Spleen volume changes during adrenergic stimulation with low doses of epinephrine.

It is generally accepted that the spleen contraction is a consequence of humoral stimulation but recent data suggest a role of neural mechanisms. This study tested the hypothesis that the reduction in spleen size in response to low dose epinephrine infusion is a consequence of neurally mediated unloading of baroreceptors. Continuous ultrasonic measurements of spleen volume in response to intravenous infusion of low doses of epinephrine (0.06 µg/kg/min for 6 minutes, followed 0.12 µg/kg/min for 3 minutes) were performed with simultaneous continuous noninvasive measurements of cardiovascular parameters in thirteen subjects. In subgroup of six subjects we also continuously measured muscle sympathetic nerve activity (MSNA) as an index of peripheral sympathetic activation. Significant spleen contraction (≈30%, p=0.008) was observed early after the onset of epinephrine infusion and was preceded by a decrease in total peripheral resistance (41%, p=0.001) and mean arterial pressure (6.2%, p=0.02) and an increase in heart rate (27%, p=0.001) and total MSNA (120%, p=0.02). Our results demonstrate rapid spleen contraction induced by low-dose epinephrine infusion in conditions of decreased blood pressure and increased MSNA suggesting that the spleen may represent a constitutive part of the sympathetic nervous system under stressful situations.

Venous gas bubble formation and decompression risk after scuba diving in persons with chronic spinal cord injury and able-bodied controls.

STUDY DESIGN: Prospective study. OBJECTIVE: To evaluate the formation of venous gas bubbles following open-sea scuba dives in persons with chronic spinal cord injury (SCI) and in able-bodied diving instructors (C) and to assess the risk for decompression sickness (DCS). SETTING: Field study at the Island of Krk, Croatia. METHODS: Gas bubbles were monitored with an ultrasound scanner 40 min after surfacing. The probability of DCS (P((DCS))) was estimated from the recorded depth-time profile using a decompression model. RESULTS: Divers completed six dives in 3 days using a modified Bühlmann decompression model, and none developed signs of DCS. Mean P((DCS)) was similar in both groups, SCI (0.51+/-0.2%) and C (0.64+/-0.27%), and was seen to increase with subsequent dives. Number of bubbles (bubbles per cm(2)) was low in both groups on all 3 days of diving. CONCLUSIONS: We have used the P((DCS)) as a severity index of diving exposure. Overall, the severity of exposure in SCI subjects was consistent with the range of typical recreational dives, suggesting that the diving profile used is very safe.