Autoregulation of cerebral blood flow in patients with orthostatic hypotension after spinal cord injury

Abstract

Summ aryTwo groups of patients who developed orthostatic hypotension (OH) after spinal cord injury (SCI) were studied. In the first group all patients (4 females and 6 males) were asymptomatic, whereas in the second group (1 female and 9 males) all had clinical manifestations of hypotension. All but 3 patients were tetraplegic , and these patients were paraplegic above the T6 level. For this study blood pressure (BP) , heart rate and cerebral blood flow (CBF) velocity were measured simultaneously on a tilt table at 0, 30 , 60, and 80 degrees. Cerebral blood flow in the middle cerebral artery was measured bilaterally utilising the transcranial Doppler technique. In asymptomatic patients the mean baseline (0 degrees) BP (110 ± 16/70 ± 77 mm Hg systolic/diastolic) was not significantly different from the BP (106 ± 16/68 ± 11 mm Hg) of symptomatic patients. The mean maximal change in BP during tilling in the asymptomatic group ( -23 ± 10/10 ± 7 mm Hg) was also not significantly different when compared to the symptomatic group (-29 ± 13/11 ± 6 mm Hg). CBF in the symptomatic group during the hypotensive reaction at 80 degrees was 32.5 ± 5 cm/sec, while at the same body position in the asymptomatic group it was 40·9 ± 8 cm/sec (significant at the p < 0·02). In addition, CBF decreased in the symptomatic group at 80 degrees to 55·5 ± 9·6% of baseline, while in the asymptomatic group the fall was 69·3 ± 7·2% (p < 0·001). Our data suggests that autoregulation of CBF rather than systemic BP plays a dominant role in the adaptation to OH in patients with SCI.

Orthostatic hypotension following spinal cord injury: understanding clinical pathophysiology

“…In SCI patients with tetraplegia, a decline in blood pressure during tilting was associated with symptoms only in those individuals in whom cerebral blood flow was reduced to low levels. 81 Indeed, in this study, cerebral blood flow was significantly lower in individuals with symptomatic orthostatic hypotension (32.575 cm/s) compared to asymptomatic individuals (40.978 cm/s, Po0.02), even though the decrease in blood pressure with postural change was similar in the two groups (Figure 4). These investigators suggested, therefore, that autoregulation of cerebral blood flow, rather than systemic blood pressure, plays the dominant role in the apparent adaptation to orthostatic hypotension in SCI patients.…”

“…These investigators suggested, therefore, that autoregulation of cerebral blood flow, rather than systemic blood pressure, plays the dominant role in the apparent adaptation to orthostatic hypotension in SCI patients. However, it is remarkable that such low pressures (approximately 85/60 mmHg) 81 should be tolerated. If the systemic blood pressure decreases to low levels, the cerebral perfusion pressure (in the upright position) will be reduced considerably further, due to the hydrostatic effect of the height difference between the head and heart when upright.…”

“…17 This is important because during orthostasis the carotid baroreceptors lie above heart level, and as such are activated by the relative fall in pressure due to the hydrostatic effects of gravity, 80 and normally bring about the coordinated reflex responses to orthostasis. In SCI, the baroreceptor pathways may be impaired, 64 and in addition there may, 82 or may not, 81,83 be a disruption of cerebral blood flow during standing.…”

Superoxide radicals play important roles in the pathogenesis of spinal cord injury

“…Furthermore, hypotensive manifestations may be present for several months, until patients develop tolerance to the low blood pressure. 3 Although it has been reported that the pathogenesis of orthostatic hypotension caused by SCI is complex and involves the cardiovascular, renal, neurological and the endocrine systems, the true cause is uncertain. 4,23 Our data demonstrated that compression and tilting increased the sensitivity of resistant arteries to Ach and the increased sensitivity was more marked in animals administered with SM-SOD during compression and tilting.…”

About orthostatic hypotension in tetraplegic individuals reflections and experience

“…15,18 Moreover, the slowing of extent of the cerebral blood¯ow as shown by the transcranial Doppler technique, does not correlate with the data given by the tensiometer but with the clinical symptoms of OH, demonstrating that the autoregulation of the cerebral blood¯ow is preserved. 21 Although OH is common in those who are tetraplegic, it does not appear in every such individual. One may wonder why: An answer could be that incomplete lesions of the autonomic nervous system may exist, similar to incomplete motor and sensory lesions but we do not have the means of detecting these clinically.…”