Previous experiments have demonstrated that the vestibular system contributes to regulating sympathetic nervous system activity, particularly the discharges of vasoconstrictor fibres. In the present study, we examined the physiological significance of vestibulosympathetic responses by comparing blood flow and vascular resistance in the forelimb and hindlimb during head-up tilt from the prone position before and after the removal of vestibular inputs through a bilateral vestibular neurectomy. Experiments were performed on conscious cats that were trained to remain sedentary on a tilt table during rotations up to 60 deg in amplitude. Blood flow through the femoral and brachial arteries was recorded during whole-body tilt using perivascular probes; blood pressure was recorded using a telemetry system and vascular resistance was calculated from blood pressure and blood flow measurements. In vestibular-intact animals, 60 deg head-up tilt produced ∼20% decrease in femoral blood flow and ∼37% increase in femoral vascular resistance relative to baseline levels before tilt; similar effects were also observed for the brachial artery (∼25% decrease in blood flow and ∼38% increase in resistance). Following the removal of vestibular inputs, brachial blood flow and vascular resistance during head-up tilt were almost unchanged. In contrast, femoral vascular resistance increased only ∼6% from baseline during 60 deg head-up rotation delivered in the first week after elimination of vestibular signals and ∼16% in the subsequent 3-week period (as opposed to the ∼37% increase in resistance that occurred before lesion). These data demonstrate that vestibular inputs associated with postural alterations elicit regionally specific increases in vascular resistance that direct blood flow away from the region of the body where blood pooling may occur. Thus, the data support the hypothesis that vestibular influences on the cardiovascular system serve to protect against the occurrence of orthostatic hypotension.

September 30, 2009; doi:10.1152 doi:10. /ajpregu.00551.2009 show that the vestibular system contributes to blood pressure regulation. Prior studies reported that lesions that eliminate inputs from the inner ears attenuate the vasoconstriction that ordinarily occurs in the hindlimbs of conscious cats during head-up rotations. These data led to the hypothesis that labyrinthine-deficient animals would experience considerable lower body blood pooling during head-up postural alterations. The present study tested this hypothesis by comparing blood flow though the femoral artery and vein of conscious cats during 20 -60°head-up tilts from the prone position before and after removal of vestibular inputs. In vestibular-intact animals, venous return from the hindlimb dropped considerably at the onset of head-up tilts and, at 5 s after the initiation of 60°rotations, was 66% lower than when the animals were prone. However, after the animals were maintained in the head-up position for another 15 s, venous return was just 33% lower than before the tilt commenced. At the same time point, arterial inflow to the limb had decreased 32% from baseline, such that the decrease in blood flow out of the limb due to the force of gravity was precisely matched by a reduction in blood reaching the limb. After vestibular lesions, the decline in femoral artery blood flow that ordinarily occurs during head-up tilts was attenuated, such that more blood flowed into the leg. Contrary to expectations, in most animals, venous return was facilitated, such that no more blood accumulated in the hindlimb than when labyrinthine signals were present. These data show that peripheral blood pooling is unlikely to account for the fluctuations in blood pressure that can occur during postural changes of animals lacking inputs from the inner ear. Instead, alterations in total peripheral resistance following vestibular dysfunction could affect the regulation of blood pressure.blood flow patterning; venous return; cardiac output; orthostatic hypotension HEAD-UP BODY ROTATIONS in humans or animals typically result in some pooling of blood in the periphery and a resulting reduction in return of blood to the heart. Because cardiac output is directly related to cardiac preload (Starling's law of the heart) (27), cardiac output tends to decrease during head-up movements (25). Furthermore, cardiac output and peripheral vascular resistance determine systemic blood pressure, such that the sympathetic nervous system must produce a rapid net increase in peripheral resistance by inducing vasoconstriction at the onset of head-up body rotations to maintain stable blood pressure (7). Arterial baroreceptor mechanisms play an important role in regulating peripheral vasoconstriction during postural alterations (23). In addition, there is considerable evidence from studies in animals (6,8,10,11,21,22,32) and humans (1,4,12,23,26,28,30) that the vestibular system also participates in triggering increases in vasomotor activity during movements that promote peripheral blood pooling...

Prior studies have shown that removal of vestibular inputs produces lability in blood pressure during orthostatic challenges (Holmes MJ, Cotter LA, Arendt HE, Cass SP, and Yates BJ. Brain Res 938: 62-72, 2002; Jian BJ, Cotter LA, Emanuel BA, Cass SP, and Yates BJ. J Appl Physiol 86: 1552-1560, 1999). Furthermore, these studies led to the prediction that the blood pressure instability results in susceptibility for orthostatic intolerance. The present experiments tested this hypothesis by recording common carotid blood flow (CCBF) in conscious cats during head-up tilts of 20, 40, and 60 degrees amplitudes, before and after the surgical elimination of labyrinthine inputs through a bilateral vestibular neurectomy. Before vestibular lesions in most animals, CCBF remained stable during head-up rotations. Unexpectedly, in five of six animals, the vestibular neurectomy resulted in a significant increase in baseline CCBF, particularly when the laboratory was illuminated; on average, basal blood flow measured when the animals were in the prone position was 41 +/- 17 (SE) % higher after the first week after the lesions. As a result, even when posturally related lability in CCBF occurred after removal of vestibular inputs, blood supply to the head was not lower than when labyrinthine inputs were present. These data suggest that vestibular influences on cardiovascular regulation are more complex than previously appreciated, because labyrinthine signals appear to participate in setting basal rates of blood flow to the head in addition to triggering dynamic changes in the circulation to compensate for orthostatic challenges.

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Summary:We report a case of spontaneous expulsion of a lipoma in a 32 year old male patient who presented with recurrent attacks of subacute intestinal obstruction. During one such episode the patient developed unusually severe abdominal pain and expelled a fleshy mass per rectum which, on histopathology, was found to be a lipoma attached to a necrosed portion of the small intestine. The pain disappeared immediately; a subsequent barium meal examination revealed normal appearances and the patient has remained completely symptom free 10 months after the incident.