure changes reflect changes in ventricular wall tension only if ventricular volume is not altered.’ Very comprehensive approaches have thought in terms of contractile element an entity based on the three component model of muscle and requiring several difficult measurements and some assumptions in its calculation. Our current understanding is relatively complete and is the result of the work of many investigators, primarily with in vitro preparations. A number of factors have been identified as determinants of myocardial oxygen consumption (TABLE l ) , but the major factors are: ( a ) the heart rate; (b) internal work, the stress or tension in the wall of the ventricle; (c ) the contractile state of the heart; and (d ) external work. The heart rate is listed first because it provides the summing factor for most of the other variables listed, which are determined on a per beat basis.“ Furthermore, in experiments comparing severe exercise and pacing to the same heart rate, it was suggested that the tachycardia alone was responsible for about one-third the increment in coronary blood flow that normally occurs during strenuous exercise.!’ The second factor, internal or pressure-generation work, accounts for about 50% of the oxygen consumption of the heart doing external work at a high level.’ The expression given for the wall stress is the familiar law of Laplace and indicates that the stress is a function of intraventricular pressure, intraventricular radius (volume), and ventricular wall thickness. Although this equation is for a sphere and the left ventricle is not spherical, it should be noted that expressions for more appropriate shapes (the prolate spheroid or the ellipsoid of revolution) have exactly the same form with the radius replaced by the semiminor axis and the one-half replaced by a dimensionless multiplier, which is a function of the semimajor and semiminor axes.l” The term “tension” has been used interchangeably with the term “stress” in the literature on cardiac rnechanics,l(’ but the two terms do have different physical meanings and there would appear to be merit in distinguishing between them in physiology also.

Hemodynamic Evaluation of Lillehei-Kaster and Starr-Edwards Prostheses

The central-flow low profile disc-valve prosthesis has been offered as an alternative to ball- and tissue-valve prostheses. Extensive laboratory investigation with both pulse duplicator and experimental animals has been reported for the Lillehei-Kaster prosthesis. A series of patients receiving this prosthesis underwent postoperative cardiac catheterization to better define the hemodynamic function of this prosthesis in vivo. Because of the variations in reports of hemodynamic data from various institutions, the results of post-operative studies in an earlier group of patients with Starr-Edwards prostheses were used as a standard for comparison. Good hemodynamic function was found with the pivoting-disc prosthesis in all but the smallest valve sizes. Lillehei-Kaster and early model Starr-Edwards prostheses with equivalent tissue annulus dimensions were found to have nearly equal valve areas in vivo in the aortic position. The Lillehei-Kaster mitral valves provided larger areas than Starr-Edwards prostheses in large tissue annulus sizes.

Serum Lactate Dehydrogenase Elevation in Ambulatory Cardiac Patients Evidence for Chronic Hemolysis

Activity of total lactate dehydrogenase (LDH) and that of the heat-stable isozyme (LDH-1) was measured by the method of Strandjord and Clayson in the serum of 62 cardiac patients with congenital and valvular heart disease before and after cardiac catheterization and at follow-up examination after cardiac surgery. A universal elevation of both total and heat-stable LDH was found in patients with prosthetic heart valves of several types. Lesser degrees of abnormalities were seen in a number of the patients without prosthetic devices. Some patients had a small increase in serum enzyme activity the day after cardiac catheterization. The evidence presented implicates hemolysis in the production of these abnormalities. It is suggested that all patients with prosthetic valves and a significant percentage of patients with severe hemodynamic abnormalities have chronic, usually compensated, intravascular hemolysis secondary to mechanical damage to red blood cells. These findings must be kept in mind in interpreting serum LDH determinations in patients with valvular prostheses or congenital and valvular heart disease who present with complaints of chest pain.

Acute Changes in Left Ventricular Volume and Contractility during Ventricular Pacing in Patients with Complete Heart Block

To determine whether changes in preload and contractility may account for clinical improvement in patients with complete heart block (CHB) when the ventricular rate is increased by pacing, 10 hemodynamic studies were performed in nine patients with CHB. Left ventricular end-diastolic volume (EDV) was measured before and during pacing by the dye-dilution and the angiographic techniques. Changes in contractility were assessed from the first derivative of ventricular pressure divided by a common peak isovolumic pressure (CPIP) to correct for afterload and by EDV to correct for preload. EDV decreased during pacing, the mean value decreasing from 242 to 180 ml (P < 0.001). Since the left ventricular dp/dt is influenced by afterload and preload, improvement in contractility indices was consistent only after allowances were made for changes in aortic diastolic pressure and EDV. The mean dp/dt/CPIP divided by EDV increased from 0.120 to 0.160 (P < 0.005). The mean left ventricular enddiastolic pressure decreased from 17.0 to 9.7 mm Hg (P < 0.05) during pacing, while the mean cardiac index increased from 2.0 to 2.5 liters/min/m2 (P < 0.025). The clinical improvement seen after pacing in patients with CHB results, in part, from an increase in contractility and a decrease in EDV and pressure.

Hemodynamic Effects of Exercise in Isolated Valvular Aortic Stenosis: The authucers reply:

Hemodynamic data, including simultaneously measured left ventricular and aortic pressures, were obtained from 20 patients with isolated valvular aortic stenosis at rest and during supine leg exercise. Changes in left ventricular end-diastolic pressure during exercise were not significantly related to the severity of aortic stenosis but were correlated with age; patients with abnormal left ventricular end-diastolic pressures during exercise were significantly older than those in whom this variable remained normal. Exercise resulted in significant increases in both the mean rate of systolic aortic blood flow and the mean systolic pressure gradient across the aortic valve. Analysis of this pressure gradient demonstrated symmetrical shortening of the ejection time per beat with an increase of the maximal systolic pressure gradient during exercise. Although changes in mean systolic aortic pressure gradient and mean aortic flow were significantly positively correlated, the increases in mean systolic pressure gradient during exercise were less than predicted from corresponding increases in mean aortic flow; thus the result was an apparent increase in computed aortic valve area.