Mitral Valve Obstruction Research Articles

Cardiac myxoma: imaging features in 83 patients.

Eighty-six cardiac myxomas were reviewed retrospectively for the clinical, pathologic, and radiologic findings. In this series, 83 patients (47 female and 36 male; age range, 2-78 years; mean age, 48 years) had 49 left atrial (60%), 23 right atrial (28%), seven right ventricular (8%), two biatrial, and two cases of multifocal myxomas. Seventy-one (88%) patients were symptomatic. Radiographs of 38 patients with left atrial myxoma showed evidence of mitral valve obstruction in 53%; radiographs of 16 patients with right atrial myxoma demonstrated calcification and cardiomegaly in 56% and 50%, respectively. Computed tomographic (CT) scans of 21 myxomas demonstrated 20 (95%) spherical or ovoid lesions, 16 (76%) with lobular borders. Seventeen (81%) were hypoattenuated; 14 (67%) were heterogeneous. Twenty-eight magnetic resonance (MR) imaging studies of 30 myxomas showed 29 (97%) spherical or ovoid lesions; 26 (87%) had lobular contours and 26 (90%) of 29 had heterogeneous signal intensity on T1-weighted images. Point of attachment was visible in 15 (83%) cases. Cine gradient recalled echo (GRE) MR images of 10 lesions showed low signal intensity in all cases. Most patients with cardiac myxomas have abnormal but usually nonspecific radiographic findings. CT demonstrates intracavitary heterogeneous, hypoattenuated lobular masses. MR imaging shows heterogeneous lobular lesions and usually allows visualization of the point of attachment. Radiologic imaging of these lesions, particularly with multiplanar and cine GRE MR imaging, can provide accurate assessment of the size, location, and point of attachment of these lesions and should assist in surgical planning.

Clinical presentation of left atrial cardiac myxoma. A series of 112 consecutive cases.

We analyzed a series of 112 consecutive cases of left atrial myxoma diagnosed in a single French hospital (72 women and 40 men; age range, 5-84 yr) over 40 years, from 1959 to 1998. Symptoms of mitral valve obstruction, the first arm of the classic triad of myxoma presentation, were present in 75 patients (67%), with mostly cardiac failure or malaise. Symptoms of embolism, the second frequent presentation in the classic triad, were observed in 33 cases (29%) with 1 or several locations, essentially cerebral emboli with stroke. Males are statistically at greater risk than females of developing embolic complications. The third arm of the classic triad consists of constitutional symptoms (34%) with fever, weight loss, or symptoms resembling connective tissue disease, due to cytokine (interleukin-6) secretion. Younger and male patients have more neurologic symptoms, and female patients have more systemic symptoms. Seventy-two patients (64%) had cardiac auscultation abnormalities, essentially pseudo-mitral valve disease (53.5%) and more rarely the suggestive tumor plop (15%). The most frequent electrocardiographic sign was left atrial hypertrophy (35%), whereas arrhythmias were uncommon. The greater number of myxoma patients (98) diagnosed preoperatively after 1977 reflects the introduction of echocardiography as a noninvasive diagnostic procedure. However, there was no significant reduction in the average time from onset of symptoms to operation between patients seen in the periods before and after 1977. The tumor diameter ranged from 1 to 15 cm with a weight of between 15 and 180 g (mean, 37 g). The myxoma surface was friable or villous in 35% of the cases, and smooth in the other 65% cases. Myxomas in patients presenting with embolism have a friable surface; those in patients with cardiac symptoms, pseudo-mitral auscultation signs, tumor plop, and electrocardiogram or radiologic signs of left atrium hypertrophy and dilatation are significantly the larger tumors. The long-term prognosis is excellent, and only 4 deaths occurred among our 112 cases over a median follow-up of 3 years. The recurrence rate is low (5%), but long-term follow-up and serial echocardiography are advisable especially for young patients.

Pulmonary vasoconstriction induced by mitral valve obstruction in sheep.

We hypothesized that left atrial hypertension results in pulmonary vasoconstriction, which is obscured by the expected passive decrease in pulmonary vascular resistance. The objectives of this study were to demonstrate and quantify the vasoconstrictive changes that occur in the pulmonary circulation during experimental left atrial hypertension, to determine the site of vasoconstriction, and to explore its mechanism. Sheep were instrumented for measurement of pulmonary arterial (Ppa), left atrial (Pla), and systemic arterial pressures (Psa) with a Foley balloon catheter to variably obstruct the mitral valve. Distal pulmonary arterial wedge pressure (Ppaw) was determined by using a 5-Fr Swan-Ganz catheter that was advanced until it wedged with the balloon deflated. Cardiac output (CO) was estimated by thermodilution; pulmonary vascular resistances (PVR) were calculated as mean (Ppa - Pla)/CO = total PVR, (Ppa - Ppaw)/CO = upstream PVR, and (Ppaw - Pla)/CO = downstream PVR. We studied 15 awake sheep at baseline and during increases in Pla of 10 and 20 cmH2O, with and without inhalation of approximately 36 parts per million of nitric oxide. Left atrial hypertension resulted in elevation of Ppa. CO decreased only slightly at both levels of Pla elevation. Nitric oxide inhalation caused a significant decrease in PVR, which was greater as Pla increased. This vasodilator effect was most striking in downstream vessels. Experiments with phentolamine, atropine, and ibuprofen failed to reveal the mechanism of the reactive pulmonary vasoconstriction.

Application of color Doppler flow mapping to calculate orifice area of St Jude mitral valve.

The effective orifice area (EOA) of a prosthetic valve is superior to transvalvular gradients as a measure of valve function, but measurement of mitral prosthesis EOA has not been reliable. In vitro flow across St Jude valves was calculated by hemispheric proximal isovelocity surface area (PISA) and segment-of-spheroid (SOS) methods. For steady and pulsatile conditions, PISA and SOS flows correlated with true flow, but SOS and not PISA underestimated flow. These principles were then used intraoperatively to calculate cardiac output and EOA of newly implanted St Jude mitral valves in 36 patients. Cardiac output by PISA agreed closely with thermodilution (r=0.91, Delta=-0.05+/-0.55 L/min), but SOS underestimated it (r=0.82, Delta=-1.33+/-0.73 L/min). Doppler EOAs correlated with Gorlin equation estimates (r=0.75 for PISA and r=0.68 for SOS, P<0.001) but were smaller than corresponding in vitro EOA estimates. Proximal flow convergence methods can calculate forward flow and estimate EOA of St Jude mitral valves, which may improve noninvasive assessment of prosthetic mitral valve obstruction.

Obstruction of Mechanical Mitral Prostheses: Analysis of Pathologic Findings

Background. The pathologic and echocardiographic findings observed in 87 patients with mitral valve obstruction were reviewed to ascertain the incidence of pannus formation versus that of thrombosis, the relationship between the two, and the time to the occurrence of pannus versus the time to thrombosis.Methods. Pannus morphology (concentric or eccentric), its location on the valve (atrial, ventricular, atrioventricular), and the presence and relationship of associated thrombi (atrial, ventricular, atrioventricular) were analyzed. The times between valve replacement and the occurrence of obstruction were also compared.Results. There were 10 caged-ball valves, 65 tilting-disc valves, and 12 bileaflet valves. Seventy-two patients underwent prosthetic replacement, and 15 underwent thrombolysis. Pannus alone was found in 27, pannus and thrombus in 39, and thrombus alone in 21. Primary thrombosis occurred earlier than pannus formation (p = 0.04); this was true for patients with bileaflet valves (p = 0.006) and those with tilting-disc valves (p = 0.04). Pannus was atrial in 19.7% (13/66), ventricular in 21.2% (14/66), and atrioventricular in 59.1% (39/66). Pannus morphology was concentric in 22.7% (15/66) and eccentric in 77.3% (51/66). Atrial secondary thrombi occur more often in patients with atrioventricular pannus (p = 0.04). Eight patients had reobstruction; this was caused by pannus formation in 5 and by thrombosis in 3. Five underwent reoperation, and 3 underwent thrombolysis. Reobstruction occurred earlier than the first event.Conclusions. The frequency of pannus formation is much higher than that of thrombus formation, but thrombosis is of earlier onset than pannus formation. Thrombosis is due to the deposition of clots on the prosthesis, and a pannus occurs as the result of an inflammatory reaction developing on both valve surfaces.(Ann Thorac Surg 1997;63:1101–6)

Clinical Applications of Inhaled Nitric Oxide in Children with Pulmonary Hypertension

We have presented our experience with the use of inhaled nitric oxide in children with congenital heart disease and pulmonary hypertension, which indicates that nitric oxide is a selective pulmonary vasodilator that may improve patient management, particularly after surgical procedures requiring cardiopulmonary bypass. Indeed, we have now seen several patients in whom all resuscitative maneuvers for the treatment of pulmonary hypertensive crises were unsuccessful until inhaled nitric oxide was added to the therapeutic regimen. In addition, our studies using inhaled nitric oxide as an investigational probe point toward endothelial injury as a contributor to post-cardiopulmonary bypass pulmonary vasoconstriction. Inhaled nitric oxide relieves pulmonary vasoconstriction associated both with left atrial or pulmonary venous hypertension and following the relief of mitral valve or pulmonary venous obstruction. Absence of a response on the usually reactive pulmonary vascular bed of the neonate should prompt a careful search for anatomic, and possibly surgically remediable, pulmonary vascular obstruction. In the short term nitric oxide is less effective in the older patient with obliterative pulmonary vascular disease. It is possible that recent experimental work with long-term nitric oxide inhalation might be applicable to this group of patients. Nitric oxide may have a unique role in the management of the patient after lung transplantation, as it both reduces right ventricular afterload and improves intrapulmonary shunting. Is nitric oxide the ideal agent for testing pulmonary vascular reactivity? Nitric oxide is simple to deliver by either mask or ventilator and, as a trial of vasoreactivity over 15 min, remains free of side effects that might be encountered during long-term administration, such as methemoglobinemia or nitrogen dioxide toxicity. Indeed, no patient developed significant methemoglobinemia after a trial of nitric oxide and neither was a level of nitrogen dioxide above 1 ppm registered during the administration. Thus, nitric oxide gas fulfills many of the ideal characteristics, as suggested by Rubin,92 required of a drug to test the acute responsiveness of the pulmonary circulation. It has better pulmonary dilating effects than systemic, a short half-life, and minimal adverse effects and it can be both easily and quickly administered. Whether it is able to reliably predict the effect of long-term administration of orally active agents awaits confirmation. Certainly, inhaled nitric oxide is rapidly becoming the standard agent to test pulmonary vascular reactivity during diagnostic cardiac catheterization at our institution.

Clinicopathological Correlates of Cardiac Myxomas: A 30-Year Experience

Between 1961 and 1991, 23 patients (eight men and 15 women, with a mean age of 50 (range 25-72) years) with cardiac myxomas were managed at the Alfred Hospital, Prahran, Victoria, Australia. Symptoms of mitral valve obstruction were present in 13 patients and of systemic embolism in nine. In the patients, 21 myxomas were confined to the left atrium. In the other two patients, one myxoma was confined to the right atrium and the other was a dumb-bell-shaped biatrial myxoma. Most tumours were diagnosed with echocardiography. Removal was achieved via a median sternotomy and by entering the involved chamber. Those myxomas presenting with systemic embolism were always soft and friable, whereas those with obstructive symptoms were large and of variable consistency. There was one operative death early in the series. The 22 surviving patients have been assessed as functional class I of the New York Heart Association at follow-up, ranging from 2 months to 23 years (mean 9 years). There were no episodes of tumour recurrence. Excellent short, intermediate and long-term results can be achieved by excision of cardiac myxomas.

Massive Pulmonary Hemorrhage Complicating Mitral Prosthetic Valve Obstruction

A case is reported of prosthetic mitral valve obstruction in a patient who had had three hospital admissions with massive hemoptysis. A diagnosis was finally made after two-dimensional echocardiography with Doppler and cardiac catheterization were performed. The patient was successfully treated with re-replacement of the valve. Any new pulmonary or cardiac symptom in a patient with a prosthetic valve requires prompt evaluation and treatment.

Morphological determinants of echocardiographic patterns of mitral valve systolic anterior motion in obstructive hypertrophic cardiomyopathy.

The morphological determinants of mitral valve systolic anterior motion (SAM) and obstruction to left ventricular outflow in patients within the broad clinical spectrum of hypertrophic cardiomyopathy (HCM) are not completely understood, particularly the contribution of mitral leaflet length and size. To clarify this issue, mitral valve specimens from 43 patients with HCM and basal outflow obstruction were used to relate morphometric measurements of leaflet area to certain morphological and functional assessments of left ventricular outflow tract geometry and valvular motion obtained from echocardiograms in the same patients. Twenty-four patients (56%) had mitral valves of normal size (leaflet area < 12.0 cm2) and 19 patients (44%) had enlarged and elongated valves (area > or = 12.0 cm2). Compared with normal-sized mitral valves, the enlarged valves were situated more posteriorly in a larger left ventricular outflow tract (cross-sectional area, 3.3 +/- 1.0 versus 1.9 +/- 0.7 cm2 for normal-sized valves; p < 0.001) and also had greater systolic excursion of the anterior leaflet (16.2 +/- 4.5 versus 13.3 +/- 3.3 mm, p < 0.02), usually with a distinctive sharp-angled bend and localized contact of the leaflet tip with ventricular septum ("typical" SAM); this pattern of SAM was possible because the central and distal portions of the leaflet were relatively free of fibrous thickening. In contrast, normal-sized mitral valves were situated more anteriorally in a smaller left ventricular outflow tract and frequently showed a different mechanism of SAM and subaortic obstruction with relatively limited leaflet motion, absence of a sharp bend, and septal contact involving more substantial portions of the anterior leaflet and contiguous chordae ("atypical" SAM); mitral-septal apposition was effected in large measure by posterior ventricular septal motion. This pattern of SAM was invariably associated with a more diffuse pattern of fibrous thickening. Patients with obstructive HCM show patterns of mitral valve SAM that are diverse and determined largely by the interrelation of left ventricular outflow tract geometry, the size and mobility of the mitral leaflets, and the presence and distribution of fibrous thickening.

Effect of percutaneous balloon valvuloplasty on pulmonary hypertension in mitral stenosis

Percutaneous mitral balloon valvuloplasty (PMBV) has been useful in decreasing mitral valve obstruction in mitral stenosis; however, the long-term effects of valvuloplasty on pulmonary artery pressure have not been extensively studied. Thirty-three patients underwent PMBV in our institution between January 1988 and December 1991. There were significant reductions in peak (19 ± 1 to 12 ± 1 mm Hg) and mean (10 ± 0.7 to 6 ± 0.4 mm Hg) mitral valve gradients estimated by Doppler techniques immediately after PMBV. The mitral valve area, as assessed by the pressure half-time method, increased from 1.06 ± 0.05 to 1.98 ± 0.08 cm 2 ( p < 0.001) after the procedure and remained significantly greater (1.68 ± 0.11 cm 2) at 17 ± 2 months. Right ventricular systolic pressure (RVSP) was estimated in patients with tricuspid regurgitation (TR) using the modified Bernoulli equation. There was a good correlation between Doppler and catheterization for RVSP ( r = 0.83 pre valvuloplasty; r = 0.87 post valvuloplasty). Right ventricular systolic pressure by Doppler was 56 ± 4 mm Hg before valvuloplasty and 48 ± 4 mm Hg immediately afterwards ( p < 0.001). Nine patients had TR on follow-up Doppler studies with an estimated RVSP of 53 ± 9 mm Hg ( p = NS compared with pre- and postvalvuloplasty values). Six of these nine patients had moderate or severe mitral regurgitation (MR), compared with one patient without TR at follow-up ( p < 0.05). There appears to be a good correlation between the RVSP determined by Doppler and measured at catheterization. Despite an initial improvement in RVSP after valvuloplasty, this effect may not persist at 17 months of follow-up. Therefore Doppler echocardiography may be used to assess pulmonary hypertension before and after PMBV in mitral stenosis and to assess possible causes of persistently elevated RVSP after valvuloplasty (such as significant MR).

Relation between pulmonary artery pressure and mitral stenosis severity in patients undergoing balloon mitral commissurotomy

In patients with mitral stenosis, the degree of pulmonary hypertension is expected to be related to the severity of mitral valve obstruction. Previous studies suggested that excessive (or “reactive”) pulmonary hypertension (specifically a pressure gradient across the pulmonary vascular bed >12 mm Hg) typically occurs when left atrial pressure is chronically >20 mm Hg. 1 However, some patients with severe mitral stenosis do not develop reactive pulmonary hypertension. 1–4 The Balloon Valvuloplasty Registry includes hemodynamic and echocardiographic data on a large series of adults with symptomatic mitral stenosis undergoing balloon mitral commissurotomy. 5 The current study examines the prevarvuloplasty data to determine if there are specific anatomic or hemodynamic factors that identify patients with pulmonary hypertension out of proportion to the severity of mitral stenosis.

Hemodynamic diagnosis of mitral valve obstruction by left atrial myxoma with transesophageal continuous wave Doppler

1. Sahasakul Y, Chaithiraphan S, Sriyoschati S. Diagnosis of a right coronary artery-left ventricular fistula by cross-sectional and Doppler echocardiography. Br Heart J 1988;59:593-5. 2. Miyatake K, Okamoto M, Kinoshita N, Fusejima K, Sakakibara H, Nimura Y. Doppler echocardiographic features of coronary arteriovenous fistula. Complementary roles of crosssectional echocardiography and the Doppler technique. Br Heart J 1984;51:508-18. 3. Velvis H, Schmidt KG, Silverman NH, Turley K. Diagnosis of coronary artery fistula by two-dimensional echocardiography, pulsed Doppler ultrasound and color flow imaging. J Am Co11 Cardiol 1989;14:968-76. 4. Sapin P, Frantz E, Jain A, Nichols TC, Dehmer GJ. Coronary artery fistula: an abnormality affecting all age groups. Medicine 1990;69:101-13. 5. Liberthson RR, Sagar K, Berkoben JP, Weintraub RM, Levine FH. Congenital coronary arteriovenous fistula. Report of 13 patients, review of the literature and delineation of management. Circulation 1979;59:849-54. 6. Calafiore PA, Raymond R, Schiavone WA, Rosenkranz ER. Precise evaluation of a complex coronary arteriovenous fistula: the utility of transesophageal color Doppler. J Am Sot Echocardiogr 1989;2:337-41.

Primary cardiac leiomyosarcomas

Two patients with primary cardiac leiomyosarcoma, one of the rarest malignant tumors of the heart, are described. The first patient had a tumor of the pulmonary trunk and was admitted with symptoms suggestive of pulmonary thromboembolism. The second had a tumor of the left atrium and had signs and symptoms of mitral valve obstruction and regurgitation. The 2 patients were operated on and later underwent adjuvant chemotherapy. Both died more than 22 months after operation, having required multiple hospital admissions for treatment of complications related to the pathology or the treatment of the primary cardiac leiomyosarcoma. Nonetheless, aggressive surgical excision followed by chemotherapy appears to have improved survival in these patients with primary cardiac leiomyosarcoma, as they are among the longest survivors reported.

Left Atrial Floating Thrombus: Echocardiographie and Clinical Findings

An atrial ball thrombus freely floating in the left atrium in a patient with mitral stenosis is a rare and dangerous event. In this case report we present a patient with mitral stenosis in whom the presence of a left atrial ball thrombus was documented by two-dimensional echocardiography. The association of mitral valve obstruction, the appearance of severe neurologic impairments, the typical échocardiographie pattern of the mass, and the surgical findings are described.

Doppler Echocardiography: Application to the Assessment of Successful Thrombolysis of Prosthetic Valve Thrombosis

Prosthetic valve thrombosis remains a significant problem despite anticoagulation therapy and advances in valve design. Thrombolytic therapy offers an alternative approach to valve replacement in patients with high surgical risk. In this article we discuss three cases in which Doppler echocardiography was used to confirm the diagnosis of prosthetic mitral valve obstruction and serially monitor the response of valvular hemodynamic measurements to thrombolysis with intravenous streptokinase. These cases illustrate how the Doppler technique, in addition to allowing the noninvasive diagnosis of prosthetic valve obstruction, is presently the ideal tool to follow serially the effect of thrombolytic therapy on prosthetic valve function.

Surgical bypass of the systemic atrioventricular valve in children by means of a valved conduit

The surgical approach to relief of mitral stenosis in children is still a controversial problem. We describe our experience with four severely symptomatic children in whom a valved conduit from the left atrium to the left ventricle was successfully used to bypass a hypoplastic systemic atrioventricular valve. A left atrial-left ventricular extracardiac conduit was implanted in these patients with a hypoplastic mitral anulus and an adequate left ventricular chamber. There were no early or late deaths. Postoperative cardiac catheterization performed in all patients 1 month after the operation showed reduced size of the left atrium, a reduction of the left atrial-left ventricular gradient from a mean of 14 mm Hg to a mean of 5 mm Hg, and an increase of the left atrial outlet from a mean diameter of 10.7 mm to 28.7 mm (including the diameter of the native mitral valve plus the internal diameter of the valved conduit). The application of this unconventional operation in children with congenital or acquired stenosis of the systemic atrioventricular valve should be considered when the mitral valve obstruction cannot be relieved by conventional valve repair or replacement. Furthermore, the left atrial-left ventricular conduit does not preclude future alternative surgical options.

Pulmonary vascular dynamics after percutaneous mitral valvotomy

Hemodynamic studies were performed immediately before, within 1/2 hour, and every 8 hours for 24 hours after percutaneous mitral valvotomy in 22 patients with severe mitral stenosis and pulmonary hypertension. The mean pressure in the left atrium decreased from 27 +/- 2 mm Hg to 14 +/- 1 mm Hg (p less than 0.01) immediately after successful valvotomy. There was no significant further drop in left atrial pressure (or pulmonary capillary wedge pressure) over 24 hours. Mean cardiac output increased from 3.9 +/- 0.3 L/min to 4.6 +/- 0.3 L/min immediately after successful valvotomy (p less than 0.01). Cardiac output continued to rise for the next 8 hours and plateaued during the 24-hour period of observation. Pulmonary vascular resistance dropped immediately after the relief of mitral valve obstruction in all patients. In the group of patients who had elevated pulmonary vascular resistance after valvotomy, resistance continued to drop significantly (p less than 0.05) over the next 24 hours. In some cases it did not fall to normal levels despite adequate relief of mitral stenosis.

Peripheral pulmonary vascular and airway abnormalities in adolescents with rheumatic mitral stenosis

Lung biopsy specimens were taken from 15 adolescents (aged 11–21 years), at the time a mitral valvotomy was performed. In addition to quantitative light microscopic studies three specimens were also examined by scanning and transmission electron microscopy. In all cases, the pulmonary vascular abnormalities were most marked in the capillary bed and in the vessels immediately proximal and distal to it. The capillaries showed a marked increase in basement membrane material at the blood/gas barrier, and were embedded in dense connective tissue within the alveolar walls. Intra-acinar and, to a lesser extent, pre- and post-acinar vessels showed an increase in muscularity, severe circumferential intimal fibrosis, and abnormally thick and dense adventitial connective tissue. The peripheral airways were encased in dense connective tissue, which appeared to compress them. Bronchial smooth muscle was increased. Six months after the mitral valvotomy was performed, the mean pulmonary arterial pressure had fallen from 42 mm Hg to 23 mm Hg. Despite this satisfactory haemodynamic result, the long-term effects of small airway compression on the growing lung indicate the need for early relief of mitral valve obstruction, possibly made easier by the new technique of balloon angioplasty.

Catheter Balloon Valvuloplasty of the Mitral Valve in Adults Using a Double-Balloon Technique

Catheter balloon valvuloplasty (CBV) using the double-balloon technique was performed on 12 symptomatic patients (mean age, 43 years) with rheumatic mitral valve stenosis. Two dilatation balloons were used in which the diameters approximately equaled the mitral valve anulus diameter as determined. After CBV, the mean mitral valve gradient decreased in all patients (mean +/- SD, 16 +/- 6 to 5 +/- 2 mm Hg), the mean left atrial pressure decreased (29 +/- 7 to 16 +/- 4 mm Hg), and the cardiac output increased (4.4 +/- 1.2 to 5.5 +/- 1.4 L/min). The mitral valve area increased from 1.0 +/- 0.3 to 2.4 +/- 0.8 cm2. Oximetry demonstrated small left to right shunts of pulmonary to systemic flow ratios of 1.4:1 and 1.3:1 in two patients. Mitral regurgitation did not increase. Gradual decreases in mean pulmonary artery pressures and pulmonary vascular resistance were recorded over the subsequent 24 hours. Our patients left the hospital two days after CBV. The New York Heart Association Functional Class improved in 11 of 12 patients. We conclude that CBV using the double-balloon technique effectively relieves mitral valve obstruction, reduces elevated pulmonary pressures, and reduces symptoms in selected adult patients with symptomatic mitral stenosis.

Canine renal responses to atrial stretch or intravenous saline are not attenuated at night

Primates develop a diuresis and natriuresis in response to stimuli that increase central blood volume. However, the renal response is markedly attenuated when these same experimental stimuli are applied at night. The purpose of the present study was to determine whether a quadruped, specifically the dog, also demonstrates attenuated renal responses to similar stimuli given at night. Two experimental protocols were performed on conscious dogs at night: 1) left atrial distension by partial mitral valve obstruction and 2) intravenous saline administration. Results from these experiments were compared with results from comparable experiments performed on the same dogs during the day. Each experimental intervention produced increases in urine flow and sodium excretion and decreases in urine osmolality during both day and night experiments (all P less than 0.05). The responses obtained during the night did not differ significantly from those obtained during the day. Thus the dog does not demonstrate an attenuated renal response to central volume expansion during the night. This contrasts with the adaptive response in primates that serves to minimize fluid loss when the intrathoracic blood pool is increased during prolonged recumbency at night. Presumably quadrupeds, with trunks horizontal both day and night, do not require nocturnal adaptive mechanisms to conserve body fluids.