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  • Title: Effects of water immersion on cardiac output of lean and fat male subjects at rest and during exercise.
    Author: Haffor AS, Mohler JG, Harrison AC.
    Journal: Aviat Space Environ Med; 1991 Feb; 62(2):123-7. PubMed ID: 1900415.
    Abstract:
    To investigate the combined effect of water immersion (WI) and lean body mass on cardiac output (Q), 12 healthy young men, 6 lean (fat less than 9%) and 6 fat (fat greater than 18%), were studied at rest and during steady state exercise approximating 30-40% Vo2 max under three experimental conditions. There were on land at 24 degrees C (LND), and immersed in water at 33-34 degrees C to hip level (HIP), and to the xiphoid (XIP). Metabolic measures were determined during 30-s periods from the average breath measurements. Mixed venous PCO2 (PVCO2) was estimated using rebreathing equilibration technique. Cardiac output was calculated by the indirect Fick's principle. In the lean individuals the average Q rose from a resting value of 5.43 +/- 0.43 (LND) to an exercise value of 7.25 +/- 0.40 L/min (XIP), and from resting value of 5.62 +/- 0.40 to an exercise 6.47 +/- 0.5 L/min in the fat individuals. During exercise, the associated increase in Q with increasing WI was significantly (p less than 0.05) higher compared with the land experiments. Inspection of the mean profile corresponding to this increase indicated that an increase in the level of immersion results in a significant (p less than 0.05) increase in the average Q for the lean group. For the fat group, the average Q was significantly (p less than 0.05) larger only at XIP level. At rest, heart rate dropped from 67 +/- 3.36 (LND) to 60 +/- 4.13 (XIP), and from 79 +/- 3.73 to 73 +/- 4.10 BPM for the lean and fat group, respectively. MANOVA analysis showed a significant (p less than 0.05) interaction between WI and group membership, indicating that the effect of WI is significantly different between the two groups. These data indicate that the change in central blood volume with WI depends, in part, on the lean mass of the body.
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