Circadian blood pressure and systemic haemodynamics during 42 days of 6 degrees head-down tilt.
Acta Physiol Scand
; 161(1): 71-80, 1997 Sep.
Article
em En
| MEDLINE
| ID: mdl-9381953
ABSTRACT
Head-down tilted bedrest is a ground-based microgravity simulation model. Since in this position the influence of chief external determinants of circadian blood pressure variation, i.e. activity and posture, are reduced, it may reveal endogenous oscillatory factors. The effects of 42 days of 6 degrees head-down tilt on the circadian profiles of continuous finger blood pressure, heart rate, stroke volume, cardiac output and total peripheral resistance were analysed. In seven healthy volunteers (25-31 years) twelve 22 h Portapres registrations were performed two in an ambulatory baseline period, eight during 42 days of head-down tilt, and two during recovery. Stroke volume was estimated by a pulse contour method ('Modelflow') from the finger arterial blood pressure tracing. Head-down tilt rapidly reduced circadian BP variation, especially for diastolic blood pressure. No effect of long-term head-down tilt on blood pressure level was observed. The day-night difference in heart rate was essentially unaffected. Cardiac output was maintained through an increase of heart rate and simultaneous decline of stroke volume. Our observations confirm the overriding importance of physical activity and orthostatic load on the diurnal variation of BP. The time-frame of the changes in stroke volume and heart rate during head-down tilt might point to a contribution of other factors besides a reduction of circulating blood volume affecting cardiovascular performance under these conditions.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Pressão Sanguínea
/
Ritmo Circadiano
/
Decúbito Inclinado com Rebaixamento da Cabeça
/
Hemodinâmica
Tipo de estudo:
Prognostic_studies
Limite:
Adult
/
Humans
/
Male
Idioma:
En
Revista:
Acta Physiol Scand
Ano de publicação:
1997
Tipo de documento:
Article