Atrial compliance determines the nature of passive atrial stretch and plasma atrial natriuretic factor in the conscious dog.

STUDY OBJECTIVE: The aim was to measure changes in atrial wall function over a wide range of atrial filling pressures in order to determine the relationship governing the atrial stretch in vivo. DESIGN: Acute graded haemorrhage, 30 ml.kg-1, was used to reduce atrial stretch, and volume loading with 1000 ml saline was used to increase atrial stretch. EXPERIMENTAL MATERIAL: Awake mongrel dogs (n = 6) were instrumented for the measurement of left atrial appendage pressure and diameter; awake mongrel dogs (n = 4) were instrumented for measurement of left and right atrial appendage pressures and diameters. MEASUREMENTS AND MAIN RESULTS: During haemorrhage, left atrial pressure and diameter decreased progressively, and plasma atrial natriuretic factor fell from 44 (SEM 10) to 25(5) pg.ml-1 (p less than 0.05). Calculated left atrial wall stress and minute wall stress fell by 80(5.8)% and 72(15)% (p less than 0.05 from control). During volume expansion, however, atrial wall stress and minute wall stress markedly increased and plasma atrial natriuretic factor increased by more than 500%. The relationship between left atrial pressure and diameter was a typical exponential compliance curve during volume loading and haemorrhage for atrial systole, the A wave, and for atrial diastole, the V wave. During volume expansion right atrial pressure and diameter were also related exponentially. Left atrial passive stretch, as measured by V wave wall stress, increased more than right atrial stretch during volume loading. Changes in atrial filling in conscious dogs therefore result in typical exponential changes in atrial pressure and diameter in both atria. Plasma atrial natriuretic factor only increased at high filling pressures. The relationship between passive V wave minute wall stress and plasma atrial natriuretic factor also fitted an exponential curve. Thus when atrial filling was reduced, plasma atrial natriuretic factor fell by only 50% from control, while when atrial filling increased over the physiological range (up to 15 mm Hg left atrial pressure), it rose only to 100 pg.ml-1. CONCLUSIONS: Very high atrial appendage wall stresses are required to increase plasma atrial natriuretic factor markedly. Atrial stretch and the release of atrial natriuretic factor are non-linearly related. The stimulus for atrial natriuretic factor release is related to the exponential changes in atrial function due to the underlying atrial compliance relationship.

Diagnosis of patent foramen ovale with transesophageal echocardiography in a patient supported with a left ventricular assist device.

Intracardiac right-to-left shunting through a patent foramen ovale is a known cause of arterial hypoxemia. We present a case report of a patient supported with a left ventricular assist device who had significant right-to-left shunting as visualized with transesophageal echocardiography. When the device was turned off, no further shunting occurred and arterial hypoxemia resolved. Our report is the first visual representation of the anatomy of a patent foramen ovale in a patient supported with a left ventricular assist device.

Coronary angiography in smokers undergoing evaluation for lung transplantation: is routine use justified?

Many patients referred for lung transplantation have a history of smoking. For the exclusion of the possibility of asymptomatic coronary artery disease, these patients undergo coronary angiography as part of their preoperative evaluation. The usefulness of this approach remains unknown. We reviewed the records of all smokers referred for lung transplantation who underwent coronary angiography (n = 77). Nine patients (12%) had significant coronary artery disease; six (8%) of these patients had their clinical management altered because of findings on angiography. Eight of nine patients with coronary artery disease (89%) and all of the six patients (100%) whose management was altered had coronary artery disease risk factors other than a history of smoking; therefore, no patient with clinically significant coronary artery disease had history of smoking as the only risk factor. The presence of other coronary artery disease risk factors was significantly associated (p < 0.0001) with the positive findings on angiography. A nonsignificant trend toward older age was found, and a higher proportion of male patients existed in the group with coronary artery disease. Routine angiography for all patients with a history of smoking referred for angiography is unjustified. A subset of patients with high risk identified primarily by the presence of additional coronary artery disease risk factors may benefit from routine angiography.

Apparent reduction in baroreflex sensitivity to adenosine in conscious dogs.

Relative effects of equihypotensive doses (-35 mmHg) of adenosine (5.0 mumol/kg) and nitroglycerin (25 micrograms/kg) on heart rate and, therefore, baroreflex sensitivity were studied in conscious dogs. Nitroglycerin increased heart rate 133 +/- 24% from 78 +/- 5.5 beats/min, whereas adenosine increased heart rate only 79 +/- 16% from 78 +/- 5.2 beats/min (P less than 0.01). Injection of nitroglycerin during combined beta-adrenergic and muscarinic receptor blockades caused arterial pressure to fall 38 +/- 3.4% from 107 +/- 3.2 mmHg without any significant change in heart rate (3.8 +/- 3.8 from 162 +/- 9.2 beats/min). During combined beta-adrenergic and muscarinic receptor blockades adenosine also reduced arterial pressure 45 +/- 2.7% from 106 +/- 2.9 mmHg but unexpectedly reduced heart rate as well by 37 +/- 1.7% from 160 +/- 9.7 beats/min. This bradycardia reflected an effect on the sinoatrial (SA) node rather than an induction of heart block, since the R-R interval increased by 70 +/- 7.8% from 371 +/- 20 ms (P less than 0.01), while the P-R interval increased only 13 +/- 2.3% from 97 +/- 7.2 ms (P less than 0.05) with no electrocardiographic evidence of nonconducted beats. Arterial plasma adenosine levels were 43 +/- 5 nmol/ml at this time. Adenosine also caused bradycardia during muscarinic blockade alone (-43 +/- 3.4% from 201 +/- 6.4 beats/min) and following bilateral vagal section (-33 +/- 1.9% from 151 +/- 5.9 beats/min). In summary, adenosine appears to alter normal baroreflex function in the conscious dog by reducing the tachycardia that normally follows a fall in systemic arterial pressure.(ABSTRACT TRUNCATED AT 250 WORDS)