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Spleen and cardiovascular function during short apneas in divers

Ivan Palada,¹ Davor Eterovi,² Ante Obad,¹ Darija Bakovic,¹ Zoran Valic,¹ Vladimir Ivancev,¹ Mihajlo Lojpur,³ J. Kevin Shoemaker,⁴ and Zeljko Dujic¹

Departments of ¹Physiology and ²Biophysics and Scientific Methodology, University of Split School of Medicine; ³Department of Anesthesiology, Clinical Hospital Split, Split, Croatia; and ⁴Neurovascular Research Laboratory, School of Kinesiology, The University of Western Ontario, London, Ontario, Canada

Submitted 13 February 2007 ; accepted in final form 11 October 2007

We investigated the spleen volume changes as related to the cardiovascular responses during short-duration apneas at rest. We used dynamic ultrasound splenic imaging and noninvasive photoplethysmographic cardiovascular measurements before, during, and after 15–20 s apneas in seven trained divers. The role of baroreflex was studied by intravenous bolus of vasodilating drug trinitrosan during tidal breathing. The role of lung volume was studied by comparing the apneas at near-maximal lung volume with apneas after inhaling tidal volume, with and without cold forehead stimulation. In apneas at near maximal lung volume, a 20% reduction in splenic volume (P = 0.03) was observed as early as 3 s after the onset of breath holding. Around that time the heart rate increased, the mean arterial pressure abruptly decreased from 89.6 to 66.7 mmHg (P = 0.02), and cardiac output decreased, on account of reduction in stroke volume. Intravenous application of trinitrosan resulted in 6-mmHg decrement in mean arterial pressure, while the splenic volume decreased for 13%. In apneas at low lung volume, the early splenic contraction was also observed, 10% without and 12% with cold forehead stimulation, although the mean arterial pressure did not change or even increased, respectively. In conclusion, the spleen contraction is present at the beginning of apnea, accentuated by cold forehead stimulation. At large, but not small, lung volume, this initial contraction is probably facilitated by downloaded baroreflex in conditions of decreased blood pressure and cardiac output.

human; breath holding; simulated apnea diving

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