October 1, 1986
View Full PaperHypotension induced by passive head-up tilt: endocrine and circulatory mechanisms
Key Result
Passive 60-degree head-up tilt induced a sudden hypotensive bradycardiac episode after 19±3 minutes, with MAP dropping from 94±3 to 50±8 mmHg and HR from 90±7 to 57±6 beats/min.
Study Design
Type
Observational (n=7)
Structured PICO
What are the endocrine and circulatory mechanisms of hypotension induced by passive head-up tilt in healthy young adults?
P
Population
7 healthy young adults
I
Intervention
30 and 60 degrees passive head-up tilt with subjects supported by a saddle
C
Comparator
Baseline measurements prior to tilt
O
Outcome
Circulatory changes (pulse pressure, heart rate, mean arterial pressure) and arterial plasma hormone concentrationssurrogate
Passive head-up tilt to 60 degrees induces a reversible hypotensive bradycardiac episode accompanied by specific endocrine changes including increased vasopressin and pancreatic polypeptide.
Abstract
Circulatory changes and arterial plasma hormone concentrations were measured in seven healthy young adults during 30 and 60 degrees passive head-up tilt with the subjects supported by a saddle. The 30 degrees tilt induced a decrease in pulse pressure (Pp) from 45 +/- 2 to 35 +/- 4 (mean +/- SE) mmHg concomitant with an increase in heart rate (HR) from 58 +/- 4 to 78 +/- 8 beats/min and a marginal increase in mean arterial pressure (MAP). Norepinephrine increased from 180 +/- 20 to 310 +/- 40 pg/ml, aldosterone increased fivefold, and angiotensin II increased from 8 +/- 2 to 22 +/- 7 pg/ml. The 60 degrees tilt initially produced changes, which were qualitatively similar to the 30 degrees tilt. However, after 19 +/- 3 min sudden decreases were seen in MAP (94 +/- 3 to 50 +/- 8 mmHg), in Pp (38 +/- 5 to 18 +/- 4 mmHg), and in HR (90 +/- 7 to 57 +/- 6 beats/min). Concomitantly, epinephrine doubled while norepinephrine remained unchanged; the vagally controlled hormone pancreatic polypeptide increased from 29 +/- 3 to 51 +/- 8 pmol/l, vasopressin from 4 +/- 1 to 126 +/- 58 pg/ml, and angiotensin II from 23 +/- 9 to 35 +/- 12 pg/ml. The hypotensive bradycardiac episode was immediately reversible on termination of the head-up tilt.(ABSTRACT TRUNCATED AT 250 WORDS)