Circulatory studies at rest and during exercise in coarctation of the aorta before and after operation

A systematic review and meta-analysis of exercise and exercise hypertension in patients with aortic coarctation

Exercise hypertension is a common occurrence among individuals with aortic coarctation. Although exercise is known to be beneficial among the general population, the risks and benefits of exercise among those with aortic coarctation are less clear. This systematic review evaluates the benefits and risks of exercise for persons with aortic coarctation. Electronic databases were systematically searched (that is, MEDLINE and EMBASE) and key reviews cross-referenced to identify articles for inclusion. Original research articles reporting exercise among individuals with aortic coarctation were included. From 2608 individual citations, 68 eligible articles were identified. Aerobic exercise stress tests were found to be useful for determining exercise hypertension experiences post-surgical repair (N=5), and other long-term secondary findings (N=3). Experiences of exercise hypertension were associated with abnormal cardiac and/or aortic geometry and cardiac function (N=7). Exercise capacity was generally found to be similar to non-aortic coarctation controls post surgery (N=6). Exercise hypertension was experienced by 27% of participants, including 10% of adults and 43% of children/youth. Individuals who experience exercise hypertension experience greater increases in systolic blood pressure with exercise. No investigations identified evaluated forms of exercise other than aerobic stress tests and no exercise training programs have been conducted to date. Exercise stress tests can be valuable in this population for determining exercise hypertension, especially in the year post-surgical repair. Additional research is urgently needed to accurately assess the benefits and risks of exercise and exercise hypertension, and applicability of exercise restrictions for this population.

Computational simulations of hemodynamic changes within thoracic, coronary, and cerebral arteries following early wall remodeling in response to distal aortic coarctation

Mounting evidence suggests that the pulsatile character of blood pressure and flow within large arteries plays a particularly important role as a mechano-biological stimulus for wall growth and remodeling. Nevertheless, understanding better the highly coupled interactions between evolving wall geometry, structure, and properties and the hemodynamics will require significantly more experimental data. Computational fluid-solid-growth models promise to aid in the design and interpretation of such experiments and to identify candidate mechanobiological mechanisms for the observed arterial adaptations. Motivated by recent aortic coarctation models in animals, we used a computational fluid-solid interaction model to study possible local and systemic effects on the hemodynamics within the thoracic aorta and coronary, carotid, and cerebral arteries due to a distal aortic coarctation and subsequent spatial variations in wall adaptation. In particular, we studied an initial stage of acute cardiac compensation (i.e., maintenance of cardiac output) followed by early arterial wall remodeling (i.e., spatially varying wall thickening and stiffening). Results suggested, for example, that while coarctation increased both the mean and pulse pressure in the proximal vessels, the locations nearest to the coarctation experienced the greatest changes in pulse pressure. In addition, after introducing a spatially varying wall adaptation, pressure, left ventricular work, and wave speed all increased. Finally, vessel wall strain similarly experienced spatial variations consistent with the degree of vascular wall adaptation.

On coupling a lumped parameter heart model and a three-dimensional finite element aorta model

Aortic flow and pressure result from the interactions between the heart and arterial system. In this work, we considered these interactions by utilizing a lumped parameter heart model as an inflow boundary condition for three-dimensional finite element simulations of aortic blood flow and vessel wall dynamics. The ventricular pressure-volume behavior of the lumped parameter heart model is approximated using a time varying elastance function scaled from a normalized elastance function. When the aortic valve is open, the coupled multidomain method is used to strongly couple the lumped parameter heart model and three-dimensional arterial models and compute ventricular volume, ventricular pressure, aortic flow, and aortic pressure. The shape of the velocity profiles of the inlet boundary and the outlet boundaries that experience retrograde flow are constrained to achieve a robust algorithm. When the aortic valve is closed, the inflow boundary condition is switched to a zero velocity Dirichlet condition. With this method, we obtain physiologically realistic aortic flow and pressure waveforms. We demonstrate this method in a patient-specific model of a normal human thoracic aorta under rest and exercise conditions and an aortic coarctation model under pre- and post-interventions.

Reduction of the veno-arteriolar reflex induced arteriolar constriction in forearm subcutaneous tissue after surgical repair of aortic coarctation

Arteriolar constriction in subcutaneous tissue elicited by the local sympathetic veno-arteriolar axon reflex was studied in subcutaneous tissue of forearm and leg in 4 patients before and after correction of aortic coarctation. Before the operation the local axon reflex induced an average increase of 154% in vascular resistance in the "hypertensive" forearm and of 76% in the leg. Following coarctectomy the local axon reflex induced increase in vascular resistance decreased in the forearm within 6 months in all patients. Now average increase in vascular resistance was only 109% 3 months after the operation and 45% 6 months after. Minimal vascular resistance in the papaverine relaxed vascular bed was reduced, whereas no systemic changes were seen in the distensibility of the vascular bed. The results indicate that adaptive vascular changes underlying the augmented arteriolar constriction during lowering as well as the increased "minimal vascular resistance" in the forearm are at least partly reversible following coarctectomy.

Paradoxical hypertension after repair of coarctation of the aorta: a review of its causes

Correction of a coarctation of the aorta, an apparent simple cause of hypertension, paradoxically can provoke two hypertensive responses, one of which is potentially fatal. The first, limited to the first 24 hours, occurs in nearly one half of the patients. This is likely due to the high set of the carotid baroreceptors. The second, which may be associated with abdominal pain and, in some, with necrosis of the small bowel as a result of severe arteritis confined to arteries arising from the aorta below the coarctation, develops in about one half of the first responders. Norepinephrine excretion greatly increases for several days, whereas angiotensin levels are elevated for 3 to 4 days. The hypertension responds to beta-blockers, to arterial smooth muscle relaxants, and to angiotensin converting enzymes. A theory is advanced to explain the second response. It is the adaptation gone awry that ensures adequate flow to exercising muscles below the coarctation, above and beyond that delivered by increasing the systolic pressure. It could be a regionally controlled mechanism similar to the rationing of blood flow in diving mammals.

Blood pressure and cardiac output during exercise: a longitudinal study of children undergoing repair of coarctation

Data were examined from 21 children who underwent graded exercise studies prior to and within 5 years after repair of coarctation. A control group of 10 normal children was also studied longitudinally on two occasions. The exercise was performed on an upright bicycle ergometer using a continuous graded exercise protocol. Parameters measured were heart rate, systolic and diastolic blood pressure at rest, and these pressures at the maximal voluntary exercise level. In addition, a subset of patients and controls had measurement of cardiac output by a modified acetylene rebreathing technique. Results indicate that coarctation patients had significant elevation of systolic and diastolic blood pressures at rest (p less than 0.001 for both) and with exercise (p less than 0.02 for both) prior to surgery. The group mean values for systolic and diastolic blood pressure did not differ from control values after surgery; however, some individuals continued to have hypertension at rest when compared to population-based norms. Heart rate, cardiac index, and stroke volume index did not differ from those of control subjects either at rest or during exercise before or after surgery. In conclusion, a group of coarctation patients studied longitudinally demonstrated marked improvement in both systolic and diastolic hypertension after surgery. The findings of normal cardiac output and stroke volume indices may have implications for the etiology of postoperative hypertension.

Exercise testing after surgical repair of coarctation of the aorta

After repair of coarctation, exercise testing was performed in 20 patients with an isolated coarctation (group I) and in 26 with additional congenital cardiac malformations (group II). Ages at time of operation were significantly different in both groups (7.9 +/- 6.0 years in group I; 4.6 +/- 3.8 years in group II; p less than or equal to 0.01). Simultaneous blood pressures were obtained from upper and lower limbs at rest and after exercise. There was no significant difference regarding the systolic blood pressures at rest (122.5 +/- 15.6 mmHg in group I versus 119 +/- 15.8 mmHg in group II). Seven (14%) of the patients were hypertensive; five of them had blood pressure gradients between arms and legs of 15-45 mmHg. But the gradients at rest were found to be significantly different in both groups (9.0 +/- 10.5 mmHg in group I; 18.5 +/- 16.1 mmHg in group II; p less than or equal to 0.05). Six patients, all in group II, had gradients greater than or equal to 30 mmHg at rest. After exercise there were no significant differences in systolic blood pressure and gradients in both groups. Values for blood pressures and gradients at rest and after exercise showed a positive correlation (blood pressure r = 0.76, p less than or equal to 0.001; gradient r = 0.44, p less than or equal to 0.01). Thus exercise testing can provide valuable information about blood pressure and gradient changes during physical activity, but angiography is required to reveal restenosis or residual stenosis.

Exercise-induced hypertension after repair of coarctation of the aorta: arm versus leg exercise

The etiology of exercise-induced upper limb hypertension after repair of coarctation of the aorta is unknown. We hypothesized that blood flow across the coarctation repair site is a major determinant of such exercise-induced hypertension. Because arm ergometry should produce a smaller increase in descending aortic blood flow than treadmill exercise, we compared the changes in upper limb pressure and the coarctation gradient produced by each type of exercise at equivalent levels of heart rate and peak oxygen consumption in 28 children with repaired coarctation of the aorta. The children were classified into three groups: Group I, resting gradient less than 15 mm Hg and treadmill gradient less than 20 mm Hg; Group II, resting gradient less than 15 mm Hg and treadmill gradient greater than 20 mm Hg; and Group III, resting gradient greater than or equal to 15 mm Hg. Twelve children with no heart disease served as control subjects. All children were exercised to exhaustion with 45 minutes' rest between the two exercise protocols. There were no differences in maximal heart rate and oxygen consumption between the two types of exercise. In all groups, treadmill exercise produced a larger increase in arm systolic blood pressure and arm-leg gradient than did arm exercise. With treadmill exercise coarctation Groups II and III developed a greater rise in both arm-leg gradient and arm systolic pressure than was observed in the control subjects (p less than 0.05). However, with arm exercise, Group III developed a significantly greater rise in both arm pressure and arm-leg gradient (p less than 0.05) than was observed in the control subjects.

Juxtaductal aortic coarctation. Analysis of 84 patients studied hemodynamically, angiographically, and morphologically after age 1 year

Although many studies of juxtaductal coarctation of the aorta have been reported, none has correlated clinical, hemodynamic, angiographic, anatomic, and operative findings. Of 84 patients (62 male and 22 female; age range, 1 to 49 years [mean 17]), all had murmurs; 76 had absent, diminished, or delayed femoral pulsations; 50 had cuff systolic blood pressures in the arm greater than 140 mm Hg, and 30 had diastolic pressures greater than 90 mm Hg. The average pressure gradients (mm Hg) by direct measurements above and below the coarctation in 35 patients were peak systolic, 45; mean, 17; and diastolic, 5. Rib notching, visible in chest roentgenograms in 43 patients, correlated directly with age and inversely with the diameter of the coarctation. Moderate or marked cardiomegaly by radiograph was present in only 1 of 48 patients with isolated coarctation and in 17 of 36 with associated cardiovascular malformations. Electrocardiograms were abnormal in more than two thirds of patients with associated anomalies, but were normal in more than three fourths of those with isolated coarctation. In 70 excised, serially sectioned coarctations the aortic lumens were completely occluded in 4 patients, up to 0.5 mm in internal diameter in 22 patients, from 0.6 to 2 mm in 26 patients, from 2.1 to 5 mm in 14, and greater than 5 mm in 4, and correlated directly with lumens measured angiographically. The most significant anatomic factor causing the coarctation was invagination of the media from the posterior aortic wall, but intimal proliferation (jet lesion) at and immediately distal to the invagination contributed to the narrowing. Three (each with associated anomalies) of 70 patients died early after coarctation repair. Systolic or diastolic blood pressures decreased early postoperatively in 58 (87%) of 67 surviving patients, and both pressures decreased in 42 (63%). Late postoperatively (mean follow-up, 4.7 years), the systolic blood pressure remained elevated in 25% of patients.

Morphology of the great arteries in chronic experimental coarctation in dogs

Vascular changes of the great arteries could be one explanation for the serious complications and persistent hypertension after coarcectomy among patients with coarctation. This possibility was studied by evaluating the morphology of the coronary artery, aorta and middle cerebral artery in 7 experimental 9-month-old dogs in which a coarctation of the thoracic aorta had been made at the age of 2 months. A classical coarctation syndrome with high blood pressure and intense collateral circulation developed during growth. Five sham-operated dogs living in the same laboratory environment served as a control group. Morphometric measurements showed medial thickening of the coronary artery wall in the coarctated dogs (135 vs 103 microns, P less than 0.05). The relative amount of glycosaminoglycans of the media was also greater in the study group (14.8% vs 8.1%, P less than 0.02). The relative number of medial nuclei was significantly greater in the coarctated dogs (P less than 0.025), reflecting medial hyperplasia. Vacuolated smooth muscle cells and fragmented elastic membranes were found in the media of the aortas of coarctated animals. No significant differences between the groups were found in the cerebral arteries. It is suggested that re-evaluation of the optimal age of patients with coarctation for surgical repair is obviously necessary.

Bretylium pharmacokinetics and bioavailabilities in man with various doses and modes of administration

The pharmacokinetics and bioavailabilities of bretylium tosylate were studied in 9 male normal volunteers by 60 min constant rate intravenous infusions of 200, 300, and 400 mg, by intramuscular injection of 300 and 400 mg, by oral administration of 100, 200, and 400 mg in solution, and by oral administration of 200 mg tablets. The latter studies were repeated in the same 5 volunteers which were also studied by all modes of administration and at several doses. Intravenous studies showed a sum of 3 exponentials to characterize plasma level-time studies with a terminal half-life of 535 +/- 32 (S.E.M.) min (n = 12). The urinary recovery of unchanged drug was 77 +/- 4(S.E.M.)(n = 14). Half-lives within a subject were correlated and independent of dose. Intramuscular administration showed an apparent half-life of first-order invasion of 79 +/- 13 (S.E.M.) min (n = 6) with no apparent dose dependency and a urinary recovery of unchanged drug of 95.4 +/- 3.2 (S.E.M.) per cent with a terminal half-life similar to the intravenous studies. Oral solutions had smaller lag times of absorption [17 +/- 4(S.E.M.) min] than tablets [56 +/- 9 (S.E.M.) min] and longer apparent half-lives of first-order absorption [231 +/- 23 (S.E.M.) min] than tablets [87 +/- 15 (S.E.M.) min]. The tablets had slightly greater bioavailabilities [27 +/- 2.3 (S.E.M.) per cent] than the oral solutions [22.1 +/- 2.2 (S.E.M.) per cent] but with no apparent dose dependencies. Renal clearances were the same for all modes of administration. Means +/- S.E.M. were 735 +/- 32, i.v., 686 +/- 38, i.m., and 623 +/- 57 ml min-1, p.o. Apparent overall volumes of distribution were 589 +/- 401, i.v. and 450 +/- 671 (S.E.M.), i.m. The i.v. studies in three dogs confirmed the three-compartment body model and the high overall volumes of distribution, had terminal half-lives similar to humans and had renal clearances of 84, 164, and 207 ml min-1 that were in excess of glomerular filtration. There were no significant changes of cardiovascular parameters with the time course of the drug in the body and no significant drug-affected clinical parameters. The only consistent side effect was a generally transient nasal congestion at plasma peak time on intravenous administration.

Blood flow resistance in the hand after coarctectomy

Patients with established hypertension have an increased blood-flow resistance at maximal vasodilatation, which has been interpreted as being caused by a wall thickening in the resistance vessels. Hand blood-flow resistance at maximal vasodilatation was estimated from intra-arterial mean blood pressure and plethysmographically determined hand blood-flow in ten young men, operated upon for coarctation of the aorta during childhood. The patients were compared with different reference groups examined in the same way. The resting mean blood pressure in the coarctation group was only slightly elevated, to the level of a group of patients with mild blood pressure elevation, while the blood-flow resistance at maximal vasodilatation was markedly increased and equalled that found in a group of patients with established hypertension. This discrepancy between blood pressure and blood-flow resistance suggests a limited reversibility of structural changes in the resistance vessels, originating from the preoperative period with high blood pressure, and might be an argument in favour of early operation and/or antihypertensive medication in children with coarctation of the aorta.

Muscle metabolism during exercise in men operated upon for coarctation of the aorta in childhood

Muscle biopsies were taken from the quadriceps muscle during rest and exercise in 16 young men (ages 16-28 years) operated upon for coarctation of the aorta during childhood and 10 healthy men (ages 19-25 years). Resting values and depletion after exercise for ATP, CP and glycogen were similar in the two groups. Muscle-lactate concentrations were higher at all levels of exercise in the operated group, while blood-lactate concentrations did not differ. It is concluded that the operated patients have a disturbed blood-flow regulation and a somewhat impaired blood-flow to the working leg muscles.

Hemodynamic responses to supine exercise in children with left-sided cardiac disease

Exercise, a physiologic stress, has been used in adults to unmask abnormalities of left ventricular hemodynamics not detectable at rest. Similar data in children are not available. An evaluation was made of the feasibility, safety and value of a graded upright and supine ergometer stress test to assess exercise hemodynamics during cardiac catheterization in 21 children with left-sided cardiac disease. The catheterization technique involved the simultaneous recording of intracardiac and great vessel pressures, thermodilution cardiac index and M mode echocardiograms of the left ventricular cavity. The method appears practical and safe. Although hemodynamic responses varied among clinical groups, the lack of control data currently prevents assessment of the value of this technique for long-term management.

Systolic hypertension: hemodynamic mechanism and choice of antihypertensive treatment

Arterial compliance and indexes of ventricular ejection were measured in 27 men with systolic hypertension. The patients were separated into two age groups, younger or older than age 35 years, and matched with normotensive control subjects. Arterial compliance was estimated from analysis of the monoexponential blood pressure-time curve during diastole, according to a simple viscoelastic model. In the younger patients, arterial compliance and stroke volume were within normal ranges. Rapid ejection time was significantly reduced (P less than 0.001), indicating an increased venlocity in the first part of ventricular ejection. Systolic pressure decreased significantly after administration of propranolol, which also caused prolongation of rapid ejection time. In the older patients, indexes of ventricular ejection were within normal limits. arterial compliance was significantly reduced (P less than 0.01) and was negatively correlated with the level of systolic pressure (P less than 0.001). Systolic pressure decreased significantly after administration of sodium nitroprusside, which caused an increase in arterial compliance. These findings provide evidence that: (1) the hemodynamic mechanisms of systolic hypertension differ in younger and older patients, and (2) these hemodynamic differences should be taken into account when choosing drugs to decrease systolic pressure.

Coarctation of the aorta

Coarctation of the aorta is a cause of hypertension that can present dramatically in the severely ill infant or appear incidentally in the asymptomatic young adult. Coarctation is easily detected and there is good evidence that the extremely poor natural history can be altered favorably by surgical correction. The elevated blood pressure can be lowered in the majority of patients, and there is every expectation that the incidence of known complications of coarctation can be decreased. However, in about three fourths of the patients, significant residual cardiovascular defects persist, with their potential for future problems as yet incompletely defined. For this reason, patients who have undergone surgery for coarctation will need to be followed carefully for an indefinite period.

The effect of propranolol on the pressor response to exercise in coarctation of the aorta

In a patient with coarctation of the aorta, blood pressure and heart rate were measured during graded exercise on a bicycle ergometer. After no treatment, and after oral hydrallazine, exercise produced large rises in systolic and diastolic blood pressures, and in heart rate. During exercise after oral propranolol, systolic and diastolic pressures did not increase, and there was a less marked tachycardia. These results suggest that propranolol should be used to minimize the dangers of elevated blood pressure associated with exercise in patients with coarctation.

Pre- and postoperative rest and exercise hemodynamics in children with pulmonary stenosis

Twenty children with pulmonary valvular stenosis were studied by cardiac catheterization both at rest and during submaximal supine exercise, prior to and following pulmonary valvotomy. The resting and exercise states were comparable preoperatively and postoperatively since cardiac output, heart rate, A - V O 2 difference and oxygen consumption were similar. Evidence of improved cardiac function was found postoperatively.

Both the rest and the exercise right ventricular end-diastolic pressure (RVEDP) decreased significantly following pulmonary valvotomy. Preoperatively, 12 of 20 patients showed an increase in RVEDP with exercise; in six of these there was a simultaneous fall in stroke index, indicating impaired myocardial function. No patient showed this response postoperatively.

This indicates that although altered cardiac function can be demonstrated in some children with pulmonary valvular stenosis, it is reversible by pulmonary valvotomy. This is in contrast to studies in adults, and suggests that a factor in the natural history of pulmonary valvular stenosis is the impact of chronically elevated afterload on the right ventricle. Hemodynamic measurements made during exercise provide a useful means of assessing patients with pulmonary stenosis before and after pulmonary valvotomy.

Postoperative assessment of patients with ventricular septal defect and pulmonary hypertension. Response to intense upright exercise

Circulatory function of patients with operatively closed ventricular septal defect and preoperative pulmonary arterial hypertension was evaluated in 11 asymptomatic subjects at rest and during intense treadmill exercise three to 15 years after operation. The pulmonary-to-systemic resistance ratio was normal or mildly to moderately elevated preoperatively. Postoperative mean pulmonary arterial pressure at the time of study was normal or mildly elevated at rest in 10 patients and moderately elevated in one (40 mm Hg). During intense upright exercise sufficient to lower pulmonary arterial oxygen saturation to 30%, cardiac output was below the normal range in five patients. Each of these patients had been operated upon after 10 years of age. The magnitude of the postoperative abnormality in cardiac output response to exercise was directly related to age at operation. Two of the five patients with impaired cardiac output response and two other patients manifested an abnormally elevated mean pulmonary arterial pressure during intense exercise. There was a positive correlation between pulmonary arterial pressure during intense exercise and age at operation. These results indicate that late postoperative cardiovascular function may be abnormal in patients with ventricular septal defect and preoperative pulmonary arterial hypertension, and that these abnormalities appear to be related to age at operation. Since all patients were asymptomatic, the long-term clinical significance of these hemodynamic abnormalities remains to be determined.

Influence of aortic coarctation on pulsatle hemodynamics in the proximal aorta

Pressure and flow were recorded in the ascending aorta of three dogs with aortic coarctation, induced surgically 3 months previously, and in three control litter mates. From these data were derived input impedance of the systemic circulation, pulsatile and steady components of external heart work, aortic systolic pressure-time index, and mean systolic and mean diastolic pressures. Results were correlated with intraoperative measurements of aortic pressure in three young patients with aortic coarctation and with records taken in another 24 patients during diagnostic catheterization. Distinctive changes in aortic impedance with coarctation were explained in terms of altered peripheral reflection. Such changes were responsible for characteristic alteration in central aortic pressure pulse contour and for change in other parameters, indicating impaired arterial function in accepting pulsatile flow from the heart. Such changes in the cushioning function appear responsible for many clinical features and complications of aortic coarctation. Surgery is probably justified for restoration of the normal cushioning function of the arterial system as well as for reduction of resistance and mean arterial pressure.

Coarctation of the aorta

In a series of 70 patients who had surgical correction of coarctation of the aorta between 1952 and 1969, the operative mortality was 7% and the complication rate was 14%. The mortality was particularly high in adult males over 30, with pre-operative evidence of left ventricular ischaemia. Simple surgical procedures had satisfactory results, but the use of prostheses carried a high risk, and turning down the left subclavian artery failed to lower the blood pressure. The blood pressure score fell by 68% after operation, and by a further 8% following discharge from hospital. This result was maintained up to 17 years after operation, and may be expected in all groups of patients.

LATE RESULTS OF THE OPERATION FOR COARCTATION IN THE GROWING CHILD

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