Cerebral reactive hyperaemia and arterial pressure in anaesthetized goats

Coronary reactive hyperaemia and arterial pressure in anaesthetized goats

To study the effects of arterial pressure on coronary reactive hyperaemia, left circumflex coronary artery flow was measured, and reactive hyperaemia was determined after 5, 10 or 20 s of occlusion of this artery in anaesthetized goats during normotension, hypertension and hypotension. During hypertension induced by aortic constriction (mean arterial pressure, MAP = 140 +/- 6 mmHg) coronary vascular resistance (CVR), reactive hyperaemia (ratio of peak in hyperaemic flow to control flow and ratio of repayment to debt) and the decrease in CVR during the peak in hyperaemic flow were comparable to those during normotension. During hypertension induced by noradrenaline (MAP = 144 +/- 6 mmHg) CVR was 16% lower (P < 0.05), reactive hyperaemia was reduced by 14-25% (P < 0.05) and the decrease in CVR during the peak in hyperaemic flow was lower than the values of these parameters during normotension. During hypotension induced by constriction of the caudal vena cava (MAP = 40 +/- 4 mmHg) CVR was 22% lower (P < 0.05), reactive hyperaemia was reduced by 25-65% (P < 0.05) and the decrease in CVR during the peak in hyperaemic flow was less compared to the values of these parameters during normotension. During hypotension induced by isoprenaline (MAP = 45 +/- 4 mmHg) CVR was 59% lower, reactive hyperaemia was reduced by 55-100% (P < 0.01) and the decrease in CVR during the peak in hyperaemic flow was less compared to the values of these parameters during normotension. Arterial pressure is a main determinant of coronary reactive hyperaemia after brief periods of ischaemia, and the relationship between arterial pressure and reactive hyperaemia may depend in part on changes in CVR after variations in arterial pressure. These changes in CVR may be related to the action on coronary vessels of myocardial factors and vascular myogenic mechanisms.

Intramedullary pressure in syringomyelia: clinical and pathophysiological correlates of syrinx distension

OBJECTIVE

The pathophysiological effects of syrinx distension are incompletely understood. Although it is generally assumed that the accumulation of fluid within syrinx cavities can contribute to neurological dysfunction, there are no reports describing intramedullary pressure in syringomyelia. The purpose of the current study was to measure syrinx pressures in patients with progressive clinical deterioration and to correlate these data with neurological deficits and intraoperative physiological findings.

METHODS

Intramedullary fluid pressure was measured manometrically in 32 patients undergoing syrinx shunting procedures. The data were correlated with syrinx morphology, intraoperative somatosensory evoked potentials, laser Doppler measurements of local spinal cord blood flow (six patients), and neurological findings before and after syrinx decompression.

RESULTS

Syrinx pressures recorded under atmospheric conditions ranged from 0.5 to 22.0 cm H2O (mean = 7.7 cm). There was a significant elevation of the cardiac pulse (mean = 0.7 cm H2O) and the respiratory pulse (mean = 1.1 cm H2O) that was consistent with raised cerebrospinal fluid pressure. Syrinx pressures decreased to subatmospheric levels after surgical drainage. In 18 of 24 patients with predrainage somatosensory evoked potential abnormalities, syrinx decompression produced a consistent reduction of N20 latencies (mean change = 0.49 ms +/- 0.094 SE right, P = 0.002; 0.61 ms +/- 0.089 SE left, P = 0.001) and a similar but less consistent increase in N20 amplitudes (mean change = 0.17 mV +/- 0.103 SE right, P = 0.115; 0.31 mV +/- 0.097 SE left, P = 0.027). Measurements of local spinal cord blood flow revealed very low baseline values (mean = 12.2 arbitrary units +/- 13.9 standard deviation), which increased to intermediate levels (mean = 144.7 arbitrary units +/- 42.6 standard deviation) after syrinx decompression. Patients with syrinx pressures greater than 7.7 cm H2O tended to have more rapidly progressive symptoms, exhibited greater improvements after shunting, and had a higher incidence of postoperative dysesthetic pain.

CONCLUSION

The current study is the first to measure intramedullary pressure in a human disease. Evidence is presented that distended syringes are associated with varying levels of raised intramedullary pressure that can accentuate or induce neurological dysfunction by the compression of long tracts, neurons, and the microcirculation. Symptoms referrable to raised intramedullary pressure are potentially reversible by syrinx decompression.