Effect of Headward and Forward Accelerations on the Cardiovascular System

Wood, Earl H.; Sutterer, William F.; Marshall, Hiram W.; Lindberg, Evan F.; Headley, Robert N.

doi:10.21236/ad0255298

Cited by 20 publications

(8 citation statements)

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“…However, in a previous study, our laboratory (35) showed that, although the mean arterial pressure (MAP) increased in hypergravity in lying subjects, there was no difference between the supine and the prone posture. Our previous finding of an increase in MAP of 21% in supine subjects during hypergravity compared with normal G is in agreement with the 17% increase observed by Wood et al (48). In our MAP measurements, we did not take into account that hypergravity could have affected the position of the heart in the thorax (46) and the thoracic shape, and it probably also compressed the padding on which the subject was lying.…”

Section: Discussionsupporting

confidence: 90%

Effects of gravity on lung diffusing capacity and cardiac output in prone and supine humans

Rohdin¹,

Petersson²,

Sundblad³

et al. 2003

Journal of Applied Physiology

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Both in normal subjects exposed to hypergravity and in patients with acute respiratory distress syndrome, there are increased hydrostatic pressure gradients down the lung. Also, both conditions show an impaired arterial oxygenation, which is less severe in the prone than in the supine posture. The aim of this study was to use hypergravity to further investigate the mechanisms behind the differences in arterial oxygenation between the prone and the supine posture. Ten healthy subjects were studied in a human centrifuge while exposed to 1 and 5 times normal gravity (1 G, 5 G) in the anterioposterior (supine) and posterioanterior (prone) direction. They performed one rebreathing maneuver after approximately 5 min at each G level and posture. Lung diffusing capacity decreased in hypergravity compared with 1 G (ANOVA, P = 0.002); it decreased by 46% in the supine posture compared with 25% in the prone (P = 0.01 for supine vs. prone). At the same time, functional residual capacity decreased by 33 and 23%, respectively (P < 0.001 for supine vs. prone), and cardiac output by 40 and 31% (P = 0.007 for supine vs. prone), despite an increase in heart rate of 16 and 28% (P < 0.001 for supine vs. prone), respectively. The finding of a more impaired diffusing capacity in the supine posture compared with the prone at 5 G supports our previous observations of more severe arterial hypoxemia in the supine posture during hypergravity. A reduced pulmonary-capillary blood flow and a reduced estimated alveolar volume can explain most of the reduction in diffusing capacity when supine.

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Section: Discussionsupporting

confidence: 90%

Effects of gravity on lung diffusing capacity and cardiac output in prone and supine humans

Rohdin¹,

Petersson²,

Sundblad³

et al. 2003

Journal of Applied Physiology

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“…Increased tolera nce a bove 10 s is proba bly circulatory reflex compensating for increased gravitational force. Shubrooks (300) found that heart rate increased in (207,208,275,357). Table 3 shows representative an almost linear fashion with increasing +G z acceler-results.…”

Section: Cardiac Output and Regional Flowmentioning

confidence: 87%

Cardiovascular Adjustments to Gravitational Stress

Blomqvist

Stone

1983

Comprehensive Physiology

198

163

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“…Positive acceleration results in pronounced haemodynamic alterations which have been reported earlier (Gauer, 1950;Gauer and Gienapp, 1950;Zuidema et al, 1956;Gauer and Zuidema, 1961;Wood et al, 1961). These consist of a fall of venous return to the heart, a decrease in left ventricular end-diastolic pressure, a diminution in the aortic root pressure and left ventricular dp/dt.…”

Section: Basalmentioning

confidence: 59%

Effect of positive acceleration (+gz) on electrocardiogram of subjects with vasoregulatory abnormality.

Khanna¹,

Balasubramanian²,

Dham³

et al. 1977

Heart

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ST-T wave changes in the electrocardiogram detected during routine examination and aggravated by erect posture, hyperventilation, and exercise in apparently healthy young individuals have been termed vasoregulatory abnormalities. No evidence of ischaemic heart disease has been found in such subjects. Ten young healthy air crew with vasoregulatory abnormalities were subjected to maximal exercise on treadmill and procedure repeated after 120 mg propranolol daily for 3 days. After one week, they were subjected to a stress of positive acceleration (+gz) in a human centrifuge at 2-5 g and 3-5 g for 15 seconds each at a constant rate of rise of 0-1 g/s and the electrocardiogram was monitored during and in the post-acceleration phase. The procedure was repeated after propranolol 120 mg daily for 3 days. The stress of positive acceleration resulted in pronounced prominence of P waves and inversion of T waves (as has been reported in normal subjects) with minimal ST depression in the electrocardiogram. ST segment depression during exercise, at heart rates corresponding to those achieved during peak centrifuge runs, was significantly more pronounced. The ST, P, and T wave changes were returned to normal after propranolol. It is concluded that minimal ST segment depression after stress of positive acceleration as compared with conspicuous ST segment depression during exercise at corresponding heart rates, and their normalisation after propranolol, rules out ischaemia as an aetiological factor in subjects with vasoregulatory abnormalities.

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Effect of Headward and Forward Accelerations on the Cardiovascular System

Cited by 20 publications

References 0 publications

Effects of gravity on lung diffusing capacity and cardiac output in prone and supine humans

Effects of gravity on lung diffusing capacity and cardiac output in prone and supine humans

Cardiovascular Adjustments to Gravitational Stress

Effect of positive acceleration (+gz) on electrocardiogram of subjects with vasoregulatory abnormality.

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