No abstract

Blood pressure, heart rate, and plasma catecholamine levels were measured in 16 quadriplegic subjects with physiologically complete cervical spinal cord transections above the level of the sympathetic outflow, and in 15 normal subjects (controls). In the quadriplegics the average resting blood pressure was 107/59 (mean, 75) mmHg, heart rate was 65 beats/min, and plasma norepinephrine (NE) and epinephrine (E) levels were 0.05 and 0.005 ng/ml, respectively. In the controls average resting blood pressure was 117/79 (mean, 92) mmHg, heart rate was 61 beats/min, and resting plasma NE and E levels were 0.20 and 0.06 ng/ml, respectively. Resting blood pressure and plasma NE and E levels were significantly lower in the quadriplegics (P less than 0.01, less than 0.001, less than 0.001, and less than 0.001, less than 0.001, respectively) than in the controls. In the quadriplegics, neurogenic hypertension was induced by bladder and muscle stimulation. This resulted in a marked elevation of both systolic and diastolic blood pressure (from an average of 109/60 (mean, 75) to 168/87 (mean, 114) mmHg) as a result of uninhibited sympathetic nervous activity through the isolated spinal cord. Plasma NE consistently rose, from an average of 0.05 to 0.16 ng/ml (P less than 0.001). There was significant linear relationship between plasma NE and mean blood pressure (P less than 0.001). In the quadriplegics infusion of l-norepinephrine to raise the blood pressure to comparable levels (from 105/58 (mean, 74) to 183/93 (mean, 123) mmHg) resulted in plasma NE levels approximately 21 times higher than during muscle and bladder stimulation. It is possible that the lower resting arterial blood pressure and plasma NE and E levels in the quadriplegics in comparison to normal subjects may reflect diminished resting sympathetic nervous activity. The rise in blood pressure following increased sympathetic nervous activity was accompanied by an elevation in plasma NE. The hypertension was not secondary to the rise in plasma NE. Plasma NE in these subjects appears to be a reliable index of prevailing sympathetic nervous activity.

Arterial blood pressure, heart-rate and the electrocardiogram were recorded in subjects tetraplegic from cervical spinal cord transections, and in control subjects, before, during and after intravenous infusions of 1-noradrenaline. Over a wide range of doses the blood pressure rose much more in the tetraplegics than in the controls. Circulating noradrenaline during infusion did not significantly differ between the two groups. The findings indicate that tetraplegic subjects have an enhanced pressor response to noradrenaline infusions. Such a response therefore does not necessarily indicate post-ganglionic sympathetic denervation. The observed responses in the tetraplegics may in part be due to exaggerated adrenergic receptor responses, but the main cause is likely to be the loss of those baroreceptor reflexes with sympathetic efferent pathways.

No abstract

No abstract