Head-out water immersion is known to increase cardiac filling pressure and volume in humans at rest. The purpose of the present study was to assess whether these alterations persist during dynamic exercise. Ten men performed upright cycling exercise on land and in water to the suprasternal notch at work loads corresponding to 40, 60, 80, and 100% maximal O2 consumption (VO2max). A Swan-Ganz catheter was used to measure right atrial pressure (PAP), pulmonary arterial pressure (PAP), and cardiac index (CI). Left ventricular end-diastolic (LVED) and end-systolic (LVES) volume indexes were assessed with echocardiography. VO2max did not differ between land and water. RAP, PAP, CI, stroke index, and LVED and LVES volume indexes were significantly greater (P less than 0.05) during exercise in water than on land. Stroke index did not change significantly from rest to exercise in water but increased (P less than 0.05) on land. Arterial systolic blood pressure did not differ between land and water at rest or during exercise. Heart rates were significantly lower (P less than 0.05) in water only during the two highest work intensities. The results indicate that indexes of cardiac preload are greater during exercise in water than on land.

Simultaneous estimates of cardiac output were made during graded upright maximal exercise in 10 male subjects by means of Doppler velocity spectrum of ascending aortic flow, apical two-dimensional echocardiograms, thermodilution, and Fick oximetry. In 15 subjects, aortic annular and root diameters were measured during similar exercise from parasternal two-dimensional echocardiograms. The linear correlation between Doppler, two-dimensional echocardiography, and the invasive estimates ranged from r = .78 to r = .92. Both echocardiographic techniques were able to predict changes in invasive flow estimates with reasonable accuracy. Two-dimensional echocardiographic flow estimates underestimated invasive values by about 60%. The accuracy of Doppler flow estimates varied with the method of estimating aortic cross-sectional area. Greatest accuracy was obtained with areas calculated from diameters measured at the aortic value anulus with the leading edge-to-leading edge method of measurement. Correlation coefficients comparing Doppler and thermodilution flow estimates were generally higher (r = .75 to .96, mean .86) for individuals than for the group, but accuracy of the Doppler estimates in single subjects was quite variable. Aortic diameters did not increase from rest to moderate levels of upright exercise. A 3% to 5% increase in resting aortic diameter was noted in the upright posture as compared with the supine. Doppler flow estimates were obtained in all subjects to maximal exertion but in only a minority of subjects with two-dimensional echocardiography or thermodilution. Thus two-dimensional and Doppler echocardiography offer a noninvasive means of estimating cardiac output during vigorous exercise. The Doppler technique is technically more suitable to the study of exercise than two-dimensional echocardiography. Aortic area estimates for Doppler flow calculations are best made from resting two-dimensional echocardiograms of the aortic anulus by means of the leading edge-to-leading edge method of measurement. There does not appear to be a significant change in aortic diameter during upright exercise, but there may be a postural effect on aortic dimensions. Circulation 76, No. 3, 539-547, 1987. STROKE VOLUME and cardiac output are fundamental descriptors of cardiovascular function. Cardiac output is the primary indicator of the functional capacity of the circulation to meet the increased demands of physical exertion. The relative contributions of changes in stroke volume and heart rate to cardiac output and other factors influencing cardiac output 12 It was selected for this study because it allowed for rapid volume calculation from easily obtained and reproducible measurements. This formula has previously been validated in our laboratory by comparing it to left ventricular volume measured by left ventricular angiography in 20 patients with symmetric left ventricular wall motion. The correlation between echocardiographic and cineangiographic estimates of volume (range 42 to 232 ml) was .92 (echocardiog...

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Head-out water immersion is known to produce several cardiopulmonary adjustments at rest due to a cephalad shift in blood volume. The purpose of this study was to determine the effect of head-out water immersion on the cardiorespiratory response to graded dynamic exercise. Nineteen healthy middle-aged men performed upright cycling exercise at 40, 60 and 80% of maximal oxygen consumption on land and in water (31.0 +/- 1.0 degrees C) to the shoulders. Cardiac output (measured by the carbon dioxide rebreathing technique) was significantly greater in water at 40 and 80% maximal oxygen consumption. Stroke volume was significantly elevated at all stages of exercise. Heart rate did not differ significantly at 40 and 60% maximal oxygen consumption but was significantly lower in water at 80% maximal oxygen consumption. Total ventilation did not differ significantly in water and on land at any stage of exercise. The results suggest that the central redistribution of blood volume with head-out water immersion leads to an increase in stroke volume. Because there is not a proportional decrease in heart rate with the elevated stroke volume, cardiac output is regulated at a higher level during upright exercise in water compared with that on land. In conclusion, there are serious limitations of available, prerecorded rhythm data bases for designing and testing of automatic external defibrillators. Performance can be adequately assessed only by extensive clinical tests, which seem mandatory for this new and important type of defibrillator.

To investigate the effect of different levels of central blood volume on cardiac performance during exercise, M-mode echocardiography was utilized to determine left ventricular size and performance during cycling exercise in the upright posture (UP), supine posture (SP), and head-out water immersion (WI). At submaximal work loads requiring a mean O2 consumption (Vo2) of 1.2 1/min and 1.5 1/min, mean left ventricular end-diastolic and end-systolic dimensions were significantly greater (P less than 0.05) with WI than UP. In the SP during exercise, left ventricular dimensions were intermediate between UP and WI. Heart rate did not differ significantly among the three conditions at rest and at submaximal exercise up to a mean Vo2 of 1.8 1/min. However, at a mean Vo2 of 2.4 1/min, heart rate in the UP was significantly greater than WI (P less than 0.01) and the SP (P less than 0.05). Maximal Vo2 did not differ statistically in the three conditions. These data indicate that a change in central blood volume results in alterations in left ventricular end-diastolic and end-systolic dimensions during moderate levels of exercise and a change in heart rate at heavy levels of exercise.