Frank‐Starling Responses during Heat Stress in Healthy Aged Humans
Abstract
Healthy aging markedly affects the cardiovascular adjustments to heat stress in humans. In particular, the increase in cardiac output can be attenuated by 50% in older individuals, which has previously been attributed to an inability of the aged to maintain stroke volume when cardiac filling pressures are reduced. In young individuals, a leftward shift in the operating point of the Frank‐Starling response is an important adjustment by which stroke volume is maintained during heat stress. It remains unknown how healthy aging affects the Frank‐Starling response during heat stress. We therefore tested the hypothesis that a leftward shift in the operating point of the Frank‐Starling response is absent in older individuals during whole‐body passive heat stress. Right heart catheterization was performed in 10 aged (A: 70 ± 3 y, 166 ± 9 cm, 68 ± 8 kg, 4 males/6 females) and 12 young (Y: 26 ± 5 y, 165 ± 6 cm, 64 ± 10 kg, 6 males/6 females) healthy individuals to measure pulmonary capillary wedge pressure, cardiac output (thermodilution) and pulmonary artery blood temperature. Heart rate was measured using an electrocardiogram and used to calculate stroke volume. These measurements were obtained at normothermic baseline, as well as at an increase in pulmonary artery blood temperature of 1.5°C achieved through whole‐body passive heat stress. Cardiac output increased in both groups during heat stress (A: 4.5 ± 0.7 to 7.0 ± 0.9 L/min vs. Y: 5.0 ± 0.7 to 9.5 ± 1.1 L/min), the magnitude of which was lower in the aged (PP<0.01). Indicative of a leftward shift in the operating point of the Frank‐Starling response, stroke volume was maintained during heat stress in both groups (A: 74 ± 13 to 78 ± 14 mL/min vs. Y: 89 ± 23 to 99 ± 21 mL/min) despite reductions in pulmonary capillary wedge pressure (A: 9.0 ± 1.9 to 6.6 ± 1.4 mmHg vs. Y: 10.6 ± 1.6 to 6.6 ± 2.0 mmHg). Overall, these results suggest that stroke volume is maintained during whole‐body passive heat stress in healthy aged humans due to an appropriate leftward shift in the Frank‐Starling response. Thus, attenuated increases in cardiac output in the aged while heat stressed are primarily due to attenuated increases in heart rate.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Apr 01, 2016
- Source ID
- 10.1096/fasebj.30.1_supplement.1290.7
Entities
People
- Benjamin D. Levine
- Craig G Crandall
- Daniel Gagnon
- Douglas Stoller
- Hai Ngo
- Paula Y.s. Poh
- Satyam Sarma
- Steven A Romero
- William K. Cornwell 3rd
Organizations
- Institute for Exercise and Environmental Medicine
- National Institutes of Health
- United States Department of Defense