Submitted on February 13, 2007
Accepted on October 11, 2007
Spleen and cardiovascular function during short apneas in divers
Ivan Palada1, Davor Eterovic2, Ante Obad3, Darija Bakovic3, Zoran Valic1, Vladimir Ivancev1, Mihajlo Lojpur4, J. Kevin Shoemaker5, and Zeljko Dujic1*
1 Physiology, University of Split School of Medicine, Split, Croatia
2 Biophysics and Scientific Methodology, University of Split School of Medicine, Split, Croatia
3 Physiology, University of Split School of Medicine, Croatia
4 Anesthesiology, Clinical Hospital Split, Croatia
5 Neurovascular Research Laboratory, The University of Western Ontario, School of Kinesiology, Canada
* To whom correspondence should be addressed. E-mail: zdujic{at}bsb.mefst.hr.
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 non-invasive photoplethysmographic cardiovascular measurements, before, during and after 15-20 s apneas in 7 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-hold. Around that time the heart rate increased, the mean arterial pressure abruptly decreased from 89.6 to 66.7 mm Hg (p=0.02) and cardiac output decreased, on account of reduction in stroke volume. Intravenous application of trinitrosan resulted in about 6 mm Hg decrement in mean arterial pressure, while the splenic volume decreased for about 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.
