title: Immediate heart rate responses to head-up tilt in healthy human subjects: response characteristics and variability.
abstract: Eight healthy adult males underwent three 70* head-up tilts within a nine day period. Immediate heart rate responses were monitored for 30 beats following completion of change to upright posture. The pooled data demonstrates a clearly demarcated bimodal heart rate response with a rise in heart rate by the 20th beat and a subsequent fall by the 30th beat. There is a secondary rise in heart rate with continuation of the tilted position. The bimodal response is at variance with several earlier reports. There is a large variability in the immediate heart rate responses, both between subjects of a homogeneous group and within subjects with repeated measurements. The large variability precludes the use of the immediate heart rate responses to passive tilting in autonomic testing.
authors.affiliation: Department of Physiology, St. John's Medical College, Bangalore.
authors.forename: M
authors.initials: M
authors.lastname: Vaz
authors.forename: R N
authors.initials: RN
authors.lastname: Kulkarni
authors.forename: D
authors.initials: D
authors.lastname: Rodrigues
authors.forename: P S
authors.initials: PS
authors.lastname: Shetty
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D006257:Head; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D011187:Posture