Resetting of the cardiopulmonary baroreflex 10 years after surgical repair of coarctation of the aorta

Abstract

Objective: To characterise cardiopulmonary baroreflex responses and examine the effects of a 45 minute cycling bout late after successful repair of coarctation of the aorta.

Subjects: 10 young adults (mean (SEM) age 18.1 (2.6 years)) operated on for coarctation of the aorta 12.7 (3.5) years earlier, and 10 healthy controls.

Design: Forearm blood flow (venous occlusion plethysmography) and vascular resistance, left ventricular internal diastolic diameter, and central venous pressure estimated from an antecubital vein were measured in the supine position at baseline and during five minute applications of lower body negative pressure (LBNP) at -15 mm Hg (LBNP(-15)) and -40 mm Hg (LBNP(-40)). Venous samples were obtained at baseline and during LBNP(-40) for noradrenaline (norepinephrine), adrenaline (epinephrine), renin activity, and aldosterone. The tests were repeated after 45 minutes of moderate exercise.

Results: Baseline heart rate (78 (9) v 64 (6) beats/min), echocardiographic cardiac output (6.9 (1.1) v 5.0 (0.2) l/min), shortening fraction (41.7 (1.8)% v 33.3 (1.3)%), and forearm blood flow (3.4 (0.4) v 2.3 (0.3) ml/100 g/min) were higher in the coarctation group than in the controls (p < 0.05). Changes in forearm blood flow and forearm vascular resistance from baseline to LBNP(-40) were similar in both groups, but the relation between forearm vascular resistance and estimated central venous pressure or left ventricular internal diastolic diameter was shifted downward in the coarctation group. Plasma adrenaline was increased in the coarctation group (baseline: 3.2 (0.6) v 2.4 (0.3) pmol/l in controls; LBNP(-40): 687 (151) v 332 (42) pmol/l) (p < 0.05). Both groups showed a similar downward displacement of forearm vascular resistance (p < 0.05) after exercise.

Conclusions: There appears to be resetting of the cardiopulmonary baroreflex to a lower forearm vascular resistance in young adults operated on for coarctation of the aorta, associated with hyperdynamic left ventricular function. Raised circulating adrenaline could contribute to the lower forearm vascular resistance.

Figure 1

Effects of lower body negative pressure (LBNP) on central vascular volume and forearm responses. Values are means of estimated central venous pressure (eCVP), left ventricular internal diastolic diameter (LVIDD), forearm blood flow (FBF), and forearm vascular resistance (FVR) in patients with coarctation of the aorta (CoAo) and control subjects (Ctrl). Error bars = SEM. *p < 0.05 v control subjects; †p < 0.01 v baseline.

Figure 2

Mean relative changes from baseline at lower body negative pressure (LBNP) of −40 mm Hg. Values are means expressed as per cent from baseline for systolic and diastolic blood pressure (SBP, DBP), heart rate (HR), forearm blood flow (FBF), forearm vascular resistance (FVR), left ventricular internal diastolic diameter (LVIDD), and estimated central venous pressure (eCVP) in patients with coarctation of the aorta (CoAo) and controls. Error bars = SEM.

Figure 3

Linear relations between forearm vascular resistance and estimated central venous pressure in coarctation of the aorta and in control subjects. Data points were obtained by averaging individual data during lower body negative pressure at −40 mm Hg and −15 mm Hg and at baseline. Regression lines reflect the mean of the slopes calculated individually for each subject. FVR, forearm vascular resistance; eCVP, central venous pressure estimated from antecubital venous pressure.

Figure 4

Effects of a single 45 minute cycling bout on systolic and diastolic blood pressure (SBP, DBP) as well as on forearm vascular resistance (FVR) responses to lower body negative pressure (LBNP). Results in patients with coarctation of the aorta (CoAo) are on the left and those of controls are on the right. Values are means, error bars = SEM. *p < 0.05 v baseline.