HUMAN CARDIOVASCULAR FUNCTION DURING EXPE RIMENTAL DIVES AT 26 ATA (HELIUM-NITROGEN-OXYGEN MIXTURE)

During two human experimental dives at 26 ATA (helium-nitrogen-oxygen gaz mixture; PIO2 = 400 mbar), the cardiac frequency (Fc) and radial a rterial pulse were continously recorded, at rest and during periods of maximal expiratory (Valsalva) or inspiratory (Muller) manoeuvres, use d to increase or decrease the intrathoracic pressure, respectively. Ca rdiovascular variables were measured at 1 and 26 ATA in resting indivi duals and during the maximal respiratory manoeuvres. Discontinuous mea surement of arterial blood pressure using a sphygomanometer allowed to calculate the mean arterial pressure. The value of mean arterial pres sure was maintained against the membrane of a radial pulse sensor. Thi s procedure, proposed by Posey et al. (1969), gives a continuous appro ximation and recording of arterial blood pressure and its components. The present results did not show significant variation in the values o f Pc nor systolic or diastolic blood pressures measured at rest or dur ing Muller manoeuvres performed at 1ATA at the maximal depth. On the o ther hand, Valsalva manoeuvres performed at depth induced significant variations in circulatory variables compared to the normobaric respons e. The most important effect was an enlargement of differential pressu re due to a marked decrease in the diastolic blood pressure. These obs ervations are discussed in terms of enlarged sensitivity of the barore flex arch under hyperbaric condition.