EFFECT OF L-NOREPINEPHRINE ON RIGHT ATRIAL PRESSURE AND THE "SQUARE WAVE RESPONSE" TO THE VALSALVA MANEUVER

Beat-to-beat blood pressure and heart rate responses to the Valsalva maneuver

Measurement of beat-to-beat blood pressure and heart rate responses to the Valsalva maneuver is the basis for a highly informative autonomic function test. Whereas in the past this measurement required intra-arterial cannulation, the development of finger cuff devices that acquire arterial pressure waveforms indistinguishable from those recorded intra-arterially has made it possible to obtain accurate measurements noninvasively. In a patient with orthostatic hypotension, the pattern of blood pressure responses during and after the release of the maneuver can identify a neurogenic basis: sympathetic neurocirculatory failure. The quantifiable change in cardiac interbeat interval per unit change in systolic pressure during the maneuver can identify baroreflex-cardiovagal failure.

Response to the Valsalva maneuver after the Fontan procedure for tricuspid valve atresia, single ventricle or pulmonic valve atresia

The Valsalva maneuver was performed during cardiac catheterization in 9 patients who had undergone a Fontan operation (Fontan group) and in 10 control subjects. The Fontan group had higher right atrial (RA) pressure (16 +/- 1 vs 4 +/- 0.5 mm Hg, p less than 0.001), lower cardiac index (2.5 +/- 0.1 vs 3.7 +/- 0.2 liters/min/m2, p less than 0.05), lower stroke index (32 +/- 2 vs 44 +/- 2 ml/beat/m2, p less than 0.05), and higher systemic vascular resistance (31 +/- 1 vs 24 +/- 1 units, p less than 0.05) than the control group. Four patients in the Fontan group had a normal 4-phase Valsalva response, and 5 did not (p less than 0.05). RA pressure was similar in those who responded normally and those who did not (16 +/- 0.5 vs 17 +/- 1 mm Hg), whereas in those who responded normally cardiac index was higher (2.9 +/- 0.2 vs 2.2 +/- 0.1 liters/min/m2, p less than 0.05), stroke index was higher (36 +/- 1 vs 28 +/- 1 ml/beat/m2, p less than 0.05), and systemic vascular resistance was lower (28 +/- 1 vs 31 +/- 1, p less than 0.05). It is concluded that cardiac output is a better predictor of a normal response to the Valsalva maneuver than RA pressure in patients after the Fontan procedure. A normal response to the supine Valsalva maneuver suggests a cardiac index greater than 2.4 liters/min/m2 and stroke index greater than 31 ml/beat/m2.

Effect of l-norepinephrine on left ventricular diastolic pressures in man

Left ventricular systolic pressure, left ventricular diastolic pressure, left ventricular end-diastolic pressure, left ventricular cardiac output, systemic vascular resistance, and central blood volume were specifically measured in seven patients with normal cardiovascular systems before and during the tenth minute of an infusion of l-norepinephrine and the emergence of a `square wave' pattern in the peripheral arterial blood pressure during Valsalva's manœuvre. At that time point the mean left ventricular systolic pressure exceeded the resting level. The mean left ventricular diastolic pressure rose by 6 mm. Hg, and the mean left ventricular end-diastolic pressure rose by 5·5 mm. Hg. The left ventricular output remained unchanged. A reduction in the heart rate of 13 beats/minute was found, and the calculated mean systemic vascular resistance, mean left ventricular stroke volume, and left ventricular stroke work continued to be above resting levels. No change was apparent in the central blood volume. The results indicate that the left ventricular diastolic pressure and left ventricular end-diastolic pressure rise significantly in the course of a prolonged infusion of l-norepinephrine coinciding with left ventricular after-loading. The magnitude of this elevation affects all diastolic pressures passively throughout the lesser circulation, including the central venous pressure. l-Norepinephrine is markedly inotropic when released within the myocardium. In the usual clinical dose and during a period of 10 minutes' infusion its efferent vagal, peripheral, arteriolar constrictor, and left ventricle after-load effects reduce the initial inotropy.